Autologous stem cell transplantation with low-dose cyclophosphamide to improve mucosal healing in adults with refractory Crohn's disease: the ASTIClite RCT

Article history

The research reported in this issue of the journal was funded by the EME programme as project number 15/178/09. The contractual start date was in August 2017. The final report began editorial review in December 2021 and was accepted for publication in April 2022. The authors have been wholly responsible for all data collection, analysis and interpretation, and for writing up their work. The EME editors and production house have tried to ensure the accuracy of the authors’ report and would like to thank the reviewers for their constructive comments on the final report document. However, they do not accept liability for damages or losses arising from material published in this report.

Copyright statement

Copyright © 2024 Lindsay et al. This work was produced by Lindsay et al. under the terms of a commissioning contract issued by the Secretary of State for Health and Social Care. This is an Open Access publication distributed under the terms of the Creative Commons Attribution CC BY 4.0 licence, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. See: https://creativecommons.org/licenses/by/4.0/. For attribution the title, original author(s), the publication source – NIHR Journals Library, and the DOI of the publication must be cited.

2024 Lindsay et al.

Crohn’s disease

Crohn’s disease (CD) affects at least 115,000 people in the UK. 1 It is characterised by chronic inflammation of the gastrointestinal tract resulting from an inappropriate and prolonged effector lymphocyte reactivity to luminal dietary and microbial antigen. In addition, there is evidence of impaired barrier function with increased permeability, microbial activation of aspects of the innate immune system and a failure of the normal process of restitution. Apart from rare cases of very early-onset CD, which can have a monogenic aetiology, CD patients have polygenic susceptibility, with each polymorphism contributing a small increased risk of disease. There are some well-described environmental risk factors for CD, including smoking, but the exact aetiology of CD is not completely defined. The peak incidence of CD is in adolescence and young adulthood, and therefore affected individuals may live with symptoms for many years. 2

Untreated active disease can progress, leading to stricturing/penetrating complications and severe and debilitating symptoms, recurrent hospitalisation and disability. 2 Disease complications are the most common indication for surgery to resect the affected intestine, which may result in a temporary or permanent stoma. In addition to the substantial impact of CD on patients’ quality of life, the economic burden of the condition is high: CD profoundly impairs work productivity and is associated with significant healthcare costs, the majority of which relate to biologic therapies such as the anti-tumour necrosis factor (TNF) agents ustekinumab and vedolizumab. 3 In the UK, CD accounts for 27,000 hospital admissions each year,4 and this figure is set to rise as the incidence of CD increases worldwide. Although the introduction of biosimilar medication has reduced anti-TNF therapy-related costs, the costs associated with medical therapy for CD continue to increase year on year, mainly because of an increasing number of patients starting biologic medications. 3,4

Current service provision

Traditional medical therapy consists of drugs that either have a broad impact on mucosal immune activity (corticosteroids) or are targeted to specific immune pathways {anti-TNF agents [infliximab/adalimumab], anti-integrins [vedolizumab (Entyvio, Takeda UK Limited, London, UK)] or antibodies that target the p40 subunit of interleukin (IL) 12 and IL-23 [ustekinumab (Stelara, Janssen Pharmaceuticals, New Brunswick, NJ, USA)]}. Early use of optimised conventional and biologic therapy is unable to deliver sustained clinical and mucosal remission in the majority of patients. In a UK trial5 of personalised anti-TNF therapy in CD, primary non-response was reported in 24% of patients at 14 weeks, and non-remission was reported in 63% of patients at 52 weeks after starting anti-TNF therapy. The National Institute for Health and Care Excellence approves second-line therapy with the monoclonal antibodies vedolizumab and ustekinumab for patients with refractory CD. However, biologic medications have reduced efficacy in sustaining remission in treatment-experienced patients. A recent meta-analysis6 showed that patients with primary non-response to anti-TNF therapy are less likely to achieve remission with ustekinumab as an induction therapy than those with secondary loss of response to anti-TNF therapy. In addition, vedolizumab as an induction therapy did not achieve a Crohn’s Disease Activity Index (CDAI)-100 response in patients previously exposed to anti-TNF in one phase III clinical trial7 and was no more effective than placebo in inducing clinical remission at week 6 in another phase III clinical trial, with approximately 30% of patients in remission at week 10. 8

Patients with treatment-refractory CD suffer from persistent physical symptoms, treatment-related morbidity associated with chronic steroid use and psychological morbidity, which in turn have an impact on work productivity and lifetime achievement. Although a single short ileo-caecal resection can result in enhanced quality of life in the short term, CD frequently recurs despite post-operative preventative medication. Repeated surgery or resections in patients with extensive small bowel disease may result in nutritional deficiency, necessitating enteral or parenteral supplementary feeding. Refractory colonic CD or complications at critical parts of the bowel such as the rectum will often result in the need for a permanent stoma.

Alternative treatment for refractory CD remains an unmet need. One potentially effective alternative is haematopoietic stem cell transplant (HSCT). Research has supported the role of HSCT in the treatment of other autoimmune diseases, including multiple sclerosis (MS). Clinical trials of HSCT in MS patients have demonstrated a halt in detectable inflammatory activity for a prolonged period following treatment,9 and prolonged time to disease progression when compared with disease-modifying therapies. 10 Previous non-randomised studies suggest remarkable benefits of HSCT for the treatment of CD, with long-term treatment-free remission in some patients,11 and, when treatment-free remission declines with time, subsequent disease control with previously ineffective treatments. 12,13

Theory of haematopoietic stem cell transplant in autoimmune disease

Haematopoietic stem cell transplant seeks to relieve symptoms by resetting the autoreactive immune system and ablating immune memory. Cyclophosphamide and granulocyte colony-stimulating factor (G-CSF) induce stem cell proliferation within the bone marrow and subsequent release of stem cells into the bloodstream (termed ‘mobilisation’), from where they can be removed (or ‘harvested’) from the body. Subsequent conditioning with high-dose chemotherapy depletes the autoreactive immunological memory, after which stem cells are reinfused to rebuild a naive immune system. 14 HSCT is believed to stimulate the renewal of regulatory T cells, increase the diversity of T-cell receptors and reduce autoantibodies. 15 However, the exact mechanisms of action and time course of response to HSCT in refractory CD remains unknown.

Haematopoietic stem cell transplant in Crohn’s disease: the ASTIC trial

Currently, HSCT is considered an experimental therapy and is rarely used for treatment of refractory CD in the UK. A randomised controlled trial (RCT) of autologous stem cell transplantation for Crohn’s disease (ASTIC) was designed under the European Society for Blood and Marrow Transplantation (EBMT) Autoimmune Diseases Working Party (ADWP). 16 Patients in the ASTIC trial underwent high-dose cyclophosphamide (4 g/m²) and G-CSF mobilisation before being randomised to receive immediate HSCT or standard care for 1 year. No benefit of HSCT compared with standard care was found using the primary end point of medication-free clinical remission for 3 months, with no imaging or endoscopic evidence of disease activity. Furthermore, HSCT was associated with a high burden of adverse events (AEs) and serious adverse events (SAEs), including one patient death. 17

Although the ASTIC trial17 did not achieve its primary end point and was associated with significant toxicity, a modified HSCT regimen may have a role in the treatment of refractory CD for a number of reasons. 13,18^-23 First, the primary end point used in the ASTIC trial was notably more ambitious than that used in any other published trial in CD. HSCT was significantly more effective than standard care in several secondary end points, including clinical remission and endoscopic disease activity, all of which are important both to patients and to the NHS. Notably, 6 out of 23 treated patients showed no evidence of active CD ulceration on endoscopic and radiological assessment, yet did not meet the primary end point owing to ongoing gastrointestinal symptoms. These symptoms were likely to reflect prior, irreversible bowel damage rather than ongoing active disease. On completion of the trial, usual-care arm patients also underwent HSCT. A subsequent analysis of the combined cohort reported regression of all endoscopic ulceration in 50% of patients at 1 year post transplantation,24 although no post-HSCT maintenance therapy was given to patients with recurrent disease. A single-centre cohort study13 of patients undergoing HSCT reported that, although treatment-free remission declined over time, 80% of patients responded to drugs to which they were previously refractory, such that the marked reduction in drug-free remission reported over the study’s 5-year period is reversed when assessing remission rates on therapy.

Despite the potential efficacy of HSCT, toxicity remains a significant barrier to the use of HSCT for CD in the UK. A large number of AEs were reported in the ASTIC trial, one resulting in death. 16 An analysis that comprised eight cohort studies and the ASTIC trial estimated a treatment-related mortality of 6.4%. 25 Specialist reviews16,18,19 of the ASTIC trial implicated the high-dose cyclophosphamide used in mobilisation and conditioning to the infectious AEs observed. Cyclophosphamide for mobilisation of peripheral blood stem cells (PBSCs) was given at a relatively high dose of 4 g/m² to both the usual-care arm and the intervention arm patients in the ASTIC trial. The dose was chosen to ensure that patients in the usual-care arm received immune-suppressing therapy that would improve disease activity and to prevent a disease flare during G-CSF treatment. Cyclophosphamide at this dose had a significant short-term benefit on disease activity, but led to an increase in the number of SAEs. 13,26 Subsequent research13,20,21,27 has linked lower-intensity mobilisation and conditioning regimens to lower morbidity in autoimmune diseases. Furthermore, clinical factors such as smoking and active perianal disease that predict AEs22 have been identified, and the importance of supportive care in reducing SAEs has been demonstrated. 13,19,27

Rationale

Patients with refractory CD experience severe and lifelong morbidity, which arises from both the condition and its treatment. The current lack of an effective alternative means that patients with refractory CD are often prescribed successive courses of biologic and conventional immune suppression, which deliver a diminishing potential for benefit and an increased likelihood of inducing further harm. Ongoing active disease results in a significant impact on patient quality of life and productivity. Disease progression may mandate repeated surgery, with the risk of short bowel syndrome and the requirement for lifelong total parenteral nutrition. When CD affects critical areas of the intestine, surgical resection requires temporary or permanent stoma formation. Given this context, HSCT may be appropriate in a carefully selected group of treatment-refractory patients despite its many side effects. The previously reported risks associated with HSCT may be decreased using reduced-intensity regimens and increased supportive care (see Chapter 1, Introduction, Haematopoietic stem cell transplant in Crohn’s disease: the ASTIC trial). Considering the subsequent analysis of the ASTIC trial and other large single-centre series,16,24 further well-designed trials are needed to determine the level and duration of benefit.

Our Trial Steering Committee (TSC) patient representative stated the following:

The prospect of a potential respite from Crohn’s Disease will give most patients such hope that they will be more than willing to take a risk that this time something may actually work. The disease is so debilitating and affects your whole life, so that any slight hope will be grasped with both hands. Every single day is made miserable by Crohn’s and the idea that, by taking part in a trial such as ASTIC, could make your quality of life so much better, most people would think that the possible benefits are well worth the risk.

The ASTIClite trial was a multicentre, parallel-group RCT that sought to assess the clinical effectiveness, safety and long-term impact of low-dose cyclophosphamide/G-CSF mobilisation with reduced-intensity conditioning (HSCTlite) compared with standard care in inducing regression of intestinal ulceration in refractory CD patients at 1 year. Patients with evidence of disease activity after HSCT could be treated with biologic therapy from week 24. As the time course of response and mechanism of action of HSCT in CD is unknown, mechanistic substudies were embedded within the ASTIClite trial to evaluate the timeline of treatment response, post-HSCTlite immune reconstitution and the mechanisms via which HSCTlite improves CD and restores responsiveness to anti-TNF therapy in patients who were previously refractory. As part of the ASTIClite trial, participants were also invited to take part in a long-term follow-up through the EBMT, to assess the safety and efficacy of HSCTlite beyond the data collected as part of the ASTIClite clinical trial.

Given the incidence of AEs in the ASTIC trial, the transplant mobilisation and conditioning regimens were modified as follows: for mobilisation, the cyclophosphamide dose was reduced from 4 g/m² to 1 g/m² given prior to G-CSF, and for the conditioning regimen the dose of cyclophosphamide was reduced from 200 mg/kg to 120 mg/kg [given as 60 mg/kg on days –3 and –2, whereas the anti-thymocyte globulin (ATG) dose remained the same as in the ASTIC trial at 2.5 mg/kg for three days (days –3, –2 and –1; total 7.5 mg/kg)]. Given the anticipated relapse rate with lower doses of cyclophosphamide, additional immunosuppression was provided with fludarabine (25 mg/m² on days –6, –5, –4, –3 and –2; total 125 mg/m²), which for many years has widely and routinely been used in combination with alkylating agent chemotherapy (including cyclophosphamide) and therapeutic antibodies (including ATG) in conditioning regimens for allogeneic HSCT. It can be also be used, in similar combinations, in conditioning regimens for patients with severe autoimmune diseases who are undergoing autologous HSCT. Otherwise the regimen included supportive care drugs, with accommodation for local protocols.

In addition, ASTIClite differed from the original ASTIC trial in its eligibility criteria, which were modified to exclude patients with penetrating intestinal and active undrained perianal disease based on the assessment of factors associated with SAEs in ASTIC.

Finally, the introduction of additional advanced and biologic means increased the range of drugs to which patients had been exposed prior to trial entry. These criteria were expected to have affected the nature of patients recruited with severe, resistant disease.

Primary objective

• To assess the efficacy of HSCTlite compared with usual care at inducing regression of intestinal ulceration in patients with refractory CD at week 48.

Secondary objective

• To assess the impact of HSCTlite on clinical disease activity and quality of life compared with usual care.

Safety objectives

• Ongoing monitoring of AEs and SAEs continued throughout the trial using the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE). The Data Monitoring and Ethics Committee (DMEC) initially assessed the safety of low-dose cyclophosphamide and G-CSF as part of an embedded pilot study.

Exploratory objectives

• To assess the safety and efficacy of anti-TNF therapy (or alternative agents where contraindicated) in HSCTlite-treated patients with endoscopic disease recurrence at week 24.

Mechanistic objectives

• To determine the early impact of HSCTlite on mucosal disease via intestinal magnetic resonance imaging (MRI) at week 4.

• Through immune profiling of peripheral blood and transcriptional profiling of mucosal biopsies:

  • Characterise immune reconstitution after HSCTlite and assess the impact of HSCTlite.

  • Assess immunological events that precede disease recurrence after HSCTlite.

  • Assess the mechanism of restoration of response to anti-TNF therapy.

The last two mechanistic objectives could not be met because of small patient numbers. Week 4 MRIs were also not assessed for the same reason.

Trial design

The ASTIClite trial was a multicentre, parallel-group RCT. Eligible patients were randomised in a 2 : 1 ratio to receive low-dose cyclophosphamide and G-CSF mobilisation and reduced-intensity conditioning (HSCTlite) or usual care.

An internal pilot study was incorporated to determine whether or not the mobilisation regimen of 1 g/m² cyclophosphamide delivered effective stem cell harvest without a CD activity flare. The ability to recruit to target was assessed after 10 months of recruitment, with stop/go criteria set at 60% of the anticipated recruitment figure at that time.

The trial is reported according to the Consolidated Standards of Reporting Trials (CONSORT) statement for individually randomised parallel group trials. 30

Important changes to methods after trial commencement

Throughout the trial, 11 substantial amendments and three non-substantial amendments were approved. Significant changes to patient care during the trial, approved via amendments, included the addition of genetic and/or functional tests during screening, to exclude monogenic causes of intestinal inflammation in patients with predictive clinical phenotype; allowing the possibility of a second attempt at mobilisation with reduced or no cyclophosphamide in patients who failed to mobilise the first time; an increase in the dose of methylprednisolone from 1 mg/kg/day to 2 mg/kg/day, with scope to increase further up to 500–1000 mg in the setting of an ATG reaction; allowing a computerised tomography (CT) scan at screening as an alternative to MRI if MRI was contraindicated, and to remove MRI from week 4, 24 and 48 visits where contraindicated; and clarification on reintroducing anti-TNF therapy at week 24 for patients with MS, where therapy was to be considered on a case-by-case basis if anti-TNF was contraindicated. Full details of each amendment can be found in Appendix 1.

Participants

Recruitment commenced on 9 May 2018. Patients with refractory CD were eligible for randomisation according to the following eligibility criteria.

Recruitment and consent procedures

Participants were identified by PIs and co-investigators across eight hospital sites in the UK, or by way of referrals from neighbouring NHS trusts. The trial was publicised through press releases, on websites and in journals. Patients who enquired about participating were advised to seek a clinical referral via their usual inflammatory bowel disease (IBD) team to one of the participating sites for consideration for the trial.

Potential participants received an approved participant information sheet and were given the opportunity to speak with both the gastroenterology and the haematology specialist teams prior to giving consent.

All potentially eligible patients consented to the trial multidisciplinary team (MDT) panel discussing and determining their eligibility for participation. A minimum of two gastroenterology members and one haematology member of the panel were required to agree that a participant was potentially eligible for the patient to proceed to give full consent and undergo screening assessments.

Patients deemed ineligible by the MDT were not consented to the study, unless specific actions were requested to subsequently confirm eligibility, in which case the MDT met to discuss the patient’s eligibility further on completion of the required actions. In some cases, to avoid delays in recruitment, MDT discussions took place via e-mail rather than in monthly meetings. In all cases, communication was saved alongside the referral forms as evidence of discussion.

When the MDT agreed that a patient was eligible, the patient was invited to give full consent to the RCT and proceed through screening investigations. A medically qualified member of the trial team provided clinical oversight for the consent process. Each patient was given the opportunity to visit their local transplant centre and receive counselling from an independent clinician. On completion of the screening investigations, each patient’s case was discussed by the trial MDT for final confirmation of eligibility. If there were no concerns raised around the information gathered during screening, the MDT approved the patient for randomisation.

Screening

Consented patients underwent screening and baseline assessments to ensure eligibility. These included:

1. Standard pre-HSCT workup, including chest radiography and echocardiography or MUGA scan (as per EBMT ADWP guidelines. 20

2. Genetic/functional assessment for monogenic cause of disease in patients with very early-onset disease or with atypical phenotypes for whom a monogenic aetiology had not been excluded.

3. Assessment of clinical disease activity [CDAI and Harvey–Bradshaw index (HBI)].

4. Assessment of quality of life using patient-completed questionnaires [Inflammatory Bowel Disease Questionnaire (IBDQ), Inflammatory Bowel Disease Control Questionnaire (IBD-Control), EuroQol-5 Dimensions, five-level version (EQ-5D-5L), Work Productivity and Impairment (WPAI) and healthcare resource utilisation].

5. Endoscopic assessment of disease at screening (local PI endoscopic disease activity assessment scored using SES-CD).

6. MRI scan of the small bowel to record disease activity [magnetic resonance index of activity (MaRIA) score] (or CT if MRI was not clinically possible) during screening.

7. MRI scan of the pelvis in patients with previous perianal disease to exclude perianal sepsis.

8. Confirmation of eligibility by the MDT.

9. Criteria for fitness for HSCT, as per exclusion criterion 17. Participants who met one or more of the exclusion criteria but who in the opinion of the PI were medically fit enough to undergo HSCT were put forward to the MDT for discussion about eligibility.

Although an 8-week window prior to randomisation was given for the assessment of disease activity (MaRIA score, SES-CD and CDAI) and screening blood tests, this was not always achieved owing to delays in randomisation visits. The participants were also asked to complete a symptom diary for 1 week prior to the assessment of the CDAI; this was not done immediately preceding a colonoscopy and participants were asked to finish the diary prior to starting bowel preparation for colonoscopy.

Study settings

The trial was co-ordinated from the Clinical Trials Research Unit (CTRU) in Sheffield at the School of Health and Related Research. The study took place at nine UK hospitals: eight recruiting centres and one treatment-only centre. All HSCT procedures were undertaken at transplant centres accredited by Joint Accreditation Committee – ISCT Europe & EBMT (JACIE) for allogeneic transplants in adults, or for autologous transplants in adults, at sites with previous experience of administering autologous HSCT for CD.

Interventions

Outcomes

Assessments and procedures

The assessments required during the study are detailed within the Statistical Analysis Plan (SAP), available on the project web page (https://www.journalslibrary.nihr.ac.uk/eme/10.3310/CGLT7102). All participants underwent the assessments, irrespective of the treatment arm to which they were randomised. Follow-up visits were carried out at weeks 8, 14, 24, 32, 40 and 48, with day 0 the date on which stem cells were reinfused for participants in the HSCTlite arm. For usual-care arm participants, day 0 was calculated as 49 days after randomisation, to align the timescales for assessments in both trial arms as much as possible. This timescale was taken from the median time to transplantation in the ASTIC trial. 17 Although a visit window of ± 1 week was initially permitted, a wider visit window was considered in the light of the COVID-19 pandemic, which led to difficulties in arranging and carrying out research visits within the permitted time windows for safety reasons. In addition to the wider visit windows, as a result of the COVID-19 pandemic, some follow-up visits were conducted over the telephone rather than in person, where appropriate.

Sample size

Sample size calculations were based on the endoscopic assessment after HSCT reported in the ASTIC trial. 17,24 To detect a significant difference in the proportion of patients with no ulceration in endoscopy assessment of 35% based on 50% in the HSCTlite arm and no more than 15% in the usual-care arm, with 90% power at 5% significance level, 62 patients were required in the HSCTlite arm, and 31 in the usual-care arm.

Based on previous experience in the ASTIC trial, a 6% drop-out rate (after enrolment) was anticipated. The recruitment target was therefore set at 99 participants, using a 2 : 1 randomisation ratio (66 participants in the intervention arm and 33 participants in the usual-care arm).

Based on the ASTIC trial, it was anticipated that recruitment would take 36 months. Ability to recruit to time and target was assessed at month 10 of recruitment with the stop/go criterion being 60% of the anticipated recruitment figure at that time.

Recruitment to the ASTIClite trial was suspended in December 2019, and a formal decision to terminate recruitment was taken in June 2020 on safety grounds. Owing to the early closure of the trial, the recruitment target was not reached. The SAP was amended accordingly.

Randomisation

Participants were centrally randomised in a 2 : 1 ratio to either the HSCTlite arm or the usual-care arm. The trial statistician, blinded to treatment allocation, generated the randomisation schedule before the start of the study using the CTRU’s online randomisation system, SCRAM. To ensure that participants were allocated in the correct ratio within each site, randomisation was stratified by site using random permuted blocks, with block sizes of ‘3’ and ‘6’. The allocation sequence was concealed from all study staff except the statisticians who generated it. Delegated site staff were given access to SCRAM. Once eligibility was confirmed, patient identification and date of birth were entered, and the treatment allocation was returned.

Blinding

Owing to the nature of HSCT, neither patients nor their treating physicians were blinded to the treatment allocation. However, central readers blinded to both the timing of the procedure and the treatment allocation assessed and scored anonymised videos of all endoscopic procedures used to determine the primary end point and also provided a a central reading score for the baseline videos. Similarly, expert physicians blinded to the timing of investigation and intervention arm performed central MRI reviews for screening, week 4 (intervention arm participants) and week 48 scans, and calculated the MaRIA score using anonymised images. Only those scans from randomised participants who completed the study were centrally verified.

The senior statistician reviewed and approved the trial SAP prior to seeing any outcome data, but was subsequently unblinded to the treatment allocation throughout the trial.

The trial statistician remained blinded throughout the study until recruitment to the trial was suspended in December 2019 on safety grounds. The nature of the discussion (including the information discussed) around the rationale for early closure effectively led to the unblinding of the TSC and the trial statistician. The SAP addendum setting out the revised plans for analysis was written and signed off prior to the trial statistician accessing the trial data.

Statistical methods

Ethics aspects

The ASTIClite trial received favourable opinion from the London-Chelsea Research Ethics Committee (REC reference number 17/LO/1690) and authorisation from the Medicines and Healthcare Products Regulatory Agency [(MHRA) reference number 14620/0051/001-0001]. The trial was conducted in accordance with the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use – Good Clinical Practice guidelines33 and the Declaration of Helsinki. 34

Patient and public involvement

To ensure readability, format and ease of understanding, all patient-facing documents were reviewed by two patients who took part in the ASTIC trial. This review process allowed for any concerns with the study design to be addressed. The trial was also presented to the British Society of Gastroenterology IBD Clinical Research Group in collaboration with Crohn’s and Colitis UK charity patient engagement panel. The feedback received was incorporated into the trial design.

For ongoing patient involvement in the management of the trial, and to obtain patient perspectives on major decisions affecting trial processes or conduct, two patient representatives sat on the panel of the TSC throughout the study. These patient representatives were also consulted when writing Plain English summaries, and materials to disseminate results to participants and the wider patient population. One TSC patient and public representative provided a quotation specifically for this report, as noted in the Discussion.

Mechanistic substudy

European Society for Blood and Marrow Transplantation long-term follow-up study

A longitudinal, observational study following participants recruited to the ASTIClite trial over a further 4–7 years via annual follow-up visits was planned to assess the long-term safety and efficacy of HSCTlite. Patients who consented to the ASTIClite RCT were also invited to take part in the ASTIClite EBMT follow-up study, regardless of the treatment they went on to receive as part of the ASTIClite RCT. However, owing to the early closure of the ASTIClite clinical trial, the EBMT long-term follow-up study was terminated before data collection began.

Early trial closure

The ASTIClite trial was paused on 30 December 2019 while a number of suspected unexpected serious adverse reactions (SUSARs) were investigated, including the death of one patient. Two further SUSARs were reported in May 2020. In June 2020, the DMEC and TSC held a joint meeting to discuss the unexplained AEs, the outcomes of the trial team’s investigations and the impact of the coronavirus pandemic. The DMEC and TSC agreed that:

• recruitment to the trial should cease

• patients who were in screening or randomised to HSCTlite but had not yet received treatment should be withdrawn

• patients that had completed the intervention or were randomised to usual care should continue to be followed up as normal.

The pandemic associated with SARS-CoV-2 was recognised as a global issue in early 2020. It had a marked impact on the delivery of health care across the UK, with the suspension of many routine services to allow focus of care for those affected by COVID-19. The impact on the delivery of clinical trials across the UK was immense, with many closing completely to recruitment. At that time the ASTIClite trial had already been halted and no additional patients were recruited after the onset of the pandemic. However, the recommendations on social distancing, travel and isolation prevented some face-to-face trial visits during the follow-up period of the trial. Pressure on endoscopy services and the British Society of Gastroenterology guidelines35 on service provision during the pandemic precluded or significantly delayed colonoscopy to assess the primary and secondary outcomes in some patients, and for others this could not be completed at all. In-person site monitoring was suspended. To our knowledge, no patient had symptomatic SARS-CoV-2 infection during the trial.

The last patient last visit was in November 2020 and the database was finalised in December 2020. The planned analyses as outlined in the study SAP were amended to account for the early trial closure and the significantly reduced sample size. These changes were documented in an addendum to the SAP and were approved by the TSC chairperson and statistician. The results presented in this report follow the analysis as stipulated in both the SAP and the addendum to the SAP.

Data completeness

In total, 23 participants were randomised between 18 October 2018 and 8 November 2019. The DMEC recommended that recruitment cease on 8 June 2020. Study follow-up concluded in November 2020. Figure 1 shows the CONSORT flow diagram of participants through the trial. Thirteen participants were randomised to receive HSCTlite (the intervention arm) and 10 were allocated to receive usual care (the usual-care arm). In the HSCTlite arm, 12 participants underwent mobilisation, of whom two withdrew pre transplantation; the reasons for these withdrawals are shown in Figure 1. Ten participants underwent transplantation and received both the conditioning regimen and stem cell infusion. In the HSCTlite arm, one patient died at 24 weeks; the remaining nine participants reached the 48-week follow-up and completed the study. In the usual-care arm, one participant was withdrawn from the study at week 8 owing to ineligibility, leaving nine participants, all of whom completed the study.

FIGURE 1.

The CONSORT flow diagram. a, Treatment for two patients was discontinued owing to early study close (one of these received mobilisation, one participant withdrew consent); b, patient was found to be ineligible and was withdrawn; c, patient died. A further participant died after their week 48 visit.

Of the nine participants followed up at week 48 in the intervention arm, one declined their week 48 colonoscopy and, for a further two patients, colonoscopies were not recorded, so could not be centrally scored. Therefore, we did not have valid primary outcome data for these patients although locally read endoscopic scores were available. The participant who died at week 24 was classified as a treatment failure according to the definition of the primary end point, which leaves seven participants in the intervention arm with valid week 48 primary outcome data. In the usual-care arm, five patients did not have valid central colonoscopy data. The reasons for missing data were as follows: two missing week 48 colonoscopies were due to the COVID-19 pandemic (one patient was shielding and one patient’s colonoscopy was cancelled due to changes to non-urgent appointment availability in the NHS at the time), one colonoscopy was not recorded and could not be centrally scored and two patients did not have their colonoscopies because of worsening disease/surgery. However, they were included in the analysis of the primary end point as treatment failures, as they did not meet the prespecified criteria. Therefore, six participants in the usual-care arm had valid data to contribute to the primary outcome. In total, 13 participants contributed week 48 primary outcome data. We followed up ongoing SAEs until resolution or database freeze, whichever came first, and from this it was recorded that one participant from the intervention arm died after the week 48 follow-up visit.

Baseline data

This section details the baseline data for the participants in the ITT population; this was defined as all randomised participants excluding those (n = 1) who were subsequently found to be ineligible post randomisation or with no recorded consent information. There were 22 participants who met these criteria, 13 in the HSCTlite arm and nine in the usual-care arm.

The baseline demographics of the ITT participants are shown in Table 5. Overall, seven centres recruited to the study, with Barts Health and Nottingham contributing over 60% of the total participants. The majority of participants were white British (82%), with the remaining participants being of Asian/Asian British ethnicity. The average age of the participants was 35 years, with participants in the usual-care arm having a slightly higher average age than those in the HSCTlite arm. Table 6 shows the baseline CD characteristics by treatment group.

The medical and drug history of the participants is shown in Table 7. Specific comorbidities are shown by treatment arm, as well as exposure to immunosuppressants, steroids and biological therapy prior to baseline. Baseline laboratory tests, disease activity scores and PROs are summarised in Table 8. Those in the intervention arm had a notably worse health state (measured by EQ-5D-5L) and illness severity (measured by CDAI) than those in the usual-care arm, but conversely experienced a lower impact on work (measured by hours of work lost to CD and self-rated effect on work productivity).

The baseline data split by completion status are shown in Appendix 4, Tables 22 and 23. Completers were defined as those who reached the week 48 follow-up. Of the 22 participants who were in the ITT population, 18 completed the study, nine in the HSCTlite arm and nine in the usual-care arm. The usual-care arm had no non-completers other than one patient who was found to be ineligible post randomisation and was therefore excluded from the ITT population. The intervention arm had four non-completers: the reasons for non-completion are shown in Figure 1. The continuous and categorical characteristics measured at baseline are shown in Appendix 4, Tables 22 and 23, respectively; they are split by treatment group and completion status. The average CDAI score in the completer group was 333.3, compared with 354.2 in the non-completers group at baseline. The participants who completed the study had a mean SES-CD score of 10.6 at baseline. It is worth noting that the non-completer group comprised only four participants, so averages and summary statistics should be taken with caution.

Treatment summaries

Table 9 shows the treatment summaries for those in the HSCTlite arm (the intervention arm). In total, 13 participants were randomised to receive HSCTlite, 12 of whom reached mobilisation, with one participant receiving two cycles of mobilisation. On average, patients received 5 days of G-CSF. The disease activity after mobilisation is also shown in Table 9. Patients reported a wide range of disease burden, with HBI scores ranging from 2 to 51 (median 12.5). Ten participants went on to receive stem cell reinfusion, on average 43 days after stem cell harvest. All 10 participants who received stem cell infusion were considered to be per protocol based on blinded treatment review by the chief investigator. The median (IQR) number of stem cells reinfused was 4.6 × 10⁶/kg (4.0–6.3). The reasons for the withdrawal participants in the HSCTlite arm are shown at the bottom of Table 9. Three of the participants withdrew pre transplantation, and one participant died at week 24.

Of the nine participants in the usual-care arm, eight received medications specifically to treat CD and one participant underwent surgery for CD (small bowel resection). Two patients received IV nutrition (one of these following complications after small bowel resection). One patient required an examination under anaesthetic and seton insertion and another had a guided drainage of a collection. Eight patients continued biologic therapy (two infliximab, one certolizumab, three ustekinumab and two vedolizumab). This was combined with azathioprine in one and methotrexate in two patients. One patient received tacrolimus. Corticosteroids were prescribed for seven patients (four received budesonide and three prednisolone).

In the HSCTlite group, the mean number of days between randomisation and stem cell infusion (time to day 0) for the 11 participants who underwent stem cell reinfusion was 99 days, with a range of 71 to 185 days. This is considerably larger than the planned 49 days, which was the median number of days (from the ASTIC trial). This increase in days between randomisation and stem cell reinfusion in the ASTIClite trial was largely due to waiting lists for haematology wards for non-urgent stem cell transplantations.

Information relating to the reintroduction of anti-TNF treatment following HSCT is provided in Appendix 5.

Summary of the primary outcome

The primary outcome and treatment success at week 48 was defined as mucosal healing [no endoscopic ulceration (SES-CD ulcer subscore of zero, assessed by central readers blinded to allocation and time of assessment)] without surgery or death. Table 10 shows the proportion of participants in each group achieving the primary outcome. Although 18 of the 22 participants in the ITT population completed the study, only 10 (n = 6, HSCTlite arm; n = 4, usual-care arm) had centrally confirmed colonoscopy data to assess absence of ulceration. Of the eight participants who did not have valid week 48 colonoscopy data, three of the colonoscopies (n = 2, HSCTlite arm; n = 1 usual-care arm) were not recorded and could not be centrally scored (two were not recorded in error, and, for one, a technical issue meant that the recording was not saved); two patients (both in the usual-care arm) did not attend their colonoscopy visit because of the COVID-19 pandemic; two (both in the usual-care arm) did not attend their week 48 colonoscopy as they were too ill; and one participant (in the HSCTlite arm) declined to attend. The two participants who did not attend their colonoscopies because of worsening disease were included as treatment failures as per the primary outcome definition, as was the one HSCTlite patient who had died prior to week 48. The primary outcome is summarised in Table 11. Three out of the seven patients undergoing HSCTlite achieved absence of ulceration, whereas no responses were seen in the usual-care arm. Of the three participants without centrally assessed colonoscopy data, local scoring by the investigator reported that the two HSCTlite-arm participants achieved absence of ulceration in their colonoscopy but the participant in the usual-care arm was classified as a treatment failure. Therefore, using the local colonoscopy data alone, five out of the nine intervention participants achieved absence of ulceration. One of the HSCTlite participants who achieved absence of ulceration subsequently died after the week 48 follow-up (further details given in Suspected unexpected serious adverse reactions).

Table 11 shows the three sensitivity analyses on the primary outcome: removing participants who had surgery for CD in the usual-care arm, imputation of missing data with week 24 colonoscopy data and removing week 48 colonoscopy data outside the extended visit window. One patient had surgery for CD in the usual-care arm. The overall proportion of participants achieving absence of ulceration following HSCTlite ranged between 40% and 50%, compared with 43% in the original analysis.

In total, six patients had missing week 48 data, but had valid week 24 data to use, three each in both the usual care and the HSCTlite arm. The results were similar to the primary analysis: the proportion of patients achieving absence of ulceration in the HSCTlite arm was 40%, and the number of treatment successes in the usual-care arm remained zero. One patient in the HSCTlite arm had their week 48 colonoscopy outside the extended visit window.

Secondary outcomes

Table 12 shows the categorical secondary outcomes, in particular several definitions of clinical remission, as well as complete endoscopic remission. In the usual-care arm, no participants achieved complete endoscopic remission, whereas two participants achieved it in the HSCTlite arm.

The continuous secondary outcomes at 48 weeks are shown in Table 13. Although 13 participants were eligible to be assessed for absence of ulceration, only eight had substantial valid colonoscopy data to calculate a SES-CD score. This was because two participants did not attend their week 48 colonoscopy because of illness and one participant died at week 24. Two additional patients had enough colonoscopy data to ascertain absence of ulceration, but they did not have centrally calculated SES-CD scores. The average SES-CD score in the HSCTlite arm was 2.8, whereas in the usual-care arm the average score was 18.7, suggesting more disease activity in the usual-care arm. This is again demonstrated in the change in SES-CD score from baseline, where the intervention arm on average had a significant decrease in SES-CD score, whereas the usual-care SES-CD score increased. The CDAI at week 48 and the change from baseline are also shown. The HSCTlite arm had a lower average CDAI score at 48 weeks, and had a larger decline in CDAI from baseline.

The CDAI and SES-CD scores across all recorded time points are presented in Figures 2 and 3, respectively. The scores are split by treatment arm, with the average for each treatment arm shown by the dashed lines. The CDAI scores for both arms fluctuates over the follow-up period; however, the average CDAI score at 48 weeks in the usual-care arm is higher than that in the HSCTlite arm. The SES-CD score for the HSCTlite arm declines over time, and is lower than in the usual-care arm at 24 and 48 weeks.

FIGURE 2.

The CDAI score over time split by treatment arm, presented on the ITT population. Dashed lines show arm averages and solid lines show individual trajectories.

FIGURE 3.

The SES-CD score over time split by treatment arm, presented on the ITT population. Dashed lines show group averages and solid lines show individual trajectories.

Subgroup and moderator analysis

Table 14 shows those who achieved the primary outcome summarised by subgroups and treatment arms. The objective of an exploratory subgroup analysis was to explore heterogeneity in the intervention effects across the following predefined subgroups:

• perianal CD

• current smoker

• disease location

• current treatment at screening.

These analyses were included within the SAP. However, numbers were small owing to the early closure of the trial, which significantly limits these analyses: the usual-care arm had no treatment successes, so the subgroup analysis affects only the HSCTlite arm. The proportion of participants in the HSCTlite arm who had perianal CD and achieved absence of ulceration was 33%. Notably, all three treatment successes in the intervention arm were non-smokers. The successfully treated patients did not have CD in the colonic or isolated upper regions. All three were receiving treatment for CD at screening. As stated above, limited conclusions can be made from this owing to the small numbers.

Safety and harms

The safety data are summarised for the extended ITT population, that is, all randomised patients including the participant found to be ineligible post randomisation. The AEs in Table 15 are split by time periods and treatment group. The time periods are as follows:

• Mobilisation phase – period from start of mobilisation to start of conditioning, randomisation to day 0 for usual-care participants.

• Transplant phase – period from start of conditioning up to 100 days from day 0 (day of autologous transplantation/infusion), day 0 to day 100 for usual-care participants.

• Follow-up phase: from ≥ 100 days post-transplantation phase on-wards, day 100 on-wards in usual care participants.

The time periods used for the intervention and usual-care arms are not exactly equivalent, but have been included so that the safety data can be compared across arms by the key stages of the intervention.

In the HSCTlite arm, all 13 participants experienced at least one AE. In total, 100 AEs occurred in the HSCTlite arm. In the usual-care arm, four people experienced at least one AE. In the HSCTlite arm, 61 AEs occurred during the transplantation phase, compared with five AEs in the usual-care arm during the same time period. A further 31 AEs occurred in the HSCTlite arm and a further 18 occurred in the usual care arm during the follow-up phase. In total, 127 AEs were recorded throughout the study.

Table 16 displays the SAEs by time point and treatment group. In total, 38 SAEs were experienced by 13 participants in the HSCTlite arm and 16 SAEs were experienced by four participants in the usual care arm. A large proportion of the SAEs occurred during the transplantation phase: 24 were recorded in the HSCTlite arm, compared with three in the usual-care arm. Four SAEs (experienced by two participants) resulted in the participants’ deaths, one during the study (at 24 weeks) and one post 48 weeks. One SAE resulted in treatment withdrawal, and the majority of SAEs required specific treatment or other action.

Table 17 details both AEs and SAEs by NCI CTCAE grade. The percentage of participants in the HSCTlite arm experiencing at least one grade 1–2 AE was 77%, compared with 30% in the usual-care arm. One participant in the usual-care arm experienced an AE above grades 1–2. Three participants experienced a grade 3 AE, but no grade 4 AEs were recorded. However, six participants in the HSCTlite arm experienced at least one grade 4 SAE, and 10 experienced one grade 3 SAE. In the HSCTlite arm, 59 AEs were grade 1–2, compared with 10 in the usual-care arm. The number of grade 3 SAEs was 27 in the HSCTlite arm and 16 in the usual-care arm, and there were eight grade 4 SAEs recorded, all of which were in the HSCTlite arm.

Suspected unexpected serious adverse reactions

In total, nine SUSARs occurred across six patients (three patients had more than one SUSAR) in the HSCTlite arm. The SAEs and SUSARs for the HSCTlite arm and the timing from stem cell reinfusion are shown in Table 18. Two SUSARs occurred on the day of stem cell reinfusion. There were three occurrences of renal biopsy-proven thrombotic microangiopathy (TMA) between days 90 and 153.

Two HSCTlite patients died after having SUSARs. One patient died approximately 24 weeks after their stem cell reinfusion, having experienced one SUSAR (pulmonary veno-occlusive disease) which occurred on day 93 (12 weeks after stem cell reinfusion). A second patient died after their 48-week follow-up (at 60 weeks post stem cell transplantation); they experienced three SUSARs. Initially, their C-reactive protein (CRP) levels were abnormal, with no apparent underlying cause; later, further SUSARs of respiratory failure and acute oliguric renal failure occurred. Respiratory failure and acute oliguric renal failure occurred on the day of stem cell reinfusion, and the patient was hospitalised during this time.

Table 19 shows the primary outcome by treatment arm and by SUSARs experienced. In the HSCTlite arm, all three participants who achieved absence of ulceration experienced at least one SUSAR. Only two participants in the HSCTlite arm did not experience a SUSAR, neither of whom achieved absence of ulceration. No patients in the usual-care arm experienced a SUSAR. Table 20 shows a line listing of the SAEs and SUSARs experienced by patients in the HSCTlite arm who had valid primary outcome data at 48 weeks. The table shows the timing of the SAE and whether or not the patient died.

Mechanistic study

Clinical data

Clinical laboratory test data (treatment group over time)

The following box plots (Figure 4) report the median, IQR and range of clinically relevant routine laboratory data by clinical arm over time. As would be expected, after receiving HSCTlite, there is a marked difference in haematological parameters between groups. Patients in the HSCTlite arm experienced anaemia after mobilisation, which persisted despite appropriate transfusion throughout the study. In addition, patients undergoing HSCTlite experienced a marked leukopenia in all lineages as well as a thrombocytopenia after conditioning. There was near-complete recovery of lymphopenia by week 48, but neutrophil, monocyte and platelet counts did not show recovery by week 48. As outlined above, several renal SUSARs were reported in the intervention group. This was confirmed by the reduction in renal function seen (elevated urea and creatinine associated with fall in estimated glomerular filtration rate (eGFR) from week 14. There was partial recovery by week 48, but clinically meaningful differences from the usual-care arm persisted.

FIGURE 4.

Clinical laboratory test data, split by treatment group, presented on the ITT population. (a) Haemoglobin; (b) white cell count; (c) platelet count; (d) neutrophils; (e) lymphocytes; (f) monocytes; (g) creatinine; (h) urea; (i) bilirubin; (j) CRP; and (k) eGFR. Note: the neutrophils plot has had an outlier at week 48 removed (value 88.4). The bilirubin plot has had an outlier at week 48 removed (value 996).

The following clinical laboratory data are not presented in graphical form, as levels remained stable throughout the trial period and/or there was no clear trend or difference between treatment arms: eosinophils, basophils, sodium, potassium, calcium, albumin, alkaline phosphatase, magnesium, gamma-glutamyl transpeptidase, glucose, protein total, aspartate aminotransferase and alanine aminotransferase.

Clinical data

As seen in Figure 5, the anaemia experienced by patients in the HSCTlite arm was more marked in those who reported a renal SUSAR than in those who did not, but both subsets of patients seemed to improve by week 48. Likewise, the thrombocytopenia was more marked in intervention patients reporting a renal SUSAR and persisted to week 48, whereas the platelet count in those with no renal SUSAR increased after week 32. All intervention patients experienced marked lymphopenia, but in those without a renal SUSAR this resolved between week 32 and week 40. In contrast, intervention patients who reported a renal SUSAR had persistent lymphopenia.

FIGURE 5.

Clinical data, split by SUSAR group. (a) eGFR; (b) creatinine; (c) urea; (d) platelet count; (e) haemoglobin; (f) neutrophils; and (g) lymphocytes. Note: split by intervention arm participants who experienced a SUSAR, HSCTlite arm participants who did not experience a SUSAR, and those in the usual-care arm. Presented on the ITT population.

Although the patients experiencing a renal SUSAR accounted for the majority of the reported deterioration in renal function in the HSCTlite arm, it does appear that renal function was impaired more in intervention patients who did not report a renal SUSAR than in those in the usual-care arm. The following variables chosen from the clinical laboratory data were selected as those that were particularly important from a clinical point of view.

Immune reconstitution data

Peripheral blood immune cell subsets by flow cytometry (split by treatment arm)

The box plots in Figure 6 report the median, IQR and range of peripheral blood immune cell subsets by clinical group over time. As would be expected, there is a marked difference in the profile of all the immune cell subsets studied between the HSCTlite and usual-care arms. Of all the subsets studied, only the numbers of CD3⁺CD8⁺CD31⁺ recent thymic emigrant cytotoxic T helper cells, CD3⁺CD8⁺CD49d⁺α4integrin⁺CCR9⁺ gut-homing cytotoxic T cells, CD3⁺CD4⁺CD45RA–CCR7^- effector memory T helper cells and CD8⁺ cytotoxic T cells had returned to equivalence with the usual-care arm at week 48, with levels of CD3⁺, CD4⁺, CD4⁺ recent thymic emigrants, CD3⁺CD4⁺CD45RA–CCR7⁺ central memory T helper cells, CD4⁺ effector T helper cells and CD3⁺CD4⁺CD45RA⁺CCR7⁺ naive T helper cells remaining lower in the HSCTlite arm.

FIGURE 6.

Peripheral blood immune cell subsets by flow cytometry, split by treatment group, presented on the ITT population. (a) Number of T cells (CD3⁺); (b) number of T helper cells (CD3⁺, CD4⁺); (c) number of cytotoxic T cells (CD3⁺, CD8⁺); (d) number of recent thymic emigrant T helper cells (CD3⁺, CD4⁺, CD31⁺); (e) number of central memory T helper cells (CD3⁺, CD4⁺, CD45RA–, CCR7⁺); (f) number of effector T helper cells (CD3⁺, CD4⁺, CD45RA⁺, CCR7–); (g) number of effector memory T helper cells (CD3⁺, CD4⁺, CD45RA–, CCR7–); (h) number of naive T helper cells (CD3⁺, CD4⁺, CD45RA⁺, CCR7⁺); (i) number of gut homing cytotoxic T cells (CD3⁺, CD8⁺ CD49d + α4integrin + CCR9⁺); and (j) number of recent thymic emigrant cytotoxic T helper cells (CD3⁺, CD8⁺, CD31⁺). Note: the number of CD3⁺, CD8⁺, CD49d + α4integrin + CCR9⁺ gut homing cytotoxic T cells per µl of peripheral blood plot has had an outlier at baseline removed (value = 425.07).

Not all patients provided samples for all time points for this analysis. The numbers of samples used are as follows:

• baseline – n = 13, HSCTlite arm; n = 8, usual-care arm

• week 8 – n = 9, HSCTlite arm; n = 7, usual-care arm

• week 14 – n = 8, HSCTlite arm; n = 6, usual-care arm

• week 24 – n = 7, HSCTlite arm; n = 7, usual-care arm

• week 32 – n = 5, HSCTlite arm; n = 5, usual-care arm

• week 48 – n = 6, HSCTlite arm; n = 5 usual-care arm.

Cytokine expression by peripheral blood CD4⁺ and CD8⁺ T cells after in vitro stimulation (treatment arm)

The following box plots (Figure 7) report the median, IQR and range of pro-inflammatory (IL-2, IL-17, TNF-α IFN-γ) and anti-inflammatory (IL-4, IL-10) cytokine production by CD4⁺ and CD8⁺ T cells after ex vivo activation by clinical group over time. The production of IL-2 and IL-10 by CD4⁺ and CD8⁺ T cells was similar in both the HSCTlite and the usual-care arms, whereas the production of IL-4, IL-17, TNFα and IFN-γ by CD4⁺ T cells was higher in the HSCTlite arm than in the usual-care arm. With regards to the CD8⁺ T cell population, the production of all cytokines was similar, apart from IL-4, which was higher in the HSCTlite arm than in the usual-care arm. Data on the cytokine generation by peripheral blood T cell subsets after stimulation according to treatment success/failure for the intervention arm for individual patients are provided in Appendix 6, Figures 10–21.

FIGURE 7.

Cytokine expression by peripheral blood CD4⁺ and CD8⁺ T cells after in vitro stimulation, split by treatment arm, presented on the ITT population. (a) CD4⁺ T cells expressing IL-2; (b) CD4⁺ T cells expressing IL-4; (c) CD4⁺ T cells expressing IL-17; (d) CD4⁺ T cells expressing TNFα; (e) CD4⁺ T cells expressing IL-10; (f) CD4⁺ T cells expressing IFNγ; (g) CD8⁺ T cells expressing IL-2; (h) CD8⁺ T cells expressing IL-4; (i) CD8⁺ T cells expressing IL-17; (j) CD8⁺ T cells expressing TNFα; (k) CD8⁺ T cells expressing IL-10; and (l) CD8⁺ T cells expressing IFNγ.

A comparison of week 32 creatinine against week 8 T cell subsets after stimulation is provided in Appendix 7, Figures 22–33.

Not all patients provided samples for all time points for this analysis. The numbers of samples used are as follows:

• baseline – n = 13, HSCTlite arm; n = 8, usual-care arm

• week 8 – n = 9, HSCTlite arm; n = 6, usual-care arm

• week 14 – n = 8, HSCTlite arm; n = 6, usual-care arm

• week 24 – n = 7, HSCTlite arm; n = 7, usual-care arm

• week 32 – n = 5, HSCTlite arm; n = 5, usual-care arm

• week 48 – n = 6, HSCTlite arm; n = 5, usual-care arm.

Analysis of recent thymic emigrants: T-cell receptor excision circle quantitation using reverse transcription polymerase chain reaction (treatment arm)

The following box plot (Figure 8) reports the median, IQR and range for the presence of recent thymic emigrants (TRECs) by clinical group over time. As would be expected, the number of TRECs was lower in the HSCTlite arm than in the usual-care arm, but had recovered to approximately those numbers in the usual-care arm by week 48.

FIGURE 8.

TREC per 10⁶ cells, split by treatment arm. Presented on the ITT population.

Not all patients provided samples for all time points for this analysis. The numbers of samples used are as follows:

• baseline – n = 13, HSCTlite arm; n = 9, usual-care arm

• week 8 – n = 9, HSCTlite arm; n = 8, usual-care arm

• week 14 – n = 8, HSCTlite arm; n = 7, usual-care arm

• week 24 – n = 8, HSCTlite arm; n = 7, usual-care arm

• week 32 – n = 5, HSCTlite arm; n = 5, usual-care arm

• week 48 – n = 6, HSCTlite arm, n = 4, usual-care arm.

Summary of findings

The ASTIClite trial was designed to determine if autologous stem cell transplantation using a lower-intensity regimen than previously trialled would, compared with usual care, lead to a significantly greater number of patients with treatment-refractory CD achieving endoscopic remission at 1 year with an acceptable safety profile. The trial was stopped before full recruitment on the advice of the DMEC and TSC owing to a high incidence of suspected unexpected SAEs and one patient death.

In total, 23 patients with advanced refractory disease were randomised (n = 13, HSCTlite arm; n = 10, usual-care arm). The efficacy analysis comprised 10 patients who completed HSCTlite treatment and nine patients who received usual care. Data on the primary outcome of death, confirmed colonoscopy or non-attendance due to progressive disease were available for 7 out of 10 HSCTlite and six out of nine usual-care patients at week 48. Absence of endoscopic ulceration without surgery or death was reported in three out of seven (43%) HSCTlite patients compared with zero out of six (0%) usual-care patients.

The endoscopic disease activity measured using the SES-CD [mean (SD)] was 10.8 (6.3) and 10.0 (6.1) at baseline, compared with 2.8 (2.9) and 18.7 (9.1) at week 48 in the HSCTlite and usual-care arms, respectively. Clinical remission (CDAI score < 150) occurred in 57% and 17% of patients in the HSCTlite and usual-care arms, respectively, at week 48.

There was a marked difference in the profile of all the immune cell subsets studied between the HSCTlite and usual-care arms after HSCTlite. Of all the subsets studied, only the numbers of recent thymic emigrant cytotoxic T helper cells, gut-homing cytotoxic T cells, effector memory T helper cells and CD8⁺ cytotoxic T cells had returned to equivalence with the usual-care arm at week 48, with levels of CD3⁺, CD4⁺, CD4⁺ recent thymic emigrants, central memory T helper cells, CD4⁺ effector T helper cells and naive T helper cells remaining lower in the HSCTlite arm. After in vitro stimulation, the CD4⁺ and CD8⁺ lymphocytes from HSCT patients expressed higher levels of Th1 and Th17 cytokines, that is, IFN-gamma, TNF and IL-17, as well as Th2 cytokines, that is, IL-4, compared with usual care at most time points.

Serious adverse events were more frequent in patients undergoing HSCTlite treatment [38 in 13 (100%) patients] than in patients undergoing usual care [16 in 4 (40%) patients]. Importantly, nine SUSARs were reported in six HSCTlite patients, including three cases of delayed renal failure due to proven TMA. Two patients in the HSCTlite arm died: one from pulmonary veno-occlusive disease at week 24 and one from infection and renal failure (not proven to be TMA) at week 60 after having completed the trial. All patients undergoing HSCTlite treatment showed evidence of re-engraftment with immune recovery during the first year.

Despite being designed as low intensity with lower doses of cyclophosphamide than used previously, the mobilisation and conditioning regimen used for HSCTlite in this trial was associated with an unacceptable rate of AEs. There was evidence of efficacy, with some patients experiencing a meaningful reduction in endoscopic disease activity. However, the observed benefit does not mitigate the AEs, and HSCTlite using this regimen should not be used as a therapy even in patients with severely active treatment-refractory CD.

Strengths and limitations

This trial was designed to be the largest ASTIC RCT to date, taking into account issues identified in the previous ASTIC trial and case series as outlined above. The inclusion criteria allowed a wide population of patients with refractory disease to be recruited, including patients with multiple previous surgeries or with a stoma. These patients are rarely eligible for clinical trials of novel therapies in CD. Patients with active perianal or penetrating disease were excluded, as previous studies24 had shown higher levels of SAEs in these patients. An endoscopic primary end point was chosen with central reading by investigators blind to treatment assignation and time of assessment to counter the fact that neither patient nor investigators were blind to treatment group. Multiple endoscopic, clinical and quality-of-life assessments were included. The key limitation of this study, as reported, was that recruitment was halted owing to safety concerns of the HSCTlite regimen after only 23 patients had been recruited. In addition, the COVID-19 pandemic prevented a number of patients undergoing some of the scheduled study visits and outcome assessments. Therefore, the total number of patients in whom the primary and secondary end points could be analysed was markedly reduced, and hence the power to detect benefit from HSCTlite was reduced. In addition, three primary end point colonoscopies were not recorded, either through error or because of technical issues, further reducing the available data on which to make conclusions. However, given the number of SAEs and SUSARs reported in the HSCTlite arm, it is clear that this HSCT regimen does not have an acceptable safety profile.

Implications for policy makers, health professionals and patients

Despite the meaningful benefits in terms of endoscopic disease regression in some patients undergoing HSCTlite, it is clear that the regimen assessed in this clinical trial is not appropriate for use in clinical practice because of the adverse safety profile. The study highlights that there are many patients with treatment-refractory CD in the UK who suffer significant morbidity related to chronic intestinal inflammation. Further studies to identify treatments that result in long-term resolution of intestinal inflammation with an acceptable safety profile for this refractory patient group are urgently required. Advanced therapies with either novel or more selective mechanisms of action are in phase III clinical trials. Although preliminary studies suggest enhanced benefit, their impact on refractory CD still requires study. It may be that combinations of advanced therapy are required to induce remission in this patient group and that studying the efficacy and, importantly, safety of these strategies is required.

Further research

There have now been two RCTs of autologous stem cell transplantation in patients with treatment-refractory CD. Both were halted on the advice of the DMEC prior to complete recruitment after a patient death. The aetiology of the TMA seen in ASTIClite has not been determined. Without modifiable cause being ascertained, a further large clinical trial of HSCTlite in patients with refractory CD is not considered appropriate. However, there may be individual situations in which HSCTlite for refractory CD is considered in expert centres, particularly those that are usually excluded from clinical trials. A prospective database of patients undergoing HSCTlite that documents baseline characteristics, HSCTlite regimen, clinical/endoscopic outcome and adverse effects could be created for such patients.

The reduced-intensity conditioning regimen (with fludarabine, cyclophosphamide and ATG) could be adapted further to deliver autologous HSCTlite, or even allogeneic HSCTlite, which is likely to be highly curative despite having a number of additional risks. Recent developments in the broader HSCT field, such as the use of antibody-targeted conditioning regimens and post-transplantation cyclophosphamide or other immunosuppressive post-transplantation therapy, could also be incorporated into both autologous and allogeneic HSCTlite regimens.

The mobilisation regimen with reduced-dose cyclophosphamide (1 g/m²) and G-CSF used in ASTIClite was safe and effective for autologous HSCTlite, and could be used in future patients, although other mobilisation regimens, including chemotherapy-free and novel antibody-targeted mobilisation regimens, could be trialled.

The prospective database could be used to compare HSCTlite interventions with other advanced and biologic therapies, both as single agents and in combination with an endoscopic primary end point.

The research priorities moving forward are to determine the optimal treatment strategy for the significant number of patients with refractory active CD who fail to respond to currently available therapy. This should include patients who have a stoma or have had multiple previous resections, who are currently excluded from most clinical trials. The intervention will likely be a combination of advanced and biologic therapies compared with a single agent. Given the population and likelihood of prior intestinal damage, an endoscopic primary end point is appropriate.

Conclusions

The ASTIClite trial was designed to assess the efficacy and safety of autologous stem cell transplantation in patients with treatment-refractory CD using a mobilisation and conditioning regimen with lower doses of cyclophosphamide than previously assessed in the hope that this would reduce the number of significant serious infections that had been observed. 17 The trial was halted early because of several SUSARs and one patient death. Although several patients undergoing HSCTlite experienced marked improvement in endoscopic disease activity, the large number of AEs (including serious reactions) preclude the use of this regimen in its current form. Patients with treatment-refractory CD nevertheless experience severe and sustained poor quality of life, and in the absence of therapeutic alternatives HSCTlite may remain a potential future treatment if a more tolerable regimen can be identified. Further research is required to identify the optimal treatment for this population with refractory disease, which is associated with poor quality of life and significant morbidity.

Contributions of authors

James O Lindsay (https://orcid.org/0000-0003-3353-9590) (Chief Investigator, Consultant Gastroenterologist) was involved in producing the first draft of the report, conceiving and designing the work, the acquisition, analysis and interpretation of data for the work, and drafting the monograph.

Daniel Hind (https://orcid.org/0000-0002-6409-4793) was involved in conceiving and designing the work.

Lizzie Swaby (https://orcid.org/0000-0001-9443-7681) (Study Manager) was involved in producing the first draft of the report, conceiving and designing the work, the acquisition, analysis and interpretation of data for the work, and drafting the monograph.

Hannah Berntsson (https://orcid.org/0000-0002-6285-6985) (Research Assistant) was involved in producing the first draft of the report, the acquisition, analysis and interpretation of data for the work, and drafting the monograph.

Mike Bradburn (https://orcid.org/0000-0002-3783-9761) (Senior Statistician) was involved in producing the first draft of the report, conceiving and designing the work, the analysis and interpretation of data for the work, and drafting the monograph.

Uday Bannur C (https://orcid.org/0000-0003-0330-0327) was involved in the acquisition of data for the work.

Jennifer Byrne (https://orcid.org/0000-0002-9381-1851) was involved in reviewing and amending the transplant and supportive care regimen in the protocol and the acquisition of data for the work.

Christopher Clarke (https://orcid.org/0000-0002-8092-9877) was involved in the acquisition of data for the work.

Lauren Desoysa (https://orcid.org/0000-0002-6151-836X) (Statistician) was involved in producing the first draft of the report, the analysis and interpretation of data for the work, and drafting the monograph.

Shahida Din (https://orcid.org/0000-0003-2855-3400) was involved in the acquisition of data for the work.

Richard Emsley (https://orcid.org/0000-0002-1218-675X) was involved in conceiving and designing the work and the analysis of data for the work.

Gemma A Foulds (https://orcid.org/0000-0002-2053-7580) (Research Fellow and Mechanistic Analytical Project Manager) was involved in producing the first draft of the report, the acquisition, analysis and interpretation of data for the work, and drafting the monograph.

John Gribben (https://orcid.org/0000-0002-8505-7430) was involved in conceiving and designing the work, reviewing and amending the transplant and supportive care regimen in the protocol, and the acquisition of data for the work.

Christopher Hawkey (https://orcid.org/0000-0002-6031-1017) was involved in conceiving and designing the work.

Peter M Irving (https://orcid.org/0000-0003-0972-8148) was involved in acquisition of data for the work.

Peter Johnson (https://orcid.org/0000-0002-8849-0790) was involved in reviewing and amending the transplant and supportive care regimen in the protocol and the acquisition of data for the work.

Majid Kazmi (https://orcid.org/0000-0002-6863-6297) was involved in reviewing and amending the transplant and supportive care regimen in the protocol.

Ellen Lee (https://orcid.org/0000-0003-4529-7410) (Statistician) was involved in producing the first draft of the report, analysis and interpretation of data for the work, and drafting the monograph.

Amanda Loban (https://orcid.org/0000-0001-7089-1580) was involved in the acquisition and analysis of data for the work.

Alan Lobo (https://orcid.org/0000-0001-8037-793X) was involved in conceiving and designing the work and acquisition of data for the work.

Yashwant Mahida (https://orcid.org/0000-0001-8666-7815) was involved in conceiving and designing the work.

Gordon Moran (https://orcid.org/0000-0002-8906-6908) was involved in conceiving and designing the work and acquisition of data for the work.

Diana Papaioannou (https://orcid.org/0000-0002-6259-0822) was involved in conceiving and designing the work.

Miles Parkes (https://orcid.org/0000-0002-6467-0631) was involved in conceiving and designing the work and acquisition of data for the work.

Andrew Peniket (https://orcid.org/0000-0002-6833-9882) was involved in acquisition of data for the work.

A Graham Pockley (https://orcid.org/0000-0001-9593-6431) (Co-Applicant, Lead for Mechanistic Analysis) was involved in producing the first draft of the report, conceiving and designing the work, analysis and interpretation of the data for the work, and drafting the monograph.

Jack Satsangi (https://orcid.org/0000-0002-6357-9684) was involved in conceiving and designing the work.

Sreedhar Subramanian (https://orcid.org/0000-0002-6483-1730) was involved in acquisition of data for the work.

Simon Travis (https://orcid.org/0000-0002-2690-4361) was involved in conceiving and designing the work and acquisition of data for the work.

Emily Turton (https://orcid.org/0000-0001-5763-9604) was involved in acquisition and analysis of data for the work.

Ben Uttenthal (https://orcid.org/0000-0002-5340-2527) was involved in reviewing and amending the transplant and supportive care regimen in the protocol and acquisition of data for the work.

Sergio Rutella (https://orcid.org/0000-0003-1970-7375) was involved in analysis and interpretation of data for the work.

John A Snowden (https://orcid.org/0000-0001-6819-3476) (Lead Consultant Haematologist) was involved in producing the first draft of the report, conceiving and designing the work, reviewing and amending the transplant and supportive care regimen in the protocol, acquisition, analysis and interpretation of data for the work, and drafting the monograph.

Amit Patel was involved in reviewing and amending the transplant and supportive care regimen in the protocol and the acquisition of data for the work.

All named authors revised the work critically for important intellectual content.

All named authors were involved in the final approval of the version to be published.

All authors agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Publications

Snowden JA, Sharrack B, Akil M, Kiely DG, Lobo A, Kazmi M, et al. Autologous haematopoietic stem cell transplantation (aHSCT) for severe resistant autoimmune and inflammatory diseases – a guide for the generalist. Clin Med 2018;18:329–34.

Pockley AG, Lindsay JO, Foulds GA, Rutella S, Gribben JG, Alexander T, Snowden JA. Immune reconstitution after autologous hematopoietic stem cell transplantation in Crohn’s disease: current status and future directions. A review on behalf of the EBMT Autoimmune Diseases Working Party and the Autologous Stem Cell Transplantation In Refractory CD-Low Intensity Therapy Evaluation study investigators. Front Immunol 2018;9:646.

Snowden JA, Hawkey C, Hind D, Swaby L, Mellor K, Emsley R, et al. Autologous stem cell transplantation in refractory Crohn’s disease – low intensity therapy evaluation (ASTIClite): study protocols for a multicentre, randomised controlled trial and observational follow up study. BMC Gastroenterol 2019;19:82.

Lindsay JO, Hind D, Swaby L, Berntsson H, Bradburn M, Bannur CU, et al. Safety and efficacy of autologous haematopoietic stem-cell transplantation with low-dose cyclophosphamide mobilisation and reduced intensity conditioning versus standard of care in refractory Crohn’s disease (ASTIClite): an open-label, multicentre, randomised controlled trial. Lancet Gastroenterol Hepatol 2024; in press. https://doi.org/10.1016/S2468-1253(23)00460-0

Data-sharing statement

Requests for patient-level data and statistical code should be made to the corresponding author.

Patient data

This work uses data provided by patients and collected by the NHS as part of their care and support. Using patient data is vital to improve health and care for everyone. There is huge potential to make better use of information from people’s patient records, to understand more about disease, develop new treatments, monitor safety, and plan NHS services. Patient data should be kept safe and secure, to protect everyone’s privacy, and it’s important that there are safeguards to make sure that it is stored and used responsibly. Everyone should be able to find out about how patient data are used. #datasaveslives You can find out more about the background to this citation here: https://understandingpatientdata.org.uk/data-citation.

Disclaimers

This report presents independent research. The views and opinions expressed by authors in this publication are those of the authors and do not necessarily reflect those of the NHS, the NIHR, the MRC, the EME programme or the Department of Health and Social Care. If there are verbatim quotations included in this publication the views and opinions expressed by the interviewees are those of the interviewees and do not necessarily reflect those of the authors, those of the NHS, the NIHR, the EME programme or the Department of Health and Social Care.