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Background and Aims The long-term safety and efficacy of allogeneic bone marrow-derived mesenchymal stromal cell [bmMSC] therapy in perianal Crohn’s disease [CD] fistulas is unknown. We aimed to provide a 4-year clinical evaluation of allogeneic bmMSC treatment of perianal CD fistulas. Methods A double-blind dose-finding study for local bmMSC therapy in 21 patients with refractory perianal fistulising Crohn’s disease was performed at the Leiden University Medical Center in 2012–2014. All patients treated with bmMSCs [1 x 107 bmMSCs cohort 1, n = 5; 3 × 107 bmMSCs cohort 2, n = 5; 9 × 107 bmMSCs cohort 3, n = 5] were invited for a 4-year evaluation. Clinical events were registered, fistula closure was evaluated, and anti-human leukocyte antigen [HLA] antibodies were assessed. Patients were also asked to undergo a pelvic magnetic resonance imaging [MRI] and rectoscopy. Results Thirteen out of 15 patients [87%] treated with bmMSCs were available for long-term follow-up. Two non-MSC related malignancies were observed. No serious adverse events thought to be related to bmMSC therapy were found. In cohort 2 [n = 4], all fistulas were closed 4 years after bmMSC therapy. In cohort 1 [n = 4] 63%, and in cohort 3 [n = 5] 43%, of the fistulas were closed, respectively. In none of the patients anti-HLA antibodies could be detected 24 weeks and 4 years after therapy. Pelvic MRI showed significantly smaller fistula tracts after 4 years. Conclusions Allogeneic bmMSC therapy for CD-associated perianal fistulas is also in the long-term a safe therapy. In bmMSC-treated patients, fistulas with closure at Week 24 were still closed after 4 years.

Background Local mesenchymal stromal cell (MSC)-therapy is approved for the treatment of Crohn’s disease-associated perianal fistulas. However, little is known about the working mechanism of local MSC-therapy. For the first time we evaluated engraftment and immunoregulatory effects of local MSC-therapy in patients with refractory proctitis. To do so, we analyzed biopsies and serum from patients with ulcerative proctitis before and after treatment with endoscopically injected MSCs in a phase IIa clinical trial (EudraCT number 2017-003524-75). Methods Thirteen therapy-refractory ulcerative proctitis patients were endoscopically injected bone marrow-derived allogeneic MSCs from healthy donors. Clinical efficacy was evaluated by the endoscopic and full Mayo score. Engraftment of the MSCs was investigated using fluorescence in-situ hybridization (FISH) of sex chromosomes on post-treatment biopsies. The presence of anti-HLA-antibodies against the MSC-donor was determined in the serum. Changes in immune cell subsets were evaluated using cytometry-by-time-of-flight (CyTOF) analysis. Results Thirteen patients with an endoscopic Mayo score of 2 (n=3) or 3 (n=10) of the rectum were treated with local MSC-therapy. Although complete remission was not achieved, full Mayo score was improved at week 6 (median 8 [IQR 6–10]) compared to baseline (median 11 [IQR 9.5–12]) (p=0.001). Preliminary data using FISH on the Y-chromosome, indicated the presence of MSCs in the rectum biopsies of female patients treated with male donor derived-MSCs at week 6. At baseline, HLA-antibodies were present in four patients. Six weeks after local injection of the MSCs, two out of thirteen patients developed new class I and II HLA-antibodies against the MSCs. Interestingly, in two patients pre-existing HLA-antibodies showed increased/boosted levels after local MSC-therapy, while one additionally developed new HLA-antibodies. CyTOF analysis of inflamed rectal biopsies 6 weeks after MSC treatment revealed significantly increased frequencies of several myeloid subsets (i.e. CD11b+CD14+CCR7+/-CD127+CD25+HLADR+ and CD14+HLA-DR-CD123-CCR7+) and a subset of CD4+ memory T cells with a more exhausted/regulated phenotype (PD-1+TIGIT+CD69+CD38+CD69). Conclusion Local MSC-therapy in patients with refractory proctitis changed the rectal immune profile characterised by a significant increase in a subset of effector memory CD4+ cells and several myeloid subsets, which might be associated with immune modulation. These results provide the basis for future studies on the mechanism of action of MSCs on rectal mucosa. New anti-HLA class antibodies developed in 2/13 patients after local administration. Whether these latter results have consequences for MSC-donor selection deserves further study.

Background Ulcerative proctitis (UP) can be refractory to treatment, which calls for development of new (local) therapies. Local injection of mesenchymal stromal cells (MSCs) has shown beneficial effects in patients with fistulizing Crohn’s disease and promising results have been obtained when MSCs were locally injected in the bowel of mice with experimental colitis. Our primary aim was to determine the safety, feasibility and tolerability of endoscopically injected allogeneic bone marrow-derived MSCs (bmMSCs) in UP patients. Methods UP patients with endoscopic Mayo score (EMS) 2 or 3, who failed on both rectal 5-ASA and corticosteroids for at least 4 weeks, were eligible for inclusion (EudraCT number 2017-003524-75). Rectal therapies were stopped 2 weeks prior to baseline, but other medication was kept stable until at least 6 weeks after MSC injection. MSCs were locally injected in 4 quadrants of the inflamed rectal submucosa if the inflammation was limited to 7 cm. If the length of inflammation was >7 cm, MSCs were injected in another 4 quadrants more proximally as well. Patients in the first cohort (n=7) were treated with 5*106 MSCs/spot and in the second cohort (n=6) with 10*106MSCs/spot. Adverse events, full Mayo score, fecal calprotectin (FCP), histologic activity (Geboes score [GS]) and quality of life (sIBDQ), were assessed at week 0, 2, 6, 12, and 24, and evaluated by non-parametric paired statistical analyses. Results All reported adverse events were minor, no patients required interventions and no feasibility issues were reported. Median[interquartile range (IQR)] full Mayo score was 11[9.5-12] at baseline, 9[8-11] at week 2 (p=0.003), 8[6-10] at week 6 (p=0.001), and 4[1.5-7] at week 24 (p Conclusion Local administration of allogeneic bmMSCs appears safe, tolerable and feasible for the treatment of refractory UP, and shows encouraging indications of clinical efficacy. Further mechanistic and immunological analyses are currently being performed.

Background Ulcerative proctitis (UP) causes a chronic rectal mucosal inflammation. A subset of patients does not respond to one or more medication options. Mesenchymal stromal cells (MSCs) show beneficial effects in animal models and patients with immune diseases. However, the effects of MSCs on the mucosal immune composition in patients with inflammatory bowel disease (IBD) are not unravelled yet. Methods Patients with UP (N = 7) were locally treated with allogeneic bone marrow-derived MSCs. A total of 20 × 106 MSCs was injected if the inflammation was restricted to 7 cm and 40 × 106 if inflammation exceeds 7 cm. Medication was stable in all patients from at least 2 weeks before treatment up to week 6 after treatment. Biopsies were taken from the affected and unaffected colon before (t = 0) and 6 weeks (t = 6) after treatment from the same locations and faecal calprotectin (FCP) was determined. Single-cell suspensions from the biopsies were stained with a 42 antibody panel and analysed with a mass cytometer to identify and characterise possible effects of MSCs on immune subsets. The generated dataset was analysed with Hierarchical SNE (HSNE) in the Cytosplore analysis and visualisation tool. Results FCP decreased significantly in four out of seven patients (419→191; 365→40; 1744→346; 3270→291), ‘responders’, while in three patients FCP increased, ‘non-responders’. Unbiased hierarchical clustering of the subsets showed no clear differences in the major immune lineages before and after treatment. In some patients; however, a prominent myeloid population was present in the affected colon, whereas the CD8+− and CD3−CD7+ populations in affected tissue were in general less frequent compared with unaffected tissue from the same patients. We then zoomed into every major lineage separately, and observed changes in the frequencies of two myeloid clusters in the affected tissue of ‘responders’ compared with the ‘non-responders’ (see figure, Cluster 1=CD11b+CD11c+CD66b+CD15intCD16+CD45RA−CD45RO+ cells, Cluster 2= CD11b+CD11c+CD66b+ CD15−CD16−CD69+CD45RA+CD45RO+ cells). Conclusion These preliminary data show differences between ‘responders’ and ‘non-responders’ in the myeloid compartment in the inflamed tissue after MSC therapy. Since CD11b+ and CD11c+ populations mediate the tolerogenic effect of MSC in mouse models, we will explore the regulatory potential of the observed populations in MSC-treated UP patients in future studies. The inclusion of patients in a second cohort (N = 7) is currently ongoing.