The reparative immunologic consequences of stem cell transplantation as a cellular therapy for refractory Crohn's disease

Background Treatment strategies for Crohn's disease (CD) suppress diverse inflammatory pathways but many patients remain refractory to treatment. Autologous hematopoietic stem cell transplantation (SCT) is an emerging therapy for medically-refractory CD though the mechanisms through which it circumvents refractory pathophysiology are unknown. Objective The objective of this study is to understand how the immune system reconstitutes post-SCT and whether SCT may function as a cellular therapy restoring appropriately responsive immune cell populations from hematopoietic stem cells (HSCs). Design Adults with CD with active clinical and endoscopic disease who failed available medical therapies were enrolled in a Phase II study of SCT for refractory CD (n=19). Blood and intestinal samples were collected longitudinally and analyzed using CyTOF, scRNA-seq and TCRß-seq. Stem cell autografts were functionally assayed in mouse xenograft models. Results scRNA-seq and CyTOF analyses reveal that SCT predominantly affected the intestinal myeloid lineage with loss of inflammatory populations and return of macrophages capable of supporting mucosal healing. Xenograft models using patient HSCs suggested HSCs support the early reconstitution of the myeloid lineage and reveal an impairment of short and long-term HSC engraftment that may determine SCT outcomes. Conclusions This study suggests SCT functions as a myeloid-directed cellular therapy reinforcing the critical role of macrophages in refractory CD pathophysiology and as a target for cellular therapies. Furthermore, we report an unrecognized functional heterogeneity among HSC subpopulations in CD that may be relevant to our understanding of CD treatment and pathophysiology. Overall design: Samples of tissue from endoscopic biopsies, peripheral blood and peripheral mobilized stem cells were collected from subjects with CD enrolled for SCT. Blood and tissue samples were processed for 10x Genomics single cell RNA sequencing (scRNA-seq) and bulk T cell receptor beta (TCRß) sequencing through Adaptive technologies.