INTRODUCTION For the treatment of refractory Crohn’s disease (CD) autologous stem cell transplant (auto-SCT) is unparalleled in its ability to induce clinical and endoscopic remission.(1, 2) Auto-SCT is unique as a cellular therapy aimed to reset immune pathophysiology to a pre-disease state using hematopoietic stem cells. As such, the study of how the immune system responds to auto-SCT will provide unique insight into CD pathogenesis and treatment. To date, no studies in any cohort have defined the mucosal and peripheral immune response to auto-SCT. Here we report initial studies of high dimensional immune phenotyping of patients with CD during auto-SCT. METHODS Patients with CD were enrolled in a Phase IIa study of auto-SCT (NCT03219359). 14 patients were transplanted (2018-2022). Paired blood and intestinal samples were taken prior to transplant and 6 months post-transplant. Fresh leukocytes were isolated and analyzed by mass cytometry (CyTOF). Supervised clustering of immune cell populations using canonical markers was performed in parallel with unsupervised clustering by FlowSOM.(3) RESULTS After 6 months post-transplant,12/13 patients had an endoscopic response (↓SES-CD by 50%) and 10/13 patients were in endoscopic remission (SES-CD CONCLUSION We demonstrate for the first time differences in the intestinal and peripheral immune response to auto-SCT. These studies highlight the changes in intestinal immune cell networks that define the transplant response perhaps through CD14+ cells.