Inflammasome-resistant IPSC-derived myeloid-derived suppressor cells (iMDSCs) ameliorate xenogeneic GVHD

Acute graft versus host disease (aGVHD) is considered a major complication of allogeneic hematopoietic stem cell transplant (aHSCT). Front-line pharmaceutical treatment is not uniformly effective and has toxic side effects. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells with potent immunosuppressive functions. Their potential to control GVHD has been proven in different rodent models. However, a high MDSC to T cell ratio and multiple doses of MDSCs are needed to achieve maximum effectiveness. Clinical translation of in vitro MDSC generation limits its clinical usage by a relatively low yield and need for personalized patient products, especially challenging for multiple treatment courses. Therefore, we developed an in vitro method to generate MDSCs on a large scale from a human induced pluripotent stem cell (iPSC)-derived CD34+ cells. iMDSCs shared a similar morphology, phenotype, and suppressive function with peripheral blood (PB)-MDSCs. In striking contrast to PB-MDSCs, iMDSCs retained 95% of suppressor function when exposed to the damage-associated molecular pattern stimuli, LPS + ATP, released during GVHD. RNAseq analysis and gene knockdown studies revealed that inflammasome-resistant iMDSCs maintained expression of phosphoglycerate dehydrogenase, an enzyme involved in purine metabolism. Consistent with the retention of suppressor function during lethal xenogeneic GVHD-induced tissue injury, recipients of human iMDSCs and peripheral blood mononuclear cells (PBMC) experienced therapeutic benefits. Together, these data provide a platform for translating in vitro generated, off-the-shelf iMDSCs into the clinic for suppressing GVHD and other adverse immune responses.