Inflammasome-resistant IPSC-derived myeloid-derived suppressor cells ameliorate xenogeneic graft-versus-host disease Available to Purchase

• First method to efficiently generate off-the-shelf human iPSC-derived MDSCs with potent T cell suppressor function in vitro and in vivo.

• iMDSCs expressed the serine-producing enzyme, PHGDH, required to overcome GVHD-related inflammasome-induced loss of suppressor function.

Front-line pharmaceutical treatment for treatment of acute graft-versus-host disease (aGVHD) is not uniformly effective and has toxic side effects. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells with potent in vitro and in vivo immunosuppressive functions. Clinical translation of in vitro generated MDSCs has been limited by the need for high MDSC:T cell ratios, multiple infusions to reduce inflammation and a relatively low peripheral blood-derived MDSC (PB-MDSCs) yield. To circumvent these obstacles, we developed a methodology to generate MDSCs using human induced pluripotent stem cell (iPSC)-derived CD34+ cells. Compared to PB-MDSCs, iPSC-MDSCs (iMDSCs) shared similar morphology, phenotype, and suppressive function. We found that the CD14+ iMDSC subset possessed the highest suppressor function. In previous studies, we reported that MDSCs transferred on day 0 into mice undergoing GVHD lost suppressor function due to inflammasome activation and immature myeloid cell maturation1. In striking contrast to human PB-MDSCs, we show here that iMDSCs retained 95% of suppressor function in vitro despite exposure to LPS+ATP, danger-associated molecular patterns inflammasome activating stimuli released early post-transplant during conditioning and GVHD-induced injury. When transferred in vivo with PB mononuclear cells, iMDSCs significantly increased recipient survival without loss of anti-leukemia effects. iMDSC RNAseq and gene knockdown studies revealed that the maintenance of the purine metabolizing enzyme, phosphoglycerate dehydrogenase, during LPS+ATP was linked to iMDSC inflammasome resistance. Taken together, these data provide a platform for translating in vitro generated, off-the-shelf iMDSCs into the clinic for suppressing a spectrum of adverse immune responses including GVHD.