192-LB: Human CD4+CD25+CD226- Regulatory T Cells Demonstrate High Purity and Lineage Stability following In Vitro Expansion for Adoptive Cell Therapy

Human regulatory T cells (Tregs) are essential for the suppression of autoimmunity and adoptive cell therapy has been proposed as a means for restoring durable immune tolerance in T1D. The rare nature of this subset requires the isolation and in vitro expansion of thymic-derived Tregs (tTregs) for adoptive cell therapies to attenuate autoimmunity or islet transplant rejection. Current approaches involve the isolation of a subset with the marker profile of CD4+CD25+CD127-/lo. This strategy yields a population of Tregs that contains both naive and peripheral Tregs (pTregs), with peripheral Tregs tending to lose lineage stability over time. Here, a novel gating strategy is presented for obtaining tTregs with high purity and extended lineage stability involving the elimination of the effector costimulatory molecule CD226. Tregs were obtained by fluorescence-activated cell sorting (FACS). This allows for the isolation of CD4+CD25+CD226- Tregs for comparison to classically sorted CD4+CD25+CD127-/lo Tregs over a 28-day culture period. Throughout the expansion, assessment of the lineage’s canonical transcription factors (FOXP3 and Helios), along with functional characteristics and epigenetic markers of the lineage occurred. Isolation of CD226- Tregs as compared to CD127- Tregs yields a Treg population with a higher proportion of tTregs (9.35%, p=0.0016), increased expression of CD25 (1.13-fold, p=0.0023), Helios (1.21-fold, p=0.0419), and CD45RA (1.24-fold, p=0.0017), equally low expression of CD127, and decreased expression of CD226 (2.27-fold, p=0.0001). Overall, this study suggests CD226- Tregs possess an increased therapeutic potential for adoptive transfer immunotherapies, including a more naive phenotype and increased suppressive capabilities - both of which are critical factors for suppressing autoimmune destruction in vivo. Disclosure M. E. Brown: None. S. R. Hanbali: None. L. Gomez rodriguez: None. J. M. Arnoletti: None. E. B. Carpenter: None. T. M. Brusko: Consultant; Self; OneVax, LLC. Funding National Institutes of Health (1R01DK106191-01A1, UG3DK122638)