The signal regulatory protein gamma (SIRPγ) signaling constrains naïve CD8+ T cell activation with T1D risk associated polymorphisms leading to augmented T cell activation

Abstract

Abstract Genome-wide association studies (GWAS) have identified single-nucleotide polymorphisms (SNPs; rs2281808 and rs6043409) in Signal Regulatory Protein Gamma (SIRPG) with increased susceptibility for type 1 diabetes (T1D). SIRPγ is highly expressed on both CD4+/CD8+ T cells, however, its influence on T cell activation state is insufficiently characterized. We hypothesize that SIRPγ restrains T cell activation and T1D-associated risk variants in SIRPγ influence interactions with its binding partner CD47 to augment CD8+ T cell activation leading to a cytotoxic phenotype. Flow cytometric analysis of PBMC identified SIRPγ/CD47 to be highly expressed on CD4+/CD8+ T cells, with a sequential decline to central memory (TCM), effector memory (TEM), and terminal effector memory cell expressing CD45RA (TEMRA). To test the impact of SIRPγ expression, we generated SIRPG and CD47 knockout (KO) of primary human CD8+ T cells by CRISPR-Cas9 gene editing. Following in vitro activation with anti-CD3/CD28, SIRPG/CD47 KO CD8+ T cells exhibited significantly higher surface activation markers (CD25/CD69) and lower co-inhibitory receptors (CTLA-4/PD-1) compared to controls. Moreover, naïve SIRPγ KO CD8+ T cells differentiated at a higher rate into TEMRA cells. In terms of effector function, SIRPG/CD47 KO CD8+ T cell cultures produced higher levels of the effector molecules TNFα, perforin, and granzyme B and exhibited significantly more cytotoxic killing potential when co-cultured with a targeted pancreatic cell line (βLox5). Overall, this study suggests the SIRPγ:CD47 signaling pathway serves as an immune checkpoint for T cell activation and differentiation of T cells, with the potential for therapeutic targeting during T1D pathogenesis.