Insulin-producing β cell replacement therapies show promise for treating type 1 diabetes (T1D), but challenges such as donor shortages and immune rejection persist. Stem cell–derived β cells (sBC) provide a renewable source but remain susceptible to immune attack. We engineered human pluripotent stem cells to express either the wild type (WT) or a high-affinity mutant (Mut) variant (rs1058402, G>A; Ala ⁶⁷ Thr) of the natural killer (NK) and T cell checkpoint inhibitor CD155 before differentiation into sBC. Modified sBC maintained up-regulated CD155 expression and showed enhanced binding to co-receptor ligands. Co-culture studies revealed CD155-expressing sBC suppressed autoreactive CD8 ⁺ T cell and NK cell activation, reducing immune cell–mediated sBC destruction and cytotoxic molecule secretion by preferentially engaging the coinhibitory receptor TIGIT. This protection was lost with TIGIT blockade, affirming the role of CD155-TIGIT signaling in antagonizing immune cell cytotoxicity. Our findings suggest that high-affinity CD155 expression enhances immune evasion of sBC, improving their potential as a therapy for T1D.