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Research Article: Mutation of conserved MHC class I cytoplasmic tyrosine affects CD8+ T cell priming, effector function, and memory response

Date Published: 2025-09-30

Abstract:
The cytoplasmic domain of MHC class I (MHC-I) molecules contains a single, highly conserved tyrosine residue (Y320). In previous work, we found that mice expressing a Y320F-mutated form of H-2K b had reduced capacity to generate K b -restricted cytotoxic T lymphocyte (CTL) responses following viral infection, due at least in part to defects in endolysosomal trafficking of H-2K b and antigen cross-presentation by dendritic cells (DCs). In this study, we investigated whether there are additional, post-presentation dependencies on Y320 for T cell priming. We engineered both human- and mouse-derived antigen-presenting cells (APCs) to express either wild-type MHC-I or variants of MHC-I containing Y320F or Y320E mutations. We found that Y320E-mutated HLA-A*0201 elicited enhanced in vitro priming and expansion of human antigen-specific CD8+ T cells, which showed a unique transcriptional profile compared to T cells primed with APCs expressing either WT or Y320F-mutated A*0201. Furthermore, the Y320E variant of H-2K b expressed in the context of a murine DC vaccine model induced altered T cell differentiation kinetics while improving both anti-tumor immunity and augmenting the magnitude of memory CD8+ T cell responses in vivo . These results suggest that Y320 phosphorylation of MHC-I may play a role in determining the fate and function of CD8+ T cells and suggest a novel strategy for improving DC-based cancer immunotherapies.

Introduction:
The short cytoplasmic domains of classical MHC-I molecules (~35 amino acids) display striking evolutionary conservation at three sites of potential phosphorylation: two serine residues (S332 and S335) encoded by exon 7, and a single tyrosine residue (Y320) encoded by exon 6 ( 1 – 6 ). Serine phosphorylation of the MHC-I cytoplasmic tail has been associated with oncogenic signaling, internalization, and intracellular trafficking, although the kinases involved have yet to be identified, and exon 7-deleted forms of…

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