Melanocyte-specific CD8+ T cells demonstrate tolerance characterized by an impaired ability to differentiate into a highly proliferative population

Abstract

The mechanisms governing non-deletional CD8+ T cell tolerance are poorly understood. We are using a physiologically-relevant mouse model to better understand the regulation of self-specific CD8+ T cells, which impact both autoimmune disease and cancer. We find a substantial number of polyclonal cells specific for an epitope from the melanocyte/melanoma-associated enzyme tyrosinase-related protein 2 (Trp2) in both wild-type (WT) C57BL/6 and Trp2-deficient (Trp2 KO) mice. In pre-immune mice, these cells have a naïve phenotype in both strains, and they respond similarly for the first several days after in vivo stimulation with Trp2 peptide alone or in combination with adjuvants (TriVax). However, significantly fewer WT Trp2-specific cells are present at an effector timepoint after TriVax or recombinant Trp2-expressing Listeria monocytogenes relative to KO Trp2-specific cells. WT Trp2-specific cells also show a deficiency in mediating vitiligo compared with KO cells when TriVax-generated effectors are transferred into recipient WT mice primed with TriVax and dinitrofluorobenzene (DNFB). Single-cell RNA sequencing at day three after stimulation reveals that KO Trp2-specific cells efficiently differentiate into a proliferative population, whereas few WT Trp2-specific cells demonstrate this phenotype. As a population, WT Trp2-specific CD8+ T cells exhibit covert anergy: despite a naïve appearance at steady state and initial acquisition of activation markers after stimulation, these self-specific cells are unable to expand productively or to efficiently mediate functional anti-melanocyte activity. These findings have implications for recently-described non-deletional CD8+ T cell tolerance in humans.