Differential expression of mannose-6-phosphate receptor regulates T cell contraction.

CD8(+) T cells provide protection against pathogens and cancer. After encountering a pathogenic antigen, CD8(+) T cells undergo a triphasic program of rapid proliferation, contraction, and memory formation. Most (∼90-95%) CD8(+) T cells die after vigorous proliferation in the T cell contraction phase, yet the mechanism that triggers apoptotic T cell death remains elusive. This study tested the hypothesis that differential cell-surface expression of M6PR, a multifunctional receptor that regulates lysozyme biogenesis, but also uptakes apoptosis-inducing serine-protease Gzm-B, critically determines life vs. death decisions in T cells. We demonstrate that M6PR-expression on CD8(+) T cell surfaces is dynamically regulated during LmOVA bacterial infection. Notably, time-lapse, confocal microscopy and flow cytometry confirms that M6PR(low) effectors, but not M6PR(high) effectors, escape Gzm-B lethal-hit derived from CD4(+)25(+) Treg cells. Adoptive cotransfer of M6PR(low) effectors and M6PR(high) effectors sorted from LmOVA-infected, congenic mice at the peak of CD8(+) T cell response, reveals that M6PR(low) effectors with the CD8(+) T cell memory precursor phenotype preferentially survive the CD8(+) T cell contraction and differentiate into functional, long-lasting memory CD8(+) T cells. Taken together, our data provide the first evidence, to our knowledge, that selective M6PR down-regulation has a critical role in CD8(+) T cell survival, and our findings have implications for efficient vaccine design and immunotherapy.