Activation of mTORC1 at late endosomes misdirects T cell fate decision in older individuals

Jin et al., Science Immunology, 2021, asked why T cells from older adults keep mTORC1 switched on when their lysosomes no longer work. The answer was a change of address. In these cells mTORC1 is activated on late endosomes rather than lysosomes, fed by cytosolic amino acids brought in through the leucine transporter SLC7A5. Removing SLC7A5 or VPS39, a component of the HOPS complex that converts early endosomes to late ones, cut mTORC1 activity in T cells from older but not younger donors. The downstream consequence was that PD-1 escaped lysosomal degradation and accumulated, which damped proliferation.

The test that mattered clinically was whether removing VPS39 could give those T cells their responses back. AUMsilence sdASOs were used for this, in human peripheral blood mononuclear cells rather than a cell line. The Results state the reason for the choice in plain terms: the oligonucleotide self-delivers and needs no transfection reagent. Two independent sequences against VPS39, and a matched scramble control, were added at 1 μM on day 0, and divided cells were counted on day 8.

Cells were stimulated with peptide megapools covering the SARS-CoV-2 proteome. Of 11 unexposed donors, 6 responded, and in those 6 both sequences significantly increased the expansion of SARS-CoV-2-reactive CD4 and CD8 T cells against the scramble control. Cultures given no peptide showed no such increase, so the effect was antigen dependent rather than a general push on proliferation. The same silencing improved responses to a pertussis peptide pool, which the paper sets beside PD-1 blockade run in the same donors. Two things a reader should keep straight: the separate small interfering RNA experiments elsewhere in this paper used a commercial pool delivered by nucleofection and are not AUM material, and the mouse arm used retroviral short hairpin RNA.