The breadth of expandable memory CD8⁺ T Cells inversely correlates with residual viral loads in HIV elite controllers

Previous studies have shown that elite controllers with minimal effector T cell responses harbor a low-frequency, readily expandable, highly functional, and broadly directed memory population. Here, we interrogated the in vivo relevance of this cell population by investigating whether the breadth of expandable memory responses is associated with the magnitude of residual viremia in individuals achieving durable suppression of HIV infection. HIV-specific memory CD8⁺ T cells were expanded by using autologous epitopic and variant peptides. Viral load was measured by an ultrasensitive single-copy PCR assay. Following expansion, controllers showed a greater increase in the overall breadth of Gag responses than did untreated progressors (P=0.01) as well as treated progressors (P=0.0003). Nef-and Env-specific memory cells expanded poorly for all groups, and their expanded breadths were indistinguishable among groups (P=0.9 for Nef as determined by a Kruskal-Wallis test; P=0.6 for Env as determined by a Kruskal-Wallis test). More importantly, we show that the breadth of expandable, previously undetectable Gag-specific responses was inversely correlated with residual viral load (r=-0.6; P=0.009). Together, these data reveal a direct link between the abundance of Gag-specific expandable memory responses and prolonged maintenance of low-level viremia. Our studies highlight a CD8⁺ T cell feature that would be desirable in a vaccine-induced T cell response.