Characterization of human soluble Tim-3 and its role in HIV infection (VIR1P.1002)

Abstract Chronic Human Immunodeficiency Virus Type-1 (HIV) infection results in a loss of HIV-specific CD8+ T cell effector function, termed “exhaustion”, which is mediated, in-part, by the co-inhibitory receptor T-cell immunoglobulin mucin domain-containing protein 3 (Tim-3). Like many other receptors, a soluble form of this protein has been described in human blood plasma. However, this soluble Tim-3 (sTim-3) is poorly characterized and it’s unclear whether it plays a role in HIV pathogenesis. Using a Tim-3 ELISA, we found that levels of sTim-3 were significantly elevated in HIV+ antiretroviral treatment naïve patient plasma compared to healthy controls or HIV+ antiretroviral treated patients, and significantly correlated positively with viral load but not with CD4+ T cell counts. To characterize this construct, we immunoprecipitated the protein from HIV+ patient plasma; western blotting analysis revealed that plasma sTim-3 is the approximate size of the Tim-3 ectodomain. Following detection of sTim-3 from activated PBMCs in culture, no alternatively spliced Tim-3 constructs were observed, however, levels of sTim-3 were abrogated with the inclusion of a matrix metalloproteinase, ADAM10, inhibitor. Further, we showed that this sTim-3 was produced from activated T cells treated with an ADAM10 agonist and was the approximate size of plasma sTim-3. Our results suggest that increasing levels of viral antigen result in increased Tim-3 shedding from the T cell surface during HIV infection.