GITR activation ex vivo impairs CD8 T cell function in people with HIV on antiretroviral therapy

Abstract

Glucocorticoid-induced tumor necrosis factor related protein (GITR) is a co-stimulatory immune checkpoint molecule constitutively expressed on regulatory Tcells (Tregs) and on activated T conventional cells (Tconv). In blood collected from PWH on suppressive ART, GITR expression was reduced in multiple activated CD4 and CD8 Tcell subsets but was increased in Tregs. HIV specific CD8 Tcells expressed higher levels of GITR and programmed cell death protein 1 (PD-1) compared to total CD8 Tcells. Following stimulation with HIV peptides and GITR-ligand (L), we demonstrated a significant decrease in killing by HIV specific CD8 Tcells and an increased exhausted profile. Tcell receptor co-stimulation with GITR-L abrogated Treg suppression and induced expansion of CD4 Tconv. We conclude that GITR activation is an additional factor contributing to an impaired HIV immune response in PWH on ART and that GITR agonist antibodies should not be pursued for HIV cure strategies.