Study of Combined GARP:TGF-β1/PD-1 Blockade as a Shock-and-Kill Strategy in HIV-1 Cure

Despite the success of ART, the need for a lifelong treatment for HIV-1 is associated with cost, stigma and toxicities accumulating over decades. The persistence of a pool of long-lived, latently infected cells carrying intact, replication-competent proviral DNA (also called HIV reservoir), constitutes the main barrier to HIV-1 cure and is responsible for systematic HIV-1 rebound after ART interruption. In that context, recent research on HIV cure has focused on developing strategies to "purge" the viral reservoir either to eradicate the infection completely (sterilizing cure) or, at least, delay the time to viral recrudescence after ART interruption (functional cure). On the other hand, chronic HIV-1 infection is characterized by a progressive dysfunctional state of CD8+ T cells called "T cell exhaustion", resulting from persistent exposure to viral antigens.

A long-standing approach has been the establishment of LR strategies, aiming to pharmacologically reactivate viral expression in latently infected cells, exposing them to clearance by CD8+ T cells or death through viral cytolysis. In parallel with LR, strategies have also been developed to restore antiviral immunity by stimulating virus-specific CD8+ T cells. This global approach is called "shock-and-kill".

Monoclonal antibodies blocking immune checkpoints, often called ICB, have been developed as an approach to enhance T cell-mediated responses. These immunostimulatory antibodies, and in particular anti-PD-1 antibodies have revolutionized cancer therapy.

Interestingly, PD-1 blockade has been shown to be able to both facilitate LR and reverse CD8+ T cell dysfunction in HIV-1 ex vivo models. Indeed, in chronic HIV-1 infection, PD-1 expression is enriched on CD4+ T cells from the reservoir, and its upregulation is correlated with reduced effector function on HIV-specific CD8+ T cells, making it a promising target for a shock-and-kill therapy.

Two dedicated clinical studies evaluating PD-(L)1 blockade in PLWHIV without cancer were published to date: a phase I trial with the anti-PD-L1 monoclonal antibody BMS-936559, and a phase I/II with the anti-PD-1 monoclonal antibody cemiplimab. Both studies had a small enrollment and limited dose escalation due to suspected immune-related adverse events (irAEs). Nevertheless, both described an improvement in HIV-specific CD8+ responses in a subgroup of individuals. In the cemiplimab trial, the single responder patient also showed an increase in HIV-1 expression, indicative of LR. These studies provide promising evidence for both immunologic and virologic response but also highlight the main limitations of ICB in PLWHIV: variable and transient responses to the treatment, and a safety concern. Combination with other ICB would be a relevant approach, but caution is warranted due to potential enhanced toxicity.