PD-1 blockade drug holiday improves exhausted progenitor CD8 T cell (Tpex) reinvigoration by avoiding Tpex adaptive resistance

Blocking the programmed cell death 1 (PD-1) pathway using monoclonal antibodies reinvigorates exhausted T cells (Tex), enhancing control of chronic viral infections and cancer. Considerable effort has focused on evaluating different PD-1 blockade agents in preclinical and clinical cancer settings, but relatively little information exists on how to optimize the pharmacodynamic effects of PD-1 pathway blockade on reinvigorating Tex. To address this question, we performed longitudinal tracking of Tex reinvigoration during chronic infection with lymphocytic choriomeningitis virus (LCMV) following different regimens of PD-1 blockade. We compared single-cycle (2 weeks of treatment), long-term continuous PD-1 pathway blockade (i.e. 3 months), or blockade followed by a drug holiday and then re-blockade (intermittent treatment). These studies revealed little benefit of continuous versus single-cycle PD-1 blockade, with both resulting in a single peak of Tex reinvigoration and similar effects on viral replication. In contrast, intermittent blockade resulted in a new cycle of secondary Tex reinvigoration upon redosing after a washout and this secondary Tex reinvigoration improved disease control. Mechanistically, long-term blockade eroded the ability of Tex progenitor cells (Tpex) to give rise to downstream, more functional Tex intermediate (Tex-Int) progeny, whereas the drug holiday restored this Tpex proliferative and differentiation capacity. Tpex from long-term treated mice showed evidence of adaptive resistance and additional layers of negative regulation, including sustained expression of the inhibitory receptor CD22. Indeed, co-blockade of PD-1 and CD22 using combination antibodies or bispecific antibody approaches improved disease control and reinvigoration of Tex. These data have implications for clinical immune pharmacodynamics of PD-1 blockade and provide insights into the biology of Tex reinvigoration. One Sentence Summary: Modifying the immunopharmacology of PD-1 blockade reveals a benefit of a drug holiday and identifies mechanisms of Tex progenitor deficiency provoked by prolonged loss of PD-1 signals including the inhibitory receptor CD22.