Clinical Staphylococcus aureus inhibits human T-cell activity through interaction with the PD-1 receptor.

() represents a major clinical challenge due to its explicit capacity to select mutations that increase antibiotic resistance and immune evasion. However, the molecular mechanisms are poorly defined, especially for adaptive immunity. Cancer immunotherapy targeting programmed cell death protein 1 (PD-1) enhances T-cell activity and is emerging for the treatment of certain viral infections, while its potential against bacterial infections remains elusive. We show that an mutant, selected during clinical antibiotic therapy, inhibits T-cell activity by directly interacting with PD-1 on human T cells. Specificity of the interaction was confirmed using recombinant PD-1, as well as PD-1 overexpressing and knock out cells. Moreover, the PD-1-binding inhibited intracellular calcium mobilization, T-cell proliferation, CD25 expression, and IL-2 secretion, while the key effects were alleviated by antibody-mediated PD-1 blockade using an engineered IgG1-based anti-PD-1 antibody. Our results suggest that mutant directly targets PD-1 to evade immune activation and that therapeutic targeting of PD-1 may be used against certain staphylococcal infections. IMPORTANCE Therapies that target and aid the host immune defense to repel cancer cells or invading pathogens are rapidly emerging. Antibiotic resistance is among the largest threats to human health globally. () is the most common bacterial infection, and it poses a challenge to the healthcare system due to its significant ability to develop resistance toward current available therapies. In long-term infections, further adapt to avoid clearance by the host immune defense. In this study, we discover a new interaction that allows to avoid elimination by the immune system, which likely supports its persistence in the host. Moreover, we find that blocking the specific receptor (PD-1) using antibodies significantly relieves the -imposed inhibition. Our findings suggest that therapeutically targeting PD-1 is a possible future strategy for treating certain antibiotic-resistant staphylococcal infections.