PDCD1 and infectious disease: Other studies in the basic Immunology and Infectious Disease literature have shown that TIM-3 is co-expressed with PD-1 in exhausted T cells in the context of anti-microbial responses26, 27, 28, 29, which support our finding of TIM-3 expression on therapeutic anti-PD-1 antibody-bound T cells in the setting of treatment failure.