PD-1 blockade carries perils
The potentiation of T cell–mediated antitumor responses achieved in multiple types of cancer via inhibition of the PD-1 checkpoint pathway has led to suggestions that anti–PD-1 therapy might also boost T cell immunity in chronic infections including tuberculosis. Kauffman et al. examined the effect of anti–PD-1 antibody treatment on the clinical course of Mycobacterium tuberculosis (Mtb) infection in rhesus macaques. CD8 T cell responses were boosted in monkeys receiving anti–PD-1 infusions, but the stronger CD8 T cell responses were coupled with increases in proinflammatory cytokines, impaired CD4 T cell function, and higher bacterial loads in lung granulomas. These findings in a nonhuman primate model signal that anti–PD-1–based therapy needs to be used cautiously in patients with cancer with a history of Mtb exposure.
Boosting immune cell function by targeting the coinhibitory receptor PD-1 may have applications in the treatment of chronic infections. Here, we examine the role of PD-1 during Mycobacterium tuberculosis (Mtb) infection of rhesus macaques. Animals treated with anti–PD-1 monoclonal antibody developed worse disease and higher granuloma bacterial loads compared with isotype control–treated monkeys. PD-1 blockade increased the number and functionality of granuloma Mtb-specific CD8 T cells. In contrast, Mtb-specific CD4 T cells in anti–PD-1–treated macaques were not increased in number or function in granulomas, expressed increased levels of CTLA-4, and exhibited reduced intralesional trafficking in live imaging studies. In granulomas of anti–PD-1–treated animals, multiple proinflammatory cytokines were elevated, and more cytokines correlated with bacterial loads, leading to the identification of a role for caspase 1 in the exacerbation of tuberculosis after PD-1 blockade. Last, increased Mtb bacterial loads after PD-1 blockade were found to associate with the composition of the intestinal microbiota before infection in individual macaques. Therefore, PD-1–mediated coinhibition is required for control of Mtb infection in macaques, perhaps because of its role in dampening detrimental inflammation and allowing for normal CD4 T cell responses.
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