BackgroundLung cancer is one of the most frequent malignancies in humans and is a major cause of death. A number of therapies aimed at reinforcing antitumor immune response, including antiprogrammed cell death protein 1 (anti-PD-1) antibodies, are successfully used to treat several neoplasias as non-small cell lung cancer (NSCLC). However, host immune mechanisms that participate in response to anti-PD-1 therapy are not completely understood.MethodsWe used a syngeneic immunocompetent mouse model of NSCLC to analyze host immune response to anti-PD-1 treatment in secondary lymphoid organs, peripheral blood and tumors, by flow cytometry, immunohistochemistry and quantitative real-time PCR (qRT-PCR). In addition, we also studied specific characteristics of selected immune subpopulations in ex vivo functional assays.ResultsWe show that anti-PD-1 therapy induces a population of circulating T follicular helper cells (cTfh) with enhanced B activation capacity, which participates in tumor response to treatment. Anti-PD-1 increases the number of tertiary lymphoid structures (TLS), which correlates with impaired tumor growth. Of note, TLS support cTfh-associated local antibody production, which participates in host immune response against tumor.ConclusionThese findings unveil a novel mechanism of action for anti-PD-1 therapy and provide new targets for optimization of current therapies against lung cancer.