Chemotherapeutic agents are widely used for cancer treatment. In addition to their direct cytotoxic effects, these agents harness the host's immune system, which contributes to their antitumor activity. Here we show that two clinically used chemotherapeutic agents, gemcitabine (Gem) and 5-fluorouracil (5FU), activate the NOD-like receptor family, pyrin domain containing-3 protein (Nlrp3)-dependent caspase-1 activation complex (termed the inflammasome) in myeloid-derived suppressor cells (MDSCs), leading to production of interleukin-1β (IL-1β), which curtails anticancer immunity. Chemotherapy-triggered IL-1β secretion relied on lysosomal permeabilization and the release of cathepsin B, which bound to Nlrp3 and drove caspase-1 activation. MDSC-derived IL-1β induced secretion of IL-17 by CD4(+) T cells, which blunted the anticancer efficacy of the chemotherapy. Accordingly, Gem and 5FU exerted higher antitumor effects when tumors were established in Nlrp3(-/-) or Casp1(-/-) mice or wild-type mice treated with interleukin-1 receptor antagonist (IL-1Ra). Altogether, these results identify how activation of the Nlrp3 inflammasome in MDSCs by 5FU and Gem limits the antitumor efficacy of these chemotherapeutic agents.

The receptor NLRP3 is involved in the formation of the NLRP3 inflammasome that activates caspase-1 and mediates the release of interleukin 1β (IL-1β) and IL-18. Whether NLRP3 can shape immunological function independently of inflammasomes is unclear. We found that NLRP3 expression in CD4(+) T cells specifically supported a T helper type 2 (TH2) transcriptional program in a cell-intrinsic manner. NLRP3, but not the inflammasome adaptor ASC or caspase-1, positively regulated a TH2 program. In TH2 cells, NLRP3 bound the Il4 promoter and transactivated it in conjunction with the transcription factor IRF4. Nlrp3-deficient TH2 cells supported melanoma tumor growth in an IL-4-dependent manner and also promoted asthma-like symptoms. Our results demonstrate the ability of NLRP3 to act as a key transcription factor in TH2 differentiation.