Th17 cells contribute to combination MEK inhibitor and anti-PD-L1 therapy resistance in KRAS/p53 mutant lung cancers

Understanding resistance mechanisms to targeted therapies and immune checkpoint blockade in mutant KRAS lung cancers is critical to developing novel combination therapies and improving patient survival. Here, we show that MEK inhibition enhanced PD-L1 expression while PD-L1 blockade upregulated MAPK signaling in mutant KRAS lung tumors. Combined MEK inhibition with anti-PD-L1 synergistically reduced lung tumor growth and metastasis, but tumors eventually developed resistance to sustained combinatorial therapy. Multi-platform profiling revealed that resistant lung tumors have increased infiltration of Th17 cells, which secrete IL-17 and IL-22 cytokines to promote lung cancer cell invasiveness and MEK inhibitor resistance. Antibody depletion of IL-17A in combination with MEK inhibition and PD-L1 blockade markedly reduced therapy-resistance in vivo. Clinically, increased expression of Th17-associated genes in patients treated with PD-1 blockade predicted poorer overall survival and response in melanoma and predicated poorer response to anti-PD1 in NSCLC patients. Here we show a triple combinatorial therapeutic strategy to overcome resistance to combined MEK inhibitor and PD-L1 blockade. Recent clinical trials combining MEK inhibitors with anti-PD-L1 in solid tumours show moderate responses. Here, the authors demonstrate that the combination of MEK inhibition and PD-L1 blockade in KRAS mutant lung cancer models leads to a transient tumour regressions and resistance due to increased infiltration of Th17 cells and that the triple therapy targeting MEK, PD-L1 and IL-17 produced better in vivo responses.

Automated summary

Understanding the resistance mechanisms in mutant KRAS lung cancers to targeted therapies and immune checkpoint blockade is crucial for developing novel combination therapies. MEK inhibition combined with anti-PD-L1 can synergistically reduce lung tumor growth, but resistance may develop eventually. Increased Th17 cell infiltration in resistant tumors promotes invasiveness and resistance to MEK inhibitors, and a triple therapy targeting MEK, PD-L1, and IL-17 may overcome this resistance for better in vivo responses.