Observing that genetically identical mice bearing transplantable tumors have heterogeneous outcomes to immune checkpoint blockade (ICB), Zemek et al. used bilateral tumor injection (both respond identically) to study indicators of ICB response by examining one tumor pre-ICB. Responding tumors showed greater inflammatory pathway gene expression and NK infiltration compared to non-responders. Identification of positive (IFNγ and STAT1) and negative (IL-10) response regulators led researchers to condition tumors with IFNγ, anti-IL-10, and STAT1 activator poly(I:C), which increased NK cells, STAT1, and IFNγ within tumors and sensitized mice to ICB.
Contributed by Alex Najibi
Cancer immunotherapy using antibodies that target immune checkpoints has delivered outstanding results. However, responses only occur in a subset of patients, and it is not fully understood what biological processes determine an effective outcome. This lack of understanding hinders the development of rational combination treatments. We set out to define the pretreatment microenvironment associated with an effective outcome by using the fact that inbred mouse strains bearing monoclonal cancer cell line-derived tumors respond in a dichotomous manner to immune checkpoint blockade (ICB). We compared the cellular composition and gene expression profiles of responsive and nonresponsive tumors from mice before ICB and validated the findings in cohorts of patients with cancer treated with ICB antibodies. We found that responsive tumors were characterized by an inflammatory gene expression signature consistent with up-regulation of signal transducer and activator of transcription 1 (STAT1) and Toll-like receptor 3 (TLR3) signaling and down-regulation of interleukin-10 (IL-10) signaling. In addition, responsive tumors had more infiltrating-activated natural killer (NK) cells, which were necessary for response. Pretreatment of mice with large established tumors using the STAT1-activating cytokine interferon-gamma (IFNgamma), the TLR3 ligand poly(I:C), and an anti-IL-10 antibody sensitized tumors to ICB by attracting IFNgamma-producing NK cells into the tumor, resulting in increased cure rates. Our results identify a pretreatment tumor microenvironment that predicts response to ICB, which can be therapeutically attained. These data suggest a biomarker-driven approach to patient management to establish whether a patient would benefit from treatment with sensitizing therapeutics before ICB.