Immune checkpoint blockade (ICB) has heralded a new era in cancer therapy. Research into the mechanisms underlying response to ICB has predominantly focused on T cells; however, effective immune... Show moreImmune checkpoint blockade (ICB) has heralded a new era in cancer therapy. Research into the mechanisms underlying response to ICB has predominantly focused on T cells; however, effective immune responses require tightly regulated crosstalk between innate and adaptive immune cells. Here, we combine unbiased analysis of blood and tumors from metastatic breast cancer patients treated with ICB with mechanistic studies in mouse models of breast cancer. We observe an increase in systemic and intratumoral eosinophils in patients and mice responding to ICB treatment. Mechanistically, ICB increased IL-5 production by CD4(+) T cells, stimulating elevated eosinophil production from the bone marrow, leading to systemic eosinophil expansion. Additional induction of IL-33 by ICB-cisplatin combination or recombinant IL-33 promotes intratumoral eosinophil infiltration and eosinophil-dependent CD8(+) T cell activation to enhance ICB response. This work demonstrates the critical role of eosinophils in ICB response and provides proof-of-principle for eosinophil engagement to enhance ICB efficacy. Show less
Neoadjuvant immunotherapy with anti-cytotoxic T lymphocyte-associated protein 4 (CTLA4) + anti-programmed cell death protein 1 (PD1) monoclonal antibodies has demonstrated remarkable pathological... Show moreNeoadjuvant immunotherapy with anti-cytotoxic T lymphocyte-associated protein 4 (CTLA4) + anti-programmed cell death protein 1 (PD1) monoclonal antibodies has demonstrated remarkable pathological responses and relapse-free survival in -80% of patients with clinically detectable stage III melanoma. However, about 20% of the treated patients do not respond. In pretreatment biopsies of patients with melanoma, we found that resistance to neoadjuvant CTLA4 + PD1 blockade was associated with a low CD4/interleukin-2 (IL-2) gene signature. Ex vivo, addition of IL-2 to CTLA4 + PD1 blockade induced T cell activation and deep immunological responses in anti-CTLA4 + anti-PD1-resistant human tumor specimens. In the 4T1.2 breast cancer mouse model of neoadjuvant immunotherapy, triple combination of anti-CTLA4 + anti-PD1 + IL-2 cured almost twice as many mice as compared with dual checkpoint inhibitor therapy. This improved efficacy was due to the expansion of tumor-specific CD8(+) T cells and improved proinflammatory cytokine polyfunctionality of both CD4(+) and CD8(+) T effector cells and regulatory T cells. Depletion studies suggested that CD4(+) T cells were critical for priming of CD8(+) T cell immunity against 4T1.2 and helped in the expansion of tumor-specific CD8(+) T cells early after neoadjuvant triple immunotherapy. Our results suggest that the addition of IL-2 can overcome resistance to neoadjuvant anti-CTLA4 +anti-PD1, providing the rationale for testing this combination as a neoadjuvant therapy in patients with early-stage cancer. Show less
