Efficacy of agonist αOX40 and antagonist αCTLA-4 cancer immunotherapy is increased by ibrutinib treatment through enhanced Eomes expression and T-cell response

Abstract

Abstract Antagonistic monoclonal antibodies targeting individual checkpoint receptors on T cells, such as CTLA-4 and PD-1, are used to treat patients with metastatic disease; however, only a subset of patients respond. Combination therapies, such as CTLA-4 blockade with agonist αOX40 mAb, are synergistic in preclinical models. αOX40/αCTLA-4 therapy synergistically enhances expression of Eomesodermin (Eomes), a transcription factor that drives CD8 T cell differentiation and memory function. We hypothesize that Eomes expression plays a critical role in the synergistic efficacy of αOX40/αCTLA-4 therapy. Compared to Eomeslo CD8 T cells, Eomeshi CD8 T cells induced by αOX40/αCTLA-4 therapy express lower levels of checkpoint receptors (PD-1, TIM-3, LAG-3) and higher levels of tumor trafficking and activation markers (CXCR3, CD44), and intratumoral cytokines (IFN-γ, TNF-α). CD8 T cell-specific Eomes−/− tumor-bearing mice did not respond to αOX40/αCTLA-4 therapy, demonstrating the necessity of Eomes expressing CD8 T cells. Interleukin-2 inducible T cell kinase (ITK) negatively regulates T cell Eomes expression following T cell receptor ligation. Thus, we asked whether enhancing T cell Eomes expression by combining ibrutinib, an FDA-approved ITK inhibitor, with αOX40/αCTLA4 therapy would further improve anti-tumor responses by increasing Eomeshi CD8 T cells. This triple combination increased CD8 T cell-specific Eomes expression, tumor-specific CD8 T cells, Ki-67 (proliferation), and Th1 cytokines (IFN-γ, TNF-α) leading to reduced tumor growth and improved survival over αOX40/αCTLA-4 alone, making ibrutinib/αOX40/αCTLA-4 a potential novel triple combination therapy.