The recent approval of immune checkpoint blockade, such as anti-PD-1, has marked a milestone in cancer therapy. Checkpoint blockade ?reinvigorates? an ?exhausted? anti-tumor T cell response, which can result in a durable clinical response. However, only a fraction of patients respond to immune checkpoint blockade, and it only works in a subset of cancers. Improving the efficacy of checkpoint blockade is of paramount importance and is seemingly within reach but will require a better understanding of the molecules that control the complex interactions of immune cells in the tumor micro-environment (TME) required for effective checkpoint blockade therapy. Chemokines are chemotactic cytokines that orchestrate the migratory behavior and cellular interactions of leukocytes, and therefore have great impact upon anti-tumor immune responses. CXCR3 is a chemokine receptor for the interferon-inducible chemokines - CXCL9, CXCL10, and CXCL11- and is highly expressed on CD4+ Th1 cells and CD8+ T effector (Teff) cells. CXCR3 ligands have been correlated with the presence of Teff within tumors and disease free survival. We have exciting data that CXCR3 is required for anti-PD-1 immunotherapy. Based on the importance of CXCR3 for T cell recruitment to sites of inflammation, it is logical to predict that CXCR3 plays an important role in Teff entry into tumors following anti-PD-1 therapy. However, recent provocative preliminary data leads us to believe that CXCR3 is playing even more important roles within the tumor following anti-PD-1, and is likely critical to ?jump start? the anti-tumor immune response in the TME. Recent studies have revealed heterogeneity in exhausted T cell (Tex) populations and defined Tex subsets that differ in their potential for reinvigoration by PD-1 blockade. We have found that CXCR3 expression on Teff inversely correlates with markers of exhaustion. We hypothesize that CXCR3 plays a functional role in the ability of Tex to become reinvigorated within the tumor following PD-1 blockade.
In Aim 1, we will define the mechanisms by which CXCR3 contributes to the efficacy of PD-1 blockade therapy for cancer. This will include examining whether CXCR3 plays a critical role enhancing the interaction of Tex with the most relevant activated antigen-presenting cells in the tumor and facilitating the ability of Teff to locate and kill cancer cells following anti-PD-1 therapy.
In Aim 2, we will determine if augmenting the CXCR3 chemokine system can improve the efficacy of anti-PD-1 therapy as well as convert anti-PD-1 nonresponsive tumors into responsive tumors. We will also determine if counter-regulatory mechanisms within the tumor, such as epigenetic silencing and CXCR3-expressing regulatory T cells, limit the effectiveness of anti-PD-1 therapy by suppressing CXCL9 and CXCL10 expression in tumors. If these pathways limit CXCR3+CD8+ T cell function in the tumor, we will devise strategies to circumvent these counter-regulatory responses. Finally, we will determine if the CXCR3 chemokine system can be used as a biomarker for response to anti-PD-1 therapy in a murine model and in patients with cancer.
Immune checkpoint blockade therapy for cancer can result in durable clinical responses; however, it is only effective in a fraction of patients. Improving the efficacy of cancer immunotherapy will require a better understanding of the molecules that control the complex interactions of immune cells in the tumor microenvironment required for effective therapy, and their regulation by checkpoint blockade. This project will study how the chemokine receptor CXCR3 and its ligands, CXCL9 and CXCL10, contribute in critical ways to efficacy of checkpoint blockade immunotherapy, and how to use this knowledge to harness the potential of this approach to benefit more cancer patients.
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