Systemic antitumor immunity by PD-1/PD-L1 inhibition is potentiated by vascular-targeted photodynamic therapy of primary tumors

Purpose: PD-1/PD-L1 pathway inhibition is effective against advanced renal cell carcinoma, although results are variable and may depend on host factors including the tumor microenvironment. Vascular-targeted photodynamic (VTP) therapy with the photosensitizer WST11 induces a defined local immune response, and we sought to determine whether this could potentiate the local and systemic antitumor response to PD-1 pathway inhibition. Experimental Design: Using an orthotopic Renca murine model of renal cell carcinoma that develops lung metastases, we treated primary renal tumors with either VTP alone, PD-1/PD-L1 antagonistic antibodies alone, or a combination of VTP and antibodies, then examined treatment responses including immune infiltration in primary and metastatic sites. Modulation of PD-L1 expression by VTP in human xenograft tumors was also assessed.Results: Treatment of renal tumors with VTP in combination with systemic PD-1/PD-L1 pathway inhibition, but neither treatment alone, resulted in regression of primary tumors, prevented growth of lung metastases and prolonged survival in a preclinical mouse model. Analysis of tumor-infiltrating lymphocytes revealed that treatment effect was associated with increased CD8+:regulatory T cell and CD4+FoxP3-:regulatory T cell ratios in primary renal tumors and increased T cell infiltration in sites of lung metastasis. Furthermore, PD-L1 expression is induced following VTP treatment of human renal cell carcinoma xenografts. Conclusions: Our results demonstrate a role for local immune modulation with VTP in combination with PD-1/PD-L1 pathway inhibition for generation of potent local and systemic antitumor responses. This combined-modality strategy may be an effective therapy in cancers resistant to PD-1/PD-L1 pathway inhibition alone.

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