A long-standing goal for melanoma immune therapy is the induction of tumor-specific T cells that effectively delay tumor progression and prolong overall patient survival. Several vaccination strategies have been attempted without success, despite often stimulating large numbers of tumor-specific T cells. Some of this failure is likely due to the active immune suppression mechanisms that operate within tumors. Moreover, it has become apparent that T cell trafficking and migration into tumors will be heavily influenced by the conditions in which those T cells were stimulated. Thus, the ideal cancer vaccine would overcome the immune suppressive environment of the tumor and produce cells that readily migrate into the primary tumor and metastases, wherever they may be. We argue here that a persistent vaccine vector, based on a spread- defective version of the herpes virus cytomegalovirus (CMV), may overcome some of these obstacles. Specifically, persistent CMV-based vectors will continuously boost the immune system outside of the tumor environment and produce T cells that are highly effective at migrating systemically. Our previous work demonstrated that a safe, spread-defective variant of CMV could persist and stimulate large T cell responses.
Our aim for this small grant application is to determine the potential for (or limitations of) such a vaccine strategy. To accomplish this, we will use a newly generated, highly relevant model of metastatic melanoma: mice in which expression of a mutant BRAF (BRAFV600E) is induced. BRAF is a serine/threonine kinase that is mutated in ~50% of human melanomas and the BRAFV600E mutation is present in ~80 to 90% of human BRAF-mutant melanomas. Thus, this model mimics human disease. Most excitingly, this model enables us to combine BRAF inhibition with vaccination. This is a great advantage important because BRAF inhibitors, such as the recently FDA approved Vemurafenib, will be widely used in the clinic and recent data suggest that Vemurafenib may synergize with immune therapies. Here we will test the efficacy of CMV-based vaccination in the presence or absence of Vemurafenib inhibition of BRAF, with specific focus on T cell infiltration of tumors and function within tumors.
Persistent vaccine vectors may overcome some of the obstacles inherent in the generation and maintenance of functional tumor-specific immunity. In this small grant proposal, we will explore the potential for a vaccine vector based on the herpes virus cytomegalovirus, in a highly relevant model of BRAF-mutant metastatic melanoma. This model will enable us to test the vaccine platform as well as the potential synergy arising from combining immune therapy with inhibition of the kinase BRAF.