Unleashing natural killer cells upon immunization with a carbohydrate mimetic peptide vaccine.

Abstract

16 Background: Immunotherapies that activate Natural Killer (NK) cells can lend to their tumor infiltration or help shape the adaptive response toward a T helper type 1 (Th1) profile thought to favor anti-tumor responses. Methods: We have analyzed the functional NK response to immunization with a carbohydrate mimetic peptide (CMP) vaccine in preclinical tumor models and in humans. This CMP, referred to as P10s, is the N-terminal half of a peptide vaccine named P10s-PADRE, the C-terminal half of which (PADRE) is a Pan-T-cell epitope. Syngeneic mouse models associated with mammary 4T1, mouse lymphoma cell line EL4, and human breast cancer MDA-MB-231 in athymic mice were immunized with the vaccine. NK infiltration was identified by staining mouse tumor tissue before and after immunization. For NK cell depletion studies Athymic mice were injected intraperitoneally with anti-asialo GM1 rabbit serum prior to challenge with MDA-MB-231 tumor cells after the last immunization and then every 4-5 days for the period of a month. A Phase 1 trial was conducted with the vaccine and the NK phenotype assessed by flow cytometry. Serum Th1/Th2 cytokine profile was determined using multiplex MSD® kits (Meso Scale diagnostics). Results: Immunization of murine models with the P10s vaccine results in infiltration of NK cells into tumors and depletion of NK cells in these models abrogate anti-tumor responses. An early phase clinical trial in Stage IV metastatic Breast Cancer patients indicated that the activates the natural cytotoxicity receptor NKp46 phenotype, which has a mouse Ortholog, with a Th1 cytokine environment marked by significant elevation of IFN-γ levels. While P10s-PADRE immunization induced proapoptotic antibodies that are caspase-3 dependent, the induced antibodies also led to ADCC targeting of human breast cancer tumor cell lines in vitro further emphasizing a role for activated NK cells. Conclusions: Our results reveal that immunization with a CMP vaccine can mediate the activation of an anti-tumor NK response that can affect tumor growth in preclinical models that might translate to humans. Clinical trial information: NCT01390064.