IM-14 * IMMUNOLOGIC TARGETING OF MEDULLOBLASTOMA SUBTYPES USING DEVELOPMENTALLY REGULATED ANTIGENS

Abstract

INTRODUCTION: Medulloblastoma (MB) remains incurable in one third of patients despite aggressive multi-modality standard therapies. Immunotherapy represents a promising strategy by specifically targeting cancer cells. To date, there have been no successful immunologic applications targeting MB. Evidence from integrated genomic studies suggests MB subtypes arise from deregulation of pathways affecting proliferation of progenitor populations within the developing cerebellum. Using total embryonic RNA as a source of tumor rejection antigens is attractive because it can be delivered as a single vaccine, target both known and unknown fetal proteins, and be refined to preferentially treat distinct MB subtypes. METHODS: We have created two transplantable, syngeneic animal MB models recapitulating human SHH and Group 3 variants to investigate the immunologic targeting of different MB subtypes. We generated T cells specific to the developing mouse cerebellum (P5) and tested their reactivity to target cells pulsed with total RNA from two MB subtypes and the normal brain. Immune responses were evaluated by measuring cytokine secretion following re-stimulation of activated T cells with both normal and tumor cell targets. In vivo antitumor efficacy was also tested in survival studies of intracranial tumor-bearing animals. RESULTS: We generated T cells specific to the developing cerebellum in vitro, confirming the immunogenicity of developmentally regulated antigens. Additionally, we have shown that developmental antigen-specific T cells produce high levels of Th1-type cytokines in response to tumor cells of two immunologically distinct subtypes of MB. Interestingly, developmental antigen specific T cells do not show cross reactivity with the normal brain or subsequent stages of the developing brain after P5. Targeting developmental antigens also conferred a significant survival benefit in a treatment model of Group 3 tumor bearing animals and 60% survivors in SHH tumor bearing animals. CONCLUSIONS: Developmental antigens can safely target multiple MB subtypes with equal effectiveness compared to previously established total tumor strategies.