CMV gB/pp65 eVLPs formulated with GM-CSF as a therapeutic vaccine against CMV-positive tumors.

Abstract

e14032 Background: Numerous laboratories have demonstrated cytomegalovirus (CMV) antigens in over 90% of GBM tumors, medulloblastoma and breast cancer. Memory CD4+ and CD8+ T cells are most frequently directed against the gB and pp65 antigens at frequencies that can exceed 10%. Thus, CMV gB and pp65 represent attractive, highly immunogenic “foreign” antigen components of a vaccine against CMV-positive tumors that can exploit high precursor frequencies of CD4+ and CD8+ T cells. Methods: Enveloped virus-like particles (eVLPs) are produced after transfection of HEK 293 cells with a plasmid encoding murine leukemia virus Gag plasmid fused in-frame with CMV pp65 antigen, which gives rise to particles. Co-transfected CMV gB plasmid enables particles budding from the cell surface to incorporate the gB protein into the lipid bilayer. Results: Ex vivo studies using PBMCs from GBM patients demonstrated that gB/pp65 eVLPs restimulate both CD4+ and CD8+ T cells at frequencies comparable to those observed for healthy CMV+ subjects, and formulation with GM-CSF augmented IFN-g and CCL3 secretion. Biodistribution studies demonstrated that the gB/pp65 eVLPs remain at the intradermal injection site for at least two weeks, with particles appearing in draining lymph nodes within a few hours. Mechanistic studies demonstrated that monocyte uptake of eVLP particles induces proinflammatory cytokines, which are amplified by gB expression on the surface of the gB/pp65 particles. Immunization of CMV+ rhesus macaques with a macaque-specific version of the vaccine demonstrated the safety of the vaccine and ability to boost pre-existing IFN-g-secreting T cell responses. Conclusions: A phase I/IIa multicenter study designed to demonstrate safety and determine the most immunogenic dose of vaccine in recurrent GBM patients was initiated, with the first subject dosed in January 2018. Up to 3 different antigen dose levels will be evaluated, with 6 subjects in each cohort. Comprehensive safety evaluations and immune-monitoring will be performed 2 weeks after each immunization. Ten additional subjects will be enrolled once an optimal vaccine dose regimen is identified. Subjects will be vaccinated monthly and followed until tumor progression.