CTIM-10. PHASE 1 TRIAL OF PERSONALIZED NEOANTIGEN VACCINES IN COMBINATION WITH STANDARD CARE TO TREAT GLIOBLASTOMA

Abstract The tumor microenvironment (TME) of glioblastoma (GBM) is populated by cells that foster immunosuppression. Reversing immunosuppression and promoting tumor surveillance by T cells that recognize the antigens generated by tumor-specific mutations (neoantigens) is critical to eliminating the tumor cells. In a phase 1 clinical trial of newly diagnosed GBM (NCT03223103), patients were treated with personalized neoantigen vaccines (PNV) combined with standard of care (resection, radiotherapy, temozolomide chemotherapy, and TTFields). The neoantigens were identified using the OpenVax computational pipeline. Primary endpoints included safety and feasibility, and the secondary endpoints included PFS, OS, TME analysis, and immunogenicity assays. The study enrolled 12 patients, ages 32-84, between December 2017 - July 2020. With a feasibility endpoint of one successful PNV administration, all patients got at least 6. All developed PNV-related injection site reactions, and flu-like symptoms grade 1-2. Concomitant use with TTFields did not increase toxicity. None of the patients exhibited dose-limiting toxicity within 30 days of receiving the PNV. However, one developed grade 3 SAE, consisting of seizures, neck pain, and progressive neurological deficits, after vaccine 10, culminating in a grade 5 SAE and brain demyelination 10 months later. Assays performed on this subject showed induction of neoantigen-specific responses with PNV. PNV induced CD4+ and CD8+ T cells reactive against multiple vaccine peptide sequences with CD8+ T cell cross-reactivity against one wild-type epitope. Other patients had immunogenicity against the vaccinated peptides. Overall, the 6 months PFS was 100%, with 67% 2-year and 58% 3-year survival. Although the mutation burden is low in GBM, neoantigens were detected in all tumors, and PNV were manufactured for all patients. PNV with synthetic long peptides combined with standard care treatment may help improve outcomes in GBM. Cross-reactivity may potentially be responsible for post-vaccination T-cell demyelination. Further evidence is needed to substantiate a direct effect. Funding: CRI - V Foundation CLIP (#3680)