CTIM-14. COMPREHENSIVE BIOMARKER ANALYSIS OF RESPONDERS AND NON-RESPONDERS IN A PHASE IIA TRIAL OF A CMV VACCINE IMMUNOTHERAPEUTIC CANDIDATE (VBI-1901)

Abstract Cytomegalovirus (CMV) antigens have been reported in over 90% of GBMs. CD4+ and CD8+ T cells are most frequently directed against the gB pp65 antigens, respectively, which immunogenic targets a CMV-based GBM immunotherapeutic. First-recurrent patients were enrolled, with Karnofsky Performance Status at least 70, to receive VBI-1901 (a gB/pp65 enveloped virus-like particle [eVLP]) adjuvanted GM-CSF given intradermally (NCT03382977). Patients vaccinated every 4 weeks, serologic immune-monitoring 2 weeks after each vaccination surveillance brain MRI scans 6 weeks. Sixteen (8 women, 8 men) median age 55 (33-67 yrs) enrolled into arm. Seven tumor responses, including two durable partial observed led an 18-month OS rate 25% mOS 56 Detailed immunological testing was performed identify potential correlations baseline treatment between biomarkers responses. Analyses included class I II HLA typing, modulation plasma cytokine chemokine boosting CMV-specific antibody IFN-g ELISPOT CD4 Tem cells, only differential trafficking appears distinguish responses from those progression. Single cell, RNAseq is underway attempt understand mechanistic differences these immune cell populations Tumor Responders vs. Non-Responders. The U.S. FDA granted Fast Track Designation first-recurrent patients, expansion ongoing trial this formulation patient population, addition randomization contemporaneous control arm, anticipated begin Q3 2022.