CTIM-01. OUTCOMES AND IMMUNE RESPONSES AFTER PEPTIDE VACCINATION TARGETING HUMAN CYTOMEGALOVIRUS ANTIGEN PP65 IN CHILDREN AND YOUNG ADULTS WITH RECURRENT HIGH-GRADE GLIOMA AND MEDULLOBLASTOMA: RESULTS OF A PHASE 1 TRIAL

Abstract INTRODUCTION The human cytomegalovirus (CMV) antigen pp65 is ubiquitously expressed in high-grade glioma (HGG) and medulloblastoma but not in adjacent brain. The primary objective of this phase I trial (NCT03299309) was to assess the safety and feasibility of a novel peptide vaccine targeting pp65 (PEP-CMV) in children/young adults with recurrent medulloblastoma and HGG. METHODS PEP-CMV is comprised of a synthetic long peptide of 26 amino acids and is administered as an emulsion in Montanide ISA 51. Patients receive a 5-day course of temozolomide to induce lymphopenia, tetanus/diphtheria toxoid site preconditioning to promote dendritic cell migration, then PEP-CMV intradermally in the groin every two weeks for 3 doses, then monthly. RESULTS 42 patients were enrolled. The mean age was 23.2 ± 9.3 years. 55% of patients were male. The median KPS was 80. The median number of prior chemotherapy regimens was 4 (range 1-15). Of the 38 patients who received PEP-CMV, the maximum grade adverse events (AE) possibly, probably, or definitely related to PEP-CMV were: 17 (45%) Grade 1 AEs, 16 (42%) Grade 2 AEs, 2 (5%) Grade 3 AEs (encephalopathy and pyramidal tract syndrome), and one (3%) Grade 4 AE (cerebral edema). One patient developed cytokine release syndrome (Grade 2). The median PFS was 2.5 months (95% CI:2.2, 3.2) and median OS was 6.4 months (95% CI:3.4, 7.9). The 12-month OS was 26.6% (95% CI:14, 41.1%). Of the 21 patients with evaluable immune monitoring data (received ≥3 vaccines/known CMV status), T cell reactivity on IFNγ pp65 ELISpot was increased after PEP-CMV delivery (median 2 vs 22, P=0.01). PFS and OS were significantly better in patients with low levels of CD56brightCD16dim phenotype NK cells: P=0.029 and P=0.047, respectively. Patients with naïve CD8+ counts over the median had significantly better PFS (P=0.006). CONCLUSIONS PEP-CMV is well-tolerated and elicits an antigen-specific immune response in heavily pretreated, multiply recurrent patients with a 12-month OS of 26.6%.