Introduction: Pediatric high-grade gliomas (pHGGs) are routinely fatal with a median overall survival (OS) at recurrence of 5.6 months (mos). A safe, effective immunotherapy for pHGG has eluded investigators. Oncolytic HSV-1 G207 contains mutations that prevent a productive infection of normal cells but permit replication in tumor cells. In addition to direct tumor cell lysis, G207 activates innate/adaptive immune cells and promotes cross-presentation of tumor antigens to generate an anti-tumor immune response. A 5 Gy radiation dose increases viral replication and spread. We evaluated the safety and efficacy of G207 alone and combined with radiation in children with progressive supratentorial HGG (NCT02457845). Methods: We employed a 3 + 3 design with 4 cohorts. Children 3-18 years old with biopsy-confirmed HGG underwent stereotactic placement of up to four intratumoral catheters. The next day, we administered 107 or 108 plaque-forming units (pfu) of G207 by controlled rate infusion over 6 hours. Within 24 hours of G207, patients in dose level 3 and 4 received 5 Gy to the gross tumor volume. The primary objective was safety/tolerability. We assessed secondary objectives of virus shedding in blood, saliva and conjunctiva by PCR, response by MRI and evaluation of matched pre- and post-G207 tissue for tumor-infiltrating lymphocytes (TILs), and seroconversion by immunofluorescence assay. Results: 12 patients (age range 7-18) with progressive, IDH wild-type pHGG received G207. At screening, 10 patients had tumors with a bi-perpendicular sum ≥ 5.5 cm, 3 had multi-focal disease, 8 had failed ≥ 2 prior treatment regimens, and 4 had failed ≥ 3 regimens. 3-4 catheters (44 total) were placed safely throughout the cerebrum and resulted in no neurologic sequelae. G207 alone or with radiation was safe and tolerable in all patients with no dose-limiting toxicities, attributable grade 3 or 4 toxicities/serious adverse events, or evidence of virus shedding. 11 participants had radiographic, neuropathologic, and/or clinical responses. Median OS was 12.2 mos (95% CI 8.0, 16.4). Thus far, 36% of patients have lived >18 mos, the median OS for newly diagnosed pHGG. Compared to patients who seroconverted post-G207 (n=3), patients with baseline HSV-1 antibodies (n=3) had a shorter median survival: 5.1 mos (3.0, 7.2) vs 18.3 mos (9.2, 27.4). G207 significantly increased CD4+ and CD8+ TILs. Conclusions: G207 alone and combined with radiation was tolerable and safe with evidence of responses in children with pHGG. The promising median OS (12.2 mos) compares favorably with historical data (5.6 mos). Baseline HSV-1 seropositivity and seroconversion are potential biomarkers of treatment response that require further investigation. Importantly, G207 converted ‘cold' tumors to ‘hot' with a dramatic increase in TILs. A multi-institutional Phase II clinical trial of G207 in pHGG is forthcoming (NCT04482933).

Citation Format: Gregory K. Friedman, James M. Johnston, Asim K. Bag, Joshua D. Bernstock, Rong Li, Inmaculada Aban, Kara Kachurak, Li Nan, Kyung-Don Kang, Stacie Totsch, Charles Schlappi, Allison M. Martin, Devang Pastakia, Sameer Farouk Sait, Yasmin Khakoo, Matthias A. Karajannis, Karina Woodling, Joshua D. Palmer, Diana S. Osorio, Jeffrey Leonard, Mohamed S. Abdelbaki, Avi Madan-Swain, T. Prescott Atkinson, Richard J. Whitley, John B. Fiveash, James M. Markert, G. Yancey Gillespie. Phase I immunovirotherapy trial of oncolytic HSV-1 G207 alone or combined with radiation in pediatric high-grade glioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT018.