Ad-RTS-hIL-12 (Ad) is a gene therapy candidate for intratumoral (IT) delivery that conditionally expresses IL-12 (IL-12) under the transcriptional control of orally administered veledimex (V) acting via the RheoSwitch Therapeutic Systemâ gene switch. Increased PD-1 expression in samples of rGBM following Ad+V (ASCO 2020) supports combination immunotherapy with a PD-1 inhibitor. Phase 1 trials in rGBM of Ad+V as monotherapy and in combination with PD-1 inhibitor revealed encouraging safety and survival data. This phase 2 trial (NCT04006119) in adults with rGBM is evaluating safety and efficacy (overall survival) of Ad + V with pre/post-operative cemiplimab-rwlc (cemi) 350 mg IV, Days -7, 15, then Q3W; Ad single IT injection (2 x 1011 viral particles, day of resection (Day 0) /craniotomy); and V (20 mg PO, Days 0-14). Longitudinal sampling of serum assessed IL-12 and endogenous cytokines production. Anti-tumor effects were described upon preliminary review. Serial MRI evaluated tumor response. Follow-up described overall survival. Initial safety data (51 unique adverse reactions in 28 subjects) appeared similar to Ad+V and the cemi label, respectively, being manageable without synergistic toxicities and generally reversible. Of 35 SAEs reported in 18 subjects, 10 SAEs in 7 subjects were related to Ad+V. IL-12 and IFN-g levels increased after Ad+V administration peaking on Day 3 at 34 ± 11 pg/mL and 13 ± 5 pg/mL (mean ± SEM), respectively. Immune-mediated anti-tumor effects were noted, including a post-treatment biopsy to rule out progression which demonstrated an immune infiltrate consistent with pseudoprogression and loss of tumor cell heterogeneity suggesting immunoediting. Enrollment is anticipated to be completed in 2Q2020 with follow-up ongoing and initial survival data will be presented. V crossed the blood-brain barrier to produce functional IL-12. Controlled IL-12 therapy and cemi is a rational combination with initial data consistent with immune-mediated anti-tumor effects with a favorable safety profile.