Background: EO2401 (EO) was designed to activate existing commensal memory T-cells cross-reacting with tumor associated antigens (TAAs). EO includes microbial-derived, synthetically produced peptides corresponding to HLA-A2 restricted epitopes with molecular mimicry to three TAAs upregulated in glioblastoma (GB), IL13Rα2, BIRC5 and FOXM1, with the CD4 helper peptide UCP2 and the adjuvant Montanide. Pre-clinically EO generates strong immune responses and cross-reactive CD8 cells recognizing the TAAs. Methods: This ongoing Ph 1/2 trial (NCT04116658) investigates EO (SC q2 wks X 4 then q4 wks), EO with nivolumab (3 mg/kg q2 wks; EN), and EN with bevacizumab (10 mg/kg q2 wks; ENB) among four Cohorts (Cs) of pts with GB at first progression after radiotherapy/temozolomide. After the Ph 1 of EO followed by EN (C1), C2 investigated EN without (C2a) or with (C2b) surgery while C3 investigated ENB (population as C2a). Results: Among 40 treated pts (C1 n = 3, C2a n = 23, C2b n = 3, C3 n = 11), median age was 60, 53% male, 40% had KPS 90-100% and 35% had O6-methylguanine DNA-methyltransferase promotor hypermethylated tumors. All evaluable pts demonstrated strong CD8 T-cell ELISPOT responses against the 3 vaccine peptides, with tetramer staining of specific CD8 detected in 24/25 investigated pts after in vitro stimulation and in 19/20 pts directly ex vivo. Cross-reactivity against targeted TAAs was confirmed in 20/21 pts. Majority of response were detected by week 4 after 1st dose and as early as 2 weeks for some pts. EO, EN, and ENB were well tolerated (max exposure EN 68 wks, ENB 30 wks) with EO associated toxicity limited to local administration site reactions (48%; grade 1-2). The frequency and severity of nivolumab- or bevacizumab-associated AEs was consistent with historical monocompound experience. With a median follow-up of 9.3 months (range, 2.8-15.6), median progression-free survival (PFS), survival at 6 months (OS-6) and at 12 months for EN (C1+C2a+C2b) were 1.8 months (3 ongoing at 5.9, 7.1, and 14.7 months), 85%, and 50.1% (19/29 alive), respectively. With a median follow-up of 3.7 months (range, 2.2-7.2), pts on ENB (C3) have median PFS and OS-6 of 5.5 months (7 ongoing), and 80% (10/11 alive), respectively. ORR for EN and ENB were 10% and 36%, respectively (5 of 7 ongoing). In C2a, 12/23 pts stopped treatment due to neurological symptoms and PD on first MRI (median 5 wks, range 2-8). In C3 (ENB), only 1/11 pts stopped early due to PD. Conclusions: EO2401 generated strong systemic immune responses and was well tolerated in combination with nivolumab +/- bevacizumab. The addition of bevacizumab to EN improved PFS while survival across treatment cohorts is pending ongoing follow-up. To prolong EN exposure that is likely required for therapeutic activity in recurrent GB, the trial has been expanded with additional pts to evaluate low-dose bevacizumab (5 mg/kg q2 wks up to x 6) for early progressive neurological symptoms. Clinical trial information: NCT04116658.