Abstract CT169: A phase Ia study to evaluate RO7198457, an individualized Neoantigen Specific immunoTherapy (iNeST), in patients with locally advanced or metastatic solid tumors

Background: Neoantigens arising from somatic mutations are attractive targets for cancer immunotherapy as they may be recognized as foreign by the immune system. RO7198457 is a systemically administered RNA-Lipoplex iNeST designed to stimulate T cell responses against neoantigens. A first-in-human Phase Ia study of RO7198457 was conducted in patients with locally advanced or metastatic solid tumors. Methods: RO7198457 is manufactured on a per-patient basis and contains up to 20 patient- specific neoantigens. Nine doses of RO7198457 were administered i.v. at weekly and bi-weekly intervals during the 12-week induction stage and every 24 weeks during the maintenance stage. Results: In total, 29 patients enrolled in cohorts with doses ranging from 25-100 μg. The most common tumor types were HR+/HER2+ breast, prostate, and ovarian cancer. The median number of prior therapies was 5 (range 1-17). 34% of patients received prior immunotherapy. Most patients had low PD-L1 expression (97% patients with