Abstract CT301: A phase Ib study to evaluate RO7198457, an individualized Neoantigen Specific immunoTherapy (iNeST), in combination with atezolizumab in patients with locally advanced or metastatic solid tumors

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Cancer Research


Background: Neoantigens arising from somatic mutations are attractive targets for cancer immunotherapy as they may be recognized as foreign by the immune system. RO7198457, a systemically administered RNA-Lipoplex iNeST was designed to stimulate T cell responses against neoantigens. A first-in-human Phase Ib study of RO7198457, in combination with the aPD-L1 antibody atezolizumab is being conducted in patients with locally advanced or metastatic solid tumors. Methods: RO7198457 is manufactured on a per-patient basis and contains up to 20 tumor-specific neoepitopes. Nine doses of RO7198457 were administered i.v. in weekly and bi-weekly intervals during the 12-week induction stage and every 24 weeks during the maintenance stage. Atezolizumab 1200 mg was administered on Day 1 of each 21-day cycle. Results: In total, 132 patients enrolled in cohorts with doses ranging from 15-50 μg RO7198457 in combination with atezolizumab. Most common tumor types were NSCLC, TNBC, melanoma and CRC. The median number of prior therapies was 3 (range 1-11). 39% of patients received prior immunotherapy. Most patients had low levels of PD-L1 expression (93% patients with <5% PD-L1 expression on tumor cells, 79% patients with <5% expression on immune cells). The median number of RO7198457 doses received was 8; 16% of patients discontinued due to PD prior to completing 6 weeks of therapy. The majority of adverse events (AE) were Grade 1-2. AEs occurring in ≥ 15% of patients included infusion related reaction (IRR)/cytokine release syndrome (CRS), fatigue, nausea and diarrhea. IRR/CRS were transient and reversible and presented primarily as Grade 1-2 chills and fever. There were no DLTs. Seven patients (5%) discontinued treatment due to AEs related to study drugs. RO1798457 induced pulsatile release of pro-inflammatory cytokines with each dose, consistent with the innate immune agonist activity of the RNA. RO7198457 induced neoantigen-specific T cell responses were observed in peripheral blood in 37/49 (77%) patients by ex vivo ELISPOT or MHC multimer analysis. Induction of up to 6% MHC multimer-stained CD8+ T-cells with memory phenotype was observed in peripheral blood. RO7198457-induced T cells against multiple neoantigens that were detected in post-treatment tumor biopsies. Of 108 patients who underwent at least one tumor assessment, 9 responded (ORR 8%, including 1 CR) and 53 had SD (49%). Conclusion: RO7198457 in combination with atezolizumab has a manageable safety profile consistent with the mechanisms of action of the study drugs and induces significant levels of neoantigen-specific immune responses. A randomized Ph2 study of RO7198457 1L melanoma patients in combination with pembrolizumab has been initiated, and two randomized clinical trials are planned for the adjuvant treatment of patients with NSCLC and CRC.

Clinical Institute



Earle A. Chiles Research Institute




Proceedings: AACR Annual Meeting 2020; April 27-28, 2020 and June 22-24, 2020; Philadelphia, PA