Background: RAS mutations occur in 25% of solid tumors with G12D being the most frequent variant. ELI-002 2P is a vaccine comprised of lymph-node targeted Amphiphile (Amph)-modified G12D and G12R mutant KRAS peptides with an Amph-modified CpG oligonucleotide adjuvant designed to expand polyfunctional mutant KRAS-specific T cells. Preclinical amphiphile data (relative to non-amphiphile controls) showed increased immunogenicity, tumor clearance and survival in mouse models. Methods: This first-in-human multicenter phase I trial assessed safety, immunogenicity and antitumor activity using a novel adjuvant trial design in patients (pts) with minimal residual disease (MRD) following standard locoregional treatment. Eligibility: elevated circulating tumor DNA (ctDNA) and/or serum tumor biomarker elevation (CA19-9/CEA), and KRAS/NRAS mutation. In a 3+3 dose escalation, n=22 received a subcutaneous course of 6 prime and 4 booster injections of fixed dose Amph-peptides (1.4 mg), admixed with escalating Amph-CpG-7909 (Table). Dose escalation based on observed safety in first 28 days. Safety, antitumor activity including biomarker reduction/clearance and relapse free survival using immune Response Evaluation Criteria in Solid Tumors (iRECIST) were assessed. Immunogenicity assessed by direct ex vivo Fluorospot and intracellular cytokine staining of peripheral blood mononuclear cells (T-cell responders = ≥ 2-fold increase over baseline) and by tumor CD3 immunohistochemistry in subset who underwent a biopsy. Results: No dose-limiting toxicities, treatment related SAEs or cytokine release syndrome were observed, and no maximum tolerated dose was identified. Safety: all grade 1, fatigue (19%), headache (19%), and injection site reaction (9.5%). Biomarker reduction was observed in 15/19 (79%) and in 5/5 at highest doses; clearance of MRD was observed in 4/19 (21% - n=2 pancreas, n=2 colorectal). Polyfunctional mKRAS-specific T cell responses observed in 80% of pts (n=12/15), with both CD8+ and CD4+ T cell responses for most, and CD3+ T cells observed on biopsies. The recommended phase 2 dose (RP2D) is 10.0 mg Amph-CpG-7909. Conclusions: ELI-002 2P, evaluated in a novel MRD+ trial, was safe with ctDNA and serum tumor biomarker reduction and clearance and notable immune responses. The RP2D is the start dose for a phase 1/randomized phase 2 study evaluating a new seven peptide formulation for G12 D, R, V, S, A, C, and G13D mutated solid tumors (NCT05726864). Clinical trial information: NCT04853017.

*Subset of pts evaluable at data cut.