623 AI-designed personalized neoantigen vaccine, EVX-02, induces robust T-cell responses in melanoma patients

Background EVX-02, a personalized neoantigen DNA vaccine, was assessed in combination with an anti-PD-1 therapy (nivolumab) in patients with fully resected melanoma and at high risk of disease recurrence. The neoantigen EVX-02 vaccines were designed by Evaxion’s proprietary AI platform, PIONEER, based on the unique mutational profile of each tumor and the patient’s HLA type. PIONEER identifies cancer-specific mutations by analyzing differences in the DNA sequences of a tumor and a healthy sample. The non-synonymous subset of these cancer-specific mutations is then further processed in silico to generate candidate neoantigen sequences. The objectives of this study were to assess safety and tolerability, vaccine neoantigen immunogenicity and relapse-free survival at 12 months after nivolumab initiation. EVX-02 treatment was found to be safe and well-tolerated. A total of 10 patients received all scheduled EVX-02 vaccinations and were relapse-free at their last assessment. Methods To monitor EVX-02 induced T-cell responses and to profile soluble serum biomarker levels, blood samples were collected before, during and after EVX-02 treatment. Peripheral blood mononuclear cells (PBMCs) were isolated from the blood samples and assessed for T-cell immunogenicity after in vitro stimulation with vaccine neoantigens to facilitate the expansion of neoantigen reactive T cells. The neoantigen-specific T-cell responses were investigated by cytokine release assays, including interferon gamma (IFNy) ELISpot and intracellular cytokine staining (ICS). T-cell reactivity was addressed by stimulating the PBMCs with the collection of neoantigens or single neoantigens. Results Measuring the T-cell responses over time showed that there on average was an increase in magnitude and that the responses were long-lasting. ICS analysis demonstrated that both CD4+ and CD8+ T cells were reactive to the vaccine neoantigens. Analysis of the immunogenic potential of the individual vaccine neoantigens revealed that around 50% of the vaccine neoantigens were immunogenic and although pre-existing immune recognition of vaccine neoantigens was observed, there was a strong increase in the number of immunogenic neoantigens after EVX-02 vaccination. Interestingly, there was a correlation between the PIONEER predicted neoantigen quality and immunogenicity. Conclusions EVX-02 successfully induced neoantigen-reactive T cells in all patients that received all scheduled EVX-02 vaccinations. The EVX-02 vaccine mobilized robust and long-lasting CD4+ and CD8+ T-cell responses, both of which are believed to be relevant for obtaining a clinical effect. The measured T-cell responses correlated with the predictions generated by PIONEER, validating the precision and predictive power of the platform. Acknowledgements Anne Lund and Marianne Blirup Jensen for technical assistance. Patients of EVX-02 study for their participation and consent to the trial. Trial Registration NCT04455503 Ethics Approval Study obtained approval from all relevant Australian authorities Consent All patients who participated in the EVX-02 clinical study have consented.