An innovative combined immunization platform for personalized cancer immunotherapy.

Abstract

e14225 Background: Activity of immune checkpoint inhibitors relies mainly on the presence of an immune response directed against neoantigens resulting from tumor specific mutations. The induction and/or amplification of such an immune response is expected to increase the activity of these therapies. We describe here a novel immunization platform developed for the purpose of personalized cancer immunotherapy. This platform integrates a DNA vector coding for neoantigens, a live modified vaccinia of strain Ankara (MVA) used as a physiologic adjuvant and anti-CTLA-4 as a locally acting early immune checkpoint blocker. Methods: Immune potency was assessed in C57BL6 mice injected subcutaneously three times five days apart with an ovalbumine (OVA) expressing DNA vector (100 µg), either alone or in combination with increasing doses of MVA (up to 2.5x107 plaque forming units, pfu) and increasing doses of anti-CTLA-4 (up to 100 µg). OVA specific immune responses were measured by ELISpot. Anti-tumor efficacy was then investigated with a similar administration scheme in a therapeutic B16F10 mice melanoma model with a DNA vector coding for the B16F10-M30 tumor neoantigen. Results: At an optimal dose of 2.5x106 pfu, MVA significantly improved OVA specific immune response up to 10 times higher as compared to vector alone. Addition of CTLA-4 blockade further increased the magnitude of response, up to 30 times higher than with vector alone. Both MVA and CTLA-4 demonstrated a bell-shaped dose dependent effect. In tumor-bearing animals, 80% experienced durable tumor-free survival when treated with the combination therapy as compared to less than 20% in untreated animals or animals treated with each component independently. Treatment appeared feasible and well-tolerated. Conclusions: Neoantigen coding DNA vector, MVA and CTLA-4 immune checkpoint blockade, when co-administered in immunocompetent C57BL6 mice, acted synergistically to induce a cellular immune response. The same approach translated into a strong anti-tumoral response in an aggressive melanoma model. This combined immunization platform appears as a potential novel way to enhance clinical benefit from current immune checkpoint inhibitors.