Neoantigen cancer vaccine augments anti-CTLA-4 efficacy

Abstract

Immune checkpoint inhibitors (ICI) based on anti-CTLA-4 (αCTLA-4) and anti-PD1 (αPD1) are being tested in combination with different therapeutic approaches including other immunotherapies such as neoantigen cancer vaccines (NCV). Here we explored, in two cancer murine models, different therapeutic combinations of ICI with personalized DNA vaccines expressing neoantigens and delivered by electroporation (EP). Anti-cancer efficacy was evaluated using vaccines with or without CD4 epitopes. Therapeutic DNA vaccines showed synergistic effects in different therapeutic protocols including established large tumors. Flow cytometry (FC) was utilized to measure CD8, CD4, Treg, and switched B cells as well as neoantigen-specific immune responses, which were also measured by IFN-γ ELIspot. Immune responses were augmented in combination with αCTLA4 but not with αPD1 in the MC38 tumor-bearing mice, significantly impacting tumor growth. Similarly, neoantigen-specific T cell immune responses were enhanced in combined treatment with αCTLA-4 in the CT26 tumor model where large tumors regressed in all mice, while monotherapy with αCTLA-4 was less efficacious. In line with previous evidence, we observed an increased switched B cells in the spleen of mice treated with αCTLA-4 alone or in combination with NCV. These results support the use of NCV delivered by DNA-EP with αCTLA-4 and suggest a new combined therapy for clinical testing.

Linear DNA amplicons as a novel cancer vaccine strategy

“…It has been already shown elsewhere that neoantigen-based DNA vaccine approach is a potential alternative to currently established cancer immunotherapies, especially when administered as cotreatment with immune checkpoint inhibitors. 5 By demonstrating that DNA amplicons encoding for neoantigens are equally effective as plasmids in antitumoral cotreatment with ICIs (Fig.5), we here validate the use of amplicon expression vectors as DNA cancer vaccines, as a more cost- and time-effective alternative to conventional plasmids, given their enhanced ability to rapidly manufacture tumor-specific cancer vaccines able to elicit antigen-specific immune responses with increased efficacy and reduced on-target off-tumor effects. Taken together, these results provide the first in vivo preclinical demonstration of linear DNA amplicons antitumoral efficacy thus encouraging further studies for clinical applications.…”

“…After proving that DNA amplicons are able to elicit antigen-specific immune responses as efficiently as plasmid DNA, we investigated whether this novel immunotherapeutic strategy could exert an antitumoral effect in a cancer murine model. To this aim, we exploited a murine cancer model previously described, 5 Interestingly, this synergistic effect was confirmed when M8 amplicon was administered in combination with CTLA-4 (Fig. 5B).…”

“…After proving that DNA amplicons are able to elicit antigen-specific immune responses as efficiently as plasmid DNA, we investigated whether this novel immunotherapeutic strategy could exert an antitumoral effect in a cancer murine model. To this aim, we exploited a murine cancer model previously described, 5 where a neoantigen-based DNA vaccine (namely, M8) was shown to induce tumor regression when administered in combination with ICIs such as αPD1 and αCTLA4, in a therapeutic setting. Briefly, as shown in Fig.5A, after tumor challenge, C57Bl/6 mice received a combination of DNA (plasmid or amplicon, administered at days 2,9 and 16) and ICIs (αCTLA-4 or αPD1, administered at days 3,6 and 9).…”

“…M8 is a polypeptide encoding 8 neoantigens expressed by MC38 murine colon cancer cells. 5,7 For conTRT and M8 constructs, a human CMV promoter/intron A drives gene expression as well.…”

“…neoantigens. 2,3,4,5 DNA cancer vaccines can induce both innate immunity and adaptive immune responses which can suppress tumor growth and, in some cases, achieve total tumor rejection or shrinkage. 6,7,8,9 To date, DNA based vaccines have involved the inoculation of a subject with plasmid DNA and/or plasmid-derived DNA.…”