Exploiting pre-existing immunity to enhance oncolytic cancer immunotherapy.

Because of the high coverage of international vaccination programs, most people worldwide have been vaccinated against common pathogens, leading to acquired pathogen-specific immunity with a robust memory T-cell repertoire. Although CD8(+) antitumor cytotoxic T lymphocytes (CTL) are the preferred effectors of cancer immunotherapy, CD4(+) T-cell help is also required for an optimal antitumor immune response to occur. Hence, we investigated whether the pathogen-related CD4(+) T-cell memory populations could be reengaged to support the CTLs, converting a weak primary antitumor immune response into a stronger secondary one. To this end, we used our PeptiCRAd technology that consists of an oncolytic adenovirus coated with MHC-I-restricted tumor-specific peptides and developed it further by introducing pathogen-specific MHC-II-restricted peptides. Mice preimmunized with tetanus vaccine were challenged with B16.OVA tumors and treated with the newly developed hybrid TT-OVA-PeptiCRAd containing both tetanus toxoid- and tumor-specific peptides. Treatment with the hybrid PeptiCRAd significantly enhanced antitumor efficacy and induced TT-specific, CD40 ligand-expressing CD4(+) T helper cells and maturation of antigen-presenting cells. Importantly, this approach could be extended to naturally occurring tumor peptides (both tumor-associated antigens and neoantigens), as well as to other pathogens beyond tetanus, highlighting the usefulness of this technique to take full advantage of CD4(+) memory T-cell repertoires when designing immunotherapeutic treatment regimens. Finally, the antitumor effect was even more prominent when combined with the immune checkpoint inhibitor anti-PD-1, strengthening the rationale behind combination therapy with oncolytic viruses. Significance: These findings establish a novel technology that enhances oncolytic cancer immunotherapy by capitalizing on pre-acquired immunity to pathogens to convert a weak antitumor immune response into a much stronger one.