ABSTRACT: Due to 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. While CD8+ anti-tumor cytotoxic T lymphocytes (CTL) are the preferred effectors of cancer immunotherapy, CD4+ T cell help is also required for an optimal anti-tumor immune response to occur. Hence, we investigated whether the pathogen-related CD4+ T cell memory populations could be re-engaged to support the CTLs, converting a weak primary anti-tumor 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 pre-immunized 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 anti-tumor efficacy and induced TT-specific, CD40 ligand-expressing CD4+ T helper cells and maturation of antigen presenting cells (APCs). 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 anti-tumor effect was even more prominent when combined with the immune checkpoint inhibitor anti-PD1, strengthening the rationale behind combination therapy with oncolytic viruses.