Harnessing SARS-CoV-2 Immunity to Promote Antitumor Responses through Intratumoral Vaccination and Adoptive Transfer

Ahmad Bakur Mahmoud^1,2*Manar Darwish^2,3Mais Eyouni³Muhammad Yasir Khan³Rofidah Alsaggaf^2,3Rahaf Alharbi³Haya Hawbani^2,3Rwaa Abdulal^3,4Rowa Alhabbab³May Alsayb^1,2Heba Zahid^1,2Mustafa Taher^1,2Almohanad A Alkayyal⁵Anwar M Hashem⁶

• ¹Faculty of Applied Medical Sciences, Taibah University, Madinah, Saudi Arabia
• ²Health and Life Research Center, Taibah University, Madinah, Saudi Arabia, Madinah, Saudi Arabia
• ³Vaccines and Immunotherapy Unit, King Fahd Medical Research Center, King Abdulaziz University, Jeddah, Saudi Arabia, Jeddah, Saudi Arabia
• ⁴Infectious Disease Research Department, King Abdullah International Medical Research Center, King Saud bin Abdulaziz for Health Sciences, Ministry of National Guard Health Affairs, jeddah, Saudi Arabia
• ⁵Department of Medical Laboratory Technology, Faculty of Applied Medical Sciences, University of Tabuk, Tabuk, Tabuk, Saudi Arabia
• ⁶Department of Clinical Microbiology and Immunology, Faculty of Medicine, King Abdulaziz University, Jeddah, Saudi Arabia, Jeddah, Saudi Arabia

Cancer immunotherapy holds promise for the treatment of malignancies by mobilizing the immune system; however, its efficacy remains limited in tumors that lack immune infiltration. Innovative approaches are therefore required to convert these immunologically "cold" tumors into "hot" tumors that are more susceptible to immune-mediated attack. Therapeutic vaccination represents one such strategy, capable of triggering robust immune activation and durable memory responses. Given that the vast majority of the global population has either been vaccinated against or exposed to SARS-CoV-2, we hypothesized that pre-existing antiviral immunity could be locally leveraged to enhance intratumoral immune responses. To test this concept, we evaluated the therapeutic efficacy of intratumoral SARS-CoV-2 vaccination in the B16F10 murine melanoma model using two SARS-CoV-2 vaccine platforms: pVAX-SARS-S, a DNA vaccine encoding the spike protein S1 subunit and rAd-SARS2-S1/CD40L, a recombinant adenovirus expressing a secreted S1-CD40L fusion protein. Tumor-bearing C57BL/6 mice were treated intratumorally with either vaccine in the presence or absence of prior immunization, which had been established six months earlier to mimic pre-existing antiviral immunity. Intratumoral vaccination with pVAX-SARS-S significantly reduced tumor burden and prolonged survival in both naïve and pre-immunized mice. Its antitumor protection could be adoptively transferred via splenocytes, indicating the involvement of systemic adaptive immunity in mediating tumor rejection. The rAd-SARS2-S1/CD40L platform conferred modest tumor control. While both vaccines were effective, the DNA platform demonstrated superior efficacy. Together, these findings provide proof-of-concept that intratumoral administration of SARS-CoV-2 vaccines can promote antitumor effects through local immune activation in the context of pre-existing antiviral immunity. This strategy may offer a translatable approach for enhancing intratumoral immunotherapy in the post-pandemic era.