Exploring the use of tolerogenic dendritic cells and pore-forming toxins in the context of oncolytic adenoviruses

[eng] Oncolytic viruses (OVs), engineered to infect preferentially and selectively replicate within cancer cells while sparing healthy tissues, have regained interest in oncology for their potential to restore host anti-tumor immunity. OVs have been evaluated in clinical settings as standalone therapies or in combination with chemotherapy, radiotherapy, and immunotherapy. Among them, oncolytic adenoviruses (OAds) are well-studied and commonly employed as OVs for their powerful oncolysis capacity and immune response stimulation. However, their therapeutic efficacy as anticancer agents remains unsatisfactory due to the limited intratumoral virus spreading and subsequent antiviral immune responses. This doctoral thesis addresses these challenges in two distinct chapters. Viral epitopes are often more immunogenic than tumor epitopes, leading to predominant antiviral immune responses following OAd administration, which can undermine or even mask antitumoral immune responses. To counteract this, we hypothesized that tolerogenic dendritic cells (tolDCs) exposed to OAd-derived epitopes could induce specific viral tolerance, thereby shifting the balance from viral to tumor antigen adaptive immune responses. Our findings revealed that IL-10-induced tolDCs primarily belonged to the CD11c+CD11b+ cDC2 subset, exhibited an anti-inflammatory cytokine profile, and demonstrated a reduced ability to drive allogeneic CD8+ T cell proliferation in mixed lymphocyte reactions (MLRs). However, in an immunocompetent model, no viral-specific tolerance but a generalized immunosuppression was elicited upon treatment with OAd peptide-pulsed tolDCs. To improve the intratumoral spread of OAds, we armed the ICOVIR15K virus with a modified version of the pore-forming toxin (PFT) Parasporin 2 (PS2), as this toxin has been reported to display a selective antitumor activity in its active form. We presumed the toxin-mediated cell lysis would amplify the OAd’s oncolytic capacity and induce an immunogenic cell death (ICD) in bystander non-infected cells. PS2-enriched supernatant treatment exhibited selective cytocidal effects against several human and murine cancer cell lines in vitro and efficiently controlled tumor growth in a lung carcinoma immunocompetent model. Moreover, vaccination with PS2- treated tumor cells acted as an ICD inducer that promoted a protective antitumor immune response in a vaccination-rechallenge setting. Finally, we showed that the ICOVIR15K-PS2 OAd significantly exerted an enhanced antitumor efficacy compared with the ICOVIR15K parental virus in an immunodeficient model, expecting better outcomes when both oncolysis and toxin ICD-mediated responses could act synergistically in clinical testing, where the OAd can replicate.