Since the discovery in 1796 by Edward Jenner of vaccinia virus as a way to prevent and finally eradicate smallpox, the concept of using a virus to fight another virus has evolved into the current approaches of viral vectored genetic vaccines. In recent years, key improvements to the vaccinia virus leading to a safer version (Modified Vaccinia Ankara, MVA) and the discovery that some viruses can be used as carriers of heterologous genes encoding for pathological antigens of other infectious agents (the concept of 'viral vectors') has spurred a new wave of clinical research potentially providing for a solution for the long sought after vaccines against major diseases such as HIV, TB, RSV and Malaria, or emerging infectious diseases including those caused by filoviruses and coronaviruses. The unique ability of some of these viral vectors to stimulate the cellular arm of the immune response and, most importantly, T lymphocytes with cell killing activity, has also reawakened the interest toward developing therapeutic vaccines against chronic infectious diseases and cancer. To this end, existing vectors such as those based on Adenoviruses have been improved in immunogenicity and efficacy. Along the same line, new vectors that exploit viruses such as Vesicular Stomatitis Virus (VSV), Measles Virus (MV), Lymphocytic choriomeningitis virus (LCMV), cytomegalovirus (CMV), and Herpes Simplex Virus (HSV), have emerged. Furthermore, technological progress toward modifying their genome to render some of these vectors incompetent for replication has increased confidence toward their use in infant and elderly populations. Lastly, their production process being the same for every product has made viral vectored vaccines the technology of choice for rapid development of vaccines against emerging diseases and for 'personalised' cancer vaccines where there is an absolute need to reduce time to the patient from months to weeks or days. Here we review the recent developments in viral vector technologies, focusing on novel vectors based on primate derived Adenoviruses and Poxviruses, Rhabdoviruses, Paramixoviruses, Arenaviruses and Herpesviruses. We describe the rationale for, immunologic mechanisms involved in, and design of viral vectored gene vaccines under development and discuss the potential utility of these novel genetic vaccine approaches in eliciting protection against infectious diseases and cancer.

Upon chronic antigen exposure, CD8 ⁺ T cells become exhausted, acquiring a dysfunctional state correlated with the inability to control infection or tumor progression. In contrast, stem-like CD8 ⁺ T progenitors maintain the ability to promote and sustain effective immunity. Adenovirus (Ad)–vectored vaccines encoding tumor neoantigens have been shown to eradicate large tumors when combined with anti–programmed cell death protein 1 (αPD-1) in murine models; however, the mechanisms and translational potential have not yet been elucidated. Here, we show that gorilla Ad vaccine targeting tumor neoepitopes enhances responses to αPD-1 therapy by improving immunogenicity and antitumor efficacy. Single-cell RNA sequencing demonstrated that the combination of Ad vaccine and αPD-1 increased the number of murine polyfunctional neoantigen-specific CD8 ⁺ T cells over αPD-1 monotherapy, with an accumulation of Tcf1 ⁺ stem-like progenitors in draining lymph nodes and effector CD8 ⁺ T cells in tumors. Combined T cell receptor (TCR) sequencing analysis highlighted a broader spectrum of neoantigen-specific CD8 ⁺ T cells upon vaccination compared to αPD-1 monotherapy. The translational relevance of these data is supported by results obtained in the first 12 patients with metastatic deficient mismatch repair (dMMR) tumors vaccinated with an Ad vaccine encoding shared neoantigens. Expansion and diversification of TCRs were observed in post-treatment biopsies of patients with clinical response, as well as an increase in tumor-infiltrating T cells with an effector memory signature. These findings indicate a promising mechanism to overcome resistance to PD-1 blockade by promoting immunogenicity and broadening the spectrum and magnitude of neoantigen-specific T cells infiltrating tumors.

Purpose: Personalized vaccines targeting multiple neoantigens (nAgs) are a promising strategy for eliciting a diversified antitumor T-cell response to overcome tumor heterogeneity. NOUS-PEV is a vector-based personalized vaccine, expressing 60 nAgs and consists of priming with a nonhuman Great Ape Adenoviral vector (GAd20) followed by boosts with Modified Vaccinia Ankara. Here, we report data of a phase Ib trial of NOUS-PEV in combination with pembrolizumab in treatment-naïve patients with metastatic melanoma (NCT04990479). Patients and Methods: The feasibility of this approach was demonstrated by producing, releasing, and administering to 6 patients 11 of 12 vaccines within 8 weeks from biopsy collection to GAd20 administration. Results: The regimen was safe, with no treatment-related serious adverse events observed and mild vaccine-related reactions. Vaccine immunogenicity was demonstrated in all evaluable patients receiving the prime/boost regimen, with detection of robust neoantigen-specific immune responses to multiple neoantigens comprising both CD4 and CD8 T cells. Expansion and diversification of vaccine-induced T-cell receptor (TCR) clonotypes was observed in the posttreatment biopsies of patients with clinical response, providing evidence of tumor infiltration by vaccine-induced neoantigen-specific T cells. Conclusions: These findings indicate the ability of NOUS-PEV to amplify and broaden the repertoire of tumor-reactive T cells to empower a diverse, potent, and durable antitumor immune response. Finally, a gene signature indicative of the reduced presence of activated T cells together with very poor expression of the antigen-processing machinery genes has been identified in pretreatment biopsies as a potential biomarker of resistance to the treatment.

The aim of personalized cancer vaccines is to elicit potent and tumor-specific immune responses against neoantigens specific to each patient and to establish durable immunity, while minimizing the adverse events. Over recent years, there has been a renewed interest in personalized cancer vaccines, primarily due to the advancement of innovative technologies for the identification of neoantigens and novel vaccine delivery platforms. Here, we review the emerging field of personalized cancer vaccination, with a focus on the use of viral vectors as a vaccine platform. The recent advancements in viral vector technology have led to the development of efficient production processes, positioning personalized viral vaccines as one of the preferred technologies. Many clinical trials have shown the feasibility, safety, immunogenicity and, more recently, preliminary evidence of the anti-tumor activity of personalized vaccination, fostering active research in the field, including further clinical trials for different tumor types and in different clinical settings.

The dichotomic contribution of cancer cell lysis and tumor immunogenicity is considered essential for effective oncovirotherapy, suggesting that the innate antiviral immune response is a hurdle for efficacy of oncolytic viruses. However, emerging evidence is resizing this view. By sensing cytosolic DNA, the cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING) axis can both counteract viral spread and contribute to the elicitation of adaptive immunity via type I interferon responses. In this paper, we analyzed the tumor-resident function of Sting-mediated DNA sensing in a combined approach of oncovirotherapy and PD-1 immune checkpoint blockade, in an immunocompetent murine model. While supporting increased lytic potential by oncolytic HER2-retargeted HSV-1 in vitro and in vivo, Sting-knockout tumors showed molecular signatures of an immunosuppressive tumor microenvironment. These signatures were correspondingly associated with ineffectiveness of the combination therapy in a model of established tumors. Results suggest that the impairment in antiviral response of Sting-knockout tumors, while favoring viral replication, is not able to elicit an adequate immunotherapeutic effect, due to lack of immunogenic cell death and the inability of Sting-knockout cancer cells to promote anti-tumor adaptive immune responses. Accordingly, we propose that antiviral, tumor-resident Sting provides fundamental contributions to immunotherapeutic efficacy of oncolytic viruses.

Cancer interception is a preventative approach aiming to reduce cancer incidence by targeting precancers and early-stage cancers. Lynch syndrome (LS) is a prevalent hereditary cancer syndrome affecting ~1 in 300 individuals, with an overall lifetime cancer risk as high as 80%. LS is caused by germline mutations in the DNA mismatch repair genes, leading to microsatellite instability (MSI) and accumulation of shared mutations. When these occur in coding regions, they generate frameshift peptides (FSPs). Nous-209 is a neoantigen-directed immunotherapy based on a heterologous prime boost using great ape adenovirus and modified vaccinia virus Ankara encoding 209 FSPs shared across MSI neoplasms. We present the results from cohort 1 of a phase 1b/2 single-arm trial of Nous-209 for cancer interception in LS carriers (n = 45). Safety and immunogenicity were coprimary endpoints. Safety was assessed in 45 participants. Vaccination was safe with no intervention-related serious adverse events (AEs). The most common AEs were injection-site reactions (any grade in 91% of participants after prime and 76% after boost with no grade 3) and fatigue (any grade in 80% after prime and 53% after boost with 4% grade 3 after prime or after boost). Neoantigen-specific immune responses were observed after vaccination in 100% of evaluable participants (n = 37), with induction of potent T cell immunity (mean response at peak of ~1,100 interferon-γ spot-forming cells per million peripheral blood mononuclear cells). The immune response was durable and detectable at 1 year in 85% of participants. Both CD8⁺ and CD4⁺ T cells were induced, recognizing multiple FSPs. Peptide–human leukocyte antigen predictions allowed the identification of >100 immunogenic FSPs with demonstration of cytotoxic activity in vitro. Immunogenic FSPs were found in independent datasets of LS MSI colorectal precancers and cancers. These results highlight Nous-209 ability to efficiently stimulate immunity against neoantigens in LS, supporting its development for cancer interception (ClinicalTrials.gov identifier: NCT05078866).