Novel and efficient method for the reconstruction of adenoviruses through isothermal assembly and its potential applications

RCAd-LTH-shPD-L1, a double-gene recombinant oncolytic adenovirus with enhanced antitumor immunity, increases lymphocyte infiltration and reshapes the tumor microenvironment

BACKGROUND

With the successful development of modern immunotherapy, immune checkpoint inhibitors (ICIs) are currently considered potential therapeutic options for patients with cancer. However, the therapeutic potential of ICIs in human cancer is mainly limited by their systemic toxicity and low response rate, which suggests the necessity of local drug delivery with an effective vector and reshaping the immunosuppressive tumor microenvironment (TME) to enhance ICI therapy. Here, we constructed a novel double-gene recombinant oncolytic adenovirus named RCAd-LTH-shPD-L1 based on the RCAd virus platform armed with a DNA fragment encoding an anti-VEGF antibody and shRNA to inhibit PD-L1 expression.

METHODS

The correct assembly of RCAd-LTH-shPD-L1 was characterized by analyzing its secretion, antigen specificity, and replication using western blotting, ELISA and quantitative PCR, respectively. The in vitro effects of RCAd-LTH-shPD-L1 on cell proliferation, vasculogenic, and cell migration were assessed. Antitumor effects and therapeutic mechanisms were evaluated in vivo using immunodeficient and humanized immune system mouse models. The TME was studied by ELISA, immunohistochemistry and flow cytometry.

RESULTS

RCAd-LTH-shPD-L1 cells secreted anti-VEGF antibodies and inhibited the expression of PD-L1 in cancer cells. Moreover, RCAd-LTH-shPD-L1 exerted a specific cytotoxic effect on human cancer cells, but not on murine cancer cells or normal human cells. RCAd-LTH-shPD-L1 elicited a more potent antitumor effect in an immunodeficient mouse model and a humanized immune system mouse model than RCAd-shPD-L1, as demonstrated by the significant decrease in tumor growth. Furthermore, RCAd-LTH-shPD-L1 modulated the TME, which led to lymphocyte infiltration and alteration of their immune phenotype, as characterized by downregulation of anoxic factor HIF-1α and angiogenesis marker CD31, upregulation of cytokine such as IFN-γ, IL-6 and IL-12.

CONCLUSIONS

In summary, our data demonstrated that the localized delivery of anti-VEGF antibodies and shPD-L1 by engineered RCAd-LTH-shPD-L1 is a highly effective and safe strategy for cancer immunotherapy. Moreover, the data underscore the potential of combining local virotherapy and anti-angiogenic therapy with ICIs as an effective TME therapy for poorly infiltrating tumors.

A recombinant virus-like particle vaccine against adenovirus-7 induces a potent humoral response

Adenoviruses (AdVs) cause infections in humans that range from mild to severe, and can cause outbreaks particularly in close contact settings. Several human AdV types have been identified, which can cause a wide array of clinical manifestations. AdV types 4 and 7 (AdV-4 and AdV-7), which are among the most commonly circulating types in the United States, are known to cause acute respiratory disease that can result in hospitalization and rarely, death. Currently, the only vaccines approved for use in humans are live virus vaccines against AdV-4 and AdV-7, though these vaccines are only authorized for use in U.S. military personnel. While they are efficacious, use of these live virus vaccines carries considerable risks of vaccine-associated viral shedding and recombination. Here, we present an alternative vaccination strategy against AdV-7 using the virus-like particle platform (AdVLP-7). We describe the production of stable recombinant AdVLP-7, and demonstrate that AdVLP-7 is structurally analogous to wild-type AdV-7 virions (WT AdV-7). Preclinical immunogenicity studies in mice show that AdVLP-7 elicits a potent humoral immune response, comparable to that observed in mice immunized with WT AdV-7. Specifically, AdVLP-7 induces high titers of antibodies against AdV-7-specific antigens that can effectively neutralize AdV-7.

Generation and Characterization of a Replication-Competent Human Adenovirus Type 55 Encoding EGFP

Human adenovirus 55 (HAdV-55) has recently caused outbreaks of acute respiratory disease (ARD), posing a significant public threat to civilians and military trainees. Efforts to develop antiviral inhibitors and quantify neutralizing antibodies require an experimental system to rapidly monitor viral infections, which can be achieved through the use of a plasmid that can produce an infectious virus. Here, we used a bacteria-mediated recombination approach to construct a full-length infectious cDNA clone, pAd55-FL, containing the whole genome of HadV-55. Then, the green fluorescent protein expression cassette was assembled into pAd55-FL to replace the E3 region to obtain a recombinant plasmid of pAd55-dE3-EGFP. The rescued recombinant virus rAdv55-dE3-EGFP is genetically stable and replicates similarly to the wild-type virus in cell culture. The virus rAdv55-dE3-EGFP can be used to quantify neutralizing antibody activity in sera samples, producing results in concordance with the cytopathic effect (CPE)-based microneutralization assay. Using an rAdv55-dE3-EGFP infection of A549 cells, we showed that the assay could be used for antiviral screening. Our findings suggest that the rAdv55-dE3-EGFP-based high-throughput assay provides a reliable tool for rapid neutralization testing and antiviral screening for HAdV-55.