A haploid HSV-1 genome platform for vector development: testing of the tetracycline-responsive switch shows interference by infected cell protein 0

Improved antitumor effects elicited by an oncolytic HSV-1 expressing a novel B7H3nb/CD3 BsAb

Oncolytic viruses have emerged as a promising modality for cancer treatment due to their unique abilities to directly destroy tumor cells and modulate the tumor microenvironment. Bispecific T-cell engagers (BsAbs) have been developed to activate and redirect cytotoxic T lymphocytes, enhancing the antitumor response. To take advantage of the specific infection capacity and carrying ability of exogenous genes, we generated a recombinant herpes simplex virus type 1 (HSV-1), HSV-1dko-B7H3nb/CD3 or HSV-1dko-B7H3nb/mCD3, carrying a B7H3nb/CD3 or B7H3nb/mCD3 BsAb that replicates and expresses BsAb in tumor cells in vitro and in vivo. The new generation of oncolytic viruses has been genetically modified using CRISPR/Cas9 technology and the cre-loxp system to increase the efficiency of HSV genome editing. Additionally, we used two fully immunocompetent models (GL261 and MC38) to assess the antitumor effect of HSV-1dko-B7H3nb/mCD3. Compared with the HSV-1dko control virus, HSV-1dko-B7H3nb/mCD3 induced enhanced anti-tumor immune responses and T-cell infiltration in both GL261 and MC38 models, resulting in improved treatment efficacy in the latter. Furthermore, flow cytometry analysis of the tumor microenvironment confirmed an increase in NK cells and effector CD8+ T cells, and a decrease in immunosuppressive cells, including FOXP3+ regulatory T cells (Tregs), myeloid-derived suppressor cells (MDSCs), and CD206+ macrophages (M2). Overall, our study identified a novel camel B7H3 nanobody and described the genetic modification of the HSV-1 genome using CRISPR/Cas9 technology and the cre-loxp system. Our findings indicate that expressing B7H3nb/CD3 BsAb could improve the antitumor effects of HSV-1 based oncolytic virus.

Herpes Simplex Virus: A Versatile Tool for Insights Into Evolution, Gene Delivery, and Tumor Immunotherapy

Herpesviruses are prevalent throughout the animal kingdom, and they have coexisted and coevolved along with their host species for millions of years. Herpesviruses carry a large (120-230 kb) double-stranded DNA genome surrounded by a protein capsid, a tegument layer consisting of viral and host proteins, and a lipid bilayer envelope with surface glycoproteins. A key characteristic of these viruses is their ability to enter a latent state following primary infection, allowing them to evade the host's immune system and persist permanently. Herpesviruses can reactivate from their dormant state, usually during times of stress or when the host's immune responses are impaired. While herpesviruses can cause complications with severe disease in immune-compromised people, most of the population experiences few ill effects from herpesvirus infections. Indeed, herpes simplex virus 1 (HSV-1) in particular has several features that make it an attractive tool for therapeutic gene delivery. Herpes simplex virus 1 targets and infects specific cell types, such as epithelial cells and neurons. The HSV-1 genome can also accommodate large insertions of up to 14 kb. The HSV-1-based vectors have already achieved success for the oncolytic treatment of melanoma. In addition to serving as a vehicle for therapeutic gene delivery and targeted cell lysis, comparative genomics of herpesviruses HSV-1 and 2 has revealed valuable information about the evolutionary history of both viruses and their hosts. This review focuses on the adaptability of HSV-1 as an instrument for gene delivery and an evolutionary marker. Overall, HSV-1 shows great promise as a tool for treating human disease and studying human migration patterns, disease outbreaks, and evolution.

Synergistic effects of deleting multiple nonessential elements in nonreplicative HSV-1 BAC genomic vectors play a critical role in their viability

Nonreplicative Herpes simplex virus type-1 (HSV-1) genomic vectors have already entered into clinical trials for neurological gene therapy thanks to their scalable growth in permissive cells. However, the small transgene capacity of this type of HSV-1 vectors currently used in the clinic represents an important limiting factor as a gene delivery system. To develop high-capacity nonreplicative genomic HSV-1 vectors, in this study we have characterized a series of multiply deleted mutants which we have constructed in bacterial artificial chromosomes (BACs), removing up to 24 kb of unstable or dispensable genomic sequences to allow insertion of transgenes up to this size. We show that synergistic effects of deletions of: the HSV-1 replication origins ori_S and ori_L, the HSV-1 internal repeat region, the remaining ICP4 gene copy and the genes encoding for ICP27, U_L56, U_L55, can severely reduce the growth of these HSV-1 vectors. Given that several of these elements have been characterized as 'non-essential' for viral growth in cell culture by single-deletion experiments of wild-type HSV-1, our study highlights the need to re-evaluate their functional contribution in the context of multiply deleted nonreplicative HSV-1 genomic vectors. Our BAC mutants described here can serve as useful starting platforms to accelerate HSV-1 vector development.