Replication-Competent Controlled Herpes Simplex Virus

A Broad Influenza Vaccine Based on a Heat-Activated, Tissue-Restricted Replication-Competent Herpesvirus

Vaccination with transiently activated replication-competent controlled herpesviruses (RCCVs) expressing influenza A virus hemagglutinins broadly protects mice against lethal influenza virus challenges. The non-replicating RCCVs can be activated to transiently replicate with high efficiency. Activation involves a brief heat treatment to the epidermal administration site in the presence of a drug. The drug co-control is intended as a block to inadvertent reactivation in the nervous system and, secondarily, viremia under adverse conditions. While the broad protective effects observed raise an expectation that RCCVs may be developed as universal flu vaccines, the need for administering a co-activating drug may dampen enthusiasm for such a development. To replace the drug co-control, we isolated keratin gene promoters that were active in skin cells but inactive in nerve cells and other cells in vitro. In a mouse model of lethal central nervous system (CNS) infection, the administration of a recombinant that had the promoter of the infected cell protein 8 (ICP8) gene of a wild-type herpes simplex virus 1 (HSV-1) strain replaced by a keratin promoter did not result in any clinical signs, even at doses of 500 times wild-type virus LD50. Replication of the recombinant was undetectable in brain homogenates. Second-generation RCCVs expressing a subtype H1 hemagglutinin (HA) were generated in which the infected cell protein 4 (ICP4) genes were controlled by a heat switch and the ICP8 gene by the keratin promoter. In mice, these RCCVs replicated efficiently and in a heat-controlled fashion in the epidermal administration site. Immunization with the activated RCCVs induced robust neutralizing antibody responses against influenza viruses and protected against heterologous and cross-group influenza virus challenges.

Very Broadly Effective Hemagglutinin-Directed Influenza Vaccines with Anti-Herpetic Activity

A universal vaccine that generally prevents influenza virus infection and/or illness remains elusive. We have been exploring a novel approach to vaccination involving replication-competent controlled herpesviruses (RCCVs) that can be deliberately activated to replicate efficiently but only transiently in an administration site in the skin of a subject. The RCCVs are derived from a virulent wild-type herpesvirus strain that has been engineered to contain a heat shock promoter-based gene switch that controls the expression of, typically, two replication-essential viral genes. Additional safety against inadvertent replication is provided by an appropriate secondary mechanism. Our first-generation RCCVs can be activated at the administration site by a mild local heat treatment in the presence of an antiprogestin. Here, we report that epidermal vaccination with such RCCVs expressing a hemagglutinin or neuraminidase of an H1N1 influenza virus strain protected mice against lethal challenges by H1N1 virus strains representing 75 years of evolution. Moreover, immunization with an RCCV expressing a subtype H1 hemagglutinin afforded full protection against a lethal challenge by an H3N2 influenza strain, and an RCCV expressing a subtype H3 hemagglutinin protected against a lethal challenge by an H1N1 strain. Vaccinated animals continued to gain weight normally after the challenge. Protective effects were even observed in a lethal influenza B virus challenge. The RCCV-based vaccines induced robust titers of in-group, cross-group and even cross-type neutralizing antibodies. Passive immunization suggested that observed vaccine effects were at least partially antibody-mediated. In summary, RCCVs expressing a hemagglutinin induce robust and very broad cross-protective immunity against influenza.

Remote control of transgene expression using noninvasive near-infrared irradiation

This study investigated whether noninvasive near-infrared (NIR) energy could be transduced into heat in deep-seated organs in which adenovirus type-5 vectors tend to accumulate, thereby activating heat shock protein (HSP) promoter-mediated transgene expression, without local administration of photothermal agents. NIR irradiation of the subdiaphragmatic and left dorsocranial part of the abdominal cavity of adult immunocompetent C3H/HeNRj mice with an 808-nm laser effectively increased the temperature of the irradiated regions of the liver and spleen, respectively, resulting in the accumulation of the heat-inducible HSP70 protein. Spatial control of transgene expression was achieved in the NIR-irradiated regions of the mice administered an adenoviral vector carrying a firefly luciferase (fLuc) coding sequence controlled by a human HSP70B promoter, as assessed by bioluminescence and immunohistochemistry analyses. Levels of reporter gene expression were modulated by controlling NIR power density. Spatial control of transgene expression through NIR-focused activation of the HSP70B promoter, as well as temporal regulation by administering rapamycin was achieved in the spleens of mice inoculated with an adenoviral vector encoding a rapamycin-dependent transactivator driven by the HSP70B promoter and an adenoviral vector carrying a fLuc coding sequence controlled by the rapamycin-activated transactivator. Mice that were administered rapamycin and exposed to NIR light expressed fLuc activity in the splenic region, whereas no activity was detected in mice that were only administered rapamycin or vehicle or only NIR-irradiated. Thus, in the absence of any exogenously supplied photothermal material, remote control of heat-induced transgene expression can be achieved in the liver and spleen by means of noninvasive NIR irradiation.

A Narrative Review of Cell-Based Approaches for Cranial Bone Regeneration

Current cranial repair techniques combine the use of autologous bone grafts and biomaterials. In addition to their association with harvesting morbidity, autografts are often limited by insufficient quantity of bone stock. Biomaterials lead to better outcomes, but their effectiveness is often compromised by the unpredictable lack of integration and structural failure. Bone tissue engineering offers the promising alternative of generating constructs composed of instructive biomaterials including cells or cell-secreted products, which could enhance the outcome of reconstructive treatments. This review focuses on cell-based approaches with potential to regenerate calvarial bone defects, including human studies and preclinical research. Further, we discuss strategies to deliver extracellular matrix, conditioned media and extracellular vesicles derived from cell cultures. Recent advances in 3D printing and bioprinting techniques that appear to be promising for cranial reconstruction are also discussed. Finally, we review cell-based gene therapy approaches, covering both unregulated and regulated gene switches that can create spatiotemporal patterns of transgenic therapeutic molecules. In summary, this review provides an overview of the current developments in cell-based strategies with potential to enhance the surgical armamentarium for regenerating cranial vault defects.

Herpes Simplex Viruses Whose Replication Can Be Deliberately Controlled as Candidate Vaccines

Over the last few years, we have been evaluating a novel paradigm for immunization using viruses or virus-based vectors. Safety is provided not by attenuation or inactivation of vaccine viruses, but by the introduction into the viral genomes of genetic mechanisms that allow for stringent, deliberate spatial and temporal control of virus replication. The resulting replication-competent controlled viruses (RCCVs) can be activated to undergo one or, if desired, several rounds of efficient replication at the inoculation site, but are nonreplicating in the absence of activation. Extrapolating from observations that attenuated replicating viruses are better immunogens than replication-defective or inactivated viruses, it was hypothesized that RCCVs that replicate with wild-type-like efficiency when activated will be even better immunogens. The vigorous replication of the RCCVs should also render heterologous antigens expressed from them highly immunogenic. RCCVs for administration to skin sites or mucosal membranes were constructed using a virulent wild-type HSV-1 strain as the backbone. The recombinants are activated by a localized heat treatment to the inoculation site in the presence of a small-molecule regulator (SMR). Derivatives expressing influenza virus antigens were also prepared. Immunization/challenge experiments in mouse models revealed that the activated RCCVs induced far better protective immune responses against themselves as well as against the heterologous antigens they express than unactivated RCCVs or a replication-defective HSV-1 strain. Neutralizing antibody and proliferation responses mirrored these findings. We believe that the data obtained so far warrant further research to explore the possibility of developing effective RCCV-based vaccines directed to herpetic diseases and/or diseases caused by other pathogens.

Replicative conditioning of Herpes simplex type 1 virus by Survivin promoter, combined to ERBB2 retargeting, improves tumour cell-restricted oncolysis

Oncolytic virotherapy is emerging as a promising therapeutic option for solid tumours. Several oncolytic vectors in clinical testing are based on attenuated viruses; thus, efforts are being taken to develop a new repertoire of oncolytic viruses, based on virulent viral genomes. This possibility, however, raises concerns dealing with the safety features of the virulent phenotypes. We generated a double regulated Herpes simplex type-1 virus (HSV-1), in which tumour cell restricted replicative potential was combined to selective entry via ERBB2 receptor retargeting. The transcriptional control of the viral alpha4 gene encoding for the infected cell protein-4 (ICP4) by the cellular Survivin/BIRC5 promoter conferred a tumour cell-restricted replicative potential to a virulent HSV-1 genome. The combination of the additional ERBB2 retargeting further improved the selectivity for tumour cells, conferring to the double regulated virus a very limited ability to infect and propagate in non-cancerous cells. Accordingly, a suitable replicative and cytotoxic potential was maintained in tumour cell lines, allowing the double regulated virus to synergize in vivo with immune checkpoint (anti-PD-1) blockade in immunocompetent mice. Thus, restricting the replicative spectrum and tropism of virulent HSV-1 genomes by combination of conditional replication and retargeting provides an improved safety, does not alter the oncolytic strength, and is exploitable for its therapeutic potential with immune checkpoint blockade in cancer.

Immunization by Replication-Competent Controlled Herpesvirus Vectors

We hypothesized that vigorous replication of a pathogen may be critical for eliciting the most potent and balanced immune response against it. Hence, attenuation/inactivation (as in conventional vaccines) should be avoided. Instead, the necessary safety should be provided by placing replication of the pathogen under stringent control and by activating time-limited replication of the pathogen strictly in an administration region in which pathology cannot develop. Immunization will then occur in the context of highly efficient pathogen replication and uncompromised safety. We found that localized activation in mice of efficient but limited replication of a replication-competent controlled herpesvirus vector resulted in a greatly enhanced immune response to the virus or an expressed heterologous antigen. This finding supports the above-mentioned hypothesis and suggests that the vectors may be promising novel agents worth exploring for the prevention/mitigation of infectious diseases for which efficient vaccination is lacking, in particular in immunocompromised patients.

Replication-competent controlled virus vectors were derived from the virulent herpes simplex virus 1 (HSV-1) wild-type strain 17syn+ by placing one or two replication-essential genes under the stringent control of a gene switch that is coactivated by heat and an antiprogestin. Upon activation of the gene switch, the vectors replicate in infected cells with an efficacy that approaches that of the wild-type virus from which they were derived. Essentially no replication occurs in the absence of activation. When administered to mice, localized application of a transient heat treatment in the presence of systemic antiprogestin results in efficient but limited virus replication at the site of administration. The immunogenicity of these viral vectors was tested in a mouse footpad lethal challenge model. Unactivated viral vectors—which may be regarded as equivalents of inactivated vaccines—induced detectable protection against lethality caused by wild-type virus challenge. Single activation of the viral vectors at the site of administration (rear footpads) greatly enhanced protective immune responses, and a second immunization resulted in complete protection. Once activated, vectors also induced far better neutralizing antibody and HSV-1-specific cellular immune responses than unactivated vectors. To find out whether the immunogenicity of a heterologous antigen was also enhanced in the context of efficient transient vector replication, a virus vector constitutively expressing an equine influenza virus hemagglutinin was constructed. Immunization of mice with this recombinant induced detectable antibody-mediated neutralization of equine influenza virus, as well as a hemagglutinin-specific cellular immune response. Single activation of viral replication resulted in a severalfold enhancement of these immune responses.

IMPORTANCE We hypothesized that vigorous replication of a pathogen may be critical for eliciting the most potent and balanced immune response against it. Hence, attenuation/inactivation (as in conventional vaccines) should be avoided. Instead, the necessary safety should be provided by placing replication of the pathogen under stringent control and by activating time-limited replication of the pathogen strictly in an administration region in which pathology cannot develop. Immunization will then occur in the context of highly efficient pathogen replication and uncompromised safety. We found that localized activation in mice of efficient but limited replication of a replication-competent controlled herpesvirus vector resulted in a greatly enhanced immune response to the virus or an expressed heterologous antigen. This finding supports the above-mentioned hypothesis and suggests that the vectors may be promising novel agents worth exploring for the prevention/mitigation of infectious diseases for which efficient vaccination is lacking, in particular in immunocompromised patients.

Targeted heat activation of HSP promoters in the skin of mammalian animals and humans

The use of highly inducible HSP promoters for exerting spatial and/or temporal control over the expression of therapeutic transgenes has long been discussed. Localized and time-limited induction of the heat shock response may potentially also be of medical interest. However, such applications would require targeted delivery of heat doses capable of activating HSP promoters in tissues or organs of interest. Accessible areas, including the skin and tissues immediately underneath it, may be most readily targeted. A few applications for heat-directed or heat-controlled therapy in the skin might involve expression of proteins to restore or protect normal skin function, protein antigens for vaccination/immunotherapy, vaccine viruses or even systemically active proteins, e.g., cytokines and chemokines. A review of the literature relating to localized heat activation of HSP promoters and HSP genes in the skin revealed that a multitude of different technologies has been explored in small animal models. In contrast, we uncovered few publications that examine HSP promoter activation in human skin. None of these publications has a therapeutic focus. We present herein two, clinically relevant, developments of heating technologies that effectively activate HSP promoters in targeted regions of human skin. The first development advances a system that is capable of reliably activating HSP promoters in human scalp, in particular in hair follicles. The second development outlines a simple, robust, and inexpensive methodology for locally activating HSP promoters in small, defined skin areas.

Development of Recombinant HSV-Based Vaccine Vectors

Herpes simplex virus (HSV) causes significant morbidity on the human population through such clinical syndromes as cold sores, genital herpes, herpes stromal keratitis, and encephalitis. Attempts to generate efficacious vaccines to date have failed. We have recently described the use of a conditionally replication-competent HSV-1 vector to immunize mice against a lethal challenge of HSV-1. The unique feature of this vaccine vector is that its replication is tightly controlled and can only occur in the presence of local heat and the presence of a small molecule inducer (an antiprogestin). This gives it the safety advantage of a replication-defective vaccine vector as well as the advantage of a replication-competent vector in that it is able to stimulate innate and adaptive aspects of the immune response in a natural context that a replication-defective vector cannot. In this chapter we provide a brief overview of HSV vaccines followed by the methodology used to propagate and utilize replication-conditional HSV vectors as vaccines.