Herpes simplex research

Research into herpes simplex is ongoing.

Vaccine Research

Various vaccine candidates have been developed, the first ones in the 1920s, but none have been successful to date.^[1]

Due to the genetic similarity of both herpes simplex virus types (HSV-1 and HSV-2), the development of a prophylactic-therapeutic vaccine which is proven effective against one type of the virus would provide fundamentals for vaccine-development for the other virus type. As of 2014, several vaccine candidates are in different stages of development as they are being tested for safety and efficacy, including at least four vaccine candidates in the US and one in Australia.

An ideal herpes vaccine should induce immune responses adequate to prevent infection. Short of this ideal, a candidate vaccine might be considered successful if it (a) mitigates primary clinical episodes, (b) prevents colonization of the ganglia, (c) helps reduce the frequency or severity of recurrences, and (d) reduces viral shedding in actively infected or asymptomatic individuals.^[2]

Attenuated Vaccines

Live, Attenuated Variant of the HSV-2 Vaccine

While until the present day, diverse subunit HSV vaccines (e.g. Herpevac) have failed to protect humans from acquiring genital herpes in several clinical trials, the success of the chickenpox vaccine demonstrates that a live and appropriately attenuated α-herpesvirus may be used to safely control a human disease. This principle may be expanded to include HSV-1 or HSV-2 as portrayed in a new approach of the HSV-2 ICP0 live-attenuated HSV-2 vaccine investigated by Professor William Halford at the Southern Illinois University (SIU) School of Medicine.^[3][4] Although already proven as very safe and effective in studies on animals, Halford's vaccine is currently not involved in any clinical trials, mainly due to lack of funding.^[5]

Replication-defective HSV-2 Vaccine

Professor David Knipe, in his laboratory at Harvard Medical School has developed dl5-29. The dl5-29 vaccine is also known under the name ACAM-529^[6] or HSV-529, a replication-defective vaccine that has proved successful in preventing both HSV-2 and HSV-1 infections and in combating the virus in already-infected hosts, in animal models.^[7] The HSV-529 is a leading vaccine candidate which has been investigated in numerous research publications, and is endorsed by many researchers in the field (i.a. Lynda A. Morrison and Jeffrey Cohen).^[8] It has also been shown that the vaccine induces strong HSV-2-specific antibody and T-cell responses, protects against challenge with a wild-type HSV-2 virus; greatly reduces the severity of recurrent disease; provides cross-protection against HSV-1; and renders the virus unable to revert to a virulent state or to become latent.^[9] The vaccine is now being researched and developed by Sanofi Pasteur.^[10] Both Sanofi Pasteur and the clinical-stage immunotherapy company Immune Design have entered a broad collaboration, which will explore the potential of various combinations of agents against HSV-2, including an adjuvanted trivalent vaccine candidate G103, consisting of recombinantly-expressed viral proteins.^[11]

The NIH in collaboration with Sanofi Pasteur is currently recruiting participants for a Phase I clinical trial of HSV-529. The trial is expected to be completed in October 2016.

Glycoprotein gD- and DNA-based vaccines

Admedus's Vaccine

Professor Ian Frazer developed an experimental vaccine with his team at Coridon, a biotechnology company he founded in 2000. The company, now known under the name Admedus Vaccines, is researching DNA technology for vaccines with prophylactic and therapeutic potential. What's different about this vaccine is the way that response is being created. Instead of introducing a weakened version of the herpes virus, this vaccine uses a small section of DNA to produce T-cells and stimulate the immune response.^[12] The new vaccine candidate is designed to prevent new infections, and to treat those who already have the infection. In February 2014, it was announced that Frazer's new vaccine against genital herpes has passed human safety trials in a trial of 20 Australians.^[13] In October 2014, Admedus announced success in creating a positive T-cell response in 95% of participants.^[14] Further research is required to determine if the vaccine can prevent transmission. In July 2014, Admedus increased its stake in Professor Frazer's vaccines by 16.2%. In addition, $18.4 million was posted as funds raised towards Phase II vaccine testing and research.^[15] The Phase II trial began in April 2015 with results expected by the end of the year.^[16]

Genocea's Vaccine

A company named Genocea Biosciences has developed GEN-003, a first-in-class protein subunit T cell-enabled therapeutic vaccine, or immunotherapy, designed to reduce the duration and severity of clinical symptoms associated with moderate-to-severe HSV-2, and to control transmission of the infection. GEN-003 includes the antigens ICP4 and gD2, as well as the proprietary adjuvant Matrix-M. Results from the 1/2a study showed a strong reduction of genital lesions by 65% and reduction by half in viral shedding.^[17]

GEN-003 is undergoing Phase II trials and is expected to report top line data in the second quarter of 2015.^[18]

Vical's Vaccine

Vical has been awarded grant funding from the National Institute of Allergy and Infectious Diseases division of the NIH to develop a plasmid DNA-based vaccine to inhibit recurring lesions in patients latently infected with herpes simplex virus type 2 (HSV-2). The plasmid DNA encoding the HSV-2 antigens was formulated with Vaxfectin, Vical's proprietary cationic lipid adjuvant. The program advanced to a phase I/II trial in December 2013 on positive preclinical results, including a reproducible statistically significant reduction in viral lesion occurrence in guinea pigs latently infected with HSV-2.^[19]

Vical is undergoing Phase I clinical trials and is expected to report baseline data by the middle of 2015.^[20]

Other Vaccines

A study from the Albert Einstein College of Medicine, where glycoprotein D (gD-2) was deleted from the herpes cell, showed positive results when tested in mice.^[21] Researches deleted gD-2 from the herpes virus, which is responsible for herpes microbes entering in and out of cells. The vaccine is still in early stages and more research needs to be conducted before receiving FDA approval for clinical trials.^[22]

HerpV, a genital herpes vaccine candidate manufactured by the company Agenus, announced Phase II clinical trial results in June 2014. Results showed up to a 75% reduction in viral load and a weak reduction in viral shedding by 14%.^[23] These results were achieved after a series of vaccinations and a booster dose after six months, signalling the vaccine may take time to become effective. Further testing results are to show if the vaccine is a viable candidate against genital herpes.^[24]

PaxVax, a specialty vaccine company has started a cooperation with the Spector Lab at the UC San Diego Department of Cellular and Molecular Medicine, regarding the development of a genital herpes viral vector vaccine, which is currently in the preclinical stage.^[25]

The research data conducted by the company NanoBio indicates that an enhanced protection from HSV-2 is a result of mucosal immunity which can be elicited by their intranasal NE vaccine. Based on these results, additional preclinical studies are to be undertaken to optimize the dosing in guinea pigs, before the research is to be pushed further in a future clinical trial.^[26]

Biomedical Research Models, a Worcester based biopharmaceutical company has been awarded a fund for the development of a novel vaccine platform to combat mucosally transmitted pathogens such as HSV-2.^[27]

Discontinued Vaccines

One vaccine that was under trial was Herpevac, a vaccine against HSV-2. The National Institutes of Health (NIH) in the United States conducted phase III trials of Herpevac.^[28] In 2010, it was reported that, after 8 years of study in more than 8,000 women in the United States and Canada, there was no sign of positive results against the sexually transmitted disease caused by HSV-2^[29] (and this despite earlier favorable interim reports^[28]).

A private company called BioVex began Phase I clinical trials for ImmunoVEX, another proposed vaccine, in March 2010.^[30] The Company had commenced clinical testing in the UK with its vaccine candidate for the prevention and potentially the treatment of genital herpes. The biopharmaceutical company Amgen bought BioVex^[31] and their proposed Immunovex vaccine appears to have been discontinued, furthermore it has been removed from the company's research pipeline.^[32]

A live, attenuated vaccine (which was proven very effective in clinical trials in Mexico) by the company AuRx has failed to proceed to a Phase III trial in the year 2006, due to financial reasons. The AuRx therapy was shown to be safe and decrease the occurrence of lesions by 86% after one year. ^[33] The fact that a live, attenuated vaccine induced better protection from HSV infection and symptoms is not new, because live-attenuated vaccines account for the most of the successful vaccines in the use until today. However, governmental and corporate bodies seem to support the more recent but possibly less effective approaches such as Glycoprotein and DNA based vaccines.

Herpes Simplex Virus Research

Researchers at the University of Florida have made a Hammerhead ribozyme that targets and cleaves the mRNA of essential genes in HSV-1. The hammerhead, which targets the mRNA of the UL20 gene, greatly reduced the level of HSV-1 ocular infection in rabbits, and reduced the viral yield in vivo.^[34] The gene-targeting approach uses a specially designed RNA enzyme to inhibit strains of the herpes simplex virus. The enzyme disables a gene responsible for producing a protein involved in the maturation and release of viral particles in an infected cell. The technique appears to be effective in experiments with mice and rabbits, but further research is required before it can be attempted in people infected with herpes.^[35]

Another possibility to eradicate the HSV-1 variant is being pursued by a team at Duke University. By figuring out how to switch all copies of the virus in the host from latency to their active stage at the same time, rather than the way the virus copies normally stagger their activity stage, leaving some dormant somewhere at all times, it is thought that immune system could kill the entire infected cell population, since they can no longer hide in the nerve cells. This is a potentially risky approach especially for patients with widespread infections as there is the possibility of significant tissue damage from the immune response. One class of drugs called antagomir could trigger reactivation. These are chemically engineered oligonucleotides or short segments of RNA, that can be made to mirror their target genetic material, namely herpes microRNAs. They could be engineered to attach and thus 'silence' the microRNA, thus rendering the virus incapable of keeping latent in their host.^[36] Professor Cullen believes a drug could be developed to block the microRNA whose job it is to suppress HSV-1 into latency.^[37]

Herpes has been used in research with HeLa cells to determine its ability to assist in the treatment of malignant tumors. A study conducted using suicide gene transfer by a cytotoxic approach examined a way to eradicate malignant tumors.^[38] Gene therapy is based on the cytotoxic genes that directly or indirectly kill tumor cells regardless of its gene expression. In this case the study uses the transfer of the Herpes simplex virus type I thymidine kinase (HSVtk) as the cytotoxic gene. Hela cells were used in these studies because they have very little ability to communicate through gap junctions.^[39] The Hela cells involved were grown in a monolayer culture and then infected with the HSV virus. The HSV mRNA was chosen because it is known to share characteristics with normal eukaryotic mRNA.^[40]

The HSVtk expression results in the phosphorylation of drug nucleoside analogues; in this case the drug ganciclovir, an anitiviral medication used to treat and prevent cytomegaloviruses, converts it into the nucleoside analogue triphosphates. Once granciclovir is phosphorylated through HSV-tk it is then incorporating DNA strands when the cancer cells are multiplying.^[39] The nucleotide from the ganciclovir is what inhibits the DNA polymerization and the replication process. This causes the cell to die via apoptosis.^[38]

Apoptosis is regulated with the help of miRNAs, which are small non-coding RNAs that negatively regulate gene expression.^[41] These miRNAs play a critical role in developing the timing, differentiation and cell death. The miRNAs effect on apoptosis has affected cancer development by the regulation of cell proliferation, as well as cell transformation. Avoidance of apoptosis is critical for the success of malignant tumors, and one way for miRNAs to possibly influence cancer development is to regulate apoptosis. In order to support this claim, Hela cells were used for the experiment discussed.

The cytotoxic drug used, ganciclovir, is capable of destroying via apoptosis transduced cells and non-transduced cells from the cellular gap junction. This technique is known as the "bystander effect,” which has suggested to scientists that the effect of some therapeutic agents may be enhanced by diffusion through gap junctional intercellular communication (GJIC) or cell coupling. GJIC is an important function in the maintaining of tissue homeostasis and it is a critical factor in balance of cells dying and surviving.

When Hela cells were transfected with the HSV-tk gene, and were then put in a culture with nontransfected cells, only the HSV-tk transfected Hela cells were killed by the granciclovir, leaving the nonviral cells unharmed.^[39] The Hela cells were transfected with the encoding for the gap junction protenin connexin 43 (Cx43) to provide a channel that permits ions and other molecules to move between neighboring cells. Both Hela cells with the HSV-tk and without the HSV-tk were destroyed. This result has led to the evidence needed to state that the bystander effect in the HSV-tk gene therapy is possibly due to the Cx-mediated GJIC.

Since the introduction of the nucleoside analogs decades ago, treatment of herpes simplex virus (HSV) infections has not seen much innovation, except for the development of their respective prodrugs. The inhibitors of the helicase–primase complex of HSV represent a very innovative approach to the treatment of herpesvirus disease.^[42]

References