Successful results of Herpes Virus Vaccine in Preclinical Study

In a recent preclinical study by researchers at the University of Cincinnati, Northwestern University, and the University of Nebraska-Lincoln, a genetically modified version of the herpes simplex virus (HSV) has outperformed a leading vaccine candidate. The vaccine, called R2, is a type 1 (HSV-1) herpes simplex virus that causes cold sores around the lip, but can cross-protect against type 2 HSV (HSV-2), the sexually transmitted type of HSV that is typically responsible for genital herpes. The virus was effectively designed to produce the vaccine to prevent it from finding shelter in the nervous system and eluding an immune response.

The newly published study showed that the production of virus-combating antibodies was significantly increased by vaccinating guinea pigs using the modified live virus vaccine. And vaccinated animals reported less genital lesions, decreased viral replication, and less of the viral shedding that spreads infection to others when challenged with a virulent strain of HSV-2.

It is very interesting that the viral shedding was knocked down so much with the R2 vaccine, since it is the viral shedding that can then pass on the virus, even though it does not cause lesions," said Gary Pickard, PhD, professor of veterinary medicine and biomedical sciences at Nebraska." You will pass that on to your significant other if you have genital herpes, without understanding that you are doing so. It's highly troublesome. So the fact that so much of the shedding was knocked down is a very positive sign." In a paper titled Pickard and colleagues published on their studies in npj Vaccines." The R2 non-neuroinvasive HSV-1 vaccine affords protection from genital HSV-2 infections in a guinea pig model "

More than 500 million people are estimated by the World Health Organization to have HSV-2, an infection that continues for a lifetime and sometimes flares up in response to stress. In immunocompromised individuals, both HSV-1 and HSV-2 may cause neonatal herpes and can cause blindness, as well as other severe infections, the authors wrote. Infection with HSV can also raise the risk of infection with HIV and can lead to Alzheimer's or other types of dementia. At present, however there is no vaccine against HSV-1 or HSV-2.

"It is a priority to develop an effective HSV vaccine because it is a widespread infection that causes physical and emotional stress and raises the risk of HIV infection," the team noted. The recent failure of the HSV subunit vaccines has highlighted the need for vaccines with a wide range of antigens, including the development of live-attenuated next-generation vaccines.

The way alpha-herpesviruses, which include HSV, have developed a sophisticated mechanism for evading immune responses that could kill them is part of the challenge of developing HSV vaccines. HSV works its way to the tips of sensory nerves after infecting mucosal tissues of the mouth or genitourinary tract that transmit signals that are responsible for sensations such as pain and touch. The virus then breaks into the nerve cell with the help of a specialised molecular switch, hitching a ride on molecules that transport it along a nerve fibre and into the sensory neuron nucleus. Thus, although the mucosal infection is soon cleared by the immune response, the neurons infected become a refuge of the immune system of the body, leaving HSV only when stirred in the host by increases in steroids or other stress-elevated hormones.

Together with Northwestern's Gregory Smith, PhD, and Tufts University's Ekaterina Heldwein, PhD, Nebraska's Pickard and Patricia Sollars, PhD, have spent years researching how to prevent HSV from achieving nervous system protection. When she characterised the architecture of a certain alpha-herpesvirus protein, pUL37, which the team believed was central to the virus travelling through nerve fibres, Heldwein advanced those efforts. Based on that architecture, computer analyses indicated that three protein regions could prove essential to the process.

Smith substituted five codons from each region of the viral genome, the fundamental coding details in the DNA, which the researchers hoped could help prevent the virus from entering the nervous system. "A live-attenuated HSV-1 strain encoding pUL37 tegument protein mutated in region 2, which is central to neuroinvasion, is the R2 vaccine evaluated here the authors wrote. Research has shown that'... the R2 approach has shown promise as a new live-attenuated HSV vaccine capable of amplifying the entire cohort of HSV antigens in the absence of complications of the nervous system or the production of latent infections.

When Pickard and Sollars injected mice with a protein virus modified in region 2, or R2, they found that the virus was trapped at the nerve terminal instead of progressing deeper into the nervous system. But the team agreed that it was not enough to change HSV and may have unintended effects. "Pickard said You can prevent the virus from getting into the nervous system, which is not that hard to do by creating mutations that are broadly debilitating." But you are not rewarded with a strong immune system that can shield you from potential infection if you knock down the virus so hard that it doesn't reproduce well.

Fortunately, experiments in mice by the team showed that the R2-mutated virus performed well in mice as a vaccine. "A live-attenuated HSV-1 strain encoding pUL37 tegument protein mutated in region 2, which is central to neuroinvasion, is the R2 vaccine evaluated here the authors wrote. "The R2 attenuated viruses were clearly ablated with neuroinvasive potential and were avirulent in mice, consistent with the axonal transport deficit," they noted. The R2 method has shown promise as a new live-attenuated HSV vaccine capable of amplifying the whole cohort of HSV antigens in the absence of complications of the nervous system or the development of latent infections.

In addition, it circumvented some stubborn problems that have arisen with other approaches to vaccines. Some methods also included confronting the immune system with only a subset of components of HSV, or antigens, priming the body to identify them but likely ignoring others. Some have changed the virus so that it can replicate only once, preventing long-term nervous system persistence, but also reducing mucosal tissue spread and a strong immune response by extension.

So it's the same storey over and over again: you either don't have enough antigens in your subunit vaccine, or you basically make the live virus so sick that it doesn't work too well to produce an immune response, Pickard said. "That's why we're so positive about our R2 platform, because it avoids all these issues." The latest R2 vaccine showed very promising results, encouragingly. "A live-attenuated HSV-1 strain encoding pUL37 tegument protein mutated in region 2, which is central to neuroinvasion, is the R2 vaccine evaluated here the authors wrote. The R2 attenuated viruses were clearly ablated of neuroinvasive potential and were avirulent in mice, consistent with the axonal transport deficit... the R2 approach showed potential as a new live-attued HSV vaccine capable of amplifying the entire cohort of HSV antigens in the absence of complications of the nervous system or the establishment of latent infections.'

David Bernstein, a Cincinnati Children's Hospital Medical Center researcher who tests herpes virus vaccine candidates through a National Institutes of Health-supported programme, took notice of the progress of the team and reached out in 2018 to Northwestern's Smith. Bernstein agreed to test the efficacy of an R2-modified form of HSV-1 in guinea pigs against HSV-2 infection. As promising as their prior findings had been, Pickard wasn't confident an HSV-1 vaccine would be up to the task of producing immunity against HSV-2.

Encouragingly, the findings showed that after being injected with HSV-2, only one of the dozen R2-inoculated guinea pigs developed acute lesions, compared with five of the 12 animals receiving another candidate vaccine that had recently failed a human clinical trial. And although the previously human-tested vaccine candidate had no discernible effect on the number of days the virus was shed by guinea pigs, the team's R2 vaccine shortened the shedding time from 29 days to approximately 13 days. "Perhaps of greatest importance, in each of the R2 vaccinated classes, recurrent virus shedding was reduced by 33-64 percent," the investigators commented. "It is of special significance because the key means of transmission of HSV is repeated virus shedding." In contrast to the guinea pigs receiving no vaccine or the unsuccessful candidate, those receiving the R2 vaccine showed no evidence of HSV-2 in the brain cell cluster that usually houses it. Meanwhile, neutralising antibodies were nearly three times higher in the R2-inoculated guinea pigs than in those inoculated with the other candidate vaccine. "A promising solution to HSV vaccines is offered by the use of live-attenuated HSV vaccines that robustly replicate in mucosal tissues but are ablated for neuroinvasion," the researchers commented.

The researchers plan to create and test an HSV-2 vaccine against the HSV-2 virus, with an HSV-1 variant of the R2 vaccine showing such promising cross-protection against its sexually transmitted counterpart. "These findings are highly encouraging, especially considering that R2 is an HSV-1 virus and has been assessed for cross-protection against the HSV-2 challenge," the investigators noted. If you make antibodies against the proteins of that same virus, Pickard said it is fair (that it would work better than if you made an antibody against anything that is slightly different." That is our hope, then.'

Pickard and Smith were launching a start-up, Thyreos, to further improve and commercialise the R2 vaccine design around the time Bernstein and his NIH programme expressed interest in the R2 vaccine design. The team is working on vaccines for livestock, especially cattle and hogs, that deal with their own alpha-herpesviruses. Bovine herpesvirus can cause respiratory disease in cattle, curb appetite, and even lead to aborted calves, all of which add up to billions of dollars in annual lost income. While there is a modified live-virus vaccine for cattle, it gets into the bovine nervous system as well. And that, Pickard said, can spell trouble just as easily in cattle as in humans.

What happens, then, is that it is a stressful situation when those cows are put on a truck and delivered to a feedlot,' he said. It reactivates the virus hiding in the immune system. They start shedding the virus from their nose excretions, and then in the feedlot they can transfer that virus on to other animals, and the cattle can get respiratory disease. "So it's not just an academic thing that our R2-modified viruses don't reach the nervous system. It has a true, practical application for the cattle industry, actually,

Pickard and Smith are embarking on an initial round of seed funding for the venture, hoping that future tests will prove the R2 design's superiority to the existing industry-wide vaccine. In fact, the team initially developed the R2 model in the alphaherpesvirus pseudorabies virus that infects pigs, and Pickard also expressed faith in the potential of the design to protect hogs. Although a U.S. campaign successfully eradicated pseudorabies from the nation during the 1990s and early 2000s, primarily by vaccination, as with cattle, the vaccine can penetrate the hog nervous system and has proven less effective in countries that are less vigilant regarding outbreaks

They added "Again we're pretty sure that our R2 vaccine for pseudorabies virus will be more successful than what's out there,' Pickard said. In terms of protecting pigs, at some point, it will have a major effect. These pathogens in feed ingredients or feed products may withstand trans-Pacific transport. When you speak to people who are worried about biosecurity, they say that in terms of these viruses, whatever happens elsewhere in the world may inevitably turn up here. It's just a question of time".