TOGAVIRUS RESEARCH... 2000-2004

DeStefano F, Thompson WW. "MMR vaccine and autism: an update of the scientific evidence." Expert Rev Vaccines. 2004 Feb;3(1):19-22.

A hypothesis published in 1998 suggested that measles-mumps-rubella vaccine may cause autism as a result of persistent measles virus infection of the gastrointestinal tract. Results of early studies were not supportive and in 2001 a review by the Institute of Medicine concluded that the evidence favors the rejection of a causal relationship at the population level between measles-mumps-rubella vaccine and autistic spectrum disorder. Studies published since the Institute of Medicine report have continued not to find an increased risk of autistic spectrum disorder associated with measles-mumps-rubella. The vaccine also has not been found to be associated with a unique syndrome of developmental regression and gastrointestinal disorders. The evidence now is convincing that the measles-mumps-rubella vaccine does not cause autism or any particular subtypes of autistic spectrum disorder.

Alphaviruses are insect-borne Togaviruses responsible for human and mammalian encephalitis and encephalomeningitis. However, research that has taken place predominately from 2001-2004 has shown alphavirus replicon particles to be ideal vaccine vectors for infectious diseases from HIV to anthrax as well as cancer vaccines.

Why alphaviruses?

Alphavirus replicons are easily engineered and can be dealt with in Biosafety Level I and II facilities. As alphaviruses cause encephalitis and meningoencephalitis, they can deliver desired gene products to dendritic cells of the central nervous system (and also the lymphoid tissues). These viruses have a broad host range (allowing for effective animal models) and induce cellular, mucosal, and humoral responses in these models. Finally, novel alphavirus vectors have been developed that are less- or non-cytopathic and are temperature-dependent.

What is an alphavirus replicon?

An alphavirus replicon is generally constructed from the Sindbis, Semliki Forest, or Venezuelan Equine Encephalitis viruses. The replicon is created by replacing the structural genes of the RNA template with one or more genes of interest. The result is a self-replicating RNA that cannot form infectious particles but does produce proteins from the gene of interest (for example the envelope or capsid protein of another virus.) Structural proteins of the alphavirus are often provided by coinfection with separate "helper-RNAs".

References:

Polo JM, Gardner JP, Ji Y, Belli BA, Driver DA, Sherrill S, Perri S, Liu MA, Dubensky TW Jr. "Alphavirus DNA and particle replicons for vaccines and gene therapy." Developmental Biology (Basel). 2000;104:181-5.

Schlesinger S. "Alphavirus vectors: development and potential therapeutic applications". Expert Opin Biol Ther. 2001 Mar;1(2):177-91. Egengruber MU. "Alphaviral vectors for gene transfer into neurons". Molecular Neurobiology. 2002 Oct-Dec;26(2-3):183-201.

1.

This article articulated the need for research into an HIV-I Clade C vaccine. More than 1 in 9 South Africans is infected with HIV, and the majority of these cases are of HIV subtype-C (less prominent in the rest of the world).

A candidate VRP HIV vaccine expressing Clade C viral proteins was created by alphaviral replicon particles expressing either the matrix-capsid portion of Gag, the full-length envelope gp160, or the secreted gp140 of cloned SIVsm H-4i. All three were mixed in a cocktail and used to immunize macaques at 0, 1, and 4 months. Neutralizing antibodies against SIVsm H-4 were induced in 6 of 6 vaccinates and CTL in 4 of 6. This vaccine has been manufactured and tested for a phase I trial in the first months of 2002.

2.

A total of 96 participants are involved in the trial - 48 in the US and 48 in South Africa. Twenty four volunteers are required at each South African site and recruitment activities are continuing in preparation for the first vaccinations. Volunteers are healthy, HIV-negative adults who are willing and able to give informed consent. Intensive pre-recruitment educational and community awareness activities have been conducted at both sites in South Africa. The study that has been approved began by enrolling 12 volunteers in the US, and additional volunteers will be enrolled in the US and South Africa once initial safety data from these 12 volunteers has been reviewed.

Here is a quote from the website about the ongoing trial (posted June 18, 2003)

"ArV is cutting-edge vaccine technology that was awarded the World Technology Forum Award for biotechnology in 2001. It utilises virus-like particles, containing parts of an attenuated strain of Venezuelan equine encephalitis (VEE) virus and a gene from a South African strain of the HIV virus, to deliver the vaccine to the immune system. This is the first trial of the ArV technology in humans."

For more information: http://www.saavi.org.za/press3Nov2003.htm

3.

This group shows that alphaviruses are versatile vectors for immunizing small animals with HIV-I envelope protein to induce HIV-I neutralizing antibodies. They first expressed large quantities of HIV-I envelope protein in vivo. Next, using alphavirus replicon particles, they found that detectable envelope proteins were expressed in vivo, followed by appearance of cross-reactive neutralizing antibodies. Other groups (noted in the paper) have used Venezuelan Equine Encephalitis vectors to induce neutralizing antibodies in primates immunized with SIV envelope protein as well. This means that vaccination by alphavirus replicons expressing HIV-I envelope protein might prevent HIV infection by inducing primary virus-neutralizing antibodies.

1.

These were the promising results…

Lassa and Ebola viruses cause acute hemorrhagic fever diseases that are fatal in up to 90% of cases, for which no effective vaccines are currently available. This group studied individual vaccines for Lassa and Ebola as well as a bivalent vaccine protecting against both. Their vaccine was created by replacement of Venezuelan Equine Encephalitis structural genes with Lassa and/or Ebola viral nucleoprotein and glycoprotein genes. The group found that guinea pigs injected with the Lassa vaccine were protected from the "lethal challenge" of Lassa fever, guinea pigs injected with Ebola vaccine were protected from the "lethal challenge" of Ebola, and guinea pigs injected with a bivalent vaccine were protected from both.

Unfortunately, read on…

2.

The group attempted to repeat the previous experiments in primates, but to no avail. They reported that, "None of these strategies successfully protected nonhuman primates from robust challenge with Ebola virus. The disease observed in primates differed from that in rodents, suggesting that rodent models of Ebola virus may not predict the efficacy of candidate vaccines in primates and that protection of primates may require different mechanisms."

A BETTER ANTHRAX VACCINE (?)

Lee JS, Hadjipanayis AG, Welkos SL. "Venezuelan equine encephalitis virus-vectored vaccines protect mice against anthrax spore challenge." Infect Immun. 2003 Mar;71(3):1491-6.

Anthrax is a deadly disease and bioterrorist threat caused by Bacillus anthracis. There is currently a vaccine for anthrax, but it is far from ideal; the vaccine consists of 6 primary doses followed by yearly boosters, and it causes reactions in up to 30% of recipients.

Venezuelan Equine Encephalitis was configured as a replicon vaccine vector by replacing the alphaviral structural genes with the protective antigen (PA) gene of bacillus anthracis. When delivered to mice, 3 doses administered subcutaneously provided complete protection against anthrax infection.

Baric RS, Yount B, Lindesmith L, Harrington PR, Greene SR, Tseng FC, Davis N, Johnston RE, Klapper DG, Moe CL. "Expression and self-assembly of norwalk virus capsid protein from venezuelan equine encephalitis virus replicons." Journal of Virology. 2002 Mar;76(6):3023-30.

Norwalk-like viruses cause roughly 85% of acute, analyzed, nonbacterial gastroenteritis. It does not replicate in cell culture and there are no good animal models for the virus. This group created an Venezuelan Equine Encephalitis replicon vaccine that created Norwalk capsid proteins identical to those that the preexisting oral vaccine (BacNor) does. Why create an alphaviral vaccine? Alphavirus can drive production higher as a recombinant vaccine vector and allows for protection at the mucosal surfaces. More importantly, this is yet another manifestation of alphavirus acting as a great vaccine vector!

1.

This group destroyed and prevented tumors in mice by delivering HPV 16 gene E7 through an alphavirus replicon (once again Venezuelan Equine Encephalitis). The HPV 16 E7 RNA induced a CD8+ T-cell response in mice. The effect: Tumor development was prevented in all mice, 7-day established tumors were eliminated in 67% of tumor-bearing mice post-vaccination, and a long-lasting T cell memory response protected vaccinated mice, completely protecting them from tumors even 3 months later. This has implications as a cervical cancer vaccine.

2.

This article (translated from Russian) tested the efficiency of numerous viral vectors in delivering an antitumor cancer drug. As compared to mumps and influenza virus vectors, Alphaviruses were, once again, found to be superior!