URMC tests HIV vaccine pill

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    Feb 08, 2015 7:14 AM GMT

    I really hope this is true. I don't understand why development on vaccines for HIV and Herpes have taken such an unreasonable amount of time.
  • Rhi_Bran

    Posts: 911

    Feb 15, 2015 4:00 AM GMT
    I really hope this is true. I don't understand why development on vaccines for HIV and Herpes have taken such an unreasonable amount of time.

    I suppose it's because a vaccine for HIV would need to prime the body to destroy HIV thoroughly and quickly following infection so that it cannot produce any latent reservoirs.

    Many viruses (herpes simplex, herpes zoster, cytomegalovirus, Epstein-Barr, etc) are able to beat the immune system to the punch, and establish themselves permanently in the body before they can be totally eliminated. The problem is that the immune response is often not swift enough to generate antibodies and thoroughly destroy any virus before it can finish the initial replication cycle and make its way into the nooks and crannies in your body which can't currently be touched by modern drugs. Herpes zoster (chickenpox) is never permanently cleared from the body - the immune system essentially just keeps it locked up in the ganglia. With help from drugs, HIV is mostly isolated to dendritic cells with some undetectable level of free virus particles in the blood. Should the immune system or drugs fail, these viruses will reactivate. Herpes zoster commonly reactivates in the elderly (because their immune systems are declining) to cause the acutely painful condition known as shingles.

    Many viruses have adaptations such as lipid envelopes or rapidly mutating antigens that confound antibodies and the immune system long enough for the viruses to replicate and establish themselves, so vaccines, which are made to stimulate production of antibodies, are ineffective. As a retrovirus, HIV integrates its genetic material into our own, making it practically invisible and silent to the immune system once it has infected a cell.

    Everyone who is infected by HIV develops antibodies to it eventually, but they have little effect because the immune cells that antibodies signal are the cells being destroyed by HIV. Because of this (and the fact that it mutates so damn quickly), it's very difficult to produce an effective vaccine for HIV - merely having antibodies against it doesn't guarantee that you won't get infected. A vaccine would have to greatly sensitize the immune system to HIV to prevent infection. It would have to at least make the immune system sensitive enough to prevent the initial high-viremia burst of HIV replication (aka acute HIV infection) which spreads the virus throughout the body and promotes viral load increase. Or, it would have to bolster the immune system so that it can sequester the virus indefinitely like it can with herpes zoster.

    Interestingly, some people with HIV eventually develop "broadly neutralizing antibodies" which are able to outright kill the virus or make it unable to enter cells, without help from other immune cells. Some people develop enough of these so quickly that they do not require medications to not progress to AIDS. However in most people, by the time the body produces these antibodies, the infection has already progressed too far to make a difference. Many HIV vaccine studies are now focused on stimulating production of these HIV-neutralizing antibodies.

    Also, there is no small-animal model that can be used to study HIV infection. SIV (simian immunodeficiency virus) is similar but not the same. The only test group we have is humans.