TreatmentUpdate57, Vol. 7, No. 3 - March 1995
Sean Hosein

During the past 10 years researchers have been constructing a number of potential anti-HIV vaccines. Most of these vaccines were designed to stimulate one arm of the immune system (humoral immunity) and cause the body to make anti-HIV antibodies. The theory supporting this design relied on a number of now outdated ideas, one of which was that anti-HIV antibodies would protect people from HIV infection. Unfortunately most people with HIV/AIDS make these antibodies which do not appear to protect them from infection or further damage to the immune system. It appears that the other arm of the immune system--CMI (cell-mediated immunity)-- weakens over time. Many of the life-threatening infections seen in AIDS occur because CMI has declined. Researchers in France, Montréal and California studying monkeys with AIDS have reached the same conclusion. They are trying to design vaccines that can boost CMI against SIV (the virus that causes AIDS in some monkeys) and HIV. These vaccines may also be used to help the immune systems of people with HIV/AIDS.

* HELPING VACCINES WORK

Usually vaccines have 2 parts. The first part (called the adjuvant) is designed to enhance the immune response to the vaccine (the second part). Adjuvants generally used in vaccines include:

- alum (aluminum hydroxide) - CFA (complete Freunds adjuvant made with light mineral oil) - extracts of bacteria such as MDP (muramyl dipeptide)

Most adjuvants stimulate production of antibodies and favour humoral immunity. Scientists working on developing HIV/AIDS vaccines are trying to find adjuvant that can help T cells respond to a vaccine. Researchers experimenting on humans with cancer are testing a number of chemicals designed to boost CMI. Reviewing their early results, it is not clear which chemicals are best for boosting CMI. Here are several chemicals that are being tested for their ability to boost T cells so that they will be stimulated by vaccines:

- interleukins 2 and 12 - DTC (Immuthiol(R) ) - MIMP (methyl inosine monophosphate) - thymic hormones such as thymosin alpha 1, thymopentin, thymic humoral factor - levamisole (Ergamisol(R) - indomethacin (Indocid(R) - complete Freunds adjuvant (CFA)

REFERENCES:

1. Hadden JW. T-cell adjuvants. International Journal of Immunopharmacology 1994; 16(9):703-70.

2. Vaslin B, Le Grand R, Vogt G, et al, Induction of Humoral and cellular immunity to simian immunodeficiency virus: what are the requirements for protection? Vaccine 1994;12(12):1132-1140.

3. Chan WL, Rodgers A, Grief C, et al. Immunization with class 1 human histocompatibility leukocyte antigen can protect macques against challenge infection with SIV MAC-32H AIDS 1995;9(3):223-228.

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