III. This text will provide you with some information about

Vaccine development. Read the text to gain the general idea of

Its contents. Say whether the following statements are true.

1. There is no hope in development of effective AIDS vaccine.

2. One of the problems in aids vaccine development is lack of avail­able animal model.

3. No success has been made since 1990 in studies of safe and effec­tive Vaccine.

THE PROSPECTS FOR AIDS VACCINES

Several vaccine strategies against HIV are under study in phase I clin­ical trials. Many involve recombinant subunit preparations, and the ques­tion is which of these components of the virus may be immunogenic. Immune effectors and mediators that protect against HIV are also unde­fined. Vaccines may ultimately be used to treat as well as prevent AIDS.

Historically, vaccines are among the best measures for preventing and controlling disease. Ever since human immunodeficiency virus was iden­tified as the cause of AIDS. The development of vaccines against HIV has been a high priority.

The obstacles involved are formidable: if viruses were ranked in terms of the difficulties they present to developers of vaccines. HIV would clear­ly be the gold standard. Nonetheless, recent studies have provided grounds for optimism that a safe and effective AIDS vaccine is feasible. Furthermore, AIDS vaccine research is spinning of technologic develop­ments applicable to the production of vaccines against other viral diseases.

Two critical questions in the development of an AIDS vaccine are what components of the immune system must be enlisted to protect against the virus, and what antigenic components of the virus must a vac­cine contain to induce that protective response.

With vaccines against other viral illnesses, such as poliomyelitis, measles, and hepatitis, the achievements of immunity correlate with pro­duction of neutralizing antibodies against the virus. Correlates of immu­nity to HIV are only now beginning to emerge. Neutralizing antibodies in persons infected with HIV, for example, are generally at low titers and do not halt progression to AIDS.

Along with neutralizing antibodies, cell-mediated immune responses may be necessary to buttress protection against the virus. Antigenic stim­ulation of monocytes and T-cells causes the release of cytokines that can activate natural killer cells and macrophages, which can then kill HIV- infected cells in vitro. Moreover, antibodies specific for HIV can arm killer cells to destroy virus-infected cells in the mechanism known as anti­body-dependent cellular cytotoxicity (ADCC). As with other viruses that, like HIV, have an envelope, ADCC may be important in protecting against in vivo challenge.

A stumbling block in AIDS vaccine development has been the lack of a readily available animal model in which to test candidate vaccines. Chimpanzees are being used because they seroconvert and generate HIV- specific T-cell responses after inoculation with HIV, and the virus can subsequently be isolated from peripheral mononuclear cells. HIV infection however doesn't produce an AIDS-like disease in chimpanzees. Fur­thermore, the number of chimpanzees available for AIDS vaccine test­ing in the United States is limited.