Attenuated vaccines for AIDS?

Progress in HIV vaccine research

The relentless expansion of the HIV pandemic has demonstrated that the need for a vaccine is desperate. However, the development of an effective vaccine against HIV is a formidable challenge. It is likely that a successful vaccine will have to induce an immune response consisting of not only neutralizing antibodies targeted to conserved epitopes of the viral envelope and cytotoxic T-lymphocytes targeted to a variety of viral antigens, but also local mucosal immunity. Furthermore, a vaccine should induce broad-spectrum immunity covering all HIV subtypes. It is unlikely that a single vaccine will achieve all this, and a combination of vaccines will probably be necessary. Although no efficacious HIV vaccine is available yet, definite progress has been made. It was demonstrated that chimpanzees could be protected from both cell-free and cell-associated HIV challenge. Protection from mucosal challenge was also demonstrated in several studies and limited cross-protection between HIV subtypes was observed in several animal models. In spite of these successes, much remains to be done. Prototype vaccines studied to date have only induced short-lived immune responses and elicited no antibodies able to neutralize clinical isolates of HIV-1. Novel ways of producing HIV-1 envelope antigens may lead to improved antibody responses and raise the chances of a vaccine inducing long-term protective immunity.

Challenges in the development of an effective HIV vaccine: current approaches and future directions

OBJECTIVE

The intent of this review is to investigate and discuss why developing a successful HIV vaccine has been so challenging, first by examining the molecular biology of the virus and how HIV interacts with the immune system, and then reviewing past viral vaccine successes as well as future directions for HIV vaccine research.

BACKGROUND

Since HIV appeared in the United States in the early 1980s, an estimated 40 million people worldwide have been infected with the virus. Despite promising advances in the pharmacotherapy of HIV infection, it is apparent that the best, most cost-effective strategy for controlling the further spread of the virus is through synthesis of a protective vaccine. Almost 2 decades into the epidemic, there are few prospects for a truly effective vaccine entering the market in the foreseeable future.

METHODS

MEDLINE was searched for articles written between 1966 and June 1999. Search terms used were AIDS, HIV vaccine, HIV-1, HIV-2, vaccines, and human immunodeficiency virus.

RESULTS

Only 2 candidates for an HIV vaccine are currently in phase III clinical trials (1 in the United States and 1 in Thailand). The efficacy of these vaccines when applied to the population as a whole is widely questioned, largely because they induce protection by an antibody response only. Several studies have suggested that this approach will likely be ineffective in providing any real protection from viral infection. It appears that a strong cellular immune response is necessary in addition to a strong antibody response.