AIDS vaccines in clinical trials

A number of approaches are being assessed with regard to developing an effective AIDS vaccine. No safe attenuated form of the virus has been recognized to date, nor is one likely to be developed in the foreseeable future. The high level of mutation associated with HIV would, in any case, heighten fears that spontaneous reversion of any such product to virulence would be possible. 

The potential of inactivated viral particles as effective vaccines has gained some attention, but again fears of accidental transmission of disease if inactivation methods are not consistently 100 per cent effective have dampened enthusiasm for such an approach. In addition, the stringent containment conditions required to produce large quantities of the virus render such production processes expensive. 

Not withstanding the possible value of such inactivated viral vaccines, the bulk of products assessed to date are subunit vaccines. Live vector vaccines expressing HIV genes have also been developed and are now coming to the fore (Table 13.12). 

Much of the preclinical data generated with regard to these vaccines entailed the use of one of two animal model systems simian immunodeficiency virus infection of macaque monkeys and HIV infection of chimpanzees. Most of the positive results observed in such systems have been in association with the chimp-HI V model. However, no such system can replace actual testing in humans. 

Most of the recombinant subunit vaccines tested in the first half of this decade employed gp 120 or gp 160 expressed in yeast, insect or mammalian (mainly CHO) cell lines. Eukaryotic systems facilitate glycosylation of the protein products. Like all subunit vaccines, these stimulate a humoral-based immune response but fail to elicit a strong T-cell response. The failure to elicit a cell-based 

Despite such difficulties, at least one such inactivated product has reached clinical trials. The viral particles are initially propagated in cultured human T cells. They are then treated with formaldehyde to inactivate them — a process which also removes the viral envelope. The virion particles are then treated with y-irradiation in order to ensure inactivation of the viral genome. The final product is administered along with an adjuvant in order to maximize the immunological response (see later). 

Live vaccines based on viral vectors Biocine 

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