HIV/AIDS Vaccine Development: Challenges, Progress and Future Directions

AIDS vaccination studies using an ex vivo feline immunodeficiency virus model: reevaluation of neutralizing antibody levels elicited by a protective and a nonprotective vaccine after removal of antisubstrate cell antibodies

In the feline immunodeficiency virus system, immunization with a fixed-infected-cell vaccine conferred protection against virulent homologous challenge but the immune effectors involved remained elusive. In particular, few or no neutralizing antibodies were detected in sera from vaccinated cats. Here we show that, when preadsorbed with selected feline cells, the same sera revealed clearly evident virus-neutralizing activity. Because high titers of neutralizing antibody in cell-adsorbed sera from 23 cats immunized with fixed-infected-cell or whole-inactivated-virus vaccines correlated with protection, it is likely that they were more important for protection than formerly realized. In vitro, the fixed-cell vaccine efficiently removed neutralizing antibody from immune sera while the whole-inactivated-virus vaccine was much less effective.

AIDS vaccination studies using an ex vivo feline immunodeficiency virus model: detailed analysis of the humoral immune response to a protective vaccine

The feline immunodeficiency virus (FIV) cat model is extensively used to investigate possible vaccination approaches against AIDS in humans. Although consistent levels of protection have been achieved with FIV, as with other model systems, by immunizing with whole inactivated virus or fixed infected cells, the mechanisms responsible for protection are elusive. In previous studies we showed that cats immunized with a vaccine consisting of fixed infected cells were protected or unprotected against cell-free or cell-associated FIV challenge depending on the time interval between completion of vaccination and challenge. In an attempt to define possible humoral immune correlates of protection, selected sera harvested at the times of challenge from such cats were examined for anti-FIV-antibody titers and properties by using binding and functional immunological assays. Binding assays included quantitative Western blotting, enzyme-linked tests for antibodies to FIV glycoproteins and immunodominant linear epitopes, and tests for measuring conformation dependence and avidity of anti-viral-envelope antibodies. Functional assays included virus neutralization performed with two different cell substrates, complement- and antibody-dependent virolysis, blocking of reverse transcriptase, and an assay that measured the ability of sera to prevent FIV growth in cocultures of infected and uninfected cells. Despite the wide spectrum of parameters investigated, no correlation between vaccine-induced protection and the humoral parameters measured was noted.

Intradermal administration of viral vaccines

Intradermal administration maybe useful in lowering the cost of vaccination against hepatitis B significantly, and may also be helpful for the rapid induction of antibodies, reversing non-responsiveness, improving postexposure prophylaxis and immunising immunocompromised people. In addition, delayed type hypersensitivity skin reaction to the vaccine could serve as a useful marker for the acquisition of T helper type 1 immunoreactivity in vivo. However, there are some disadvantages when using intradermal vaccinations, including the requirement for skilful administration, the absence of approval from licensing authorities, the development of local skin reactions and a lower antibody response when 1/10 of the standard vaccine dose is used. This requires that appropriate vaccination regimens, including the correct vaccine dosage, and vaccination schedule are followed. In the future, a similar vaccination strategy might also be applied for the prevention and control of other infectious diseases. Copyright 1998 John Wiley & Sons, Ltd.

HIV vaccines: problems and prospects

Several lines of evidence now argue strongly that a successful HIV vaccine does not need to block infection completely. It has to mimic what already occurs in a minority of unvaccinated individuals--namely, rapid clearance of infection or reduction of viral load to a level that does not produce symptoms or permit transmission to others. The various vaccine candidates are reviewed.