Recombinant subunit vaccines against primate lentiviruses

Immune mechanisms associated with protection from vaginal SIV challenge in rhesus monkeys infected with virulence-attenuated SHIV 89.6

Although live-attenuated human immunodeficiency virus-1 (HIV) vaccines may never be used clinically, these vaccines have provided the most durable protection from intravenous (IV) challenge in the simian immunodeficiency virus (SIV)/rhesus macaque model. Systemic infection with virulence attenuated-simian-human immunodeficiency virus (SHIV) 89.6 provides protection against vaginal SIV challenge. This paper reviews the findings related to the innate and adaptive immune responses and the role of inflammation associated with protection in the SHIV 89.6/SIVmac239 model. By an as yet undefined mechanism, most monkeys vaccinated with live-attenuated SHIV 89.6 mounted effective anti-viral CD8+ T cell responses while avoiding the self-destructive inflammatory cycle found in the lymphoid tissues of unprotected and unvaccinated monkeys.

Rational development of prophylactic HIV vaccines based on structural and regulatory proteins

The severity of the AIDS epidemic clearly emphasises the urgent need to expedite HIV vaccine candidates into clinical trials. Prophylactic HIV vaccine candidates have been evaluated in non-human primates. Based on specific proof of principle studies the first phase III clinical studies have recently begun in humans. However, a truly effective HIV vaccine is not yet at hand and many problems related to specific properties of the virus remain to be overcome. Previously proven empirical approaches have largely failed and now rational thinking based on an understanding of immunity to lentiviral infections is needed. This review addresses the scientific problems and complications facing the development of an HIV vaccine as well as the possible strategies currently available to overcome these problems. Recent attention has focussed on identifying the immune correlates and mechanisms of protection from either HIV infection or protection from disease progression. Based on these observations, the logic and rational behind the development of multiple component vaccine strategies are highlighted.

Prospect of a prophylactic vaccine for HIV

Human immunodeficiency virus (HIV) continues to infect about 15,000 people every day, 90% of whom live in non-industrialised countries. So far, education programmes have only managed to slow, but not cease, the HIV spread, while powerful drug combinations are too costly and complex for the majority of HIV-infected people and in any case fail to clear HIV from the body. Under these circumstances, the best hope for controlling the HIV pandemic is the development of an effective prophylactic vaccine. With a series of new technologies and increased political and financial commitments, a growing momentum in the field of HIV-vaccine development promises exciting years ahead.

Variability and immunogenicity of caprine arthritis-encephalitis virus surface glycoprotein

The complete surface glycoprotein (SU) nucleotide sequences of three French isolates of caprine arthritis-encephalitis virus (CAEV) were determined and compared with those of previously described isolates: three American isolates and one French isolate. Phylogenetic analyses revealed the existence of four distinct and roughly equidistant evolutionary CAEV subtypes. Four conserved and five variable domains were identified in the SU. The fine specificities of antibodies produced against these domains during natural infection were examined using a pepscan analysis. Nine immunogenic segments were delineated throughout the conserved and variable domains of SU, two of them corresponding to conserved immunodominant epitopes. Antigenic determinants which may be involved in the immunopathogenic process induced by CAEV were identified. These results also provide sensitive and specific antigen peptides for the serological detection and differentiation of CAEV and visna/maedi virus infections.

Recombinant modified vaccinia virus ankara expressing the surface gp120 of simian immunodeficiency virus (SIV) primes for a rapid neutralizing antibody response to SIV infection in macaques

Neutralizing antibodies were assessed before and after intravenous challenge with pathogenic SIVsmE660 in rhesus macaques that had been immunized with recombinant modified vaccinia virus Ankara expressing one or more simian immunodeficiency virus gene products (MVA-SIV). Animals received either MVA-gag-pol, MVA-env, MVA-gag-pol-env, or nonrecombinant MVA. Although no animals were completely protected from infection with SIV, animals immunized with recombinant MVA-SIV vaccines had lower virus loads and prolonged survival relative to control animals that received nonrecombinant MVA (I. Ourmanov et al., J. Virol. 74:2740-2751, 2000). Titers of neutralizing antibodies measured with the vaccine strain SIVsmH-4 were low in the MVA-env and MVA-gag-pol-env groups of animals and were undetectable in the MVA-gag-pol and nonrecombinant MVA groups of animals on the day of challenge (4 weeks after final immunization). Titers of SIVsmH-4-neutralizing antibodies remained unchanged 1 week later but increased approximately 100-fold 2 weeks postchallenge in the MVA-env and MVA-gag-pol-env groups while the titers remained low or undetectable in the MVA-gag-pol and nonrecombinant MVA groups. This anamnestic neutralizing antibody response was also detected with T-cell-line-adapted stocks of SIVmac251 and SIV/DeltaB670 but not with SIVmac239, as this latter virus resisted neutralization. Most animals in each group had high titers of SIVsmH-4-neutralizing antibodies 8 weeks postchallenge. Titers of neutralizing antibodies were low or undetectable until about 12 weeks of infection in all groups of animals and showed little or no evidence of an anamnestic response when measured with SIVsmE660. The results indicate that recombinant MVA is a promising vector to use to prime for an anamnestic neutralizing antibody response following infection with primate lentiviruses that cause AIDS. However, the Env component of the present vaccine needs improvement in order to target a broad spectrum of viral variants, including those that resemble primary isolates.