Recent trends in clinical trials of vaccines to prevent HIV/AIDS:

HIV-vaccines: lessons learned and the way forward

A safe and efficacious preventive HIV vaccine, as part of a comprehensive prevention program, remains among the highest public health priorities. It would be the best tool that could reduce the spread of HIV significantly in the long run. Current AIDS vaccine candidates are unable to induce neutralizing antibodies against primary HIV isolates or only to a very limited and narrow extent, representing a major obstacle in the development of an efficacious HIV vaccine. Clinical efforts have mainly focused on T-cell vaccines such as DNA and various recombinant vectors alone or in prime-boost regimens. The Merck Ad5 vaccine not only failed to show efficacy but also was associated with increased risk of HIV acquisition in vaccinees in a Phase IIb trial. While gp120 alone was not efficacious, the ALVAC prime and gp120 boost regimen showed 31% efficacy in a Phase III trial in Thailand. These contrasting results illustrate the limitations of available laboratory assays to assess the vaccine-induced immune responses and the lack of understanding of immune correlates of protection. Efforts should therefore focus on developing vaccine candidates inducing broadly neutralizing antibodies. Similarly, new vector strategies such as replicating vectors should be explored to induce strong and broad T-cell responses in the systemic and mucosal compartments. Innovation in immune assay development and testing algorithms is critically needed. The standardization of more relevant and predictive non-human primate models for immunogenicity and efficacy studies will contribute to better and faster vaccine assessment. HIV vaccine development requires innovative ideas and a sustained long-term commitment of the scientific community, civil society, politicians, and donors and participants for clinical research.

Laboratory expansion to large-scale international HIV preventive vaccine trials

PURPOSE OF REVIEW

The purpose of this article is to describe the requirements for clinical laboratories supporting large-scale multinational trials of prophylactic AIDS vaccine trials and review the progress made.

RECENT FINDINGS

There is an increasing need for laboratories in Africa, Asia and the Caribbean to support internationally initiated and funded clinical trials of preventive HIV vaccine candidates. A number of qualified laboratories are currently supporting AIDS vaccine trials in these regions, although there remains a need to develop capacity further. The standardization of all tests is key in order that data can be pooled and compared across multiple sites and products. Significant progress has been made towards this aim. The recent development of quality programmes including good clinical laboratory practices are key to ensuring data are reliable and meet the requirements of regulatory bodies. In addition, HIV diagnostic tests are being developed to distinguish true HIV infection from vaccine-induced antibodies.

SUMMARY

Significant advances have been made to develop laboratories capable of supporting multinational AIDS vaccine trials.

HIV vaccines: current status worldwide and in Africa

Since HIV-1 was identified, development of a preventive vaccine has been a major goal. Significant progress toward that goal has been made by 2010. In macaques, a vigorous T effector cell response has protected some animals from disease caused by simian immunodeficiency virus (SIV). Broadly, neutralizing human anti-HIV antibodies have been isolated and their structures, and targets are rapidly being elucidated. For the first time an AIDS vaccine has shown modest protective efficacy in a human clinical trial. To reach the final goal, there is a need for a coordinated global effort, including a range of approaches including novel high-throughput screening techniques, X-ray crystallography, and monoclonal antibody isolation, analysis of T cell responses and their impact on disease progression, human epidemiology, as well as targeted studies in nonhuman primates. African research teams as well as cohorts of healthy volunteers and HIV-infected individuals have contributed to HIV vaccine research and development in many important ways. It is essential that this work continue to speed the development and deployment of a vaccine suitable for African populations.

A Phase 1 study to evaluate the safety and immunogenicity of a recombinant HIV type 1 subtype C-modified vaccinia Ankara virus vaccine candidate in Indian volunteers

A recombinant modified vaccinia Ankara virus vaccine candidate (TBC-M4) expressing HIV-1 subtype C env, gag, tat-rev, and nef-RT genes was tested in a randomized, double-blind, dose escalation Phase I trial in 32 HIV-uninfected healthy volunteers who received three intramuscular injections of TBC-M4 at 0, 1, and 6 months of 5 x 10(7) plaque-forming units (pfu) (low dosage, LD) (n = 12) or 2.5 x 10(8) pfu (high dosage, HD) (n = 12) or placebo (n = 8). Local and systemic reactogenicity was experienced by approximately 67% and 83% of vaccine recipients, respectively. The reactogenicity events were mostly mild in severity. Severe but transient systemic reactogenicity was seen in one volunteer of the HD group. No vaccine-related serious adverse events or events suggesting perimyocarditis were seen. A higher frequency of local reactogenicity events was observed in the HD group. Cumulative HIV-specific IFN-gamma ELISPOT responses were detected in frozen PBMCs from 9/11 (82%), 12/12 (100%), and 1/8 (13%) volunteers after the third injection of the LD, HD, and placebo groups, respectively. Most of the responses were to gag and env proteins (maximum of 430 SFU/10(6) PBMCs) persisting across multiple time points. HIV-specific ELISA antibody responses were detected in 10/11, 12/12, and 0/8 volunteers post-third vaccination, in the LD, HD, and placebo groups, respectively. No neutralizing activity against HIV-1 subtype C isolates was detected. TBC-M4 appears to be generally safe and well-tolerated. The immune response detected was dose dependent, modest in magnitude, and directed mostly to env and gag proteins, suggesting further evaluation of this vaccine in a prime-boost regimen.

A phase 1 study to evaluate the safety and immunogenicity of a recombinant HIV type 1 subtype C adeno-associated virus vaccine

A novel prophylactic AIDS vaccine candidate, consisting of single-stranded DNA for HIV-1 subtype C gag, protease, and part of reverse transcriptase genes, enclosed within a recombinant adeno-associated virus serotype-2 protein capsid (tgAAC09) induced T cell responses and antibodies in nonhuman primates. In this randomized, dose escalation phase I trial, HIV-uninfected healthy volunteers (50 in Europe, 30 in India) received a single intramuscular injection of tgAAC09 at 3 x 10(9) DNase resistant particles (DRP) (n = 16), 3 x 10(10) DRP (n = 23), 3 x 10(11) DRP (n = 25), or placebo (n = 16). Twenty-one participants in Europe received a second (boost) dose of 3 x 10(11) DRP tgAAC09 or placebo at least 24 weeks after the first injection. The vaccine was safe and well-tolerated after initial and boost vaccination. Local and systemic reactogenicity was experienced by 13-25% of participants and was not dose related. No vaccine-related serious adverse events were reported. Modest HIV-specific T cell responses were detected in 7/64 vaccinees (40-385 SFC/10(6) PBMC), with 16% (4/25) responders in the highest dose group. All responses were to Gag epitopes. tgAAC09 appears to be safe, well-tolerated, and modestly immunogenic. Further evaluation of higher doses of tgAAC09 and boost injections is ongoing in Africa.