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Trial results presented at CROI

By Kristen Jill Kresge

Results from two recently-conducted clinical trials of different prime-boost AIDS vaccine regimens were presented at the 15th Conference on Retroviruses and Opportunistic Infections (CROI), held February 3-6 in Boston.

The first trial, conducted by the HIV Vaccine Trials Network (HVTN) at multiple sites in the US, tested an immunization regimen consisting of two injections of a DNA candidate followed by two injections of a modified vaccinia Ankara (MVA) vector-based candidate, both developed at the Emory Vaccine Center and now licensed to the biotechnology company GeoVax. Both candidates contain fragments of HIV to stimulate an immune response against the virus, but neither can cause an HIV infection. Harriet Robinson, who recently left Emory to join GeoVax, presented results from this trial, known as HVTN 065.

Researchers evaluated the safety and immunogenicity of two different doses of the DNA and MVA-based candidates, each in 30 volunteers (see VAX August 2007 Primer on Understanding Immunogenicity). Researchers assessed the immune responses induced by the candidates two weeks after each injection of the MVA candidate. Based on these results, Robinson said the higher dose of the prime-boost combination will be tested further. In a second phase of this study, two groups of 30 volunteers will receive either a single injection of the DNA candidate followed by two injections of the MVA-based candidate, or three injections of the MVA-based vaccine candidate.

Researchers also presented data from another Phase I/II trial in Mbeya, Tanzania at CROI. This trial tested the safety and immunogenicity of the DNA and adenovirus serotype 5 (Ad5)-based candidates developed by the Vaccine Research Center (VRC), part of the US National Institute of Allergy and Infectious Diseases. This trial was conducted by the United States Military HIV Research Program and was one of a series of Phase I and II studies with the VRC’s candidates in preparation for the originally-planned Phase IIb test-of-concept trial known as PAVE 100. The start of the PAVE 100 trial, however, was placed on hold after the results of the STEP trial were released (see VAX October-November 2007 Spotlight article, A STEP back?).

The majority of participants in this trial had high levels of anti-Ad5 antibody at the start of the trial, resulting from exposure to the naturally-circulating Ad5 virus. Yet all individuals mounted some level of HIV-specific immune responses following receipt of the Ad5 candidate. This indicates that pre-existing immunity to Ad5 did not completely mitigate immune response to the Ad5 vaccine candidate.