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Two new preventive AIDS vaccine trials initiated in Africa

In December researchers at the Karolinska Institute in Stockholm, Sweden and colleagues at the US Military HIV Research Program (USMHRP) and the Muhimbili University College of Health Sciences in Tanzania began a second vaccine trial to evaluate the safety and immunogenicity of administering immunizations of two vaccine candidates sequentially. This Phase I/II trial will enroll 60 volunteers in Dar es Salaam, Tanzania.

The first vaccine candidate is a DNA plasmid comprised of several HIV genes. This candidate is given as a prime immunization and then is followed by a booster immunization with a modified vaccinia Ankara (MVA) vaccine candidate also containing HIV genes. Neither candidate can cause HIV infection. The DNA vaccine candidate was developed at the Swedish Institute for Infectious Disease Control and is based on HIV strains circulating in Tanzania. The MVA candidate, known as MVA-CMDR, was developed by the US National Institute of Allergies and Infectious Diseases (NIAID) and is manufactured by the Walter Reed Army Institute of Research (WRAIR). The Karolinska Institute is also conducting another Phase I trial in Sweden evaluating the safety and immunogenicity of the MVA candidate alone in 38 volunteers.

Last year at the 2006 AIDS Vaccine Conference in Amsterdam, Eric Sandström of the Karolinska Institute presented preliminary results of another placebo-controlled, Phase I trial in Sweden where volunteers received the DNA and MVA candidates in a prime-boost manner. This combination induced promising immune responses in the volunteers without causing serious safety issues.

More recently the South African AIDS Initiative (SAAVI) and the HIV Vaccine Trials Network (HVTN), which is part of NIAID, initiated a second Phase IIb test-of-concept trial in collaboration with Merck to evaluate the company's adenovirus-based vaccine candidate (MRKAd5). The trial is being called Phambili, which means 'going forward' in Xhosa, and will recruit 3000 volunteers in four South African provinces, including trial sites in Soweto, Cape Town, Klerksdorp, Medunsa, and Durban.

Another test-of-concept trial, known as the Step study, with the MRKAd5 candidate is currently ongoing at HVTN sites in the US, Canada, Peru, Dominican Republic, Haiti, Puerto Rico, Australia, Brazil, and Jamaica. South Africa is currently hosting other AIDS vaccine trials as well as other HIV prevention trials; however, the Phambili trial is the country's largest AIDS vaccine trial to date. It also marks the first time Merck's leading vaccine candidate is being evaluated in a population where the predominately circulating strain of HIV is not genetically matched with the antigens in the vaccine candidate (see VAX July 2006 Primer on Understanding HIV Clades). The epidemic in South Africa is primarily clade C HIV and the candidate is based on clade B. For more information about these or other ongoing preventive AIDS vaccine trials, visit the IAVI Report clinical trials database and the January 2007 Special Issue of VAX.

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All articles written by Kristen Jill Kresge