The two vaccine components differ in how the genes are packaged. One contains only the naked gene fragments, which cannot reconstitute into an infectious virus. The other uses a weakened type of respiratory virus known as adenovirus as a vector to shuttle the non-infectious gene fragments into the body.

Adenoviruses cause upper respiratory tract illness, such as the common cold. However, because the vaccine contains only HIV gene fragments housed in an adenovirus that cannot replicate, study participants cannot become infected with HIV or get a respiratory infection from the vaccine.


The use of adenovirus vectors appears to be the most promising advance in recent years in the search for an HIV vaccine, says Peggy Johnston, Ph.D., director of the Vaccine and Prevention Research Program in DAIDS, NIAID. Lawrence Corey, M.D., principal investigator of the HVTN, adds, We are excited to work with the VRC on this new vaccine candidate. This prime-boost approach incorporating adenovirus vector seems to generate the type and quantity of immune responses we feel will be necessary to impact an infection like HIV. This study will define more completely the levels of immunity this novel approach will achieve in a broad range of people.

The DNA components of the vaccine were manufactured by the San Diego-based Vical, Inc. The adenovirus vector was developed by VRC in collaboration with GenVec Inc., of Gaithersburg, Md., which also manufactured the adenovirus vector vaccine.

HVTN 204 Study Details
The HVTN 204 Phase II study will test the safety and ability of the vaccine to generate an immune response in 480 healthy, HIV-negative adults ages 18 to 50. The researchers plan to recruit volunteers from populations particularly hard-hit by AIDS, including African Americans and other ethnic minorities.

The study is being led by Michael Keefer, M.D., of the University of Rochester, NY, and Gavin Churchyard, M.B.B.Ch., F.C.P., M.Med., Ph.D., of Aurum Health Research Ltd. in South Africa.

The trial opened at the University of Alabama at Birmingham and is designed to include 13 HVTN sites, provided that regulatory and ethical approval is granted at each site:

* North America Baltimore, Maryland; Boston, MA; Providence, RI; Birmingham, AL; Nashville, TN; and Rochester, NY

* South America Rio de Janeiro and So Paulo, Brazil

* Caribbean Port-au-Prince, Haiti; Kingston, Jamaica

* Africa Gaborone, Botswana; and Cape Town, Soweto, and KOSH (Klerksdorp, Orkney, Stilfontein, and Hartbeesfontein), South Africa

Half of the 480 trial participants will be enrolled in the Americas (Haiti, Jamaica, Brazil and the United States) and half in southern Africa (Botswana and South Africa). The geographic diversity of participants allows the researchers to evaluate whether the immune responses generated to the vaccine vary according to the amount of prior exposure to adenovirus, as measured by pre-existing levels of adenovirus antibodies. Africans, for example, generally have had greater exposure to adenovirus than people living in North America.

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