A preventive vaccine will need to generate immune responses that protect uninfected individuals from all the different HIV subtypes to which they may be exposed. Scientists are looking for conserved regions of HIV genes, those that produce proteins common to all or most subtypes. If such common proteins are not found, a cocktail vaccine comprising several proteins or peptides from different HIV strains may be necessary to invoke broad-based immunity. HIV Transmission is Complex Unlike some other viruses, HIV can be transmitted and can exist in the body not only as free virus but also within infected cells. Thus, a vaccine against HIV may be required to stimulate the two main types of immunity.
Humoral immunity uses antibodies to defend against free virus.
Cellular immunity directly or indirectly results in the killing of infected cells by immune cells. Data from animal models and long-term HIV survivors, and human clinical trials of experimental HIV vaccines, may offer clues to the answer. Another factor complicates the attempt to define HIV protection. Thus, to be effective, an HIV vaccine also may need to stimulate mucosal immunity. Mucosal immune cells that line the respiratory, digestive and reproductive tracts and those found in nearby lymph nodes are the first line of defense against infectious organisms.