HIV virus is of two types - Type 1 & 2. Also there are several subtypes for e.g., in India HIV-1 subtype C is prevalent whereas in Africa HIV-1 subtype B is prevalent. Thus the vaccine should provide protection against all types & subtypes of HIV virus.

HIV virus mutates very rapidly. Thus vaccine should take care of mutated virus too.

CD4 cells are the helper T cells that help for both cell mediated as well as humoral immunity. With a vaccine, the antigen is presented by skin dendritic cell and macrophages to the T lymphocytes that form neutralizing antibodies by stimulating B cells and memory cells by stimulating other T cells. Thus, on exposure to the HIV virus, the memory cells are activated and neutralizing antibodies are produced in large amount that destroy the virus. However in HIV infection, the virus affects the CD4 cells itself and thus vaccine induced memory cells may not function.

Prevent infection with HIV virus.

In case infection still occurs, it should prevent progression of the disease

In case infection still occurs, it should prevent transmission of the HIV virus from an infected person to a non-infected person.