The HIV virus enters the body via one of the fluids through which it is transmissible e.g. blood. It then binds itself to CD4 on the body's T cells and enters the cell via endocytosis. Once it is inside the cell it then has to replicate. It releases the enzyme reverse transcriptase which turns the viral RNA (single stranded) into DNA (double stranded). This means that it can be move into the nucleus and integrate itself into the host cell's DNA with the help of another enzyme integrase. The viral DNA replicated by the cell's own protein synthesising structures. This new viral DNA then makes its way to the surface of the cell and buds off.