No cure currently exists for HIV/AIDS. However, thousands of scientists are involved in an unprecedented worldwide effort to ultimately cure and/or prevent this horrific disease. This war is being waged on several fronts, including attempts to develop effec­tive antiretroviral drugs that will kill or at least neutralize HIV and efforts to create a vaccine effective against HIV.

As we described earlier, HIV is classified as a retrovirus because, after invading a living cell, it works backward, using an enzyme called reverse transcriptase. This enzyme transcribes the viral RNA into DNA, which then acts to direct further synthesis of the lethal HIV RNA. HIV also encodes another enzyme, called a protease (protein digest­ing), that is equally critical to its reproduction. Once HIV invades a host CD4 cell, it eventually takes over the host cell’s genetic material and manufacturing capacity, pro­ducing additional viruses to infect other cells. During this process, HIV kills the host cell and injects copies of its own lethal RNA into the blood to invade other healthy cells.

To date, treatment strategies have focused on drug interventions designed to block the proliferation and seeding of HIV throughout the immune system and other bodily tissues and organs. Up to the mid-1990s the main class of drugs used to combat HIV comprised products that inhibited the action of the reverse transcriptase enzyme. These reverse transcriptase (RT) inhibitors were designed to prevent the virus from copy­ing its own genetic material and making more viruses. A major breakthrough in drug

Sexually Transmitted Infections

therapy took place in 1996 with the emergence of a new class of drugs that inhibit HIV’s protease enzyme, which the virus uses to assemble new copies of itself. When a protease inhibitor (PI) drug was combined with two RT inhibitor drugs in early clinical trials, the combination was shown to dramatically reduce viral load in blood to minimal or undetectable levels in most patients (Louis et al., 1997; Wong et al., 1997).