The long-term goal of anti-HIV therapy is to improve health and prolong life. However, HIV disease can take years or decades to progress to the point of AIDS-defining illness or death. Because researchers and patients do not want to wait this long to see if a treatment is working, clinical trials of new therapies look at short-term markers of response, namely HIV viral load (which shows whether the virus is replicating) and CD4 cell count (an indicator of immune function).