The capacity of HIV-1 to establish latent infection of CD4+ T cells may allow viral
persistence despite immune responses and antiretroviral therapy. Measurements of infectious
virus and viral RNA in plasma and of infectious virus, viral DNA and viral messenger
RNA species in infected cells all suggest that HIV-1 replication continues throughout
the course of infection. Uncertainty remains over what fraction of CD4+ T cells are
infected and whether there are latent reservoirs for the virus. We show here that
during the asymptomatic phase of infection there is an extremely low total body load
of latently infected resting CD4+ T cells with replication-competent integrated provirus
(<10(7) cells). The most prevalent form of HIV-1 DNA in resting and activated CD4+
T cells is a full-length, linear, unintegrated form that is not replication competent.
The infection progresses even though at any given time in the lymphoid tissues integrated
HIV-1 DNA is present in only a minute fraction of the susceptible populations, including
resting and activated CD4+ T cells and macrophages.