The major factors that determine the extent of CD4 T-cell recovery remain a topic of ongoing research. Among the factors that have been linked to immune recovery are pre-treatment CD4 cell count (including ‘nadir’ or lowest-ever level), speed of immune reconstitution after starting treatment, HIV viral load and patient age.

The same factors have been implicated in discordant responses to therapy, in which patients achieve viral load suppression below 50 copies/ml but do not experience substantial CD4 cell gains. This is further discussed in Discordant viral load and CD4 cell count responses.