CD4 and immunodeficiency disease: In fact, the standardized mortality ratio for the latter group (that is, those able to recover to a CD4 count above 500 cells/μl from typical low nadir CD4 levels (<200 cells/μl)) approaches one [41,42], suggesting that prior severe immunodeficiency may not lead to long-term harm as long as the person recovers a substantive number of CD4+ lymphocytes and hence experiences optimal benefit of ART.