The current definition of IRU (similarly IRIS) includes at least five main criteria: (1) being a patient with AIDS, (2) receiving HAART, (3) achieving an immune reconstitution indicated by increased CD4+ T cell count over 100 cells/mm3 for at least two months, (4) having preexisting CMV retinitis which is currently in the inactive state, and (5) developing an intraocular inflammation that cannot be explained by drug toxicity or a new opportunistic infection. This evidence concerns the gene CD4 and cytomegalovirus retinitis.