Background: The advent of HAART has greatly reduced CMV disease incidence. While it has been proposed that recovery of CMV-specific CD4⁺ T-cells is a critical mediator of HAART’s protective effect, little is known about the determinants of CMV-specific CD4⁺ T-cell recovery or the relationship between CMV-specific CD4⁺ and CD8⁺ T-cells during virologically suppressive HAART.

Methods: Homosexual men treated with HAART with ≥ 3 months (mos) of plasma viral load (VL) < 1000 copies/ml were consecutively sampled from the Study of the Consequences of the Protease Inhibitor Era (SCOPE). The percentage of CD4⁺ and CD8⁺ T-cells that were CMV-specific was determined by flow cytometric detection of CD69⁺ cells producing intracellular interferon-γ after stimulation with a mixture of overlapping 15 amino acid peptides of CMV pp65. Overall T-cell activation was defined by percentage of CD8⁺ cells that were CD38⁺/HLA-DR⁺.

Results: Among 74 subjects, the median duration of virologic suppression on HAART was 21 mos (range 3.1– 56); none had active CMV disease. Median values were: age 43 yrs; nadir CD4 T-cell count 99 cells/mm³; current CD4 count 442; pre-HAART VL 4.4 log₁₀ copies/ml; and CD8⁺ activation 9.3%. All but 3 subjects had detectable CMV-specific CD4⁺ T-cells and all but 1 had detectable CMV-specific CD8⁺ cells. The median percentage of CMV-specific cells was 0.12 (IQR 0.05–0.30) for CD4⁺ T-cells, which was lower than the median of 1.55 (IQR 0.72–3.24) for CD8⁺ cells (p < 0.001). The percentage of CMV-CD4⁺ T-cells was directly related to percentage CMV-CD8⁺ cells (Spearman rho = 0.29, p = 0.01). In a multivariable linear regression model, duration of suppression (mean gain of 0.01 log₁₀ percentage CMV-CD4⁺ cells per month, p =0.03) and pre-HAART VL (mean of 0.22 fewer log₁₀ percentage CMV-CD4⁺ cells per log₁₀ increase in VL, p = 0.003) were independently associated with percentage CMV-CD4⁺ cells. There was no evidence for an association with nadir CD4 count, current CD4 count or VL, age, or overall T-cell activation.

Conclusion: Flow cytometric techniques using pp65 peptide stimulation can be used to sensitively detect CMV-specific CD4⁺ and CD8⁺ T-cells in HLA-unselected HIV-infected patients. Among patients with HAART-related virologic suppression, the percentage CMV-CD4⁺ T-cells is related to CMV-CD8⁺ T-cells, increases with length of virologic suppression and is not influenced by nadir CD4 count. Use of this assay may prove useful in determining a threshold of protective levels of CMV-specific T-cells for management of anti-CMV chemoprophylaxis.