Background:  CD8 cells can be divided by phenotype into naive (CD27⁺CD28⁺), intermediate (CD27^–CD28⁺), and terminally differentiated subsets (CD27^–CD28^–). Despite effective HAART, there is an expansion of CD8⁺CD28^– T cells in HIV-infected children. The cytokine production and specificity of terminally differentiated CD8 T cells in chronic virus infection is unclear.

Methods:  For the cytokine studies, we collected blood samples of 26 pediatric HIV-infected patients, 10 chronically hepatitis-infected children (9 hepatitis B and 1 hepatitis C; with no evidence of significant transaminase elevation, and normal liver ultrasound findings) and 10 healthy controls. Cytokine production was assessed after stimulation with Ionophor/phytohemagglutinin by flow cytometry with intracellular staining for interferon-gamma (IFN-γ) and interleukin-2 (IL-2). For HIV-specifity studies 69 HIV-infected children were investigated. We included 13 HLA A02⁺ children using PE-conjugated gag/pol tetrameric complexes. Co-staining with anti-CD8, -CD27, and -CD28 was done to identify CD8 subsets.

Results:  Focusing on terminally differentiated CD8 cells in HIV-infected children, the number of IFN-γ-producing cells was significantly higher (85.0%±20.7 SD) than in chronically hepatitis-infected children (64.1% ±21.8; p = 0.02) or healthy controls (60.1% ±22.8; p <0.01). This finding was not specific for terminally differentiated cells; naive/intermediate subsets also showed an increased percentage of IFN-γ⁺ cells (HIV:  50.3% ±19.7; hepatitis: 26.4% ±14.9; healthy controls: 26.0% ±6.7). In terminally differentiated CD8 cells <4% of the cells produce IL-2, while <15% of naive/intermediate CD8 subsets are IL-2⁺. Concerning HIV specificity, gag/pol⁺ CD8 T cells were identified in 8 of 13 patients (0.3 to 6.3% of total CD8 cells). None of the HIV-specific CD8 cells showed a terminally differentiated phenotype. No apparent correlation to age, viral load, immunological or clinical parameters was found.

Conclusions:  Increased production of INF-γ in CD8 T-cell subsets is specific for HIV infection (as compared with chronic hepatitis) and might be important for immunomodulation and containment of HIV. The expanded population of terminally differentiated CD8⁺CD27^–CD28^– T cells does not include HIV gag/pol-specific T cells, suggesting that in children this subset plays a minor role in antiviral cytotoxicity.