Background:  Delayed type hypersensitivity (DTH) reaction is impaired in advanced HIV-1 infection. We investigated cell-mediated immunity by DTH reactions in patients with HIV-1 infection and relatively preserved numbers of circulating CD4⁺ T-cell counts.

Methods:  At 48 to 72 hours following the intradermal injection of Candida, mumps, tuberculin, and tetanus antigens or normal saline as a control, sites of injection or induration were sampled from HIV-1-seropositive and HIV-1-seronegative individuals with a 4-mm punch cylinder and were snap frozen in ice-cold isopentane. On frozen tissue, 5- to 7-µm histological sections were performed and monoclonal antibodies against CD4, CD8, HLADR, granulysin, CD1a, and FoxP3 were used to label cells for immunohistochemical characterization by digital imaging analysis.

Results:  Five HIV⁺ patients and 4 HIV^­ controls were recruited. All HIV⁺ patients were ART naïve. In patients, median CD4⁺ cell counts were 650/µL (range: 170 to 830) and median HIV-RNA levels were 3650 copies/mL (range: 157 to 750,000). In HIV^­ persons, the staining for CD4 (p = 0.049), CD8 (p = 0.007), granulysin (p = 0.002), CD1a (p = 0.049), and FoxP3 (p = 0.024) was significantly greater at sites of antigen injection than at the site of saline injection, whereas among the HIV⁺ patients, only staining for CD4 (p = 0.048), and HLA-DR (p = 0.008) at antigen sites exceeded that at control sites. At these sites, CD4 staining was highly correlated with staining for CD1a (p <0.001, ρ = 0.87), HLADR (p = 0.003, ρ = 0.76), FOXp3 (p = 0.004, ρ = 0.65), and granulysin (p <0.001, ρ = 0.77) but none of these in situ indices was predicted by circulating CD4⁺ T-cell counts.

Conclusions:  In vivo measures of adaptive cellular immune responses are impaired even in early HIV infection and are not well reflected by numbers of circulating CD4⁺ T cells.