Optimization and validation of an 8-color intracellular cytokine staining (ICS) assay to quantify antigen-specific T cells induced by vaccination.

Candidate HIV-1 vaccines currently being evaluated in clinical trials are designed to elicit HIV-1-specific cellular immunity. Intracellular cytokine staining (ICS) assays allow sensitive, quantitative ex vivo assessments of antigen-specific T cells including immunophenotyping of responding cells and measurement of multiple effector functions. Additionally, the use of banked cryopreserved PBMC samples makes this assay attractive in the setting of large efficacy trials where it is less feasible to perform immunoassays on freshly isolated samples. Here we describe extensive studies to optimize and quantitatively validate the 8-color ICS assay for use in clinical trials of candidate vaccines, which includes measurement of viable IFN-gamma, IL-2, TNF-alpha and IL-4 producing CD4+ and CD8+ T cells. We show that omission of viability dye staining results in an over-estimate of the true antigen-specific T cell response by up to two-fold. After optimization, the 8-color assay was validated for specificity, precision, linearity, limit of quantitation and robustness. The assay has a lower quantitation limit generally below 0.04%, depending on the cytokine subset. Additionally, with appropriate gating, the 8-color assay gives comparable cytokine-positive responses to those observed with the conventional 4-color assay. In conclusion, we provide the first description of a quantitatively validated ICS assay, which permits quantitative and qualitative evaluation of vaccine-induced immunogenicity and analysis of immune correlates of protection.

Safety and acceptability of the Reality condom for anal sex among men who have sex with men.

OBJECTIVES: To assess safety and acceptability of Reality condoms for anal sex among men who have sex with men. METHODS: Crossover study among HIV-seroconcordant (33 HIV-negative and 5 HIV-positive) monogamous male couples, randomized to latex male and Reality condom use with anal sex. RESULTS: Slippage with removal was reported more frequently with Reality than male latex condoms [odds ratio (OR), 2.7; 95% confidence interval (CI), 1.2-5.8 for receptive partners and OR, 34.1; 95% CI, 13.8-84.1 for insertive partners]. Receptive partners more frequently reported pain or discomfort (OR, 5.0; 95% CI, 2.6-9.4) and rectal bleeding (OR, 1.9; 95% CI, 0.9-4.1) with Reality condoms than male condoms. Over 20% reported willingness to use the Reality condom in the future with a partner of unknown HIV status; willingness was associated with past problems with male condoms and no problems with Reality condoms among receptive partners, and with past use of Reality condoms and HIV seropositivity among insertive partners. CONCLUSIONS: Men reported more frequent problems with Reality condoms than male latex condoms used for anal intercourse, particularly slippage, discomfort, and rectal bleeding. Design modifications, training, and research on the clinical significance of safety outcomes are needed for use of Reality condoms with anal sex.