115 HIV-1 TAT PROTEIN IMPAIRS CD8 T-CELL FUNCTION BY DOWN REGULATING TRANSCRIPTION OF THE IL-7R ALPHA CHAIN (CD127) E Faller, M McVey, J Kakal, P MacPherson Objective: We have previously demonstrated that the HIV Tat protein specifically down regulates the IL-7 receptor alpha-chain (CD127) on healthy CD8 T-cells in a dose- and time-dependent manner. Since Tat influences transcription of other host genes, we hypothesized that Tat affects CD127 expression at the level of transcription initiation and that this down regulation impairs CD8 T-cell function.
Ottawa Health Research Institute, Ottawa, Ontario
Methods: CD8 T-cells were isolated from healthy volunteers and incubated with purified HIV Tat protein. Expression of cellular proteins was analyzed by flow cytometry. CD8 T-cells exposed to Tat were sorted by FACS into CD127hi and CD127lo populations and after harvesting total RNA, CD127 transcripts were quantified by Real Time PCR. Proliferation assays were carried out by stimulating with anti-CD3 and anti-CD28 monoclonal antibodies ±IL-7.
Results: Tat reduced CD127 expression on CD8 T-cells including the naïve and memory subsets. Removal of Tat from the medium after up to 72 hours allowed complete recovery of CD127. Preincubation of Tat with anti-Tat monoclonal antibodies or with heparin abolished its ability to down regulate CD127. Decreased CD127 expression in response to Tat was not associated with CD8 T-cell activation. CD8 T-cells shifting from CD127hi to CD127lo surface expression after exposure to Tat demonstrated a 6-fold decrease in CD127 mRNA. Studies with Actinomycin D demonstrated Tat does not enhance CD127 mRNA degradation but rather down regulates CD127 expression at the level of transcription initiation. Tat-induced decrease in CD127 expression resulted in a reduction in both perforin expression and cell proliferation following CD8 T-cell stimulation.
Conclusions: The HIV Tat protein inhibits CD127 gene expression and consequently down regulates expression of the IL-7 receptor on CD8 T-cells. By preventing efficient IL-7 signalling, Tat is thus able to impair CD8 T-cell proliferation and function. Tat is thus implicated as an important viral factor in HIV induced immune dysregulation.