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194 HIV-1 Tat Targets Monocyte-Derived Dendritic Cells (MDDC) and Induces Their Maturation and Antigen Presenting Function
E. Fanales-Belasio*1, S. Moretti1, F. Nappi1, G. Barillari2, F. Micheletti3, A. Cafaro1, and B. Ensoli1
1Inst. Superiore di Sanità, Rome, Italy; 2Univ. of Tor Vergata, Rome, Italy; and 3Univ. of Ferrara, Italy
Background: HIV-1 Tat is produced early after infection, is essential for virus replication, and is released extracellularly in a biologically active form. Vaccination of monkeys with native Tat protein or tat DNA induces specific Th-1 responses and protects from challenge with pathogenic viruses, whereas inactivated Tat or Tat peptides induce mostly Th2 responses and are less effective as vaccines. We asked whether the native conformation of Tat protein was required for eliciting an effective cellular immune response and investigated its uptake and effects on antigen-presenting cells.
Methods: The uptake of both native or oxidized-inactivated Tat protein was evaluated in flow cytometry after intracellular staining, in MDDC, B-lymphoblastoid cell lines (BLCL), and T-cell blasts (TCB). The expression of MHC and costimulatory molecules and the production of cytokines and b-chemokines were evaluated by FACS and ELISA, respectively. MDDC antigen presenting function was determined by allogeneic cultures or with tetanus toxoid (TT)-specific autologous lymphocytes.
Results: MDDC, but not BLCL or TCB, efficiently took up native Tat after 5 min of culture and at doses as low as 0.1 ng/ml. Uptake was markedly reduced or absent with the oxidized Tat. Maturation of MDDC markedly enhanced native Tat uptake. Only native Tat enhanced MDDC expression of MHC-I and -II, CD40, CD80, CD83, and CD86 molecules and production of IL-12, TNF-alpha, MIP-1alpha, MIP-1beta, and RANTES. Finally, Tat-treated MDDC presented antigen more efficiently to both allogeneic and TT-specific lymphocytes.
Conclusions: Native Tat protein specifically targets MDDC, particularly after maturation, but not BLCL or TCB. Tat promotes MDDC maturation, production of Th-1 cytokines, and antigen-presenting function. Thus, Tat has both antigen and adjuvant properties driving cellular responses, which make it an optimal candidate for an HIV vaccine.
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