Efficient priming of protein antigen-specific human CD4(+) T cells by monocyte-derived dendritic cells

Dendritic cells (DCs) have the unique ability to initiate an immune respons e in vivo by capturing antigens (Ags) in peripheral tissues and migrating t o secondary lymphoid organs,where they sensitize naive CD4(+) T cells. To m imic this process in vitro, previous studies have shown that DCs directly i solated from peripheral blood can be used to elicit primary responses to ne oantigens (neoAgs). In other studies, when monocyte-derived DCs have been u tilized to sensitize total CD4(+) T cells in vitro, only secondary prolifer ation to neoAgs could be elicited, In the present study the relative abilit ies of CD40 ligation, protein kinase C activation, and culture in tumor nec rosis factor alpha (TNF-alpha) to induce functional and phenotypic maturati on of human DCs from monocyte precursors were compared. Optimal TNF-alpha - induced maturation of DCs required a prolonged 4-day culture. It was then f ound that loading immature DCs with the neoAgs keyhole limpet hemocyanin or human immunodeficiency virus-1 p24 gag prior to TNF-alpha -induced maturat ion, rather than after maturation, was crucial to sensitize CD4(+) T cells to new Ags, This primary proliferation to neoAgs was initiated from the CD4 (+) CD45RA(+) naive T-cell population. Finally, it was found that monocyte- derived DCs acquired the ability to secrete interleukin-12 p70, after conta ct with Ag-specific T cells. The ability to prime and expand Ag-specific CD 4(+) T cells ex vivo to neoAgs in serum-free conditions has potential appli cation for cellular vaccination and adoptive immunotherapy. (C) 2000 by The American Society of Hematology.