The conditions favouring effective specific cytotoxic T lymphocyte (CTL) priming have been exploited to set up a simple and reproducible method to Induce a primary CTL response In vitro. We report that cultured monocytes, as well as activated T cells, pulsed with exogenous HLA-A2 binding immunogenic peptides, can induce primary peptlde-specific CTL responses In vitro in a T h -lndependent manner. Primary viral peptide-induced CTL were HLA-A2 restricted, and recognized both peptlde-pulsed target

more »

... cells and targets infected with recomblnant vaccinia virus expressing viral endogenous antigens. In addition, both cultured monocytes and activated T cells primed peptide-speciflc CD8 + T cells depleted from the CD45RO+ memory cell fraction. The efficiency of CTL priming by monocytes was dependent upon the strong up-regulation of class I, adhesion and co-stimulatory molecules occurring spontaneously upon In vitro culture. The Inability of unseparated peripheral blood mononuclear cells to mount a peptlde-speclflc CTL response could be reverted by direct co-stimulation of responding CD8 + T cells by soluble B7.1 or a stimulatory anti-CD28 antibody, that allowed a specific response to take place. Although co-stimulation via the B7-CD28 interaction appeared sufficient to trigger CTL responses, it was not essential for CTL priming, since neither anti-B7.1 mAb nor soluble CTLA-4 Inhibited Induction of primary CTL response. This new method for Induction of specific CD8 + T cell response In vitro may be exploited in adoptive Immunotherapy in cancer or In HIV-lnfected patients. Correspondence to. V. Barnaba Transmitting editor. E. Sercarz