Figure 2.

Pathways of activation and inhibition via costimulatory molecules. Dendritic cell (DC)-mediated T-cell activation requires a second, antigen nonspecific signal. Costimulatory molecules are not constitutively expressed by DCs; they are upregulated during maturation and as a consequence of environmental conditions. Similarly, DCs can inhibit T-cell activation or suppress T-cell activity, especially in the context of pre-existing tumors. Gene modification of DCs has been utilized both to enhance expression of activating costimulatory molecules and to inhibit expression of inhibitory molecules shown in this figure. As described in the text, costimulatory molecules can be delivered by gene transfection or recombinant viruses; inhibitory molecules can be knocked-down using siRNA. SOCS, suppressors of cytokine signaling.