Human vascular endothelial cells stimulate memory but not naive CD8(+) T cells to differentiate into CTL retaining an early activation phenotype

Endothelial cell (EC)-selective alloreactive CTL may mediate alloimmune vas cular injury. In the present study, EC-selective CTL were generated in cocu ltures of purified human CD8(+) T cells with allogeneic EC and were compare d with conventional CTL against corresponding B lymphoblastoid cells (BLC), EC caused activation and expansion of memory but not naive CD8(+) T cells, which differentiated into EC-selective CTL that retained high surface expr ession of CD69, CD25, and CD62L and displayed low intracellular perforin co ntent. In contrast, BLC-stimulated CTL could be generated from naive or mem ory CD8(+) T cells and showed a more mature phenotype (low CD69, CD25, and CD62L with higher levels of perforin), The expansion of alloreactive T cell s by EC stimulation was 5- to 20-fold less effective than in corresponding BLC-stimulated cultures, accounting for a reduction in the assayable cytoto xicity of individual microcultures. In these IL-2-supplemented cocultures, no effect on CTL generation or phenotype was observed by mAb blocking of co stimulation provided by LFA-3, ICAM-1, or CD40, by addition of comitogenic anti-CD28 mAb, or by preactivation of EC with CD40 ligand. Cyclosporine inh ibited CTL expansion and cytotoxicity similarly in both EC- and BLC-stimula ted cultures but did not affect the phenotype of those CTL that did emerge. This study extends the characterization of endothelium as an immunoregulat ory cell type distinct from conventional APC and may explain why graft reje ction within the arterial intima, an anatomic compartment in which EC may b e the primary type of APC, is separable from rejection in the graft parench yma.