Homing of in vitro-generated donor antigen-reactive CD4(+) T lymphocytes to renal allografts is alpha(4)beta(1) but not alpha(L)beta(2) integrin dependent

The extravasation and sequestration of Ag-reactive T lymphocytes into vascu larized organ allografts depend on a cascade of complex interactions among circulating lymphocytes, endothelial cells, and extracellular matrix protei ns, Ag-activated donor-specific CD4 T cells are major initiators and effect ers in the allograft rejection response. Interfering with the intragraft ho ming of activated CD4 T cells may represent a novel therapeutic approach in transplant recipients. We have developed a FAGS-based short-term homing as say that allows tracing in vitro-generated Ag-reactive CD4 T cells after ad optive transfer in test rat recipients. Allospecific cell lines were preinc ubated with anti-alpha (4)beta (1) or anti-alpha (L)beta (2) mAb, because o f enhanced expression of both integrin receptors after alloactivation, The pretreated Lewis(BN) lymphocytes were carboxyfluorescein diacetate succinim idyl ester labeled and adoptively transferred into Lewis rat recipients of Brown Norway kidney allografts, The injection of equal numbers of PKH-26-la beled untreated cells allowed quantitative comparison of both populations i n the same animal. Ex vivo treatment with anti-alpha (4)beta (1) mAb dimini shed intragraft infiltration of adoptively transferred T cells by 85% in a donor-specific fashion, In contrast, treatment with anti-alpha (L)beta (2) mAb did not affect intragraft cell sequestration. Hence, blocking alpha (4) beta (1) integrin interactions represents a novel strategy in preventing lo cal intragraft recruitment of Ag-reactive CD4 T cells in transplant recipie nts.