Suppression of established experimental autoimmune uveitis by anti-LFA-1alpha Ab.

Experimental autoimmune uveitis (EAU) is a well-characterized model that is useful in the study of human idiopathic uveitis.1–3 Although both genetic and environmental factors4 are important in the pathogenesis of uveitis, studies in rodents have demonstrated that the transfer of nonactivated or partially activated autoreactive T cells does not cause disease,3,5 suggesting that only activated autoreactive T cells are pathogenic. The inhibition of autoreactive T-cell activation therefore becomes a primary therapeutic goal. Given that T-cell activation requires two signals, one from ligation of T-cell receptors (TCRs) by complexed antigen-MHC molecules and the other from costimulatory molecules,6 it is generally believed that blockade of costimulation may effectively prevent T-cell activation, especially when multiple and/or undefined autoantigens are involved in a single disease. Nevertheless, studies by other laboratories and our own have shown that, although many costimulatory molecule blockers effectively prevent disease when administered before disease onset, they are less effective after disease onset.7–14 Furthermore, although many treatments have a therapeutic effect on disease induced by active immunization, they are less effective in treating disease induced by adoptive transfer in which the autoreactive T cells are subjected to in vitro activation and the activated T cells may be more resistant to costimulatory blockade.15 Since the major goal of clinical treatment is to impede disease progression, it is important to identify costimulatory signals, the blocking of which is effective in the treatment of already initiated diseases. Leukocyte function associated antigen (LFA)-1 was one of the first cell-surface heterodimeric integrins to be discovered.16–18 It interacts primarily with intracellular adhesion molecule (ICAM)-1, but also with ICAM-2 and -3, and junctional adhesion molecule (JAM)-1.19 As an one of the major molecules involved in the immunologic synapse, LFA-1 rapidly clusters after T-cell ligation, optimizing T cell–antigen-presenting cell (APC) contact and increasing the number of ligated TCRs.20–23 Various studies have shown that LFA-1 has multiple roles in immune responses, such as cell adhesion,24 T-cell activation,25 and the trafficking of leukocyte populations.26–28 LFA-1 therefore appears to be an attractive target for therapies aimed at attenuating clinical disease mediated by activated T cells. Antibodies interfering with the LFA-1/ICAM-1 interaction have been extensively evaluated in numerous preclinical studies on transplantation and autoimmune diseases,29–37 including animal models of uveitis.38–40 In the present study, we tested the effect of a panel of costimulatory molecule-specific Abs or the fusion protein, CTLA4-FC. Our results showed that, although many of these could block the function of activated autoreactive T cells isolated from antigen-immunized recipient mice (primary T-cell response), only anti-LFA-1α Ab inhibited the proliferative response of autoimmune T cells isolated from animals with adoptively induced EAU and of (interphotoreceptor-binding protein) IRBP-specific T-cell lines (secondary T-cell response). Of importance, in vivo injection of anti-LFA 1α Ab greatly reduced the incidence and severity of disease induced by adoptive transfer of in vitro activated T cells reactive with the peptide IRBP1-20 and suppressed disease development, even when administered after disease onset. The inhibitory effect of anti-LFA-1α Ab during the effector phase of disease was shown to be due to its blocking effector T-cell activation in peripheral lymphoid organs and inside the eye and preventing the trafficking of pathogenic T cells into the target organ.