Treatment of cardiac allografts with established leukocyte infiltration by modulation of alpha4 (CD49d) and leukocyte...

Leukocyte infiltration is a landmark feature of organ rejection. The present study was undertaken to determine whether monoclonal antibodies (mAb) against alpha4 (CD49d) and/or leukocyte function-associated antigen-1 (LFA-1; CD11a/CD18) would reverse ongoing rejection in a mouse C57BL/6-to-BALB/c heart transplant model.

Control animals had rejection on postoperative day (POD) 8. Treatment with mAb started on POD 4 when leukocyte infiltration was well established. The recipients were treated with (1) mAb LFA-1, (2) mAb alpha4, and (3) mAbs LFA-1 + alpha4 at a dose of 6 mg/kg/day i.v. on PODs 4, 5, and 7. Untreated and rat IgG-treated animals were used as controls.

Control animals experienced rejection on POD 8. Treatment with mAb against LFA-1 or alpha4 alone prolonged allograft survival to 17.0+/-3.2 and 24.3+/-4.6 days, respectively (P < 0.01 vs. controls). Combination therapy with both mAb increased allograft survival to 28.2+/-3.7 days (P < 0.01 vs. controls). Sequential pathological studies showed the mAb to alpha4, but not LFA-1, markedly reduced the degree of lymphocytic infiltration in cardiac allografts. In contrast, a different pattern was observed using in vitro studies: mAb to LFA-1, not alpha4, significantly reduced proliferative responses in mixed lymphocyte culture and interleukin-2 production from recipient splenocytes on POD 8.

These data indicate that integrins play an important role in rejection. Although the effect of mAb against alpha4 and LFA-1 may involve different mechanisms, treatment with mAbs to integrins may be valuable in future clinical transplantation by averting ongoing rejection and prolonging graft survival.