ANTI-CD2 AND ANTI-CD3 MONOCLONAL-ANTIBODIES SYNERGIZE TO PROLONG ALLOGRAFT SURVIVAL WITH DECREASED SIDE-EFFECTS

Anti-CD3 monoclonal antibody suppresses immunity and prolongs allograft survival; however, it induces T cell activation and overproduction of soluble factors that result in a deleterious cytokine syndrome. Anti-CD2 mAb also prolongs allograft survival, by suppression of mature and precursor CD4 and CD8 T cells and NK cells, without an associated cytokine release. Because of the close physical and functional association of CD2 and CD3 on the T cell surface, we tested whether alphaCD2 mAb in combination with alphaCD3 mAb could act synergistically to prolong allograft survival, and whether the combination would affect the alphaCD3-associated cytokine syndrome. (57BL/6 (H-2b) hearts were transplanted to CBA (H-2k) recipients in a heterotopic nonvascularized model. Recipients received alphaCD2 (12-15) or alphaCD3 (145-2C11) mAb i.v. alone or in combination. Lymphocytes from treated animals were also analyzed by fluorescent flow cytometry and stimulated in vitro and assessed for proliferation and lymphokine production. Anti-CD2 and alphaCD3 each prolong allograft survival (mean survival time 22.4+/-1.0 and 27.4+/-3.3 days, respectively vs. 14.0+/-0.6 for control mAb, P<0.001 for both vs. control). Combinations of mAbs show a more complicated interaction. Very low doses (1 mug) of alphaCD2 and alphaCD3, which have no effect when given alone, are synergistic (16.5+/-1.3 days, P<0.02). A high dose of alphaCD2 (100 mug), which is immunosuppressive, is additive with a moderate dose of alphaCD3 (10 mug), which is immunostimulatory. The two mAbs are again synergistic when a high dose of alphaCD2 (100 mug) is combined with a high dose of alphaCD3 (1 mg) (>51.5+/-23.0 days, P<0.001). Furthermore, high-dose alphaCD2 administered 48 h prior to high-dose alphaCD3 was a more effective combination for prolonging allograft survival than both antibodies administered simultaneously (67.1+/-10 vs. 35.8+/-0.7 days, P<0.05). Anti-CD2 also diminishes the alphaCD3-associated cytokine syndrome, and prior in vivo treatment with alphaCD2 decreases the subsequent in vitro proliferative response to alphaCD3 and the alphaCD3-stimulated production of IL-2 and IL-4. Flow cytometry demonstrates that in general these mAbs do not deplete but leave T cell populations intact with altered receptor expression. These results show that the combination of alphaCD2 and alphaCD3 mAbs prolongs cardiac allograft survival in a synergistic fashion while decreasing the side effects of alphaCD3 mAb alone. The synergism between these mAbs is probably related to the close physical and functional association of the CD2 and CD3 receptors and the ability of CD2-mediated signaling to abrogate some aspects of CD3-mediated signaling.