A HUMANIZED THERAPEUTIC CD4 MAB INHIBITS TCR-INDUCED IL-2, IL-4, AND IL-10 SECRETION AND EXPRESSION OF CD25, CD40L, AND CD69

The actions of a humanised therapeutic CD4 mAb YHB.46 on T cell activa tion were investigated in vitro. Soluble YHB.46 IgG or YHB.46-derived F(ab')(2) fragments caused inhibitions of up to 100% of the proliferat ion of purified CD4(+) T cells activated with immobilised CD3 mAb. The inhibitory effects of the CD4 mAb were equally potent in both CD45RA( +) and CD45RO(+) T cell subset proliferation assays. Inhibitory effect s on DNA synthesis were not explicable by increased T cell apoptosis. YHB.46 was inhibitory even when added 70 h after exposure of cells to immobilised CD3 mAb, but it had little effect on IL-2 receptor-driven proliferation signals. The CD4 mAb inhibited the CD3-induced expressio n of the CD25 and CD69 activation markers on the T cell surface and su ppressed CD40 ligand expression, but not that of CD25 and CD69, when t heir expression was induced by phorbol ester plus ionomycin. YHB.46 al so exerted a profound inhibitory effect on the production of IL-2, IL- 4, and IL-10, irrespective of whether T cells were activated with CD3 mAb or with phorbol ester plus ionomycin. The inhibitory effects of YH B.46 on CD4(+) T cell proliferation were partially prevented by the ad dition of exogenous IL-2 or autologous monocytes and were completely p revented by activating T cells with a novel CD3-CD28 bivalent F(ab')(2 ) reagent. However, the inhibitory effects of YHB.46 on T cell prolife ration were equipotent in the presence or the absence of CTLA-4Ig, sho wing that the CD4 mAb was not acting on CD28-induced activation signal s per se. Our results show that the inhibitory effects of YHB.46 on T cell activation do not involve CD28 or IL-2 receptor signalling, but a re directed at the TCR-mediated G0-G1 transition. These findings in vi tro predict that YHB.46 may act as a potent immunosuppressant in the c linical context. (C) 1998 Academic Press.