CLUSTER-FUNCTION RELATIONSHIP OF RAT-ANTIMOUSE P55 IL-2 RECEPTOR MONOCLONAL-ANTIBODIES - INVITRO STUDIES OF THE CTL-L2 MOUSE-CELL LINE AND INVIVO STUDIES IN A DELAYED-TYPE HYPERSENSITIVITY MODEL IN MICE

Monoclonal antibodies directed against the P55 component of the interleukin 2 receptor (IL-2-R) have been used to prevent allograft rejection in various animal models, including primates and man. This study compares the functional effects of seven MoAbs directed against the mouse IL-2-R P55 chain both in vitro using the mouse CTL-L2 cell line and in vivo in a sheep red blood cell-induced delayed-type hypersensitivity model. Data from in vitro studies showed that a cluster of four MoAbs (cluster I: 5A2, 125, 135 [IgG2a] and AMT13 [IgG2b]) competed with IL-2 for binding to the P55 chain and caused an inhibition of IL-2-induced proliferation on CTL-L2. The respective dissociation constants (Kd) of the four MoAbs were 1.1, 1.4, 2.5, and 5.5 nM, and they all displayed a common maximal binding capacity of 2 x 10(5) sites per cell on CTL-L2. None of these MoAbs were found to fix rabbit complement. The three other MoAbs (2E4: IgG2a, 7D4: IgM, PC61: IgG1) with respective Kd of 0.8, 0.2, and 0.85 nM and maximal binding capacities of 2 x 10(5), 4 x 10(4) and 10(5) sites per cell did not interfere with IL-2 binding and did not affect the IL-2-induced proliferation of the murine cell line. All three MoAbs were found to define three separate epitopic clusters independent of cluster I. Among them, only 2E4 induced a strong complement-mediated cytotoxicity. In vivo experiments showed that all MoAbs from cluster I were efficient in suppressing the DTH reaction and that the magnitude of their effect was consistent with their respective Kds. At a suboptimal dose of 1-mu-g per day, the DTH inhibition indices were 40%, 43%, 23%, and 9% for 5A2, 125, 135, and AMT13, respectively. The 2E4 MoAb was found to be as efficient as cluster I MoAbs in suppressing DTH (53% inhibition at 1-mu-g/day) while 7D4 and PC61 induced only a moderate inhibitory effect (37% inhibition for each MoAb given at 10-mu-g/day, compared with 70% inhibition for cluster I MoAbs). Taken together, our results indicate that blocking the IL-2/IL-2-R interaction without complement fixation is sufficient per se to attenuate the DTH reaction, and conversely that strong complement-mediated cytotoxicity in the absence of a functional effect in the IL-2/IL-2-R interaction is also effective in this system. Finally, no synergistic effect between MoAbs belonging to different clusters was evidenced in the DTH model.