title: Cluster-function relationship of rat-antimouse P55 IL-2 receptor monoclonal antibodies. In vitro studies of the CTL-L2 mouse cell line and in vivo studies in a delayed-type hypersensitivity model in mice.
abstract: 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(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 microgram 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 microgram/day) while 7D4 and PC61 induced only a moderate inhibitory effect (37% inhibition for each MoAb given at 10 micrograms/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.
authors.affiliation: National Institute of Health and Research, INSERM U211, University of Nantes, France.
authors.forename: J
authors.initials: J
authors.lastname: Dantal
authors.forename: Y
authors.initials: Y
authors.lastname: Jacques
authors.forename: J P
authors.initials: JP
authors.lastname: Soulillou
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D001667:Binding, Competitive; D002455:Cell Division / Q000276:immunology; D003602:Cytotoxicity, Immunologic / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005260:Female; D006968:Hypersensitivity, Delayed / Q000188:drug therapy / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D015375:Receptors, Interleukin-2 / Q000276:immunology*; D013602:T-Lymphocytes, Cytotoxic / Q000187:drug effects / Q000276:immunology
chemical_list: D000911:Antibodies, Monoclonal; D015375:Receptors, Interleukin-2