Serum half-life and tumor localization of a chimeric antibody deleted of the CH2 domain and directed against the disialoganglioside GD2

Recombinant techniques allow one to engineer an antibody molecule and, in this way, manipulate its properties and functions. The authors engineered a chimeric human/mouse antibody to the tumor-associated antigen ganglioside GD2, with the aim of decreasing its serum half-life, maintaining its full antigen-binding capacity, and deleting its effector functions, thus making it a potentially useful reagent for the radioimaging of tumors. To this end, the constant region of the human γ1 chain was mutated by deleting the second domain (CH2). Here the authors show that the CH2-deleted antibody (ch14.18-ΔCH2) was cleared from the blood of athymic (nu/nu) mice bearing human melanoma tumors with the same kinetics as human IgG F(ab')2. At a β t1/2 of 12 hr, 0.9% of the injected dose of 125I-labeled ch14.18-ΔCH2 was found per milliliter of blood 24 hr after i.v. injection. In biodistribution experiments, 125I-labeled ch14.18-ΔCH2 targeted specifically to melanoma xenografts, achieving optimal tumor-to-tissue ratios 12-16 hr after i.v. injection. ch14.18-ΔCH2 was localized to the melanoma tumors more rapidly and with better localization ratios than the intact chimeric antibody ch14.18. Sixteen hours after i.v. injection, the tumor-to-blood and tumor-to-liver ratios of ch14.18-ΔCH2 were 5 and 12, respectively, while optimal localization ratios obtained for ch14.18 were 1 and 5, respectively, but 96 hr after injection. A reagent such as ch14.18-ΔCH2 should be useful for radioimmunodetection of human tumors because of reduced immunogenicity, increased targeting specificity, and rapid clearance from circulation