Construction and Expression of Mouse-human Chimeric Antibody SZ-51 Specific for Human Activated Platelets.

SZ-51, a murine monoclonal antibody (McAb) specific for alpha-granule membrane protein (GMP-140) on the surface of the activated human platelets, has shown promise for thrombus imaging and thrombolysis. In order to reduce the immunogenicity of the murine McAb SZ-51 in man and to obtain a high level of antibody production, we constructed two chimeras (alpha-Lys17-51BVK/Hu, alpha-Lys30-51VH/Hu) by joining the variable regions gene of mouse antibody to the constant regions gene of human immunoglobulin (Ig)(gamma1,k). Both chimeric genes were cloned into two selectable expression vectors separately, which were co-transfected into a non-Ig secreting murine myeloma cell line SP2/0 with the Lipofectin reagent. One transfectoma, which showed stable antigen (GMP-140) binding ability and a high level expression of 5 mg/L, was obtained. Immunoblotting analysis demonstrated that the chimeric antibody in the supernatant, like the native mouse SZ-51, had the characteristic of binding to GMP-140. In addition, the chimeric antibody can bind competitively to activated platelets with (125)I-labeled mouse SZ-51. Therefore, the SZ-51 chimeric antibody may be a potential agent for the diagnosis and therapy of thrombotic diseases in future.