Idarubicin-145-2C11-F(ab ')2 promotes peripheral tolerance and reduces chronic vascular disease in mouse cardiac allografts

In order to reduce the toxic effects of the T cell activating anti-CD3 mono clonal antibody, 145-2C11, F(ab')2 fragments were prepared by pepsin digest ion. These fragments were then used as nonimmunosuppressive carriers for th e cytotoxic drug idarubicin (IDA), to reduce toxicity of both the monodonal antibodies (mAb) and the drug and to increase the specificity of drug deli very. The IDA-145-2C11 F(ab')2 immunoconjugate was tested for specificity b y fluorometry. 145-2C11 intact antibody, 145-2C11 F(ab')2 and IDA conjugate s of the antibody and F(ab')2 were used to treat CBA recipients of BALB/c v ascularized cardiac allografts. Mice with hearts surviving >100 days were c hallenged with donor and third party (C57BL/6) skin grafts. Although both a ntibody and F(ab')2 blocked the binding of 145-2C11-FITC to CBA spleen cell s, only the intact antibody caused sustained depletion of CD3 cells in vivo . 145-2C11 F(ab')2 blocked cell surface CD3 within 30 min, but was cleared in 24 h without depletion of CD3 cells from the spleen. In BALB/c to CBA ca rdiac allografts (rejected in 12-17 days), IDA-145-2C11 F(ab')2 (0.2 mg/ 20 g mouse i.p. at the time of transplantation) induced >100 days' allograft survival and specific tolerance, in contrast to the equivalent dose of 145- 2C11 F(ab')2 (mean survival 25 days). Hearts from IDA-145-2C11 F(ab')2-trea ted mice at >100 days showed decreased cellular infiltration and less chron ic vascular disease than long-surviving hearts from mice treated with an al ternative antibody, KT3. Thus, F(ab')2 prepared from 145-2C11 provided a su itable CD3-specific, nonimmunosuppressive carrier for IDA. This immunoconju gate was more effective against both acute and chronic rejection than other conjugates or whole antibody. IDA-145-2C11 F(ab')2 is an effective, nontox ic tolerogen in the mouse cardiac allograft model.