Functional properties of antibody insulin-like growth factor fusion proteins

Genetic engineering and expression techniques have been used to produce antibody growth factor fusion proteins. Insulin-like growth factors (IGFs) 1 and 2 have been fused to mouse-human chimeric IgG3 at the end of CH1, immediately after the hinge, and at the end of CH3. Fusion heavy chains of the expected molecular weight were expressed, assembled with a co-expressed light chain, and secreted. The resulting molecules continued to bind antigen; they also bound the growth factor receptors, albeit with decreased affinity. The molecule with IGF1 attached after CH3 (CH3-IGF1) had reduced ability to carry out complement-mediated cytolysis. In contrast the molecule with IGF2 attached after CH3 (CH3-IGF2) showed an approximately 50-fold increase in its ability to effect complement-mediated cytolysis and so should be an effective cytolytic agent. Both CH3-IGF1 and CH3-IGF2 bound Fc gamma RI with affinity similar to that of IgG3. The growth factor fusion proteins showed small but significant uptake into the brain parenchyma.