Recombinant anti-human HER2/neu IgG3-(GM-CSF) fusion protein retains antigen specificity and cytokine function and demonstrates antitumor activity

Anti-HER2/neu therapy of human HER2/neu-expressing malignancies such as bre ast cancer has shown only partial success in clinical trials, To expand the clinical potential of this approach, we have genetically engineered an ant i-HER2/neu IgG3 fusion protein containing GM-CSF, Anti-HER2/neu IgG3-(GM-CS F) expressed in myeloma cells was correctly assembled and secreted. It was able to target HER2/neu-expressing cells and to support growth of a GM-CSF- dependent murine myeloid cell line, FDC-P1. The Ab fusion protein activated J774.2 macrophage cells so that they exhibit an enhanced cytotoxic activit y and was comparable to the parental Ab in its ability to effect Ab-depende nt cellular cytotoxicity-mediated tumor cell lysis, Pharmacokinetic studies showed that anti-HER2/neu IgG3-(GM-CSF) is stable in the blood, Interestin gly, the half-life of anti-HER2/neu IgG3-(GM-CSF) depended on the injected dose with longer in vivo persistence observed at higher doses, Biodistribut ion studies showed that anti-HER2/neu IgG3-(GM-CSF) is mainly localized in the spleen, In addition, anti-HER2/neu IgG3-(GM-CSF) was able to target the HER2/neu-expressing murine tumor CT26-HER2/neu and enhance the immune resp onse against the targeted Ag HER2/neu. Anti-HER2/neu IgG3-(GM-CSF) is able to enhance both Th1- and Th2-mediated immune responses and treatment with t his Ab fusion protein resulted in significant retardation in the growth of s.c, CT26-HER2/neu tumors. Our results suggest that anti-HER2/neu TgG3-(GM- CSF) fusion protein is useful in the treatment of HER2/neu-expressing tumor s.