Chimeric immunoglobulin E reactive with tumor-associated antigen activates human FcεRI bearing cells

Crosslinking of immunoglobulin E molecules that are bound to the Fcε receptors expressed on mast cells or basophils triggers activation of these cells, resulting in the development of a type I hypersensitivity. Targeting this potent immune reaction towards tumors by using IgE that reacts with a tumor-associated antigen, may induce a local inflammation at the tumor site, and may therefore promote tumor regression. We have previously shown that murine IgE bound to tumor cells can activate murine mast cells to release TNF-α and histamine. To further investigate the therapeutic potential of IgE-mediated immunotherapy of carcinomas, we have developed human/murine chimeric versions, containing the murine variable regions and human constant regions, of both G250 and 323/A3 IgE. These chimeric IgEs are reactive respectively with the G250 renal cell carcinoma antigen and the Ep-CAM molecule, which is highly expressed by most carcinomas. Transfection of the respective chimeric heavy and light chain genes into recipient Sp2/0 myeloma cells yielded chimeric IgE-producing clones. Chimeric G250 and 323/A3 IgE reacted with tumor cells expressing the G250 antigen or Ep-CAM, respectively. To generate a cell line that expresses Fe receptors for human or chimeric IgE, the rat basophilic leukemia cell line RBL-7 was transfected with the human FcεRI α chain (RBL-7TZ) and subsequently tested for binding of chimeric IgE. Functional assays showed that both chimeric IgEs activated RBL-7TZ cells to release TNF-α when cultured with tumor cells that express the respective specific antigen. Furthermore, both chimeric IgEs were able to activate freshly isolated human basophils.