TARGETED ELIMINATION OF CELLS EXPRESSING THE HIGH-AFFINITY RECEPTOR FOR IGE (FC-EPSILON-RI) BY A PSEUDOMONAS EXOTOXIN-BASED CHIMERIC PROTEIN

The interaction between IgE and its high-affinity receptor Fc epsilon RI found on mast cells and basophils is the primary effector pathway i n allergic response. To achieve a targeted elimination of cells expres sing Fc epsilon RI receptors, we constructed a chimeric protein in whi ch a Fc fragment of mouse IgE is attached to a truncated form of Pseud omonas exotoxin (PE). To prepare the targeting moiety, we used a DNA s equence corresponding to amino acids 301-437, representing 30 residues of domain 2 and domain 3 of the mouse IgE constant region. This seque nce was fused at the 5' of a cDNA encoding PE(40), a truncated form of PE lacking the cell binding domain. The chimeric protein, termed FC2' -3-PE(40), was expressed in Escherichia coli and partially purified. T he protein is highly cytotoxic to mouse mast cell lines and bone marro w-derived primary mast cells. This cytotoxicity is specific, as it cou ld be blocked upon addition of whole IgE. Moreover, the protein had no effect on other cell lines of hemopoietic origin. The FC2'-3-PE(40) c himeric protein offers a new approach to the treatment of allergic dis orders.