Targeted Fc2'-3-PE40 chimeric protein abolishes passive cutaneous anaphylaxis in mice.

The alarming increase in the incidence of allergic diseases in the past decade has led to a clear call for more effective treatment. Recently, we reported on the construction of a chimeric protein for targeted elimination of cells expressing FcepsilonRI receptors. This chimeric protein, designated Fc2'-3-PE40, is composed of a Fc fragment of mouse IgE attached to a truncated form of Pseudomonas exotoxin. The Fc2'-3-PE40 chimeric protein was found to be highly cytotoxic to mouse mast cell lines and primary mouse mast cells. We now demonstrate that Fc2'-3-PE40 successfully prevents the development of passive cutaneous anaphylaxis reaction (PCA) in mice. Treatment with Fc2'-3-PE40 for 7 days prevented the PCA reaction in mice by 80% compared with that in control mice given only PBS. Fc2'-3-PE40M, the mutated, enzymatically inactive analogue of Fc2'-3-PE40, did not display this activity. Fc2'-3-PE40 was also effective when given as a single dose 16 h before antigen exposure, resulting in complete inhibition of the PCA reaction. Moreover, treatment with Fc2'-3-PE40 did not cause mast cell degranulation, as the serum histamine values of mice treated with Fc2'-3-PE40 were within the range obtained for control, untreated mice. Thus, the Fc2'-3-PE40 chimeric protein offers a novel approach to the treatment of allergic disorders.