Apoptosis-Inducing Human-Origin Fcε-Bak Chimeric Proteins for Targeted Elimination of Mast Cells and Basophils: A New Approach for Allergy Treatment

Abstract

During the past few years, many chimeric proteins have been developed to specifically target and kill cells expressing specific surface molecules. Generally these molecules carry a bacterial or plant toxin to destroy the unwanted cells. The major obstacle regarding these molecules in their clinical application is the immunogenicity and nonspecific toxicity associated with bacterial or plant toxins. We lately reported a new approach for construction of chimeric proteins: we successfully replaced bacterial or plant toxins with human apoptosis-inducing proteins. The resulting chimeras were shown to specifically induce apoptosis in the target cells. Taking advantage of the human apoptosis inducing proteins Bak and Bax as novel killing components, we have now constructed new chimeric proteins targeted against the human FcεRI, expressed mainly on mast cells and basophils. These cells are the main effectors of the allergic response. Treatment of the target cells with the new chimeric proteins, termed Fcε-Bak/Bax, had a dramatic effect on cell survival, causing apoptosis. The effect was specific to cells expressing the FcεRI of both human and, very unexpectedly, also of mouse origin. Moreover, interaction of the chimeric proteins with the mast cells did not cause degranulation. Fcε-Bak/Bax are new chimeric proteins of human origin and, as such, are expected to be both less immunogenic and less toxic and, thus, may be specific and efficient reagents for the treatment of allergic diseases.

Current Progress in the Understanding of IgE-FcεRI Interaction

“…In a strategy to deplete granulocytes expressing FcεRI, Cε3 fusion to the N-terminus of Bak, an apoptosis-inducing protein acting in the cytoplasm, was reported [32]. Surprisingly, the chimeric protein was refolded from E. coli inclusion bodies, presented internalization by granulocytes and was effective in inducing apoptosis [32]. These results are in contradiction with the above-mentioned expression of Cε3 in E. coli , probably implying that fusion to Bak helps refolding.…”

“…It is now clear that, due to FcεRI asymmetric interaction with IgE, Cε3 needs to be dimeric to present a complete binding site to FcεRI [13]. In a strategy to deplete granulocytes expressing FcεRI, Cε3 fusion to the N-terminus of Bak, an apoptosis-inducing protein acting in the cytoplasm, was reported [32]. Surprisingly, the chimeric protein was refolded from E. coli inclusion bodies, presented internalization by granulocytes and was effective in inducing apoptosis [32].…”

Induction of Apoptosis in Human Basophils by Anti-Fas Antibody Treatment in vitro

“…In spite of the importance of basophils in allergic inflammation [1, 11], the details of basophil-targeting therapy have not been investigated [41]. The intraperitoneal administration of anti-Fas mAb in mice rapidly killed wild-type mice but not lpr mice, by severely damaging the liver through the induction of apoptosis [42].…”

Mitochondria as therapeutic targets for cancer chemotherapy

“…Similarly, Bak can be targeted to the Fce receptor by fusing it to the constant region of the immunoglobulin E molecule. This fusion protein has been shown to selectively induce apoptosis in vitro in IgE producing cells, such as mast cells and basophils (Belostotsky and Lorberboum-Galski, 2001). An antisense oligonucleotide designed to downregulate the expression of Bcl-2 (Genasense, G3139, Oblimersen) is being evaluated in phase I/II trials against solid and hematopoietic neoplasia (Tolcher, 2005).…”