Therapeutic potency of IL2-caspase 3 targeted treatment in a murine experimental model of inflammatory bowel disease.

BACKGROUND: Inflammatory bowel disease (IBD) comprises primarily the two disorders - ulcerative colitis and Crohn's disease - that involve deregulated T cell responses. The ever-increasing incidence rate of Crohn's disease and ulcerative colitis during recent decades, combined with the limited efficacy and potential adverse effects of current treatments, explain the real need for seeking more specific and selective methods for treating these diseases. AIM: To investigate the ability of interleukin 2 (IL2)-caspase 3 chimeric protein, designed to target activated T lymphocytes that express the high-affinity IL2 receptor, to ameliorate the clinical symptoms of acute murine experimental colitis, using a mouse model of dextran sodium sulfate (DSS)-induced colitis. METHODS: Mice with DSS-induced colitis were treated with IL2-caspase 3 for 7 days and disease severity was assessed in parallel to control, non-treated mice, receiving only daily injections of phosphate-buffered saline. IL2-caspase 3 was tested both for its ability to prevent the development of colitis, and for its therapeutic potential to cure on-going, active acute disease. In addition, colon tissue samples were used for myeloperoxidase assays and RNA isolation followed by polymerase chain reaction to determine mRNA expression levels of specific genes. RESULTS: Treatment with IL2-caspase 3 dose-dependently ameliorated the disease activity index (DAI) of mice colitis. We achieved up to 78% improvement in DAI with intravenous injections of 15 microg/mouse/day. Furthermore, IL2-caspase 3 decreased neutrophil and macrophage infiltration to the inflamed tissue by up to 57%. IL2-caspase 3 was proven as a therapeutic reagent in another model, where treatment begins only after disease onset. Here we demonstrated a 70% decrease in DAI when compared to non-treated sick mice. A reduction in mRNA expression levels of both IL1 beta and tumour necrosis factor alpha was found in lysates of total colon tissue of treated mice, as compared to sick, untreated mice. We also found that expression levels of Bcl2 were significantly decreased after treatment, while Bax was upregulated in comparison to non-treated mice. Moreover, the Bcl2/Bax ratio, which is elevated in both experimental colitis and in human Crohn's disease, decreased dramatically after treatment. CONCLUSIONS: IL2-caspase 3 chimeric protein may provide a novel approach to the therapy of human IBD, and a possible suggested treatment for other pathological conditions that involve uncontrolled expansion of activated T cells.

B-cell non-Hodgkin's lymphoma: evidence for the t (14;18) translocation in all hematopoietic cell lineages.

BACKGROUND: B cells of patients with non-Hodgkin's lymphoma (B-NHL) harbor specific chromosomal translocations, including t(14;18), the most common aberration found in this disease. The translocation involves the immunoglobulin (Ig) heavy-chain joining (JH) region gene on chromosome 14 and the BCL2 gene on chromosome 18, resulting in dysregulated expression of the BCL2 gene. The t(14;18) translocation has been thought to occur in the pre-B-cell stage, during the first event of Ig gene rearrangement. PURPOSE: This study was conducted to investigate the potential involvement of nonlymphoid lineages in B-NHL. METHODS: We studied the t(14;18) translocation and other frequently occurring translocations in total bone marrow aspirates of 10 patients with B-NHL, with the use of the fluorescence in situ hybridization (FISH) technique. We also performed cytogenetic analyses on representative bone marrow aspirates from the patients. Moreover, to define which of the major cell lineages present in the bone marrow carry the t(14;18) translocation, we used a series of monoclonal antibodies together with fluorescence-activated cell sorter (FACS) analyses to purify cells positive for CD3 (T cells), CD19 (B cells), CD10 (CALLA-positive cells), CD41a (megakaryocytic cells), CD13 (myeloid cells), and glycophorin A (erythroid cells). The cells of each subgroup underwent FISH analysis with the use of JH and BCL2 probes to detect the t(14;18) translocation. Bone marrow samples obtained from five healthy donors served as controls. RESULTS: Bone marrow cells from eight of the 10 patients studied carried the t(14;18) translocation. When present, the translocation was observed in many or even all of the cell lineages (lymphoid, myeloid, megakaryocytic, and erythroid) present in the bone marrow, including peripheral blood progenitor stem cells; for seven of the eight patients carrying the translocation, it was found in 96%-100% of the unfractionated bone marrow cells as well as in all of the FACS-purified cell fractions in which it could be detected or studied. Conventional cytogenetic analyses performed on representative bone marrow aspirates confirmed the results obtained by FISH analysis. Cells in control bone marrow samples obtained from the five healthy donors were negative for the t(14;18) translocation by FISH analysis. CONCLUSIONS: Our findings indicate that the t(14;18) translocation most probably occurs in a very early multilineage progenitor stem cell. IMPLICATIONS: Given that the t(14;18) chromosomal translocation was found in all types of bone marrow cells when only the B cells were malignant, our results suggest that this translocation is not sufficient to induce neoplastic transformation. This finding underscores the need for the development of new approaches for the detection and surveillance of B-NHL.

Characteristics of Mitochondrial Transformation into Human Cells.

Mitochondria can be incorporated into mammalian cells by simple co-incubation of isolated mitochondria with cells, without the need of transfection reagents or any other type of intervention. This phenomenon was termed mitochondrial transformation, and although it was discovered in 1982, currently little is known regarding its mechanism(s). Here we demonstrate that mitochondria can be transformed into recipient cells very quickly, and co-localize with endogenous mitochondria. The isolated mitochondria interact directly with cells, which engulf the mitochondria with cellular extensions in a way, which may suggest the involvement of macropinocytosis or macropinocytosis-like mechanisms in mitochondrial transformation. Indeed, macropinocytosis inhibitors but not clathrin-mediated endocytosis inhibition-treatments, blocks mitochondria transformation. The integrity of the mitochondrial outer membrane and its proteins is essential for the transformation of the mitochondria into cells; cells can distinguish mitochondria from similar particles and transform only intact mitochondria. Mitochondrial transformation is blocked in the presence of the heparan sulfate molecules pentosan polysulfate and heparin, which indicate crucial involvement of cellular heparan sulfate proteoglycans in the mitochondrial transformation process.

Surface antigens/receptors for targeted cancer treatment: the GnRH receptor/binding site for targeted adenocarcinoma therapy.

Colon, breast and lung adenocarcinomas - three of the major malignancies occurring in humans, together with ovarian, endometrial, kidney and liver adenocarcinomas, account for more then 50% of cancer-related death. As the number of cancer-related deaths has not decreased in recent years, major efforts are being made to find new and more specific drugs for cancer treatment. One of the approaches developed in recent years for targeted cancer therapy is the construction and use of chimeric proteins. Chimeric cytotoxins are a class of targeted molecules designed to recognize and specifically destroy cells over-expressing specific receptors. These molecules, designed and constructed by gene fusion techniques, comprise both the cell-targeting and the cell-killing moieties. Our laboratory has developed a number of chimeric proteins based on an analog of Gonadotropin Releasing Hormone (GnRH) as their targeting moiety. These chimeras recognize a GnRH-binding site that, we found, was over-expressed on a surprisingly wide variety of cancers, all confined to the adenocarcinoma type. A GnRH analog was fused to a large number of killing moieties, including bacterial or human pro-apoptotic proteins. All GnRH-based chimeric proteins selectively killed adenocarcinoma cells both in vitro and in vivo. Utilizing GnRH-based chimeric proteins for targeted therapy could open up new vistas in the fight against adenocarcinomas in humans. This review summarizes the latest developments in the area of targeted cancer therapy via specific antigens/receptors, as well as our latest findings in targeting GnRH-binding sites using GnRH-based chimeric proteins for specific and targeted adenocarcinoma therapy in humans.

Interleukin 2-Bax: a novel prototype of human chimeric proteins for targeted therapy.

During the past few years many chimeric proteins have been developed to target and kill cells expressing specific surface molecules. Generally, these molecules carry a bacterial or plant toxin that destroys the unwanted cells. The major obstacle in the clinical application of such chimeras is their immunogenicity and non-specific toxicity. We have developed a new generation of chimeric proteins, taking advantage of apoptosis-inducing proteins, such as the human Bax protein, as novel killing components. The first prototype chimeric protein, IL2-Bax, directed toward IL2R-expressing cells, was constructed, expressed in Escherichia coli and partially purified. IL2-Bax increased the population of apoptotic cells in a variety of target T cell lines, as well as in human fresh PHA-activated lymphocytes, in a dose-dependent manner and had no effect on cells lacking IL2R expression. The IL2-Bax chimera represents an innovative approach for constructing chimeric proteins comprising a molecule that binds a specific cell type and an apoptosis-inducing protein. Such new chimeric proteins could be used for targeted treatment of human diseases.

Chimeric cytotoxin IL2-PE40 inhibits relapsing experimental allergic encephalomyelitis.

IL2-PE40 is a chimeric protein composed of human interleukin-2 (IL2) genetically fused to a modified form of Pseudomonas exotoxin lacking the cell recognition domain. IL2-PE40 is cytotoxic for IL2 receptor-bearing lymphocytes in culture and can inhibit activation of T cells in vivo. IL2-PE40 can significantly diminish antigen-stimulated proliferation of lymphocytes sensitized to myelin basic protein. Intraperitoneal administration of IL2-PE40 not only markedly inhibits the clinical manifestations of adoptively transferred relapsing experimental allergic encephalomyelitis but also dramatically reduces both inflammation and demyelination characteristic of the disease.

Treatment of corneal allograft rejection with the cytotoxin IL-2-PE40.

IL-2-PE40 is a recombinant chimeric protein composed of IL-2, fused to a modified pseudomonas exotoxin. This molecule is extremely toxic to activated T cells expressing high-affinity IL-2R. We used this new molecule for selective immunosuppression to treat corneal allograft rejection in the rat, using Fisher and Lewis rats, a strain combination differing only in medial and minor histocompatibility antigens. The effect of IL-2-PE40 on the immunologic response was studied using both a heterotopic corneal graft model and orthotopic grafts. At the dose of 0.31 micrograms/g given intraperitoneally every 12 hr, IL-2-PE40 produced a significant reduction of both total lymph node cells and cytotoxic-T-cell (CTL) activity in draining lymph nodes (DLN) of heterotopically grafted animals. IL-2-PE40 treatment also significantly reduced the clinical rejection score and cumulative rejection rate (CRR) in orthotopic grafts and appears to be a very effective immunosuppressive agent.

A novel antigen-toxin chimeric protein: myelin basic protein-pseudomonas exotoxin (MBP-PE 40) for treatment of experimental autoimmune encephalomyelitis.

Myelin basic protein (MBP), is a major component of the central nervous system (CNS) myelin. MBP can stimulate T cells that migrate into the CNS, initiating a cascade of events that result in perivascular infiltration and demyelination. EAE is an inflammatory and demyelinating autoimmune disease of the CNS that serves as a model for the human disease Multiple Sclerosis (MS). Taking advantage of the fact that EAE can be mediated by T cells, able to recognize MBP or its peptides, we developed a new approach to target anti-MBP T cells by fusing an MBP-sequence to a toxin. In the new chimeric protein, an oligonucleotide coding for the guinea pig MBP encephalitogenic moiety (residues 68-88) was fused to a cDNA encoding a truncated form of the PE gene (PE40). The chimeric gene termed MBP-PE was expressed in E. coli and highly purified. MBP-PE chimeric protein was cytotoxic to various anti-MBP T cells. Moreover, treatment with the novel MBP-toxin blocked the clinical signs of EAE as well as CNS inflammation and demyelination. A chimeric protein such as MBP-PE40 presents a novel prototype of chimeric proteins, composed of antigen/peptide-toxin, that could prove to be an efficient and specific immunotherapeutic agent for autoimmune diseases in which a known antigen is involved.

Detection of minimal residual disease state in chronic myelogenous leukemia patients using fluorescence in situ hybridization.

Detection of minimal residual disease and relapse remain major problems in chronic myelogenous leukemia (CML) patients following bone marrow transplantation (BMT). In order to disclose the 9;22 Philadelphia translocation, we used a fluorescence in situ hybridization (FISH) technique. BCR and ABL gene fragments were used as probes for the detection of the BCR/ABL fusion product in peripheral blood and bone marrow cells from 11 CML patients in which 5 were post-BMT. The sensitivity and specificity of this approach were compared to conventional cytogenetic and polymerase chain reaction (PCR) methods. FISH demonstrated a high degree of sensitivity (1%) for the detection of the BCR/ABL translocation in these patients. A linear correlation was found between FISH detection of the BCR/ABL fusion product and routine chromosomal analysis (r = 0.995; p < 0.001). Detection of the BCR/ABL signal by FISH was observed in all patients showing a positive PCR signal. A significant reduction in BCR/ABL signal was observed post-transplant (p < 0.001). However, the BCR/ABL translocation was detected in four of five transplanted patients immediately (0.75-2.5 months) following transplant and was found in patients with a low expression of the translocation.

Interleukin-2 Pseudomonas exotoxin chimeric protein is cytotoxic to B cell cultures derived from myasthenia gravis patients.

IL-2-PE664Glu is a chimeric cytotoxin consisting of interleukin-2 (IL-2) fused to a mutant form of Pseudomonas exotoxin (PE664Glu). The chimeric cytotoxin has been previously shown to be extremely toxic to both phytohaemagglutinin blasts and mixed leukocyte reaction blasts prepared from monkey and human lymphocytes. To explore the possible clinical utility of IL-2-PE664Glu for autoimmune diseases, particularly in which B cells are involved, we tested the sensitivity of B cell lines derived from myasthenia gravis patients to this chimeric cytotoxin. 65% (15 out of 23) of the tested B cell lines were sensitive to IL-2-PE664Glu mediated cytotoxicity. B cell lines from control donors as well as from patients with another autoimmune disease, multiple sclerosis, were much less sensitive to IL-2-PE664Glu cytotoxicity. Moreover, a control protein lacking the IL-2 as the targeting moiety of the chimera, had no effect toward all B cell lines tested, thus establishing its specific activity. A detailed study of the IL-2 receptor of the patients' B cells, using the PCR technique and FACS analysis, showed that the cells express mainly the beta and gamma chains and at a lower level also the alpha-chain of the IL-2 receptor. Our results suggest that IL-2-PE664Glu could be effective for selective targeted immunotherapy of myasthenia gravis patients.

Ocular distribution of the chimeric protein IL2-PE40.

A construct of IL-2 and pseudomonas exotoxin (PE40) has been genetically engineered. An aliquot of 100 microliter of the chimeric protein, radiolabelled with I125, was administered to healthy rats by various routes. At different intervals, ocular and non ocular tissues were removed and the levels of the radiolabelled chimeric protein IL-2-PE40 measured. Systemic administration of IL2-PE40 either intravenously (IV) or intraperitoneally (IP) leads to high levels of the drug in the blood, liver and spleen. Little or no radioactivity is observed within the ocular tissues using this route. On the other hand, local administration of the drug either as subtenon injection or as eye drops resulted in a very high concentration of the drug within the conjunctiva, cornea and sclera, with little radioactivity detected systemically. Subtenon injection induced a significant drug level within the optic nerve. With the drops, the chimeric protein was also detected, in low levels, intraocularly.

Linker-based GnRH-PE chimeric proteins inhibit cancer growth in nude mice.

Since the number of cancer-related deaths has not decreased in recent years, major efforts are being made to find new drugs for cancer treatment. In this report we introduce the gonadotropin releasing hormone-Pseudomonas exotoxin (GnRH-PE) based chimeric proteins L-GnRH-PE66 and L-GnRH-PE40. These proteins are composed of a GnRH moiety attached to modified forms of Pseudomonas exotoxin via a polylinker (gly4ser)2. The chimeric proteins L-GnRH-PE66 and L-GnRH-PE40 have the ability to target and kill adenocarcinoma cell lines in vitro, whereas non-adenocarcinoma cell lines are not affected. We demonstrate that L-GnRH-PE66 and L-GnRH-PE40 efficiently inhibit cancer growth. Nude mice were injected subcutaneously with the SW-48 adenocarcinoma cell line to produce xenograft tumours. When the tumours were established and visible, the animals were injected with chimeric proteins for 10 days. At the end of this period, a reduction of up to 3-fold in tumor size was obtained in the treated mice, as compared with the control group, which received equivalent amounts of GnRH; the difference was even greater 13 days after termination of treatment. Thus, the chimeric proteins L-GnRH-PE66 and L-GnRH-PE40 are promising candidates for treatment of a variety of adenocarcinomas and their use in humans should be considered.

GnRH-Bik/Bax/Bak chimeric proteins target and kill adenocarcinoma cells; the general use of pro-apoptotic proteins of the Bcl-2 family as novel killing components of targeting chimeric proteins.

In recent years chimeric proteins carrying bacterial toxins as their killing moiety, have been developed to selectively recognize and kill cell populations expressing speciific receptors. The involvement of Gonadotropin releasing hormone (GnRH) has been demonstrated in several adenocarcinomas and a GnRH-bacterial toxin chimeric protein (GnRH-PE66) was thus developed and found to specifically target and kill adenocarcinoma cells both in vitro and in vivo. Because of the immunogenicity and the non-specific toxicity of the bacterial toxins, we have developed new chimeric proteins, introducing apoptosis inducing proteins of the Bcl-2 family as novel killing components. Sequences encoding the human Bik, Bak or Bax proteins were fused to the GnRH coding sequence at the DNA level and were expressed in E. coli. GnRH-Bik, GnRH-Bak and GnRH-Bax new chimeric proteins efficiently and specifically inhibited the cell growth of adenocarcinoma cell lines and eventually led to cell death. All three Bcl2-proteins-based chimeric proteins seem to induce apoptosis within the target cells, without any additional cell death stimulus. Apoptosis-inducing-proteins of the Bcl-2 family targeted by the GnRH are novel potential therapeutic reagents for adenocarcinoma treatment in humans. This novel approach could be widely applied, using any molecule that binds a specific cell type, fused to an apoptosis-inducing protein.

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 in allergic response. To achieve a targeted elimination of cells expressing Fc epsilon RI receptors, we constructed a chimeric protein in which a Fc fragment of mouse IgE is attached to a truncated form of Pseudomonas exotoxin (PE). To prepare the targeting moiety, we used a DNA sequence corresponding to amino acids 301-437, representing 30 residues of domain 2 and domain 3 of the mouse IgE constant region. This sequence was fused at the 5' of a cDNA encoding PE40, a truncated form of PE lacking the cell binding domain. The chimeric protein, termed Fc(2'-3)-PE40, was expressed in Escherichia coli and partially purified. The protein is highly cytotoxic to mouse mast cell lines and bone marrow-derived primary mast cells. This cytotoxicity is specific, as it could be blocked upon addition of whole IgE. Moreover, the protein had no effect on other cell lines of hemopoietic origin. The Fc(2'-3)-PE40 chimeric protein offers a new approach to the treatment of allergic disorders.

Apoptosis-inducing human-origin Fcepsilon-Bak chimeric proteins for targeted elimination of mast cells and basophils: a new approach for allergy treatment.

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 FcepsilonRI, 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 Fcepsilon-Bak/Bax, had a dramatic effect on cell survival, causing apoptosis. The effect was specific to cells expressing the FcepsilonRI of both human and, very unexpectedly, also of mouse origin. Moreover, interaction of the chimeric proteins with the mast cells did not cause degranulation. Fcepsilon-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.

IL-2-PE40 is cytotoxic for activated T lymphocytes expressing IL-2 receptors.

IL-2-PE40 is a chimeric molecule in which IL-2 is attached to the amino end of modified Pseudomonas exotoxin molecule lacking cell recognition domain. This molecule was extremely toxic for Con A-stimulated spleen cells from mice. Moreover, IL-2-PE40 has suppressive effect against Ag-activated cells; it inhibits the generation of cytotoxic T lymphocyte activity in a MLC. IL-2-PE40 could be a useful agent in IL-2R targeting therapy including immunosuppressive therapy for allograft rejection or some autoimmune diseases.

Adenocarcinoma cells are targeted by the new GnRH-PE66 chimeric toxin through specific gonadotropin-releasing hormone binding sites.

Luteinizing hormone-releasing hormone, also termed gonadotropin-releasing hormone (GnRH), accounts for the hypothalamic-pituitary gonadal control of human reproduction. The involvement of GnRH has been demonstrated in several carcinomas of hormone-responsive tissues. Exploiting this common feature, we constructed a Pseudomonas exotoxin (PE)-based chimeric toxin (GnRH-PE66) aimed at targeting those cancer cells bearing GnRH binding sites. We report here the strong growth inhibition and killing of a surprisingly wide variety of cancers, confined to the adenocarcinoma type. These cancer cells arising from hormone-responsive tissues, as well as non-responsive ones, express specific GnRH binding sites as indicated by the marked killing of ovarian, breast, endometrial, cervical, colon, lung, hepatic, and renal adenocarcinoma. This cytotoxicity is specific as it could be blocked upon addition of excess GnRH. The specificity of GnRH-PE66 chimeric toxin was also confirmed by GnRH binding assays, and its ability to prevent the formation of colon cancer xenografts in nude mice is presented. Although the functional role of specific GnRH binding sites in human carcinomas remains obscure, GnRH-PE66 displays considerable targeting potential and its use as a therapeutic agent for cancer should be considered.

I.V. Administration of L-GNRH-PE66 efficiently inhibits growth of colon adenocarcinoma xenografts in nude mice.

When developing new anti-cancer therapeutic treatments, it is crucial to find the correct route of administration and timetable for treatment. Recently, we constructed the L-GnRH-PE66 chimeric protein, which can target and kill adenocarcinoma cells both in vitro and in vivo. We examined the ability of the L-GnRH-PE66 chimeric protein to inhibit tumor growth in colon carcinoma xenografted nude mice, using different routes of administration and various timetables of treatment. In addition, we examined the ability of the chimeric protein to inhibit tumor growth of large tumors that resemble those encountered in human patients in the clinical setting. We found that an i.v. dose of 12.5 microg given every 48 hr was the most efficacious in inhibiting tumor growth. Tumors treated with this concentration of the chimeric protein were 4.4 times smaller in volume and 3.4 times smaller in weight than those in the control groups. This protocol of L-GnRH-PE66 treatment is an improvement on our previously suggested treatment for adenocarcinoma in humans. An i.v. injection every 48 hr is effective, less toxic and less painful. Our results further support the use of L-GnRH-PE66 as an effective treatment for adenocarcinoma in humans.

Interleukin 2 pseudomonas exotoxin (IL2-PE66(4)Glu) chimeric protein kills B cells from patients with Myasthenia gravis.

IL2-PE66(4)Glu is a chimeric cytotoxin consisting of interleukin 2 (IL2) fused to a mutant form of Pseudomonas exotoxin (PE66(4)Glu). The chimeric cytotoxin has been previously shown to be extremely toxic to both phytohemagglutinin blasts and mixed leukocyte reaction blasts prepared from monkey and human lymphocytes. To explore the possible clinical utility of IL2-PE66(4)Glu for autoimmune diseases, particularly in which B cells are involved, we tested fresh B cells from patients with myasthenia gravis for sensitivity to this chimeric cytotoxin. Seventy-six percent (16 of 21) of the B cells tested were markedly sensitive to IL2-PE66(4)Glu-mediated cytotoxicity, with inhibition of protein synthesis ranging from 20 to 92%. B cells from control donors were much less sensitive to IL2-PE66(4)Glu cytotoxicity. Moreover, a control protein lacking IL2 as the targeting moiety of the chimera had no effect toward all B cells tested, thus establishing its specific activity. Our results suggest that IL2-PE66(4)Glu could be an effective tool for selective targeted immunotherapy of myasthenia gravis patients.

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.