A phase 1 study of a novel fully human BCMA-targeting CAR (CT103A) in patients with relapsed/refractory multiple myeloma.

B-cell maturation antigen (BCMA)-specific chimeric antigen receptor (CAR) T-cell therapies have shown efficacy in relapsed/refractory multiple myeloma (RRMM). Because the non-human originated antigen-targeting domain may limit clinical efficacy, we developed a fully human BCMA-specific CAR, CT103A, and report its safety and efficacy in a phase 1 trial. Eighteen consecutive patients with RRMM, including 4 with prior murine BCMA CAR exposures, were enrolled. CT103A was administered at 1, 3, and 6 × 106 CAR-positive T cells/kg in the dose-escalation phase, and 1 × 106 CAR-positive T cells/kg in the expansion cohort. The overall response rate was 100%, with 72.2% of the patients achieving complete response or stringent complete response. For the 4 murine BCMA CAR-exposed patients, 3 achieved stringent complete response, and 1 achieved a very good partial response. At 1 year, the progression-free survival rate was 58.3% for all cohorts and 79.1% for the patients without extramedullary myeloma. Hematologic toxicities were the most common adverse events; 70.6% of the patients experienced grade 1 or 2 cytokine release syndromes. No immune effector cell-associated neurotoxicity syndrome was observed. To the cutoff date, CAR transgenes were detectable in 77.8% of the patients. The median CAR transgene persistence was 307.5 days. Only 1 patient was positive for the anti-drug antibody. Altogether, CT103A is safe and highly active in patients with RRMM and can be developed as a promising therapy for RRMM. Patients who relapsed from prior murine BCMA CAR T-cell therapy may still benefit from CT103A. This trial was registered at http://www.chictr.org.cn as #ChiCTR1800018137.

Enhancing durability of CIS43 monoclonal antibody by Fc mutation or AAV delivery for malaria prevention.

CIS43 is a potent neutralizing human mAb that targets a highly conserved "junctional" epitope in the Plasmodium falciparum (Pf) circumsporozoite protein (PfCSP). Enhancing the durability of CIS43 in vivo will be important for clinical translation. Here, 2 approaches were used to improve the durability of CIS43 in vivo while maintaining potent neutralization. First, the Fc domain was modified with the LS mutations (CIS43LS) to increase CIS43 binding affinity for the neonatal Fc receptor (FcRn). CIS43LS and CIS43 showed comparable in vivo protective efficacy. CIS43LS had 9- to 13-fold increased binding affinity for human (6.2 nM versus 54.2 nM) and rhesus (25.1 nM versus 325.8 nM) FcRn at endosomal pH 6.0 compared with CIS43. Importantly, the half-life of CIS43LS in rhesus macaques increased from 22 days to 39 days compared with CIS43. The second approach for sustaining antibody levels of CIS43 in vivo is through adeno-associated virus (AAV) expression. Mice administered once with AAV-expressing CIS43 had sustained antibody levels of approximately 300 µg/mL and mediated protection against sequential malaria challenges up to 36 weeks. Based on these data, CIS43LS has advanced to phase I clinical trials, and AAV delivery provides a potential next-generation approach for malaria prevention.

Preparation and identification of an anti-idiotypic antibody antagonist (FG8) for EGFR that shows potential activity against liver cancer cells.

OBJECTIVE: Currently, there are two categories of epidermal growth factor receptor (EGFR) antagonists, small molecule antagonists and anti-EGFR antibodies. In the current study, we developed a new EGFR antagonist employing the anti-idiotypic antibodies strategy. RESULTS: First, using EGF as an antigen, through a series of immunological protocols and hybridoma technology, we obtained an anti-idiotypic antibody against EGF receptor-binding epitopes. On this basis, we screened and characterized the anti-idiotype antibodies against EGFR through competitive ELISA, co-localization analysis, competitive receptor binding analysis, and immunofluorescence. Finally, an internal image anti-idiotype antibody called FG8 was successfully prepared. Experiment result shows that FG8 inhibits EGFR-mediated signaling pathways in vitro. Additionally, FG8 inhibits liver tumor cell proliferation as well as induces tumor cell apoptosis. CONCLUSIONS: The present study suggests that FG8 is a potential therapeutic agent for liver cancer. In addition, this study provides a novel method for the preparation of EGFR antagonists.

Production of an anti-TM4SF5 monoclonal antibody and its application in the detection of TM4SF5 as a possible marker of a poor prognosis in colorectal cancer.

The cell surface transmembrane 4 superfamily member 5 protein (TM4SF5) has been implicated in various human cancers. Immunization with a peptide vaccine targeting human TM4SF5 has been shown to exert prophylactic and therapeutic effects against the development of hepatocellular carcinoma and colon cancer in mouse models. In this study, we developed a novel monoclonal antibody (mEC2­CF) targeting a cyclic epitope of TM4SF5 and evaluated its reactivity to TM4SF5 in colorectal cancer (CRC) cells and cancer tissues. The isotype of mEC2­CF was IgG2a and the antibody specifically recognized the cyclic peptide, based on ELISA. The antibody recognized recombinant TM4SF5 overexpressed in 293F cells, irrespective of N­glycosidase F treatment. The antibody was internalized into the cytosol after binding to the surface of TM4SF5­expressing CRC cells, suggesting that this antibody may be useful in therapeutics. In addition, we evaluated TM4SF5 expression in the tissues of patients with CRC patients to determine its prognostic significance. TM4SF5 expression was assessed by immunohistochemistry using mEC2­CF and tissue microarray blocks of 204 primary CRC samples. The overall rate of TM4SF5 overexpression in the samples (immunohistochemical score >4) was 27.0% (55 of 204). The increased expression of TM4SF5 was significantly associated with a shorter survival rate (P=0.0014) and a worse disease­free survival (P=0.0483) of patients with CRC. No association was observed between TM4SF5 expression and clinicopathological characteristics, apart from tumor depth of invasion (P=0.027). These results suggest that our novel antibody can be used to detect endogenous and recombinant TM4SF5, and that TM4SF5 may be a possible marker for the poor prognosis of patients with CRC.

Reprint of "Anti-therapeutic antibodies and their clinical impact in patients treated with the TNF antagonist adalimumab".

Patients treated with the TNF antagonist adalimumab develop anti-therapeutic antibodies (ATA), the prevalence of which varies depending on the assay used. Most assays are compromised due to the presence of adalimumab in the clinical samples. Our objective was to develop an antibody assay, applicable for clinical testing, which overcomes the limitation of therapeutic interference and to further determine the relationship between ATA development, adalimumab levels and disease activity in patients with rheumatoid arthritis (RA), psoriatic arthritis (PsA) or ankylosing spondylitis (AS). Use of an electrochemiluminescence platform permitted development of fit-for-purpose immunoassays. Serum samples from patients, taken prior to and at 12 and 24 weeks of treatment, were retrospectively analysed for levels of adalimumab and ATA. Overall, the antibody prevalence was 43.6% at 12 weeks and 41% at 24 weeks of treatment. Disruption of immune complexes by acid dissociation, a strategy often adopted for this purpose, only marginally increased the antibody prevalence to 48.7% and 46% at 12 and 24 weeks respectively. We found that antibody formation was associated with decreasing levels of circulating adalimumab, but no direct effect on disease activity was evident as assessed using DAS28 for RA patients and BASDAI for PsA and AS patients. However, a negative correlation of free adalimumab trough levels with disease activity scores was observed. Data showed that adalimumab levels can serve as an indicator of ATA development which can then be confirmed by ATA testing. Monitoring of both therapeutic and antibodies should be considered during adalimumab therapy to allow clinicians to personalise treatments for maximal therapeutic outcomes.

Isolation, production, and characterization of a new single chain anti-idiotypic antibody against benzo[a]pyrene.

Polycyclic aromatic hydrocarbons are chemical carcinogens which could induce the development of human cancers. Anti-idiotypic antibodies against benzo[a]pyrene (BP) are perspective for human cancer immunoprophylaxis and tumor immunodiagnostic techniques. The purpose of this study was to isolate anti-idiotypic antibodies against BP from human lymphocytes naïve phage library. The anti-idiotypic antibody, named B5, was selected. Analysis of the nucleotide and amino acid sequences B5 showed no similarity to known protein databases antibodies. B5 bound idiotypic antibodies against BP in direct and competitive ELISA. It was suggested that the B5 carried an immunological image of BP and bound the idiotypic antibodies against BP. ABBREVIATIONS: scFv: single-chain variable fragment; Ab1: idiotypic antibodies; Ab2: anti-idiotypic antibodies; CBD: cellulose binding domain; BSA: bovine serum albumin; PBS: phosphate buffer; BP-BSA: benzo[a]pyrene-BSA conjugate; Cr-BSA: chrysene-BSA conjugate; Py-BSA: pyrene-BSA conjugate; Ac-BSA: anthracene-BSA conjugate; Ba-BSA: benz[a]anthracene-BSA conjugate; PAH: polycyclic aromatic hydrocarbons; pSh: mouse idiotypic single-chain variable fragment against benzo[a]pyrene; T72: human idiotypic single-chain variable fragment against benzo[a]pyrene.

Incidence, Prevention and Management of Anti-Drug Antibodies Against Therapeutic Antibodies in Inflammatory Bowel Disease: A Practical Overview.

The introduction of biologic therapy has revolutionized the treatment of inflammatory bowel disease (IBD). However, like all therapeutic proteins, monoclonal antibodies have immunogenic potential which is influenced by multiple drug- and patient-related factors. The reported incidence of anti-drug antibodies (ADAs) towards biologic drugs in IBD varies greatly in the literature and depends not only on differences in sensitization but also on the assay methodology and the timepoint of measurement. Sensitization with formation of ADAs is associated with an increased risk of infusion reactions, accelerated drug clearance, and a loss of response (LOR) to drug. Recently, a greater understanding of the pharmacokinetics of therapeutic antibodies has led to the development of new strategies to reduce immunogenicity and more efficient use of these drugs. These preventive strategies include regular scheduled dosing with maintenance of stable therapeutic trough drug concentrations, and co-administration of an immunosuppressive. Sub-therapeutic drug concentrations with low levels of ADAs can generally be overcome with dose escalation, whereas the presence of high concentrations of ADAs requires a switch to another therapeutic agent.

Humanized mouse G6 anti-idiotypic monoclonal antibody has therapeutic potential against IGHV1-69 germline gene-based B-CLL.

In 10-20% of the cases of chronic lymphocytic leukemia of B-cell phenotype (B-CLL), the IGHV1-69 germline is utilized as VH gene of the B cell receptor (BCR). Mouse G6 (MuG6) is an anti-idiotypic monoclonal antibody discovered in a screen against rheumatoid factors (RFs) that binds with high affinity to an idiotope expressed on the 51p1 alleles of IGHV1-69 germline gene encoded antibodies (G6-id(+)). The finding that unmutated IGHV1-69 encoded BCRs are frequently expressed on B-CLL cells provides an opportunity for anti-idiotype monoclonal antibody immunotherapy. In this study, we first showed that MuG6 can deplete B cells encoding IGHV1-69 BCRs using a novel humanized GTL mouse model. Next, we humanized MuG6 and demonstrated that the humanized antibodies (HuG6s), especially HuG6.3, displayed ∼2-fold higher binding affinity for G6-id(+) antibody compared to the parental MuG6. Additional studies showed that HuG6.3 was able to kill G6-id(+) BCR expressing cells and patient B-CLL cells through antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). Finally, both MuG6 and HuG6.3 mediate in vivo depletion of B-CLL cells in NSG mice. These data suggest that HuG6.3 may provide a new precision medicine to selectively kill IGHV1-69-encoding G6-id(+) B-CLL cells.

Neural Stem Cells Secreting Anti-HER2 Antibody Improve Survival in a Preclinical Model of HER2 Overexpressing Breast Cancer Brain Metastases.

The treatment of human epidermal growth factor receptor 2 (HER2)-overexpressing breast cancer has been revolutionized by trastuzumab. However, longer survival of these patients now predisposes them to forming HER2 positive brain metastases, as the therapeutic antibodies cannot cross the blood brain barrier. The current oncologic repertoire does not offer a rational, nontoxic targeted therapy for brain metastases. In this study, we used an established human neural stem cell line, HB1.F3 NSCs and generated a stable pool of cells secreting a high amount of functional full-length anti-HER2 antibody, equivalent to trastuzumab. Anti-HER2Ab secreted by the NSCs (HER2Ab-NSCs) specifically binds to HER2 overexpressing human breast cancer cells and inhibits PI3K-Akt signaling. This translates to HER2Ab-NSC inhibition of breast cancer cell growth in vitro. Preclinical in vivo experiments using HER2Ab overexpressing NSCs in a breast cancer brain metastases (BCBM) mouse model demonstrate that intracranial injection of HER2Ab-NSCs significantly improves survival. In effect, these NSCs provide tumor localized production of HER2Ab, minimizing any potential off-target side effects. Our results establish HER2Ab-NSCs as a novel, nontoxic, and rational therapeutic approach for the successful treatment of HER2 overexpressing BCBM, which now warrants further preclinical and clinical investigation.

Yeast killer toxin-like candidacidal Ab6 antibodies elicited through the manipulation of the idiotypic cascade.

A mouse anti-anti-anti-idiotypic (Id) IgM monoclonal antibody (mAb K20, Ab4), functionally mimicking a Wyckerhamomyces anomalus (Pichia anomala) killer toxin (KT) characterized by fungicidal activity against yeasts presenting specific cell wall receptors (KTR) mainly constituted by ß-1,3-glucan, was produced from animals presenting anti-KT Abs (Ab3) following immunization with a rat IgM anti-Id KT-like mAb (mAb K10, Ab2). MAb K10 was produced by immunization with a KT-neutralizing mAb (mAb KT4, Ab1) bearing the internal image of KTR. MAb K20, likewise mAb K10, proved to be fungicidal in vitro against KT-sensitive Candida albicans cells, an activity neutralized by mAb KT4, and was capable of binding to ß-1,3-glucan. MAb K20 and mAb K10 competed with each other and with KT for binding to C. albicans KTR. MAb K20 was used to identify peptide mimics of KTR by the selection of phage clones from random peptide phage display libraries. Using this strategy, four peptides (TK 1-4) were selected and used as immunogen in mice in the form of either keyhole limpet hemocyanin (KLH) conjugates or peptide-encoding minigenes. Peptide and DNA immunization could induce serum Abs characterized by candidacidal activity, which was inhibited by laminarin, a soluble ß-1,3-glucan, but not by pustulan, a ß-1,6-glucan. These findings show that the idiotypic cascade can not only overcome the barrier of animal species but also the nature of immunogens and the type of technology adopted.

Psoriasis: to treat or to manage?

The recognition of psoriasis as a systemic disorder with characteristic skin symptoms and associated diseases has changed treatment concepts substantially. The complexity of psoriasis disease not only requires appropriate therapy but also weight-loss and smoking cessation programmes as well as trigger factor elimination. The term 'management' may better reflect the aim for a holistic approach of disease control. Comorbidity and the presence of psoriatic arthritis are important denominators for drug selection. However, there is a lack of prospective data substantiating a benefit of associated diseases by antipsoriatic therapy. Securing success using treatment goals helps to establish an efficacious therapy and to control inflammation. A regular scoring of disease severity, patients' quality of life and assessment of other clinically relevant conditions are mandatory to closely follow the disease course. There is debate whether an early treatment may modulate the future course of psoriasis. Concepts of minimal disease activity have not been implemented in psoriasis yet. There is a lack of evidence how long any treatment should be given and when and how to terminate. Finally, outcome tools should specifically be tailored for psoriasis to evaluate disease-related items as well as the benefit of management from the patient's perspective.

A phase 2 multicentre study of siltuximab, an anti-interleukin-6 monoclonal antibody, in patients with relapsed or refractory multiple myeloma.

Interleukin-6 (IL6) plays a central role in multiple myeloma pathogenesis and confers resistance to corticosteroid-induced apoptosis. We therefore evaluated the efficacy and safety of siltuximab, an anti-IL6 monoclonal antibody, alone and in combination with dexamethasone, for patients with relapsed or refractory multiple myeloma who had ≥ 2 prior lines of therapy, one of which had to be bortezomib-based. Fourteen initial patients received siltuximab alone, 10 of whom had dexamethasone added for suboptimal response; 39 subsequent patients were treated with concurrent siltuximab and dexamethasone. Patients received a median of four prior lines of therapy, 83% were relapsed and refractory, and 70% refractory to their last dexamethasone-containing regimen. Suppression of serum C-reactive protein levels, a surrogate marker of IL6 inhibition, was demonstrated. There were no responses to siltuximab but combination therapy yielded a partial (17%) + minimal (6%) response rate of 23%, with responses seen in dexamethasone-refractory disease. The median time to progression, progression-free survival and overall survival for combination therapy was 4.4, 3.7 and 20.4 months respectively. Haematological toxicity was common but manageable. Infections occurred in 57% of combination-treated patients, including ≥ grade 3 infections in 18%. Further study of siltuximab in modern corticosteroid-containing myeloma regimens is warranted, with special attention to infection-related toxicity.

Chronic lymphocytic leukemia monitoring with a Lamprey idiotope-specific antibody.

For antigen recognition, lampreys use leucine-rich repeats (LRR) instead of immunoglobulin V-(D)-J domains to generate variable lymphocyte receptors (VLR) of three types, VLRA, VLRB, and VLRC. VLRB-bearing lymphocytes respond to immunization with proliferation and differentiation into plasmacytes that secrete multivalent VLRB antibodies. Here we immunized lampreys with B cells from patients with chronic lymphocytic leukemia (CLL) to generate recombinant monoclonal VLRB antibodies, one of which, VLR39, was specific for the donor CLL cells. The target epitope of VLR39 was shown to be the complementarity determining region 3 (CDR3) of the heavy chain variable region (VH) of the B cell receptor. Using this antibody to monitor the CLL donor after chemo-immunotherapy-induced remission, we detected VLR39(+) B cells in the patient 51 months later, before significant increase in lymphocyte count or CD5(+) B cells. This indication of reemergence of the leukemic clone was verified by VH sequencing. Lamprey antibodies can exhibit exquisite specificity for a protein epitope, a CLL signature VH CDR3 sequence in this case, and offer a rapid strategy for generating anti-idiotype antibodies for early detection of leukemia recurrence.

Physicochemical and biological characterization of 1E10 anti-idiotype vaccine.

BACKGROUND: 1E10 monoclonal antibody is a murine anti-idiotypic antibody that mimics N-glycolyl-GM3 gangliosides. This antibody has been tested as an anti-idiotypic cancer vaccine, adjuvated in Al(OH)3, in several clinical trials for melanoma, breast, and lung cancer. During early clinical development this mAb was obtained in vivo from mice ascites fluid. Currently, the production process of 1E10 is being transferred from the in vivo to a bioreactor-based method. RESULTS: Here, we present a comprehensive molecular and immunological characterization of 1E10 produced by the two different production processes in order to determine the impact of the manufacturing process in vaccine performance. We observed differences in glycosylation pattern, charge heterogeneity and structural stability between in vivo-produced 1E10 and bioreactor-obtained 1E10. Interestingly, these modifications had no significant impact on the immune responses elicited in two different animal models. CONCLUSIONS: Changes in 1E10 primary structure like glycosylation; asparagine deamidation and oxidation affected 1E10 structural stability but did not affect the immune response elicited in mice and chickens when compared to 1E10 produced in mice.

Expression and activity identification of a human nasopharyngeal carcinoma I50 anti-idiotype antibody.

OBJECTIVE: To obtain I50 anti-idiotype antibody and identify its activity in vitro. METHODS: I50 anti-idiotype (Id) antibody gene was amplified from the template of fuse 5-I50 by PCR to construct a prokaryotic expression vector pET25b-I50. The expression of pET25b-I50 in E. coli BL21(DE3) was induced by isopropylthio-ß-D-galactopyranoside (IPTG) and was confirmed by SDS-PAGE and Western blot with Ab1(FC2) monoclonal antibody and an anti-hexahistidine tag antibody. The method of dialysis refolding was used to restore the activity of I50 anti-Id antibody, which was measured by Dot-ELISA and lymphocyte proliferation assay. RESULTS: The recombinant vector was successfully constructed and the recombinant protein was successfully expressed and purified with 90% purity. The relative molecular weight of the expressed protein was 15 kD, which was in accordance with expectation. The activity of I50 anti-Id antibody could be restored and could promote the proliferation of lymphocyte in a dose-dependent manner. CONCLUSION: These results suggested that I50 anti-Id protein vaccine is likely an option in the therapy against nasopharyngeal carcinoma in vivo.

The idiotype (Id) cascade in mice elicited the production of anti-R24 Id and anti-anti-Id monoclonal antibodies with antitumor and protective activity against human melanoma.

Gangliosides have been considered as potential targets for immunotherapy because they are overexpressed on the surface of melanoma cells. However, immunization with purified gangliosides results in a very poor immune response, usually mediated by IgM antibodies. To overcome this limitation, we immunized mice with R24, a monoclonal antibody (mAb) that recognizes the most tumor-restricted ganglioside (GD3); our goal was to obtain anti-idiotype (Id) antibodies bearing the internal image of GD3. Animals produced anti-Id and anti-anti-Id antibodies. Both anti-Id and anti-anti-Id antibodies were able to inhibit mAb R24 binding to GD3. In addition, the anti-anti-Id antibodies were shown to recognize GD3 directly. Anti-Id and anti-anti-Id mAb were then selected from two fusion experiments for evaluation. The most interesting finding emerged from the characterization of the anti-anti-Id mAb 5.G8. It was shown to recognize two different GD3-expressing human melanoma cell lines in vitro and to mediate tumor cell cytotoxicity by complement activation and antibody-dependent cellular cytotoxicity. The biological activity of the anti-anti-Id mAb was also tested in a mouse tumor model, in which it was shown to be a powerful growth inhibitor of melanoma cells. Thus, activity of the anti-anti-Id mAb 5.G8 matched that of the prototypic anti-GD3 mAb R24 both in vitro and in vivo. Altogether, our results indicate that the idiotype approach might produce high affinity, specific and very efficient antitumor immune responses.

A novel strategy to reduce the immunogenicity of biological therapies.

Biological therapies, even humanized mAbs, may induce antiglobulin responses that impair efficacy. We tested a novel strategy to induce tolerance to a therapeutic mAb. Twenty patients with relapsing-remitting multiple sclerosis received an initial cycle of alemtuzumab (Campath-1H), up to 120 mg over 5 d, preceded by 500 mg SM3. This Ab differs from alemtuzumab by a single point mutation and is designed not to bind to cells. Twelve months later, they received a second cycle of alemtuzumab, up to 72 mg over 3 d. One month after that, 4 of 19 (21%) patients had detectable serum anti-alemtuzumab Abs compared with 145 of 197 (74%) patients who received two cycles of alemtuzumab without SM3 in the phase 2 CAMMS223 trial (p < 0.001). The efficacy and safety profile of alemtuzumab was unaffected by SM3 pretreatment. Long-lasting "high-zone" tolerance to a biological therapy may be induced by pretreatment with a high i.v. dose of a drug variant, altered to reduce target-binding.

Persistent expression of biologically active anti-HER2 antibody by AAVrh.10-mediated gene transfer.

Trastuzumab (Herceptin) is a recombinant humanized monoclonal antibody (mAb) directed against an extracellular region of the human epidermal growth-factor receptor type 2 (HER2) protein. We hypothesized that a single adeno-associated virus (AAV)-mediated genetic delivery of an anti-HER2 antibody should be effective in mediating long-term production of anti-HER2 and in suppressing the growth of human tumors in a xenograft model in nude mice. The adeno-associated virus gene transfer vector AAVrh.10alphaHER2 was constructed based on a non-human primate AAV serotype rh.10 to express the complementary DNAs for the heavy and light chains of mAb 4D5, the murine precursor to trastuzumab. The data show that genetically transferred anti-HER2 selectively bound human HER2 protein and suppressed the proliferation of HER2(+) tumor cell lines. A single administration of AAVrh.10alphaHER2 provided long-term therapeutic levels of anti-HER2 antibody expression without inducing an anti-idiotype response, suppressed the growth of HER2(+) tumors and increased the survival of tumor bearing mice. In the context that trastuzumab therapy requires frequent and repeated administration, this strategy might be developed as an alternate platform for delivery of anti-HER2 therapy.

Development and characterization of a novel anti-IgE monoclonal antibody.

IgE is the central macromolecular mediator responsible for the progression of allergic reactions. Omalizumab (Xolair) is a humanized monoclonal anti-IgE antibody directed at the FcepsilonRI-binding domain of human IgE, which represents a novel therapeutic approach in the management of asthma. In this study, we developed a monoclonal antibody (7A5) against human IgE via hybridoma technique. Our data showed that 7A5 could inhibit free IgE molecules to bind to receptors without affecting IgE already bound to cellular receptors. Importantly, 7A5 was able to inhibit IgE-induced histamine release of basophilic leukemia cells. Next, the phage display peptide library technology was employed to select peptides binding to 7A5 and a striking peptide sequence motif was recovered, which is homologous to the sequence (391)KQR(393) within the Cepsilon3 domain of IgE-Fc, Our results further indicated that 7A5 specifically bound to the synthesized peptide "(388)KEEKQRN(394)" containing the (391)KQR(393) motif in IgE-Fc. The epitope of 7A5 was found to be spatially close to the FcepsilonRI-binding site, suggesting that 7A5 binding to IgE might block IgE binding to receptors via steric hindrance. The anti-IgE monoclonal antibody 7A5 may have the potential to be developed as a therapeutic agent for the treatment of allergic diseases.