title: Isolation of human mAbs that directly modulate FMS-related tyrosine kinase 3 signaling.
abstract: FMS-related tyrosine kinase 3 (FLT3) is a class III receptor tyrosine kinase that plays important roles in hematopoiesis, including early progenitors and dendritic cell development. FLT3 is expressed at high levels in 70-100% of cases of AML and in virtually all cases of B-lineage acute lymphoblastic leukemia. FLT3 is regarded as a molecular target in the development of novel therapies for acute leukemia patients. Currently, many small-molecule FLT3 inhibitors have been developed, but clinical trials have resulted in limited antileukemia effects because of off-target toxicities and drug resistance. The development of anti-FLT3 Abs might overcome these difficulties and enhance the antileukemia efficacy of FLT3 inhibitors. In the present study, we demonstrate the isolation of novel human mAbs against FLT3 with antagonistic or agonistic activities. An antagonistic Ab, designated A2, continuously inhibits FLT3 ligand (FL)-induced phosphorylation of FLT3 and MAPK. A2 cooperatively induces apoptosis with daunorubicin, even in the presence of FL. An agonistic Ab, designated 3E6, surprisingly induces the phosphorylation of FLT3 and MAPK, and supports the growth of a factor-dependent cell line independently of FL addition. In addition, A2 showed complement-dependent cytotoxicity activity, but was devoid of Ab-dependent cell mediated cytotoxicity. Finally, we evaluated Ab internalization in a cell line. Immunofluorescence and flow cytometry analyses revealed that A2 is efficiently internalized. Collectively, these data demonstrate that A2 is a potent human Ab that might be capable of delivering cytotoxic reagents and that has antagonistic effects on FLT3 signaling. In addition, 3E6 might be a potential scaffold for novel dendritic cell-based immunotherapies.
authors: Department of Hematology, School of Medicine, Fujita Health University, Aichi, Japan. yyukiya@fujita-hu.ac.jp
authors: Yukiya
authors: Y
authors: Yamamoto
authors: Sachiko
authors: S
authors: Tsuzuki
authors: Yasushi
authors: Y
authors: Akahori
authors: Yoshinori
authors: Y
authors: Ukai
authors: Mariko
authors: M
authors: Sumitomo
authors: Yuko
authors: Y
authors: Murayama
authors: Kiyoko
authors: K
authors: Yamamoto
authors: Youko
authors: Y
authors: Inaguma
authors: Masutaka
authors: M
authors: Tokuda
authors: Akihiro
authors: A
authors: Abe
authors: Yoshiki
authors: Y
authors: Akatsuka
authors: Nobuhiko
authors: N
authors: Emi
authors: Yoshikazu
authors: Y
authors: Kurosawa
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology* / Q000302:isolation & purification* / Q000378:metabolism / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D003630:Daunorubicin / Q000494:pharmacology; D006801:Humans; D015470:Leukemia, Myeloid, Acute / Q000235:genetics / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010766:Phosphorylation; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D051941:fms-Like Tyrosine Kinase 3 / Q000819:agonists / Q000037:antagonists & inhibitors / Q000276:immunology* / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D000970:Antineoplastic Agents; C497970:FLT3 protein, human; D051941:fms-Like Tyrosine Kinase 3; D020928:Mitogen-Activated Protein Kinases; D003630:Daunorubicin