EP3997128A1 - Verfahren zur eliminierung von hämatopoetischen stammzellen/hämatopoetischen vorläuferzellen (hsc/hp) in einem patienten mit bi-spezifischen antikörpern - Google Patents

Verfahren zur eliminierung von hämatopoetischen stammzellen/hämatopoetischen vorläuferzellen (hsc/hp) in einem patienten mit bi-spezifischen antikörpern

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Publication number
EP3997128A1
EP3997128A1 EP20836912.4A EP20836912A EP3997128A1 EP 3997128 A1 EP3997128 A1 EP 3997128A1 EP 20836912 A EP20836912 A EP 20836912A EP 3997128 A1 EP3997128 A1 EP 3997128A1
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Prior art keywords
cells
antibody
cell
antigen
flt3
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EP20836912.4A
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English (en)
French (fr)
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EP3997128A4 (de
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Vladislav Sandler
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Hemogenyx Pharmaceuticals LLC
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Hemogenyx Pharmaceuticals LLC
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Priority claimed from US16/506,764 external-priority patent/US11104738B2/en
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Publication of EP3997128A1 publication Critical patent/EP3997128A1/de
Publication of EP3997128A4 publication Critical patent/EP3997128A4/de
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K16/00—Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies
    • C07K16/18—Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies against material from animals or humans
    • C07K16/28—Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies against material from animals or humans against receptors, cell surface antigens or cell surface determinants
    • C07K16/2803—Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies against material from animals or humans against receptors, cell surface antigens or cell surface determinants against the immunoglobulin superfamily
    • C07K16/2809—Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies against material from animals or humans against receptors, cell surface antigens or cell surface determinants against the immunoglobulin superfamily against the T-cell receptor (TcR)-CD3 complex
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
    • A61P37/00—Drugs for immunological or allergic disorders
    • A61P37/02—Immunomodulators
    • A61P37/06—Immunosuppressants, e.g. drugs for graft rejection
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K16/00—Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies
    • C07K16/18—Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies against material from animals or humans
    • C07K16/28—Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies against material from animals or humans against receptors, cell surface antigens or cell surface determinants
    • C07K16/2863—Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies against material from animals or humans against receptors, cell surface antigens or cell surface determinants against receptors for growth factors, growth regulators
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K39/00—Medicinal preparations containing antigens or antibodies
    • A61K2039/505—Medicinal preparations containing antigens or antibodies comprising antibodies
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K2317/00—Immunoglobulins specific features
    • C07K2317/30—Immunoglobulins specific features characterized by aspects of specificity or valency
    • C07K2317/31—Immunoglobulins specific features characterized by aspects of specificity or valency multispecific
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K2317/00—Immunoglobulins specific features
    • C07K2317/50—Immunoglobulins specific features characterized by immunoglobulin fragments
    • C07K2317/55—Fab or Fab'
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K2317/00—Immunoglobulins specific features
    • C07K2317/70—Immunoglobulins specific features characterized by effect upon binding to a cell or to an antigen
    • C07K2317/73—Inducing cell death, e.g. apoptosis, necrosis or inhibition of cell proliferation
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K2317/00—Immunoglobulins specific features
    • C07K2317/70—Immunoglobulins specific features characterized by effect upon binding to a cell or to an antigen
    • C07K2317/77—Internalization into the cell
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K2317/00—Immunoglobulins specific features
    • C07K2317/90—Immunoglobulins specific features characterized by (pharmaco)kinetic aspects or by stability of the immunoglobulin
    • C07K2317/92—Affinity (KD), association rate (Ka), dissociation rate (Kd) or EC50 value

Definitions

  • the described invention generally relates to hematopoietic cell transplantation, therapeutic antibody preparations and their uses.
  • the hematopoietic stem cell is the common ancestor of all blood cells. As multipotent cells, they can differentiate into multiple cell lineages, but not all the lineages derived from the three germ layers. Hematopoietic stem cell differentiation gives rise to the lymphoid and myeloid cell lineages, the two major branches of hematopoiesis. (Kondo, M. “Lymphoid and myeloid lineage commitment in multipotent hematopoietic progenitors,” Immunol. Rev. 2010 Nov; 238(1): 37-46). Lymphoid lineage cells include T, B, and natural killer (NK) cells.
  • the myeloid lineage includes megakaryocytes and erythrocytes (MegE) as well as different subsets of granulocytes (neutrophils, eosinophils and basophils), monocytes, macrophages, and mast cells (GM), which belong to the myeloid lineage (Id. citing Kondo M, et al. Biology of hematopoietic stem cells and progenitors: implications for clinical application. Ann. Rev Immunol. 2003;21 :759-806., Weissman IL. Translating stem and progenitor cell biology to the clinic: barriers and opportunities. Science (New York, NY. 2000 Feb 25;287(5457): 1442-6; see also Iwaskaki, H. and Akashi, K. “Myeloid lineage commitment from the hematopoietic stem cell,” Immunity 26(6) June 2007, 726-40).
  • MegE megakaryocytes and erythrocytes
  • GM mast cells
  • HSCs present self-renewal potential and differentiation capacity into blood lineages; i.e., when stem cells divide, 50% of the daughter cells, on average, are committed with a cell lineage, while the remaining 50% do not differentiate.
  • the process maintains the same number of stem cells by asymmetric cell division, so that each dividing stem cell originates one new stem cell and one differentiated cell.
  • the stem cells originate 100% of identical stem cells.
  • CLPs Common lymphoid progenitors
  • CLPs can differentiate into all types of lymphocytes without noticeable myeloid potential under physiological conditions (Kondo M, Scherer DC, Miyamoto T, King AG, Akashi K, Sugamura K, et al. Cell-fate conversion of lymphoid- committed progenitors by instructive actions of cytokines. Nature. 2000 Sep
  • CMPs common myeloid progenitors
  • B-cell potential A clonogenic common myeloid progenitor that gives rise to all myeloid lineages. Nature. 2000 Mar 9;404(6774): 193-7.
  • DCs dendritic cells
  • CMPs can proliferate and differentiate into megakaryocyte-erythrocyte (MegE) progenitors and granulocyte-monocyte (GM) progenitors, which further give rise to megakaryocytes, erythrocytes, granulocytes, monocytes and others.
  • MeE megakaryocyte-erythrocyte
  • GM granulocyte-monocyte
  • transcription factors PU.l and GATA-1 have been implicated in myeloid and erythroi d/megakaryocyte lineage
  • HSCs are undifferentiated and resemble small lymphocytes. A large fraction of HSCs is quiescent, in the GO phase of the cell cycle, which protects them from the action of cell cycle-dependent drugs. The quiescent state of stem cells is maintained by
  • TGF-b transforming growth factor-b
  • the activity of TGF-b is mediated by p53, a tumor suppressor gene that regulates cell proliferation and targets the cyclin-dependent kinase inhibitor p21 (Gordon, M. Stem cells and haemopoiesis. In: Hoffbrand, V., Catovsky, D., Tuddenham, E.G., 5 th ed. Blackwell Publishing, (2005): Differential niche and Wnt requirements during acute myeloid leukemia, pp. 1-12. New York.).
  • Quiescence of HSCs is critical not only for protecting the stem cell compartment and sustaining stem cell pools during long periods of time, but also for minimizing the accumulation of replication- associated mutations.
  • HSCs quiescence Many of the intrinsic transcriptional factors that maintain HSCs quiescence are found to be associated with leukemias. For example, chromosomal translocations resulting in the fusion of FoxOs and myeloid/lymphoid or mixed lineage leukemia have been reported in acute myeloid leukemias (See, e.g., Sergio Paulo Bydlowski and Felipe de Lara Janz (2012). Hematopoietic Stem Cell in Acute Myeloid Leukemia Development, Advances in Hematopoietic Stem Cell Research, Dr. Rosana Pelayo (Ed.), ISBN: 978-953-307-930-1).
  • CD34+/CD38+ cell fractions contain some HSCs endowed with short-term repopulating activity.
  • Other recognized markers include the tyrosine kinase receptor c-kit (CD117) coupled with a lack of terminal differentiation markers such as CD4 and CD8 (Rossi et ah, Methods in Molecular Biology (2011) 750(2): 47-59).
  • the hematopoietic stem cell pool can be subdivided into three main groups:
  • short-term HSCs capable of generating clones of differentiating cells for only 4-6 weeks
  • intermediate-term HSCs capable of sustaining a differentiating cell progeny for 6-8 months before becoming extinct
  • long-term HSCs capable of maintaining hematopoiesis indefinitely.
  • Hematopoiesis is a highly coordinated process wherein HSCs differentiate into mature blood cells supported by a specialized regulatory microenvironment, consisting of components which control the fate specification of stem and progenitor cells, as well as maintaining their development by supplying the requisite factors (“niche”).
  • the term“bone marrow (BM) niche” as used herein refers to a well-organized architecture composed of elements (e.g., osteoblasts, osteoclasts, bone marrow endothelial cells, stromal cells, adipocytes and extracellular matrix proteins (ECM)) that play an essential role in the survival, growth and differentiation of diverse lineages of blood cells.
  • the bone marrow niche is an important post-natal microenvironment in which HSCs proliferate, mature and give rise to myeloid and lymphoid progenitors.
  • Bone marrow is present in the medullary cavities of all animal bones. It consists of a variety of precursor and mature cell types, including hematopoietic cells (the precursors of mature blood cells) and stromal cells (the precursors of a broad spectrum of connective tissue cells), both of which appear to be capable of differentiating into other cell types.
  • the mononuclear fraction of bone marrow contains stromal cells, hematopoietic precursors, and endothelial precursors.
  • BM Unlike secondary lymphoid organs such as spleen with distinct gross structures including red and white pulp, BM has no clear structural features, except for the endosteum that contains osteoblasts. The endosteum region comes in contact with calcified hard bones and provides a special microenvironment which is necessary for the maintenance of HSC activity (Kondo M, Immunology Reviews (2010) 238(1): 37-46; Sergio Paulo Bydlowski and Felipe de Lara Janz (2012). Hematopoietic Stem Cell in Acute Myeloid Leukemia Development, Advances in Hematopoietic Stem Cell Research, Dr. Rosana Pelayo (Ed.), ISBN: 978-953-307-930-1).
  • HSCs are believed to receive support and growth signals originating from several sources, including: fibroblasts, endothelial and reticular cells, adipocytes, osteoblasts and mesenchymal stem cells (MSCs).
  • the main function of the niche is to integrate local changes in nutrients, oxygen, paracrine and autocrine signals and to change HSCs quiescence, trafficking, and/ or expansion in response to signals from the systemic circulation (Broner, F. & Carson, M C. Topics in bone biology. Springer. 2009; 4: pp. 2-4. New York, USA.).
  • CXC chemokine ligand 12 (CXCL12) - expressing CD146 MSCs were recently reported to be self-renewing progenitors that reside on the sinusoidal surfaces and contribute to organization of the sinusoidal wall structure, produce angiopoietin-1 (Ang-1), and are capable of generating osteoblasts that form the endosteal niche (Konopleva, MY, & Jordan, CT, Biology and Therapeutic Targeting (2011) 9(5): 591-599).
  • Ang-1 angiopoietin-1
  • These CXCL12 reticular cells may serve as a transit pathway for shuttling HSCs between the osteoblastic and vascular niches where essential but different maintenance signals are provided.
  • Cytokines and chemokines produced by bone marrow MSCs concentrate in particular niches secondary to varying local production and through the effects of cytokine binding glycosaminoglycans.
  • CXCL 12/ stromal cell-derived factor- 1 alpha positively regulates HSCs homing
  • FMS-like tyrosine kinase 3 (Flt3) ligand and Ang-1 act as quiescence factors (See, e.g., Sergio Paulo
  • CXCL12-CXCR4 signaling is involved in homing of HSCs into BM during ontogeny as well as survival and proliferation of colony-forming progenitor cells.
  • the CXCR4-selective antagonist-induced mobilization of HSCs into the peripheral blood further indicates a role for CXCL 12 in retaining HSCs in hematopoietic organs.
  • BM engraftment involves subsequent cell-to-cell interactions through the BMSC-produced complex extracellular matrix.
  • vascular cell adhesion molecule-1 VCAM-1
  • fibronectin is critical for adhesion to the BM derived MSCs.
  • control of hematopoietic stem cell proliferation kinetics is critically important for the regulation of correct hematopoietic cell production.
  • HSC self-renewal and differentiation can be controlled by external factors (extrinsic control), such as cell-cell interactions in the hematopoietic microenvironment or cytokines, such as SCF (stem cell factor) and its receptor c-kit, Flt-3 ligand, TGF-b, TNF-a and others.
  • cytokines such as SCF (stem cell factor) and its receptor c-kit, Flt-3 ligand, TGF-b, TNF-a and others.
  • Cytokines regulate a variety of hematopoietic cell functions through the activation of multiple signal transduction pathways.
  • the major pathways relevant to cell proliferation and differentiation are the Janus kinase (Jak)/signal transducers and activators of transcription (STATs), the mitogen-activated protein (MAP) kinase and the
  • PI phosphatidylinositol
  • SCL stem cell leukemia
  • GATA-2 GATA-2
  • CKIs cyclin dependent kinase inhibitors
  • Notch-l-Jagged pathway may serve to integrate extracellular signals with intracellular signaling and cell cycle control.
  • Notch-1 is a surface receptor on hematopoietic stem cell membranes that binds to its ligand. Jagged, on stromal cells. This results in cleavage of the cytoplasmic portion of Notch-1, which can then act as a transcription factor (Gordon, M. Stem cells and haemopoiesis. In: Hoffbrand, V., Catovsky, D., Tuddenham, E.G., 5 th ed. Blackwell Publishing, (2005): Differential niche and Wnt requirements during acute myeloid leukemia, pp. 1-12. New York.).
  • BM Bone Marrow
  • HSC Hematopoietic Stem Cell
  • disorders that are treated using Bone Marrow (BM)/Hematopoietic Stem Cell (HSC) transplantation include, without limitation, Acute Myeloid Leukemia (AML), Acute Lymphoblastic Leukemia (ALL), Chronic Lymphocytic Leukemia (CLL), Chronic Myeloid Leukemia (CML), peripheral T cell lymphoma, follicular lymphoma, diffuse large B cell lymphoma, Hodgkin lymphoma, non-Hodgkin lymphoma, neuroblastoma, non-malignant inherited and acquired marrow disorders (e.g.
  • cancer stem cells are so named because they possess qualities reminiscent of normal tissue stem cells including self-renewal, prolonged survival, and the ability to give rise to cells with more differentiated characteristics (Jones RJ and Armstrong SA, Biol Blood Marrow
  • a transforming event in hematopoietic stem cells can produce several different malignancies, including, without limitation, chronic myeloid leukemia, myelodysplastic syndrome, acute myeloid leukemia, and probably even acute lymphocytic leukemia, depending on the degree of differentiation associated with the oncogenic hit (Jones RJ and Armstrong SA, Biol Blood Marrow Transplant. 2008 Jan; 14 (Supplement 1): 12-16).
  • the cancer stem cell concept is based on the idea that tumors of a specific tissue often appear to“attempt” to recapitulate the cellular heterogeneity found in the tissues of origin, and thus there are cells in the tumor that are stem-cell like giving rise to the varied cell types.
  • a fundamental test for this hypothesis is whether tumor cells can be separated into those that have the ability to regenerate the tumor, and those that do not possess this ability.
  • This cellular hierarchy has been most clearly demonstrated in acute myelogenous leukemias where some AMLs possess cells with a unique immunophenotype that are able to initiate leukemias in immunodeficient mice whereas most cells are unable to initiate leukemia development.
  • the cells that initiate leukemias also give rise to cells that have lost tumor-initiating activity and thus recapitulate the cellular heterogeneity found in the original tumor (Lapidot T et ah, Nature. 1994; 367: 645-648; Bonnet D et ah, Nat Med. 1997; 3: 730-737).
  • Acute myeloid leukemia is a clonal disorder characterized by arrest of differentiation in the myeloid lineage coupled with an accumulation of immature progenitors in the bone marrow, resulting in hematopoietic failure (Pollyea DA et ah, British Journal of Haematology (2011) 152(5): 523-542). There is wide patient-to-patient heterogeneity in the appearance of the leukemic blasts.
  • AMLs acute myeloid leukemias
  • class I activating mutations such as mutations in the receptor tyrosine kinase genes FLT3 and KIT, RAS family members, and loss of function of neurofibromin 1, confer proliferative and/or survival advantage to hematopoietic progenitors, typically as a consequence of aberrant activation of signal transduction pathways.
  • the class II mutations lead to a halt in differentiation via interference with transcription factors or co-activators (Frankfurt O et ak, Current Opinion in Oncology (2007) 19(6): 635-649).
  • LSC leukemia stem cell
  • Thy-1 has been described as potentially specific of the LSC compartment. Thy-1 is downregulated in normal hematopoiesis as the most primitive stem cells progress toward the progenitor stage. (Hope KJ et ak, Archives of Medical Research (2003) 34(6): 507-514).
  • CXCL12 stromal cell-derived factor-1 alpha
  • CXCR4 receptor CXCR4
  • FLT3 a member of the class III tyrosine kinase receptor family, is expressed in normal hematopoietic progenitors as well as in leukemic blasts, and it plays an important role in cell proliferation, differentiation, and survival.
  • Activation of the FLT3 receptor by the FLT3 ligand leads to receptor dimerization and phosphorylation, and activation of downstream signaling pathways, including the Janus kinase (JAK) 2 signal transducer (JAK2), signal transducer and activator of transcription (STAT) 5, and mitogen-activated protein kinase (MAPK) pathways.
  • JK Janus kinase
  • JAT signal transducer
  • MAPK mitogen-activated protein kinase
  • somatic hypermutation identifies a tumor as having arisen in germinal center or post- germinal center B cells, while the absence of mutation identifies pre-germinal center B cells.
  • immunoglobulin (Ig) mutation patterns suggest that B cell malignancies can arise from cells throughout the stages of B cell differentiation (Lapidot T et al., Nature. 1994;
  • MM multiple myeloma
  • normal plasma cells are terminally differentiated and lack self-renewal capacity and it has been clear for over 30 years that only a minority of cells from mouse and human MM were clonogenic. These rare clonogenic cells have been termed“tumor stem cells” (Park CH et al., J Natl Cancer Inst. 1971; 46: 411-422; Hamburger AW and Salmon SE, Science. 1977; 197: 461-463).
  • MM plasma cells arise from a small population of self- renewing cancer stem cells that resemble memory B cells.
  • Reed-Stemberg (RS) cells the hallmark of Hodgkin’s lymphoma (HL), are the only blood cells other than plasma cells to occasionally express CD138 (Carbone A et al., Blood. 1998; 92: 2220-2228). It has been shown that HL cell lines include a small population of cells that lack the RS markers CD15 and CD30 present on the rest of the cells, while expressing markers consistent with a memory B cell phenotype (Newcom SR et al.,
  • HSCs Hematopoietic stem cells
  • BM bone marrow
  • BM/HSC bone marrow/hematopoietic stem cell
  • BM/HSC bone marrow/hematopoietic stem cell
  • the described invention provides compositions and methods for eliminating hematopoietic stem cells/hematopoietic progenitors (HSC/HP) in a patient using bi-specific antibodies that bind to human tyrosine kinase receptor FLT3/FLK2 receptor protein and to CD3 receptor protein expressed on T-cells.
  • the described invention provides a method for preparing or conditioning a patient in need thereof for hematopoietic cell transplantation comprising: providing a recombinant single chain bi-specific antibody that binds to both human FLT3 and human CD3, and administering a therapeutic amount of a pharmaceutical composition comprising the bi-specific antibody to the patient; wherein the therapeutic amount is effective: to reduce by at least 90% a level in peripheral blood of a cell population expressing one or more of CD45, CD3, FLT3, CD19, CD33, and to reduce toxicity of protocols for preparing or conditioning the patient.
  • an amino acid sequence of a heavy chain of an antigen-binding portion of the bispecific antibody that binds FLT3 is SEQ ID NO: 1 and an amino acid sequence of a light chain of the antigen-binding portion of the bispecific antibody that binds FLT3 is SEQ ID NO: 2.
  • the bi- specific antibody comprises a monoclonal antibody that reacts with a subunit of human CD3.
  • the bi-specific antibody or antigen-binding portion thereof comprises an isotype selected from the group consisting of an immunoglobulin G (IgG), an IgM, an IgE, an IgA, and an IgD isotype.
  • the effective amount comprises 0.01 mg/kg to 10 mg/kg, better 0.05 mg/kg to 2 mg/kg, better 0.1 mg/kg to 0.5 mg/kg, better 0.1 mg/kg to 0.3 mg/kg, better 0.1 mg/kg.
  • the patient in need thereof is suffering from acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), chronic myeloid leukemia (CLL), CML, peripheral T cell lymphoma, follicular lymphoma, diffuse large B cell lymphoma, Hodgkin lymphoma, non-Hodgkin lymphoma, neuroblastoma, a non- malignant inherited and acquired marrow disorder, multiple myeloma, or SCID.
  • AML acute myeloid leukemia
  • ALL acute lymphoblastic leukemia
  • CLL chronic myeloid leukemia
  • peripheral T cell lymphoma follicular lymphoma
  • diffuse large B cell lymphoma Hodgkin lymphoma
  • non-Hodgkin lymphoma non-Hodgkin lymphoma
  • neuroblastoma a non- malignant inherited and acquired marrow disorder
  • multiple myeloma or SCID.
  • the non-malignant inherited and acquired marrow disorder is selected from sickle cell anemia, beta-thalassemia major, refractory Diamond-Blackfan anemia, myelodysplastic syndrome, idiopathic severe aplastic anemia, paroxysmal nocturnal hemoglobinuria, pure red cell aplasia, Fanconi anemia, amegakaryocytosis, and congenital thrombocytopenia.
  • the composition further comprises an antitumor agent.
  • the bispecific antibody is a humanized antibody.
  • the described invention provides a method for preparing a recombinant single chain bi-specific antibody that binds to both human FLT3 and human CD3 comprising: joining a C-terminus of an Fab antigen-binding fragment of an Flt3 monoclonal antibody to a CH2 domain of IgGl, and joining to the CH2 domain of the IgGl a single chain variable fragment (ScFv) of a monoclonal antibody that reacts with a subunit of human CD3 (UCHT1).
  • the described invention provides a recombinant single chain bi-specific antibody that binds to both human FLT3 and human CD3 comprising: a C-terminus of an Fab antigen-binding fragment of an Flt3 monoclonal antibody that is joined to a CH2 domain of IgGl, and a single chain variable fragment (ScFv) of a monoclonal antibody that reacts with a subunit of human CD3 (UCHT1) joined to the CH2 domain of the IgGl .
  • a recombinant single chain bi-specific antibody that binds to both human FLT3 and human CD3 comprising: a C-terminus of an Fab antigen-binding fragment of an Flt3 monoclonal antibody that is joined to a CH2 domain of IgGl, and a single chain variable fragment (ScFv) of a monoclonal antibody that reacts with a subunit of human CD3 (UCHT1) joined to the CH2 domain of the IgGl .
  • an amino acid sequence of a heavy chain binding domain of the Fab antigen-binding fragment is SEQ ID NO: 1 (H3113) and an amino acid sequence of a light chain binding domain of the Fab antigen-binding fragment is SEQ ID NO: 2 (L3133).
  • the described invention provides a monoclonal antibody or antigen binding fragment thereof, wherein an amino acid sequence of a light chain of an antigen-binding portion of the antibody or fragment thereof that binds to human FLT3/FLK2 receptor protein is SEQ ID NO: 5 and an amino acid sequence of a heavy chain of the antigen-binding portion of the antibody or fragment thereof that binds to human FLT3/FLK2 receptor protein is SEQ ID NO: 7.
  • the described invention provides a monoclonal antibody or antigen binding fragment thereof, wherein an amino acid sequence of a light chain of an antigen-binding portion of the antibody or fragment thereof that binds to human FLT3/FLK2 receptor protein is SEQ ID NO: 9 and an amino acid sequence of a heavy chain of the antigen-binding portion of the antibody or fragment thereof that binds to human FLT3/FLK2 receptor protein is SEQ ID NO: 11.
  • the described invention provides a monoclonal antibody or antigen binding fragment thereof, wherein an amino acid sequence of a light chain of an antigen-binding portion of the antibody or fragment thereof that binds to human FLT3/FLK2 receptor protein is SEQ ID NO: 13 and an amino acid sequence of a heavy chain of the antigen-binding portion of the antibody or fragment thereof that binds to human FLT3/FLK2 receptor protein is SEQ ID NO: 15.
  • the described invention provides a monoclonal antibody or antigen binding fragment thereof, wherein an amino acid sequence of a light chain of an antigen-binding portion of the antibody or fragment thereof that binds to human FLT3/FLK2 receptor protein is SEQ ID NO: 17 and an amino acid sequence of a heavy chain of the antigen-binding portion of the antibody or fragment thereof that binds to human FLT3/FLK2 receptor protein is SEQ ID NO: 19.
  • the described invention provides a monoclonal antibody or antigen binding fragment thereof, wherein an amino acid sequence of a light chain of an antigen-binding portion of the antibody or fragment thereof that binds to human FLT3/FLK2 receptor protein is SEQ ID NO: 21, and an amino acid sequence of a heavy chain of the antigen-binding portion of the antibody or fragment thereof that binds to human FLT3/FLK2 receptor protein is SEQ ID NO: 23.
  • the described invention provides a monoclonal antibody or antigen binding fragment thereof, wherein an amino acid sequence of a light chain of an antigen-binding portion of the antibody or fragment thereof that binds to human FLT3/FLK2 receptor protein is SEQ ID NO: 25, and an amino acid sequence of a heavy chain of the antigen-binding portion of the antibody or fragment thereof that binds to human FLT3/FLK2 receptor protein is SEQ ID NO: 27.
  • a half maximal effective concentration (EC50) of the antibody or fragment thereof is between 1 ng/mL (6.25 pM) and 2,000 ng/mL (12.5nM).
  • the half maximal effective concentration (EC50) of the antibody or antigen-binding fragment thereof is between 10 ng/mL (62.5 pM) and 200 ng/mL (1.25nM).
  • FLT3 antibody binding to human FLT3/FLK2 receptor protein on a cell is effective for the cell to internalize the bound antibody or antigen-binding fragment.
  • FIGS. 1A, IB, 1C [57] FIGS. 1A, IB, 1C.
  • FIGS. 1A and IB native fluorescence of amino acids such as phenylalanine, tyrosine and tryptophan.
  • FIG. 1C measurement of purity of the synthesized antibody.
  • FIGS. 2A, 2B, 2C, 2D Administering bi-specific antibodies that bind to FLT3/FLK2 expressed by HSC/HP and CD3 expressed by T-cells reduces the level of chimerism in the peripheral blood in the humanized immune-compromised mice.
  • FIG. 2A an_example of flow cytometry analysis of the peripheral blood of a humanized NOG mouse before (Control; upper row) and three weeks after application of CD3-FLT3 bi-specific antibodies.
  • FIGS. 3A and 3B Screening of culture supernatants from clonally expanded hybridomas.
  • FIG. 3 A fluorescence intensity histograms obtained from flow cyto etry analysis of supernatants of nine positive hybridoma clones. The supernatants show immune- reactivity against FLT3/FLK2 expressed by REH (human B cell precursor leukemia cells, established from the peripheral blood of a 15 year old girl with ALL at first relapse) cells.
  • FIG. 3B a table showing median fluorescence intensity (MFI) of the histograms in FIG. 3 A. All nine clones reacted with REH cells that express human FLT3/FLK2 receptor proteins.
  • MFI median fluorescence intensity
  • FIGS. 4A and 4B Screening of purified monoclonal antibodies from expanded hybridomas.
  • FIG. 4A fluorescence intensity histograms obtained from flow cytometry analysis of purified monoclonal antibodies from nine positive hybridoma clones. The supernatants show immune-reactivity to the human FLT3/FLK2 receptor protein expressed by SP2/0 cells. Monoclonal antibodies were non-reactive with wild-type SP2/0 cells that do not express human FLT3/FL2 receptor protein.
  • FIG. 4B a table showing median fluorescence intensity (MFI) of the histograms in FIG. 4A. All nine clones reacted with SP2/0 cells that express human FLT3/FLK2 receptor proteins and did not react with wild-type SP2/0 cells.
  • MFI median fluorescence intensity
  • FIGS. 5A, 5B, 5C, 5D, and 5E Affinity of anti-human FLT3/FLK2 antibodies determined by Effective Concentration (EC) curve using flow cytometry.
  • FIG. 5A, 5B, 5C, 5D, and 5E Affinity of anti-human FLT3/FLK2 antibodies determined by Effective Concentration (EC) curve using flow cytometry.
  • FIG. 5 A antibody clone Ab2-81.
  • FIG. 5B antibody clone Abl-23DA.
  • FIG. 5C antibody_clone Ab3-16HA.
  • FIG. 5D antibody clone Ab0-30A.
  • FIG. 5E antibody_clone Abl-18New.
  • FIG. 6 Time Course of Anti-FLT3/FLK2 Antibody Internalization.
  • Mean fluorescent intensity (MFI) of monoclonal mouse anti-human CD135 antibodies was detected with a secondary Alexa Fluor 488 plotted versus time for the live Reh cell population. Internalization assays were conducted at 37°C in parallel with control cells that were kept on ice at 4°C for 10, 30, 60 and 120 minutes. The percent change in MFI for each antibody (clones 123D, A281A, 330A and 316HA) was graphed versus time at 4°C and 37°C in triplicate over 2 hours, with MFI at 10 minutes set to 100%.
  • MFI Mean fluorescent intensity
  • activation refers to stimulation of lymphocytes by specific antigens, nonspecific mitogens, or allogeneic cells resulting in synthesis of RNA, protein and DNA and production of lymphokines; it is followed by proliferation and differentiation of various effector and memory cells.
  • a mature B cell can be activated by an encounter with an antigen that expresses epitopes that are recognized by its cell surface immunoglobulin Ig).
  • the activation process may be a direct one, dependent on cross-linkage of membrane Ig molecules by the antigen (cross- linkage-dependent B cell activation) or an indirect one, occurring most efficiently in the context of an intimate interaction with a helper T cell (“cognate help process”).
  • T-cell activation is dependent on the interaction of the TCR/CD3 complex with its cognate ligand, a peptide bound in the groove of a class I or class II MHC molecule.
  • the molecular events set in motion by receptor engagement are complex. Among the earliest steps appears to be the activation of tyrosine kinases leading to the tyrosine phosphorylation of a set of substrates that control several signaling pathways.
  • TCR tumor necrosis factor receptor
  • phospholipase Cyl phospholipase Cyl
  • APC antigen presenting cell
  • the soluble product of an activated B lymphocyte is immmunoglobulins (antibodies).
  • the soluble product of an activated T lymphocyte is lymphokines.
  • administer means to give or to apply.
  • administering as used herein and its various grammatical forms includes in vivo administration, as well as administration directly to tissue ex vivo.
  • Antibodies are serum proteins the molecules of which possess small areas of their surface that are complementary to small chemical groupings on their targets. These complementary regions (referred to as the antibody combining sites or antigen binding sites) of which there are at least two per antibody molecule, and in some types of antibody molecules ten, eight, or in some species as many as 12, may react with their corresponding complementary region on the antigen (the antigenic determinant or epitope) to link several molecules of multivalent antigen together to form a lattice.
  • the antibody combining sites or antigen binding sites of which there are at least two per antibody molecule, and in some types of antibody molecules ten, eight, or in some species as many as 12, may react with their corresponding complementary region on the antigen (the antigenic determinant or epitope) to link several molecules of multivalent antigen together to form a lattice.
  • the basic structural unit of a whole antibody molecule consists of four polypeptide chains, two identical light (L) chains (each containing about 220 amino acids) and two identical heavy (H) chains (each usually containing about 440 amino acids).
  • the two heavy chains and two light chains are held together by a combination of noncovalent and covalent (disulfide) bonds.
  • the molecule is composed of two identical halves, each with an identical antigen-binding site composed of the N-terminal region of a light chain and the N-terminal region of a heavy chain. Both light and heavy chains usually cooperate to form the antigen binding surface.
  • Human antibodies show two kinds of light chains, k and l; individual molecules of immunoglobulin generally are only one or the other.
  • IgA In mammals, there are five classes of antibodies, IgA, IgD, IgE, IgG, and IgM, each with its own class of heavy chain - a (for IgA), d (for IgD), e (for IgE), g (for IgG) and m (for IgM).
  • IgG immunoglobulins IgGl, IgG2, IgG3, IgG4 having g ⁇ , g2, g3, and g4 heavy chains respectively.
  • IgM In its secreted form, IgM is a pentamer composed of five four-chain units, giving it a total of 10 antigen binding sites. Each pentamer contains one copy of a J chain, which is covalently inserted between two adjacent tail regions.
  • heterogeneity - that individual IgG molecules, for example, differ from one another in net charge - is an intrinsic property of the immunoglobulins.
  • An“antigenic determinant” or“epitope” is an antigenic site on a molecule. Sequential antigenic determinants/epitopes essentially are linear chains. In ordered structures, such as helical polymers or proteins, the antigenic determinants/epitopes essentially would be limited regions or patches in or on the surface of the structure involving amino acid side chains from different portions of the molecule which could come close to one another. These are conformational determinants.
  • Antigen-antibody interactions show a high degree of specificity, which is manifest at many levels. Brought down to the molecular level,“specificity” means that the combining sites of antibodies to an antigen have a complementarity not at all similar to the antigenic determinants of an unrelated antigen. Whenever antigenic determinants of two different antigens have some structural similarity, some degree of fitting of one determinant into the combining site of some antibodies to the other may occur, and that this phenomenon gives rise to cross-reactions. Cross reactions are of major importance in understanding the complementarity or specificity of antigen-antibody reactions. Immunological specificity or complementarity makes possible the detection of small amounts of impurities/contaminations among antigens
  • “Monoclonal antibodies” can be generated by fusing mouse spleen cells from an immunized donor with a mouse myeloma cell line to yield established mouse hybridoma clones that grow in selective media.
  • A“hybridoma cell” is an immortalized hybrid cell resulting from the in vitro fusion of an antibody-secreting B cell with a myeloma cell.
  • VH and V immunoglobulin heavy chain variable genes from peripheral blood lymphocytes
  • PCR polymerase chain reaction
  • Genes encoding single polypeptide chains in which the heavy and light chain variable domains are linked by a polypeptide spacer can be made by randomly combining heavy and light chain V-genes using PCR.
  • a combinatorial library then can be cloned for display on the surface of filamentous bacteriophage by fusion to a minor coat protein at the tip of the phage.
  • the technique of guided selection is based on human immunoglobulin V gene shuffling with rodent immunoglobulin V genes.
  • the method entails (i) shuffling a repertoire of human l light chains with the heavy chain variable region (VH) domain of a mouse monoclonal antibody reactive with an antigen of interest; (ii) selecting half-human Fabs on that antigen (iii) using the selected l light chain genes as“docking domains” for a library of human heavy chains in a second shuffle to isolate clone Fab fragments having human light chain genes; (v) transfecting mouse myeloma cells by electroporation with mammalian cell expression vectors containing the genes; and (vi) expressing the V genes of the Fab reactive with the antigen as a complete IgGl, l antibody molecule in the mouse myeloma.
  • ADCC antibody-dependent cell mediated cytotoxicity
  • CD3 (TCR complex) is a protein complex composed of four distinct chains.
  • the complex contains a CD3y chain, a CD35 chain, and two CD3e chains, which associate with the T cell receptor (TCR) and the z-chain to generate an activation signal in T lymphocytes.
  • TCR T cell receptor
  • the z-chain and CD3 molecules comprise the TCR complex.
  • the intracellular tails of CD3 molecules contain a conserved motif known as the immunoreceptor tyrosine-based activation motif (IT AM), which is essential for the signaling capacity of the TCR.
  • ITAM immunoreceptor tyrosine-based activation motif
  • the CD3 chain can bind ZAP70 (zeta associated protein), a kinase involved in the signaling cascade of the T cell.
  • binding and its various grammatical forms means a lasting attraction between chemical substances. Binding specificity involves both binding to a specific partner and not binding to other molecules. Functionally important binding may occur at a range of affinities from low to high, and design elements may suppress undesired cross-interactions. Post-translational modifications also can alter the chemistry and structure of interactions.“Promiscuous binding” may involve degrees of structural plasticity, which may result in different subsets of residues being important for binding to different partners. “Relative binding specificity” is a characteristic whereby in a biochemical system a molecule interacts with its targets or partners differentially, thereby impacting them distinctively depending on the identity of individual targets or partners.
  • composition to a target destination such as, but not limited to, an organ, a tissue, or a cell, may occur by any means of administration known to the skilled artisan.
  • ECso half maximal effective concentration
  • HCT hematopoietic-cell transplantation
  • BMT blood and marrow transplantation
  • lymphocyte refers to a small white blood cell formed in lymphatic tissue throughout the body and in normal adults making up about 22-28% of the total number of leukocytes in the circulating blood that plays a large role in defending the body against disease.
  • lymphocytes are specialized in that they are committed to respond to a limited set of structurally related antigens. This commitment, which exists before the first contact of the immune system with a given antigen, is expressed by the presence on the lymphocyte’s surface membrane of receptors specific for determinants (epitopes) on the antigen. Each lymphocyte possesses a population of receptors, all of which have identical combining sites.
  • lymphocytes differs from another clone in the structure of the combining region of its receptors and thus differs in the epitopes that it can recognize. Lymphocytes differ from each other not only in the specificity of their receptors, but also in their functions.
  • B- cells B-lymphocytes
  • T-cells T-lymphocytes
  • B-lymphocytes are derived from hematopoietic cells of the bone marrow.
  • a mature B-cell can be activated with an antigen that expresses epitopes that are recognized by its cell surface.
  • the activation process may be direct, dependent on cross-linkage of membrane Ig molecules by the antigen (cross-linkage-dependent B-cell activation), or indirect, via interaction with a helper T-cell, in a process referred to as cognate help.
  • cognate help In many physiological situations, receptor cross-linkage stimuli and cognate help synergize to yield more vigorous B-cell responses.
  • Cross-linkage dependent B-cell activation requires that the antigen express multiple copies of the epitope complementary to the binding site of the cell surface receptors because each B-cell expresses Ig molecules with identical variable regions. Such a requirement is fulfilled by other antigens with repetitive epitopes, such as capsular polysaccharides of microorganisms or viral envelope proteins. Cross-linkage-dependent B- cell activation is a major protective immune response mounted against these microbes.
  • Cognate help allows B-cells to mount responses against antigens that cannot cross-link receptors and, at the same time, provides costimulatory signals that rescue B cells from inactivation when they are stimulated by weak cross-linkage events.
  • Cognate help is dependent on the binding of antigen by the B-celTs membrane immunoglobulin (Ig), the endocytosis of the antigen, and its fragmentation into peptides within the B-celTs membrane immunoglobulin (Ig), the endocytosis of the antigen, and its fragmentation into peptides within the
  • the resultant peptides are loaded into a groove in a specialized set of cell surface proteins known as class II major histocompatibility complex (MHC) molecules.
  • MHC major histocompatibility complex
  • the resultant class IEpeptide complexes are expressed on the cell surface and act as ligands for the antigen-specific receptors of a set of T-cells designated as CD4+ T-cells.
  • the CD4+ T-cells bear receptors on their surface specific for the B-celTs class IEpeptide complex.
  • T cell receptor TCR
  • CD40 ligand activation ligand on the T-cell
  • CD40 B-cell signaling B-cell activation
  • T helper cells secrete several cytokines that regulate the growth and differentiation of the stimulated B-cell by binding to cytokine receptors on the B cell.
  • the CD40 ligand is transiently expressed on activated CD4+ T helper cells, and it binds to CD40 on the antigen-specific B cells, thereby tranducing a second costimulatory signal.
  • the latter signal is essential for B cell growth and differentiation and for the generation of memory B cells by preventing apoptosis of germinal center B cells that have encountered antigen.
  • Hyperexpression of the CD40 ligand in both B and T cells is implicated in the pathogenic autoantibody production in human SLE patients. (Desai-Mehta, A. et al.,“Hyperexpression of CD40 ligand by B and T cells in human lupus and its role in pathogenic autoantibody production,” J. Clin. Invest., 97(9): 2063-2073 (1996)).
  • T-lymphocytes derive from precursors in hematopoietic tissue, undergo differentiation in the thymus, and are then seeded to peripheral lymphoid tissue and to the recirculating pool of lymphocytes. T-lymphocytes or T cells mediate a wide range of immunologic functions. These include the capacity to help B cells develop into antibody- producing cells, the capacity to increase the microbicidal action of monocytes/macrophages, the inhibition of certain types of immune responses, direct killing of target cells, and mobilization of the inflammatory response. These effects depend on their expression of specific cell surface molecules and the secretion of cytokines. (Paul, W. E.,“Chapter 1 : The immune system: an introduction,” Fundamental Immunology, 4th Edition, Ed. Paul, W. E., Lippicott-Raven Publishers, Philadelphia (1999)).
  • T cells differ from B cells in their mechanism of antigen recognition.
  • Immunoglobulin the B cell’s receptor, binds to individual epitopes on soluble molecules or on particulate surfaces. B-cell receptors see epitopes expressed on the surface of native molecules. Antibody and B-cell receptors evolved to bind to and to protect against microorganisms in extracellular fluids. In contrast, T cells recognize antigens on the surface of other cells and mediate their functions by interacting with, and altering, the behavior of these antigen-presenting cells (APCs).
  • APCs antigen-presenting cells
  • Immature dendritic cells are located in tissues throughout the body, including the skin, gut, and respiratory tract. When they encounter invading microbes at these sites, they endocytose the pathogens and their products, and carry them via the lymph to local lymph nodes or gut associated lymphoid organs. The encounter with a pathogen induces the dendritic cell to mature from an antigen-capturing cell to an antigen-presenting cell (APC) that can activate T cells.
  • APC antigen-presenting cell
  • APCs display three types of protein molecules on their surface that have a role in activating a T cell to become an effector cell: (1) MHC proteins, which present foreign antigen to the T cell receptor; (2) costimulatory proteins which bind to complementary receptors on the T cell surface; and (3) cell-cell adhesion molecules, which enable a T cell to bind to the antigen-presenting cell (APC) for long enough to become activated.
  • MHC proteins which present foreign antigen to the T cell receptor
  • costimulatory proteins which bind to complementary receptors on the T cell surface
  • cell-cell adhesion molecules which enable a T cell to bind to the antigen-presenting cell (APC) for long enough to become activated.
  • T-cells are subdivided into two distinct classes based on the cell surface receptors they express.
  • the majority of T cells express T cell receptors (TCR) consisting of a and b chains.
  • TCR T cell receptors
  • a small group of T cells express receptors made of g and d chains.
  • CD4+ T cells those that express the coreceptor molecule CD4
  • CD8+ T cells those that express CD8
  • CD4+ T cells are the major regulatory cells of the immune system. Their regulatory function depends both on the expression of their cell-surface molecules, such as CD40 ligand whose expression is induced when the T cells are activated, and the wide array of cytokines they secrete when activated. [91] T cells also mediate important effector functions, some of which are determined by the patterns of cytokines they secrete. The cytokines can be directly toxic to target cells and can mobilize potent inflammatory mechanisms.
  • T cells particularly CD8+ T cells, can develop into cytotoxic T- lymphocytes (CTLs) capable of efficiently lysing target cells that express antigens recognized by the CTLs.
  • CTLs cytotoxic T- lymphocytes
  • T cell receptors recognize a complex consisting of a peptide derived by proteolysis of the antigen bound to a specialized groove of a class II or class I MHC protein.
  • the CD4+ T cells recognize only peptide/class II complexes while the CD8+ T cells recognize peptide/class I complexes.
  • the TCR’s ligand i.e., the peptide/MHC protein complex
  • APCs antigen-presenting cells
  • class II MHC molecules bind peptides derived from proteins that have been taken up by the APC through an endocytic process. These peptide-loaded class II molecules are then expressed on the surface of the cell, where they are available to be bound by CD4+ T cells with TCRs capable of recognizing the expressed cell surface complex.
  • CD4+ T cells are specialized to react with antigens derived from extracellular sources.
  • class I MHC molecules are mainly loaded with peptides derived from internally synthesized proteins, such as viral proteins. These peptides are produced from cytosolic proteins by proteolysis by the proteosome and are translocated into the rough endoplasmic reticulum. Such peptides, generally nine amino acids in length, are bound into the class I MHC molecules and are brought to the cell surface, where they can be recognized by CD8+ T cells expressing appropriate receptors.
  • T cell system particularly CD8+ T cells, the ability to detect cells expressing proteins that are different from, or produced in much larger amounts than, those of cells of the remainder of the organism (e.g., vial antigens) or mutant antigens (such as active oncogene products), even if these proteins in their intact form are neither expressed on the cell surface nor secreted.
  • vial antigens e.g., vial antigens
  • mutant antigens such as active oncogene products
  • T cells can also be classified based on their function as helper T cells; T cells involved in inducing cellular immunity; suppressor T cells; and cytotoxic T cells.
  • Helper T cells are T cells that stimulate B cells to make antibody responses to proteins and other T cell-dependent antigens.
  • T cell-dependent antigens are immunogens in which individual epitopes appear only once or a limited number of times such that they are unable to cross-link the membrane immunoglobulin (Ig) of B cells or do so inefficiently.
  • B cells bind the antigen through their membrane Ig, and the complex undergoes endocytosis. Within the endosomal and lysosomal compartments, the antigen is fragmented into peptides by proteolytic enzymes and one or more of the generated peptides are loaded into class II MHC molecules, which traffic through this vesicular compartment.
  • the resulting peptide/class II MHC complex is then exported to the B-cell surface membrane.
  • T cells with receptors specific for the peptide/class II molecular complex recognize this complex on the B-cell surface.
  • B-cell activation depends both on the binding of the T cell through its TCR and on the interaction of the T-cell CD40 ligand (CD40L) with CD40 on the B cell.
  • T cells do not constitutively express CD40L. Rather, CD40L expression is induced as a result of an interaction with an APC that expresses both a cognate antigen recognized by the TCR of the T cell and CD80 or CD86.
  • CD80/CD86 is generally expressed by activated, but not resting, B cells so that the helper interaction involving an activated B cell and a T cell can lead to efficient antibody production.
  • CD40L on T cells is dependent on their recognition of antigen on the surface of APCs that constitutively express CD80/86, such as dendritic cells.
  • Such activated helper T cells can then efficiently interact with and help B cells.
  • Cross-linkage of membrane Ig on the B cell even if inefficient, may synergize with the CD40L/CD40 interaction to yield vigorous B-cell activation.
  • the subsequent events in the B-cell response, including proliferation, Ig secretion, and class switching (of the Ig class being expressed) either depend or are enhanced by the actions of T cell-derived cytokines.
  • CD4+ T cells tend to differentiate into cells that principally secrete the cytokines IL-4, IL-5, IL-6, and IL-10 (TH2 cells) or into cells that mainly produce IL-2, IFN-g, and lymphotoxin (TH1 cells).
  • the TH2 cells are very effective in helping B-cells develop into antibody-producing cells, whereas the THl cells are effective inducers of cellular immune responses, involving enhancement of microbicidal activity of monocytes and macrophages, and consequent increased efficiency in lysing microorganisms in intracellular vesicular compartments.
  • TH1 cells Although the CD4+ T cells with the phenotype of TH2 cells (i.e., IL-4, IL-5, IL-6 and IL-10) are efficient helper cells, TH1 cells also have the capacity to be helpers. (Paul, W. E.,“Chapter 1 : The immune system: an introduction,” Fundamental Immunology, 4th Edition, Ed. Paul, W. E., Lippicott-Raven Publishers, Philadelphia (1999)).
  • T cells also may act to enhance the capacity of monocytes and macrophages to destroy intracellular microorganisms.
  • interferon-gamma IFN-D
  • helper T cells enhances several mechanisms through which mononuclear phagocytes destroy intracellular bacteria and parasitism including the generation of nitric oxide and induction of tumor necrosis factor (TNF) production.
  • the THl cells are effective in enhancing the microbicidal action because they produce IFN-g.
  • two of the major cytokines produced by TH2 cells IL-4 and IL-10, block these activities.
  • a controlled balance between initiation and downregulation of the immune response is important to maintain immune homeostasis.
  • Both apoptosis and T cell anergy are important mechanisms that contribute to the downregulation of the immune response.
  • a third mechanism is provided by active suppression of activated T cells by suppressor or regulatory CD4+ T (Treg) cells. (Reviewed in Kronenberg, M. et ak, “Regulation of immunity by self-reactive T cells,” Nature 435: 598-604 (2005)).
  • CD4+ Tregs that constitutively express the IL-2 receptor alpha (IL-2RD) chain are a naturally occurring T cell subset that are anergic and suppressive.
  • IL-2RD IL-2 receptor alpha
  • CD4+ CD25+ are a naturally occurring T cell subset that are anergic and suppressive.
  • Depletion of CD4+CD25+ Tregs results in systemic autoimmune disease in mice. Furthermore, transfer of these Tregs prevents development of autoimmune disease.
  • Human CD4+CD25+ Tregs similar to their murine counterpart, are generated in the thymus and are characterized by the ability to suppress proliferation of responder T cells through a cell-cell contact-dependent mechanism, the inability to produce IL-2, and the anergic phenotype in vitro.
  • Human CD4+CD25+ T cells can be split into suppressive (CD25high) and nonsuppressive (CD251ow) cells, according to the level of CD25 expression.
  • CD25high suppressive
  • CD251ow nonsuppressive
  • CD4+CD25+ Tregs and appears to be a master gene controlling CD4+CD25+ Treg development.
  • CTL Cytotoxic T Lymphocytes
  • the CD8+ T cells that recognize peptides from proteins produced within the target cell have cytotoxic properties in that they lead to lysis of the target cells.
  • the mechanism of CTL-induced lysis involves the production by the CTL of perforin, a molecule that can insert into the membrane of target cells and promote the lysis of that cell.
  • Perforin-mediated lysis is enhanced by a series of enzymes produced by activated CTLs, referred to as granzymes. Many active CTLs also express large amounts of fas ligand on their surface. The interaction of fas ligand on the surface of CTL with fas on the surface of the target cell initiates apoptosis in the target cell, leading to the death of these cells.
  • CTL- mediated lysis appears to be a major mechanism for the destruction of virally infected cells. Priming
  • the term“unprimed cells” (also referred to as virgin, naive, or inexperienced cells) as used herein refers to T cells and B cells that have generated an antigen receptor (TCR for T cells, BCR for B cells) of a particular specificity, but have never encountered the antigen.
  • the term“priming” as used herein refers to the process whereby T cells and B cell precursors encounter the antigen for which they are specific.
  • helper T cells and B cells can interact to produce specific antibody
  • the antigen-specific T cell precursors must be primed. Priming involves several steps: antigen uptake, processing, and cell surface expression bound to class II MHC molecules by an antigen presenting cell, recirculation and antigen-specific trapping of helper T cell precursors in lymphoid tissue, and T cell proliferation and differentiation. Janeway, CA, Jr.,“The priming of helper T cells, Semin. Immunol. 1(1): 13-20 (1989).
  • Helper T cells express CD4, but not all CD4 T cells are helper cells. Id. The signals required for clonal expansion of helper T cells differ from those required by other CD4 T cells.
  • the critical antigen-presenting cell for helper T cell priming appears to be a macrophage; and the critical second signal for helper T cell growth is the macrophage product interleukin 1 (IL- 1). Id. If the primed T cells and/or B cells receive a second, co-stimulatory signal, they become activated T cells or B cells.
  • IL-1 macrophage product interleukin 1
  • transplantation refers to removal and transfer of cells, a tissue or an organ from one part or individual to another.
  • the described invention provides a recombinant bispecific antibody that binds to both human Flt3 and human CD3.
  • the Flt3 antibody binds to a FLT3/FLK2 receptor protein.
  • the FLT3/FLK2 receptor protein is a mammalian protein.
  • the FLT3/FLK2 receptor protein is human.
  • the FLT3/FLK2 receptor protein is native.
  • the FLT3/FLK2 receptor protein is native.
  • the FLT3/FLK2 receptor protein is in a modified form. According to some embodiments, the FLT3/FLK2 receptor protein is in a denatured form. According to some embodiments, the FLT3/FLK2 receptor protein is in an unmodified form.
  • the Flt3 antibody is selected from the group consisting of a monoclonal antibody, a polyclonal antibody, an antibody fragment and a synthetic antibody mimic. According to some embodiments, the Flt3 antibody is a monoclonal antibody. According to some embodiments, the FLt3 monoclonal antibody is selected from the group consisting of a synthetic antibody and an engineered antibody. According to some embodiments, the synthetic antibody is a recombinant antibody.
  • the recombinant antibody is a single-chain variable fragment (scFv) antibody.
  • the single chain antibody comprises a C terminus of an Fab fragment of an Flt3 antibody that is joined to a CH2 domain of an IgGl.
  • the CH2 domain of IgGl is joined to a single chain variable fragment (ScFv) of an antibody that reacts with a subunit of human CD3.
  • the single chain variable fragment is a monoclonal antibody.
  • the subunit of human CD3 is UCHT1.
  • the engineered antibody is a chimeric antibody.
  • the engineered antibody is a humanized antibody.
  • the FLT3 antibody binding to Flt3 is effective to block the binding of an FLT3 ligand to FLT3/FLK2 receptor protein. According to some embodiments, the FLT3 antibody binding to Flt3 on the cell is effective for the cell to internalize the bound antibody.
  • the Flt3 antibody has a half maximal effective concentration (EC o) between about 1 ng/mL (6.25 pM) and about 2,000 ng/mL (12.5 nM). According to some embodiments, the Flt3 antibody has a half maximal effective concentration (EC50) between about 10 ng/mL (62.5 pM) and about 200 ng/mL (1.25 nM).
  • the bispecific antibody that binds to both human Flt3 and human CD3 is effective to eliminate one or more of hematopoietic stem cells (HPC), early hematopoietic progenitors (HP), and cancer cells.
  • HPC hematopoietic stem cells
  • HP early hematopoietic progenitors
  • cancer cells express FLT3.
  • a subject in need thereof is a patient that qualifies for, will be receiving or is receiving
  • the cancer cells include, without limitation, blast cells of acute myeloid leukemia (AML), acute lymphocytic leukemia (ALL), blast-crisis phase of chronic myeloid leukemia (BC-CML) and chronic lymphocytic leukemia (CLL).
  • AML acute myeloid leukemia
  • ALL acute lymphocytic leukemia
  • BC-CML blast-crisis phase of chronic myeloid leukemia
  • CLL chronic lymphocytic leukemia
  • the bispecific antibody is effective to condition patients undergoing bone marrow (BM)/hematopoietic stem cell (HSC) transplantation.
  • the HSC/HP transplantation is for treating a hematological malignancy or hyperproliferative disorder, e.g., Acute Myeloid Leukemia (AML), Acute Lymphoblastic Leukemia (ALL), Chronic Lymphocytic Leukemia (CLL), Chronic Myeloid Leukemia (CML), peripheral T cell lymphoma, follicular lymphoma, diffuse large B cell lymphoma, Hodgkin lymphoma, non-Hodgkin lymphoma, neuroblastoma, non-malignant inherited and acquired marrow disorders (e.g.
  • AML Acute Myeloid Leukemia
  • ALL Acute Lymphoblastic Leukemia
  • CLL Chronic Lymphocytic Leukemia
  • CML Chronic Myeloid Leukemia
  • peripheral T cell lymphoma follicular lymphoma
  • diffuse large B cell lymphoma Hodgkin lymphoma
  • non-Hodgkin lymphoma neuroblastoma
  • a method for preparing a recombinant single chain bi-specific antibody that binds to both human FLT3 and human CD3 comprises joining a C-terminus of an Fab fragment of an Flt3 monoclonal antibody to a CH2 domain of IgGl, and joining to the CH2 domain of the IgGl a single chain variable fragment (ScFv) of a monoclonal antibody that reacts with a subunit of human CD3 (UCHT1).
  • the described invention provides for a method of eliminating hematopoietic stem cells/hematopoietic progenitors (HSC/HP) in patients in need thereof.
  • the method comprises administering to said patients a bi-specific antibody that specifically binds to HSC/HP and to T-cells.
  • the bi-specific antibody binds to human FLT3 expressed by HSC/HP and to human CD3 expressed by T cells.
  • the simultaneous binding of the antibody redirects T- cells to specifically eliminating the HSC/HP of the patients.
  • the method provides also the administration of an effective amount of the specific antibody to the patient.
  • the effective amount goes from 0.01 mg/kg to 10 mg/kg, better 0.05 mg/kg to 2mg/kg, better 0. lmg/kg to 0.5mg/kg, better 0. lmg/kg to 0.3mg/kg, better 0. lmg/kg.
  • the bi-specific antibody that binds to primate and human CD3 is a humanized antibody.
  • the bi-specific antibody or antigen-binding portion thereof comprises amino acid sequences of FLT3 antibody.
  • the bi-specific antibody or antigen-binding portion thereof comprises amino acid sequences of CD3 antibody.
  • the bi-specific antibody or antigen-binding portion thereof comprises an isotype selected from the group consisting of: an
  • immunoglobulin G an IgM, an IgE, an IgA, or an IgD isotype.
  • the invention also provides for a method of eliminating HSC/HP in a patient in need thereof, wherein the HSC/HP express FLT3.
  • the method comprises selecting a patient in need of eliminating HSC/HP and administering to the patient a therapeutically effective amount of a pharmaceutical composition comprising a bi-specific antibody specifically binding to human FLT3 expressed by HSC/HP and to human CD3 expressed by T-cells, wherein the bi-specific antibody redirects T-cells to kill HSC/HP of the patient.
  • the patients in need of eliminating HSC/HP are patients suffering from Acute Myeloid Leukemia (AML), Acute Lymphoblastic Leukemia (ALL), Chronic Lymphocytic Leukemia (CLL), Chronic Myeloid Leukemia (CML), peripheral T cell lymphoma, follicular lymphoma, diffuse large B cell lymphoma, Hodgkin lymphoma, non-Hodgkin lymphoma, non-hematological malignancies such as neuroblastoma, non-malignant inherited and acquired marrow disorders (e.g.
  • BM Hematopoietic Stem Cell
  • the pharmaceutical composition comprises the antibody and pharmaceutically acceptable carriers, diluents or excipients.
  • the carriers are selected from for example, one or more of water, saline, phosphate buffered saline, dextrose, glycerol, ethanol and the like, as well as combinations thereof.
  • Pharmaceutically acceptable carriers can further comprise minor amounts of auxiliary substances such as wetting or emulsifying agents, preservatives or buffers, which enhance the shelf life or effectiveness of the binding proteins.
  • the pharmaceutical compositions can, as is well known in the art, be formulated so as to provide rapid, sustained or delayed release of the active ingredient after administration (Mishra, M. K. (2016). Handbook of encapsulation and controlled release. Boca Raton, CRC Press, Taylor & Francis Group, CRC Press is an imprint of the Taylor & Francis Group, an Informa business, incorporated herein by reference in its entirety).
  • the pharmaceutical composition may further comprise another component such as T-cells or an antitumor agent.
  • Antitumor agents administered in conjunction with the antibody include any agents which destroy or damage a tumor or malignant cells.
  • the antitumor agent is selected from the group consisting of suitable anti neoplastic agents that are known to those skilled in the art and include anthracyclines (e.g. daunomycin and doxorubicin), auristatin, methotrexate (MTX), vindesine, neocarzinostatin, cis-platinum, chlorambucil, cytosine arabinoside, 5-fluorouridine, melphalan, ricin and calicheamicin including combination chemotherapy such with doxorubicin, bleomycin, vinblastine, and dacarbazine (ABVD), BEACOPP or escalated BEACOPP (bleomycin, etoposide, doxorubicin, cyclophosphamide, vincristine, procarbazine, and prednisone) and Stanford V (doxorubicin, vinblastine, mechlorethamine, vincristine, bleomycin, etopo
  • the antitumor agent can also be immunotherapy (e.g. anti-CD20 antibody rituximab), immunotoxins (e.g. Brentuximab vedotin (SGN-35) is an immunotoxin comprised of a CD-30 directed antibody linked to the antitubulin agent monomethyl auristatin E (MMAE)), adoptive immunotherapy (cytotoxic T lymphocytes), programmed death 1 (PD-1) blockade (eg, nivolumab, pembrolizumab).
  • immunotherapy e.g. anti-CD20 antibody rituximab
  • immunotoxins e.g. Brentuximab vedotin (SGN-35
  • SGN-35 is an immunotoxin comprised of a CD-30 directed antibody linked to the antitubulin agent monomethyl auristatin E (MMAE)
  • adoptive immunotherapy cytotoxic T lymphocytes
  • PD-1 blockade eg, nivolumab, pembroli
  • the invention further provides for a method of testing of bi-specific antibodies redirecting T-cells to kill HSC/HP in an animal model in vivo , wherein said animal model is immune-compromised humanized mice with a chimeric mouse-human hematopoietic system, wherein said humanized mice are created by transplantation of human HSC/HP or transplantation of human post-natal hemogenic endothelial cells into said myeloablated immune-compromised mice.
  • the bi-specific antibody of the present invention has been synthesized according to the method described in Durben et al. (Molecular Therapy, vol. 23, no. 4 April 2015), which is incorporated herein by reference in its entirety.
  • Fabsc is a recombinant bispecific antibody format.
  • the Fabsc format for a bispecific antibody targeting FLT3 (using 4G8 clone) and CD3 (using UCHT1 antibody sequence, also referred to as huxCD3vl) is as follows: C-terminus of Fab fragment of Flt3 mAb will be joined to the CH2 domain of IgGl, followed by the ScFv of UCHT1.
  • Study Report including: Certificate of Analysis, CE-SDS analysis, SE-HPLC analysis report.
  • the Fabsc antibody was cloned into a high expression mammalian vector system and a small-scale (0.1 liter) premium transient production was completed in HEK293 cells.
  • the protein was purified by Protein L purification and 20.17 mg of protein was obtained. Yields were reported and client confirmed that SE-HPLC should be performed.
  • the antibody was determined to be 92% non-aggregated monomer by SE-HPLC.
  • HEK293 cells were seeded in a shake flask one day before transfection, and were grown using serum-free chemically defined media.
  • the DNA expression constructs were transiently transfected into 0.1 liter of suspension HEK293 cells using standard operating procedure for transient transfection. After 20 hours, cells were sampled to obtain the viability and viable cell count, and titer was measured (Octet QKe, ForteBio). The culture was harvested at day 5 and additional readings were taken.
  • the conditioned media for Fabsc was harvested and clarified from the transient transfection production run by centrifugation and filtration. The supernatant was run over a Protein L column and eluted with a low pH buffer. Filtration using a 0.2 pm membrane filter was performed before aliquoting. After purification and filtration, the protein concentration was calculated from the OD280 and the extinction coefficient. See Table 1 for a summary of yields and aliquots.
  • CE- SDS analysis was performed (LabChip GXII, Perkin Elmer) and the electropherogram was plotted and is shown in FIG. 1 A and IB.
  • the Fabsc antibody was cloned into LakePharma’s high expression mammalian vector system and a small-scale (0.1 liter) premium transient production was completed in HEK293 cells.
  • the protein was purified by Protein L purification and 20.17 mg of protein was obtained and 19.07 mg was delivered.
  • the antibody was determined to be 92% non-aggregated by SE-HPLC. See Table 1 for a summary of yields and aliquots.
  • BM/HSC Marrow/Hematopoietic Stem Cell
  • BM/HSC bone marrow/hematopoietic stem cell
  • HSC/HP hematopoietic stem cells/hematopoietic progenitors
  • CB treated with anti -coagulant was mixed with phosphate-buffered saline (PBS) in the 1 : 1 ratio and overlaid (35ml of the mixture) on a layer of Ficoll-Paque (10ml) in 50ml conical centrifuge tubes. The tubes were then spun at a speed of 400 x g. A monocyte lymphocyte layer was carefully removed and cells obtained from that layer were washed twice with PBS.
  • PBS phosphate-buffered saline
  • CD34+ HSC/HP were isolated by negative selection with platelet depletion (Stemcell Technologies). Unwanted cells were targeted for removal with Tetrameric Antibody Complexes recognizing CD2, CD3, CDl lb, CDl lc, CD14, CD16, CD19, CD24, CD56, CD61, CD66b, glycophorin A and dextran-coated magnetic particles. The labeled cells were separated using an Easy SepTM magnet without the use of columns.
  • CD34+ HSC/HP were re-suspended in PBS at 10,000-50,000 cells per 200 m ⁇ for transplantation into a myeloablated NOG mouse.
  • mice were myeloablated using Busulfan (10 mg/kg) via intra-peritoneal injection twenty-four hours before the transplantation.
  • Eighteen (18) weeks post transplantation peripheral blood of transplanted mice was tested for the presence of human CD45 + cells.
  • IGEIDP SD S YKD YNQKFKDKATLT VDRS SNT AYMHLS SLTSDD S AVYY C ARAITTTPFDF W GQGTTLT
  • spleens of immunized mice were collected and used for isolation of splenocytes. Isolated splenocytes we fused with SP2/0 cells and selected for the hybrid phenotype (hybridomas). Hybidomas were cultured in vitro and supernatants from the culture of the hybridomas were screened for the presence of anti-FLT3/FLK2 antibodies by flow cytometry (FIGS. 3 A and 3B). Nine hybridoma clones demonstrated production of anti-FLT3/FLK2 antibodies. These hybridoma clones were expanded for isolation of monoclonal antibodies.
  • FLT3/FLK2 antibody (BioLegend #313302, Clone BV10A4H2) and a 4pg/ml isotype control (BioLegend #400102, Clone MOPC-21) were prepared as positive and negative CD135 staining controls, respectively.
  • Reh cells a human cell line that expresses CD 135, were washed and re-suspended in staining buffer at a concentration of 2xl0 6 cells/ml.

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