Bi-specific T-cell engagers (BiTEs) are a class of artificial

bispecific monoclonal antibodies A bispecific monoclonal antibody (BsMAb, BsAb) is an artificial protein that can simultaneously bind to two different types of antigen or two different epitopes on the same antigen. Naturally occurring antibodies typically only target one antigen. ...

that are investigated for use as

anti-cancer drug Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a type of cancer treatment that uses one or more anti-cancer drugs ( chemotherapeutic agents or alkylating agents) as part of a standardized chemotherapy regimen. Chemothera ...

s. They direct a host's immune system, more specifically the

T cell A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell r ...

cytotoxic Cytotoxicity is the quality of being toxic to cells. Examples of toxic agents are an immune cell or some types of venom, e.g. from the puff adder (''Bitis arietans'') or brown recluse spider (''Loxosceles reclusa''). Cell physiology Treating cells ...

activity, against cancer cells. ''BiTE'' is a registered

trademark A trademark (also written trade mark or trade-mark) is a type of intellectual property consisting of a recognizable sign, design, or expression that identifies products or services from a particular source and distinguishes them from others ...

of Micromet AG (fully owned subsidiary of Amgen Inc). BiTEs are

fusion protein Fusion proteins or chimeric (kī-ˈmir-ik) proteins (literally, made of parts from different sources) are proteins created through the joining of two or more genes that originally coded for separate proteins. Translation of this ''fusion gene'' r ...

s consisting of two

single-chain variable fragment A single-chain variable fragment (scFv) is not actually a fragment of an antibody, but instead is a fusion protein of the variable regions of the heavy (VH) and light chains (VL) of immunoglobulins, connected with a short linker peptide of ten ...

s (scFvs) of different antibodies, or

amino acid sequence Protein primary structure is the linear sequence of amino acids in a peptide or protein. By convention, the primary structure of a protein is reported starting from the amino-terminal (N) end to the carboxyl-terminal (C) end. Protein biosynthe ...

s from four different genes, on a single

peptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. A ...

chain of about 55

kilodalton The dalton or unified atomic mass unit (symbols: Da or u) is a non-SI unit of mass widely used in physics and chemistry. It is defined as of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at ...

s. One of the scFvs binds to T cells via the CD3 receptor, and the other to a tumor cell via a tumor specific molecule.

Mechanism of action

Like other bispecific antibodies, and unlike ordinary monoclonal antibodies, BiTEs form a link between T cells and tumor cells. This causes T cells to exert

activity on tumor cells by producing proteins like

perforin Perforin-1 is a protein that in humans is encoded by the ''PRF1'' gene and the ''Prf1'' gene in mice. Function Perforin is a pore forming cytolytic protein found in the granules of cytotoxic T lymphocytes (CTLs) and natural killer cells (NK ce ...

and

granzyme Granzymes are serine proteases released by cytoplasmic granules within cytotoxic T cells and natural killer (NK) cells. They induce programmed cell death (apoptosis) in the target cell, thus eliminating cells that have become cancerous or are infec ...

s, independently of the presence of

MHC I MHC class I molecules are one of two primary classes of major histocompatibility complex (MHC) molecules (the other being MHC class II) and are found on the cell surface of all nucleated cells in the bodies of vertebrates. They also occur on pla ...

co-stimulatory Co-stimulation is a secondary signal which immune cells rely on to activate an immune response in the presence of an antigen-presenting cell. In the case of T cells, two stimuli are required to fully activate their immune response. During the activa ...

molecules. These proteins enter tumor cells and initiate the cell's

apoptosis Apoptosis (from grc, ἀπόπτωσις, apóptōsis, 'falling off') is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes (morphology) and death. These changes incl ...

. This action mimics physiological processes observed during T cell attacks against tumor cells.

BiTEs in clinical assessment or with clinical approvals

Several BiTEs are currently in preclinical and clinical trials to assess their therapeutic efficacy and safety.

Blinatumomab

Blinatumomab links T cells with CD19 receptors found on the surface of B cells. The Food and Drug Administration (US) and the European Medicines Agency approved this therapy for adults with Philadelphia chromosome-negative relapsed or refractory acute lymphoblastic leukemia.

Solitomab

Solitomab links T cells with the

EpCAM Epithelial cell adhesion molecule (EpCAM), also known as CD326 among other names, is a transmembrane glycoprotein mediating Ca2+-independent homotypic cell–cell adhesion in epithelia. EpCAM is also involved in cell signaling, migration, prol ...

antigen which is expressed by colon, gastric, prostate, ovarian, lung, and pancreatic cancers.

Tebentafusp

After clinical trials, in Jan 2022 the

US FDA The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food s ...

approved tebentafusp (a BiTE targeting the gp100 peptide) for HLA-A*02:01-positive adult patients with unresectable or metastatic

uveal melanoma Uveal melanoma is a type of eye cancer in the uvea of the eye. It is traditionally classed as originating in the Iris (anatomy), iris, choroid, and ciliary body, but can also be divided into class I (low metastatic risk) and class II (high metasta ...

Further research

Utilizing the same technology,

melanoma Melanoma, also redundantly known as malignant melanoma, is a type of skin cancer that develops from the pigment-producing cells known as melanocytes. Melanomas typically occur in the skin, but may rarely occur in the mouth, intestines, or eye ( ...

(with MCSP specific BiTEs) and

acute myeloid leukemia Acute myeloid leukemia (AML) is a cancer of the myeloid line of blood cells, characterized by the rapid growth of abnormal cells that build up in the bone marrow and blood and interfere with normal blood cell production. Symptoms may includ ...

(with

CD33 CD33 or Siglec-3 (sialic acid binding Ig-like lectin 3, SIGLEC3, SIGLEC-3, gp67, p67) is a transmembrane receptor expressed on cells of myeloid lineage. It is usually considered myeloid-specific, but it can also be found on some lymphoid cells. ...

specific BiTEs) can be targeted. , research in this area is active. Another avenue for novel anti-cancer therapies is re-engineering some of the currently used conventional antibodies like

trastuzumab Trastuzumab, sold under the brand name Herceptin among others, is a monoclonal antibody used to treat breast cancer and stomach cancer. It is specifically used for cancer that is HER2 receptor positive. It may be used by itself or together wit ...

(targeting

HER2/neu Receptor tyrosine-protein kinase erbB-2 is a protein that in humans is encoded by the ''ERBB2'' gene. ERBB is abbreviated from erythroblastic oncogene B, a gene originally isolated from the avian genome. The human protein is also frequently refer ...

cetuximab Cetuximab, sold under the brand name Erbitux, is an epidermal growth factor receptor (EGFR) inhibitor medication used for the treatment of metastatic colorectal cancer and head and neck cancer. Cetuximab is a chimeric (mouse/human) monoclonal an ...

and

panitumumab Panitumumab, sold under the brand name Vectibix, is a fully human monoclonal antibody specific to the epidermal growth factor receptor (also known as ''EGF receptor'', ''EGFR'', ''ErbB-1'' and ''HER1'' in humans). Panitumumab is manufactured by ...

(both targeting the

EGF receptor EGF may refer to: * E.G.F., a Gabonese company * East Grand Forks, Minnesota, a city * East Garforth railway station in England * Epidermal growth factor * Equity Group Foundation, a Kenyan charity * European Gendarmerie Force, a military unit of ...

), using the BiTE approach. , BiTEs against CD66e and

EphA2 EPH receptor A2 (ephrin type-A receptor 2) is a protein that in humans is encoded by the ''EPHA2'' gene. Function This gene belongs to the ephrin receptor subfamily of the protein- tyrosine kinase family. EPH and EPH-related receptors have be ...

are being developed as well.