Atacicept is a

recombinant 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 ...

designed to inhibit

B cell B cells, also known as B lymphocytes, are a type of white blood cell of the lymphocyte subtype. They function in the humoral immunity component of the adaptive immune system. B cells produce antibody molecules which may be either secreted or ...

s, thereby suppressing

autoimmune disease An autoimmune disease is a condition arising from an abnormal immune response to a functioning body part. At least 80 types of autoimmune diseases have been identified, with some evidence suggesting that there may be more than 100 types. Nearly a ...

. The designer protein combines the binding site for two

cytokine Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm. Cytokines have been shown to be involved in autocrin ...

s that regulate maturation, function, and survival of B cells - B-lymphocyte stimulator (BLyS) and A proliferation-inducing ligand (APRIL), with the constant region of

immunoglobin An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...

. Atacicept blocks activation of B cells by the tumor necrosis factor receptor superfamily member 13B (more commonly known as TACI), a transmembrane receptor protein found predominantly on the surface of B cells. Like the

monoclonal antibody A monoclonal antibody (mAb, more rarely called moAb) is an antibody produced from a cell Lineage made by cloning a unique white blood cell. All subsequent antibodies derived this way trace back to a unique parent cell. Monoclonal antibodies ca ...

belimumab Belimumab, sold under the brand name Benlysta, is a human monoclonal antibody that inhibits B-cell activating factor (BAFF), also known as B-lymphocyte stimulator (BLyS). It is approved in the United States, Canada, and the European Union to treat ...

, atacicept blocks the binding of BLyS, but it also blocks APRIL. Binding of these TACI ligands induces proliferation, activation, and longevity of B cells and thus their production of

autoantibodies An autoantibody is an antibody (a type of protein) produced by the immune system that is directed against one or more of the individual's own proteins. Many autoimmune diseases (notably lupus erythematosus) are associated with such antibodies. Pr ...

. Atacicept is thought to selectively impair mature B cells and plasma cells with less impact on

progenitor cell A progenitor cell is a Cell (biology), biological cell that can Cellular differentiation, differentiate into a specific cell type. Stem cells and progenitor cells have this ability in common. However, stem cells are less specified than progenitor ...

s and

memory B cell In immunology, a memory B cell (MBC) is a type of B lymphocyte that forms part of the adaptive immune system. These cells develop within germinal centers of the secondary lymphoid organs. Memory B cells circulate in the blood stream in a quiescen ...

s. Studies have looked at atacicept in animal models of autoimmune disease and in patients with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and optic neuritis. A phase II/III trial for

systemic lupus erythematosus Lupus, technically known as systemic lupus erythematosus (SLE), is an autoimmune disease in which the body's immune system mistakenly attacks healthy tissue in many parts of the body. Symptoms vary among people and may be mild to severe. Comm ...

is due to run from 2008 to 2012. The subcutaneously injected protein failed a phase II trial for

multiple sclerosis Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This d ...

. The trials of atacicept in people with MS were suspended when some people taking the drug in one trial had an unexpected increase in inflammatory activity. An independent data monitoring board for the MS study found "subjects receiving atacicept were having more relapses and new MRI lesions than those on the placebo." The drug is also being studied for treatment of B-cell malignancies, including

multiple myeloma Multiple myeloma (MM), also known as plasma cell myeloma and simply myeloma, is a cancer of plasma cells, a type of white blood cell that normally produces antibodies. Often, no symptoms are noticed initially. As it progresses, bone pain, an ...

B-cell chronic lymphocytic leukemia Chronic lymphocytic leukemia (CLL) is a type of cancer in which the bone marrow makes too many lymphocytes (a type of white blood cell). Early on, there are typically no symptoms. Later, non-painful lymph node swelling, feeling tired, fever, nigh ...

, and

non-Hodgkin's lymphoma Non-Hodgkin lymphoma (NHL), also known as non-Hodgkin's lymphoma, is a group of blood cancers that includes all types of lymphomas except Hodgkin lymphomas. Symptoms include lymphadenopathy, enlarged lymph nodes, fever, night sweats, weight los ...

. Atacicept was developed by a Seattle-based biotech company, ZymoGenetics, which handed the product over to Merck Serono for further development.

References

{{reflist Engineered proteins Merck brands