CD22, or cluster of differentiation-22, is a molecule belonging to the SIGLEC family of lectins.[5] It is found on the surface of mature B cells and to a lesser extent on some immature B cells. Generally speaking, CD22 is a regulatory molecule that prevents the overactivation of the immune system and the development of autoimmune diseases.[6]
CD22 is a sugar binding transmembrane protein, which specifically binds sialic acid with an immunoglobulin (Ig) domain located at its N-terminus. The presence of Ig domains makes CD22 a member of the immunoglobulin superfamily. CD22 functions as an inhibitory receptor for B cell receptor (BCR) signaling. It is also involved in the B cell trafficking to Peyer's patches in mice.[7] In mice, it has been shown that CD22 blockade restores homeostatic microglial phagocytosis in aging brains.[8]
An immunotoxin, BL22 (CAT-3888), that targets this receptor was developed at the NIH.[9] BL22 was superseded by moxetumomab pasudotox (HA22, CAT-8015).[10] Moxetumomab pasudotox is approved in the EU and USA for treatment of relapsed or refractory hairy cell leukemia.[11][12]
As a treatment for acute lymphoblastic leukemia (ALL), Inotuzumab ozogamicin is an antibody-drug conjugate that targets this molecule.
^"Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^"Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^Crocker PR, Clark EA, Filbin M, Gordon S, Jones Y, Kehrl JH, et al. (February 1998). "Siglecs: a family of sialic-acid binding lectins". Glycobiology. 8 (2): v. doi:10.1093/glycob/8.2.0. PMID9498912.
^Hatta Y, Tsuchiya N, Matsushita M, Shiota M, Hagiwara K, Tokunaga K (April 1999). "Identification of the gene variations in human CD22". Immunogenetics. 49 (4): 280–6. doi:10.1007/s002510050494. PMID10079291. S2CID22947237.
^Clinical trial number NCT00074048 for "BL22 Immunotoxin in Treating Patients Previously Treated With Cladribine for Hairy Cell Leukemia" at ClinicalTrials.gov
^ abGreer SF, Justement LB (May 1999). "CD45 regulates tyrosine phosphorylation of CD22 and its association with the protein tyrosine phosphatase SHP-1". Journal of Immunology. 162 (9): 5278–86. PMID10228003.