CD22 Chimeric Monoclonal Antibody (Clone hL22 (Epratuzumab))

CD22 is a transmembrane receptor and member of the sialic acid-binding immunoglobulin-type (Ig-type) lectin (SIGLEC) family.^1,2 It is composed of N-terminal extracellular Ig-like variable (IgV) and Ig-like constant 2 (IgC2) domains, a membrane-spanning region, and an intracellular immunoreceptor tyrosine-based inhibitory motif (ITIM) domain. CD22 has two isoforms formed via alternative splicing, CD22β, which is the full-length form and contains six IgC2 domains, and CD22α, which lacks the third and fourth IgC2 domains. It is expressed in the cytosol of premature B cells and on the cell surface of resting and activated B lymphocytes but is not expressed in differentiated B cells.³ CD22 is an inhibitory receptor activated by binding of α2,6-linked sialic acid-containing molecules, such as glycoproteins, which stimulates phosphorylation of tyrosine in the ITIM domain, leading to recruitment of Src homology 2 domain-containing phosphatases (SHPs), including SHP-1, spleen tyrosine kinase (Syk), LYN, and PI3K.^1,2 Knockout of Cd22 decreases IgG1 titers in mice immunized with OVA/alum and expression of human CD22 in Cd22 ^-/- mice rescues this phenotype.⁴ CD22 is overexpressed in cancer cells isolated from patients with hairy cell leukemia.³ Cayman’s CD22 Chimeric Monoclonal Antibody (Clone hL22 (Epratuzumab)) was produced recombinantly from the humanized EPB-2/LL2 antibody sequence and can be used for flow cytometry (FC) and immunoprecipitation (IP) applications. The humanized EPB-2/LL2 antibody was generated by fusing human IgG1 constant domains to the antigen-binding domain of the anti-CD22 mouse monoclonal antibody, EPB-2/mLL2.^5,6

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1. Clark, E.A., and Giltiay, N.V. CD22: A regulator of innate and adaptive B cell responses and autoimmunity. Front. Immunol. 9, 2235 (2018).

2. Tedder, T.F., Tuscano, J., Sato, S., et al. CD22, a B lymphocyte-specific adhesion molecule that regulates antigen receptor signaling. Annu. Rev. Immunol. 15, 481-504 (1997).

3. Dörken, B., Moldenhauer, G., Pezzutto, A., et al. HD39 (B₃), a B lineage-restricted antigen whose cell surface expression is limited to resting and activated human B lymphocytes. J. Immunol. 136(12), 4470-4479 (1986).

4. Bednar, K.J., Shanina, E., Ballet, R., et al. Human CD22 inhibits murine B cell receptor activation in a human CD22 transgenic mouse model. J. Immunol. 199(9), 3116-3128 (2017).

5. Pawlak-Byczkowska, E.J., Hansen, H.J., Dion, A.S., et al. Two new monoclonal antibodies, EPB-1 and EPB-2, reactive with human lymphoma. Cancer Res. 49(16), 4568-4577 (1989).

6. Leung, S.-O., Goldenberg, D.M., Dion, A.S., et al. Construction and characterization of a humanized, internalizing, B-cell (CD22)-specific, leukemia/lymphoma antibody, LL2. Mol. Immunol. 32(17-18), 1413-1427 (1995).