Biology:CD20

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Short description: Mammalian protein found in Homo sapiens


A representation of the 3D structure of the protein myoglobin showing turquoise α-helices.
Generic protein structure example

B-lymphocyte antigen CD20 or CD20 is expressed on the surface of all B-cells beginning at the pro-B phase (CD45R+, CD117+) and progressively increasing in concentration until maturity.[1]

In humans CD20 is encoded by the MS4A1 gene.[2][3]

This gene encodes a member of the membrane-spanning 4A gene family. Members of this nascent protein family are characterized by common structural features and similar intron/exon splice boundaries and display unique expression patterns among hematopoietic cells and nonlymphoid tissues. This gene encodes a B-lymphocyte surface molecule that plays a role in the development and differentiation of B-cells into plasma cells. This family member is localized to 11q12, among a cluster of family members. Alternative splicing of the human MS4A1 gene results in at least three transcript variants (1 to 3) that encode the same protein.[3] Variants 1 and 2 are poorly translated due to inhibitory upstream open reading frames and stem-loop structures within their 5' untranslated regions. The relative abundance of translation-competent variant 3, as opposed to the poorly translated variants 1 and 2, may be a key determinant of CD20 levels in normal and malignant human B cells and their responses to CD20-directed immunotherapies. [4]

Function

The protein has no known natural ligand[5] and its function is to enable optimal B-cell immune response, specifically against T-independent antigens.[6] It is suspected that it acts as a calcium channel in the cell membrane. CD20 is induced in the context of microenvironmental interactions by CXCR4/SDF1 (CXCL12) chemokine signaling and the molecular function of CD20 has been linked to the signaling propensity of B-cell receptor (BCR) in this context.[7]

Expression

CD20 is expressed on all stages of B cell development except the first and last; it is present from late pro-B cells through memory cells, but not on either early pro-B cells or plasma blasts and plasma cells.[8][9] It is found on B-cell lymphomas, hairy cell leukemia, B-cell chronic lymphocytic leukemia, and melanoma cancer stem cells.[10]

Immunohistochemistry can be used to determine the presence of CD20 on cells in histological tissue sections. Because CD20 remains present on the cells of most B-cell neoplasms, and is absent on otherwise similar appearing T-cell neoplasms, it can be very useful in diagnosing conditions such as B-cell lymphomas and leukaemias. However, the presence or absence of CD20 in such tumours is not relevant to prognosis, with the progression of the disease being much the same in either case. CD20 positive cells are also sometimes found in cases of Hodgkins disease, myeloma, and thymoma.[11]

Antibody FMC7 (Flinders Medical Centre) appears to recognise a conformational variant of CD20[12][13] also known as the FMC7 antigen.[14]

Clinical significance

CD20 is the target of the monoclonal antibodies rituximab, ocrelizumab, obinutuzumab, ofatumumab, ibritumomab tiuxetan, tositumomab, and ublituximab, which are all active agents in the treatment of all B cell lymphomas, leukemias, and B cell-mediated autoimmune diseases.

The anti-CD20 mAB ofatumumab (Genmab) was approved by FDA in October 2009 for chronic lymphocytic leukemia.

The anti-CD20 mAB obinutuzumab (Gazyva) was approved by FDA in November 2013 for chronic lymphocytic leukemia.

Ocrelizumab was approved by the FDA in March 2017 for multiple sclerosis as the first treatment of the primary progressive form of MS. Clinical trials in rheumatoid arthritis and systemic lupus erythematosus were discontinued in 2010 due to an infection related safety risk.[15]

Although phase II trials for the use of Rituximab in myalgic encephalomyelitis showed promising results, these could not be replicated in a large randomized controlled trial [16] and preliminary results from a Phase III trial were negative.[17]

Additional anti-CD20 antibody therapeutics under development (phase II or III clinical trials in 2008) include :

B cells, CD20, and diabetes mellitus

A link between the immune system's B cells and diabetes mellitus has been determined.[20] In cases of obesity, the presence of fatty tissues surrounding the body's major organ systems results in cell necrosis and insulin insensitivity along the boundary between them. Eventually, the contents of fat cells that would otherwise have been digested by insulin are shed into the bloodstream. An inflammation response that mobilizes both T and B cells results in the creation of antibodies against these cells, causing them to become less responsive to insulin by an as-yet-unknown mechanism and promoting hypertension, hypertriglyceridemia, and arteriosclerosis, hallmarks of the metabolic syndrome. Obese mice administered anti-B cell CD-20 antibodies, however, did not become less responsive to insulin and as a result, did not develop diabetes mellitus or the metabolic syndrome, the posited mechanism being that anti-CD20 antibodies rendered the T cell antibodies dysfunctional and therefore powerless to cause insulin insensitivity by a B cell antibody-modulated autoimmune response. The protection afforded by anti-CD-20 lasted approximately forty days—the time it takes the body to replenish its supply of B cells—after which repetition was necessary to restore it. Hence, it has been argued that diabetes mellitus be reclassified as an autoimmune disease rather than a purely metabolic one and focus treatment for it on immune system modulation.[21]

References

  1. ↑ "Chapter 7: B Lymphocyte Development and Biology". Fundamental Immunology (Book) (6th ed.). Philadelphia: Lippincott Williams & Wilkins. 2008. pp. 237–269. ISBN 978-0-7817-6519-0. 
  2. ↑ "Isolation and structure of a cDNA encoding the B1 (CD20) cell-surface antigen of human B lymphocytes". Proceedings of the National Academy of Sciences of the United States of America 85 (1): 208–212. January 1988. doi:10.1073/pnas.85.1.208. PMID 2448768. Bibcode: 1988PNAS...85..208T. 
  3. ↑ 3.0 3.1 "Entrez Gene: MS4A1 membrane-spanning 4-domains, subfamily A, member 1". https://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=931. 
  4. ↑ "Alternative splicing of its 5' UTR limits CD20 mRNA translation and enables resistance to CD20-directed immunotherapies". Blood 142 (20): 1724–1739. September 2023. doi:10.1182/blood.2023020400. PMID 37683180. 
  5. ↑ "The biology of CD20 and its potential as a target for mAb therapy". B Cell Trophic Factors and B Cell Antagonism in Autoimmune Disease. Current Directions in Autoimmunity. 8. 2005. pp. 140–74. doi:10.1159/000082102. ISBN 978-3-8055-7851-6. 
  6. ↑ "CD20 deficiency in humans results in impaired T cell-independent antibody responses". The Journal of Clinical Investigation 120 (1): 214–222. January 2010. doi:10.1172/JCI40231. PMID 20038800. 
  7. ↑ "Rituximab primarily targets an intra-clonal BCR signaling proficient CLL subpopulation characterized by high CD20 levels". Leukemia 32 (9): 2028–2031. September 2018. doi:10.1038/s41375-018-0211-0. PMID 30030508. 
  8. ↑ Janeway's Immunobiology (7th ed.). New York: Garland Science. 2008. ISBN 978-0-8153-4123-9. https://archive.org/details/janewaysimmunobi00murp. 
  9. ↑ "5". Textbook of Immunology. Boca Raton: CRC. 1996. p. 102. ISBN 978-3-7186-0596-5. 
  10. ↑ "A tumorigenic subpopulation with stem cell properties in melanomas". Cancer Research 65 (20): 9328–9337. October 2005. doi:10.1158/0008-5472.CAN-05-1343. PMID 16230395. 
  11. ↑ Manual of diagnostic antibodies for immunohistology (2nd ed.). London: Greenwich Medical Media. 2003. ISBN 978-1-84110-100-2. 
  12. ↑ "A cholesterol-dependent CD20 epitope detected by the FMC7 antibody". Leukemia 17 (7): 1384–1389. July 2003. doi:10.1038/sj.leu.2402978. PMID 12835728. 
  13. ↑ "Monoclonal antibody FMC7 detects a conformational epitope on the CD20 molecule: evidence from phenotyping after rituxan therapy and transfectant cell analyses". Cytometry 46 (2): 98–104. April 2001. doi:10.1002/cyto.1071. PMID 11309819. 
  14. ↑ "FMC7 is an epitope of CD20". Blood 111 (4): 2492; author reply 2493-2492; author reply 2494. February 2008. doi:10.1182/blood-2007-11-126243. PMID 18263793. 
  15. ↑ "Roche and Biogen Idec Announce Their Decision to Discontinue the ocrelizumab Clinical Development Programme in Patients with Rheumatoid Arthritis". https://investors.biogen.com/news-releases/news-release-details/roche-and-biogen-idec-announce-their-decision-discontinue. 
  16. ↑ "B-Lymphocyte Depletion in Patients With Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: A Randomized, Double-Blind, Placebo-Controlled Trial". Annals of Internal Medicine 170 (9): 585–593. May 2019. doi:10.7326/M18-1451. PMID 30934066. 
  17. ↑ "ME-studie med negative resultater" (in no). https://www.dagensmedisin.no/artikler/2017/11/24/me-studie-med-negative-resultater/. 
  18. ↑ "Trubion announces Pfizer's decision to discontinue development of TRU-015 for RA". Trubion Pharmaceuticals, Inc. press release. 15 June 2010. http://www.news-medical.net/news/20100615/Trubion-announces-Pfizers-decision-to-discontinue-development-of-TRU-015-for-RA.aspx. 
  19. ↑ Note: information included in this article only found in table present in print version of article. "Methods for Maximizing Antibody Yields". Genetic Engineering & Biotechnology News (Mary Ann Liebert, Inc.): p. 36. 2008-06-15. http://www.genengnews.com/articles/chitem.aspx?aid=2514. 
  20. ↑ "B cells promote insulin resistance through modulation of T cells and production of pathogenic IgG antibodies". Nature Medicine 17 (5): 610–617. May 2011. doi:10.1038/nm.2353. PMID 21499269. 
  21. ↑ "Diabetes Mellitus". https://www.lecturio.com/concepts/diabetes-mellitus/. 

Further reading

External links



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