CD20 explained

B-lymphocyte antigen CD20 or CD20 is B lymphocyte cell-surface molecule.

It is a 33-37 kDa non-glycosylated protein. CD20 is expressed on the surface of B-cells from the pre-B phase, the expression is lost in terminally differentiated plasma cells.[1] [2]

CD20 is used as a therapeutical target of B-cell malignancies and autoimmune diseases.

Gene

In humans CD20 is encoded by the MS4A1 gene localized to 11q12.[3] [4]

The gene is 16 kbp long and consists of 8 exons. There are at least 3 mRNA transcripts (resulting from alternative splicing), that are all translated into an identical full-length CD20 protein product. 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.[5]

MS4A1 gene is 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 non-lymphoid tissues.

Structure

CD20 is a transmembrane protein consisting of four hydrophobic transmembrane domains, one intracellular domain and two extracellular loops. There are three different forms of CD20 according to variable phosphorylation.

CD20 is located on the cell surface as homo-dimeric and homo-tetrameric oligomers. It is associated with other cell-surface and cytoplasmic proteins connected to the signal transduction (CD53, CD81, CD82).

CD20 is also known to be physically coupled to major histocompatibility complex class II (MHCII), CD40 and B-cell receptor (BCR).

Function

The biological function of CD20 as well as its natural ligand is not fully elucidated.[6]

CD20 deletion in mice does not impair B-cell differentiation, isotype switch, maturation, proliferation or tissue localization. However, CD20−/− mice show decreased humoral immunity responses in both T-cell dependent and T-cell independent manner.

Functional studies suggest that CD20 molecule is required for efficient BCR signaling. It possibly acts as a calcium channel (CD20 has structural similarities with some known ion channels) or is directly connected to calcium flux.

It is not fully understood, if other molecular pathways or B and T-cell interactions might be affected by CD20 levels on the B-cell surface.[7]

Expression

CD20 is expressed on all stages of B cell development from pre-B cells in the bone-marrow through immature, naive, mature and memory cells in lymphoid tissues and blood. The expression is lost on plasma blasts and plasma cells.[8] [9]

CD20 is a marker of B cell malignancies. 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]

Even though B cells represent the majority of CD20+ cells, a subset of CD3+ T cells also expresses CD20. CD20+ T cells are mostly CD8+ effector memory T cells with proinflammatory features. Further work is needed to understand the contribution of these cells to immune responses.[12]

Anti-CD20 monoclonal antibodies

The targeting of CD20 molecule is highly effective way to deplete B-cell populations. Thus, anti-CD20 monoclonal antibodies (mAbs) play a crucial role in the management of B cell malignancies as well as some inflammatory and autoimmune diseases. The first anti-CD20 mAb approved by FDA in 1997 was Rituximab, defining a new epoch in hematooncology.

The advantages of CD20 as a therapeutic target are:

Mechanism

Mechanism of action of anti-CD20 effects include:[13]

In clinical practise

Examples of anti-CD20 mAbs and their approval status:

CD20 is the target of the mAbs 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.[14]

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 [15] and preliminary results from a Phase III trial were negative.[16]

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

Clinical significance

Diabetes mellitus

A link between the immune system's B cells and diabetes mellitus has been determined.[19]

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.[20]

Further reading

External links

Notes and References

  1. Book: Fundamental Immunology . Hardy R . Lippincott Williams & Wilkins . 2008 . 978-0-7817-6519-0 . Paul W . 6th . Philadelphia . 237–269 . Chapter 7: B Lymphocyte Development and Biology . Book.
  2. Pavlasova G, Mraz M . The regulation and function of CD20: an "enigma" of B-cell biology and targeted therapy . Haematologica . 105 . 6 . 1494–1506 . June 2020 . 32482755 . 7271567 . 10.3324/haematol.2019.243543 .
  3. Tedder TF, Streuli M, Schlossman SF, Saito H . 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 . 2448768 . 279513 . 10.1073/pnas.85.1.208 . free . 1988PNAS...85..208T .
  4. Web site: Entrez Gene: MS4A1 membrane-spanning 4-domains, subfamily A, member 1.
  5. Ang Z, Paruzzo L, Hayer KE, Schmidt C, Torres Diz M, Xu F, Zankharia U, Zhang Y, Soldan S, Zheng S, Falkenstein CD, Loftus JP, Yang SY, Asnani M, King Sainos P, Pillai V, Chong E, Li MM, Tasian SK, Barash Y, Lieberman PM, Ruella M, Schuster SJ, Thomas-Tikhonenko A . Alternative splicing of its 5'-UTR limits CD20 mRNA translation and enables resistance to CD20-directed immunotherapies . Blood . 142 . 20 . 1724–1739 . November 2023 . 37683180 . 10667349 . 10.1182/blood.2023020400 . 261620430 . free .
  6. Book: Cragg MS, Walshe CA, Ivanov AO, Glennie MJ . B Cell Trophic Factors and B Cell Antagonism in Autoimmune Disease . The biology of CD20 and its potential as a target for mAb therapy . 8 . 140–74 . 2005 . 15564720 . 10.1159/000082102 . 978-3-8055-7851-6 . Current Directions in Autoimmunity .
  7. Casan JM, Wong J, Northcott MJ, Opat S . Anti-CD20 monoclonal antibodies: reviewing a revolution . Human Vaccines & Immunotherapeutics . 14 . 12 . 2820–2841 . 2018-12-02 . 30096012 . 6343614 . 10.1080/21645515.2018.1508624 .
  8. Book: Walport M, Murphy K, Janeway C, Travers PJ . Janeway's Immunobiology . 7th . Garland Science . New York . 2008 . 978-0-8153-4123-9 .
  9. Book: Bonilla FA, Bona CA . Textbook of Immunology . CRC . Boca Raton . 1996 . 978-3-7186-0596-5 . 5 . 102.
  10. Fang D, Nguyen TK, Leishear K, Finko R, Kulp AN, Hotz S, Van Belle PA, Xu X, Elder DE, Herlyn M . A tumorigenic subpopulation with stem cell properties in melanomas . Cancer Research . 65 . 20 . 9328–9337 . October 2005 . 16230395 . 10.1158/0008-5472.CAN-05-1343 . free .
  11. Book: Cooper K, ((Anthony Leong AS-Y)) . Manual of diagnostic antibodies for immunohistology . Greenwich Medical Media . London . 2003 . 978-1-84110-100-2 . 2nd .
  12. de Sèze J, Maillart E, Gueguen A, Laplaud DA, Michel L, Thouvenot E, Zephir H, Zimmer L, Biotti D, Liblau R . Anti-CD20 therapies in multiple sclerosis: From pathology to the clinic . Frontiers in Immunology . 14 . 1004795 . 2023-03-23 . 37033984 . 10.3389/fimmu.2023.1004795 . free . 10076836 .
  13. Marshall MJ, Stopforth RJ, Cragg MS . Therapeutic Antibodies: What Have We Learnt from Targeting CD20 and Where Are We Going? . Frontiers in Immunology . 8 . 1245 . 2017-10-04 . 29046676 . 5632755 . 10.3389/fimmu.2017.01245 . free .
  14. Web site: Roche and Biogen Idec Announce Their Decision to Discontinue the ocrelizumab Clinical Development Programme in Patients with Rheumatoid Arthritis . investors.biogen.com . 6 January 2022.
  15. Fluge Ø, Rekeland IG, Lien K, Thürmer H, Borchgrevink PC, Schäfer C, Sørland K, Aßmus J, Ktoridou-Valen I, Herder I, Gotaas ME, Kvammen Ø, Baranowska KA, Bohnen LM, Martinsen SS, Lonar AE, Solvang AH, Gya AE, Bruland O, Risa K, Alme K, Dahl O, Mella O . 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 . 30934066 . 10.7326/M18-1451 . 91186383 .
  16. Web site: ME-studie med negative resultater . Dagens Medicin . 6 January 2022 . no.
  17. Web site: Trubion announces Pfizer's decision to discontinue development of TRU-015 for RA . 15 June 2010 . Trubion Pharmaceuticals, Inc. press release.
  18. Note: information included in this article only found in table present in print version of article. News: Morrow Jr KJ . Methods for Maximizing Antibody Yields . . . 36 . 2008-06-15 . 2008-07-06 . 13 February 2009 . https://web.archive.org/web/20090213120207/http://www.genengnews.com/articles/chitem.aspx?aid=2514 . dead .
  19. Winer DA, Winer S, Shen L, Wadia PP, Yantha J, Paltser G, Tsui H, Wu P, Davidson MG, Alonso MN, Leong HX, Glassford A, Caimol M, Kenkel JA, Tedder TF, McLaughlin T, Miklos DB, Dosch HM, Engleman EG . B cells promote insulin resistance through modulation of T cells and production of pathogenic IgG antibodies . Nature Medicine . 17 . 5 . 610–617 . May 2011 . 21499269 . 3270885 . 10.1038/nm.2353 .
  20. Web site: Diabetes Mellitus. The Lecturio Medical Concept Library . 9 July 2021.

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