|Cytotoxic T-lymphocyte-associated protein 4|
Structure of murine CTLA4 (CD152)
|Symbols||; CD; CD152; CELIAC3; CTLA-4; GRD4; GSE; IDDM12|
|External IDs||IUPHAR: GeneCards:|
|RNA expression pattern|
CTLA4 or CTLA-4 (cytotoxic T-lymphocyte-associated protein 4), also known as CD152 (cluster of differentiation 152), is a protein receptor that downregulates the immune system. CTLA4 is found on the surface of T cells, which lead the cellular immune attack on antigens. The T cell attack can be turned on by stimulating the CD28 receptor on the T cell. The T cell attack can be turned off by stimulating the CTLA4 receptor, which acts as an "off" switch.
Function and mechanism
CTLA4 is a member of the immunoglobulin superfamily, which is expressed on the surface of Helper T cells and transmits an inhibitory signal to T cells. CTLA4 is similar to the T-cell co-stimulatory protein, CD28, and both molecules bind to CD80 and CD86, also called B7-1 and B7-2 respectively, on antigen-presenting cells. CTLA4 transmits an inhibitory signal to T cells, whereas CD28 transmits a stimulatory signal. Intracellular CTLA4 is also found in regulatory T cells and may be important to their function. T cell activation through the T cell receptor and CD28 leads to increased expression of CTLA-4, an inhibitory receptor for B7 molecules.
The mechanism by which CTLA-4 acts in T cells remains somewhat controversial. Biochemical evidence suggested that CTLA-4 recruited a phosphatase to the T cell receptor, thus attenuating the signal. This work remains unconfirmed in the literature since its first publication. More recent work has suggested that CTLA-4 may function in vivo by capturing and removing B7-1 and B7-2 from the membranes of antigen-presenting cells, thus making these unavailable for triggering of CD28.
CTLA-4 may also function via modulation of cell motility and/or signaling through PI3 kinase Early multiphoton microscopy studies observing T-cell motility in intact lymph nodes appeared to give evidence for the so-called ‘reverse-stop signaling model’. In this model CTLA 4 reverses the TCR-induced ‘stop signal’ needed for firm contact between T cells and antigen-presenting cells (APCs). However, those studies compared CTLA-4 positive cells, which are predominantly regulatory cells and are at least partially activated, with CTLA-4 negative naive T cells. The disparity of these cells in multiple regards may explain some of these results. Other groups who have analyzed the effect of antibodies to CTLA-4 in vivo have concluded little or no effect upon motility. Antibodies to CTLA-4 may exert additional effects when used in vivo, by binding and thereby depleting regulatory T cells.
The protein contains an extracellular V domain, a transmembrane domain, and a cytoplasmic tail. Alternate splice variants, encoding different isoforms, have been characterized. The membrane-bound isoform functions as a homodimer interconnected by a disulfide bond, while the soluble isoform functions as a monomer. The intracellular domain is similar to that of CD28, in that it has no intrinsic catalytic activity and contains one YVKM motif able to bind PI3K, PP2A and SHP-2 and one proline-rich motif able to bind SH3 containing proteins. The first role of CTLA-4 in inhibiting T cell responses seem to be directly via SHP-2 and PP2A dephosphorylation of TCR-proximal signalling proteins such as CD3 and LAT. CTLA-4 can also affect signalling indirectly via competing with CD28 for CD80/86 binding. CTLA-4 can also bind PI3K, although the importance and results of this interaction are uncertain.
Mutations in this gene have been associated with insulin-dependent diabetes mellitus, Graves' disease, Hashimoto's thyroiditis, celiac disease, systemic lupus erythematosus, thyroid-associated orbitopathy, primary biliary cirrhosis and other autoimmune diseases.
Polymorphisms of the CTLA-4 gene are associated with autoimmune diseases such as autoimmune thyroid disease and multiple sclerosis, though this association is often weak. In Systemic Lupus Erythematosus (SLE), the splice variant sCTLA-4 is found to be aberrantly produced and found in the serum of patients with active SLE.
Germline haploinsufficiency of CTLA4 leads to CTLA4 deficiency or CHAI disease (CTLA4 haploinsufficiency with autoimmune infiltration), a rare genetic disorder of the immune system. This may cause a dysregulation of the immune system and may result in lymphoproliferation, autoimmunity, hypogammaglobulinemia, recurrent infections, and may slightly increase one’s risk of lymphoma. CTLA4 mutations have first been described by a collaboration between the groups of Dr. Gulbu Uzel, Dr. Steven Holland, and Dr. Michael Lenardo from the National Institute of Allergy and Infectious Disease, Dr. Thomas Fleisher from the NIH Clinical Center at the National Institutes of Health, and their collaborators in 2014. In the same year a collaboration between the groups of Dr. Bodo Grimbacher, Dr. Shimon Sakaguchi, Dr. Lucy Walker and Dr. David Sansom and their collaborators described a similar phenotype.
CTLA4 mutations are inherited in an autosomal dominant manner. This means a person only needs one abnormal gene from one parent. The one normal copy is not enough to compensate for the one abnormal copy. Dominant inheritance means most families with CTLA4 mutations have affected relatives in each generation on the side of the family with the mutation.
Clinical and laboratory manifestations
Symptomatic patients with CTLA4 mutations are characterized by an immune dysregulation syndrome including extensive T cell infiltration in a number of organs, including the gut, lungs, bone marrow, central nervous system, and kidneys. Most patients have diarrhea or enteropathy. Lymphadenopathy and hepatosplenomegaly are also common, as is autoimmunity. The organs affected by autoimmunity vary but include thrombocytopenia, hemolytic anemia, thyroiditis, psoriasis, and arthritis. Respiratory infections are also common. Importantly, the clinical presentations and disease courses are variable with some individuals severely affected, whereas others show little manifestation of disease. This “variable expressivity,” even within the same family, can be striking and may be explained by differences in lifestyle, exposure to pathogens, treatment efficacy, or other genetic modifiers.
The clinical symptoms are caused by abnormalities of the immune system. Most patients develop reduced levels of at least one immunoglobulin isotype, and have low CTLA4 protein expression in T regulatory cells, hyperactivation of effector T cells, low switched memory B cells, and progressive loss of circulating B cells.
Once a diagnosis is made, the treatment is based on an individual’s clinical condition and may include standard management for autoimmunity and immunoglobulin deficiencies. Additionally, treatment with the CTLA4 mimetic, CTLA4-Ig, which reduces immune activity, may be a potential therapeutic intervention.
Agonists to reduce immune activity
The comparatively higher binding affinity of CTLA4 has made it a potential therapy for autoimmune diseases. It plays a role in the initial immune response to and infection of immune cells by, HIV, along with the PD-1 pathway and others. Fusion proteins of CTLA4 and antibodies (CTLA4-Ig) have been used in clinical trials for rheumatoid arthritis. The fusion protein CTLA4-Ig is commercially available as Orencia (abatacept). A second generation form of CTLA4-Ig known as belatacept was recently approved by the FDA based on favorable results from the randomized Phase III BENEFIT (Belatacept Evaluation of Nephroprotection and Efficacy as First Line Immunosuppression) study. It was approved for renal transplantation in patients that are sensitized to EBV, or Epstein Barr Virus.
Antagonists to increase immune activity
Conversely, there is increasing interest in the possible therapeutic benefits of blocking CTLA4 (using antagonistic antibodies against CTLA such as ipilimumab (FDA approved for melanoma in 2011) as a means of inhibiting immune system tolerance to tumours and thereby providing a potentially useful immunotherapy strategy for patients with cancer. This is the first approved immune checkpoint blockade therapy.
CTLA-4 has been shown to interact with:
- Brunet JF, Denizot F, Luciani MF, Roux-Dosseto M, Suzan M, Mattei MG et al. (1987). "A new member of the immunoglobulin superfamily--CTLA-4". Nature 328 (6127): 267–70. doi:10.1038/328267a0. PMID 3496540.
- Dariavach P, Mattéi MG, Golstein P, Lefranc MP (December 1988). "Human Ig superfamily CTLA-4 gene: chromosomal localization and identity of protein sequence between murine and human CTLA-4 cytoplasmic domains". Eur. J. Immunol. 18 (12): 1901–5. doi:10.1002/eji.1830181206. PMID 3220103.
- Krummel MF, Allison JP (1995). "CD28 and CTLA-4 have opposing effects on the response of T cells to stimulation". J. Exp. Med. 182 (2): 459–65. doi:10.1084/jem.182.2.459. PMC 2192127. PMID 7543139.
- Walunas TL, Bakker CY, Bluestone JA (1996). "CTLA-4 ligation blocks CD28-dependent T cell activation". J. Exp. Med. 183 (6): 2541–50. doi:10.1084/jem.183.6.2541. PMC 2192609. PMID 8676075.
- Walunas TL, Lenschow DJ, Bakker CY, Linsley PS, Freeman GJ, Green JM et al. (August 1994). "CTLA-4 can function as a negative regulator of T cell activation". Immunity 1 (5): 405–13. doi:10.1016/1074-7613(94)90071-x. PMID 7882171.
- Waterhouse P, Penninger JM, Timms E, Wakeham A, Shahinian A, Lee KP et al. (November 1995). "Lymphoproliferative disorders with early lethality in mice deficient in Ctla-4". Science 270 (5238): 985–8. doi:10.1126/science.270.5238.985. PMID 7481803.
- Harding FA, McArthur JG, Gross JA, Raulet DH, Allison JP (1992). "CD28-mediated signalling co-stimulates murine T cells and prevents induction of anergy in T-cell clones". Nature 356 (6370): 607–9. doi:10.1038/356607a0. PMID 1313950.
- Magistrelli G, Jeannin P, Herbault N, Benoit De Coignac A, Gauchat JF, Bonnefoy JY et al. (November 1999). "A soluble form of CTLA-4 generated by alternative splicing is expressed by nonstimulated human T cells". Eur. J. Immunol. 29 (11): 3596–602. doi:10.1002/(SICI)1521-4141(199911)29:11<3596::AID-IMMU3596>3.0.CO;2-Y. PMID 10556814.
- Lee KM, Chuang E, Griffin M, Khattri R, Hong DK, Zhang W et al. (1998). "Molecular basis of T cell inactivation by CTLA-4". Science 282 (5397): 2263–6. doi:10.1126/science.282.5397.2263. PMID 9856951.
- Qureshi OS, Zheng Y, Nakamura K, Attridge K, Manzotti C, Schmidt EM et al. (2011). "Trans-endocytosis of CD80 and CD86: a molecular basis for the cell-extrinsic function of CTLA-4". Science 332 (6029): 600–3. doi:10.1126/science.1202947. PMC 3198051. PMID 21474713.
- Knieke K, Lingel H, Chamaon K, Brunner-Weinzierl MC (2012). "Migration of Th1 lymphocytes is regulated by CD152 (CTLA-4)-mediated signaling via PI3 kinase-dependent Akt activation". PLoS ONE 7 (3): e31391. doi:10.1371/journal.pone.0031391. PMC 3295805. PMID 22412835.
- Schneider H, Downey J, Smith A, Zinselmeyer BH, Rush C, Brewer JM et al. (September 2006). "Reversal of the TCR stop signal by CTLA-4". Science 313 (5795): 1972–5. doi:10.1126/science.1131078. PMID 16931720.
- Rudd CE, Taylor A, Schneider H (May 2009). "CD28 and CTLA-4 coreceptor expression and signal transduction". Immunol. Rev. 229 (1): 12–26. doi:10.1111/j.1600-065X.2009.00770.x. PMID 19426212.
- Fife BT, Pauken KE, Eagar TN, Obu T, Wu J, Tang Q et al. (November 2009). "Interactions between PD-1 and PD-L1 promote tolerance by blocking the TCR-induced stop signal". Nat. Immunol. 10 (11): 1185–92. doi:10.1038/ni.1790. PMC 2778301. PMID 19783989.
- Simpson TR, Li F, Montalvo-Ortiz W, Sepulveda MA, Bergerhoff K, Arce F et al. (2013). "Fc-dependent depletion of tumor-infiltrating regulatory T cells co-defines the efficacy of anti-CTLA-4 therapy against melanoma". J. Exp. Med. 210 (9): 1695–710. doi:10.1084/jem.20130579. PMC 3754863. PMID 23897981.
- Kuehn HS, Ouyang W, Lo B, Deenick EK, Niemela JE, Avery DT et al. (2014). "Immune dysregulation in human subjects with heterozygous germline mutations in CTLA4". Science 345 (6204): 1623–7. doi:10.1126/science.1255904. PMID 25213377.
- Schubert D, Bode C, Kenefeck R, Hou TZ, Wing JB, Kennedy A et al. (2014). "Autosomal dominant immune dysregulation syndrome in humans with CTLA4 mutations". Nat. Med. 20 (12): 1410–6. doi:10.1038/nm.3746. PMID 25329329.
- Zeissig S, Petersen BS, Tomczak M, Melum E, Huc-Claustre E, Dougan SK et al. (2014). "Early-onset Crohn's disease and autoimmunity associated with a variant in CTLA-4". Gut: 1-9. doi:10.1136/gutjnl-2014-308541. PMID 25367873.
- Arthritis Research & Therapy | Meeting Abstract | Abatacept (CTLA4Ig) treatment increases the remission rate in rheumatoid arthritis patients refractory to methotrexate treatment
- Pardoll DM (April 2012). "The blockade of immune checkpoints in cancer immunotherapy". Nat. Rev. Cancer 12 (4): 252–64. doi:10.1038/nrc3239. PMID 22437870.
- Follows ER, McPheat JC, Minshull C, Moore NC, Pauptit RA, Rowsell S et al. (October 2001). "Study of the interaction of the medium chain mu 2 subunit of the clathrin-associated adapter protein complex 2 with cytotoxic T-lymphocyte antigen 4 and CD28". Biochem. J. 359 (Pt 2): 427–34. doi:10.1042/0264-6021:3590427. PMC 1222163. PMID 11583591.
- Chuang E, Alegre ML, Duckett CS, Noel PJ, Vander Heiden MG, Thompson CB (July 1997). "Interaction of CTLA-4 with the clathrin-associated protein AP50 results in ligand-independent endocytosis that limits cell surface expression". J. Immunol. 159 (1): 144–51. PMID 9200449.
- Peach RJ, Bajorath J, Naemura J, Leytze G, Greene J, Aruffo A et al. (September 1995). "Both extracellular immunoglobin-like domains of CD80 contain residues critical for binding T cell surface receptors CTLA-4 and CD28". J. Biol. Chem. 270 (36): 21181–7. doi:10.1074/jbc.270.36.21181. PMID 7545666.
- Stamper CC, Zhang Y, Tobin JF, Erbe DV, Ikemizu S, Davis SJ et al. (March 2001). "Crystal structure of the B7-1/CTLA-4 complex that inhibits human immune responses". Nature 410 (6828): 608–11. doi:10.1038/35069118. PMID 11279502.
- Baroja ML, Vijayakrishnan L, Bettelli E, Darlington PJ, Chau TA, Ling V et al. (May 2002). "Inhibition of CTLA-4 function by the regulatory subunit of serine/threonine phosphatase 2A". J. Immunol. 168 (10): 5070–8. doi:10.4049/jimmunol.168.10.5070. PMID 11994459.
- Liossis SN, Sfikakis PP, Tsokos GC (1998). "Immune cell signaling aberrations in human lupus". Immunol. Res. 18 (1): 27–39. doi:10.1007/BF02786511. PMID 9724847.
- Chang TT, Kuchroo VK, Sharpe AH (2002). "Role of the B7-CD28/CTLA-4 pathway in autoimmune disease". Curr. Dir. Autoimmun. 5: 113–30. doi:10.1159/000060550. PMID 11826754.
- Alizadeh M, Babron MC, Birebent B, Matsuda F, Quelvennec E, Liblau R et al. (2003). "Genetic interaction of CTLA-4 with HLA-DR15 in multiple sclerosis patients". Ann. Neurol. 54 (1): 119–22. doi:10.1002/ana.10617. PMID 12838528.
- Chistiakov DA, Turakulov RI (2003). "CTLA-4 and its role in autoimmune thyroid disease". J. Mol. Endocrinol. 31 (1): 21–36. doi:10.1677/jme.0.0310021. PMID 12914522.
- Vaidya B, Pearce S (2004). "The emerging role of the CTLA-4 gene in autoimmune endocrinopathies". Eur. J. Endocrinol. 150 (5): 619–26. doi:10.1530/eje.0.1500619. PMID 15132716.
- Brand O, Gough S, Heward J (2005). "HLA , CTLA-4 and PTPN22 : the shared genetic master-key to autoimmunity?". Expert Rev Mol Med 7 (23): 1–15. doi:10.1017/S1462399405009981. PMID 16229750.
- Kavvoura FK, Akamizu T, Awata T, Ban Y, Chistiakov DA, Frydecka I et al. (2007). "Cytotoxic T-lymphocyte associated antigen 4 gene polymorphisms and autoimmune thyroid disease: a meta-analysis". J. Clin. Endocrinol. Metab. 92 (8): 3162–70. doi:10.1210/jc.2007-0147. PMID 17504905.