CD Markers List
CD Markers List: Function, Expression & Disease
Cluster of differentiation (CD) markers are the cell-surface antigens immunologists use to identify, isolate and characterise cells. This reference profiles 20 key CD markers in depth — function, expression, role in disease and therapeutic potential — alongside a searchable quick-reference table of the most widely used markers.
CD markers: an overview
Cluster of differentiation markers (CD markers) are a type of antigen used to identify and isolate cells that belong to a particular lineage or subset. Found on the cell surface, they reveal the stage of development, maturity or activation of a cell. CD markers are expressed across a wide variety of cells — lymphocytes, monocytes, neutrophils, eosinophils, basophils and platelets among them — and each marker is specific to a certain cell type or lineage.
CD markers are widely used in cancer research to identify tumour cells, distinguish cancer types from one another and track disease progression. They help monitor the effects of chemotherapy and radiotherapy, support the diagnosis of cancers such as leukaemia and lymphoma, and, increasingly, serve as therapeutic targets. At Assay Genie we have compiled this reference to outline the function, expression and binding, role in disease and therapeutic potential of each marker.
Precise cell identification
CD markers are antigens vital for identifying cell types, developmental stages and functions within the immune system.
Central to cancer research
These markers assist in diagnosis, in monitoring response to therapy, and as targets for antibody and CAR-T treatments.
Quick reference: markers profiled on this page
The 20 CD markers covered in detail below, at a glance. Select a marker name to jump to its full profile.
| Marker | Also known as | Main expression | Example therapeutic |
|---|---|---|---|
| CD2 | LFA-2, T-cell co-receptor | T cells, NK cells | Siplizumab |
| CD3d | CD3 delta (TCR complex) | T cells (~80–90%) | Teplizumab |
| CD4 | T-cell surface glycoprotein CD4 | T-helper cells, macrophages | Ibalizumab |
| CD10 | Neprilysin, CALLA | Lymphoid progenitors, kidney | Neprilysin inhibitors (e.g. sacubitril) |
| CD19 | B-lymphocyte antigen CD19 | B cells | CAR-T (tisagenlecleucel), blinatumomab |
| CD20 | MS4A1 | Pre-B & mature B cells | Rituximab, ocrelizumab |
| CD22 | SIGLEC-2 | Mature B cells | Inotuzumab, epratuzumab |
| CD24 | Heat-stable antigen | Immune & epithelial cells | Anti-CD24 mAbs (investigational) |
| CD25 | IL-2Rα (IL2RA) | Activated T cells, Tregs | Basiliximab, daclizumab |
| CD30 | TNFRSF8, Ki-1 | Activated T & B cells, Reed-Sternberg cells | Brentuximab vedotin |
| CD31 | PECAM-1 | Endothelium, platelets, leukocytes | Research target |
| CD33 | SIGLEC-3 | Myeloid lineage cells | Gemtuzumab ozogamicin |
| CD34 | Haematopoietic progenitor antigen | Stem/progenitor & endothelial cells | Stem-cell selection |
| CD38 | ADP-ribosyl cyclase 1 | Plasma cells, lymphocytes | Daratumumab, isatuximab |
| CD40 | TNFRSF5 | APCs, B cells | Selicrelumab (investigational) |
| CD52 | CAMPATH-1 | Lymphocytes, monocytes | Alemtuzumab |
| CD54 | ICAM-1 | Endothelium, leukocytes | BI-505 (investigational) |
| CD58 | LFA-3 | Leukocytes, epithelium | Research target |
| CD66 | CEACAM family | Granulocytes, epithelium | Research target |
| CD74 | Invariant chain (Ii) | Antigen-presenting cells | Milatuzumab (investigational) |
Extended CD marker reference
A quick-reference table of additional commonly used CD markers, their primary cell type or lineage and their key function. Use the search bar above to filter by marker, cell type or function.
| Marker | Also known as | Primary cell type / lineage | Key function |
|---|---|---|---|
| CD1a | T-cell surface glycoprotein CD1a | Cortical thymocytes, Langerhans & dendritic cells | Presentation of lipid and glycolipid antigens |
| CD3 | CD3 complex (ε/γ/δ) | T cells (pan-T marker) | T-cell receptor signal transduction |
| CD5 | Leu-1, T1 | T cells, B1 B-cell subset | Modulates antigen-receptor signalling |
| CD8 | T-cell co-receptor CD8 | Cytotoxic T cells, NK subset | MHC class I co-receptor |
| CD11b | Integrin αM, Mac-1 | Monocytes, macrophages, granulocytes, NK cells | Adhesion, phagocytosis, complement receptor |
| CD11c | Integrin αX | Dendritic cells, myeloid cells | Adhesion; dendritic-cell marker |
| CD14 | Monocyte differentiation antigen | Monocytes, macrophages | Co-receptor for bacterial LPS (innate immunity) |
| CD15 | Lewis-X, SSEA-1 | Neutrophils, eosinophils, monocytes | Phagocytosis and adhesion; Reed-Sternberg marker |
| CD16 | FcγRIII | NK cells, neutrophils, macrophages | Antibody-dependent cellular cytotoxicity (ADCC) |
| CD21 | Complement receptor 2 (CR2) | Mature B cells, follicular dendritic cells | Complement receptor; Epstein-Barr virus receptor |
| CD23 | FcεRII | Mature B cells | Low-affinity IgE receptor; IgE regulation |
| CD27 | TNFRSF7 | T cells, memory B cells, NK cells | Co-stimulation and lymphocyte survival |
| CD28 | Tp44 | T cells | Co-stimulatory receptor (binds CD80/CD86) |
| CD44 | HCAM, Pgp-1 | Broad (leukocytes, epithelial, stem cells) | Hyaluronan receptor; adhesion, homing, cancer stem cells |
| CD45 | Leukocyte common antigen (LCA) | All leukocytes (pan-leukocyte) | Protein tyrosine phosphatase; antigen-receptor signalling |
| CD45RA / CD45RO | LCA isoforms | Naïve vs memory T cells | Distinguish naïve and memory T-cell subsets |
| CD56 | NCAM | NK cells, NKT cells | Natural killer cell marker; cell adhesion |
| CD57 | HNK-1, Leu-7 | NK cells, T-cell subset | Marker of terminally differentiated lymphocytes |
| CD61 | Integrin β3 | Platelets, megakaryocytes | Platelet aggregation and adhesion |
| CD64 | FcγRI | Monocytes, macrophages, activated neutrophils | High-affinity IgG receptor |
| CD68 | Macrosialin | Macrophages, monocytes | Pan-macrophage marker (lysosomal glycoprotein) |
| CD71 | Transferrin receptor | Proliferating cells, erythroid precursors | Iron uptake; proliferation marker |
| CD79a / CD79b | Igα / Igβ | B cells | B-cell receptor signalling component |
| CD80 / CD86 | B7-1 / B7-2 | Antigen-presenting cells | Co-stimulatory ligands for CD28 and CTLA-4 |
| CD90 | Thy-1 | Thymocytes, stem cells, fibroblasts | Adhesion; mesenchymal stem-cell marker |
| CD105 | Endoglin | Endothelial cells, mesenchymal stem cells | TGF-β co-receptor; angiogenesis |
| CD117 | c-Kit, SCFR | Haematopoietic stem/progenitor cells, mast cells | Stem cell factor receptor |
| CD133 | Prominin-1 | Stem and progenitor cells | Stem-cell and cancer stem-cell marker |
| CD138 | Syndecan-1 | Plasma cells, epithelial cells | Plasma-cell and multiple myeloma marker |
| CD152 | CTLA-4 | Activated T cells, regulatory T cells | Inhibitory immune checkpoint receptor |
| CD154 | CD40L | Activated T cells | Ligand for CD40; drives B-cell help |
| CD163 | Haemoglobin scavenger receptor | M2 macrophages, monocytes | Scavenger receptor; anti-inflammatory macrophage marker |
| CD206 | Mannose receptor (MRC1) | Macrophages, dendritic cells | Pathogen recognition; M2 macrophage marker |
| CD273 / CD274 | PD-L2 / PD-L1 | Antigen-presenting & tumour cells | Ligands for PD-1 (immune checkpoint) |
| CD279 | PD-1 | Activated / exhausted T cells | Inhibitory checkpoint receptor |
Expression patterns are simplified for quick reference; many CD markers are expressed on more than one cell type. For detailed function, disease and therapeutic information on the markers below, see the full profiles.
Detailed CD marker profiles
Twenty key markers, each covering function, expression and binding, role in disease and therapeutic potential.
Function
CD2 is a small glycoprotein also known as T-cell co-receptor. It has an important role in antigen receptor signal transduction alongside other surface molecules of the immunoglobulin superfamily such as MHC. CD2 is expressed on all T cells and is involved in their activation, proliferation and apoptosis. It is important in the activation of T cells and NK cells, coordinating with proteins like Lyn and Lck, and is essential for the activation and maturation of cytotoxic T cells. Its principal ligand is CD58 (LFA-3) on antigen-presenting and target cells, and this adhesion interaction strengthens the immune response. The CD2 receptor is composed of an amino-terminal portion that binds the TCR complex and a carboxy-terminal portion with immunoreceptor tyrosine-based activation motifs (ITAMs) important for signal transduction.
Expression / binding
CD2 is highly expressed on T lymphocytes and to a lesser extent on other immune cells such as B cells, NK cells, dendritic cells, macrophages, neutrophils and eosinophils, where it acts as a signalling molecule to help these cells interact with T cells. It is present in the T-cell receptor (TCR) complex along with CD3, CD4 and CD8, and has a unique role in cross-linking TCRs and CD28. Binding of CD2 to the Ig domain of the TCR complex allows LFA-1 (ICAM-1) molecules to bind, bringing the TCR complex and CD28 into close contact and triggering phosphorylation events that set off the immune cascade. CD2 also interacts with kinases such as ZAP-70, Lck and Fyn to ensure efficient signal transduction.
Role in disease
CD2 has been identified as a possible tumour or cancer stem cell antigen; its expression was found to be lost at both mRNA and protein levels in cancer cells. It can be used as a diagnostic marker for cancers such as Hodgkin's disease, chronic lymphocytic leukaemia and non-Hodgkin's lymphoma, and has been used as a biomarker for autoimmune activation of T cells, primarily in animal models of experimental and rheumatoid arthritis.
Therapeutic potential
Siplizumab is an anti-CD2 monoclonal antibody directed against the CD2 molecule on T cells. Studies suggest it may be effective as a first-line therapy for T-cell lymphoma, and clinical trials of anti-CD2 antibodies in T-cell lymphomas have shown promising results both as monotherapy and in combination with conventional treatments. Anti-CD2 therapy also has potential for autoimmune disorders such as multiple sclerosis and rheumatoid arthritis.
Function
CD3d is a 34 kDa type I transmembrane protein of the immunoglobulin superfamily, containing four extracellular immunoglobulin domains, a single transmembrane region and a cytoplasmic tail. It forms a homodimer when bound to its epsilon ligand on the T-cell receptor complex. CD3d is important in immunological self/non-self recognition and plays an important role in regulating the immune system. Used in immunohistochemistry to identify T cells that mediate antigen-specific responses, it also serves as a marker for malignant T-cell differentiation and for final identification of maturing T lymphocytes within tissues.
Expression / binding
CD3d is expressed on ~80–90% of circulating T cells and is an excellent marker for helper/inducer T cells, which activate cytotoxic T cells and B cells. It is also expressed on NK cells and some monocytes. CD3d binds to the epsilon domain of the TCR complex, an interaction responsible for activating regulatory T cells, inducing their proliferation and secreting IL-2. It carries a carbohydrate alpha epitope that binds MHC class II molecules on antigen-presenting cells.
Role in disease
The CD3d marker is used in the diagnosis of acute myeloid leukaemia, being detectable in 80–90% of cases. It is expressed by T cells involved in transplant rejection (graft-versus-host disease), where CD3d expression on donor tissue drives rejection by the recipient. CD3d also plays a role in autoimmune diseases such as lupus, though the exact mechanism remains unclear.
Therapeutic potential
CD3d antibodies are emerging as an innovative approach for treating autoimmune diseases, though clinical use has been limited by the short plasma half-life of murine antibodies — prompting development of humanised versions. Teplizumab, a humanised monoclonal antibody that binds CD3d on T cells, is being developed as a treatment for type 1 diabetes and was the first anti-CD3d monoclonal antibody tested in clinical trials with an acceptable safety profile.
Function
CD4 is a transmembrane glycoprotein of the immunoglobulin superfamily expressed mainly on helper T cells, where it acts as a co-receptor for MHC class II molecules during antigen recognition. The CD4 receptor is an essential component of the cell-mediated immune response and is also involved in B-cell activation and dendritic-cell maturation. CD4 plays an important role in the central, T-cell-independent activation pathway of B cells.
Expression / binding
CD4 is expressed on T-helper cells, B cells, macrophages and dendritic cells. It binds HIV-1 gp120 and CD154, and CD4+ T cells help IgA class switching by activating dendritic cells through interactions with B7 molecules. Binding of CD4 to gp120 transduces signals that ultimately lead to T-cell activation.
Role in disease
Expression of CD4 by T-helper cells makes them vulnerable to HIV infection; absence or dysfunction of CD4 causes the severe immunodeficiency known as AIDS. CD4 can be used to identify proliferation in neoplastic cells and to determine the tumour-infiltrating lymphocyte (TIL) population within a tumour. Elevated CD4 on tumour cells correlates with decreased survival in colorectal and stomach cancer patients.
Therapeutic potential
CD4 is a cell-surface receptor for HIV-1 gp120 that mediates viral entry, so inhibiting CD4 can prevent infection of susceptible cells. Ibalizumab, a humanised monoclonal antibody targeting CD4, is approved for the treatment of HIV-1 infection. Zanolimumab, a monoclonal antibody that inhibits CD4, has been studied for CD4-dependent tumours such as leukaemias and lymphomas.
Function
CD10, also known as neprilysin, is a single-pass type II transmembrane 100 kDa cell-surface glycoprotein of the peptidase family. It is a membrane metalloprotease released into the extracellular domain after transport from the Golgi apparatus to the cell surface. Regulated expression of CD10 is necessary for angiogenesis.
Expression / binding
CD10 is expressed specifically at early lymphoid progenitor stages of an immature phenotype, suggesting a role in lymphoid cell development and differentiation, and is present in several tissues, especially the kidneys. It is found in various malignancies and plays a significant role in cancer development and progression.
Role in disease
CD10 expression is a biomarker for cancer response and prognosis. CD10-positive stromal cells are present at the invasive front of cancer cells, and their presence is linked to nodal metastasis, tumour grade, tumour size, lymph node involvement and poor prognosis. CD10 has also been linked to oxidative damage implicated in Alzheimer's disease and dementia; neprilysin activity declines with age, and CD10 may be useful for prognosis and treatment planning in Alzheimer's disease.
Therapeutic potential
Analgesic agents that prevent neprilysin from inhibiting signalling peptides have been developed, and the prodrug sacubitril is used for heart failure. CD10 monoclonal antibodies can inhibit cell differentiation and proliferation; JMAM-1 mAb binds the CD10 antigen and may aid the diagnosis of mesothelioma and the prognosis of other cancers.
Function
CD19 is a protein marker found on B cells, involved in their development into antibody-producing plasma cells. Cell differentiative processes including B-1, germinal centre and marginal-zone B-cell formation require CD19. As a B-cell marker, CD19 staining can show how well chemotherapy has worked in certain lymphomas such as diffuse large B-cell lymphoma.
Expression / binding
CD19 acts as a co-receptor for CD21, CD81 and CD225. It binds CD81 to CD19 and CD21, contributing to T-cell co-stimulation by antigen-presenting cells. The CD81 ectodomain binds CD19 and promotes its export to the cell surface, an interaction also linked to B-cell activation state.
Role in disease
CD19 abnormalities have been linked to autoimmune diseases including rheumatoid arthritis and multiple sclerosis. Mutations in CD21 and CD81 can induce primary immunodeficiency through their role in the CD19/CD21/CD81 complex, leading to hypogammaglobulinaemia and poor immunological memory. CD19-related immunodeficiency causes hyporesponsiveness to transmembrane signals and a weak T-cell-dependent immune response.
Therapeutic potential
CD19 is a marker for B cells in lymphomas such as diffuse large B-cell lymphoma, though it is not very sensitive and must be combined with CD20 or CD79a immunostaining if DLBCL is suspected. A positive CD19 result indicates the patient will benefit from B-cell-depleting therapy using drugs such as rituximab, and CD19-directed CAR-T cells have shown remarkable promise for relapsed cases of several cancers.
Function
CD20 is a cell-surface antigen present on lymphocytes — a small (10–12 kDa) glycoprotein with an α-bundle structure. It plays an important role in B-cell function and in specific defence against infection, protects lymphocytes from natural-killer-cell-mediated lysis, and contributes to antigen presentation of B-cell-origin antigens to T-helper cells. CD20 facilitates migration of activated B cells into areas of inflammation under the influence of chemokines and is involved in the development of memory B cells. It can be detected in malignant disorders and serves as a tumour marker.
Expression / binding
CD20 is expressed on pre-B cells and mature B lymphocytes and, to a lesser extent, on some NK cells and myeloid progenitor cells. It is abundantly expressed by all B cells regardless of maturation stage, with expression decreasing with age. CD20 binds MHC class II, CD40, the BCR and C-terminal Src kinase-binding protein (CBP), and as a receptor binds ligands including anionic phospholipids, lipopolysaccharides and sulfated moieties to modulate cell activation, proliferation and protection from apoptosis.
Role in disease
Expression of CD20 on malignant cells correlates with their proliferation rate and poor prognosis. Reduced numbers of CD20-positive lymphocytes impair T-cell-mediated immunity and increase susceptibility to infection, while CD20 can be re-expressed by tumour cells in the presence of TNFα. CD20 expression increases in inflammatory conditions such as rheumatoid arthritis and psoriasis, is expressed in most follicular lymphomas, and is a prognostic marker in both Hodgkin's and non-Hodgkin's lymphomas.
Therapeutic potential
CD20 is a target for monoclonal antibodies that induce cell lysis or inhibit cellular function, including rituximab, ocrelizumab and ofatumumab. Rituximab is a chimeric monoclonal antibody approved for non-Hodgkin's lymphoma and chronic lymphocytic leukaemia. Anti-CD20 CAR-T cell therapy is a promising approach for B-cell malignancies, and CD20 is a target for autoimmune diseases such as rheumatoid arthritis, polymyositis, relapsing-remitting multiple sclerosis and idiopathic thrombocytopenic purpura.
Function
CD22 is a transmembrane glycoprotein expressed on the surface of mature lymphocytes and a member of the SIGLEC family (sialic-acid-binding immunoglobulin-like lectins). It regulates B-cell trafficking through blood vessels, apoptosis, T-cell regulation and probably cell proliferation, plays an important role in lymphocyte migration, contributes to the formation of B-cell germinal centres, facilitates antigen-receptor clustering and helps initiate B-cell differentiation from bone-marrow stem cells.
Expression / binding
CD22 is expressed on ~90% of peripheral blood lymphocytes and is found on most non-Hodgkin's lymphomas, as well as on monocytes and eosinophils. As a SIGLEC, CD22 recognises α2,6-linked sialic acids on cell-surface glycoproteins, and interacts with the B-cell receptor to modulate antigen-independent proliferation and immunoglobulin synthesis.
Role in disease
CD22 is associated with cancers such as T-cell acute lymphoblastic leukaemia and T-cell large granular lymphocyte leukaemia, and can drive proliferation of leukaemia cells via cAMP or Lyn signalling. An abnormal lack of functional CD22 is seen in chronic lymphocytic leukaemia and correlates with disease progression, while CD22 deficiency impairs control of viral infections. CD22 has been implicated in autoimmune diseases including systemic lupus erythematosus.
Therapeutic potential
Several strategies targeting CD22 are in clinical trials for autoimmune diseases and B-cell proliferative disorders, and CD22-targeted CAR-T cell therapy has been effective in B-cell malignancies. Epratuzumab, a high-affinity anti-CD22 monoclonal antibody, is used for B-cell proliferative disorders and studied in autoimmune diseases, particularly lupus erythematosus and Sjögren's syndrome.
Function
CD24 is a differentiation antigen on the surface of lymphocytes that acts as a co-stimulatory molecule on T cells (with OX40L and ICOSLG), increasing T-cell proliferation, survival and cytokine production. Effector T cells express high levels of CD24 whereas central memory and regulatory T cells express low levels, allowing differentiation between T-cell responses. CD24 is required for NK-cell development, and NK/NKT interaction with CD24 increases IL-2 production, cytotoxicity and cytokine release.
Expression / binding
CD24 is expressed on T cells, B cells, NK cells and dendritic cells, and detectable on hepatocytes, endothelial cells, intestinal epithelium and renal tubular epithelial cells. It provides functional advantages through increased adhesion to CD24-ligand molecules and binds the chemokine receptor CXCR4 and its ligand SLC to facilitate immune-cell migration.
Role in disease
CD24 is involved in the pathogenesis of several autoimmune diseases, with CD24-positive B cells identified in psoriasis vulgaris, vitiligo, rheumatoid arthritis and Crohn's disease. It is expressed in most polyclonal B-cell non-Hodgkin lymphomas, where it may help tumour cells evade immune surveillance, and is overexpressed in several endometrial cancers as a tumour marker. CD24 is prognostic for survival in gastrointestinal stromal tumours (GIST) and diffuse large B-cell lymphoma.
Therapeutic potential
Monoclonal antibodies targeting CD24 enhance phagocytosis and killing of CD24+ cancer cells by macrophages. Ovarian and triple-negative breast cancers expressing CD24 can be treated with antibodies that block the CD24–Siglec-10 interaction. Anti-CD24 antibodies inhibit growth of colorectal and pancreatic cancer cells by suppressing cancer stem-cell properties, and show potent antitumour activity against neuroblastoma.
Function
CD25 is a 65 kDa transmembrane glycoprotein, the alpha chain of the high-affinity interleukin-2 receptor, found on the surface of activated lymphocytes. Studies of mice deficient in IL-2 or its receptor show defective T-cell immunity, indicating that CD25 mediates cellular immune responses. Loss of CD25 correlates with increased IL-2 production and improved cytotoxic T-cell function, whereas upregulation limits immune responsiveness towards self antigens.
Expression / binding
CD25 is expressed on activated T lymphocytes and mature NK cells, recent thymic emigrants, eosinophils, basophils and some CD34+ haematopoietic progenitors. It binds high-affinity IL-2, transmitting an intracellular signalling cascade that upregulates Bcl-2 family members and suppresses apoptosis of CD4 T cells, thereby mediating T-cell proliferation.
Role in disease
CD25 is routinely used as a surrogate biomarker for regulatory T cells (Tregs). High CD25 levels serve as a biomarker for autoimmune diseases such as lupus, Addison's disease, multiple sclerosis, myasthenia gravis, rheumatoid arthritis and Graves' disease. CD25 expression is detectable in more than 90% of malignant lymphomas and correlates with poor prognosis, and can indicate response to treatment for Hodgkin's disease.
Therapeutic potential
CD25 has been used as an immunotherapy target for treating multiple sclerosis with regulatory T cells and identified as a potential target in Hashimoto's thyroiditis. Approved anti-CD25 monoclonal antibodies include basiliximab (used to prevent transplant rejection) and daclizumab; because anti-CD25 agents can also deplete regulatory T cells, selective approaches that target activated effector T cells while sparing Tregs are in development.
Function
CD30 is a cell-surface receptor involved in the activation and differentiation of T and B cells. A member of the tumour necrosis factor receptor superfamily, it encodes a protein with an extracellular cysteine-rich domain, a transmembrane region and a cytoplasmic tail involved in cell differentiation. CD30 has been suggested to play a role in cell adhesion and has a crucial role in the rejection of tumours by cytotoxic T lymphocytes.
Expression / binding
CD30 is found on endothelial cells, epithelial cells, keratinocytes and lymphoid cells, and notably on Reed-Sternberg cells in Hodgkin lymphoma. It binds its ligand CD30L (CD153), which regulates cell proliferation and differentiation, and interacts with other TNF receptor family members such as CD27, TNFAIP3 and TRAF6.
Role in disease
CD30 is an immunohistochemical marker for Hodgkin lymphoma, being expressed on 100% of Reed-Sternberg cells, and is detected in T-cell leukaemia and anaplastic large-cell lymphomas. Genetic variations in the CD30 gene are associated with autoimmune diseases, most notably systemic lupus erythematosus, and CD30 has been linked to neuroblastoma.
Therapeutic potential
Brentuximab vedotin is a CD30-directed antibody-drug conjugate consisting of an anti-CD30 monoclonal antibody linked to a chemotherapeutic agent. It is approved for refractory Hodgkin lymphoma and systemic anaplastic large-cell lymphoma and is studied in other CD30-positive lymphomas and autoimmune diseases. CAR-T cell therapies targeting CD30 have also shown benefit in CD30-positive lymphomas.
Function
CD31, also known as PECAM-1, was originally described as a cell-surface antigen on platelets and megakaryocytes and is expressed on cells of all lineages within the vascular system. Belonging to the immunoglobulin superfamily, it acts as an adhesion molecule that facilitates leukocyte migration to sites of infection or tissue damage by binding ICAM-1 on endothelial cells. CD31 is an established biomarker for angiogenesis during vascularisation and is believed to play an important role in cancer metastasis through its multi-directional interactions with proteins on endothelial cells and platelets.
Expression / binding
CD31 is expressed on CD34+ haematopoietic stem cells, CD14+ monocytes and CD16+ NK cells, and is present on platelets at their proplatelet extensions. It binds thrombospondin-1 (TSP1), CD41a, CD36, CD24 and neural cell adhesion molecules (NCAM), and binds fibrinogen directly or indirectly through TSP1.
Role in disease
CD31 has been used as a cancer biomarker due to increased expression in various cancers including myeloid malignancies, and plays an important role in tumour angiogenesis. It can help discriminate malignant from benign oral tumours, predict metastatic disease in lung cancer, and serves as a prognostic marker in gastric, hepatocellular and renal cell carcinoma. CD31 expression is associated with poor prognosis in colorectal cancer.
Therapeutic potential
CD31 is a promising therapeutic target in cancer; antibodies against CD31 can deplete CD31+ cells. It interacts with anti-cancer drugs such as elesclomol, mocetinostat and the CDK inhibitor roscovitine, and anti-CD31 monoclonal antibodies and CD31 siRNA have been used for CD31-targeted therapy of myeloid malignancies. CD31 has also been explored as an immune-checkpoint-inhibitor target for solid tumours.
Function
CD33 (SIGLEC-3) is a sialic-acid-binding immunoglobulin-like lectin found on the surface of myeloid-lineage cells. It functions largely as an inhibitory receptor, modulating myeloid cell activation, phagocytosis and cytokine signalling. Anti-CD33 antibodies can induce apoptosis in CD33-expressing cells, and the receptor's cytoplasmic immunoreceptor tyrosine-based inhibitory motifs (ITIMs) dampen downstream signalling.
Expression / binding
CD33 is expressed on early haematopoietic precursors, proplatelet-forming megakaryocytes, mature neutrophils and a subset of monocytes/macrophages. Although usually considered myeloid-specific, it can be upregulated on lymphoid cells in conditions such as cancer, and its expression decreases as a myeloid stem cell matures towards its final granulocyte form.
Role in disease
CD33 has been studied as a cancer biomarker, particularly in myeloproliferative disorders such as chronic myeloid leukaemia, and is one of the antigens used in a "pan-CD" test for leukaemia diagnosis. It has been identified as a possible prognostic marker for poor survival in acute myeloid leukaemia.
Therapeutic potential
CD33 is a validated therapeutic target in acute myeloid leukaemia: gemtuzumab ozogamicin, an anti-CD33 antibody-drug conjugate, is approved for CD33-positive AML. CD33-targeted nanotherapies designed to accumulate in tumours and deliver a chemotherapeutic payload are also in development, and — through its role in microglial function — CD33 is being investigated in neurodegenerative conditions such as Alzheimer's disease.
Function
CD34 is a surface glycoprotein on peripheral blood stem cells and progenitor cells that plays an important role in cell division, proliferation and maturation. In normal cells it is involved in maturation and release of growth factors; in malignant cells it plays a role in division and metastasis. CD34 is implicated in the transport of molecules across endothelial cells and functions in the adhesion and extravasation of quiescent progenitor cells during bone-marrow haematopoiesis.
Expression / binding
CD34 is expressed on haematopoietic stem cells, precursors of monocytes and macrophages, endothelial precursor cells and the early thymocyte progenitor population, and is present on osteoblasts in growing bone. It binds Von Willebrand Factor to regulate proliferation and differentiation, and binds integrin α6β1 to regulate adhesion of haematopoietic cells to the vascular wall.
Role in disease
CD34 is expressed at abnormally high levels in tumours and is used in immunohistochemistry to diagnose haematological cancers including acute myeloid leukaemia, promyelocytic leukaemia and T-cell prolymphocytic leukaemia. Its presence in tumour tissue generally indicates disease progression, and elevated levels in melanoma contribute to angiogenesis and metastasis.
Therapeutic potential
Anti-CD34 therapy has been tested to both kill cancer cells and study protection from immune attack. Antibodies against CD34 are an important tool for adoptive immunotherapy, and monoclonal antibodies against the CD34 receptor enhance NK-cell killing of certain cancer cells. Anti-CD34 antibodies are also being studied for autoimmune diseases.
Function
CD38 is a cell-surface glycoprotein that can function as an enzyme with NAD-depleting and intracellular signalling activity, or as a receptor with adhesive functions. It affects a variety of immune-cell functions, including immunomodulation and effector activities during inflammation, and has been used to determine the pluripotency of embryonic stem cells and as an efficient human erythroid differentiation marker on CD34+ cells.
Expression / binding
CD38 is widely expressed on CD4+ and CD8+ T lymphocytes, NK cells, monocytes/macrophages, granulocytes, platelets and B lymphocytes. It binds CD31/CD157 to aid cell adhesion and migration, regulates leukocyte extravasation, and its NAD-depleting activity stimulates the cADPR/PARP pathway for intracellular signalling. CD38 activates the JNK, NF-κB and MAPK pathways, driving transcription of pro-inflammatory cytokines such as TNFα and IL-6.
Role in disease
CD38 surface levels are a marker for B-cell chronic lymphocytic leukaemia (B-CLL), being found at high levels in B-CLL tumour cells, in a subset of acute myeloid leukaemia and commonly in non-Hodgkin's lymphoma. It has potential as a biomarker for early detection of pancreatic cancer, and higher expression correlates with larger tumour size and greater histological grade. CD38 may contribute to breast cancer progression by modulating cytokine production and inflammation.
Therapeutic potential
Monoclonal antibodies against CD38 are effective in killing malignant cells with lower risk than chemotherapy. Daratumumab, an anti-CD38 human monoclonal antibody, has shown promising results in myeloma, and isatuximab is another CD38-specific antibody in clinical use. CD38-CAR T cell therapy can deplete CD38+ cells from the tumour microenvironment, and single-domain antibodies (nanobodies) against CD38 can inhibit its enzymatic activity.
Function
CD40 is a member of the tumour necrosis factor receptor family found on activated T cells and is central to B-cell homeostasis and activation. Defects in CD40 may lead to antibody deficiency due to a lack of mature B cells. It plays a role in T-cell adhesion, activation, differentiation and signalling in lymphocytes.
Expression / binding
CD40 is expressed on activated T cells, B cells, NKT cells, macrophages, myeloid cells, dendritic cells and epithelial cells. On endothelial and thymic-cortex epithelial cells it acts as a co-stimulatory molecule for T-cell proliferation. When bound by CD154 (CD40L), CD40 provides a co-stimulatory signal for T-cell activation, and it interacts with TRAF1 in neuronal cells.
Role in disease
CD40 is involved in the pathogenesis of autoimmune thyroid disease and systemic lupus erythematosus, and autoantibodies to CD40 are associated with Sjögren's syndrome. Anti-CD40L antibodies are significantly increased in active SLE. CD40 expression has been demonstrated in malignant neoplasms such as B-cell chronic lymphocytic leukaemia, mantle cell lymphoma, diffuse large-cell lymphoma and multiple myeloma; its ligand CD154 is a marker for disease severity in B-cell malignancies.
Therapeutic potential
CD40 agonists activate antigen-presenting cells and promote anti-tumour T-cell responses. Selicrelumab, an anti-CD40 antibody, showed safety and efficacy in advanced solid tumours and lymphomas, and anti-CD40 monoclonal antibodies can foster cytotoxic myeloid cells that control cancer even in the absence of T-cell immunity. Anti-CD40 antibody KPL-404 is used to treat autoimmune disorders such as rheumatoid arthritis and lupus.
Function
CD52 is a highly expressed membrane glycoprotein present on immune cells such as lymphocytes, monocytes, eosinophils and dendritic cells, and helps researchers distinguish healthy from cancerous cells. Its 12-amino-acid peptide is anchored to glycosylphosphatidylinositol, and its negative charge is thought to give an anti-adhesion function that allows cells to migrate freely. CD52 binds the immunoreceptor tyrosine-based inhibitory motif that contains a sialic-acid-binding lectin.
Expression / binding
CD52 is found on white blood cells, dendritic cells and monocytes. Although its function is not fully known, it is present on chronic lymphocytic leukaemia (CLL) and B-cell non-Hodgkin's lymphoma cancer cells, and on immune cells affected by autoimmune disease.
Role in disease
CD52 is used to treat certain types of arthritis and lupus, and its levels tend to decrease as a patient recovers from autoimmune disease, allowing treatment monitoring. CD52 testing is being explored for early detection of macular degeneration, and CD52-based therapies are being developed for Alzheimer's disease and multiple sclerosis. Alemtuzumab is an anti-CD52 recombinant humanised monoclonal antibody used to treat B-cell chronic lymphocytic leukaemia.
Therapeutic potential
Because CD52 is central to CD52-directed immunotherapy, it allows oncologists to restrict treatment to CD52-expressing tumour cells. CD52 is also used in stem-cell transplantation for cancers such as leukaemia and lymphoma, where CD52-positive cells can be removed and healthy cells reintroduced after chemotherapy or radiotherapy.
Function
CD54, also known as intercellular adhesion molecule-1 (ICAM-1), is expressed primarily on hematopoietic cells such as CD34+ stem cells, CD19+ B cells, CD4 T cells, CD14 macrophages and epithelial cells. It acts as an adhesion molecule, binding the leukocyte β2 integrins LFA-1 (CD11a/CD18) and Mac-1 (CD11b/CD18) to mediate the firm adhesion and transendothelial migration of leukocytes during inflammation — a process also implicated in cancer metastasis. CD54 is involved in migration and phagocytosis of neutrophils, lymphocytes and monocytes, and has been used to track CD34+ stem cells in umbilical cord blood transplants.
Expression / binding
CD54 expression is upregulated on neutrophil activation and increases on monocytes when stimulated by cytokines such as IL-4 or GM-CSF. It is involved in innate immunity through recognition by CTLA-4 on killer T cells and in adaptive immunity through increased binding with E-selectin on endothelial cells, and participates in angiogenesis by binding CD166 on endothelial cells.
Role in disease
CD54 interacts with VCAM-1 at transition zones between tumour cells and lymphatic vessels. Its expression is increased in cancers including pancreatic cancer and melanoma and promotes tumour-cell metastasis and angiogenesis by increasing VEGF secretion. CD54 is elevated in most primary gastric and hepatocellular carcinomas, is used as a biomarker for circulating tumour cells, and is positively correlated with reduced survival and poor prognosis in pancreatic cancer.
Therapeutic potential
Targeting CD54 has been proposed to prevent tumour-cell invasion. CD54 inhibition can suppress angiogenesis by blocking CD44/MMP2 signalling and decreasing VEGF secretion. BI-505, a fully human IgG1 monoclonal antibody against CD54, has been studied for cancers such as melanoma and lung cancer, blocking CD54 binding to CD44 and CD166 and exerting antineoplastic effects via antibody-dependent cellular cytotoxicity (ADCC).
Function
CD58 is a protein found on the surface of white blood cells, with two immunoglobulin-like regions and an alpha-helix that mediates binding. It plays an important role in the immune response by recruiting other white blood cells to fight infection, helps protect white blood cells from phagocytosis or apoptosis, and is involved in the complement system, binding immune complexes to facilitate their clearance.
Expression / binding
CD58 is expressed on T cells, B cells, NK cells and monocytes. After activation by an antigen-presenting cell, the CD58 complex binds 2B4 or CD48 on T cells, triggering upregulation of CD28 and downregulation of CTLA-4 and leading to T-cell proliferation. CD58 can also bind phosphocholine on apoptotic neutrophils and acts as an adhesion molecule by binding LFA-1, enabling adhesion of leukocytes to endothelial cells.
Role in disease
CD58 is a marker of activation that increases in white blood cells during disease progression. Higher CD58 levels are associated with significantly lower survival from AIDS-related lymphomas, and upregulation correlates with abnormal tissue architecture and the onset of Kaposi sarcoma lesions. CD58 is upregulated in autoimmune diseases such as systemic lupus erythematosus, multiple sclerosis and Sjögren's syndrome, and is elevated in synovial cells from rheumatoid arthritis patients.
Therapeutic potential
CD58 is over-expressed in B-cell haematological cancers and T-cell lymphomas. Anti-CD58 monoclonal antibodies impede binding of thymocytes to thymic epithelial cells and suppress T-cell activation, inducing unresponsiveness to mitogenic or antigenic stimuli. Therapies targeting CD58 reduced the risk of cancer recurrence in T-cell lymphoma patients and can block lysis by lymphokine-activated killer cells in chronic myeloid leukaemia.
Function
CD66 is a protein found on the surface of certain blood cells that plays an important role in the immune system, helping to protect the body from infection by identifying and destroying foreign cells and activating other immune cells. It is involved in cell signalling, regulating the activity of other proteins, and promotes cell adhesion, migration and invasion.
Expression / binding
CD66 is expressed on a variety of blood cells, including neutrophils, monocytes, eosinophils, basophils and lymphocytes, and is also found on some cancer cells. It binds a variety of extracellular-matrix ligands, including fibronectin, vitronectin, fibrinogen and laminin.
Role in disease
CD66 is expressed in a range of cancers, including colorectal, breast and pancreatic cancers, contributing to progression by promoting cell adhesion, migration and invasion and playing a role in the development of metastases. Notably, increased CD66 levels were associated with improved survival in ovarian cancer, suggesting that targeting CD66 could help improve prognosis and treatment outcomes.
Therapeutic potential
Anti-CD66 antibodies are thought to interfere with tumour growth by targeting CD66 on cancer cells and preventing them from interacting with other cells in the tumour microenvironment. There is evidence that anti-CD66 antibodies can reduce tumour growth and metastasis in animal models, and research into their therapeutic uses is ongoing.
Function
CD74, also known as the human invariant chain (Ii), is a cell-surface protein of the immunoglobulin superfamily. Initially reported as a T-cell-receptor-associated antigen, it is commonly expressed on antigen-presenting cells such as dendritic cells, macrophages and B cells, and acts as a co-stimulatory molecule involved in both innate and adaptive immunity. CD74 is expressed during early stages of antigen presentation, with expression downregulated after stimulation with CD80 or CD86 ligands.
Expression / binding
CD74 is expressed on activated CD4+ and CD8+ T cells but not resting T cells, with expression upregulated by activation of NF-κB or p38 MAPK. Beyond the immune system, CD74 can act as a regulator of cell adhesion and motility, and has recently been linked to autoimmune diseases including multiple sclerosis and rheumatoid arthritis.
Role in disease
CD74 is overexpressed in cancerous tissues through aberrant upregulation on CD8+ T cells, and has been found in colon, gastric, lung, hepatocellular, renal, cervical and breast cancer. It is involved in tumour progression through enhanced antigen presentation to CD8+ T cells, is a marker for tumour-associated macrophages, and correlates with poor prognosis of non-small-cell lung cancer and reduced overall survival in gastric cancer.
Therapeutic potential
Targeting CD74 blocks cancer growth by preventing tumour development via inhibition of antigen presentation to CD8+ T cells, and CD74 blockade inhibits CD80-induced proliferation and cytokine production from CD4+ T cells. Because CD74 is also expressed by regulatory T cells, it is an attractive therapeutic target for autoimmune diseases such as multiple sclerosis; milatuzumab is an anti-CD74 monoclonal antibody studied in this context.
Frequently asked questions
What are CD markers?
Cluster of differentiation (CD) markers are cell-surface antigens used to identify and isolate cells belonging to a particular lineage or subset. They indicate a cell's type, stage of development, maturity and activation state, and are central tools in immunology, flow cytometry and cancer research.
What does “CD” stand for?
CD stands for cluster of differentiation. The nomenclature groups monoclonal antibodies that recognise the same cell-surface molecule, assigning each molecule a standardised CD number such as CD4, CD20 or CD34.
How are CD markers used in cancer research?
CD markers help identify and distinguish tumour cell types, track disease progression, monitor the effects of chemotherapy and radiotherapy, and support diagnosis of cancers such as leukaemia and lymphoma. Many are also therapeutic targets for monoclonal antibodies and CAR-T cell therapies.
Which CD markers identify T cells, B cells and NK cells?
CD3 is a pan-T-cell marker, with CD4 and CD8 distinguishing helper and cytotoxic T cells. CD19 and CD20 identify B cells, while CD16 and CD56 identify natural killer (NK) cells. CD45 is a pan-leukocyte marker expressed on all white blood cells.
Are CD markers used as drug targets?
Yes. Several CD markers are validated therapeutic targets, including CD20 (rituximab), CD30 (brentuximab vedotin), CD38 (daratumumab), CD52 (alemtuzumab) and CD19 (CAR-T cell therapy).
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