Understanding CD Markers in Cancer Diagnosis and Treatment

How CD Antigens are Used in Cancer and Lymphoma Diagnosis and Treatment

Lymphoma cancer cell, SEM. Credit: Steve Gschmeissner/Science Photo Library / Getty Images

CD stands for cluster of differentiation. CD markers, or CD antigens, are a group of special molecules on the surface of cells in the body—markers that help differentiate one cell type from the next. Some people may already be familiar with CD4 and CD8 markers, which help differentiate your body's T cells in the immune system.

Well, it turns out that virtually all cells in the body have one or more CD markers, and a particular pattern or combination of CD markers can be indicative of a particular cell type.

There are more than 300 types of CD molecules and the list continues to grow. The CD number for each molecule is determined at international workshops in which scientists exchange information about human cells and the antibodies that react with them.

CD markers are perhaps most useful for classifying the white blood cells (WBCs), which are part of the immune system and help fight infections. Researchers develop antibodies in the laboratory called monoclonal antibodies (mAbs) that are specifically matched against each type of CD antigen. Ideally, these mABs, or in some cases a particular set or panel of mABs, can be used to diagnose different types of cancers of the white blood cells. Such mABs can also be used in targeted immunotherapy, whereby an antibody is developed that can target the cancerous cells for destruction with minimal or manageable collateral damage to healthy cells.

Why CD Markers Are Important in Cancer Diagnosis

There are different types of WBCs and you can't always tell one from another based on their appearance under the microscope.

One of the most precise ways to identify different types of WBC malignancies is to see what CD molecules appear on their surface. Analysis of the cancer cell’s genes and mutations is another powerful tool.

This testing for CD markers is especially important in the diagnosis of many blood cancers, such as lymphomas, leukemias and myeloma.

Knowing which CD markers appear on the cancerous cells helps doctors pinpoint what type of cell lead to the cancer and how that type of cancer might be expected to behave, going forward—including which therapies would be most appropriate.

As an example of the usefulness of CD markers, consider two different lymphomas: diffuse large B-cell lymphoma (DLBCL) and anaplastic large cell lymphoma (ALCL).  Under the microscope, these two lymphomas can have a similar appearance in that both may occur with large cancer cells. Yet, the prognosis and treatments are different. CD markers can tell them apart: DLBCL is CD20-positive, while ALCL is CD20-negative but positive for CD30. Pathologists, the kinds of doctors who specialize in assessing blood and tissue samples for disease, often use CD markers to distinguish between different lymphomas.

Identification of CD Antigen Molecules

The CD molecules themselves cannot be seen with the eye. They are identified using antibodies that in some way show up under the microscope or in a particular test. Tests using antibodies can make the cells with a particular CD marker become “visible” in a variety of different ways, including through differently colored tags and enzymatic reactions.

Using antibodies in the lab, samples from blood and lymph nodes can be checked for CD molecules and the type of cancer precisely determined.

CD Molecules in Cancer Treatment

Special drugs have been designed that identify and attack cells that have a particular type of CD molecule. These drugs are called monoclonal antibodies, and they can attack the types of cells that contain the specific target CD molecule. Monoclonal antibodies can also be tagged to drugs or radiation-emitting substances that add to the ability to kill the targeted cells.

Examples of CD markers targeted in lymphoma treatment:

  • Rituxan (Rituximab) - a monoclonal antibody against CD20.
  • Zevalin (Ibritumomab Tiuxetan) - another antibody against CD20, tagged with a radiation emitting substance (Y90).
  • Bexxar (Tositumomab) - similar to Zevalin, only the radiation emitting substance is different (I131)
  • Gazyva (Obinutuzumab): targets CD20 antigen, used in initial treatment for small lymphocytic lymphoma/chronic lymphocytic leukemia.
  • Arzerra (Ofatumumab): targets CD 20 antigen, used in SLL/CLL.
  • Campath (Alemtuzumab): targets CD52 antigen in SLL/CLL and peripheral T-cell lymphomas.
  • Adcetris (Brentuximab vedotin): targets CD30 and is attached to a chemotherapy drug. Used in anaplastic large cell lymphoma.

Sources:

Wintrobe's Clinical Hematology (11th Edition). Editors J.P. Greer, J. Foerster, J.N. Lukens. Published by Lippincott Williams & Wilkins.

Immunotherapy for non-Hodgkin Lymphoma, American Cancer Society, updated 01/22/2016.

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