Lymphocytes are white blood cells that help the body defend against disease. There are different types of lymphocytes, which include B-lymphocytes and T-lymphocytes.
Acute lymphoblastic leukemia (ALL) occurs when the DNA inside an immature lymphocyte (lymphoblast) changes. This mutation can happen at different developmental stages of the lymphocyte. Depending on whether the genetic change takes place in a developing B-lymphocyte or T-lymphocyte, ALL can be further broken down into different subtypes. Identifying your child’s ALL subtype will help doctors decide their treatment plan.
What are the subtypes of ALL?
The World Health Organization’s (WHO) 2016 revision of myeloid neoplasms and acute leukemia now classifies ALL as B-lymphoblastic leukemia or T-lymphoblastic leukemia, with further subdivisions based on molecular characteristics.
- Precursor B-cell ALL occurs when DNA changes in young B-cells (B-lymphoblasts).
- T-cell ALL occurs when DNA changes in young T-cells (T-lymphoblasts).
How common is each ALL subtype?
Precursor B-cell ALL is the most common subtype of ALL. It accounts for about 80-85% of childhood ALL cases.
How do we identify each ALL subtype?
Normal lymphocytes have specific proteins on their surface, called antigens. Cancerous B-cells and T-cells also have similar antigens. Diagnostic techniques can distinguish the type of antigen on the surface of leukemic cells. These tests are called immunophenotyping (or flow cytometry).
Precursor B-cell ALL
Precursor B-cell ALL is identified because of unique antigens on the surface of precursor B-lymphoblasts, such as CD10, CD19, CD79a, and HLA-DR and other B-cell associated antigens.
T-cell ALL
Immunophenotyping detects T-lymphoblasts that express surface antigens including CD7 plus CD2 or CD5, as well as a unique antigen that floats inside T-lymphoblasts called cytoplasmic CD3.