How do lymphocytes develop?

  • Blood cells are produced in the bone marrow. In a normally functioning bone marrow, the blood‑forming stems cells either create more stem cells, or divide and transform into either a myeloid cell or a lymphoid cell, (Figure 1).
  • Normal myeloid cells become one of the three types of lymphocyte cells:
  • B-lymphocytes (B-cells) that make antibodies to invading organisms.
  • T-lymphocytes (T-cells) that destroy invading organisms and cells that have become cancerous.
  • Natural killer cells (NK‑cells) that attack cancer cells and viruses.

Figure 1         Development of stem cells in the bone marrow

Source: Leukaemia Care

  • In ALL, the large numbers of leukaemia cells begin to accumulate in the bone marrow (Figure 2).

Figure 2        Bone marrow in ALL with numerous lymphocyte leukaemia cells



Limited cytoplasm
with single long projection


There are two main subtypes of ALL. They are:

  • B-cell ALL which occurs in 75% of adults
  • T-cell ALL which occurs in 25% of adults
  • Since the treatments used for B-cell ALL and T-cell ALL are similar, the information in this e-learning module applies to both types.