Early on, stem cells commit to following one of two development pathways called "cell lines." These cell lines are the myeloid cell line and the lymphoid cell line.
The lymphoid cell line begins with a lymphoid stem cell or lymphoblast. As these stem cells divide and become more specialized in their function, they ultimately become blood cells, including:
Lymphoid lineage cells make up about 15% of the cells in healthy bone marrow. But in such conditions as acute lymphocytic leukemia (ALL) and chronic lymphocytic leukemia (CLL), it is the lymphoid cell line that is affected.
Williams, L. "Comprehensive Review of Hematopoiesis and Immunology: Implications for Hematopoietic Stem Cell Transplant Recipients" in Ezzone, S. (2004) Hematopoietic Stem Cell Transplantation: A Manual for Nursing Practice Oncology Nursing Society: Pittsburgh, PA (pp.1- 12)