Morphology and incidence of the "posttherapeutic lymphoid cell" in the bone marrow of children with acute lymphoblastic leukemia.

In the posttherapeutic bone marrow of a group of 30 children with acute lymphoblastic leukemia (ALL), small numbers of a particular lymphoid cell with a comparatively large size and large dark nucleus were found. This cell was called the "posttherapeutic lymphoid cell." This type of cell is easily distinguishable in the May-Grünwald-Giemsa-stained smears as well as in semi- and ultrathin Epon sections. Immunoelectron-microscopically it proved to be positive for common ALL. It is hypothesized that the cell might be characteristic for ALL. However, it appeared that this cell could equally be found in non-Hodgkin's malignant lymphoma after a treatment comparable to that in ALL. Furthermore, the cell could be detected in the posttherapeutic bone marrow of children with nonlymphoid malignancies as well as the marrow of very young children (under 2 years of age) with nonmalignant diseases. The results showed that the cell in question is not associated with a particular disease but, rather, represents a special type of lymphoid cell in the regenerating or actively proliferating bone marrow.