Influence of T lymphocytes on hematopoiesis in a patient with T cell hypoplasia

In this communication, we describe an unusual patient with a reported lifelong history of anemia. Investigation of the pathogenesis of this patient's bone marrow failure provided an interesting opportunity to determine the role of T cells in the regulation of human blood cell production. Phenotyping of the patient's mononuclear cells revealed severe T cell hypoplasia in both the peripheral blood and bone marrow. The patient's bone marrow was capable of producing 50–60% of the normal numbers of burst‐forming units—erythroid (BFU‐E) in the presence of optimal concentrations of erythropoietin, suggesting that marrow BFU‐E formation is in part independent of T cells. Addition of small numbers of class I identical donor T cells enhanced BFU‐E cloning efficiency to a level observed in normal controls. This enhancing effect was supplied by a T4 + (CD4) population of donor cells. The addition of donor T cells partially corrected the inability of patient marrow cells to produce megakaryocyte and mixed colonies. These studies suggest that prolonged T cell hypoplasia might deprive marrow progenitor and stem cells of a necessary enhancing effect that is required for sustained normal hemato‐poiesis. Such a T cell defect in rare instances may result in bone marrow failure.