Childhood polyclonal T cell lymphocytosis with neutropenia: effects of antilymphocyte globulin and granulocyte colony stimulating factor in vitro and in vivo.

The pathogenesis of the neutropenia that occurs in some patients with chronic T cell lymphocytosis is not well understood. We have investigated a 15-year-old girl with this syndrome. Initial committed bone marrow progenitor numbers (CFUgm) were low but markedly increased in vitro following T cell depletion. Similarly a transient correction of neutropenia was observed following in vivo lymphocyte depletion with antilymphocyte globulin. A sustained neutrophil recovery was achieved with daily therapy using recombinant human granulocyte colony stimulating factor (rhG-CSF) despite persistence of the lymphocytosis; during successful therapy CFUgm numbers remained low, and were not increased by the in vitro addition of rhG-CSF. These observations suggest the possibility of an inhibitory regulatory mechanism specifically acting on neutrophil granulopoiesis.