Possible extrathymic development of nonfunctional T cells in a patient with complete DiGeorge syndrome

Complete DiGeorge syndrome is characterized by the clinical triad of cardia c malformation, hypocalcemia and T cell immunodeficiency due to congenital athymia. We describe an infant with complete DiGeorge syndrome who at prese ntation had no circulating T cells detectable by flow cytometry. The patien t spontaneously developed circulating T cells but these cells did not proli ferate in response to mitogens. The T cell receptor V beta repertoire was s everely restricted. All T cells were host, not maternal, as assessed by flu orescent in situ hybridization evaluation of 22q11 hemizygosity. At autopsy , this patient had no grossly detectable thymus tissue and no microscopic e vidence for thymopoiesis. These findings suggest that clearance of T cells in infants with complete DiGeorge syndrome may represent oligoclonal expans ions of a small number of T cells that may have matured extrathymically and which do not respond in vitro to mitogen stimulation. (C) 1999 Academic Pr ess.