Bone marrow from a patient with aplastic anemia was shown by multiple criteria to have a block in early myeloid differentiation. This block was overcome in vitro by elimination of marrow lymphocytes. Furthermore, this differentiation block was transferred in vitro to normal marrow by coculturing with the patient's marrow. We suggest that some cases of aplastic anemia may be due to an immunologically based suppression of marrow cell differentiation rather than to a defect in stem cells or their necessary inductive environment.The hematopoietic system in man is thought to develop from a common stem cell analogous to the spleen colony forming unit in mice (CFU-s) (1), which then differentiates into committed progenitor cells of the granulocytic and monocytic series (CFU-c) (2), megakaryocytic, lymphoid, and erythroid lines, and then passes through several more differentiation steps into mature effector cells. Aplastic anemia is a disease characterized by a marked decrease in the production of erythrocytes, leukocytes, and platelets. The etiology of this kind of bone marrow failure is complex, and about 50% of all cases are idiopathic. There has been considerable speculation about the possible role of an immunologic mechanism in the pathogenesis of some cases (3, 4), but this mechanism has not yet been fully documented. We present here evidence for such a mechanism. The number of thymus-derived (T) lymphocytes was determined by spontaneous rosette formation with SRBC (8). Fifty microliters of bone marrow cells at 3 X 106 cells per ml were mixed with 50 Ml of washed SRBC at 2 X 108 cells per ml and 25 ,l of heat-inactivated SRBC-absorbed fetal calf serum. This mixture was incubated for 5 min at 37?, centrifuged at 200 X g for 5 min at 24°, and then incubated for 3-6 hr at 4°. Four fields of 100 cells were counted in a hemocytometer, and cells were scored as positive if they bound four or more SRBC. CASE REPORTSurface Marker Induction. Separated bone marrow cell fractions were incubated at 1.5 X 106 cells per ml in RPMI-1640 containing 5% fetal calf serum for 8 hr at 37°in humidified 5% CO2 and 95% air. These cultures contained either medium alone (control), or ubiquitin (0.5 ,g/ml). After incubation, the cells were washed twice, resuspended in RPMI-1640 to 3 X 106 cells per ml, and assayed for surface markers. Ubiquitin was prepared as described (9).Spontaneous DNA Synthesis. In the course of studying the response of marrow cells in mixed leukocyte culture, the spontaneous DNA synthesis of cells was measured by substituting irradiated autologous marrow cells for irradiated allogenic peripheral blood lymphocytes.Cells were resuspended at 1 X 106 cells per ml in RPMI-1640 with penicillin (50 units/ml), streptomycin (50 Mug/ml) and 15% 2890Abbreviations: CFU-s, colony forming unit (spleen); CFU-c, colony forming unit (culture); SRBC, sheep erythrocytes; T cell, thymusderived lymphocyte.

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Bone marrow cells from a patient with severe combined immunodeficiency were studied in vitro for thymus-dependent lymphocyte (T cell) Severe combined immunodeficiency disease (SCID) is a diagnostic term for a heterogeneous group of congenital disorders usually ascribed to a defect in the development or function of lymphoid stem cells (1). Such patients usually have defective development and function of both thymus-dependent lymphocyte (T cell) and thymus-independent lymphocyte (B cell) populations (2). Immunologic reconstitution in patients with this disease has been repeatedly achieved after transplantation of marrow from related, histocompatible donors (3)(4)(5)(6)(7)(8) In this report, we present evidence to indicate that, in certain variants of SCID, transplantation of both fetal liver and thymus may be necessary to provide both the stem cell and an inductive influence necessary for immunologic reconstitution. MATERIALS AND METHODSCase Report. The patient, a 20-month-old white boy, was a full-term 3.8-kg product of a normal pregnancy. Growth and development were normal until age 10 weeks, at which time a monilial rash was first noted behind his right ear; this was followed by severe oral moniliasis at age 4 months. Both conditions were refractory to antifungal therapy. At 5 months of age, poor feeding and progressive weight loss developed. On Sept., 18, 1975, at age 7 months, he was admitted to our hospital.At the time of admission, the patient was markedly cachectic, weighed 5.5 kg, and had severe moniliasis involving the oral cavity and perineal area. Clinical and roentgenographic evidence of interstitial pneumonia, subsequently documented to be due to Pneumocystis carinii, was noted. No

Thymic function was evaluated by quantitation of circulating thymic factor in patients with several forms of severe infantile immunodeficiency diseases. Direct quantitation of thymic factor in serum of patients with severe combined immunodeficiency revealed heterogeneity of this syndrome by this parameter, as was also shown by study of susceptibility of the marrow cells to differentiation in vitro. Thymic factor was not detectable in one patient with severe combined immunodeficiency, but was present in normal or near-normal concentrations in three others. Circulating levels of this hormonal activity were also not detectable in a patient with DiGeorge athymic syndrome. Following marrow or fetal liver transplantation, which corrected the severe combined immunodeficiency, thymic factor levels either increased slightly or did not change appreciably. Fetal thymic transplantation, which together with fetal liver transplantation corrected the immunodeficiency in one patient with severe combined immunodeficiency, was associated with increase of thymic factor to normal levels. Fetal thymus transplantation alone, which was employed to correct the immunodeficiency of DiGeorge athymic syndrome, caused an increase in thymic factor activity to normal or near normal levels in this patient.

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