Prolonged hematopoietic chimerism in normal mice transplanted in utero with human hematopoietic stem cells.

We have previously reported prolonged hematopoietic chimerism in normal mice transplanted in utero with human fetal hematopoietic stem cells (HSC) by flow cytometry. We now further confirm the human origin of these cells by demonstrating human DNA in the marrow of one such chimeric mouse. We also examined 42 mice born after in utero transplantation with HSC enriched from human adult marrow cells. All live-born mice were treated with recombinant human growth factors. Twelve had human cells in the peripheral blood (range: 01.-2.93%). Thymic samples were positive in 3 cases. The bone marrow of 2 mice contained cells expressing human CD34 antigen. Light scatter characteristics support the presence of multilineage hematochimerism. Human IgM was present in 2 of 4 chimeric sera tested. Thus, normal mice transplanted in utero with human HSC may permit long-term engraftment and differentiation of the human HSC.

Felty's Syndrome.

Felty's syndrome is a complication of rheumatoid arthritis whereby patients develop neutropenia of varying severity. Although the main clinical concern is the development of serious infections, often patients remain asymptomatic or continue with clinical problems related to the rheumatoid arthritis and not to the neutropenia. There is now considerable clinical experience with the use of the recombinant human haemopoietic growth factors granulocyte and granulocyte-macrophage colony-stimulating factors (G-CSF and GM-CSF) in the treatment of patients with Felty's syndrome. The only indication for the use of either growth factor for Felty's syndrome is the onset of infectious complications, which may be recurrent and serious. In general, when this occurs, the neutropenia is severe (<10(8) cells/L). The mechanism(s) underlying development of the neutropenia in Felty's syndrome is similar to that in other forms of immune-mediated neutropenia, and in general is associated with a terminal defect in neutrophil maturation. It is likely that the maturational defect is a consequence of ;immune based' inhibition, although we lack detailed understanding of this inhibitory process. Growth factor therapy does not relieve the defect in terminal maturation, but in general may induce a significant improvement in the peripheral white cell count. Instances where growth factor therapy does not work appear to be due to an inability to overcome the maturational defect. Thus, the level of granulopoietic inhibition mediated by the rheumatoid process varies in severity among patients. To date, treatment options for Felty's syndrome have included disease-modifying antirheumatic drugs, corticosteroids and splenectomy. The addition of growth factor therapy is a welcome addition to these less than optimal treatment options. However, all of the above therapies fail on occasion. Moreover, the dosage and frequency of growth factors must be titrated to keep the white blood cell count <5 x 10(9) cells/L, since overshoot may result in complications, the most common being exacerbation of the rheumatoid arthritis. Another mechanism by which these drugs may exacerbate rheumatoid arthritis is through activation of neutrophils. The addition of disease-modifying drugs may relieve the maturational defect, improve the peripheral white cell count and minimise disease exacerbation by limiting neutrophil exposure to the administered haemopoietic growth factor. However, long term monotherapy with G-CSF has been successfully employed without requiring disease-modifying therapy.

Transplantation in utero of fetal human hematopoietic stem cells into mice results in hematopoietic chimerism.

Allogeneic and xenogeneic hematolymphoid chimerism has been achieved in large and small animals using varied techniques to circumvent immune mediated graft rejection by the recipient. We show here the establishment of long-term chimerism in normal mice transplanted in utero with human fetal hematopoietic stem cells (HSC). HSCs from fetal (13-20 weeks' gestation) human livers were injected into fetal mouse peritoneal cavities on days 11-13 of gestation. Histologic examination demonstrated human chimerism in 29% of 38 live born mice using fluorescein conjugated antibodies to both the CD45 and CD14 antigens present on human peripheral blood (PB) cells. Further investigation using flow cytometric analysis of cells from 70 mice transplanted in utero revealed 28% of mice greater than 16 weeks of age contained human cells in at least one organ at the following frequencies: 14% PB, 8% bone marrow, 8% spleen and 12% thymus. These data indicate that human fetal HSC can be engrafted into mouse fetuses. Additionally, the identification of circulating human cells 18 months following transplantation supports the engraftment and proliferation of a primitive hematopoietic progenitor.

Sequential administration of cyclophosphamide and granulocyte-colony stimulating factor relieves impaired myeloid maturation in Felty's syndrome.

A patient with Felty's syndrome (FS) and persistent profound neutropenia developed recurrent infections and sepsis syndrome. No impairment of granulocyte-macrophage colony development was observed in vitro. Marrow morphology revealed an absence of mature neutrophil forms despite administration of granulocyte-colony stimulating factor (G-CSF). However, pretreatment with bolus cyclophosphamide (CY) permitted the growth factor to relieve this impairment of late myeloid maturation and resulted in a brisk, albeit short, burst of neutrophilia. This suggests that immune interference in myelopoiesis can be overcome by growth factor administration if immune activity is adequately dampened by immunosuppressive therapy.

Erythropoietin does not cross the placenta into the fetus.

Erythropoiesis in the fetus is controlled by erythropoietin (Ep). To determine the role of maternal Ep in this process, we used catheterized preparations of sheep and monkey fetuses to assess the ability of Ep administered to the mother to cross the placental barrier into the fetus. Ep was injected into pregnant sheep (3,600 IU/sheep) or monkeys (800-2,000 IU/animal) as a single intravenous dose, or into sheep in intravenous doses of 2,000 IU once every 12 h for a total of 4 injections. Maternal and fetal blood samples for Ep and reticulocyte determinations were obtained before and at intervals after Ep injections. The administration of Ep resulted in significant increases in maternal circulating Ep levels in sheep and monkeys. Despite the presence of high levels of maternal Ep, however, no increase in fetal plasma Ep levels was detected. The administration of Ep to the mother caused significant increases in reticulocyte production in the mother but not the fetus; injection of Ep directly to the fetus stimulated fetal erythropoiesis. These results demonstrate that Ep does not cross the placenta into the fetus even under conditions of chronically elevated maternal Ep levels, and suggest that red cell production in the fetus is regulated by Ep produced from sites within the fetus.

Anemia of inflammation: role of T lymphocyte activating factor.

Varied conditions associated with immune activation (rheumatic, infectious and malignant) are associated with a syndrome characterized by selective erythropoietic suppression. The pathogenesis of this anemia is unknown. We have cultured intact marrows from 11 patients and found decreased erythroid colony forming activity (CFU-E: colony forming unit-erythroid; p < 0.01). We analyzed sera from 23 patients with infectious, rheumatic and malignant disorders for their ability to render normal human T lymphocytes inhibitory to autologous CFU-E and burst forming unit-erythroid in vitro. Following exposure to serum from some anemic patients, normal T cells were observed to inhibit autologous CFU-E when compared to the effect elicited by T cells incubated with heterologous normal serum. Pooled data from 19 (7 not anemic, 12 anemic) serum samples using 8 different normal T cell and marrow donors revealed a significant correlation (r = 0.65, p < 0.01) between each patient's hemoglobin level and the ability of his/her serum to render T cells suppressive to CFU-E in vitro. The suppression mediated by patient serum exposed T cells on autologous CFU-E could be ameliorated by increased concentrations of erythropoietin. The serum factor was heat stable (56 degrees C) and could not be eliminated by neutralizing antibody to either gamma-interferon or tumor necrosis factor-alpha. We conclude that some patients with anemia of inflammation may have a circulating factor(s) which renders normal T lymphocytes suppressive to autologous CFU-E in vitro. The presence of a circulating serum factor in these patients may help explain how inflammatory events distant from the marrow mediate the erythropoietic suppression characteristic of this syndrome.

Mechanism of ranitidine associated anemia.

Ranitidine, an H2 receptor antagonist, has been associated with hematotoxicity. The mechanism(s) underlying the toxicity is not well understood. The authors studied the mechanism of anemia in a patient with ranitidine associated anemia and thrombocytopenia. Clinical evaluation suggested drug-induced Coombs' positive reticulocytopenic hemolysis. In vitro, with the patient off ranitidine, the authors were able to induce Coombs' positivity by incubating patient's red cells with ranitidine and his serum. This process was inhibited by prior exposure of his red cells to histamine. In vitro studies using clonal assays for hematopoietic progenitors revealed that while the patient's serum or ranitidine alone did not affect the patient's or normal bone marrow hematopoiesis, the simultaneous presence of both agents significantly suppressed both patient's and normal erythroid progenitor (BFU-E) colony development. This suppressive effect was prevented by the prior exposure of marrow to histamine and was not observed when the patient's serum was heat inactivated. These studies suggest that the anemia may have resulted from complement-dependent autoimmune destruction/inhibition of progenitor/mature erythroid cells by a process critically dependent on the presence of ranitidine and possibly acting at or near the histamine receptor.

Comparison of once-daily captopril or enalapril in mild essential hypertension.

The purpose of this study was to assess the effect of a daily low dose of the angiotensin-converting enzyme (ACE) inhibitors, captopril or enalapril, in mild essential hypertension. Nine men with seated diastolic blood pressure between 95 and 104 mm Hg on placebo participated in the study. After one month of placebo, captopril 25 mg was administered; blood pressure, heart rate, ACE activity and plasma renin activity were measured hourly for 4 hours. Each patient then received captopril 50 mg once daily for 8 weeks and similar measurements were made 24 hours post-dose every 2 weeks. After another month of placebo, the identical protocol was repeated after enalapril 5 mg. Although blood pressure and ACE activity decreased significantly (P less than 0.05) within 2-4 hours of the acute doses of each inhibitor, neither captopril or enalapril produced significant reductions 24 hours after the small daily dose. Thus, neither ACE inhibitor alone was adequate to control blood pressure in mild hypertension when given once daily during 8 weeks of treatment.