Transplantation of unrelated placental blood cells in children with high-risk sickle cell disease.

The lack of healthy HLA-identical sibs limits the use of allogeneic hematopoietic cell transplantation in children with high-risk sickle cell disease (SCD). We evaluated unrelated placental blood cell transplantation (UPBCT) after a preparative regimen of busulfan, cyclophosphamide and antithymocyte globulin in three children with SCD who had cerebrovascular accidents (CVAs) and did not have HLA-matched sib donors. The placental blood cell units were matched with the recipients at four of six HLA-A, HLA-B and HLA-DRB1 antigens. Neutrophil levels above 0.5 x 10(9)/l occurred at 23, 38 and 42 days after UPBCT, and platelet levels above 50 x 10(9)/l without transfusions occurred at 62, 81 and 121 days after UPBCT. All patients developed acute graft-versus-host disease (GVHD; two grade II, one grade III), and one developed extensive chronic GVHD. One patient had graft failure and autologous hematopoietic recovery. Two patients have complete donor hematopoietic chimerism without detectable hemoglobin S or symptoms of SCD at 40 and 61 months, respectively, after UPBCT. These observations demonstrate the feasibility of UPBCT in children with SCD. Further studies of UPBCT for SCD are needed but, because of risks of procedure-related morbidity and graft rejection, should be restricted to pediatric patients with high-risk manifestations of SCD.

Genetic divergence in cellular resistance to heat shock in cattle: differences between breeds developed in temperate versus hot climates in responses of preimplantation embryos, reproductive tract tissues and lymphocytes to increased culture temperatures.

The detrimental effects of heat stress on fertility in cattle are less pronounced in heat-tolerant breeds. Although these genetic differences reflect differences in thermoregulation, cells from heat-tolerant breeds are less adversely compromised by increased temperature (that is, heat shock) than cells from heat-sensitive breeds. Experiments were performed to test the hypothesis that cells and tissues from two thermotolerant breeds (Brahman and Senepol) are better able to survive and function after exposure to increased temperature than cells and tissues from two thermosensitive breeds (Holstein and Angus). Exposure of embryos at>eight-cell stage at day 5 after insemination to heat shock of 41.0 degrees C for 6 h decreased development to the blastocyst stage and the number of cells per embryo. However, the deleterious effect of heat shock on blastocyst formation and the number of cells per embryo was less pronounced for Brahman than for Holstein and Angus breeds. Embryos from Senepol cows had very low development and it was not possible to determine heat shock effects in this breed. In contrast to the sensitivity of embryos to heat shock, there was no effect of a 41.0 degrees C heat shock on [(3)H]leucine incorporation into proteins secreted by oviductal or endometrial explants. Lymphocytes from Brahman and Senepol cows were more resistant to heat-induced apoptosis than lymphocytes from other breeds. Heat shock reduced lymphocyte glutathione content but the magnitude of the decrease was not affected by breed. In conclusion, embryos from Brahman cows are more resistant to heat shock than embryos from Holstein or Angus cows. Genetic differences are also present in thermotolerance for apoptosis response in lymphocytes, with Brahman and Senepol cattle being more resistant to heat shock than Angus and Holstein breeds. It is likely that the evolutionary forces that led to the Brahman and Senepol breeds being adapted to hot climates resulted in the selection of genes controlling resistance to cellular heat shock.

Inhibition of angiogenesis and tumour growth by VEGF121-toxin conjugate: differential effect on proliferating endothelial cells.

Vascular endothelial growth factor (VEGF) plays an important role in tumour angiogenesis. VEGF binds to tyrosine kinase receptors, which are expressed almost exclusively on tumour endothelium. Therefore, VEGF can be used to target toxin molecules to tumour vessels for anti-angiogenic therapy. However, recent evidence suggests that VEGF can also bind in an isoform-specific fashion to a newly identified neuropilin-1 (NP-1) receptor. NP-1 is widely expressed in normal tissue and presents a potential target for unwanted toxicity. As a consequence, we investigated whether the VEGF121 isoform, which lacks the NP-1 binding domain, could be used to target toxin polypeptides to tumour vasculature. Treatment of endothelial cells with a VEGF121-diphtheria toxin (DT385) conjugate selectively inhibited proliferating endothelial cells, whereas confluent cultures were completely resistant to the construct. In addition, VEGF121-DT385 conjugate treatment completely prevented tumour cell induced angiogenesis in vivo. Most importantly, the conjugate inhibited tumour growth in athymic mice and induced tumour-specific vascular damage. There was also no apparent toxicity associated with the treatment. Our results suggest that proliferating endothelial cells are highly sensitive to VEGF121-toxin conjugates and that the binding to NP-1 receptors is not necessary for efficient inhibition of tumour growth.

Ovarian and endocrine characteristics during an estrous cycle in Angus, Brahman, and Senepol cows in a subtropical environment.

To determine breed differences in ovarian function and endocrine secretion, daily rectal ultrasonography was conducted on multiparous lactating Angus (temperate Bos taurus; n = 12), Brahman (tropical Bos indicus; n = 12), and Senepol (tropical Bos taurus; n = 12) cows during an estrous cycle in summer. Blood was collected daily to quantify plasma concentrations of FSH, LH, progesterone, estradiol, GH, insulin-like growth factor (IGF)-I, IGF-II, IGF binding proteins (IGFBP), insulin, glucose, and plasma urea nitrogen (PUN). Numbers of small (2 to 5 mm), medium (6 to 8 mm), and large follicles (> or = 9 mm) were greater (P < .05) in Brahman than in Angus and(or) Senepol cows. Length of the estrous cycle (SEM = .6 d) was similar (P > .10) among Senepol (20.4 d), Angus (19.5 d), and Brahman (19.7 d) cows. Senepol cows had greater (P < .05) diameters of the corpus luteum (CL) and a delayed regression of the CL as compared with Angus cows. The secondary surge of FSH (between d 1 and 2; d 0 = estrus) was greater in Angus than Brahman or Senepol cows (breed x day, P < .05). Between d 2 and 14 of the estrous cycle, concentrations of progesterone, LH, IGF-II, and binding activities of IGFBP-3, IGFBP-2, and the 27- to 29-kDa IGFBP in plasma did not differ (P > .10) among breeds. Concentrations of GH, IGF-I, insulin, and PUN were greater (P < .001) and binding activities of the 22-kDa and 20-kDa IGFBP tended (P < .10) to be greater in plasma of Brahman than in Angus or Senepol cows. Plasma glucose concentrations were greater (P < .05) in Senepol than in Brahman or Angus cows. In conclusion, Brahman (Bos indicus) and Senepol cows (tropical Bos taurus) had greater numbers of follicles in all size categories and greater diameter of CL than Angus (temperate Bos taurus) cows. These ovarian differences may be due to changes in the pattern of secretion of FSH, insulin, IGF-I, and GH but not LH, IGF-II, or IGFBP-2 or -3.

Patterns of ovarian growth and development in cattle with a growth hormone receptor deficiency.

Nutritionally induced changes in growth hormone (GH) and IGF-I are associated with decreased ovarian function and may partially explain infertility and anestrus in undernourished cattle. The reproductive importance of GH and IGF-I was tested in cattle with a GH receptor deficiency (GHRD) that have reduced blood IGF-I. Blood was collected daily for plasma, and ovaries were examined daily by ultrasonography for 3 wk during an estrous cycle (estrus = d 0) in GHRD (n = 8) and control (n = 8) cattle. On d 18, blood samples were collected every 10 min for 6 h to measure LH. The GHRD cattle had fewer small antral ovarian follicles (2 to 5 mm, P < .01). After estrous cycle d 5, the first-wave dominant follicle stopped growing in GHRD but continued growing in controls (P < .001). Size of the CL was equivalent for GHRD and controls until d 5, after which CL development slowed in GHRD (P < .01). Likewise, plasma progesterone concentrations were less in GHRD (P < .001). During the luteal phase, GHRD cattle failed to develop follicles greater than 10 mm in diameter (endocrine status x day, P < .05). Size and rate of growth of preovulatory follicles, plasma estradiol, plasma FSH, and plasma LH (d 18 bleed) were similar in GHRD and controls. In conclusion, an important role for GH, GH receptor, and IGF-I in ovarian function was supported because GHRD cattle had distinctly different patterns of ovarian development compared with control cattle.

Targeting the tumor vasculature: inhibition of tumor growth by a vascular endothelial growth factor-toxin conjugate.

Tumor-derived vascular endothelial growth factor (VEGF)/ vascular permeability factor (VPF) plays an important role in neovascularization and the development of tumor stroma. Furthermore, VEGF receptors are over-expressed in the endothelial cells of tumor vasculature and almost non-detectable in the vascular endothelium of adjoining normal tissues. The differential expression of receptor offers a selective advantage for targeting cytotoxic toxin polypeptides. We have prepared a vascular targeting reagent by chemically linking recombinant VEGF to a truncated form of diphtheria toxin. The VEGF-toxin conjugate was selectively toxic to endothelial cell lines and inhibited experimental neovascularization of the chick chorioallantoic membrane. In the present study, we examined the effects of VEGF-toxin conjugate on solid tumor growth. Athymic nude mice with established subcutaneous tumors were treated with daily intraperitoneal injections of the VEGF-toxin conjugate or free toxin. When compared with control animals treated with the toxin polypeptide alone, the conjugate-treated animals displayed a significant inhibition of tumor growth. Histological analysis of tumors from conjugate-treated animals revealed hemorrhagic necrosis consistent with a vascular-mediated injury. In contrast, highly vascularized normal tissues from conjugate-treated animals demonstrated no evidence of hemorrhage or tissue injury. The conjugate was well tolerated without apparent toxicities. Our results illustrate the anti-tumor activity of a VEGF-toxin conjugate selectively targeting the tumor neovasculature.

Vascular endothelial growth factor (VEGF) expression and survival in human epithelial ovarian carcinomas.

Vascular endothelial growth factor (VEGF) expression and microvessel density were studied in cases of advanced epithelial ovarian carcinoma to evaluate their usefulness as prognostic variables. Tumor samples from 18 patients with advanced stage serous epithelial ovarian cancer were evaluated for VEGF expression by reverse-transcriptase polymerase chain reaction (RT-PCR) analysis. Immunohistochemical study of corresponding archival tissues with an antibody to von Willebrand factor (vWF; FVIII-RA) was used for tumor microvessel count determinations. The correlation of VEGF expression and mean microvessel counts was determined by an unpaired t-test. Survival analysis for known prognostic factors and VEGF expression was performed. Survival distributions were calculated by the product limit of Kaplan and Meier and significant differences between distributions were analyzed with a log rank test. From the RT-PCR analysis of tumor VEGF expression, 12 samples were found to be strongly positive, whereas six samples had low/negative VEGF expression. The median survival was 60 months for the VEGF-low/negative group and 28 months for the VEGF-positive group (P = 0.058). Other prognostic variables had minimal impact on survival, i.e. age < 65 years (P = 0.873), FIGO stage (P = 0.06), grade (P = 0.236) and debulking status (P = 0.842). Fourteen of 18 tumor specimens were suitable for microvessel counting. The mean microvessel counts of the VEGF-positive group and the VEGF-negative group were 27/hpf and 35/hpf, respectively (P = 0.16). In this preliminary analysis, high VEGF expression in epithelial ovarian carcinomas was associated with poor overall survival. Further study will be necessary to elucidate the lack of association of VEGF expression and tumor microvessel counts.

Characterization of vasoactive intestinal peptide receptors on human megakaryocytes and platelets.

Vasoactive intestinal peptide receptor I (VIPRI) expression was examined in megakaryocytes using reverse transcriptase-polymerase chain reaction (RT-PCR). VIPRI protein was characterized in platelet membranes using covalent crosslinking techniques. Human megakaryocytes were isolated from suspension cultures of cord blood and adult bone marrow mononuclear cells using a murine monoclonal antibody to human platelet glycoprotein IIB/IIIA (CD41) and immunomagnetic beads. RT-PCR primers were constructed for the VIP, VIPRI, and VIPRII genes as well as for megakaryocyte specific genes, c-mpl and platelet factor 4 (PF-4). VIP, VIPRI, c-mpl, and PF-4 were coexpressed in megakaryocyte mRNA. Southern blot analysis confirmed the expression of VIPRI. 125I-VIP was covalently cross-linked to human platelet membranes using the homobifunctional reagent disuccinimidyl suberate, followed by polyacrylamide gel electrophoresis and autoradiography. A 125I-VIP-protein complex of Mr = 50,000 was identified. Labeling of the Mr = 50,000 component was completely abolished by unlabeled VIP, but not by peptide histidine methionine or growth hormone releasing factor, indicating specific binding of VIP to the platelet membranes. Taken together, these results suggest that VIP may have direct effects on megakaryocytopoiesis and support our earlier observations of VIP modulation of platelet aggregation.

Prevention of postoperative adhesions by an antibody to vascular permeability factor/vascular endothelial growth factor in a murine model.

OBJECTIVE: Our purpose was to test the ability of an antiserum to vascular permeability factor/vascular endothelial growth factor to inhibit postoperative adhesion formation in a murine model. STUDY DESIGN: After a standardized peritoneal injury, 28 Balb/c mice were randomized and treated intraperitoneally with either vascular permeability factor antiserum (n = 14) or preimmune serum (n = 14) at the time of abdominal closure. Mice were killed on postoperative day 14, and the development of intraabdominal adhesions was determined. Adhesion scoring was based on an overall assessment of the extent, location, and type of adhesions present. Statistical analyses were performed with the Mann-Whitney and Fisher's exact tests. RESULTS: The mice treated with the vascular permeability factor antiserum had significantly lower adhesion scores than did the control group (mean +/- SD 1.5 +/- 0.9, median 1.0, vs control 2.5 +/- 0.7, median 3.0). When the groups were analyzed for the presence of grade 2 or 3 adhesions, the group treated with vascular permeability factor antiserum had a significantly lower incidence of advanced adhesions (38%, vs control 92%). CONCLUSION: This study demonstrates that the intraperitoneal administration of a neutralizing antiserum to vascular permeability factor/vascular endothelial growth factor limits postoperative adhesion formation. These observations, to the best of our knowledge, are the first to suggest a role for vascular permeability factor in the pathogenesis of adhesion formation.

Vascular endothelial growth factor-toxin conjugate specifically inhibits KDR/flk-1-positive endothelial cell proliferation in vitro and angiogenesis in vivo.

Inhibition of tumor neovascularization has profound effects on the growth of solid tumors. An endothelial cell-specific cytotoxic conjugate was prepared by chemically linking recombinant vascular endothelial growth factor (VEGF165) and a truncated diphtheria toxin molecule (DT385). The treatment of subconfluent cultures of human umbilical vein endothelial cells and human microvascular endothelial cells with the VEGF165-DT385 conjugate resulted in a selective, dose-dependent inhibition of growth. Parallel experiments with either the free toxin or a mixture of VEGF and the toxin polypeptide did not affect proliferation (DNA synthesis) of these cells. The selective cytotoxicity correlated with the appropriate receptor expression (KDR/flk-1 positive) on the target cells. VEGF-toxin conjugate inhibited the growth of a murine hemangioma-derived endothelial cell line (Py-4-1), which was positive for flk-1 expression. Under similar conditions, the conjugate did not affect the proliferation of a receptor-negative ovarian cancer cell line in vitro. In an in vivo model of angiogenesis, the VEGF165-DT385 conjugate blocked basic fibroblast growth factor-induced neovascularization of the chick chorioallantoic membrane. These studies demonstrate the successful targeting of a cytotoxic polypeptide to proliferating vascular endothelial cells (normal and tumorigenic) and the potential utility of such conjugates in blocking tumor neovascularization.

Successful treatment of disseminated central nervous system malignant rhabdoid tumor.

PURPOSE: Malignant rhabdoid tumor (MRT) of the central nervous system (CNS) is pathologically identical to MRT of the kidney. CNS MRTs have the clinicopathological behavior of a high-grade intracranial sarcoma, and the children have a very poor prognosis. We report on three cases of primary CNS MRT with a review and summary of the pediatric literature with respect to demographic features and multidisciplinary management. PATIENTS AND METHODS: The 18 cases reviewed had a male to female ratio of 1.0 and an extremely young median age of 32 months. Our three cases of CNS MRT were treated with surgery, chemotherapy, radiotherapy, and triple intrathecal (TIT) chemotherapy similar to the Intergroup Rhabdomyosarcoma Study III guidelines for parameningeal primary tumors with intracranial extension. RESULTS: The three patients described in this report are surviving with no evidence of disease at 5 years, 2 years, and 9 months from diagnosis. Before these three cases, only four of 16 reported patients were known to have survived. One unique case in our report involved disease in the cerebral cortex, sinuses, and orbit with metastases to the subarachnoid space. This metastatic MRT responded to treatment with TIT, multiagent chemotherapy and cranial-spinal radiation after partial resection of only the cortical portion of the MRT. CONCLUSIONS: Disseminated CNS MRTs can be treated using multidisciplinary management with an approach similar to that used to treat rhabdomyosarcoma.

The response of cord blood megakaryocyte progenitors to IL-3, IL-6 and aplastic canine serum varies with gestational age.

Fetal cord blood (CB) is rich in haemopoietic stem cells and progenitors. We studied the clonogenic, proliferative and maturational responses of megakaryocyte (MK) progenitors in CB, from different gestational ages, to various cytokines: IL-3, IL-6, IL-3 + IL-6, and aplastic canine serum (PICS-J), and compared their responses to those of progenitors in adult peripheral blood (PB) or bone marrow (BM). We found that 34-week gestation CB produced some spontaneous colonies 28 +/- 4.7 CFU-MK in the absence of exogenous cytokines, and produced more CFU-MK and BFU-MK in response to IL-3, IL-6 and IL-3 + IL-6 than the other samples tested. Proliferation of CFU-MK was maximal at 34 weeks and decreased gradually toward term. When compared to adult BM or PB, the CB-derived CFU-MK had increased cellularity and contained significantly more cells undergoing fragmentation into platelet-like particles after stimulation with IL-3 or IL-6. Post-irradiation aplastic canine serum (PICS-J) was a highly potent stimulator of MK progenitors at all developmental stages. Our results indicate that CB MK progenitors are exquisitely sensitive to exogenous cytokines and that the magnitude of their proliferative and maturational responses to cytokines is related to developmental age.

Responses of bovine lymphocytes to heat shock as modified by breed and antioxidant status.

We tested whether resistance of lymphocytes to heat stress is modified by breed, intracellular glutathione content, and extracellular antioxidants. In the first experiment, lymphocytes from Angus (Bos taurus, non-heat-tolerant), Brahman (B. indicus, heat-tolerant), and Senepol (B. taurus, heat-tolerant) heifers (12 heifers per breed) were cultured at 45 degrees C for 3 h to evaluate thermal killing, at 42 degrees C for 12 h in a 60-h phytohemagglutinin-induced proliferation test, and at 42 degrees C for 1 h to measure induction of heat shock protein 70 (HSP70). Killing at 45 degrees C was affected by breed x temperature (P < .01); the decrease in viability caused by a temperature of 45 degrees C was greater for Angus than for Brahman or Senepol. For phytohemagglutinin-stimulated lymphocytes, heating to 42 degrees C reduced [3H]thymidine incorporation equally for all breeds. Viability at the end of culture was affected (P < .001) by a breed x temperature interaction because the decrease in viability caused by culture at 42 degrees C was greatest for lymphocytes from Angus heifers. Heat shock for 1 h at 42 degrees C caused a two- to threefold increase in intracellular concentrations of HSP70, but there was no interaction of temperature with breed. In another experiment (with lymphocytes harvested from three Holstein cows), buthionine sulfoximine, a glutathione synthesis inhibitor, inhibited (P < .01) proliferation of phytohemagglutinin-stimulated lymphocytes at 38.5 and 42 degrees C. Addition of the antioxidants glutathione or thioredoxin to culture did not reduce the effects of heating to 42 degrees C on proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)

Vascular permeability factor gene expression in normal and neoplastic human ovaries.

Epithelial ovarian cancer is an aggressive malignancy with a generally poor outcome. To improve survival, novel therapeutic strategies for this disease are needed and require elucidation of the biological events that underlie transformation and tumor growth. Vascular permeability factor (VPF), also known as vascular endothelial growth factor, is a homodimeric glycoprotein that acts on vascular endothelium as a potent permeability-inducing agent and mitogen. The present study demonstrates for the first time the constitutive gene expression of VPF in normal and neoplastic human ovaries. Abundant levels of VPF have been identified by an immunoassay in the ascites of patients with epithelial ovarian cancer (K-T. Yeo et al., Cancer Res., 53: 2912-2918, 1993). We have identified the malignant epithelium as one source of VPF in the ascites. Reverse transcription-polymerase chain reaction has demonstrated the expression of the two secreted isoforms, VPF121 and VPF165, in normal and neoplastic ovaries. Western blotting and an endothelial cell proliferation assay confirmed secretion of a biologically active product. VPF may be an important mediator of ascites formation and tumor metastasis observed in neoplastic conditions of the ovary.

Megakaryocyte colony stimulating activity in allogenic bone marrow recipients prepared with busulfan and cyclophosphamide.

Increased megakaryocyte colony stimulating activity (MK-CSA) has been reported after total body irradiation (TBI) for bone marrow transplant (BMT). We studied the effect of a busulfan (Bu) and cyclophosphamide (Cy) marrow transplant conditioning regimen, without radiation, on MK-CSA production. Initial screening of MK-CSA was done on previously collected and banked sera from 14 BMT patients. MK-CSA was expressed as the ability to stimulate growth of megakaryocyte progenitors (CFU-MK) in standard plasma clot cultures. In the initial samples, MK-CSA peaked at day 7. This preliminary data led to a prospective study of MK-CSA and clinical parameters in seven allogeneic recipients. MK-CSA activity increased from day -7 pre-transplant (2.9 +/- 1.7 CFU-MK/10(5) NATD, mean +/- SD) to day 0 (10.3 +/- 4.7 CFU-MK) and peaked by day 9 post-transplant (20.6 +/- 6.4 CFU-MK). MK-CSA activity decreased in all seven patients by day 21 at which time five of seven patients studied had recovery of platelet counts to greater than 100 x 10(9)/l. MK-CSA activity rose rapidly in both groups of sera after the initiation of this non-irradiation, BMT preparative regimen. High MK-CSA levels, early after transplant, may contribute to the rapid platelet recovery in some patients.

Antibody response in patients with Gaucher disease after repeated infusion with macrophage-targeted glucocerebrosidase.

Recent clinical data have shown that enzyme replacement therapy with macrophage-targeted glucocerebrosidase (GCR) can be effective in treating type 1 Gaucher disease. Sera from 262 patients, repeatedly infused with GCR, were assessed for the presence of antibodies to this therapeutic protein. Patient serum samples obtained at 3-month intervals were assessed by enzyme-linked immunosorbent assay and those with values greater than two standard deviations above the mean value obtained with a pool of normal human sera were further characterized by radioimmunoprecipitation. At the time of these analyses, the duration of patient treatment varied from 3 months to approximately 3 years. Of the 262 patients analyzed, 34 (12.9%) showed IgG antibodies, as confirmed by radioimmunoprecipitation. All patients who seroconverted did so within 1 year of treatment. The predominant antibody developed was the IgG1 subclass. Fourteen patients in the study experienced periodic symptoms suggestive of immediate hypersensitivity. Nine of these 14 patients had antibody to GCR as determined by radioimmunoprecipitation, whereas 5 patients were antibody negative. There was no evidence of the development of IgE antibodies in these 14 patients. The presence of GCR antibodies did not appear to effect efficacy of therapy in any of the patients treated to date.

Megakaryocytes and megakaryocyte progenitors in human cord blood.

Thrombocytopenia contributes significantly to morbidity in the sick term or preterm infant. However, few data exist on newborn's megakaryocytes and megakaryocyte progenitor cells (CFU-MK). We therefore studied CFU-MK in term and preterm infant cord blood and compared the results with data on CFU-MK from adult bone marrow and adult peripheral blood in a plasma clot culture with postirradiated aplastic canine serum (PIACS) as a source of megakaryocyte colony-stimulating activity. The number of CFU-MK and the number of cells per CFU-MK were counted with an immunofluorescent method at day 12. The effect of T-lymphocyte depletion on cord blood cultures for CFU-MK was studied with PIACS and a partially purified product of PIACS. We also studied individual megakaryocytes from newborns. The number and sizes of circulating megakaryocytes, isolated from adult peripheral blood and term venous cord blood by elutriation, were compared. Term and preterm cord blood contained more CFU-MK than adult peripheral blood. The numbers of CFU-MK in preterm cord blood were comparable to those in adult bone marrow. When the number of cells per colony were compared, cord blood contained significantly more cells than adult marrow CFU-MK. The depletion of T lymphocytes did not significantly change the growth of CFU-MK compared to nondepleted cultures. A substantial number of circulating megakaryocytes were obtained from venous cord blood, though they were significantly smaller than adult peripheral blood megakaryocytes. Since cord blood is easily obtained and contains large numbers of megakaryocytes and CFU-MK, it may provide a convenient model for studying the regulation of fetal megakaryocytopoiesis.

Familial thrombocytopenia with micromegakaryocytes.

Chronic thrombocytopenia was noted in two siblings and a first cousin. The initial impression was of immune thrombocytopenic purpura (ITP) with decreased megakaryocytes. One patient had splenectomy for presumed chronic ITP but showed no improvement. Bone marrow buffy coat slides were examined in the three children with thrombocytopenia, four normal controls, and five children with "classic" acute ITP. Megakaryocyte size, maturation, and ploidy were determined with Wright-Giemsa and Feulgen-stained material. Mean megakaryocyte diameters were 23.1 microns in the three related patients, 30.8 microns in normal controls, and 63.1 microns in children with "classic" acute ITP. Many "micromegakaryocytes" were noted in the three related children with chronic thrombocytopenia. An exhaustive family history was obtained, which showed multiple points of consanguinity. These patients represent an apparently new autosomal recessive disorder of megakaryocytopoiesis, characterized by disturbed megakaryocyte ploidization and maturation. More sensitive recognition of micromegakaryocytes should be attempted in children with atypical chronic thrombocytopenia, familial history of thrombocytopenia, or patients who have ITP and who have not responded to initial therapy.