A recycling defect as a characteristic of natural killer cells in childhood acute lymphoblastic leukemia

The cytolytic function of natural killer (NK) cells and their responsiveness to interferon-alpha and IL-2 were investigated in children with acute lymphoblastic leukemia (ALL) using 51Cr-release and single-cell assays. For comparison, such NK cell functions were similarly assayed in neuroblastoma. NK activity in ALL children was extremely low at onset, but it increased gradually during remission and finally reached normal levels. At the single-cell level, their NK cells at onset were defective in the binding, lytic, and recycling abilities. Although the binding and lytic defects improved to normal levels during remission, the recycling, which increased gradually during remission, was still low even after the long-term remission in ALL: the maximal recycling capacity values were 1.9 +/- 0.4 (p less than 0.001) at onset and 4.6 +/- 0.6 (p less than 0.05) after 5 y of complete remission, as compared to the value in control children of 5.4 +/- 0.7. On the other hand, children with neuroblastoma had no recycling defect after completing the therapy: their maximal recycling capacity value was 5.6 +/- 0.7. Bone marrow cells in ALL were also depressed in their recycling ability at all stages. Interferon-alpha and IL-2 could enhance NK activity and IL-2 could generate lymphokine-activated killer activity at all stages of ALL; however, the recycling defect hardly improved with these treatments. Thus, NK cells in childhood ALL have a recycling defect as a functional characteristic.     

Natural killer cell immunodeficiency in siblings: defective killing in the absence of natural killer cytotoxic factor activity in natural killer and lymphokine-activated killer cytotoxicities

A immunodeficiency of natural killer cells as effectors for natural killer and lymphokine-activated killer cytotoxicities was first demonstrated in siblings. Two of three male siblings persistently lacked natural killer activity against K562 target cells as assayed by a 51Cr-release assay: percent lysis values were less than 1.0% as compared to the normal lymphocyte values of 43.5% +/- 6.2% (mean +/- SD). Their lymphocytes did not develop natural killer cell activity by changing effector to target ratios, prolonging the incubation time, or stimulating them with interferon-alpha or interleukin 2. Numbers of lymphocytes bearing Leu-7, CD16, or NKH-1 were normal but those of Leu-7-, CD16+ cells were decreased as estimated by flow cytometry. Single cell-in-agarose assays showed normal numbers of natural killer cells capable of binding to a target cell but incapable of killing it. They had depressed levels of lymphokine-activated killer activity, which was totally eliminated by the treatment with OKT3 and complement. This result indicates that the patients' natural killer cells are also defective in the capacity to work as effectors for lymphokine-activated killer activity. The patients' natural killer cells did not produce natural killer cytotoxic factor activity. Antibody-dependent cellular cytotoxicity and cytotoxic T lymphocyte cytotoxicity were normal. These results demonstrate a selective natural killer cell deficiency as effectors for natural killer and lymphokine-activated killer cytotoxicities with a familial tendency, in which there is defective killing with the absence of natural killer cytotoxic factor activity.     

Evaluation of cytotoxic function and apoptosis in interleukin (IL)-12/IL-15-treated umbilical cord or adult peripheral blood natural killer cells by a propidium-iodide based flow cytometry

Both deficient natural killer (NK) cell effector function and increased propensity to apoptosis of neonatal NK cells contribute to the increased susceptibility to infection in the neonates. Interleukin (IL)-12 and IL-15 are two immunoregulatory cytokines known to enhance cytolytic function of neonatal NK cells. The present study aims to simultaneously investigate the effect of IL-12/IL-15 on K562 cytotoxicity as well as NK cells apoptosis of enriched umbilical cord blood (CB) and adult peripheral blood (APB) NK cells, using flow cytometric cytotoxicity assays. The results indicated that (i) prior to cytotoxicity assays, CB NK cells underwent greater degree of spontaneous apoptosis than did APB NK cells; (ii) both IL-12 and IL-15 inhibited the spontaneous apoptosis of CB NK cells, while IL-15 promoted the apoptosis in APB NK cells; (iii) the deficient K562 cytotoxicity of CB NK cells could be enhanced to levels comparable with that of APB NK cells by IL-15; (iv) IL-15 increased the percentages of apoptosis in NK–K562 conjugates in a dose-dependant manner in both CB and APB with a greater effect seen with APB NK cells; (v) target-induced apoptosis was observed with APB NK cells which were further enhanced with IL-15. However, CB NK cells, unstimulated or IL-15-activated, were resistant to K562-induced apoptosis. Thus, the multi-parameter flow cytometry analysis not only demonstrates better for the deficient CB NK function but also provides greater details for cytotoxic mechanisms of NK cells.     

Defects in interleukin-2 stimulation of neonatal natural killer cytotoxicity to herpes simplex virus-infected cells

Natural killer cytotoxicity (NKC) is an important early defense mechanism in viral infections. We determined the ability of interleukin-2 (IL-2), an NKC stimulator, to enhance defective neonatal NKC to virus-infected cells. Human recombinant IL-2-stimulated adult and cord blood NKC to herpes simplex virus-infected cells in a time-dependent and dose-dependent fashion. The highest level of neonatal IL-2-stimulated cytotoxicity approached the level of unstimulated cytotoxicity when adult cells are used. Single-cell experiments suggested that the cord blood defect was due not to decreased adherence but to lysis or recycling defects. IL-2 stimulated adhesion in the presence of antibody but had no stimulatory effect on antibody-dependent cellular cytotoxicity. The relative defects in IL-2 stimulation of neonatal NKC suggest that its lone use as a therapeutic or protective agent against herpes simplex virus infections is unlikely to be successful, and may require concomitant adult cells if NKC is a critical mechanism.     

Chronic natural killer cell lymphocytosis is associated with elevated cytotoxic activity of natural killer cells

The authors describe a 16-year-old girl who has suffered from chronic natural killer cell lymphocytosis (CNKL) for 12 years. From age 4 years, she has shown a persistent lymphadenopathy and lymphocytosis. Clinically, she developed allergic skin involvement, thrombocytopenia, and peripheral polyneuropathy. Annual flow cytometry analyses of lymphocyte subsets revealed persistently elevated NK cell levels (55-75% of the lymphocyte fraction and 0.7-10 x 10(3) NK cells per microliter of blood). Furthermore, IgE serum concentrations were markedly increased. Based on CD16, CD161, and CD94 surface antigen expression, the NK cell population was characterized as mature NK cells. Functional analysis of these cells showed a 2-fold increase of intrinsic cytotoxic activity toward K-562 cells compared with NK cells from healthy controls. The authors present a clinical case of rare CNKL. The patient's NK cells possess significantly increased cytotoxic activity. These findings are discussed in context with elevated IgE concentrations.     

Two different maturational stages of natural killer lymphocytes in human newborn infants.

The objective of this study was to assess the basis for the diminished natural killer (NK) lymphocyte activity of neonates. We found either severely reduced (63% of 68 neonates) or normal (similar to healthy adult) levels of NK activity. The percentages of cord blood mononuclear cells from the two groups of infants that expressed CD16, a differentiation antigen found in NK cells, were similar and within the range found in peripheral blood mononuclear cells of adults. However, infants with low NK activity had reduced numbers of cells in the CD16+56+ subpopulation, whereas the number of these effector cells present in cord blood mononuclear cells from infants with normal NK activity was within the range found in adults. Recombinant interleukin-2, but not recombinant interferon-gamma, normalized the low NK activity of infants in a dose- and time-dependent manner. Analysis of the pattern of target cell susceptibility to lysis, together with the CD16+CD3- phenotype of the precursor and effector lymphocytes, demonstrated that the induced cytotoxicity was mediated by NK cells. In contrast, NK cells from infants with normal cytotoxic levels exhibited a functional response to interleukin-2 and interferon-gamma similar to that of adults. Our results indicate that NK cells in human neonates go through two different maturational stages.     

Effect of human colostrum on interleukin-2 production and natural killer cell activity.

The effect of human colostrum on the production of interleukin-2 (IL-2) and on natural killer (NK) cell activity by peripheral blood mononuclear cells (PBMC) was investigated in 50 healthy women. At concentrations as low as 0.5%, human colostrum stimulated IL-2 production; at a higher concentration (10%), IL-2 secretion was inhibited. A time and dose dependent inhibitory effect of colostrum on NK cytotoxicity was also observed. This inhibition could be reversed by the addition of human recombinant IL-2 (hrIL-2). The stimulation of IL-2 production induced by human colostrum might compensate for its inhibitory effect on NK cell activity. These findings suggest an additional mechanism by which breast feeding may affect the neonatal immune system.     

Adhesion defects of antibody-mediated target cell binding of neonatal natural killer cells

Neonates are unusually susceptible to herpes simplex virus infection, which may be explained in part by defects in killing of herpes simplex virus-infected cells by natural killer (NK) cell cytotoxicity and antibody-dependent cellular cytotoxicity. The mechanism for these defects remains poorly defined. We have for the first time used immunomagnetically enriched NK cells to explore neonatal NK cell phenotype and target cell adhesion. CD56-positive neonatal NK cells had markedly lower CD57 expression, but adult level expression of adhesive glycoproteins (CD18, CD44) and Fc receptor for IgG (CD16). Although the cells conjugated normally with target cells in the absence of antibody, antibody-mediated conjugation was significantly lower than that of NK cells from adults (p < 0.002). These results demonstrate intact adhesion in neonatal NK cell cytotoxicity. In contrast, defective neonatal antibody-dependent cellular cytotoxicity is caused, in part, by an adhesion defect in the presence of antibody.     

自然杀伤细胞与丙型肝炎病毒感染的Huh7.5细胞体外共培养后的功能变化

目的探讨体外丙型肝炎病毒(HCV)感染对NK细胞功能产生的影响及其可能的机制。方法利用质粒JC1-Flag2体外转录得到的HCV感染性颗粒(HCVcc)以MOI4.8感染Huh7.5细胞(Huh7.5-HCVcc),与健康人外周血分离得到的NK细胞进行共培养。与Huh7.5-HCVcc细胞共培养前后,采用ELISA法和MTT比色法分别检测NK分泌细胞因子IFN-γ、TNF-α和IL-10的水平和细胞杀伤活性,以评估HCV感染对NK细胞功能的影响。结果与MOI4.8的Huh7.5-HCVcc细胞共培养,NK细胞分泌IFN-γ、TNF-α和IL-10水平受到抑制,其中IFN-γ在共培养6 h(P0.001)、9 h(P0.001)、12 h(P0.001)受到显著抑制,TNF-α在共培养6 h(P0.001)、9 h(P0.001)、12 h(P=0.001)受到显著抑制,IL-10在共培养6 h(P0.001)、9 h(P=0.006)受到显著抑制;且NK细胞分泌细胞因子IFN-γ、TNF-α和IL-10的功能均在共培养6 h受到的抑制效应最大,平均抑制率分别为24.1%、20.7%和24.3%。NK细胞杀伤活性在共培养6 h(P=0.023)受到抑制,平均抑制率为16.6%。结论在体外与MOI4.8的Huh7.5-HCVcc细胞共培养,NK细胞分泌细胞因子(IFN-γ、TNF-α和IL-10)和细胞杀伤功能均受到抑制,且在不同时间点受到的抑制程度不同,提示NK细胞在HCV感染的不同阶段可能起到不同的作用。     

Characterization of trisomic natural killer cell abnormalities in a patient with constitutional trisomy 8 mosaicism

Malignancies found in children and adults with constitutional trisomy 8 mosaicism (CT8M) could be in part the consequence of dysfunction of trisomic immune cells. An adult patient exhibiting trisomy in the entire natural killer (NK) cell population has made possible the characterization of trisomy 8-positive NK cells. The study showed normal cytotoxic activity but predominance of an immunosenescent phenotype (CD56(dim)CD94/NKG2(bright)) characterized by a weak response to IL-2, increased upregulation of CD95/Fas, and impaired TNF-alpha production. As these defects may contribute to the escape and expansion of neoplastic cells, the authors hypothesize that cancer predisposition in CT8M may be partly a result of altered immunosurveillance.     

Effect of interleukin-2 on natural killer-cell activity in children with malignant solid tumors

The purpose of the study was to determine the activity of natural killer (NK) cells in children with malignant tumors and the effect of interleukin-2 (IL-2) in enhancing NK-cell activity of these patients in vitro. The NK-cell activity in mononuclear cells of peripheral blood was measured by the ¹²⁵ IUdR release assay. The mean level of NK-cell activity in children with cancer (16.52%) was significantly lower than that for normal controls (29.75%) and no significant difference of NK-cell activity was found between children with different cancers. After mononuclear cells were incubated with recombinant IL-2 (rIL-2), NK cells from 96% (22/23) of the samples showed augmented cytotoxicity. The levels of NK-cell activity of patients, either prior to therapy or with treatment (operation or chemotherapy), were very low (1.36%–30.69%; 6.17%–33.64%, respectively) before rIL-2 stimulation and significantly increased (15.41%–65.80%; 23.85%–49.36%, respectively) after stimulation, suggesting a potential therapeutic role for rIL-2 in the treatment of malignant solid tumors of childhood and providing a rationale for the clinical use of rIL-2. Offprint requests to: She Yaxiong     

Ex vivo expansion of highly purified NK cells for immunotherapy after haploidentical stem cell transplantation in children

BACKGROUND: Allogeneic natural killer (NK) cells are known to show medium to high cytotoxic activity against HLA-nonidentical leukemia or tumor cells. For a possible benefit of post transplant treatment with NK cells after haploidentical stem cell transplantation (haplo-SCT) we developed a clinical scale procedure for NK cell processing observing Good Manufacturing Practice (GMP). METHODS: Allogeneic donor NK cells were selected from 15 unstimulated leukaphereses using two rounds of immunomagnetic T cell depletion, followed by an NK cell enrichment step. CD56 (+)CD3 (-) NK cells were stimulated and expanded in vitro according to GMP. Quality control of NK cell purity, residual T cells and cytotoxic activity was done by multi-coloured flow cytometric analyses. RESULTS: Purification led to an absolute number of 234-1 237 x 10 (6) CD56 (+)CD3 (-) NK cells from leukapheresis harvests with a median purity of 95 % and a 4 to 6(1/2) log depletion of T cells. After two weeks stimulation with IL-2 a five-fold expansion of NK cells with a T cell contamination below 0.1 % was reached. Median cell viability was 95 % after purification and 99 % after expansion. The IL-2 stimulated NK cells showed a highly increased lytic activity against the MHC-I deficient K562 cells compared to freshly isolated NK cells and a medium cytotoxicity against patients' leukemic cells. CONCLUSIONS: Clinical scale enrichment and activation of allogeneic donor NK cells is feasible. High dose NK cell application may be a new treatment option for pediatric patients with leukemia or solid tumors in case of minimal residual disease or unbalanced chimerism post haplo-SCT as we could show for the first three patients .     

Natural killer cell dysfunction in patients with systemic-onset juvenile rheumatoid arthritis and macrophage activation syndrome

OBJECTIVES: To assess natural killer (NK) and cytotoxic functions in patients with systemic-onset juvenile rheumatoid arthrithis (soJRA) complicated by macrophage activation syndrome (MAS). METHODS: NK cells (CD56+/TCRalphabeta-), NK T cells (CD56+/TCRalphabeta+) and CD8+ cells were assessed for perforin expression by flow cytometry. NK cytotoxic activity was measured after coincubation of mononuclear cells with an NK-sensitive K562 cell line. RESULTS: Two major patterns of immunologic abnormalities were detected. Four of 7 patients had decreased NK activity, low NK cell numbers, and mildly increased levels of perforin expression in CD8+ and CD56+ cytotoxic cells. Three remaining patients with MAS, however, had decreased NK activity associated with low levels of perforin expression in all cytotoxic cell populations, a pattern indistinguishable from that in carriers of perforin-deficient familial hemophagocytic lymphohistiocytosis. Remarkably, two of these patients had previous episodes of MAS. CONCLUSIONS: NK dysfunction is an immunologic abnormality common to both familial hemophagocytic lymphohistiocytosis and MAS of soJRA. The extent of NK cell abnormalities in soJRA needs to be further investigated.     

Age-related changes in intracellular TH1/TH2 cytokine production, immunoproliferative T lymphocyte response and natural killer cell activity in newborns, children and adults

To evaluate the development of the neonatal immune system, we measured T lymphocyte response to Con A, intracellular IL-2, IL-4, IFN-gamma and IL-10 production, and natural killer cell (NKC) activity in 12 very preterm, 12 preterm and 20 term neonates, 10 children and 10 adults. Immunoproliferation to Con A was significantly lower in cord blood than in children or adults. The percentage of CD4+ lymphocytes was significantly higher in newborns while CD8+ cells were higher at older ages, with a resulting gradual decline of the CD4+/CD8+ ratio. The percentage of IL-2-producing CD4+ and CD8+ cells was higher in all newborn groups than in children and adults, while the percentage of IL-4-producing cells was higher for CD8+ and lower for CD4+ cells in cord blood than in children and adults. Neonates had substantially lower percentages of CD4+ and CD8+ IFN-gamma-producing cells. A significant negative correlation was observed between gestational age and IFN-gamma-CD4+-, IL-2-CD8+-, and IL-10- CD4+-producing cells. In addition, a positive correlation was found between gestational age and IL-10-CD8+-producing cells. Percentages of CD4+/CD45RA+ cells were higher and CD4+/CD45RO+ percentages were lower in newborns than in children and adults. NKC activity in infants was significantly correlated with gestational age and significantly impaired compared to children and adults. On the whole, these results suggest a gradual development of immunity during gestation and show significant immaturity of cellular immune response at birth. The reduction of NKC activity, the lower proliferative response of T cells, the reduced cytotoxic response and a dysregulated cytokine production may contribute to the neonatal increased risk of infection and to the low incidence of graft-versus-host disease after cord blood transplantation.     

Polymorphonuclear leucocyte and natural killer cell functions in mature and premature newborns

In this study the phagocytic and natural killer cell (NK) functions in 17 premature and 30 mature newborns are compared. The ability of polymorphonuclear phagocytes (PMNs) to ingest, digest and lyse (antibody-dependent cell-mediated cytotoxicity, ADCC) opsonized sheep red blood cells and NK activity were tested. Examinations were performed in cord and venous blood within 6 h or 3-4 days after delivery. Results of examinations were compared with normal values for the group of healthy 4- to 15-year-old children. To assess the influence of the newborn's maturity and age on the tested PMNs and NK functions, the following comparisons were made. (1) Cord vs. peripheral venous blood: only ADCC was higher in peripheral than in cord blood. (2) Mature newborn cells obtained either 6 h or 3-4 days after delivery: ingestion and ADCC were lower and NK activity was higher 3-4 days after delivery. (3) Premature vs. mature newborn cells tested 3-4 days after delivery: ingestion and ADCC were higher while NK activity was lower in premature newborns. (4) Premature newborns tested at 3-4 days vs. mature newborns tested within 6 h after birth: ingestion was lower in the prematures while digestion, ADCC and NK activity were similar. (5) Cells from all newborns tested vs. those of healthy older children: results depend on the interval after birth when newborns were tested. Thus, within the first 6 h after delivery, mature newborns had higher ingestion and ADCC capacity but lower digestion and NK activity. Later, 3-4 days after birth, ingestion, ADCC and NK activity were lower in mature newborns. In the prematures at that interval NK activity was lower. (6) There was a positive correlation between gestational age and NK activity of newborns.     

病毒性肺炎患儿自然杀伤细胞亚群、T细胞亚群及血IL-2、IL-4、INF-γ变化的研究

目的 探讨病毒性肺炎患儿自然杀伤(NK)细胞亚群、T细胞亚群及血IL-2、IL-4、INF-γ的动态变化及临床意义.方法 采用流式细胞术测定32例病毒性肺炎患儿急性期(肺炎起病2?d内)、恢复期(肺炎起病5?d内)外周血NK细胞亚群、T细胞亚群,用ELISA法测定血IL-2、IL-4、INF-γ水平,用乳酸脱氢酶释放法测定NK细胞活性变化,并与30例健康对照组儿童进行比较.结果 (1) 病毒性肺炎患儿CD16+CD56+、CD16+NK细胞在急性期分别为(0.73±0.17)%、(0.39±0.2)%,恢复期分别为(1.47±0.22)%、(0.89±0.14)%;急性期与恢复期比较,恢复期CD16+CD56+、CD16+NK细胞明显升高(P<0.01),但均显著低于对照组(P<0.01).两组NK细胞亚群变化与其活性改变呈正相关.病毒性肺炎患儿CD56+NK细胞与健康儿童差异无显著性(P>0.05).(2) 与对照组相比,病毒性肺炎患儿的急性期、恢复期IL-2、IL-4均无明显改变,差异无显著性(P>0.05);急性期INF-γ无明显改变,差异无显著性(P>0.05),而恢复期INF-γ[(28.10±1.38)?μg/L]明显高于急性期[(22.78±1.19)?μg/L],差异有非常显著性(P<0.01).(3) 与对照组相比,病毒性肺炎患儿CD4+、CD4+/CD8+T细胞计数在急性期与恢复期均无明显改变,差异无显著性(P>0.05).病毒性肺炎急性期、恢复期CD8+T细胞均低于对照组,差异有显著性(P<0.05),但病毒性肺炎急性期、恢复期间差异无显著性(P>0.05).结论 病毒性肺炎患儿NK细胞活性降低,活性与亚群数目呈正相关;病毒性肺炎患儿抑制性T细胞功能低下.病毒性肺炎急性期NK细胞激活是多因素共同作用的结果 .     

Lymphokine-activated killer cytotoxicity in neonatal mononuclear cells: in vitro responses to tumor cell lines from pediatric solid tumors

The presence of neonatal (cord) lymphokine-activated killer (LAK) cell activity toward natural killer cell resistant Raji and Daudi cell lines has recently been reported from our laboratory. We investigated the future therapeutic use of LAK adoptive immunotherapy by examining LAK in vitro cytotoxicity from both neonatal and adult mononuclear cells against solid tumor cell lines of relevance to pediatric oncology: SH-SY5Y (neuroblastoma), SK-NM-C (neuroblastoma-neuroepithelioma), NEP-1 (Wilms' tumor), SK-ES-1 (Ewing's sarcoma), and A-204 (rhabdomyosarcoma). Cord and adult mononuclear cells were activated by recombinant IL-2 (100 mu/ml) for 5-7 days and added in an effector:target ratio of 40:1 to 51Cr-labeled target cells. Specific cell lysis was determined after a 4-h incubation. There was a significantly high level of cord and adult LAK cytotoxicity against Wilms' (76.4 +/- 9.8 versus 77.3 +/- 6.8%) and Ewing's (84.2 +/- 5.5 versus 71.1 +/- 6.5%) cell lines and significant but moderate LAK activity against neuroepithelioma (52.0 +/- 6.6 versus 55.4 +/- 4.5%) and rhabdomyosarcoma (46.6 +/- 5.7 versus 43.9 +/- 5.2%) cell lines. There was no difference between cord and adult LAK activity toward these targets. However, a differential response toward the more classical neuroblastoma cell line, SH-SY5Y, was noted with significantly more LAK cytotoxicity from cord mononuclear cells than adult mononuclear cells (51.2 +/- 6.9 versus 28.5 +/- 8.2%) (p less than or equal to 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Cytokine-stimulated human natural killer cytotoxicity: response to rotavirus-infected cells

The ability of rotavirus-infected cells to stimulate leukocytes to release a cytokine which enhanced the subsequent leukocyte cytotoxicity to a second set of [51Cr] labeled rotavirus-infected cells was analyzed. Human interferon increased leukocyte cytotoxicity to Simian rotavirus (SA-11)-infected target cells. Similarly, 11 of 12 supernates of SA-11-stimulated peripheral blood leukocyte cultures increased the killing of SA-11-infected cells (P less than 0.005). This resulted in a calculated cytokine-dependent cellular cytotoxicity value of 9.6 +/- 1.9%. Three of five of the supernates tested contained measurable levels of interferon (12-48 unit/ml). In contrast, SA-11-stimulated colostral leukocyte culture supernates neither increased leukocyte cytotoxicity nor contained measurable levels of interferon.     

Cytotoxic function of umbilical cord blood natural killer cells: relevance to adoptive immunotherapy

Decreased graft-versus-host disease (GVHD), ease of accessibility, and sustained engraftment encourage the use of umbilical cord blood (UCB) as an alternative source to bone marrow for immune reconstitution in children with leukemia. Natural killer (NK) cells rapidly expand after stem cell transplantation and are important for regulating GVHD and providing graft-versus-leukemia (GVL) effects. This review highlights the phenotypic and functional differences between UCB NK cells and adult peripheral blood (APB) NK cells, and discusses the possible therapeutic benefit of using UCB NK cells for adoptive immunotherapy in leukemia. Alloreactive NK cells show potent cytotoxic activities against human leukocyte antigen (HLA)-nonidentical leukemic cells and reduce leukemia relapses. The higher numbers of NK progenitors in UCB makes it a convenient source for ex vivo expansion of UCB NK cells for posttransplant treatment. UCB NK cells readily respond to interleukin-15, which may greatly enhance their antitumor effect. Activation and expansion protocols for UCB NK cells are currently being developed.     

The clinical course and echocardiographic features of Marfan's syndrome in childhood

The clinical and echocardiographic manifestations in 25 patients with Marfan's syndrome diagnosed during infancy and childhood (mean [+/- SD] age, 8.1 +/- 4.8 years; range 0 to 16 years) were evaluated. Twenty-one patients (84%) had a midsystolic click, 11 patients (44%) had mitral regurgitation (MR), and five patients (20%) had combined MR and aortic regurgitation (AR). Echocardiography demonstrated mitral valve prolapse in all 25 patients, aortic root dilatation in 20 patients (80%), AR in seven patients (28%), and aortic aneurysm in five patients (20%). During the follow-up period (mean, 5 +/- 4.5 years), progressive AR and aortic aneurysm were documented in four patients, progressive MR in three patients, and progressive aortic root dilatation in two patients. Five patients (22%) died during the follow-up period. Among patients with a positive family history of Marfan's syndrome, MR was less frequent as compared with sporadic cases (29.4% vs 75%, respectively). Progressive cardiovascular involvement was more frequent among patients diagnosed before 10 years of age compared with those diagnosed later (60% vs 12.5%, respectively). Cardiovascular involvement was a common feature of childhood Marfan's syndrome, causing significant morbidity and mortality. Sporadic cases and children diagnosed before 10 years of age represented a particularly high-risk group.