Abundant expression of parathyroid hormone-related protein in primary rat aortic smooth muscle cells accompanies serum-induced proliferation.

Parathyroid hormone-related protein (PTHrP), which is responsible for producing hypercalcemia in patients with humoral hypercalcemia of malignancy, has recently been identified in several normal tissues. Because PTHrP, like parathyroid hormone (PTH), is known to exhibit vasodilatory properties, we investigated the expression and regulation of PTHrP mRNA in cultured rat aortic smooth muscle cells (SMC). We report here that PTHrP mRNA is expressed in SMC and is markedly induced by serum in a time- and concentration-dependent fashion. Addition of 10% fetal calf serum to serum-deprived, confluent cells, resulted in a marked induction of PTHrP mRNA by 2 h with a peak at 4-6 h. PTHrP was detected in SMC by immunocytochemistry and radioimmunoassay of conditioned medium, and was shown to be up-regulated within 24 h after the addition of serum. The serum induction of PTHrP mRNA was blocked by actinomycin D and by cycloheximide indicating the need for protein synthesis to evoke the serum effect on PTHrP gene transcription. In addition, treatment with dexamethasone, which has been previously shown to reduce the constitutive expression of PTHrP in human cancer cells, also blunted the serum induction of PTHrP mRNA in SMC. Treatment of quiescent cells with the serum mitogens platelet-derived growth factor or insulin-like growth factor-I had no effect on PTHrP, whereas the vasoactive peptides endothelin, norepinephrine and thrombin stimulated PTHrP expression. Exogenous addition of recombinant PTHrP-(1-141) had no significant effect on SMC DNA synthesis as measured by [3H]thymidine incorporation. In summary, the abundance of PTHrP mRNA and the characteristics of its regulation in SMC suggest a major role for PTHrP as a local modulator in vascular smooth muscle.

Mutations of the p53 gene are involved in Ewing's sarcomas but not in neuroblastomas.

We have investigated the frequency of p53 gene mutations in Ewing's sarcoma (ES) and neuroblastoma (NB) by using polymerase chain reaction-single strand conformation polymorphism analysis for genomic DNA or complementary DNA generated from total RNA. Mutations of the p53 gene were found in six of seven ES cell lines: a missense mutation of TGC (Cys)-->TAC (Try) at codon 141 in one, a missense mutation of CGT (Arg)-->TGT (Cys) at codon 273 in one, a missense mutation of TGC (Cys)-->TTC (Phe) at codon 176 in three, and one base deletion of CGC-->CG at codon 283 in one. Further analysis of 14 ES and related primary tumors showed mutations of the p53 gene in only two: one base insertion of CCG-->CCCG at codon 152 in one and a missense mutation of GGC (Gly)-->GTC (Val) at codon 154 in the other. Both of the two tumors were obtained from patients with an advanced stage disease. Three of the eight ESs with mutations of the p53 gene showed the same missense mutation at codon 176, suggesting the mutational hot spot of the p53 gene in ESs. In contrast to ES, none of 6 NB cell lines or 48 NB tumors including advanced-stage ones with or without N-myc amplification showed any aberration of the p53 gene. Our findings suggest that mutations of the p53 gene in ES might represent late genetic events related to tumor progression, and that aberrations of the p53 gene might not be involved in the development or the progression of NB.

Extensive brain hemorrhage and embryonic lethality in a mouse null mutant of CREB-binding protein.

CREB-binding protein (CBP) is a transcriptional co-activator which is required by many transcription factors. Rubinstein-Taybi syndrome (RTS), which is an autosomal dominant syndrome characterized by abnormal pattern formation, is associated with mutations in the human CBP gene. Various abnormalities occur at high frequency in the skeletal system of heterozygous Cbp-deficient mice, but some features of RTS such as cardiac anomalies do not, suggesting that some symptoms of RTS are caused by a dominant-negative mechanism. Here we report the characterization of homozygous Cbp-deficient mice. Homozygous mutants died around E10.5-E12.5, apparently as a result of massive hemorrhage caused by defective blood vessel formation in the central nervous system, and exhibited apparent developmental retardation as well as delays in both primitive and definitive hematopoiesis. Cbp-deficient embryos exhibited defective neural tube closure which was similar to those observed in twist-deficient embryos. However, a decrease in the level of twist expression was not observed in Cbp-deficient embryos. Anomalous heart formation, a feature of RTS patients and mice mutated in the CBP-related molecule, p300, was not observed in Cbp-deficient embryos. Since both Cbp and p300 are ubiquitously expressed in embryonic tissues including the developing heart, these results suggest that cardiac anomalies observed in RTS patients may be caused by a dominant negative effect of mutant CBP.

Clinical relevance of in vitro chemoresistance in childhood acute myeloid leukemia.

To determine the clinical relevance of in vitro drug chemoresistance in childhood acute myeloid leukemia, we used an MTT assay to test leukemic cells from 132 newly diagnosed children. Patients were diagnosed according to the French-American-British (FAB) classification as follows: M0 (n = 12), M1 (n = 16), M2 (n = 53), M4 (n = 17), M5 (n = 19) and M7 (n = 15). The results revealed that, compared to leukemic cells from complete-responders (n = 107), those from non-responders who failed induction therapy (n = 17) were 1.4 to 5.0 times more resistant in vitro to cytarabine (P = 0.005), melphalan (P = 0.003), etoposide (P = 0.011), L-asparaginase (P = 0.017), aclarubicin (P = 0.026) and dexamethasone (P = 0.039). For seven other drugs tested, the median lethal dose of 70% and leukemic cell survival of non-responders were higher than those of complete-responders, but the difference was not statistically significant. We sought correlations between FAB subtypes and in vitro drug resistance. Leukemias of the FAB M4 and M5 subtype were more sensitive to L-asparaginase (P = 0.01, P = 0.0036) than those of the FAB M2 subtype. FAB M5 leukemia was more sensitive to etoposide than were the FAB M2, M4 and M7 subtypes (P = 0.001, P = 0.034, P = 0.023, respectively). By contrast, FAB M5 leukemia was significantly more resistant to prednisolone and dexamethasone than were the FAB M0, M1, M2, M4 and M7 subtypes. We sought correlations between in vitro drug resistance and long-term clinical outcome, but found no associations in this case. These results suggest that in vitro resistance to cytarabine, melphalan, etoposide, L-asparaginase, aclarubicin and dexamethasone might represent factors that can predict response to the early course of therapy. Selecting an appropriate anti-cancer drug according to the FAB classification together with drug sensitivity testing may contribute to improved prognoses in childhood acute myeloid leukemia.

Homozygous deletions of p16/MTS1 and p15/MTS2 genes are frequent in t(1;19)-negative but not in t(1;19)-positive B precursor acute lymphoblastic leukemia in childhood.

We analyzed 60 B precursor acute lymphoblastic leukemia (ALL) primary samples and 15 cell lines for homozygous deletions of p16 and p15 genes and mutations of p16 gene. These included five cell lines and 13 primary samples with the t(1;19)(q23;pl3), and eight primary samples with the t(9;22)(q34;qll). Of 10 cell lines without t(1;19), homozygous deletion of both p16 and p15 genes was found in eight cell lines (80%), and a rearrangement of p16 in one cell line (10%). In contrast, only one (20%) of the five cell lines with t(1;19) showed homozygous deletion or rearrangement of p16/p15 gene. Thirteen of 60 (22%) primary samples demonstrated p16 gene homozygous deletion. No case with t(1;19) showed homozygous deletion of p16 gene (0/13, 0%), while cases without t(1;19) showed considerable incidence of p16 gene homozygous deletion (13/47, 28%). These results suggest that the incidence of deletions of p16 gene differs according to the subtypes of B precursor ALL. We also compared the frequency of p16 gene homozygous deletion between the patients at diagnosis and at relapse. Nine of 45 (20%) samples at diagnosis and four of 22 (18%) samples at relapse showed p16 homozygous deletions. The similarity of the rate in these two groups raises the question of the role of p16 gene in progression of B precursor ALL. Mutations were found in three of the primary cases (5%); the mutations included two nonsense mutations at codon 72 and one missense mutation at codon 98. All the mutations found in this study were heterozygous, and the clinical relevance of p16 gene mutation is yet to be determined in these case

The synthetic human parathyroid hormone-related protein is inhibited by a parathyroid hormone antagonist in rats in vivo.

The structure of a novel protein, parathyroid hormone-related protein (PTHrP), secreted by human tumors associated with hypercalcemia has recently been determined. Administration of a synthetic fragment of this protein in vivo reproduces features of the clinical paraneoplastic syndrome of humoral hypercalcemia of malignancy and produces biologic responses closely similar to those obtained with parathyroid hormone (PTH). A PTH antagonist designed to reversibly occupy PTH receptors inhibited major actions of the tumor peptide in vivo, including phosphaturia, urinary cAMP excretion, and increased serum ionized calcium. These studies indicate that PTHrP and PTH mediate their bioactivities through shared receptors in vivo and establish a potential specific mechanism-based approach utilizing PTH antagonists for the therapy of tumor-associated hypercalcemia.

Constitutive expression of a vitamin D 1-hydroxylase in a myelomonocytic cell line: a model for studying 1,25-dihydroxyvitamin D production in vitro.

The capacity of the v-myc-transformed, chicken myelomonocytic cell line HD-11 to metabolize 25-hydroxyvitamin D3 (25-OHD3) was examined. HD-11 cells produced and secreted a metabolite of 25-OHD3 that was bound with high affinity by receptor for 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. On normal-phase HPLC, this metabolite cochromatographed with authentic 1,25-(OH)2D3 in both hexane- and methylene chloride-based solvent systems. The 25-OHD3 1-hydroxylation reaction was substrate saturable with a Km of 73 nM 25-OHD3 and a maximal velocity of 167 fmol per 10(6) cells per h. This reaction was inhibited by ketoconazole, a recognized inhibitor of cytochrome P450 mixed-function oxidases including the authentic, renal 25-OHD3 1-hydroxylase. On the other hand, HD-11 cell 1,25-(OH)2D3 production was not affected by the antioxidant DPPD, a known inhibitor of free radical-generated 1,25-(OH)2D3. In addition to synthesizing 1,25-(OH)2D3, this monocyte-macrophage cell line also has the potential to be a target for the hormone; HD-11 cells express high-affinity receptor for 1,25-(OH)2D3 (Kin = 0.06 nM).

Trajectory of group Ia afferent fibers stained with horseradish peroxidase in the lumbosacral spinal cord of the cat: three dimensional reconstructions from serial sections.

A reconstruction was made of the intramedullary trajectory of 23 physiologically identified Ia afferents from cat hind limb muscles (medial gastrocnemius, soleus, plantaris, flexor digitorum-hallucis longus, and hamstring). The afferents were stained by intra-axonally injected HRP. The axons of these afferents were traced over distances of 5.8 mm to 15.7 mm rostrocaudally. In the dorsal funiculus fibers from all the muscles showed a similar course and similarly bifurcated into an ascending and a descending branch. The mean diameters of stem axons, ascending branches, and descending branches were 6.6 micrometer, 5.8 micrometer, and 3.0 micrometer, respectively. Within the analyzed lengths of the spinal cord five to eleven collaterals were given off from the two branches. The distances between adjacent collaterals of the ascending and descending branches averaged 1200 micrometer and 790 micrometer, respectively. The collaterals as a rule passed through the medial half of the dorsal horn before they entered the deeper parts of the gray matter. The terminal distribution areas common to all Ia collaterals were: (1) the medial half of the base of the dorsal horn, mainly lamina VI: (2) lamina VII; and (3) lamina IX. The numbers of terminals were largest in lamina IX and smallest in lamina VII. The density of terminals in lamina IX was highest in the homonymous motor cell column. The terminal distribution areas of adjacent collaterals showed no overlap in the sagittal plane. Terminal branches carried one bouton terminal and up to six boutons en passage with an average of 1.8 terminals per terminal branch. Apparent axosomatic and axodendritic contacts were seen on small-sized and medium-sized neurons in laminae V-VI, medium-sized neurons in lamina VII, and large neurons in lamina IX. One motoneurons was contacted by an average of 3.3 terminals. In addition to the common features, Ia collaterals of various muscles of origin showed some differences in their trajectories in the ventral horn, and in their terminations in the gray matter.

Trajectory of group Ia and Ib fibers from the hind-limb muscles at the L3 and L4 segments of the spinal cord of the cat.

Nineteen physiologically identified group Ia and five group Ib fibers at the L3 and L4 levels of the spinal cord originating from various hind-limb muscles were intraaxonally injected with horseradish peroxidase (HRP). The trajectories of the stained axons were reconstructed. They extended for distances of 8.6 mm-18.0 mm rostrocaudally. Ascending axons ran in various regions of the dorsal funiculus: The ascending axon from a toe muscle (3 microns in diameter) ran in the ventral most part of the paramedian region; those from shank muscles (3.0-5.0 microns) in both dorsal and ventral paramedian regions; those from thigh muscles (5.0-7.0 microns) in both the paramedian and the more lateral regions; and those from hip muscles (6.0-7.0 microns) in the lateral region. Main collaterals arising from the parent fiber were given off at intervals of 0.5-6.2 mm (mean 2.4 mm). Collaterals of a fiber from a toe muscle (1.0 micron in diameter) entered Clarke's column from the dorsomedial side and ramified mostly in the dorsomedial one-third of the column. Collaterals of fibers from shank muscles (1.0-2.0 microns) entered Clarke's column from the dorsal side and terminated in its middle parts as well as in laminae V-VII. Collaterals of fibers from thigh muscles (1.0-2.5 microns) passed lateral to or through the lateral part of Clarke's column and terminated in its ventrolateral part and in laminae V-VIII. Collaterals of fibers from hip muscles (1.5-2.5 microns) passed lateral to Clarke's column and ramified mostly in laminae VII-IX. As the muscle of origin became more proximal, the proportion of termination outside of Clarke's column progressively increased. Thus, the trajectory of group I fibers was somatotopically organized both in the dorsal funiculus and in the gray matter. The long axis of boutons ranged from 0.5 to 17 microns in Ia fibers and from 0.5 to 8 microns in Ib fibers. "Giant" Ia boutons (above 7 microns) were found both in and outside Clarke's column.

A randomised dose-comparison trial of granisetron in preventing emesis in children with leukaemia receiving emetogenic chemotherapy.

This randomised study was performed to assess the anti-emetic efficacy and tolerability of two-dose regimens of granisetron in children with leukaemia. 49 children with leukaemia were treated with three consecutive courses of high-dose methotrexate or cytarabine regimen. During the first course, patients were evaluated regarding the emetogenicity of each regimen. They were randomised in a crossover manner to receive 20 or 40 micrograms/kg of granisetron before the second and third course of chemotherapy. Neither emesis nor severe appetite loss were observed in over 80% of patients within the first 24 h in all treatment groups. There was no significant difference in the anti-emetic efficacy between the two-dose regimens of granisetron. However, complete protection was achieved less frequently on days 2 and 3. Older children and girls appeared to be less well protected. No adverse events attributable to granisetron were observed. Granisetron dose regimens of 20 and 40 micrograms/kg are, comparably, well tolerated and effective in controlling chemotherapy-induced emesis in the first 24 h, though this protection fails thereafter, particularly in older patients and girls.

Alterations of the p53, p21, p16, p15 and RAS genes in childhood T-cell acute lymphoblastic leukemia.

We investigated the alterations of the p53, p21, p16, p15 and RAS genes in childhood T-cell acute lymphoblastic leukemia (T-ALL) and T-ALL cell lines by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis and direct sequencing. Mutations of the p53 gene were found in three of 57 (5%) patients at diagnosis, one of 14 (7%) patients at relapse and in 12 of 18 (67%) cell lines. In these 12 cell lines, four had more than two mutations of the p53 gene. The p53 mutations were found in four of five cell lines whose original fresh leukemic cells were simultaneously examined original fresh leukemic cells. However, only one of the four fresh leukemic cells had the same mutation. All patients with p53 mutations in the course of disease died. Mutations of the p21 gene were not identified in 71 fresh samples and in 18 cell lines. N-RAS mutations were found in two of 57 (4%) fresh T-ALL patients at diagnosis, and four of 18 cell lines (22%), whereas no mutations were detected in any samples at relapse. Alterations of the p16 gene were found in 18 of 47 (38%) patients at diagnosis and in seven of 14 (50%) at relapse. These differences were not statistically significant. There were no differences in the frequency of alteration of the p16 and p15 genes between event-free patients and the remaining patients. Furthermore, we found the methylation of p16 gene in three of seven patients lacking homozygous deletions, suggesting higher frequency of p16 inactivation than previous reports in T-ALL. Interestingly, we found that one allele is inactivated by methylation and another allele had nonsense mutation in one cell line (KOPT-KI), resulting in loss of protein expression of p16. This type of p16 inactivation has not been so far reported in leukemia. We conclude that, (1) p53 mutations are infrequent at diagnosis but tend to be associated with poor clinical outcome; (2) RAS and p21 mutations may not be involved in the pathogenesis of T-ALL; (3) not only frequent alterations of p16 and p15 genes but also methylation of p16 gene are involved in initiating the leukemogenesis of T-ALLs, and (4) these 5 genes are independently involved in T-ALL.

Real-time sound spectroanalysis for diagnosis of malfunctioning prosthetic valves.

A newly developed real-time sound spectroanalyzer was found to be capable of diagnosing malfunction of prosthetic heart valves. Sound spectroanalysis is believed to be superior to other methods such as phonocardiography and echocardiography. This system, developed in our institute, allows display on a cathode ray oscilloscope of five different modes of the valvular click, including the sound spectrograph and section pattern. Analysis of the section pattern allows measurement of the high-frequency components of the valvular click, which is normalized so as to be applicable to a click of any intensity. This parameter is called normalized maximal frequency (NMF). Sound spectroanalyses were carried out 228 times on 127 patients having a prosthetic heart valve. NMF values of normally functioning valves differed characteristically according to the type of valve, but did not change during the postoperative time course. Three of seven patients who had cerebral embolism showed significantly lower NMF values than normal, as did all four patients whose valve had become thrombosed.

Successful unrelated bone marrow transplantation for a patient with chronic granulomatous disease and associated resistant pneumonitis and Aspergillus osteomyelitis.

We describe the successful treatment of a 20-year-old patient with chronic granulomatous disease (CGD), by unrelated bone marrow transplantation (UBMT). The patient is relatively old compared to other CGD patients treated with BMT. He had had repeated serious infections from early childhood and was diagnosed as CGD, gp91-phox deficiency. Prolonged antibiotic-resistant pneumonitis worsened when the patient was 18 years old. In addition, he suffered Aspergillus osteomyelitis and acute renal failure due to amphotericin B. He received 94 granulocyte transfusions from 94 adult donors and the infections gradually improved. In September 1998, at 20 years of age, he underwent UBMT from an HLA 6 antigen-matched male donor, with CY and TBI conditioning. He received MTX and CsA as prophylaxis against GVHD. No serious complications occurred and rapid engraftment was achieved. Acute GVHD (grade 2, at day 19) and chronic GVHD (limited, at day 192) occurred. However, both were easily controlled. The patient is alive and well with no late rejection 26 months after UBMT.

Spontaneous formation of a monolayer membrane from sarcoplasmic reticulum at an air-water interface.

Surface pressure was found to be produced spontaneously at the interface between air and a suspension containing fragmented sarcoplasmic reticulum (FSR) from rabbit white muscle. Large and stable surface pressure was formed only in a limited concentration range of FSR in the suspension and the pressure formation was proved to be an irreversible phenomenon, suggesting the formation of a monolayer membrane resulting from the disruption of FSR vesicles. Monolayer formation was directly confirmed by analyzing the components included in the membrane and by calculating the surface area occupied by these components. The monolayer included phospholipids, cholesterol and proteins, and appeared to originate from FSR vesicles since the molecular ratios of these components as well as the results of the SDS polyacrylamide gel electrophoresis were similar in both membranes. This phenomenon can be utilized as a method of monolayer preparation from biological membrane vesicles, and should be very useful for the reconstitution of planar biological membranes.

Orientation of platelets on the surfaces of glass and Teflon plates as studied by a spin label technique.

Platelets were found by a spin label technique to orient on flat surfaces of glass as well as of Teflon. This kind of platelet orientation was not caused by centrifugation or partial dehydration of the membrane preparation as employed usually to make oriented planar multilayers of biological membranes on the surface of a supporting plate (1-8), but was considered to be closely related to the adhesion or the aggregation properties of platelets. The amount of oriented platelets varied depending on the platelet treatment and was estimated from a computer simulation of the observed ESR spectra to be about one-half of that of the non-oriented ones in the case of thrombin-treated platelets. This technique may be useful as a new tool to explore the adhesion or aggregation properties of platelets.

Antibody to platelet activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine; PAF).

Specific antibodies to platelet activating factor (PAF) were prepared by immunizing rabbits with a hapten-bovine serum albumin (BSA) conjugate. As the hapten we used the synthetic PAF derivative which is resistant against enzymatic inactivation by plasma or tissues and which can bind to BSA through covalent bonding. Antibody activity was determined by an enzyme-linked immunosorbent assay (ELISA). Anti-PAF IgG reacted strongly with PAF. By means of the ELISA inhibition assay, we found that the antibody did not cross-react with phosphocholine, glycerophosphocholine, dilaurylglycerophosphocholine or PAF analogues which have ethanolamine-type polar head groups instead of choline group.

Light-induced potential and current across a large bacteriorhodopsin-asolectin planar membrane stabilized on a polyacrylamide gel surface.

A phospholipid bilayer membrane was spread from an organic solvent solution between a polyacrylamide gel surface and an aqueous buffer solution. The membrane was quite similar to the conventional black lipid membrane, but was of a large size and was stable since it was supported on the gel surface. Bacteriorhodopsin, impregnated into the membrane, generated membrane potential and current upon illumination. The induced current was large, and this was attributed to the large area of the present membrane. Remarkable responses of the light-induced potential and current were also observed with a thick layer of organic solvent containing phospholipids. The effects of applied membrane potential, carbonylcyanide-m-chlorophenyl hydrazone (CCCP) and gramicidin were examined on these photoresponses. Steady-state current, which is due to protons flowing through the membrane, was enormously enhanced by applying membrane potential opposite to the photopotential or by adding gramicidin to the membrane-forming solution.

Comments on group II excitation in hindlimb motoneurones in high and low spinal cats.

Effects from group II muscle afferents on gastrocnemius-soleus (G-S) motoneurones were compared in unanaesthetized anaemically decerebrated high (C1) and low (Th10) spinal cats. The proportion of G-S motoneurones receiving group II excitation was about the same in low and in high spinal cats. No overall decrease in the strength of group II excitation could be demonstrated after low spinalization. It is postulated that the previously observed low incidence of group II EPSPs in G-S motoneurones in low spinal cats was due to anaesthesia.

In vitro chemosensitivity of lymphoblasts at relapse in childhood leukemia using the MTT assay.

Lymphoblasts from 21 previously untreated patients with acute lymphoblastic leukemia (ALL) and 31 patients in relapse were tested for chemosensitivity. Blast cells were cultured with 22 anticancer drugs for 4 days and assayed by MTT dye using a scanning microplate photometer. The percent cytotoxicity index (%CI) and LD50 (micrograms/ml) were calculated for each drug. The mean absorbances (+/- S.D.) of 1 x 10(5) cells in the untreated group and relapsed groups in control wells were 0.219 (+/- 0.126) and 0.385 (+/- 0.147), respectively (p less than 0.01). Cells in the untreated group were more sensitive in vitro to vincristine, prednisolone, L-asparaginase (L-ASP), vinblastine, 5-fluorouracil, epirubicin, bleomycin (BLM), and etoposide (VP16) with respect to the %CI value and to L-ASP, VP16, BLM, and mitoxantrone with respect to the LD50 value than those in the relapsed groups. In contrast, no significant differences were observed for the other 13 drugs. There was also a significant difference in sensitivity within the relapsed group--13 having good clinical response and 15 showing no response to chemotherapy--with regard to four drugs, mitomycin C, neocarzinostatin, L-ASP, and teniposide. Cells in the relapsed group had more heterogeneous chemosensitivity than those in the untreated group, and divided into sensitive and resistant types, but large interindividual differences existed. The MTT assay and LD50-drug resistance percentile curves are useful for the selection of effective drugs in both untreated and relapsed patients with acute leukemia.

Distinctive multidrug sensitivity and outcome of acute erythroblastic and megakaryoblastic leukemia in children with Down syndrome.

We assessed the in vitro chemosensitivity of acute erythroblastic and megakaryoblastic leukemia cells from children with Down syndrome (DS) compared to non-DS children. We conducted in vitro tests using the MTT assay of bone marrow samples from 12 children with DS and 16 children without DS. Patients were newly diagnosed based on the morphology and expression of platelet-specific antigens. Induction failure occurred more frequently in the non-DS group (n = 4) than in the DS group (n = 0, P = .053). Children with DS had a superior event-free survival (EFS) probability of 0.750 at 4 years, compared to an EFS probability of 0.375 for non-DS children (P = .049). Blast cells from DS patients were significantly more sensitive to daunorubicin, melphalan, mitoxantrone, 4-hydroperoxy-cyclophosphamide, vincristine, etoposide, bleomycin, and pirarubicin than those from non-DS patients. Four of the 16 non-DS patients were found to have acquired an extra chromosome 21 in their leukemia cells: blasts from these patients also tended to have greater chemosensitivity than those from patients without an extra chromosome 21. Blast cells from DS patients are markedly sensitive to various drugs. These results suggest that the fragility of blast cells derived from DS patients may be related to an increased susceptibility to apoptosis.