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We conducted a prospective randomized study to assess the optimal postremission therapy for adult acute myeloid leukemia in patients younger than 65 years in the first complete remission. A total of 781 patients in complete remission were randomly assigned to receive consolidation chemotherapy of either 3 courses of high-dose cytarabine (HiDAC, 2 g/m(2) twice daily for 5 days) alone or 4 courses of conventional standard-dose multiagent chemotherapy (CT) established in the previous JALSG AML97 study. Five-year disease-free survival was 43% for the HiDAC group and 39% for the multiagent CT group (P = .724), and 5-year overall survival was 58% and 56%, respectively (P = .954). Among the favorable cytogenetic risk group (n = 218), 5-year disease-free survival was 57% for HiDAC and 39% for multiagent CT (P = .050), and 5-year overall survival was 75% and 66%, respectively (P = .174). In the HiDAC group, the nadir of leukocyte counts was lower, and the duration of leukocyte less than 1.0 × 10(9)/L longer, and the frequency of documented infections higher. The present study demonstrated that the multiagent CT regimen is as effective as our HiDAC regimen for consolidation. Our HiDAC regimen resulted in a beneficial effect on disease-free survival only in the favorable cytogenetic leukemia group. This trial was registered at www.umin.ac.jp/ctr/ as #C000000157.

We conducted a multi-institutional randomized study to determine whether high-dose daunorubicin would be as effective as standard-dose idarubicin in remission-induction therapy for newly diagnosed adult patients younger than 65 years of age with acute myeloid leukemia. Of 1064 patients registered, 1057 were evaluable. They were randomly assigned to receive either daunorubicin (50 mg/m(2) daily for 5 days) or idarubicin (12 mg/m(2) daily for 3 days) in combination with 100 mg/m(2) of cytarabine by continuous infusion daily for 7 days as induction therapy. Complete remission was achieved in 407 (77.5%) of 525 patients in the daunorubicin group and 416 (78.2%) of 532 in the idarubicin group (P = .79). Patients achieving complete remission received intensive postremission therapy that consisted of either 3 courses of high-dose cytarabine or 4 courses of standard-dose therapy. Overall survival rates at 5 years were 48% for the daunorubicin group and 48% for the idarubicin group (P = .54), and relapse-free survival rates at 5 years were 41% and 41% (P = .97), respectively. Thus, high-dose daunorubicin and standard-dose idarubicin were equally effective for the treatment of adult acute myeloid leukemia, achieving a high rate of complete remission and good long-term efficacy. This study is registered at http://www.umin.ac.jp/ctrj/ as C000000157.

To examine the efficacy of intensified maintenance chemotherapy, we conducted a prospective multicenter trial in adult patients with newly diagnosed acute promyelocytic leukemia treated with all-trans retinoic acid and chemotherapy. Of the 302 registered, 283 patients were assessable and 267 (94%) achieved complete remission. Predicted 6-year overall survival in all assessable patients and disease-free survival in patients who achieved complete remission were 83.9% and 68.5%, respectively. A total of 175 patients negative for PML-RARalpha at the end of consolidation were randomly assigned to receive either intensified maintenance chemotherapy (n = 89) or observation (n = 86). Predicted 6-year disease-free survival was 79.8% for the observation group and 63.1% for the chemotherapy group, showing no statistically significant difference between the 2 groups (P = .20). Predicted 6-year survival of patients assigned to the observation was 98.8%, which was significantly higher than 86.2% in those allocated to the intensified maintenance (P = .014). These results indicate that the intensified maintenance chemotherapy did not improve disease-free survival, but rather conferred a significantly poorer chance of survival in acute promyelocytic leukemia patients who have become negative for the PML-RARalpha fusion transcript after 3 courses of intensive consolidation therapy.

The outcome for adult patients with BCR-ABL-positive acute lymphoblastic leukemia (ALL) remains dismal and long-term survival can hardly be achieved except by allogeneic hematopoietic stem cell transplantation (HSCT). The Japan Adult Leukemia Study Group (JALSG) has recently started a phase 2 trial with intensive chemotherapy and imatinib for newly diagnosed BCR-AB-positive ALL patients, and we present here the interim results for the first 24 patients. All patients except one case of early death (96%) attained complete remission (CR) after a single course of remission induction therapy. Polymerase chain reaction (PCR) negativity was achieved in 28% of the patients on day 28, in 50% on day 63, and in up to 78% during the follow-up period. The toxicity profile was almost similar to that with chemotherapy alone. As a result, 15 patients (63%) could receive an allogeneic HSC transplant during their first CR. Although the number of patients is small and the observation period is too short, the combination therapy is very promising and produces high-quality CR for most newly diagnosed patients with BCR-ABL-positive ALL. This is especially useful because it provides the patients with a better chance to receive an allogeneic HSC transplant.

Although FLT3 mutations are essentially found in myeloid-lineage leukemia cells, a high level of FLT3 expression was recently observed in MLL gene-rearranged acute lymphoblastic leukemia without FLT3 mutations. Here, we analyzed the biologic and clinical significance of the FLT3 transcript level in comparison with several gene alterations in 181 de novo acute myeloid leukemia (AML) cases. The mean expression level in AML was higher than that in normal mononuclear cells, whereas the range varied widely. A high level of FLT3 is related to internal tandem duplication of the FLT3 gene (FLT3/ITD), the mutations within the activation loop of FLT3 (FLT3/D835Mt), and tandem duplication of the MLL gene (MLL-TD) but not to p53 or N-RAS gene mutations. Furthermore, a high expression level in AML cases with FLT3 mutations was not related to MLL-TD. Overexpressed FLT3 revealed autophosphorylation and had the same sensitivity to the FLT3 inhibitor as FLT3/ITD. Overexpression of FLT3 (more than 200,000 copies/microgRNA) was an unfavorable prognostic factor for overall survival in 91 AML cases without FLT3/ITD. These results indicated that FLT3 overexpression may distinguish a novel disease entity in AML without FLT3 mutations and serve as a therapeutic target for FLT3 inhibitors.

Mutations of receptor tyrosine kinases are implicated in the constitutive activation and development of human malignancy. An internal tandem duplication (ITD) of the juxtamembrane (JM) domain-coding sequence of the FLT3 gene (FLT3/ITD) is found in 20% of patients with acute myeloid leukemia (AML) and is strongly associated with leukocytosis and a poor prognosis. On the other hand, mutations of the c-KIT gene, which have been found in mast cell leukemia and AML, are clustered in 2 distinct regions, the JM domain and D816 within the activation loop. This study was designed to analyze the mutation of D835 of FLT3, which corresponds to D816 of c-KIT, in a large series of human hematologic malignancies. Several kinds of missense mutations were found in 30 of the 429 (7.0%) AML cases, 1 of the 29 (3.4%) myelodysplastic syndrome (MDS) cases, and 1 of the 36 (2.8%) acute lymphocytic leukemia patients. The D835Y mutation was most frequently found (22 of the 32 D835 mutations), followed by the D835V (5), and D835H (1), D835E (1), and D835N (1) mutations. Of note is that D835 mutations occurred independently of FLT3/ITD. An analysis in the 201 patients newly diagnosed with AML (excluding M3) revealed that, in contrast to the FLT3/ITD mutation (n = 46), D835 mutations (n = 8) were not significantly related to the leukocytosis, but tended to worsen disease-free survival. All D835-mutant FLT3 were constitutively tyrosine-phosphorylated and transformed 32D cells, suggesting these mutations were constitutively active. These results demonstrate that the FLT3 gene is the target most frequently mutated to become constitutively active in AML.

Internal tandem duplication of the FLT3 gene and point mutations of the N-RAS gene are the most frequent somatic mutations causing aberrant signal-transduction in acute myeloid leukemia (AML). However, their prognostic importance is unclear. In this study, their prognostic significance was analyzed in 201 newly diagnosed patients with de novo AML except acute promyelocytic leukemia. Three patients had mutations in both genes, 43 had only the FLT3 gene mutation, 25 had only the N-RAS gene mutation, and 130 had neither. These mutations seemed to occur independently. Both mutations were related to high peripheral white blood cell counts, and the FLT3 gene mutation was infrequently observed in the French-American-British (FAB)-M2 type. AML cases with wild FLT3/mutant N-RAS had a lower complete remission (CR) rate than those with wild FLT3/wild N-RAS, whereas the presence of mutant FLT3 did not affect the CR rate. Univariate analysis showed that unfavorable prognostic factors for overall survival were age 60 years or older (P =.0002), cytogenetic data (P =.002), FAB types other than M2 (P =.002), leukocytosis over 100 +/- 10(9)/L (P =.003), and the FLT3 gene mutation (P =.004). However, the N-RAS gene mutation was only a marginal prognostic factor (P =.06). For the subjects under 60 years old, multivariate analysis showed that the FLT3 gene mutation was the strongest prognostic factor (P =.008) for overall survival. The FLT3 gene mutation, whose presence is detectable only by genomic polymerase chain reaction amplification and gel electrophoresis, might serve as an important molecular marker to predict the prognosis of patients with AML.

Differentiation therapy with all-trans retinoic acid (ATRA) has marked a major advance and become the first choice drug in the treatment of acute promyelocytic leukemia (APL). However, patients who relapse from ATRA-induced complete remission (CR) have difficulty in obtaining a second CR with a second course of ATRA therapy alone. We tested the efficacy of a new synthetic retinoid, Am80, in APL that had relapsed from CR induced by ATRA in a prospective multicenter study. Am80 is approximately 10 times more potent than ATRA as an in vitro differentiation inducer, is more stable to light, heat, and oxidation than ATRA, has a low affinity for cellular retinoic acid binding protein, and does not bind to retinoic acid receptor-gamma. Patients received Am80, 6 mg/m2, orally alone daily until CR. Of 24 evaluable patients, 14 (58%) achieved CR. The interval from the last ATRA therapy was not different between CR and failure cases. The clinical response was well correlated with the in vitro response to Am80 in patients examined. Adverse events included 1 retinoic acid syndrome, 1 hyperleukocytosis, 9 xerosis, 8 cheilitis, 16 hypertriglyceridemia, and 15 hypercholesterolemia, but generally milder than those of ATRA, which all patients had received previously. Am80 is effective in APL relapsed from ATRA-induced CR and deserves further trials, especially in combination with chemotherapy.

From the viewpoint of T-cell receptor (TCR) repertoire, we studied the role of T cells in acute graft-versus-host disease (GVHD) after allogeneic bone marrow transplantation (allo-BMT) from an HLA-identical sibling. By means of inverse polymerase chain reaction method and DNA sequencing, we analyzed TCR-alpha and -beta transcripts from GVHD lesions and peripheral blood (PB) in a patient with typical GVHD together with PB from donor. At the initial onset of GVHD, V alpha-7 and -19 subfamilies were oligoclonally expanded in the PB compared with those in the oral mucosal lesions. At the second onset, V alpha-2, and V beta-6 subfamilies were more frequently detected in the cutaneous lesion than in the PB. Some TCR transcripts were recurrently found either in the mucosal or cutaneous lesions (or in both) and not in the PB. Furthermore, some of recurrent TCR transcripts in the lesions shared V gene segments and common motifs of complementarity determining region-3. These findings suggested that T cells infiltrating the GVHD lesions recognized a limited kind of antigens presented by patient's tissues with GVHD, and that T-cell repertoire in the GVHD lesions was different from that in the PB.

A multicenter randomized study was conducted to compare the effect of interferon-alpha (IFN-alpha) with that of busulfan in newly diagnosed patients with chronic myelogenous leukemia (CML) in chronic phase. From October 1988 to October 1991, 170 patients were randomized to receive either IFN-alpha or busulfan. Of 159 eligible patients, 31 (38.8%) of 80 patients in the IFN-alpha group and 43 (54.4%) of 79 patients in the busulfan group achieved complete hematologic remission, and 38.8% in the IFN-alpha group and 43.0% in the busulfan group achieved partial hematologic remission. A complete cytogenetic response was induced in seven (8.8%) of 80 patients treated with IFN-alpha and two (2.5%) of 79 patients treated with busulfan, and a partial cytogenetic response was 7.5% (6/80) and 2.5% (2/79), respectively. The difference in major (complete and partial) cytogenetic response between the two groups was significant (P = .046). At a median follow-up of 50 months, the predicted 5-year survival rate was 54% in the IFN-alpha group and 32% in the busulfan group (P = .0290), and the predicted 5-year rate of remaining in chronic phase was 41% in the IFN-alpha group and 29% in the busulfan group (P = .1165). As compared with the patients with no cytogenetic response, the patients with any cytogenetic response (complete, partial or minor) after the IFN-alpha or busulfan treatment were significantly superior in the duration of chronic phase (IFN-alpha group; P = .0017, busulfan group; P = .0010) even after correction for the time to response using the landmark analysis. However, there was no significant difference in survival rate in the IFN-alpha group (P = .1065). There was no significant difference in survival rate (P = .3923) and the duration of chronic phase (P = .6258) between the IFN-alpha and the busulfan group in the patients with a cytogenetic response (complete, partial or minor). These results demonstrate that IFN-alpha treatment produces a significantly superior cytogenetic response and survival rate as compared with the busulfan treatment, and unexpectedly, that busulfan can also eliminate Philadelphia chromosome positive clone in a few patients who showed prolonged survival rate and duration of chronic phase.

The platelet membrane glycoprotein (GP)Ib/IX complex is composed of three polypeptides, GPIb alpha, GPIb beta, and GPIX, and functions as a platelet receptor for von Willebrand factor. All three subunits are reported to be requisite for efficient surface expression of the complex. The absence of the GPIb/IX complex on platelet membrane is the hallmark of a congenital qualitative platelet disorder, termed the Bernard-Soulier syndrome (BSS). We describe here the molecular basis of a novel variant phenotype of BSS in a female patient, designated as BSS Kagoshima. Her platelets completely lacked the surface expression of GPIb alpha, but expressed a residual amount of GPIb beta and GPIX. Unexpectedly, her platelets and plasma contained a truncated GPIb alpha polypeptide with an apparent molecular weight of 116 kD (under nonreducing conditions). The amounts of truncated protein were 23% and 60% of the normal values in platelets and plasma, respectively. The abnormal protein contained a normal amount of sialic acid as demonstrated by digestion with neuraminidase. DNA sequencing analysis showed a homozygous single nucleotide substitution from the serine codon (TCA) to a nonsense codon (TAA) at residue 444 in the GPIb alpha gene. The mutant gene generated a truncated GPIb alpha molecule lacking the transmembrane region and cytoplasmic tail. Her parents were heterozygotes for the mutation. These findings suggest that this type of truncated GPIb alpha was produced, normally glycosylated, and subsequently secreted into the plasma. Furthermore, the truncated GPIb alpha might be associated with the process of the surface expression of incomplete GPIb/IX complex, GPIb beta and GPIX.

We conducted a prospective, double-blind controlled study to determine the efficacy of a recombinant granulocyte colony-stimulating factor (G-CSF, 200 microgram/m2) starting daily from 2 days before an induction therapy until neutrophils recovered to above 1,500/microL or until 35 days after the therapy in 58 patients with relapsed or refractory acute myeloid leukemia (AML). Twenty-eight patients in the G-CSF group showed significantly faster recovery of neutrophils (P < .001) than 30 patients in the placebo group. The incidence of febrile episodes and of documented infections was almost the same in both groups. However, among 39 patients who did not show any infectious episodes during the 2-week period after the start of chemotherapy, the incidence of documented infections after the third week tended to be lower in the G-CSF group, but not statistically significantly. There was no evidence that G-CSF stimulated the growth of AML cells in the bone marrow during the 2-day period before the chemotherapy, nor that G-CSF accelerated the regrowth of AML cells during the 5-week period after the therapy. Fifty percent of patients in the G-CSF group and 37% in the placebo group had complete remission (CR). Although the rate was higher in the G-CSF group, the difference was not statistically significant (P = .306). There was no difference between the two groups in event-free survival of all patients and in disease-free survival of patients who had achieved CR.

We treated 23 patients with myelodysplastic syndromes (MDS); 2 refractory anemia (RA) with prior therapy, 11 RA with excess of blasts (RAEB), and 10 RAEB in transformation (RAEB-T), with daily oral 45 mg/m2 all-trans retinoic acid (ATRA) in a multiinstitutional prospective study. In two patients with RAEB and one with RAEB-T, a more than 1,000/microL increase of peripheral neutrophil counts was observed with some reduction of blast percentage in the bone marrow 2 to 9 weeks after the start of ATRA. However, the effect was transient and did not last for more than 5 weeks despite the continuation of ATRA therapy. In one other patient with RA, one patient with RAEB, and one patient with RAEB-T, slight increase of hemoglobin levels or reduction of blast percentage in bone marrow was noted. Toxicities attributable to ATRA were minimal and included cheilitis, xerosis, dermatitis, gastrointestinal disorders, abnormal liver function tests, and high serum triglyceridemia. Although ATRA works remarkably as a differentiation therapy in acute promyelocytic leukemia, its effect in MDS included in this study was modest. Further study of this agent alone or in combination may be warranted in less advanced stages of this disease.

The early event of thymocyte maturation has been analyzed using acute lymphoblastic leukemia (ALL) cells. A group of ALL cells whose cell surface phenotype was CD2 (SRBC receptor) negative and CD7 (T cell antigen) positive has been considered as precursor thymocyte ALL (pre-T-ALL). No rearrangements of the T cell receptor beta-gene (TCR beta) and gamma-gene (TCR gamma) were found in three of four pre-T-ALL patients. Stimulation of these pre-T-ALL cells with 12-0-tetradecanoylphorbol-13-acetate (TPA) induced only CD25 (Tac) antigen but no other T cell antigens. These findings suggest that the activation pathway of interleukin 2 (IL-2) receptor already exists in the most immature precursor thymocytes. Pre-T-ALL cells from the fourth patients showed the expression of CD3 antigen, and both TCR beta and TCR gamma rearrangement. TPA induced the differentiation of the more mature pre-T-ALL cells of this case in vitro, and not only CD25 (Tac) antigen but also CD4 and CD8 antigens appeared on the cell surface. The low affinity binding of 125I-IL-2 to TPA-stimulated leukemia cells was observed in the three cases of pre-T-ALL tested, and the addition of recombinant IL-2 to TPA-stimulated cells showed no effect on cell proliferation.

The effect of differentiation induction by a tumor-promoting phorbol diester, 12-O-tetradecanoylphorbol-13-acetate (TPA) on a clonal human megakaryoblastic cell line, MEG-O1s, was investigated, and a prominent response was demonstrated. The cells became weakly adherent, developed conspicuous cytoplasmic blebs, and displayed mature megakaryocytic characteristics by light microscopy such as the development of azurophilic cytoplasmic granules and a mosaic pattern of oxyphilic patches, multiplication of nuclei, and enhancement of the PAS reaction and alpha-naphthyl acetate esterase staining. Ultrastructural studies demonstrated the development of prominent cytoplasmic blebs, budding of blebs, and multiplication of nuclei. Numerous granules with central nucleoids that are similar to alpha granules had developed as well as granules with high electron density and clearly demarcated zones. Surface marker analysis revealed a moderate increase in IgG Fc receptor levels and a profound decrease in C3 receptor sites. By an immunofluorescent technique using monoclonal and polyclonal antibodies, a dramatic change in the expression of several megakaryocyte-platelet-specific proteins was demonstrated. All the proteins that had been expressed before induction such as platelet glycoprotein (GP) IIb/IIIa, fibrinogen, von Willebrand factor, factor XIIIA, beta-thromboglobulin (beta-TG), and HLA class 1 antigen were profoundly enhanced after induction by TPA. Induction by TPA led to the expression of fibronectin and factor V, which were not detected on nontreated cells. An ultrastructural immunoperoxidase study demonstrated platelet GPIb and GPIIb/IIIa in both plasma membranes and protein synthesis areas such as perinuclear cisternae and endoplasmic reticulum after TPA induction. beta-TG was also observed in some cytoplasmic granules of TPA-treated cells. TPA remarkably increased the secretion of beta-TG into the culture medium of MEG-01s. Ploidy was also increased from 2C to 4C to 4C to 8C. Similar maturation of MEG-01s was induced by other phorbol diester analogues such as phorbol-12,13-dibutyrate, but not by phorbol itself. These results indicate that phorbol diester, TPA, can bring about differentiation and maturation of a human megakaryoblastic cell line (MEG-01s) and that MEG-01s cells will provide a useful model for studying megakaryocytic differentiation and numerous megakaryocyte-platelet-specific proteins.

A megakaryoblastic cell line, designated MEG-01, was established from the bone marrow of a patient with blast crisis of Philadelphia (Ph1) chromosome-positive chronic myelogenous leukemia. MEG-01 cells grew in single-cell suspension with a doubling time of 36 to 48 hours. Under the usual culture conditions, approximately half of the cells adhered to the culture flask with extention of pseudopods. MEG-01 cells were positive for the periodic acid-Schiff reaction, alpha-naphthyl acetate esterase, and acid phosphatase, and negative for myeloperoxidase, alpha-naphthyl butyrate esterase, naphthol AS-D chloroacetate esterase, and alkaline phosphatase. Ultrastructural platelet peroxidase was positive in MEG-01 cells. Cytoplasmic factor VIII (FVIII)-related antigen was weakly positive in larger MEG-01 cells by both an indirect immunofluorescent technique with monoclonal antibodies and a direct immunoperoxidase technique using horseradish peroxidase-conjugated conventional rabbit anti-human FVIII antibody. Platelet glycoprotein (GP) IIb/IIIa antigen was uniformly demonstrated on the surface of MEG-01 cells by both indirect immunofluorescent and immunoperoxidase techniques using antiplatelet GP IIb/IIIa monoclonal antibodies; platelet GP lb antigen was demonstrated only in the cytoplasm of larger MEG-01 cells. MEG-01 cells possessed no markers for B or T lymphocytes or for myeloid cells. Chromosome analysis of this cell line revealed a human male hyperdiploid karyotype with a modal chromosome number of 56 to 58. The Ph1 chromosome was observed in all karyotypes analyzed. This novel human megakaryoblastic cell line may provide a useful model for the study of human megakaryopoiesis and of the biosynthetic mechanisms of proteins unique to megakaryocytic lineage.

Four distinct intragenic polymorphisms in the coagulation factor IX gene which have been reported to be important for family diagnosis of Caucasian hemophilia B were studied in 51 normal Japanese subjects (21 males and 30 females). High-molecular-weight DNA prepared from peripheral blood lymphocytes were digested with endonuclease, Ddel, Mspl, Taql or Xmnl, and were studied by Southern blot analysis with factor IX complementary DNA as a probe. None of the minor fragments produced by these enzymes was found in the normal Japanese DNA samples tested, although the probe detects minor allelic forms in control Caucasian DNA samples. Our data suggest that the frequent polymorphic sites found in Caucasians are possibly absent in the Japanese population.

The effects of recombinant human tumor necrosis factor (rH-TNF) on the colony growth of human leukemia progenitor cells (L-CFU), granulocyte-macrophage progenitor cells (CFU-GM), and erythroid progenitor cells (BFU-E) were studied. L-CFU was assayed with leukemia cells obtained from patients with acute myelogenous leukemia. CFU-GM and BFU-E were assayed with bone marrow cells obtained from hematologically normal donors and patients with acute leukemia or non-Hodgkin's lymphoma in complete remission. A dose-dependent growth inhibition of L-CFU as well as CFU-GM and BFU-E was observed by rH-TNF at concentrations of 1 to 100 U/mL. The inhibitory effect on L-CFU was significantly greater than that on CFU-GM. No correlation was observed between the inhibitory effect on L-CFU and the number of colonies formed in the cultures without rH-TNF. Preincubation of the progenitor cells in culture medium containing 20% fetal calf serum with up to 1,000 U/mL of rH-TNF for 24 hours did not result in the inhibition of colony growth of L-CFU or CFU-GM. The inhibitory effect of rH-TNF was neutralized by an anti-rH-TNF murine monoclonal antibody.

Japanese patients with leukemia who received bone marrow from human leukocyte antigen (HLA)-compatible siblings had a low incidence of acute graft-versus-host disease (GVHD). Twenty-five (21%) of 120 patients developed moderate (grade II) to severe (grades III to IV) acute GVHD. Severe GVHD was only seen in patients older than 20 years of age. It is also notable that only 2 (5%) of 39 patients who received the combination of methotrexate and cyclosporine (MTX/CSP) for the prevention of GVHD developed grade II acute GVHD, and none developed grades III to IV acute GVHD. Thirteen (30%) of 44 patients receiving MTX alone and 10 (27%) of 37 patients receiving CSP alone developed grades II to IV acute GVHD. Multivariate life-table analysis indicated that the prophylaxis by MTX/CSP was the risk factor for the low incidence of grades II to IV acute GVHD. Compared with the reported incidence of acute GVHD in the patients of the United States, lower incidence of acute GVHD in Japanese BMT patients might be attributable to a lesser degree of genetic diversity in histocompatibility antigens among Japanese.