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Biomedical subjects

W C Chan

Publications and source records attributed to W C Chan.

At least 109 records · Page 6Linked to original sources

Aggressive natural killer cell lymphoma of the small intestine.

We report a case of aggressive non-Hodgkin's lymphoma of the small cell type arising in the small intestine and having a natural killer cell phenotype. Immunophenotyping of frozen tissue sections revealed a lack of reactivity with the pan-T-cell markers CD3 and CD5, and no reaction with B-cell markers. Positive staining was obtained with antibodies to CD2, CD7, and CD56. Molecular studies were negative for clonal T gamma, T beta and immunoglobulin heavy-chain gene rearrangements. Natural-killer-cell-associated cytotoxin was demonstrated by positive staining with an antibody to perforin, a protein present in the granules of large granular lymphocytes. Despite its indolent histologic appearance, the aggressive nature of this neoplasm was suggested by the expression of the activation markers CD38 and CD71, and the nuclear proliferation marker Ki67, and confirmed clinically by its rapid recurrence with extensive involvement of the pelvic organs, resistance to chemotherapy, and the short survival of the patient. Distinct from many Asian cases, Epstein-Barr virus genome was not detectable in the tumor. This case emphasizes the importance of recognizing non-Hodgkin's lymphomas with a natural killer cell phenotype as a distinct entity, both biologically and clinically.

Biomarkers, Tumor↗

High levels of protection induced by a 40-mer synthetic peptide vaccine against the intestinal nematode parasite Trichinella spiralis.

Parenteral vaccination, using a 40-mer synthetic peptide from a 43,000 MW immunodominant glycoprotein secreted by the intestinal nematode parasite Trichinella spiralis, induced high levels of protection against a subsequent challenge infection in mice. The expulsion of adult worms from the gut was accelerated following vaccination with peptide 40-80, but peptides 81-120 and 121-160 were not protective. Mesenteric lymph node cells taken from T. spiralis-infected mice showed some proliferation in response to in vitro stimulation with peptide 40-80, but were unaffected by peptide 81-120. As expulsion of T. spiralis is known to be brought about by T-cell-mediated inflammatory events in the intestine, the ability of the 40-80 sequence to promote accelerated worm expulsion upon challenge infection may reflect induction of a specific and appropriate T-cell response. To our knowledge, this is the first report of a protective synthetic peptide vaccine against an intestinal nematode.

Amino Acid Sequence↗

Lymphocyte predominance Hodgkin's disease: lineage and clonality determination using a single-cell assay.

Lymphocyte predominance Hodgkin's disease (LPHD) is a clinically indolent condition. Although there is evidence that the putative neoplastic cell in this disease, the "L&H" cell, is of B-cell lineage, there is conflicting data concerning the clonality of these cells. Our study was aimed at clarifying the issue of lineage and clonality of the L&H cells of LPHD using a single-cell assay. Four cases of LPHD were studied. To circumvent the difficulties of obtaining fresh tissue and to be able to study representative cases, a new method was developed to obtain single-cell suspensions of L&H cells from archival formalin-fixed paraffin-embedded tissue. Single L&H cells were identified by morphology and immunostaining for epithelial membrane antigen, isolated using a micropipette, and subjected to polymerase chain reaction (PCR) amplification of the complematarity determining region 3 (CDR3) of the Ig heavy chain (IgH) gene, which is B-cell clone-specific. The PCR products were size-fractionated by polyacrylamide gel electrophoresis and representative products were directly sequenced. Single T cells and small B cells were also isolated from the tissues and used as negative and positive controls, respectively. In all four cases of LPHD, the IgH CDR3 of single L&H cells could be amplified. Within each case, the IgH CDR3 of single L&H cells was found to be of different length or of different sequence. Therefore, our results provide strong evidence for the B-cell origin of the L&H cells and the polyclonal nature of LPHD.

Antigens, CD↗

T-cell receptor gene rearrangement in T-cell large granular leukocyte leukemia: preferential V alpha but diverse J alpha usage in one of five patients.

T-gamma lymphoproliferative disease (T-gamma LPD) is a chronic disorder of mature T cells that is associated with neutropenia and autoimmune phenomena. Although the progression of the lymphoproliferation is indolent, it is often associated with a monoclonal proliferation of T-cell-type large granular lymphocytes (LGL) that manifest multiple in vitro suppressor and cytotoxic activities. We considered the possibility that the granulocytopenia or anemia might represent an autoimmune disorder mediated by the monoclonal LGL via T-cell receptor (TCR) recognition of an antigen involved in hematopoiesis. Therefore, in an effort to characterize the usage of the TCR alpha- and beta-chain genes in patients with T-gamma LPD, we cloned and sequenced TCR alpha- and beta-chain mRNAs derived from the T-cell type LGL of five patients. The five patients studied did not use a common V alpha nor a common J alpha segment. However, an unusual finding was observed in one of the patients where the occurrence of a single variable-diversity-junctional (VDJ) rearrangement of the beta chain confirmed the monoclonal origin of the LGL proliferation. In accord with this evidence for monoclonality, many of the cells studied used a common V alpha (V alpha 19.1). In contrast to this common V alpha usage, there was a marked diversity of the J alpha segments and N-region addition that were associated with the V alpha 19.1 segment. This pattern of common V alpha usage associated with different N and J alpha segments suggests an immune-mediated selection process affecting the TCR alpha chain occurring after the transformation event that established the clone. We suggest that the T-cell-type LGL malignant clone might have developed autoreactivity conferred by the selected TCR alpha chain and that this autoreactivity might be implicated in this patient's anemia.

Amino Acid Sequence↗

Detection of tumor contamination of peripheral stem cells in patients with lymphoma using cell culture and polymerase chain reaction technology.

The important question of whether residual tumor in the bone marrow or peripheral blood stem cell graft contributes to relapse in autologous bone marrow transplantation in patients with non-Hodgkin's lymphoma can be addressed only if there is an accurate and sensitive measurement of tumor cell contamination of the graft. Assays utilizing DNA amplification based on the polymerase chain reaction (PCR) are highly sensitive. Tumor-specific primers and probes can be designed for the clonally rearranged Ig or T cell antigen receptor genes in the original tumors, and these can then be used to detect minimal residual disease in subsequent specimens. Specific translocations can also be exploited as tumor markers, and the t(14;18) translocation has been widely employed for detecting tumor cells in blood and bone marrow samples. Lymphoma cells have also been grown successfully in tissue culture, and the detection of tumor contamination of autologous grafts has been associated with a poorer prognosis in patients with intermediate- or high-grade lymphoma. It is of interest to compare the sensitivity of tumor detection and the predictive value for patient survival of the PCR-based and culture-based assays. The information obtained may help to determine whether minimal tumor contamination of an autologous graft is clinically significant and, if so, the assay(s) that should be employed.

Bone Marrow↗

Incidence and characterization of secondary myelodysplastic syndrome and acute myelogenous leukemia following high-dose chemoradiotherapy and autologous stem-cell transplantation for lymphoid malignancies.

PURPOSE: To analyze the risk of developing myelodysplastic syndrome (MDS) or acute myelogenous leukemia (AML) following autologous bone marrow transplantation (ABMT) or peripheral stem-cell transplantation (PSCT) and to determine the impact on failure-free survival (FFS). PATIENTS AND METHODS: Patients underwent ABMT or PSCT for the treatment of Hodgkin's disease (HD) and non-Hodgkin's lymphoma (NHL) at the University of Nebraska Medical Center. For those patients who went on to develop MDS/AML, controls were selected and a case-control-within-a-cohort study undertaken. RESULTS: Twelve patients developed MDS or AML a median of 44 months following ABMT/PSCT. The cumulative incidence (P = .42) and the conditional probability (P = .32) of MDS/AML were not statistically different between HD and NHL patients. Age greater than 40 years at the time of transplant (P = .05) and receipt of a total-body irradiation (TBI)-containing regimen (P = .06) were predictive for developing MDS/AML in patients with NHL. CONCLUSION: There is an increased risk of MDS/AML following ABMT/PSCT for lymphoid malignancies. NHL patients age > or = 40 years at the time of transplant and who received TBI are at greatest risk.

Adult↗

Quality assessment and improvement: what radiologists do and think.

OBJECTIVE: The main objectives of the study were as follows: first to study the nature and extent of radiologists' involvement in and their attitudes toward quality assessment (QA) and continuous quality improvement (CQI)/total quality management (TQM) in hospitals and in offices; and second, to ascertain whether differences in size, type, and location among hospitals and nonhospital radiology offices affect the QA and CQI/TQM activities of radiologists. We analyzed data from a national survey conducted by the American College of Radiology (ACR) in 1993. MATERIALS AND METHODS: Questionnaires about QA and CQI/TQM activities and attitudes were mailed to 216 hospital-affiliated diagnostic radiology group practices using a sample selected from the ACR master list of radiology practices in the United States. The response rate was 90%. A stratified random sample ensured representation of different geographic regions, various group sizes, and both academic and nonacademic groups. Responses were weighted so that our data show what answers about hospitals would have been if (i) the survey had been answered by all hospital radiology departments in the United States (except for those few staffed by solo practitioners or nonradiologists) and (ii) our questions about nonhospital offices had been answered by all radiology groups in the United States (except those few having no hospital activity). RESULTS: The majority (86%) of hospital radiology departments report having a program to monitor and evaluate physicians' performances. Fifty-one percent collect incorrect diagnoses by specific radiologist. Twenty-eight percent collect some of their QA data through computerized information systems. We found some statistically significant differences by hospital size and location, with larger hospitals and urban hospitals being more likely to engage in some QA activities. Multivariate analyses, once controlled for hospital size and location, found no significant differences in QA activity between university and community hospitals or between hospitals with and without a residency program. QA and CQI programs were less common in offices than in hospitals. With the exception of mammographic interpretations, most practices did not monitor and evaluate physicians' performances in the office setting. Respondents representing 58% of hospital radiology departments thought that QA and CQI contributed to improvement in patient care. Only 19% of radiology practices answered that CQI has been of cost benefit to their organization. CONCLUSION: Most radiology practices engage in a variety of QA and CQI activities in hospitals. However, this is less true in offices, in which radiologists have more discretion, and radiologists remain skeptical about the usefulness of CQI.

Attitude of Health Personnel↗

Myeloperoxidase gene expression in normal granulopoiesis and acute leukemias.

Myeloperoxidase (MPO) is an abundant heme protein found in granulocytes and monocytes, which plays an important role in host defense against infection. MPO enzyme activity as determined by light microscopic cytochemistry has long been an important marker used in the diagnosis of acute leukemias and other hematopoietic disorders. Recently, MPO expression has been studied at the electron microscopic level, and monoclonal antibodies (mAbs) against MPO protein have been developed. Furthermore, techniques and probes for analysing MPO expression at the RNA level are now available. This has made possible more extensive studies of MPO expression in a wide range of neoplastic and preneoplastic blood disorders. This review will discuss the fundamental biology of MPO as well as recent developments in our understanding of MPO expression in leukemic cells and cell lines of various lineages.

Acute Disease↗

Precision of genotyping of Epstein-Barr virus by polymerase chain reaction using three gene loci (EBNA-2, EBNA-3C, and EBER): predominance of type A virus associated with Hodgkin's disease.

To precisely determine the genotype of Epstein-Barr virus (EBV) in Hodgkin's disease (HD), we simultaneously analyzed three divergent gene loci (EBNA-2, EBNA-3C, and EBER) that distinguish type A and B viruses. The primers designed to amplify these three gene loci encompass either type-specific deletion sequences (EBNA-2 and EBNA-3C) or type-specific point mutations (EBER) that identify the virus strain based on the sizes of the polymerase chain reaction (PCR)-amplified products or the mobility shifts in single-strand conformation polymorphism analysis. The locations of point mutations were identified by direct sequencing of the PCR-amplified DNA. We analyzed 15 EBV-infected cell lines and found a good correlation between EBNA-2 and EBNA-3C typing results. In contrast, approximately 33% of the cell lines analyzed maintained type A sequences in EBNA-2 and EBNA-3C genes while carrying type B sequences in the EBER region. Data obtained from analysis of cell lines served as a reference for studying HD samples. EBV DNA was detected in about 70% of HD. Among the EBV-positive samples, 56% were associated with type A virus, 13% with type B, and 31% with dual viral sequences. Thus, type A virus is predominant in HD. Based on the histology, the frequencies of EBV positivity were 83%, 71%, and 33% for mixed cellularity, nodular sclerosis, and lymphocyte predominance, respectively. The detection of high frequency of both type A and B sequences in HD may provide a lead in investigating the role of dual viral infection in EBV pathogenesis.

Antigens, Viral↗

A novel post-translational modification of the peptide antibiotic subtilin: isolation and characterization of a natural variant from Bacillus subtilis A.T.C.C. 6633.

A variant of the peptide antibiotic subtilin has been isolated from Bacillus subtilis A.T.C.C. 6633, and its structure has been shown to be [N alpha-succinyl-Trp1]subtilin. The chemical structure of a fragment derived by tryptic hydrolysis of the variant is shown to be N alpha-succinyl-Trp-Lys by 1H and 13C n.m.r., fast-atom-bombardment m.s. and total chemical synthesis [N alpha-Succinyl-Trp1]-subtilin is produced later in the growth of the bacterium than is subtilin; reverse-phase h.p.l.c. analysis shows that after 24 h growth the ratio subtilin/[N alpha-succinyl-Trp1]subtilin is approx. 1:2. Although [N alpha-succinyl-Trp1]subtilin retains significant antibacterial activity, it is 10-20 times less active than subtilin.

Amino Acid Sequence↗

Combinatorial mutagenesis of the lamB gene: residues 41 through 43, which are conserved in Escherichia coli outer membrane proteins, are informationally important in maltoporin structure and function.

A new strategy for combinatorial mutagenesis was developed and applied to residues 40 through 60 of LamB protein (maltoporin), with the aim of identifying amino acids important for LamB structure and function. The strategy involved a template containing a stop codon in the target sequence and a pool of random degenerate oligonucleotides covering the region. In vitro mutagenesis followed by selection for function (Dex+, ability to utilize dextrins) corrected the nonsense mutation and simultaneously forced incorporation of a random mutation(s) within the region. The relative importance of each residue within the target was indicated by the frequency and nature of neutral and deleterious mutations recovered at each position. Residues 41 through 43 in LamB accepted few neutral substitutions, whereas residues 55 through 57 were highly flexible in this regard. Consistent with this finding was that the majority of defective mutants were altered at residues 41 to 43. Characterization of these mutants indicated that the nature of residues 41 to 43 influenced the amount of stable protein in the outer membrane. These results, as well as the conserved nature of this stretch of residues among outer membrane proteins, suggest that residues 41 to 43 of LamB play an important role in the process of outer membrane localization.

Amino Acid Sequence↗

Radiologists in the United States: demographic, professional, and practice characteristics.

OBJECTIVE: The purpose of this report is to present a statistical portrait of radiologists in the United States based on the 1990 American College of Radiology Manpower Survey. Unlike previous surveys, this survey included radiologists who were not members of the College and was thus more representative of all radiologists. (Approximately three quarters of radiologists are College members.) We examined how the demographic, professional, and practice characteristics of radiologists vary among major groups within the profession. MATERIALS AND METHODS: A stratified random sample of 2804 radiologists and nuclear medicine specialists was drawn from the American Medical Association Physician Masterfile, which is the most complete and extensive single source of information on physicians in the United States. Because the total numbers of female radiologists, nuclear medicine specialists, and radiologists less than 35 years old are relatively small, these groups were deliberately "oversampled" (hence the term stratified random sample) to ensure sufficient numbers of responses in these categories for meaningful analysis. A total of 1845 completed questionnaires were received, which yields a response rate of 68% if the questionnaires sent to invalid addresses are excluded. Responses were weighted to make the data representative of all radiologists, despite differences in sampling rates. RESULTS: Findings for professionally active radiologists who completed their training included the following: 94% were certified by the American Board of Radiology, 13% were women, 47% were less than 45 years old, fees for service were the primary remuneration for 62%, and 72% are in practices owned by physician members of the practice. By major activity in radiology, 69% were diagnostic radiology generalists; 11% were radiation oncologists; 18% were diagnostic radiology subspecialists; and 2% were nuclear medicine specialists. A breakdown by age indicated that the age group of radiologists less than 45 years old included more women, diagnostic subspecialists, and persons who had fellowship training than other age groups did. Percentages of diagnostic radiology generalists and solo practitioners were lower among younger radiologists. Radiation oncologists, compared with all others, were the most likely to practice solo or in small groups of two to four members. The subfields with the highest percentages (60% or more) of diagnostic radiologists reporting expertise or proficiency were CT, mammography, and sonography. Among radiologists who were retired, half had retired by the time they were 65 years old. However, a majority of radiologists 65-69 years old were still working, as were 40% of those 70-74 years old. CONCLUSION: The profession of radiology is changing, with more women, subspecialists, and fellowship-trained radiologists in younger age groups and fewer solo practitioners. Only a small percentage of radiologists are not board certified. Radiologists typically remain professionally active into their late 60s or even beyond.

Adult↗

Oncogene rearrangement in non-Hodgkin's lymphoma with a 14q+ chromosome of unknown origin.

Southern blot analysis was performed with a panel of DNA probes to detect rearrangements of c-myc, bcl-1, bcl-2 and bcl-3 in 14 cases of B-cell non-Hodgkin's lymphoma (NHL) with a clonal cytogenetic rearrangement involving the chromosome 14q32 locus and no known donor chromosome [t(14;?)(q32;?)]. In our experience, 21% of all chromosomal abnormalities involving the 14q32 locus in B-cell NHL are of this type. We found oncogene rearrangements in five of the 14 cases: bcl-1 rearrangement on one mantle zone lymphoma, bcl-2 rearrangements in two follicular lymphomas, and c-myc rearrangements in two small noncleaved cell lymphomas. We conclude that a 14q32+ abnormality of unknown origin is a relatively frequent karyotypic finding in B-cell NHL. In one third of the cases, known oncogenes that have been previously described in reciprocal translocations involving the immunoglobulin heavy chain locus were shown to be involved in the 14q32+ abnormality. The translocations in the other cases are likely to have involved one of the above oncogenes with breakpoints not revealed by the probes employed, other known oncogenes, or oncogenes that have not yet been identified.

Adolescent↗

HTLV-I sequence in lymphoproliferative disorders.

Several recent studies reported the detection of partially deleted HTLV-I provirus in biopsies of lesions from patients with mycosis fungoides (MF) and T-cell anaplastic large-cell lymphoma. We studied lesions from 59 patients (21 B-cell lymphomas: 16 diffuse and five follicular; 11 cutaneous T-cell lymphomas, including seven MF; one T-immunoblastic lymphoma; 10 diffuse anaplastic large-cell lymphomas: two B, four T, and four of indeterminate phenotype; three Hodgkin's lymphomas; eight atypical lymphoid proliferations; four other lymphoid lesions, and one squamous-cell carcinoma) using primers to the gag, pol and pX regions of HTLV-I in the polymerase chain reaction (PCR) to detect relevant sequences. A total of 10 patients showed one or more PCR-amplifiable products, including five of 11 patients with cutaneous T-cell lymphomas (45%) as compared with one of 21 patients with B-cell lymphomas (4.3%). We did not find a high incidence of positivity in anaplastic large-cell lymphomas, as reported previously. Detectable HTLV-I sequences were not limited to any subtype of lymphoma, and a pX sequence was detected in a squamous-cell carcinoma. Sequence analysis of one amplified product from each of the three regions studied showed a 94.2, 100, and 98.9% homology to the corresponding prototypical gag, pol, and pX HTLV-I sequences, respectively, indicating that the amplified sequences were derived from HTLV-I or a very closely related virus. HTLV-I sequences were detected in a significant proportion of patients with cutaneous T-cell lymphoma, but their role in the pathogenesis of the neoplasm is still unclear.

Base Sequence↗