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M Haber

Publications and source records attributed to M Haber.

At least 91 records · Page 5Linked to original sources
PubMed1995

Detection of evolving immunoglobulin heavy-chain gene rearrangements in acute lymphoblastic leukemia: a PCR-based assay employing overlapping DJH primers.

The use of the polymerase chain reaction (PCR) to amplify clonal immunoglobulin heavy-chain (IgH) gene rearrangements appears to be a particularly promising technique for detecting minimal residual disease (MRD). However, a major obstacle to successful implementation of this technique involves the problem of clonal evolution, in which instability of the VHDJH region leads to the generation of further rearrangements of the IgH gene over time. Such clonal evolution results in a high likelihood of false negative results when detecting MRD using clone-specific primers based on the rearrangement present at diagnosis. Since in acute lymphoblastic leukemia (ALL), clonal evolution commonly involves alterations of the VHD joining but not the DJH joining, we have devised a novel PCR strategy to circumvent the problem of false negativity in these evolved leukemias. The strategy, which involves construction of overlapping clone-specific DJH primers for use with a consensus VH segment primer, can be used to amplify both evolved and nonevolved ALL populations with high sensitivity and specificity. The method does not require radioactivity and should prove valuable for improving the effectiveness of PCR-based detection of residual leukemia.

Base Sequence↗
PubMed1994

Expression of the multidrug resistance-associated protein (MRP) gene correlates with amplification and overexpression of the N-myc oncogene in childhood neuroblastoma.

The MRP gene (Cole et al., Science (Washington DC), 258: 1650-1654, 1992) encodes a membrane-bound glycoprotein the expression of which correlates with non-P-glycoprotein-mediated multidrug resistance in a variety of cultured human cell lines. Using an RNA-polymerase chain reaction assay, expression of this gene was examined in the highly chemoresistant pediatric malignancy, neuroblastoma. MRP expression was observed in 5 human neuroblastoma cell lines and in all 25 primary neuroblastoma tumors of stage I through IVS. Tumors with amplification of the N-myc oncogene were found to have significantly higher MRP expression that those with no amplification (P = 0.0016). Expression of the MRP gene in the tumor specimens was highly correlated with expression of the N-myc gene (P = 0.0009), while expression of the MDR1 gene, encoding P-glycoprotein, was not related to expression of either the N-myc or MRP genes. Decreased expression of the N-myc oncogene in neuroblastoma cell lines SH-SY5Y and BE(2)-C, following treatment with retinoic acid, was paralleled by down-regulation of MRP gene expression, contrasting with increased expression of the MDR1 gene. Expression of the MRP gene is thus common in both primary neuroblastoma tumors and cultured cell lines, and correlates with amplification and overexpression of the N-myc oncogene, which is central to the malignant phenotype of this disease.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1994

Dietary glutathione intake and the risk of oral and pharyngeal cancer.

Glutathione, a tripeptide found in a variety of foods, may function as an anticarcinogen by acting as an antioxidant and by binding with cellular mutagens. The association between dietary glutathione intake and risk of oral and pharyngeal cancer was investigated using data from 1,830 white participants (855 cases and 975 controls) in a population-based case-control study conducted in New Jersey; metropolitan Atlanta, Georgia; Los Angeles County, California; and Santa Clara and San Mateo counties, south of San Francisco-Oakland, California, during 1984-1985. The estimated relative risk of cancer among people with the highest quartile of glutathione intake from all sources was 0.5 (95% confidence interval 0.3-0.7). When analyzed by dietary source, however, glutathione intakes derived from all vegetables and from meat were not related to risk of cancer. Only glutathione derived from fruit and from vegetables commonly consumed raw was associated with reduced oral cancer risk. Relative to the lowest level of combined intake of fruit and of fruit-derived glutathione, risk of cancer decreased slightly with increasing intake of fruit glutathione. This analysis was limited, however, by the small numbers of subjects with extreme combinations of intakes. Further studies are needed to distinguish the potential effect of glutathione from that of fruit and raw vegetables per se or from the influence of other constituents in these foods.

Adult↗
PubMed1994

Models for three-dimensional contingency tables with completely and partially cross-classified data.

We develop models for three-dimensional contingency tables containing both completely and partially cross-classified data for which one of the variables is regarded as dependent and the other two variables are regarded as independent variables. Parameters of interest include the cell probabilities and the probabilities that the observations on one or both independent variables are missing. The models allow inferences on these two sets of probabilities to be made independently. Maximum likelihood methods for estimating and testing hypotheses regarding these parameters are described, along with conditional goodness-of-fit test statistics, which display a convenient additivity property. The methodology is applied to cervical cancer data from a case-control study performed in Atlanta, Georgia, 1985-1988.

Adult↗
PubMed1993

Resistance to tetracycline, a hydrophilic antibiotic, is mediated by P-glycoprotein in human multidrug-resistant cells.

Two multidrug-resistant human leukemic CCRF-CEM sublines (CEM/VCR R and CEM/VLB100) were significantly more resistant to tetracycline, a hydrophilic antibiotic, than parental cells (P < 0.001). Verapamil and cyclosporin A completely reversed tetracycline resistance in CEM/VCR R cells, which also accumulated and retained significantly less [3H]tetracycline than CCRF-CEM cells. Like verapamil, addition of tetracycline to CEM/VCR R cells which had achieved steady-state vincristine levels resulted in augmented vincristine accumulation. [3H]Azidopine photoaffinity labelling of CEM/VCR R membrane proteins was inhibited by tetracycline in a dose-dependent manner. Although drugs associated with the multidrug-resistance phenotype are typically hydrophobic compounds, these data suggest that resistance to tetracycline, despite its hydrophilic nature, is mediated by P-glycoprotein in these cell lines.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1993

Measuring vaccine efficacy from epidemics of acute infectious agents.

A good measure of field vaccine efficacy should evaluate the direct protective effect of vaccination on the person who receives the vaccine. The conventional estimator for vaccine efficacy depends on population level factors that are either unrelated or indirectly related to the direct biological action of the vaccine on persons, including population structure, duration of the study, the fraction vaccinated, and herd immunity, that is, indirect effects. Indirect effects can cause the conventional vaccine efficacy estimator to be inaccurate. We review alternative vaccine efficacy estimators that control for indirect effects at the population level. Thus, they are more accurate than the conventional estimator. We use epidemic simulations to explore the robustness of the conventional and proposed estimators under different field conditions. In addition, we apply the different vaccine efficacy estimators to data from a measles epidemic in Muyinga, Burundi.

Burundi↗
PubMed1993

Determination of N-myc gene amplification in neuroblastoma by differential polymerase chain reaction.

Determination of N-myc gene amplification, a powerful prognostic indicator in the childhood tumour, neuroblastoma, has routinely been performed by Southern analysis. We have developed a differential polymerase chain reaction (PCR) assay, in which the N-myc target gene is co-amplified with a control gene, glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Following electrophoresis, a ratio between the two PCR products within a given DNA sample is then determined by densitometry. This assay was applied to DNA isolated from 32 primary neuroblastoma tumours for which the N-myc status had previously been determined by Southern analysis. Following PCR, samples containing a single copy of the N-myc oncogene were clearly distinguishable from samples with N-myc gene amplification, based on an N-myc/GAPDH ratio of below or above 1.0, respectively. Linear regression indicated a highly significant relationship (R = 0.94; P < 0.0001) between N-myc copy number (Southern) and N-myc/GAPDH ratio (PCR). Serial dilution of N-myc amplified DNA with non-amplified control DNA indicated that the PCR assay was sufficiently sensitive to detect two-fold amplification. Moreover, such serial dilution allowed determination of N-myc copy number. The assay, which requires only small amounts of tissue and does not utilize 32P-radioactivity, therefore provides a rapid and sensitive alternative to Southern analysis.

Base Sequence↗
PubMed1993

Methotrexate cytotoxicity determination using the MTT assay following enzymatic depletion of thymidine and hypoxanthine.

Methotrexate, an important agent in the treatment of childhood acute lymphoblastic leukaemia, has generally failed to induce dose-dependent cytotoxicity of patient-derived leukaemic blasts when tested in the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. This effect is apparently due to salvage from the medium, by surviving leukaemic cells, of metabolites such as hypoxanthine and thymidine. In an attempt to address this problem, we have examined the effect, on leukaemic cell populations, of enzymatically depleting these metabolites from the culture medium employed during the MTT assay, using xanthine oxidase and thymidine phosphorylase. Specifically we have assessed methotrexate cytotoxicity in the paediatric acute lymphoblastic T cell leukaemia, GKTL, which is maintained as a xenograft, and like primary leukaemias, has poor viability in vitro. Although little cytotoxicity of GKTL cells was observed when the MTT assay was performed in supplemented RPMI-1640 medium, dose-dependent cytotoxicity of these cells was clearly apparent when the same medium was enzymatically depleted. In contrast, the ID50 for methotrexate of control CCRF-CEM cells was unaltered in enzymatically depleted medium. In the absence of methotrexate, enzymatic depletion of the medium did not affect leukaemic cell survival. We are currently investigating the general applicability of this approach for assaying the response to methotrexate of primary leukaemia samples.

Coloring Agents↗
PubMed1992

Interpretation and estimation of vaccine efficacy under heterogeneity.

Interpretation and estimation of vaccine efficacy is complicated when the vaccine effect is heterogeneous across vaccinated strata. If a person has a certain susceptibility, or probability of becoming infected conditional on a specified exposure to infection, then one effect of a vaccine would be to reduce that susceptibility, possibly to zero. Vaccine efficacy is a function of the relative susceptibilities in the vaccinated and unvaccinated persons. Under heterogeneity of vaccine effect, a general expression for a summary vaccine efficacy parameter is a function of the vaccine efficacy in the different vaccinated strata weighted by the fraction of the vaccinated subpopulations in each stratum. Interpretation and estimability of the summary vaccine efficacy parameter depends on whether the strata are identifiable, and whether the heterogeneity is host- or vaccine-related. Bounds are derived for the summary vaccine efficacy when the strata are not identifiable for the case of an outbreak of an acute infectious disease. The upper bound assumes that everyone is equally affected by the vaccine, and the lower bound assumes that some are completely protected while others have no protection. The biologic interpretation of the two bounds is different.

Disease Susceptibility↗
PubMed1992

Soft tissue effects of the THC:YAG laser on canine vocal cords.

Recently, a laser based on a thulium-holmium-chromium (THC) doped Yttrium-aluminum-garnet (YAG) rod has been developed that produces light of 2.15 microns wavelength and can be transmitted through a low OH- silica fiberoptic cable. This wavelength falls on one of the peaks of the energy absorption spectrum of water. Thus, the THC:YAG laser eliminates the disadvantage of a cumbersome delivery system found in the CO2 laser while still providing precise cutting and minimal tissue injury inherent in lasers emitting light absorbed by water. We evaluated the soft tissue effects of this laser on canine vocal cords. Ablative lesions were produced by the THC:YAG laser and histologically examined on postoperative days 1, 7, and 28. Results indicate that the depth of tissue penetration is easily controlled and the healing response to tissue injury is comparable to that of the CO2 laser. The THC:YAG laser should prove to be a superior laser for use in otorhinolaryngology, especially when adapted to a flexible endoscope.

Aluminum Silicates↗
PubMed1992

A discrete-time model for the statistical analysis of infectious disease incidence data.

A discrete-time model is devised for the per-time-unit distribution of infectious disease cases in a sample of households. Using the time at which an individual is identified (e.g., when illness symptoms appear) as a marker for being infected, the probabilities of becoming infected from the community or from a single infectious household member are estimated for various risk factor levels. Maximum likelihood procedures for estimating the model parameters are given. An individual may be classified with regard to level of susceptibility and level of infectiousness. The model is fitted to a combination of symptom and viral culture data from a rhinovirus epidemic in Tecumseh, Michigan. In general, it is observed that decreasing risk of infection is associated with increasing age.

Adult↗
PubMed1991

Reduced drug accumulation as the mechanism of extreme clinical resistance to methotrexate in the human T-cell leukemia xenograft, LALW-2.

The mechanisms were examined that underlie the extreme resistance to methotrexate (MTX) by near diploid leukemic T-cells (LALW-2) exposed to the drug only during the course of therapy administered to the patient of origin. Despite the LALW-2 cells being highly resistant to MTX (inhibitory dose for 50% of cells, more than 10(-3) mol/l), southern blot analysis did not show any amplification of the dihydrofolate reductase gene, nor was there any evidence, by comparison with drug-sensitive CCRF-CEM cells, that the gene was overexpressed. Kinetic analysis of dihydrofolate reductase activity in the presence of MTX provided no basis for attributing resistance in LALW-2 cells to a change in enzyme structure. By contrast, studies of MTX accumulation revealed that the LALW-2 cells accumulated significantly less drug than either CCRF-CEM cells or a MTX-resistant CCRF-CEM subline with a characterized transport defect. These data suggest that extreme MTX resistance in LALW-2 cells is mediated by reduced drug accumulation in the absence of any effect on the target enzyme.

Animals↗
PubMed1991

Direct and indirect effects in vaccine efficacy and effectiveness.

In 1915, Greenwood and Yule noted that for valid vaccine efficacy studies, exposure to infection in the vaccinated and the unvaccinated must be equal (Proc R Soc Med 1915;8(part 2):113-94). The direct effect of a vaccine, however, needs to be defined by the protection it confers given a specific amount of exposure to infection, not just a comparable exposure. In this paper, two classes of parameters are distinguished along lines differing from the conventional distinction between efficacy and effectiveness. Efficacy parameters attempt to control for exposure to infection and represent direct effects on individuals. Direct effectiveness parameters represent a mixture of direct effects on individuals and indirect effects in the population.

Environmental Exposure↗
PubMed1991

Estimation of vaccine efficacy in outbreaks of acute infectious diseases.

In a previous paper we defined the efficacy of a vaccine as 1-beta 1/beta 0, where beta 0 is the instantaneous probability of transmission of infection to an unvaccinated person exposed to a single infectious person, and beta 1 is similarly defined for a vaccinated person. We showed that under the conditions of an outbreak of an acute, directly transmitted infectious disease in a homogeneous and randomly mixing population, an estimate of this measure of vaccine efficacy is 1-[1n(1-A1)/1n(1-A0)], where A0 and A1 are the observed final attack rates among unvaccinated and vaccinated persons, respectively. In the present work we present an approximation for the standard error of this estimator, accounting for both the sampling and process variation. We extend the results of our previous paper to a stratified population, where the strata correspond to different levels of susceptibility and may have different vaccination coverage. We also consider populations that consist of small units (for example, households) where individuals mix primarily in these units. In this case, definition of vaccine efficacy is in terms of the within-unit transmission probabilities and is estimable by using transmission models for infectious diseases. We apply the estimation methods described above to data from influenza and measles outbreaks. We also examine, via a stochastic simulation study, the robustness of the vaccine efficacy estimators under various population structures and mixing patterns.

Adolescent↗
PubMed1991

Measures of the effects of vaccination in a randomly mixing population.

Vaccine efficacy in the field is often derived from the relative attack rates in the vaccinated and unvaccinated after an outbreak. In this paper, vaccine efficacy is defined in terms of the probability that the infectious agent is transmitted from an infected to a susceptible person, and a method for estimating it from the usual attack rate data is given. We explore two mechanisms of vaccine action defined by Smith et al, but include an underlying dynamic epidemic model of an acute directly transmitted disease. We show analytically that under the model in which the vaccine mechanism reduces the probability of infection given a certain exposure, vaccine efficacy based on the relative attack rates underestimates the protective effect of the vaccine based on the relative transmission probabilities. Under the other model in which the vaccine mechanism offers complete protection to a certain proportion of those vaccinated, and no protection to the other vaccinated proportion, the vaccine efficacy based on the relative attack rates will equal that based on the transmission probabilities. Parameters for the effectiveness of a vaccination programme are defined in terms of the direct and indirect benefit to a single person as well as the total and average benefit to the entire population, and derived from the dynamic model for an outbreak of an acute directly transmitted disease. These effects can also be estimated without an actual separate unvaccinated population, independent of assumptions about the vaccine mechanism. The variation of these measures as functions of the fraction of vaccinated people in the population is explored numerically.

Cohort Studies↗