Cross comparison of rapid mycoplasma detection platforms

The use of animal and plant derived raw materials in mammalian cell culture processes may provide a possible route of entry for adventitious contaminants such as mycoplasma. Mycoplasma contaminations of cell culture represent a serious challenge to the production of biotechnology derived therapeutics. The slow growing nature of mycoplasma can disguise their infection of cultures since cells may continue to proliferate, though at reduced levels and with lesser output of engineered protein. Rapid identification of mycoplasma contaminated cell cultures and materials enables a faster response time to prevent the spread of the contamination. We describe here the comparison of different mycoplasma detection methods: two nucleic acid-based technologies, the standard mycoplasma culture procedure, and a hybrid culture-quantitative PCR assay. In this study, a cell line infected with two species of mycoplasma was used to compare the different detection methods. Our data demonstrates that the two nucleic acid-based techniques are robust methods for detection of mycoplasma and have similar detection capability. In contrast, no mycoplasma was detected in the standard culture assay or in a hybrid culture-quantitative PCR assay. This shows a potential limitation of the culture assay that relies on the ability of mycoplasma to grow in broth media.     

Systematic evaluation of medium-throughput mRNA abundance platforms

Profiling of mRNA abundances with high-throughput platforms such as microarrays and RNA-seq has become an important tool in both basic and biomedical research. However, these platforms remain prone to systematic errors and have challenges in clinical and industrial applications. As a result, it is standard practice to validate a subset of key results using alternate technologies. Similarly, clinical and industrial applications typically involve transitions from a high-throughput discovery platform to medium-throughput validation ones. These medium-throughput validation platforms have high technical reproducibility and reduced sample input needs, and low sensitivity to sample quality (e.g., for processing FFPE specimens). Unfortunately, while medium-throughput platforms have proliferated, there are no comprehensive comparisons of them. Here we fill that gap by comparing two key medium-throughput platforms—NanoString''s nCounter Analysis System and ABI''s OpenArray System—to gold-standard quantitative real-time RT-PCR. We quantified 38 genes and positive and negative controls in 165 samples. Signal:noise ratios, correlations, dynamic range, and detection accuracy were compared across platforms. All three measurement technologies showed good concordance, but with divergent price/time/sensitivity trade-offs. This study provides the first detailed comparison of medium-throughput RNA quantification platforms and provides a template and a standard data set for the evaluation of additional technologies.     

Frequency and rationale of fine needle aspiration biopsy conversion to core biopsy as a result of onsite evaluation

OBJECTIVE: To measure the frequency and analyze the rationale and potential diagnostic benefits of converting the fine needle aspiration (FNA) procedure to core biopsy. STUDY DESIGN: The frequency of conversion to core biopsy was calculated over 13 months. Analysis of these cases was conducted in regard to the appropriateness for conversion and whether the core biopsy provided additional specific diagnostic information. RESULTS: During this period, the onsite triaging pathologist recommended FNA conversion to core biopsy in 31 of 821 procedures (3.7%). In 3 instances, the core biopsy could not be performed. The rationale for conversion in the remaining 28 cases (3.4%) included either scant aspirated material in 9 cases (32%) or an anticipated need for additional histologic material to further characterize the lesion in the other 19 (68%). In 27 cases (96%), the rationale for conversion was considered to be appropriate, and in 3 of these (11%) the core provided a change in diagnosis. Additional useful diagnostic information was identified in 12 cases (44%). CONCLUSION: Conversion to core biopsy during FNA is infrequent but justified in most cases. Appropriate utilization of this approach is helpful and may be cost effective.     

Haemopoietic progenitors in different parts of one femur perform different functions during regeneration

Femoral haemopoietic tissue was divided into cells released by flushing and cells released by grinding and washing flushed femora. The flushed femur contained 5 times more nucleated cells than the ground femur, 40 times more macrophage colony-forming cells and 6 times more developmentally late, day 8, and developmentally early, day 13, spleen colony-forming cells. However, the ground femur contained 2 times more developmentally early high proliferation potential colony-forming cells and 3 times more late ones. Haemopoietic regeneration of mice treated with fluorouracil was compared in samples obtained by flushing alone and grinding flushed femora. The number of nucleated cells recovered by flushing fell thirteen-fold by the sixth day after administration of the drug and the number recovered by grinding fell six-fold by the eighth day. Developmentally early high-proliferation-potential colony-forming cells which were recovered by grinding doubled their number in half the time taken by similar cells recovered by flushing. These observations are consistent with haemopoietic cells in different parts of the same bone performing different functions during regeneration. Large numbers of high-proliferation-potential colony-forming cells were not found in the circulation until 8 days after treatment with fluorouracil. Five days after mice had been treated with fluorouracil, when their blood forming systems were regenerating, early high-proliferation-potential colony-forming cells in one sample of marrow were derived from different founder cells than were late cells in the same sample. At the same time, early high-proliferation-potential colony-forming cells in the ground sample of a femur were derived from different founder cells than were cells at the same stage of development in the flushed sample of the femur. These observations are consistent with the view that haemopoietic regeneration after treatment with fluorouracil is due to the growth of few founder cells whose progeny have migrated little within 5 days of drug treatment.     

Genetic engineering approaches to improve posttranslational modification of biopharmaceuticals in different production platforms

The number of approved biopharmaceuticals, where product quality attributes remain of major importance, is increasing steadily. Within the available variety of expression hosts, the production of biopharmaceuticals faces diverse limitations with respect to posttranslational modifications (PTM), while different biopharmaceuticals demand different forms and specifications of PTMs for proper functionality. With the growing toolbox of genetic engineering technologies, it is now possible to address general as well as host- or biopharmaceutical-specific product quality obstacles. In this review, we present diverse expression systems derived from mammalians, bacteria, yeast, plants, and insects as well as available genetic engineering tools. We focus on genes for knockout/knockdown and overexpression for meaningful approaches to improve biopharmaceutical PTMs and discuss their applicability as well as future trends in the field.     

Cheap, rapid and efficient DNA extraction method to perform multilocus microsatellite genotyping on all Schistosoma mansoni stages

Schistosomes are endoparasites causing a serious human disease called schistosomiasis. The quantification of parasite genetic diversity is an essential component to understand the schistosomiasis epidemiology and disease transmission patterns. In this paper, we propose a novel assay for a rapid, low costly and efficient DNA extraction method of egg, larval and adult stages of Schistosoma mansoni. One euro makes possible to perform 60,000 DNA extraction reactions at top speed (only 15 min of incubation and 5 handling steps).     

Artifact due to differential error when cases and controls are imputed from different platforms

Including previously genotyped controls in a genome-wide association study can provide cost-savings, but can also create design biases. When cases and controls are genotyped on different platforms, the imputation needed to provide genome-wide coverage will introduce differential measurement error and may lead to false positives. We compared genotype frequencies of two healthy control groups from the Nurses’ Health Study genotyped on different platforms [Affymetrix 6.0 (n = 1,672) and Illumina HumanHap550 (n = 1,038)]. Using standard imputation quality filters, we observed 9,841 single-nucleotide polymorphisms (SNPs) out of 2,347,809 (0.4%) significant at the 5 × 10⁻⁸ level. We explored three methods for controlling for this Type I error inflation. One method was to remove platform effects using principal components; another was to restrict to SNPs of highest quality imputation; and a third was to genotype some controls alongside cases to exclude SNPs that are statistical artifact. The first method could not reduce the Type I error rate; the other two could dramatically reduce the error rate, although both required that a portion of SNPs be excluded from analysis. Ideally, the biases we describe would be eliminated at the design stage, by genotyping sufficient numbers of cases and controls on each platform. Researchers using imputation to combine samples genotyped on different platforms with severely unbalanced case–control ratios should be aware of the potential for inflated Type I error rates and apply appropriate quality filters. Every SNP found with genome-wide significance should be validated on another platform to verify that its significance is not an artifact of study design.     

Comparative evaluation of mass spectrometry platforms used in large-scale proteomics investigations

Researchers have several options when designing proteomics experiments. Primary among these are choices of experimental method, instrumentation and spectral interpretation software. To evaluate these choices on a proteome scale, we compared triplicate measurements of the yeast proteome by liquid chromatography tandem mass spectrometry (LC-MS/MS) using linear ion trap (LTQ) and hybrid quadrupole time-of-flight (QqTOF; QSTAR) mass spectrometers. Acquired MS/MS spectra were interpreted with Mascot and SEQUEST algorithms with and without the requirement that all returned peptides be tryptic. Using a composite target decoy database strategy, we selected scoring criteria yielding 1% estimated false positive identifications at maximum sensitivity for all data sets, allowing reasonable comparisons between them. These comparisons indicate that Mascot and SEQUEST yield similar results for LTQ-acquired spectra but less so for QSTAR spectra. Furthermore, low reproducibility between replicate data acquisitions made on one or both instrument platforms can be exploited to increase sensitivity and confidence in large-scale protein identifications.     

An analysis of identical single-nucleotide polymorphisms genotyped by two different platforms

The overlap of 94 single-nucleotide polymorphisms (SNP) among the 4,720 and 11,120 SNPs contained in the linkage panels of Illumina and Affymetrix, respectively, allows an assessment of the discrepancy rate produced by these two platforms. Although the no-call rate for the Affymetrix platform is approximately 8.6 times greater than for the Illumina platform, when both platforms make a genotypic call, the agreement is an impressive 99.85%. To determine if disputed genotypes can be resolved without sequencing, we studied recombination in the region of the discrepancy for the most discrepant SNP rs958883 (typed by Illumina) and tsc02060848 (typed by Affymetrix). We find that the number of inferred recombinants is substantially higher for the Affymetrix genotypes compared to the Illumina genotypes. We illustrate this with pedigree 10043, in which 3 of 7 versus 0 of 7 offspring must be double recombinants using the genotypes from the Affymetrix and the Illumina platforms, respectively. Of the 36 SNPs with one or more discrepancies, we identified a subset that appears to cluster in families. Some of this clustering may be due to the presence of a second segregating SNP that obliterates a XbaI site (the restriction enzyme used in the Affymetrix platform), resulting in a fragment too long (>1,000 bp) to be amplified.     

How to perform meaningful estimates of genetic effects

Although the genotype-phenotype map plays a central role both in Quantitative and Evolutionary Genetics, the formalization of a completely general and satisfactory model of genetic effects, particularly accounting for epistasis, remains a theoretical challenge. Here, we use a two-locus genetic system in simulated populations with epistasis to show the convenience of using a recently developed model, NOIA, to perform estimates of genetic effects and the decomposition of the genetic variance that are orthogonal even under deviations from the Hardy-Weinberg proportions. We develop the theory for how to use this model in interval mapping of quantitative trait loci using Halley-Knott regressions, and we analyze a real data set to illustrate the advantage of using this approach in practice. In this example, we show that departures from the Hardy-Weinberg proportions that are expected by sampling alone substantially alter the orthogonal estimates of genetic effects when other statistical models, like F₂ or G2A, are used instead of NOIA. Finally, for the first time from real data, we provide estimates of functional genetic effects as sets of effects of natural allele substitutions in a particular genotype, which enriches the debate on the interpretation of genetic effects as implemented both in functional and in statistical models. We also discuss further implementations leading to a completely general genotype-phenotype map.     

Bioprocessing of bacteriophages via rapid drying onto microcrystals

We present an alternative bioprocess for bacteriophages involving room temperature coprecipitation of an aqueous mixture of phage (Siphoviridae) and a crystallizable carrier (glutamine or glycine) in excess of water miscible organic solvent (isopropanol or isobutanol). The resultant suspension of phage-coated microcrystals can be harvested by filtration and the residual solvent removed rapidly by air-drying at a relative humidity of 75%. Albumin or trehalose added at 5% w/w of the crystalline carrier provide for better stabilization of the phage during co-precipitation. Free-flowing dry powders generated from an aqueous solution of phage (～13 log(10) pfu/mL) can be reconstituted in the same aqueous volume to a phage titer of almost 10 log(10) pfu/mL; high enough to permit subsequent formulation steps following bioprocessing. The phage-coated microcrystals remain partially stable at room temperature for at least one month, which compares favorably with phage immobilized into polyester microcarriers or lyophilized with excipient (1-5% polyethylene glycol 6000 or 0.1-0.5 M sucrose). We anticipate that this bioprocessing technique will have application to other phage families as required for the development of phage therapies.     

Comparison of biosensor platforms in the evaluation of high affinity antibody-antigen binding kinetics

The acquisition of reliable kinetic parameters for the characterization of biomolecular interactions is an important component of the drug discovery and development process. While several benchmark studies have explored the variability of kinetic rate constants obtained from multiple laboratories and biosensors, a direct comparison of these instruments' performance has not been undertaken, and systematic factors contributing to data variability from these systems have not been discussed. To address these questions, a panel of ten high-affinity monoclonal antibodies was simultaneously evaluated for their binding kinetics against the same antigen on four biosensor platforms: GE Healthcare's Biacore T100, Bio-Rad's ProteOn XPR36, ForteBio's Octet RED384, and Wasatch Microfluidics's IBIS MX96. We compared the strengths and weaknesses of these systems and found that despite certain inherent systematic limitations in instrumentation, the rank orders of both the association and dissociation rate constants were highly correlated between these instruments. Our results also revealed a trade-off between data reliability and sample throughput. Biacore T100, followed by ProteOn XPR36, exhibited excellent data quality and consistency, whereas Octet RED384 and IBIS MX96 demonstrated high flexibility and throughput with compromises in data accuracy and reproducibility. Our results support the need for a “fit-for-purpose” approach in instrument selection for biosensor studies.     

Comparative evaluation of current peptide production platforms used in absolute quantification in proteomics

Absolute quantification of peptides by mass spectrometry requires a reference, frequently using heavy isotope-coded peptides as internal standards. These peptides have traditionally been generated by chemical stepwise synthesis. Recently a new way to supply such peptides was described in which nucleotide sequences coding for the respective peptides are concatenated into a synthetic gene (QconCAT). These QconCATs are then expressed to produce a polypeptide consisting of concatenated peptides, purified, quantified by various methods, and then digested to yield the final internal standard peptides. Although both of these methods for peptide production are routinely used for absolute quantifications, there is currently no information regarding the accuracy of the quantifications made in each case. In this study, we used sets of synthetic and biological peptides in parallel to evaluate the accuracy of either method. We also addressed some technical issues regarding the preparation and proper utilization of such standard peptides. Twenty-five peptides derived from the Caenorhabditis elegans proteome were selected for this study. Twenty-four were successfully chemically synthesized. Five QconCAT genes were designed, each a concatenation of the same 25 peptides but each in separate, different randomized order, and expressed via in vitro translation reactions that contained heavy isotope-labeled lysine and arginine. Three of the five QconCATs were successfully produced. Different digestion conditions, including various detergents and incubation conditions, were tested to find those optimal for the generation of a reproducible and accurate reference sample mixture. All three QconCAT polypeptides were then digested using the optimized conditions and then mixed in a 1:1 ratio with their synthetic counterparts. Multireaction monitoring mass spectrometry was then used for quantification. Results showed that the digestion protocol had a significant impact on equimolarity of final peptides, confirming the need for optimization. Under optimal conditions, however, most QconCAT peptides were produced at an equimolar ratio. A few QconCAT-derived peptides were largely overestimated due to problems with solubilization or stability of the synthetic peptides. Although the order in which the peptide sequences appeared in the QconCAT sequence proved to affect the success rate of in vitro translation, it did not significantly affect the final peptide yields. Overall neither the chemical synthesis nor the recombinant genetic approach proved to be superior as a method for the production of reference peptides for absolute quantification.     

Production of anti-idiotype antibodies for deoxynivalenol and their evaluation with three immunoassay platforms

Immunoassays for deoxynivalenol (DON) that involve binding to DON-specific antibodies have been widely developed. In such assays, the responses of samples are generally compared with calibration curves generated by using DON in competition with labeled reagents such as enzymatic or fluorescent conjugates of the toxin. However, materials that mimic the toxin can also be used, provided that they compete effectively with the labeled reagents for the DON-specific antibodies. Examples include certain types of anti-idiotype antibodies, obtained by the immunization of animals with toxin-specific antibodies. In the present work, anti-idiotype antibodies were developed which mimicked DON in the ability to bind to a DON-specific monoclonal antibody (Mab). Fab fragments of the Mab (Ab1) were used to immunize rabbits. Sera were screened by competitive direct enzyme linked immunosorbent assay (CD-ELISA) for the presence of anti-idiotype antibodies (Ab2). In order to determine the most effective screening format and also the potential efficacy in various forms of biosensors, the sera were further evaluated in biolayer interferometry (BLI) and fluorescence polarization immunoassay (FPIA) formats. All three formats were used to demonstrate the presence of anti-idiotypes capable of binding to the paratope of the DON antibody (subtypes Ab2β or Ab2γ). Such materials have the potential to replace DON as calibrants in immunoassays for this toxin.