Informing Building Strategies to Reduce Infectious Aerosol Transmission Risk by Integrating DNA Aerosol Tracers with Quantitative Microbial Risk Assessment.

Using aerosol-based tracers to estimate risk of infectious aerosol transmission aids in the design of buildings with adequate protection against aerosol transmissible pathogens, such as SARS-CoV-2 and influenza. We propose a method for scaling a SARS-CoV-2 bulk aerosol quantitative microbial risk assessment (QMRA) model for impulse emissions, coughing or sneezing, with aerosolized synthetic DNA tracer concentration measurements. With point-of-emission ratios describing relationships between tracer and respiratory aerosol emission characteristics (i.e., volume and RNA or DNA concentrations) and accounting for aerosolized pathogen loss of infectivity over time, we scale the inhaled pathogen dose and risk of infection with time-integrated tracer concentrations measured with a filter sampler. This tracer-scaled QMRA model is evaluated through scenario testing, comparing the impact of ventilation, occupancy, masking, and layering interventions on infection risk. We apply the tracer-scaled QMRA model to measurement data from an ambulatory care room to estimate the risk reduction resulting from HEPA air cleaner operation. Using DNA tracer measurements to scale a bulk aerosol QMRA model is a relatively simple method of estimating risk in buildings and can be applied to understand the impact of risk mitigation efforts.

Droplet Digital™ PCR quantitation of HER2 expression in FFPE breast cancer samples.

UNLABELLED: The human epidermal growth factor receptor 2 (HER2, also known as erbB2) gene is involved in signal transduction for cell growth and differentiation. It is a cell surface receptor tyrosine kinase and a proto-oncogene. Overexpression of HER2 is of clinical relevance in breast cancer due to its prognostic value correlating elevated expression with worsening clinical outcome. At the same time, HER2 assessment is also of importance because successful anti-tumor treatment with Herceptin® is strongly correlated with HER2 overexpression in the tumor (approximately 30% of all breast tumors overexpress HER2). In a comprehensive national study, Wolff et al. [1] state that "Approximately 20% of current HER2 testing may be inaccurate" which underscores the importance of developing more accurate methods to determine HER2 status. Droplet Digital™ PCR (ddPCR™) has the potential to improve upon HER2 measurements due to its ability to quantitate DNA and RNA targets with high precision and accuracy. Here we present a study which investigates whether ddPCR can be used to assess HER2 transcript levels in formalin-fixed paraffin embedded (FFPE) human breast tumors and whether these ddPCR measurements agree with prior assessments of these same samples by pathologists using immunohistochemistry (IHC) and in some cases fluorescence in situ hybridization (FISH). We also determined the copy number of HER2 in these samples as compared to the CEP17 reference gene. RESULTS: Clinical FFPE samples were successfully studied using ddPCR and compared to results from standard FISH and IHC methodology. The results demonstrate that ddPCR can rank order the samples in complete agreement with the current standard methods and that ddPCR has the added benefit of providing quantitative results, rather than relying on the expert skill of a seasoned pathologist for determination.

High-throughput droplet digital PCR system for absolute quantitation of DNA copy number.

Digital PCR enables the absolute quantitation of nucleic acids in a sample. The lack of scalable and practical technologies for digital PCR implementation has hampered the widespread adoption of this inherently powerful technique. Here we describe a high-throughput droplet digital PCR (ddPCR) system that enables processing of ~2 million PCR reactions using conventional TaqMan assays with a 96-well plate workflow. Three applications demonstrate that the massive partitioning afforded by our ddPCR system provides orders of magnitude more precision and sensitivity than real-time PCR. First, we show the accurate measurement of germline copy number variation. Second, for rare alleles, we show sensitive detection of mutant DNA in a 100,000-fold excess of wildtype background. Third, we demonstrate absolute quantitation of circulating fetal and maternal DNA from cell-free plasma. We anticipate this ddPCR system will allow researchers to explore complex genetic landscapes, discover and validate new disease associations, and define a new era of molecular diagnostics.

In vitro double transposition for DNA identification.

We present a double transposition technique that inserts two different transposons into target DNA to act as priming sites for amplifying the region between the two transposons for sequencing applications. Unlike some current sequencing approaches, the genome of the unknown target remains intact in this method. The transposition reaction, DNA repair, and subsequent sequencing were performed entirely in vitro, without the need for transformation into bacteria, and resulted in sequence homology with the plasmid DNA target. This approach can reduce the time required for the assay by more than a day compared with standard techniques and reduces the number of required enzymatic steps. In addition, the in vitro method enables transposition to be carried out in automated microfluidic platforms without the need for significant sample manipulation. As a demonstration of incorporating transposition techniques into high-throughput technologies, single transposition reactions were carried out in picoliter-sized droplets generated on a microfluidic platform.

Droplet Digital™ PCR Next-Generation Sequencing Library QC Assay.

Digital PCR is a valuable tool to quantify next-generation sequencing (NGS) libraries precisely and accurately. Accurately quantifying NGS libraries enable accurate loading of the libraries on to the sequencer and thus improve sequencing performance by reducing under and overloading error. Accurate quantification also benefits users by enabling uniform loading of indexed/barcoded libraries which in turn greatly improves sequencing uniformity of the indexed/barcoded samples. The advantages gained by employing the Droplet Digital PCR (ddPCR™) library QC assay includes the precise and accurate quantification in addition to size quality assessment, enabling users to QC their sequencing libraries with confidence.