Digital PCR: Principles and Applications

Techniques for assessing telomere length: A methodological review

Telomeres are located at the ends of chromosomes and have specific sequences with a distinctive structure that safeguards genes. They possess capping structures that protect chromosome ends from fusion events and ensure chromosome stability. Telomeres shorten in length during each cycle of cell division. When this length reaches a certain threshold, it can lead to genomic instability, thus being implicated in various diseases, including cancer and neurodegenerative disorders. The possibility of telomeres serving as a biomarker for aging and age-related disease is being explored, and their significance is still under study. This is because post-mitotic cells, which are mature cells that do not undergo mitosis, do not experience telomere shortening due to age. Instead, other causes, for example, exposure to oxidative stress, can directly damage the telomeres, causing genomic instability. Nonetheless, a general agreement has been established that measuring telomere length offers valuable insights and forms a crucial foundation for analyzing gene expression and epigenetic data. Numerous approaches have been developed to accurately measure telomere lengths. In this review, we summarize various methods and their advantages and limitations for assessing telomere length.

DMPK perspective on quantitative model analysis for chimeric antigen receptor cell therapy: Advances and challenges

Chimeric antigen receptor (CAR) cells are genetically engineered immune cells that specifically target tumor-associated antigens and have revolutionized cancer treatment, particularly in hematological malignancies, with ongoing investigations into their potential applications in solid tumors. This review provides a comprehensive overview of the current status and challenges in drug metabolism and pharmacokinetics (DMPK) for CAR cell therapy, specifically emphasizing on quantitative modeling and simulation (M&S). Furthermore, the recent advances in quantitative model analysis have been reviewed, ranging from clinical data characterization to mechanism-based modeling that connects in vitro and in vivo nonclinical and clinical study data. Additionally, the future perspectives and areas for improvement in CAR cell therapy translation have been reviewed. This includes using formulation quality considerations, characterization of appropriate animal models, refinement of in vitro models for bottom-up approaches, and enhancement of quantitative bioanalytical methodology. Addressing these challenges within a DMPK framework is pivotal in facilitating the translation of CAR cell therapy, ultimately enhancing the patients' lives through efficient CAR cell therapies.

Establishment of a chip digital PCR detection method for canine circovirus

Canine circovirus (CanineCV), which is a new mammalian circovirus first reported in the United States in 2012, mainly causes diarrhea and vomiting in dogs. As CanineCV evolves and new subtypes emerge, there is an urgent need for new detection technologies to improve the sensitivity and detection rates of viruses in complex scenarios. A chip digital PCR(cdPCR) assay was established for the detection of CanineCV in this study. The results showed good reproducibility, specificity and a linear relationship; the minimum detection limit of CanineCV by cdPCR was 6.62 copies/μL, which is 10 times more sensitive than quantitative real-time PCR (qPCR). The qPCR-positive detection rate was 1 %, while CanineCV cdPCR (2.1 %) exhibited a greater positive detection rate. Fifteen complete genomes were sequenced and subdivided into CanineCV-1 and CanineCV-3. In conclusion, we developed a rapid, reliable, and specific cdPCR method for screening and monitoring canine CV.

Immunogenicity and Protective Efficacy of Psoralen-Inactivated SARS-CoV-2 Vaccine in Nonhuman Primates

COVID-19 caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has significantly impacted public health and the economy worldwide. Most of the currently licensed COVID-19 vaccines act by inhibiting the receptor-binding function of the SARS-CoV-2 spike protein. The constant emergence of SARS-CoV-2 variants resulting from mutations in the receptor-binding domain (RBD) leads to vaccine immune evasion and underscores the importance of broadly acting COVID-19 vaccines. Inactivated whole virus vaccines can elicit broader immune responses to multiple epitopes of several antigens and help overcome such immune evasions. We prepared a psoralen-inactivated SARS-CoV-2 vaccine (SARS-CoV-2 PsIV) and evaluated its immunogenicity and efficacy in nonhuman primates (NHPs) when administered with the Advax-CpG adjuvant. We also evaluated the SARS-CoV-2 PsIV as a booster shot in animals vaccinated with a DNA vaccine that can express the full-length spike protein. The Advax-CpG-adjuvanted SARS-CoV-2 PsIV elicited a dose-dependent neutralizing antibody response in the NHPs, as measured using a serum microneutralization assay against the SARS-CoV-2 Washington strain and the Delta variant. The animals vaccinated with the DNA vaccine followed by a boosting dose of the SARS-CoV-2 PsIV exhibited the highest neutralizing antibody responses and were able to quickly clear infection after an intranasal challenge with the SARS-CoV-2 Delta variant. Overall, the data show that the Advax-CpG-adjuvanted SARS-CoV-2 PsIV, either by itself or as a booster shot following nucleic acid (NA) vaccines, has the potential to protect against emerging variants.

A ddPCR platform based on a microfluidic chip with a dual-function flow-focusing structure for sample-to-result DNA quantification analysis

Droplet digital PCR (ddPCR) is a powerful method for absolute nucleic acid quantification with high precision and accuracy. However, complicated operational steps have hampered the use and diffusion of ddPCR. Therefore, an automated, easy-to-use, low-sample-consumption, and portable ddPCR platform is urgently needed. This paper proposes a microfluidic ddPCR platform based on a microfluidic chip that can realize the sample-to-result function by switching the rotary valve, achieving the dual function of the flow-focusing structure for droplet generation and readout. Sample, generation oil, and analysis oil were pre-added to the reservoirs. Droplets were generated due to focusing flow, and after passing through the integrated temporary storage bin in the rotary valve, the droplets and oil subsequently entered the collecting tube, improving the droplet-to-oil volume ratio for enhanced thermal cycle performance. Droplets with an average diameter of 107.44 μm and a CV of 2.38% were generated using our chip under the optimal pressures. High-performance thermal cycling was achieved through improvements of the droplet-to-oil volume ratio of the sample, the integrated heating lid, the pure copper heating base, and the temperature-controlling algorithm. Gradient quantification experiments were conducted for the HER2 and CEP17 genes extracted from breast cancer cells, yielding strong linear correlations with R2 values of 0.9996 for FAM and 0.9989 for CY5. Moreover, pronounced linearity was obtained between the detected concentrations of HER2 and CEP17, indicated by a slope of 1.0091 and an R2 of 0.9997, signifying consistent HER2 : CEP17 ratios across various sample dilutions. The outcomes of the quantitative analysis, encompassing the dynamic range and the consistency of the HER2 : CEP17 ratio using our ddPCR platform, meet the standards required for breast cancer assessment and therapy. Our ddPCR platform is automated, portable, and capable of stable droplet generation, high-efficiency amplification, realization of the sample-to-result function based on dual-function flow-focusing structure, and accuracy absolute quantification, underscoring its significant potential for ddPCR analysis in clinical diagnostics.

Applications of Digital Polymerase Chain Reaction (dPCR) in Molecular and Clinical Testing

BACKGROUND

Digital polymerase chain reaction (dPCR) is an accurate and sensitive molecular method that can be used in clinical diagnostic, prognostic, and predictive tests. The key component of the dPCR method is the partitioning of a single reaction into many thousands of droplets, nanochannels or other nano- or picoliter-sized reactions. This results in high enough sensitivity to detect rare nucleic acid targets and provides an absolute quantification of target sequences or alleles compared to other PCR-based methods.

CONTENT

An increasing number of dPCR platforms have been introduced commercially in recent years and more are being developed. These platforms differ in the method of partitioning, degree of automation, and multiplexing capabilities but all can be used in similar ways for sensitive and highly accurate quantification of a variety of nucleic acid targets. Currently, clinical applications of dPCR include oncology, microbiology and infectious disease, genetics, and prenatal/newborn screening. Commercially available tests for clinical applications are being developed for variants with diagnostic, prognostic, and therapeutic significance in specific disease types.

SUMMARY

The power of dPCR technology relies on the partitioning of the reactions and results in increased sensitivity and accuracy compared to qPCR. More recently, the sensitivity of dPCR has been applied to the detection of known variants in cell-free DNA and circulating tumor DNA. Future clinical applications of dPCR include liquid biopsy, treatment resistance detection, screening for minimal residual disease, and monitoring allograft engraftment in transplanted patients.

A Droplet Digital PCR-Based Approach for Quantitative Analysis of the Adulteration of Atlantic Salmon with Rainbow Trout

Low-cost fish species are often used to adulterate or substitute for Atlantic salmon products, posing a serious threat to market order and public health. Hence, reliable techniques are urgently needed to detect Atlantic salmon adulteration. In this study, a precise method for identifying and quantifying adulterated Atlantic salmon with rainbow trout based on droplet digital PCR (ddPCR) testing was developed. Species-specific primers and probes were designed targeting the single-copy nuclear gene myoglobin of two salmonids. A quantitative formula for calculating the mass fraction of adulterated Atlantic salmon with rainbow trout was established based on a one-step conversion strategy, in which the DNA copy number ratios were directly transformed to meat mass fractions by introducing a fixed constant (the transfer coefficient). The dynamic range of the established ddPCR method was from 1% to 90%, with a limit of detection (LOD) of 0.2% and a limit of quantification (LOQ) of 0.8% for rainbow trout in Atlantic salmon, respectively. The quantification method demonstrated an acceptable level of repeatability and reproducibility, as the values of the relative standard deviation (RSD) for the tested meat mixtures with the known fractions were all less than 5%. Thermal and freezing treatments, as well as adding food additives within the recommended dosage limits, had no significant effect on the quantification accuracy. The method was successfully applied to detect rainbow trout adulteration in commercial raw and processed Atlantic salmon products. In comparison to real-time quantitative PCR (qPCR) testing, the established ddPCR method exhibited a higher level of stability and accuracy. Overall, the ddPCR-based quantitative method exhibited high levels of accuracy, stability, sensitivity, and practicability, suitable for applications in the routine surveillance and quality assurance of salmon products.

Digital PCR: a tool in clostridial mutant selection and detection

The ClosTron mutagenesis system has enabled researchers to efficiently edit the clostridial genome. Since site-specific insertion of the mobile ClosTron insert may cause errors, validation is key. In this paper we describe the use of digital PCR (dPCR) as an alternative tool in selecting clostridial mutant strains. Clostridium perfringens chitinase mutant strains were constructed in which the mobile ClosTron intron was inserted into one of the chitinase genes. On-target insertion of the mobile intron was validated through conventional PCR. In order to confirm the absence of off-target insertions, dPCR was used to determine the amount of the ClosTron intron as well as the amount of a reference gene, located in close proximity to the interrupted gene. Subsequently, mutant strains containing an equivalent amount of both genes were selected as these do not contain additional off-target mobile ClosTron inserts. The outcome of this selection procedure was confirmed through a validated PCR-based approach. In addition to its application in mutant selection, dPCR can be used in other aspects of clostridial research, such as the distinction and easy quantification of different types of strains (wildtype vs. mutant) in complex matrices, such as faecal samples, a process in which other techniques are hampered by bacterial overgrowth (plating) or inhibition by matrix contaminants (qPCR). This research demonstrates that dPCR is indeed a high-throughput method in the selection of clostridial insertion mutants as well as a robust and accurate tool in distinguishing between wildtype and mutant C. perfringens strains, even in a complex matrix such as faeces. KEY POINTS: • Digital PCR as an alternative in ClosTron mutant selection • Digital PCR is an accurate tool in bacterial quantification in a complex matrix • Digital PCR is an alternative tool with great potential to microbiological research.

Absolute Quantification of mRNA Isoforms in Adult Stem Cells Using Microfluidic Digital PCR

Adult stem cells play key roles in homeostasis and tissue repair. These cells are regulated by a tight control of transcriptional programs. For example, muscle stem cells (MuSCs), located beneath the basal lamina, exist in the quiescent state but can transition to an activated, proliferative state upon injury. The control of MuSC state depends on the expression levels of myogenic transcription factors. Recent studies revealed the presence of different mRNA isoforms, with distinct biological regulation. Quantifying the exact expression levels of the mRNA isoforms encoding these myogenic transcription factors is therefore key to understanding how MuSCs switch between cell states. Previously, quantitative real-time polymerase chain reaction (qRT-PCR) has been used to quantify RNA expression levels. However, qRT-PCR depends on large amounts of RNA input and only measures relative abundance. Here, we present a protocol for the absolute quantification of mRNA isoforms using microfluidic digital PCR (mdPCR). Primary MuSCs isolated from individual skeletal muscles (gastrocnemius and masseter) are lysed, and their RNA is reverse-transcribed into cDNA and copied into double-stranded DNA. Following exonuclease I digestion to remove remaining single-stranded DNA, the samples are loaded onto a mdPCR chip with TaqMan probes targeting the mRNA isoforms of interest, whereupon target molecules are amplified in nanoliter chambers. We demonstrate that mdPCR can give exact molecule counts per cell for mRNA isoforms encoding the myogenic transcription factor Pax3. This protocol enables the absolute quantification of low abundant mRNA isoforms in a fast, precise, and reliable way.

A Chamber-Based Digital PCR Based on a Microfluidic Chip for the Absolute Quantification and Analysis of KRAS Mutation

The Kirsten rat sarcoma virus gene (KRAS) is the most common tumor in human cancer, and KRAS plays an important role in the growth of tumor cells. Normal KRAS inhibits tumor cell growth. When mutated, it will continuously stimulate cell growth, resulting in tumor development. There are currently few drugs that target the KRAS gene. Here, we developed a microfluidic chip. The chip design uses parallel fluid channels combined with cylindrical chamber arrays to generate 20,000 cylindrical microchambers. The microfluidic chip designed by us can be used for the microsegmentation of KRAS gene samples. The thermal cycling required for the PCR stage is performed on a flat-panel instrument and detected using a four-color fluorescence system. "Glass-PDMS-glass" sandwich structure effectively reduces reagent volatilization; in addition, a valve is installed at the sample inlet and outlet on the upper layer of the chip to facilitate automatic control. The liquid separation performance of the chip was verified by an automated platform. Finally, using the constructed KRAS gene mutation detection system, it is verified that the chip has good application potential for digital polymerase chain reaction (dPCR). The experimental results show that the chip has a stable performance and can achieve a dynamic detection range of four orders of magnitude and a gene mutation detection of 0.2%. In addition, the four-color fluorescence detection system developed based on the chip can distinguish three different KRAS gene mutation types simultaneously on a single chip.

Overview on Therapeutic Options in Uncommon EGFR Mutant Non-Small Cell Lung Cancer (NSCLC): New Lights for an Unmet Medical Need

The majority of epidermal growth factor receptor (EGFR) mutations (85-90%) are exon 19 deletions and L858R point mutations of exon 21, characterized by high sensitivity to EGFR-tyrosine kinase inhibitors (TKIs). Less is known about uncommon mutations (10-15% of EGFR mutations). The predominant mutation types in this category include exon 18 point mutations, exon 21 L861X, exon 20 insertions, and exon 20 S768I. This group shows a heterogeneous prevalence, partly due to different testing methods and to the presence of compound mutations, which in some cases can lead to shorter overall survival and different sensitivity to different TKIs compared to simple mutations. Additionally, EGFR-TKI sensitivity may also vary depending on the specific mutation and the tertiary structure of the protein. The best strategy remains uncertain, and the data of EGFR-TKIs efficacy are based on few prospective and some retrospective series. Newer investigational agents are still under study, and there are no other approved specific treatments targeting uncommon EGFR mutations. Defining the best treatment option for this patient population remains an unmet medical need. The objective of this review is to evaluate existing data on the outcomes, epidemiology, and clinical characteristics of lung cancer patients with rare EGFR mutations, with a focus on intracranial activity and response to immunotherapy.

Novel Cell Quantification Method Using a Single Surrogate Calibration Curve Across Various Biological Samples

Quantitative polymerase chain reaction (qPCR) is generally used to quantify transplanted cell therapy products in biological samples. As the matrix effects on PCR amplification and variability in DNA recovery from biological samples are well-known limitations that hinder the assay's performance, a calibration curve is conventionally established for each matrix. Droplet digital PCR (ddPCR) is based on the endpoint assay and advantageous in avoiding matrix effects. Moreover, the use of an external control gene may correct assay fluctuations to minimize the effects caused by inconsistent DNA recovery. In this study, we aimed to establish a novel and robust ddPCR method capable of quantifying human cells across various mouse biological samples using a single surrogate calibration curve in combination with an external control gene and DNA recovery normalization. Acceptable accuracy and precision were observed for quality control samples from different tissues, indicating the excellent quantitative and versatile potential of the developed method. Furthermore, the established method enabled the evaluation of human CD8⁺ T cell biodistribution in immunodeficient mice. Our findings provide new insights into the use of ddPCR-based quantification methods in biodistribution studies of cell therapy products.

Genetic and Molecular Quality Control of Genetically Engineered Mice

Genetically engineered mice are used as avatars to understand mammalian gene function and develop therapies for human disease. During genetic modification, unintended changes can occur, and these changes may result in misassigned gene-phenotype relationships leading to incorrect or incomplete experimental interpretations. The types of unintended changes that may occur depend on the allele type being made and the genetic engineering approach used. Here we broadly categorize allele types as deletions, insertions, base changes, and transgenes derived from engineered embryonic stem (ES) cells or edited mouse embryos. However, the methods we describe can be adapted to other allele types and engineering strategies. We describe the sources and consequ ences of common unintended changes and best practices for detecting both intended and unintended changes by screening and genetic and molecular quality control (QC) of chimeras, founders, and their progeny. Employing these practices, along with careful allele design and good colony management, will increase the chance that investigations using genetically engineered mice will produce high-quality reproducible results, to enable a robust understanding of gene function, human disease etiology, and therapeutic development.

Epstein-Barr virus miR-BART2-5p and miR-BART11-5p regulate cell proliferation, apoptosis, and migration by targeting RB and p21 in gastric carcinoma

Epstein-Barr virus (EBV) was the first tumor virus discovered in humans and can cause various types of tumors. Molecular classification suggests that EBV-associated gastric cancer (EBVaGC) is a unique subtype of gastric cancer.EBV was also the first virus found to encode its own microRNAs. However, the functions of many miRNAs remain unknown. This study investigated the roles and targets of miR-BART2-5p (BART2-5p) and miR-BART11-5p (BART11-5p) in EBVaGC. The expression of RB and p21 in EBVaGC and EBV negative GC (EBVnGC) cells was evaluated by western blotting. Expression of BART2-5p and BART11-5p in EBVaGC cells was evaluated by droplet digital PCR. The effects of BART2-5p or BART11-5p and their potential mechanisms were further investigated using cell counting kit-8, colony formation assay, flow cytometry analysis, and transwell assay. BART2-5p and BART11-5p were abundantly expressed and RB and p21 were downregulated in EBVaGC cells. BART2-5p regulates RB and p21 expression by directly targeting them. BART11-5p regulates RB expression by directly targeting RB. Both BART2-5p and BART11-5p promoted proliferation and migration of gastric cancer cells, while inhibiting apoptosis and promoting S-phase arrest of the cell cycle. Thus, BART2-5p and BART11-5p play important roles in promoting proliferation and migration, and inhibiting apoptosis in EBVaGC by targeting RB and p21, thus providing new potential therapeutic targets for EBVaGC.

Digital PCR as a New Method for Minimal Residual Disease Monitoring and Treatment Free Remission Management in Chronic Myeloid Leukemia Patients: Is It Reliable?

The effective and sensitive monitoring of Minimal Residual Disease or Measurable Residual Disease (MRD) is a very important aspect in the management of patients affected by hematologic malignancies. The recent availability of new technologies has opened to the improvement of MRD monitoring. It is particularly relevant in patients affected by Chronic Myeloid Leukemia (CML). MRD monitoring is key in the management of CML patients thanks to the efficacy of TKIs therapy. Moreover, the policies of TKIs discontinuation aimed at treatment free remission are strongly based on the good selection of patients eligible for stopping TKIs therapy. The recently described application of digital PCR in CML patients monitoring seems to improve the accuracy and precision in the identification of optimal responders. The present review reports an overview on the application of digital PCR in the monitoring of MRD in CML and its impact on TKIs discontinuation trials and, consequently, on TFR success.

Advances in liquid biopsy in neuroblastoma

Even with intensive treatment of high-risk neuroblastoma (NB) patients, half of high-risk NB patients still relapse. New therapies targeting the biological characteristics of NB have important clinical value for the personalized treatment of NB. However, the current biological markers for NB are mainly analyzed by tissue biopsy. In recent years, circulating biomarkers of NB based on liquid biopsy have attracted more and more attention. This review summarizes the analytes and methods for liquid biopsy of NB. We focus on the application of liquid biopsy in the diagnosis, prognosis assessment, and monitoring of NB. Finally, we discuss the prospects and challenges of liquid biopsy in NB.

A Digital Microfluidic RT-qPCR Platform for Multiple Detections of Respiratory Pathogens

The coronavirus disease 2019 pandemic has spread worldwide and caused more than six million deaths globally. Therefore, a timely and accurate diagnosis method is of pivotal importance for controlling the dissemination and expansions. Nucleic acid detection by the reverse transcription-polymerase chain reaction (RT-PCR) method generally requires centralized diagnosis laboratories and skilled operators, significantly restricting its use in rural areas and field settings. The digital microfluidic (DMF) technique provides a better option for simultaneous detections of multiple pathogens with fewer specimens and easy operation. In this study, we developed a novel digital microfluidic RT-qPCR platform for multiple detections of respiratory pathogens. This method can simultaneously detect eleven respiratory pathogens, namely, mycoplasma pneumoniae (MP), chlamydophila pneumoniae (CP), streptococcus pneumoniae (SP), human respiratory syncytial virus A (RSVA), human adenovirus (ADV), human coronavirus (HKU1), human coronavirus 229E (HCoV-229E), human metapneumovirus (HMPV), severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), influenza A virus (FLUA) and influenza B virus (FLUB). The diagnostic performance was evaluated using positive plasmids samples and clinical specimens compared with off-chip individual RT-PCR testing. The results showed that the limit of detections was around 12 to 150 copies per test. The true positive rate, true negative rate, positive predictive value, negative predictive value, and accuracy of DMF on-chip method were 93.33%, 100%, 100%, 99.56%, and 99.85%, respectively, as validated by the off-chip RT-qPCR counterpart. Collectively, this study reported a cost-effective, high sensitivity and specificity on-chip DMF RT-qPCR system for detecting multiple respiratory pathogens, which will greatly contribute to timely and effective clinical management of respiratory infections in medical resource-limited settings.

The Future of ctDNA-Defined Minimal Residual Disease: Personalizing Adjuvant Therapy in Colorectal Cancer

Our understanding of the diagnostic and prognostic use of circulating tumor DNA (ctDNA) in colorectal cancer (CRC) has broadly expanded over the past few years. The utilization of ctDNA to detect minimal residual disease is currently being employed across the continuum of cancer care. The lead-time of ctDNA positivity to radiographic recurrence in stage I to III CRC is up to 9 months on average, which provides a therapeutic window for a group of high-risk patients who will ultimately recur. There are several ongoing prospective clinical trials that investigate whether ctDNA can be used as an integral biomarker to risk stratify CRC patients and guide adjuvant treatment decisions. In this review, we summarize the evidence supporting the promise of ctDNA-defined MRD in CRC and highlight the current ctDNA guided adjuvant prospective clinical trials.

Molecular Diagnostic Tools Applied for Assessing Microbial Water Quality

Microbial water quality is of vital importance for human, animal, and environmental health. Notably, pathogenically contaminated water can result in serious health problems, such as waterborne outbreaks, which have caused huge economic and social losses. In this context, the prompt detection of microbial contamination becomes essential to enable early warning and timely reaction with proper interventions. Recently, molecular diagnostics have been increasingly employed for the rapid and robust assessment of microbial water quality implicated by various microbial pollutants, e.g., waterborne pathogens and antibiotic-resistance genes (ARGs), imposing the most critical health threats to humans and the environment. Continuous technological advances have led to constant improvements and expansions of molecular methods, such as conventional end-point PCR, DNA microarray, real-time quantitative PCR (qPCR), multiplex qPCR (mqPCR), loop-mediated isothermal amplification (LAMP), digital droplet PCR (ddPCR), and high-throughput next-generation DNA sequencing (HT-NGS). These state-of-the-art molecular approaches largely facilitate the surveillance of microbial water quality in diverse aquatic systems and wastewater. This review provides an up-to-date overview of the advancement of the key molecular tools frequently employed for microbial water quality assessment, with future perspectives on their applications.

Extensive allele mining discovers novel genetic diversity in the loci controlling frost tolerance in barley

Exome sequencing-based allele mining for frost tolerance suggests HvCBF14 rather than CNV at Fr-H2 locus is the main responsible of frost tolerance in barley. Wild relatives, landraces and old cultivars of barley represent a reservoir of untapped and potentially important genes for crop improvement, and the recent sequencing technologies provide the opportunity to mine the existing genetic diversity and to identify new genes/alleles for the traits of interest. In the present study, we use frost tolerance and vernalization requirement as case studies to demonstrate the power of allele mining carried out on exome sequencing data generated from > 400 barley accessions. New deletions in the first intron of VRN-H1 were identified and linked to a reduced vernalization requirement, while the allelic diversity of HvCBF2a, HvCBF4b and HvCBF14 was investigated by combining the analysis of SNPs and read counts. This approach has proven very effective to identify gene paralogs and copy number variants of HvCBF2 and the HvCBF4b-HvCBF2a segment. A multiple linear regression model which considers allelic variation at these genes suggests a major involvement of HvCBF14, rather than copy number variation of HvCBF4b-HvCBF2a, in controlling frost tolerance in barley. Overall, the present study provides powerful resource and tools to discover novel alleles at relevant genes in barley.

Molecular Epidemiology of Ovine Papillomavirus Infections Among Sheep in Southern Italy

Ovine papillomaviruses (OaPVs) were detected and quantified, for the first time, using droplet digital polymerase chain reaction (ddPCR) and real-time quantitative PCR (qPCR) via blood samples of 165 clinically healthy sheep. OaPV DNA was detected in 126 blood samples (~76.4%). DdPCR detected OaPV DNA in 124 samples; in only two additional samples positive for real-time qPCR, ddPCR failed to detect the presence of any OaPVs. In 70 of the positive samples (~55.6%), a single OaPV infection was observed, 12 of which were caused by OaPV1 (~17.1%) and 14 by OaPV2 (20%). OaPV3 was responsible for 19 single infections (~27.1%), and OaPV4 for 25 single infections (~35.7%). Multiple OaPV coinfections were observed in 56 (~44.4%) positive samples. OaPV coinfections caused by two genotypes were observed in 31 positive samples (~55.4%), with dual OaPV3/OaPV4 infection being the most prevalent as seen in 11 blood samples. In addition, five OaPV1/OaPV4, four OaPV1/OaPV2, four OaPV2/OaPV3, four OaPV1/OaPV3, and three OaPV2/OaPV4 dual coinfections were also detected. OaPV coinfections by triple and quadruple genotypes were detected in 24 (~42.8%) and only one (~1.8%) of coinfected blood samples, respectively. Multiple infections caused by OaPV1/OaPV3/OaPV4 genotypes were the most prevalent, as observed in 12 (50%) blood samples harboring triple OaPV infections. This study showed that ddPCR is the most sensitive and accurate assay for OaPV detection and quantification thus outperforming real-time qPCR in terms of sensitivity and specificity. Therefore, ddPCR may represent the molecular diagnostic tool of choice, ultimately providing useful insights into OaPV molecular epidemiology and field surveillance.

Diagnostic Techniques for COVID-19: A Mini-review of Early Diagnostic Methods

The outbreak of severe pneumonia at the end of 2019 was proved to be caused by the SARS-CoV-2 virus spreading out the world. And COVID-19 spread rapidly through a terrible transmission way by human-to-human, which led to many suspected cases waiting to be diagnosed and huge daily samples needed to be tested by an effective and rapid detection method. With an increasing number of COVID-19 infections, medical pressure is severe. Therefore, more efficient and accurate diagnosis methods were keen urgently established. In this review, we summarized several methods that can rapidly and sensitively identify COVID-19; some of them are widely used as the diagnostic techniques for SARS-CoV-2 in various countries, some diagnostic technologies refer to SARS (Severe Acute Respiratory Syndrome) or/and MERS (Middle East Respiratory Syndrome) detection, which may provide potential diagnosis ideas.

Biomarkers in Acute Myeloid Leukemia: Leveraging Next Generation Sequencing Data for Optimal Therapeutic Strategies

Next generation sequencing (NGS) is routinely used for mutation profiling of acute myeloid leukemia. The extensive application of NGS in hematologic malignancies, and its significant association with the outcomes in multiple large cohorts constituted a proof of concept that AML phenotype is driven by underlying mutational signature and is amenable for targeted therapies. These findings urged incorporation of molecular results into the latest World Health Organization (WHO) sub-classification and integration into risk-stratification and treatment guidelines by the European Leukemia Net. NGS mutation profiling provides a large amount of information that guides diagnosis and management, dependent on the type and number of gene mutations, variant allele frequency and amenability to targeted therapeutics. Hence, molecular mutational profiling is an integral component for work-up of AML and multiple leukemic entities. In addition, there is a vast amount of informative data that can be obtained from routine clinical NGS sequencing beyond diagnosis, prognostication and therapeutic targeting. These include identification of evidence regarding the ontogeny of the disease, underlying germline predisposition and clonal hematopoiesis, serial monitoring to assess the effectiveness of therapy and resistance mutations, which have broader implications for management. In this review, using a few prototypic genes in AML, we will summarize the clinical applications of NGS generated data for optimal AML management, with emphasis on the recently described entities and Food and Drug Administration approved target therapies.

Accurate quantification of bacterial abundance in metagenomic DNAs accounting for variable DNA integrity levels

The quantification of the total microbial content in metagenomic samples is critical for investigating the interplay between the microbiome and its host, as well as for assessing the accuracy and precision of the relative microbial composition which can be strongly biased in low microbial biomass samples. In the present study, we demonstrate that digital droplet PCR (ddPCR) can provide accurate quantification of the total copy number of the 16S rRNA gene, the gene usually exploited for assessing total bacterial abundance in metagenomic DNA samples. Notably, using DNA templates with different integrity levels, as measured by the DNA integrity number (DIN), we demonstrated that 16S rRNA copy number quantification is strongly affected by DNA quality and determined a precise correlation between quantification underestimation and DNA degradation levels. Therefore, we propose an input DNA mass correction, according to the observed DIN value, which could prevent inaccurate quantification of 16S copy number in degraded metagenomic DNAs. Our results highlight that a preliminary evaluation of the metagenomic DNA integrity should be considered before performing metagenomic analyses of different samples, both for the assessment of the reliability of observed differential abundances in different conditions and to obtain significant functional insights.

Identification and monitoring of Copy Number Variants (CNV) in monoclonal gammopathy

Monoclonal gammopathy of undetermined significance (MGUS) represents the pre-clinical stage of Multiple Myeloma (MM) with the 5% of MGUS progresses to MM. Although the progression from MGUS to MM has not been completely characterized, it is possible to monitor the DNA modifications of patients diagnosed with MGUS to detect early specific genomic abnormalities, including copy number variations (CNV). The CNVs of chromosome 1q and chromosome 13q are associated with a worse prognosis in MM.In the present study, we showed that it is possible to monitor the 1q21 gain and 13q deletion frequencies in gDNA using digital PCR. The CNV analysis of three cell lines with a well-characterized cytogenetic profile were compared with measures performed by a real-time PCR approach and with a digital PCR approach. Then, we analyzed CNVs in CD138⁺ plasma cells isolated from bone marrow of MGUS and MM patients.Our results show that digital PCR and targeted DNA monitoring represent a specific and accurate technique for the early detection of specific genomic abnormalities both in MM and in MGUS patients.Our results could represent a remarkable advancement in MM and MGUS diagnosis and in CNV analysis for the evaluation of the risk of progression from MGUS to MM.

Detection and quantification of bovine papillomavirus DNA by digital droplet PCR in sheep blood

Highly pathogenic bovine papillomaviruses (BPVs) were detected and quantified for the first time using digital droplet polymerase chain reaction (ddPCR) by liquid biopsy in 103 clinically healthy sheep. Overall, ddPCR detected BPVs in 68 blood samples (66%). BPV infection by a single genotype was revealed in 61.8% of the blood samples, and BPV coinfection by double, triple or quadruple genotypes was observed in 38.2% of liquid biopsies. The BPV-2 genotype was most frequently seen in sheep, whereas BPV-1 was the least common. Furthermore, ddPCR was very useful for detection and quantification; the BPV-14 genotype was observed for the first time in ovine species, displaying the highest prevalence in some geographical areas (Apulia). In 42 of the positive samples (61.8%), a single BPV infection was observed, 26 of which were caused by BPV-2 (61.9%) and 7 by BPV-13 (16.7%). BPV-14 was responsible for 7 single infections (16.7%) and BPV-1 for 2 single infections (4.7%). Multiple BPV coinfections were observed in the remaining 26 positive samples (38.2%), with dual BPV-2/BPV-13 infection being the most prevalent (84.6%). BPV infection by triple and quadruple genotypes was also observed in 11.5% and 3.8% of cases, respectively. The present study showed that ddPCR, a biotechnological refinement of conventional PCR, is by far the most sensitive and accurate assay for BPV detection compared to conventional qPCR. Therefore, ddPCR displayed an essential diagnostic and epidemiological value very useful for the identification of otherwise undetectable BPV genotypes as well as their geographical distributions and suggesting that animal husbandry practices contribute to cross-species transmission of BPVs.

Copy Number Variation and Rearrangements Assessment in Cancer: Comparison of Droplet Digital PCR with the Current Approaches

The cytogenetic and molecular assessment of deletions, amplifications and rearrangements are key aspects in the diagnosis and therapy of cancer. Not only the initial evaluation and classification of the disease, but also the follow-up of the tumor rely on these laboratory approaches. The therapeutic choice can be guided by the results of the laboratory testing. Genetic deletions and/or amplifications directly affect the susceptibility or the resistance to specific therapies. In an era of personalized medicine, the correct and reliable molecular characterization of the disease, also during the therapeutic path, acquires a pivotal role. Molecular assays like multiplex ligation-dependent probe amplification and droplet digital PCR represent exceptional tools for a sensitive and reliable detection of genetic alterations and deserve a role in molecular oncology. In this manuscript we provide a technical comparison of these two approaches with the golden standard represented by fluorescence in situ hybridization. We also describe some relevant targets currently evaluated with these techniques in solid and hematologic tumors.

Universal LNA Probe-Mediated Multiplex Droplet Digital Polymerase Chain Reaction for Ultrasensitive and Accurate Quantitative Analysis of Genetically Modified Organisms

Multiplex and high-throughput assays are becoming the main trends in the development of new nucleic acid detection and quantification methods, such as those for genetically modified organism (GMO) analysis. Here, we report a novel universal LNA probe-mediated droplet digital polymerase chain reaction (PCR) method (ULNA-ddPCR) for multiple DNA target quantification in GMOs. In ULNA-ddPCR, only one universal LNA probe is used for multiple DNA targets instead of using one to one TaqMan probe. The specificity, sensitivity, dynamic range, and accuracy of the ULNA-ddPCR method are determined by employing GM rice analysis as an example. Simplex and triplex ULNA-ddPCR assays for three GM rice events, T2A-1, T1C-19, and G6H1, are established and evaluated. All results indicate that the developed simplex and triplex ULNA-ddPCR assays are suitable for quantitative analysis of GM rice events with high sensitivity, accuracy, and low cost. The ULNA-ddPCR method also has the potential for multiple DNA target quantification in other research fields.

Molecular Testing in CML between Old and New Methods: Are We at a Turning Point?

Molecular monitoring of minimal residual disease (MRD) and BCR-ABL1 kinase domain (KD) mutation testing have a well consolidated role in the routine management of chronic myeloid leukemia (CML) patients, as they provide precious information for therapeutic decision-making. Molecular response levels are used to define whether a patient has an "optimal", "warning", or "failure" response to tyrosine kinase inhibitor (TKI) therapy. Mutation status may be useful to decide whether TKI therapy should be changed and which alternative TKI (or TKIs) are most likely to be effective. Real-time quantitative polymerase chain reaction (RQ-qPCR) and Sanger sequencing are currently the gold standard for molecular response monitoring and mutation testing, respectively. However, in recent years, novel technologies such as digital PCR (dPCR) and next-generation sequencing (NGS) have been evaluated. Here, we critically describe the main features of these old and novel technologies, provide an overview of the recently published studies assessing the potential clinical value of dPCR and NGS, and discuss how the state of the art might evolve in the next years.

Currently Applied Molecular Assays for Identifying ESR1 Mutations in Patients with Advanced Breast Cancer

Approximately 70% of breast cancers, the leading cause of cancer-related mortality worldwide, are positive for the estrogen receptor (ER). Treatment of patients with luminal subtypes is mainly based on endocrine therapy. However, ER positivity is reduced and ESR1 mutations play an important role in resistance to endocrine therapy, leading to advanced breast cancer. Various methodologies for the detection of ESR1 mutations have been developed, and the most commonly used method is next-generation sequencing (NGS)-based assays (50.0%) followed by droplet digital PCR (ddPCR) (45.5%). Regarding the sample type, tissue (50.0%) was more frequently used than plasma (27.3%). However, plasma (46.2%) became the most used method in 2016-2019, in contrast to 2012-2015 (22.2%). In 2016-2019, ddPCR (61.5%), rather than NGS (30.8%), became a more popular method than it was in 2012-2015. The easy accessibility, non-invasiveness, and demonstrated usefulness with high sensitivity of ddPCR using plasma have changed the trends. When using these assays, there should be a comprehensive understanding of the principles, advantages, vulnerability, and precautions for interpretation. In the future, advanced NGS platforms and modified ddPCR will benefit patients by facilitating treatment decisions efficiently based on information regarding ESR1 mutations.

Overexpression of microRNA-130a predicts adverse prognosis of primary gastrointestinal diffuse large B-cell lymphoma

Primary gastrointestinal diffuse large B-cell lymphoma (PGI-DLBCL) is a highly heterogeneous type of non-Hodgkin lymphoma. A number of studies have demonstrated that microRNA-130a (miR-130a) serves a role in the tumorigenesis and prognosis of numerous human tumors. However, to the best of our knowledge, the prognostic significance of miR-130a in PGI-DLBCL remains unknown. The present study explored the association between miR-130a and the clinical outcomes of PGI-DLBCL. Relative miR-130a expression was assessed by reverse transcription-quantitative PCR. Immunohistochemistry was used to detect expression levels of BCL-2, c-MYC, neprilysin, B-cell lymphoma 6 protein, PWWP domain-containing DNA repair factor 3A and proliferation marker protein Ki-67. A receiver operating characteristic curve was constructed to analyze the specificity and sensitivity of microRNA levels in the diagnosis of PGI-DLBCL. Survival curves were constructed using the Kaplan-Meier method. In the present study, miR-130a expression was notably higher in patients with PGI-DLBCL compared with in the controls (P<0.0001). miR-130a overexpression was closely associated with a high International Prognostic Index score (3–5) and drug resistance (P=0.017 and P=0.044, respectively). No significant difference in other clinical features was observed. Patients with increased expression levels of miR-130a had lower overall survival [hazard ratio (HR), 2.998; 95% CI, 1.347-6.673; P=0.007] and progression-free survival (HR, 3.325; 95% CI, 1.488-7.429; P=0.003) compared with patients who had lower expression levels of miR-130a. Furthermore, multivariate Cox regression analysis suggested that miR-130a was a negative prognostic parameter in PGI-DLBCL. Therefore, upregulation of miR-130a could become a potential prognostic marker for PGI-DLBCL. Additionally, further study of these results may have important guiding significance for the prognosis of patients with PGI-DLBCL in the clinical setting.

Quantification of Plasmodiophora brassicae Resting Spores in Soils Using Droplet Digital PCR (ddPCR)

Plasmodiophora brassicae, an obligate soilborne pathogen that causes clubroot on Brassica crops, is spreading rapidly in western Canada, threatening canola production in the region. Bioassays and molecular assays have been used to estimate the concentration of P. brassicae resting spores in soil, which can affect clubroot incidence and severity on crops. Droplet digital PCR (ddPCR) is a promising new approach for quantification of pathogen inoculum owing to its low sensitivity to inhibitors and consistency at low target concentrations. The objective of this study was to assess ddPCR against existing quantitative PCR (qPCR) for potential advantage and/or improvement in quantifying P. brassicae resting spores in soil. The new protocol enumerated resting spores accurately in spiked potting mix or soil samples ranging from 10² to 10⁷ spores per gram. At a spore concentration ≥10⁷ spores per gram, however, ddPCR became less accurate, with a tendency of overestimation. The protocol was validated by quantifying the resting spores in spiked brown, dark brown, and black soils using both ddPCR and qPCR simultaneously. These soil types are found commonly on the Canadian Prairies, and they vary in texture, pH, and organic content. ddPCR showed similar results among the different soil types, whereas qPCR often displayed lower counts for the same spore concentration, with the amplification of DNA inhibited completely in black soil samples. The inhibition can be removed by a 10-fold dilution of DNA samples. The results show that ddPCR can be a more versatile tool than qPCR for detection and quantification of P. brassicae resting spores in soil samples.

How close are we to incorporating measurable residual disease into clinical practice for acute myeloid leukemia?

Assessment of measurable residual disease, also called "minimal residual disease," in patients with acute myeloid leukemia in morphological remission provides powerful prognostic information and complements pretreatment factors such as cytogenetics and genomic alterations. Based on data that low levels of persistent or recurrent residual leukemia are consistently associated with an increased risk of relapse and worse long-term outcomes, its routine assessment has been recommended by some experts and consensus guidelines. In addition to providing important prognostic information, the detection of measurable residual disease may also theoretically help to determine the optimal post-remission strategy for an individual patient. However, the full therapeutic implications of measurable residual disease are uncertain and thus controversy exists as to whether it should be routinely incorporated into clinical practice. While some evidence supports the use of allogeneic stem cell transplantation or hypomethylating agents for some subgroups of patients in morphological remission but with detectable residual leukemia, the appropriate use of this information in making clinical decisions remains largely speculative at present. To resolve this pressing clinical issue, several ongoing studies are evaluating measurable residual disease-directed treatments in acute myeloid leukemia and may lead to new, effective strategies for patients in these circumstances. This review examines the common technologies used in clinical practice and in the research setting to detect residual leukemia, the major clinical studies establishing the prognostic impact of measurable residual disease in acute myeloid leukemia, and the potential ways, both now and in the future, that such testing may rationally guide therapeutic decision-making.

The Minimal Residual Disease in Non-Hodgkin's Lymphomas: From the Laboratory to the Clinical Practice

Minimal residual disease (MRD) in non-Hodgkin's lymphomas (NHLs) still represents matter of interest and debate: indeed, the new available treatments offer higher rates of complete responses and MRD negativity than in the past, with a positive impact on the long-term survival. Furthermore, the introduction of more sensitive and accurate molecular techniques, such as digital PCR (ddPCR) and the next generation sequencing techniques (NGS), increased the possibility of identifying molecular targets to be followed after therapy (such as rearrangement of immunoglobulins, fusion genes, or mutations). This review focused on how molecular biology can help to detect MRD in different types of NHLs and how MRD can change the clinical practice in 2019. In follicular lymphoma (FL), contamination of the grafts and molecular disease persistence after transplantation represent a negative prognostic factors. The combination of Rituximab or Obinutuzumab with Bendamustine seems to be the most effective way to clear MRD in FL patients receiving chemo-immunotherapy (further studies are in progress), and also ⁹⁰Yttrium-Ibritumomab-Tiuxetan offers a deep clearance of molecular disease. Finally, molecular MRD can further stratify PET-negative cases, with subjects both PET- and MRD-negative presenting the best outcome. In aggressive lymphomas, MRD has a relevant prognostic power and can represent the platform for immunotherapy (such as CAR-T). In diffuse large B-cell lymphoma (DLBCL), the assessment of MRD in the plasma (where cell-free DNA and exosomes circulate) seems to be more predictive than the bone marrow analysis or peripheral blood mononuclear cells. Finally, NGS technologies could be more useful than the classical "patient allele-specific PCR" because they can identify any possible clone emerging during the treatment or follow-up, even if different from that identified at diagnosis, thus predicting relapse. After all, the present available molecular approaches can move MRD from the bench side to the clinical practice.

Multiplex real-time PCR assay combined with rolling circle amplification (MPRP) using universal primers for non-invasive detection of tumor-related mutations

With the continuous development and application of targeted drugs, it is particularly desirable to find a non-invasive diagnostic approach to screen patients for precision treatment. Specifically, detection of multiple cancer-related mutations is very important for targeted therapy and prediction of drug resistance. Although numerous advanced PCR methods have been developed to discriminate single nucleotide polymorphisms, their drawbacks significantly limit their application, such as low sensitivity and throughput, complicated operations, and expensive costs. In order to overcome these challenges, in this study, we developed a method combining multiplex and sensitive real-time PCR assay with rolling circle amplification. This allows specific and sensitive discrimination of the single nucleotide mutation and provides convenient multiplex detection by real-time PCR assay. The clinical potential of the MPRP assay was further demonstrated by comparing samples from 8 patients with a digital PCR assay. The coincident results between these two methods indicated that the MPRP assay can provide a specific, sensitive, and convenient method for multiplex detection of cancer-related mutations.

Chip-based digital PCR as a novel detection method for quantifying microRNAs in acute myocardial infarction patients

miRNAs have shown promise as potential biomarkers for acute myocardial infarction (AMI). However, the current used quantitative real-time PCR (qRT-PCR) allows solely for relative expression of nucleic acids and it is susceptible to day-to-day variability, which has limited the validity of using the miRNAs as biomarkers. In this study we explored the technical qualities and diagnostic potential of a new technique, chip-based digital PCR, in quantifying the miRNAs in patients with AMI and ischaemia-reperfusion injury (I/R). In a dilution series of synthetic C.elegans-miR-39, chip-based digital PCR displayed a lower coefficient of variation (8.9% vs 46.3%) and a lower limit of detection (0.2 copies/μL vs 1.1 copies/μL) compared with qRT-PCR. In the serum collected from 24 patients with ST-elevation myocardial infarction (STEMI) and 20 patients with stable coronary artery disease (CAD) patients after percutaneous coronary intervention (PCI), we used qRT-PCR and multiplexed chip-based digital PCR to quantify the serum levels of miRNA-21 and miRNA-499 as they have been validated in AMI in prior studies. In STEMI, I/R injury was assessed via measurement of ST-segment resolution (ST-R). Chip-based digital PCR revealed a statistical significance in the difference of miR-21 levels between stable CAD and STEMI groups (118.8 copies/μL vs 59 copies/μL; P=0.0300), whereas qRT-PCR was unable to reach significance (136.4 copies/μL vs 122.8 copies/μL; P=0.2273). For miR-499 levels, both chip-based digital PCR and qRT-PCR revealed statistically significant differences between stable CAD and STEMI groups (2 copies/μL vs 8.5 copies/μL, P=0.0011; 0 copies/μL vs 19.4 copies/μL; P<0.0001). There was no association between miR-21/499 levels and ST-R post-PCI. Our results show that the chip-based digital PCR exhibits superior technical qualities and promises to be a superior method for quantifying miRNA levels in the circulation, which may become a more accurate and reproducible method for directly quantifying miRNAs, particularly for use in large multi-centre clinical trials.