- Clinical Pathology
- Molecular Pathology
Board Certification, American Board of Pathology, Molecular Genetic Pathology (2022)
Board Certification: American Board of Pathology, Clinical Pathology (2022)
Residency: Stanford University Pathology Residency (2022) CA
Fellowship: Stanford University Pathology Fellowships (2021) CA
Medical Education: Emory University Medical School (2018) GA
M.D., Emory University (2018)
Ph.D., Georgia Institute of Technology, Biomedical Engineering (2015)
B.S., University of California, Berkeley, Bioengineering (2009)
Potential pitfalls in multiplex PCR-based next-generation sequencing: a case-based report.
Journal of clinical pathology
Amplicon-based next-generation sequencing (NGS) assays employ highly sensitive, rapid, and cost-effective methods to detect clinically actionable mutations for the diagnosis, prognosis, and treatment of patients with cancer. However, recognition of certain limitations inherent to amplicon-based NGS assays is crucial for the correct interpretation and reporting of variants in the clinical setting. In this report, we illustrate three different potential pitfalls related to amplicon-based NGS assays based on our institutional experience and highlight how the risk of such events can be minimised.
View details for DOI 10.1136/jclinpath-2021-208105
View details for PubMedID 35145018
Detection of cryptogenic malignancies from metagenomic whole genome sequencing of body fluids.
2021; 13 (1): 98
BACKGROUND: Metagenomic next-generation sequencing (mNGS) of body fluids is an emerging approach to identify occult pathogens in undiagnosed patients. We hypothesized that metagenomic testing can be simultaneously used to detect malignant neoplasms in addition to infectious pathogens.METHODS: From two independent studies (n = 205), we used human data generated from a metagenomic sequencing pipeline to simultaneously screen for malignancies by copy number variation (CNV) detection. In the first case-control study, we analyzed body fluid samples (n = 124) from patients with a clinical diagnosis of either malignancy (positive cases, n = 65) or infection (negative controls, n = 59). In a second verification cohort, we analyzed a series of consecutive cases (n = 81) sent to cytology for malignancy workup that included malignant positives (n = 32), negatives (n = 18), or cases with an unclear gold standard (n = 31).RESULTS: The overall CNV test sensitivity across all studies was 87% (55 of 63) in patients with malignancies confirmed by conventional cytology and/or flow cytometry testing and 68% (23 of 34) in patients who were ultimately diagnosed with cancer but negative by conventional testing. Specificity was 100% (95% CI 95-100%) with no false positives detected in 77 negative controls. In one example, a patient hospitalized with an unknown pulmonary illness had non-diagnostic lung biopsies, while CNVs implicating a malignancy were detectable from bronchoalveolar fluid.CONCLUSIONS: Metagenomic sequencing of body fluids can be used to identify undetected malignant neoplasms through copy number variation detection. This study illustrates the potential clinical utility of a single metagenomic test to uncover the cause of undiagnosed acute illnesses due to cancer or infection using the same specimen.
View details for DOI 10.1186/s13073-021-00912-z
View details for PubMedID 34074327
Validation of a Next-Generation Sequencing-based T-Cell Receptor Gamma Gene Rearrangement Diagnostic Assay: Transitioning from Capillary Electrophoresis to Next-Generation Sequencing.
The Journal of molecular diagnostics : JMD
Assessment of T-cell receptor gamma (TRG) gene rearrangement is an important consideration in the diagnostic workup of lymphoproliferative diseases. Although fragment analysis by PCR and capillary electrophoresis (CE) is the current standard for such assessment in clinical molecular diagnostic laboratories, it does not provide sequence information and is only semi-quantitative. Next-generation sequencing (NGS)-based assays are an attractive alternative to the conventional fragment-size based methods since they generate results with specific clonotype sequence information and allow for more accurate quantitation. We therefore evaluated various test parameters and performance characteristics for a commercially available NGS-based TRG gene rearrangement assay by testing 101 clinical samples previously characterized by fragment analysis. The NGS TRG assay showed an overall accuracy of 83% and an analytical specificity of 100%, as compared to the CE-based assay. The concordance rate was 88∼95% for Vγ1-8, Vγ10 and Vγ11 gene families, but lower for the Vγ9 gene family. This difference was mostly attributed to the incomplete polyclonal symmetry resulting from the two-tube CE assay versus the one-tube design of the NGS assay. The NGS assay also demonstrated strengths in distinguishing different clonotypes with the same fragment size. Our clinical validation demonstrated robust performance of the NGS-based TRG assay and identified potential pitfalls associated with CE assay design that are important for understanding the observed discrepancies with the CE-based assay.
View details for DOI 10.1016/j.jmoldx.2021.03.008
View details for PubMedID 33892183
Accurate detection and quantification of FLT3 internal tandem duplications in clinical hybrid capture next-generation sequencing data.
The Journal of molecular diagnostics : JMD
FLT3 internal tandem duplications (ITDs) are found in approximately one third of patients with acute myeloid leukemia (AML) and have important prognostic and therapeutic implications that have supported its assessment in routine clinical practice. Conventional methods for assessing FLT3-ITD status and allele burden have been primarily limited to PCR fragment size analysis due to the inherent difficulty in detecting large ITD variants by next-generation sequencing (NGS). In this study, we assess the performance of publicly available bioinformatic tools for the detection and quantification of FLT3-ITDs in clinical hybridization-capture NGS data. We found that FLT3_ITD_ext had the highest overall accuracy for detecting FLT3-ITDs and was able to accurately quantify allele burden. Although all other tools evaluated were able to detect FLT3-ITDs reasonably well, allele burden was consistently underestimated. We were able to significantly improve quantification of FLT3-ITD allelic burden independent of the detection method by utilizing soft-clipped reads and/or ITD junctional sequences. In addition, we show that identifying mutant reads by previously identified junctional sequences further improves the sensitivity of detecting FLT3-ITDs in post-treatment samples. Our results demonstrate that FLT3-ITDs can be reliably detected in clinical NGS data using available bioinformatic tools. We further describe how accurate quantification of FLT3-ITD allele burden can be added on to existing clinical NGS pipelines for routine assessment of FLT3-ITD status in patients with AML.
View details for DOI 10.1016/j.jmoldx.2021.07.012
View details for PubMedID 34363960
Improved trafficking and expression of luminopsins for more efficient optical and pharmacological control of neuronal activity.
Journal of neuroscience research
2020; 98 (3): 481-490
Luminopsins (LMOs) are chimeric proteins consisting of a luciferase fused to an opsin that provide control of neuronal activity, allowing for less cumbersome and less invasive optogenetic manipulation. It was previously shown that both an external light source and the luciferase substrate, coelenterazine (CTZ), could modulate activity of LMO-expressing neurons, although the magnitudes of the photoresponses remained subpar. In this study, we created an enhanced iteration of the excitatory luminopsin LMO3, termed eLMO3, that has improved membrane targeting due to the insertion of a Golgi trafficking signal sequence. In cortical neurons in culture, the expression of eLMO3 resulted in significant reductions in the formation of intracellular aggregates, as well as in a significant increase in total photocurrents. Furthermore, we corroborated the findings with injections of adeno-associated viral vectors into the deep layers of the somatosensory cortex (the barrel cortex) of male mice. We observed greatly reduced numbers of intracellular puncta in eLMO3-expressing cortical neurons compared to those expressing the original LMO3. Finally, we quantified CTZ-driven behavior, namely whisker-touching behavior, in male mice with LMO3 expression in the barrel cortex. After CTZ administration, mice with eLMO3 displayed significantly longer whisker responses than mice with LMO3. In summary, we have engineered the superior LMO by resolving membrane trafficking defects, and we demonstrated improved membrane targeting, greater photocurrents, and greater functional responses to stimulate with CTZ.
View details for DOI 10.1002/jnr.24546
View details for PubMedID 31670406
View details for PubMedCentralID PMC6980770
Motoneuron activity is required for enhancements in functional recovery after peripheral nerve injury in exercised female mice.
Journal of neuroscience research
2020; 98 (3): 448-457
Inhibitory luminopsins (iLMO2) integrate opto- and chemo-genetic approaches and allow for cell-type specific inhibition of neuronal activity. When exposed to a Renilla luciferase substrate, Coelenterazine (CTZ), iLMO2 generates bioluminescence-mediated activation of its amino-terminal halorhodopsin, resulting in neuronal inhibition. Moderate daily exercise in the form of interval treadmill-training (IT) applied following a peripheral nerve injury results in enhanced motor axon regeneration and muscle fiber reinnervation in female mice. We hypothesized that iLMO2 mediated inhibition of motoneuron activity during IT would block this enhancement. Unilateral intramuscular injections of Cre-dependent AAV2/9-EF1a-DIO-iLMO2 (∼8.5 x 1013 vg/ml) were made into the gastrocnemius and tibialis anterior muscles of young female ChAT-IRES-Cre mice, thereby limiting iLMO2 expression specifically to their motoneurons. Four to six weeks were allowed for retrograde viral transduction after which a unilateral sciatic nerve transection (Tx) and repair was performed. Animals were randomized into four groups: IT only, IT + CTZ, CTZ only, and untreated (UT). Three weeks post Tx-repair, the maximal amplitude direct muscle responses (M-max) in both muscles in the IT only group were significantly greater than in UT mice, consistent with the enhancing effects of this exercise regimen. Inhibiting motoneuron activity during exercise by a single injection of CTZ, administered 30 minutes prior to exercise, completely blocked the enhancing effect of exercise. Similar treatments with CTZ in mice without iLMO2 had no effect on regeneration. Neuronal activity is required for successful enhancement of motor axon regeneration by exercise.
View details for DOI 10.1002/jnr.24109
View details for PubMedID 28771790
View details for PubMedCentralID PMC5797526
Comparison of the Accula SARS-CoV-2 Test with a Laboratory-Developed Assay for Detection of SARS-CoV-2 RNA in Clinical Nasopharyngeal Specimens.
Journal of clinical microbiology
Background: Several point-of-care (POC) molecular tests have received emergency use authorization (EUA) from the Food and Drug Administration (FDA) for diagnosis of SARS-CoV-2. The test performance characteristics of the Accula (Mesa Biotech) SARS-CoV-2 POC test need to be evaluated to inform its optimal use.Objectives: The aim of this study was to assess test performance of the Accula SARS-CoV-2 test.Study design: The performance of the Accula test was assessed by comparing results of 100 nasopharyngeal swab samples previously characterized by the Stanford Health Care EUA laboratory-developed test (SHC-LDT) targeting the envelope (E) gene. Assay concordance was assessed by overall percent agreement, positive percent agreement (PPA), negative percent agreement (NPA), and Cohen's kappa coefficient.Results: Overall percent agreement between the assays was 84.0% (95% confidence interval [CI] 75.3 to 90.6%), PPA was 68.0% (95% CI 53.3 to 80.5%) and the kappa coefficient was 0.68 (95% CI 0.54 to 0.82). Sixteen specimens detected by the SHC-LDT were not detected by the Accula test, and showed low viral load burden with a median cycle threshold value of 37.7. NPA was 100% (95% CI 94.2 to 100%).Conclusion: Compared to the SHC-LDT, the Accula SARS-CoV-2 test showed excellent negative agreement. However, positive agreement was low for samples with low viral load. The false negative rate of the Accula POC test calls for a more thorough evaluation of POC test performance characteristics in clinical settings, and for confirmatory testing in individuals with moderate to high pre-test probability of SARS-CoV-2 who test negative on Accula.
View details for DOI 10.1128/JCM.01072-20
View details for PubMedID 32461285
An N-terminal BRAF deletion accounting for acquired resistance to RAF/EGFR inhibition in colorectal cancer.
Cold Spring Harbor molecular case studies
Although combination therapy with RAF and EGFR inhibitors have improved the survival outcomes of patients with BRAF-mutated colorectal cancer (CRC), acquired resistance invariably develops. The mechanisms of acquired resistance to RAF inhibitors have been largely attributed to activating Ras mutations, MAP2K mutations, and amplifications in BRAF, Ras, and EGFR. In this report, we describe a patient with BRAF-mutated CRC who acquired a N-terminal BRAF deletion involving the Ras-binding domain (RBD) after treatment with RAF/EGFR inhibitor therapy. N-terminal BRAF deletions involving the RBD are a rare mechanism of acquired resistance to RAF inhibitors, particularly in CRC where there is only one prior report in the literature.
View details for DOI 10.1101/mcs.a005140
View details for PubMedID 32669268
Optochemogenetic Stimulation of Transplanted iPS-NPCs Enhances Neuronal Repair and Functional Recovery after Ischemic Stroke.
The Journal of neuroscience : the official journal of the Society for Neuroscience
2019; 39 (33): 6571-6594
Cell transplantation therapy provides a regenerative strategy for neural repair. We tested the hypothesis that selective excitation of transplanted induced pluripotent stem cell-derived neural progenitor cells (iPS-NPCs) could recapitulate an activity-enriched microenvironment that confers regenerative benefits for the treatment of stroke. Mouse iPS-NPCs were transduced with a novel optochemogenetics fusion protein, luminopsin 3 (LMO3), which consisted of a bioluminescent luciferase, Gaussia luciferase, and an opsin, Volvox Channelrhodopsin 1. These LMO3-iPS-NPCs can be activated by either photostimulation using light or by the luciferase substrate coelenterazine (CTZ). In vitro stimulations of LMO3-iPS-NPCs increased expression of synapsin-1, postsynaptic density 95, brain derived neurotrophic factor (BDNF), and stromal cell-derived factor 1 and promoted neurite outgrowth. After transplantation into the ischemic cortex of mice, LMO3-iPS-NPCs differentiated into mature neurons. Synapse formation between implanted and host neurons was identified using immunogold electron microscopy and patch-clamp recordings. Stimulation of transplanted cells with daily intranasal administration of CTZ enhanced axonal myelination, synaptic transmission, improved thalamocortical connectivity, and functional recovery. Patch-clamp and multielectrode array recordings in brain slices showed that CTZ or light stimulation facilitated synaptic transmission and induced neuroplasticity mimicking the LTP of EPSPs. Stroke mice received the combined LMO3-iPS-NPC/CTZ treatment, but not cell or CTZ alone, showed enhanced neural network connections in the peri-infarct region, promoted optimal functional recoveries after stroke in male and female, young and aged mice. Thus, excitation of transplanted cells via the noninvasive optochemogenetics treatment provides a novel integrative cell therapy with comprehensive regenerative benefits after stroke.SIGNIFICANCE STATEMENT Neural network reconnection is critical for repairing damaged brain. Strategies that promote this repair are expected to improve functional outcomes. This study pioneers the generation and application of an optochemogenetics approach in stem cell transplantation therapy after stroke for optimal neural repair and functional recovery. Using induced pluripotent stem cell-derived neural progenitor cells (iPS-NPCs) expressing the novel optochemogenetic probe luminopsin (LMO3), and intranasally delivered luciferase substrate coelenterazine, we show enhanced regenerative properties of LMO3-iPS-NPCs in vitro and after transplantation into the ischemic brain of different genders and ages. The noninvasive repeated coelenterazine stimulation of transplanted cells is feasible for clinical applications. The synergetic effects of the combinatorial cell therapy may have significant impacts on regenerative approach for treatments of CNS injuries.
View details for DOI 10.1523/JNEUROSCI.2010-18.2019
View details for PubMedID 31263065
View details for PubMedCentralID PMC6697405
A Machine Learning Approach to Characterize the Modulation of the Hippocampal Rhythms Via Optogenetic Stimulation of the Medial Septum.
International journal of neural systems
The medial septum (MS) is a potential target for modulating hippocampal activity. However, given the multiple cell types involved, the changes in hippocampal neural activity induced by MS stimulation have not yet been fully characterized. We combined MS optogenetic stimulation with local field potential (LFP) recordings from the hippocampus and leveraged machine learning techniques to explore how activating or inhibiting multiple MS neuronal subpopulations using different optical stimulation parameters affects hippocampal LFP biomarkers. First, of the seven different optogenetic viral vectors used for modulating different neuronal subpopulations, only two induced a substantial change in hippocampal LFP. Second, we found hippocampal low-gamma band to be most effectively modulated by the stimulation. Third, the hippocampal biomarkers were sensitive to the optogenetic virus type and the stimulation frequency, establishing those parameters as the critical ones for the regulation of hippocampal biomarker activity. Last, we built a Gaussian process regression model to describe the relationship between stimulation parameters and activity of the biomarker as well as to identify the optimal parameters for biomarker modulation. This new machine learning approach can further our understanding of the effects of neural stimulation and guide the selection of optimal parameters for neural control.
View details for DOI 10.1142/S0129065719500205
View details for PubMedID 31505977
- Impact of underfilling heparinized collection tubes on ionized calcium measurements. Clinica chimica acta; international journal of clinical chemistry 2019
Chemically activated luminopsins allow optogenetic inhibition of distributed nodes in an epileptic network for non-invasive and multi-site suppression of seizure activity.
Neurobiology of disease
2018; 109 (Pt A): 1-10
Although optogenetic techniques have proven to be invaluable for manipulating and understanding complex neural dynamics over the past decade, they still face practical and translational challenges in targeting networks involving multiple, large, or difficult-to-illuminate areas of the brain. We utilized inhibitory luminopsins to simultaneously inhibit the dentate gyrus and anterior nucleus of the thalamus of the rat brain in a hardware-independent and cell-type specific manner. This approach was more effective at suppressing behavioral seizures than inhibition of the individual structures in a rat model of epilepsy. In addition to elucidating mechanisms of seizure suppression never directly demonstrated before, this work also illustrates how precise multi-focal control of pathological circuits can be advantageous for the treatment and understanding of disorders involving broad neural circuits such as epilepsy.
View details for DOI 10.1016/j.nbd.2017.09.007
View details for PubMedID 28923596
View details for PubMedCentralID PMC5696076
C3 transferase gene therapy for continuous conditional RhoA inhibition.
2016; 339: 308-318
Regrowth inhibitory molecules prevent axon regeneration in the adult mammalian central nervous system (CNS). RhoA, a small GTPase in the Rho family, is a key intracellular switch that mediates the effects of these extracellular regrowth inhibitors. The bacterial enzyme C3-ADP ribosyltransferase (C3) selectively and irreversibly inhibits the activation of RhoA and stimulates axon outgrowth and regeneration. However, effective intracellular delivery of the C3 protein in vivo is limited by poor cell permeability and a short duration of action. To address this, we have developed a gene therapy approach using viral vectors to introduce the C3 gene into neurons or neuronal progenitors. Our vectors deliver C3 in a cell-autonomous (endogenous) or a cell-nonautonomous (secretable/permeable) fashion and promote in vitro process outgrowth on inhibitory chondroitin sulfate proteoglycan substrate. Further conditional control of our vectors was achieved via the addition of a Tet-On system, which allows for transcriptional control with doxycycline administration. These vectors will be crucial tools for promoting continued axonal regeneration after CNS injuries or neurodegenerative diseases.
View details for DOI 10.1016/j.neuroscience.2016.10.022
View details for PubMedID 27746349
View details for PubMedCentralID PMC5118153
Optogenetic Approaches for Controlling Seizure Activity.
2016; 9 (6): 801-810
Optogenetics, a technique that utilizes light-sensitive ion channels or pumps to activate or inhibit neurons, has allowed scientists unprecedented precision and control for manipulating neuronal activity. With the clinical need to develop more precise and effective therapies for patients with drug-resistant epilepsy, these tools have recently been explored as a novel treatment for halting seizure activity in various animal models. In this review, we provide a detailed and current summary of these optogenetic approaches and provide a perspective on their future clinical application as a potential neuromodulatory therapy.
View details for DOI 10.1016/j.brs.2016.06.055
View details for PubMedID 27496002
View details for PubMedCentralID PMC5143193
A therapeutic HIV-1 vaccine enhances anti-HIV-1 immune responses in patients under highly active antiretroviral therapy.
2016; 34 (19): 2225-32
HIV-1 specific cellular immunity plays an important role in controlling viral replication. In this first-in-human therapeutic vaccination study, a replication-defective HIV-1 vaccine (HIVAX) was tested in HIV-1 infected participants undergoing highly active antiretroviral therapy (HAART) to enhance anti-HIV immunity (Clinicaltrials.gov, identifier NCT01428596).A010 was a randomized, placebo-controlled trial to evaluate the safety and the immunogenicity of a replication defective HIV-1 vaccine (HIVAX) given as a subcutaneous injection to HIV-1 infected participants who were receiving HAART with HIV-1 viral load <50 copies/ml and CD4 cell count >500 cells/mm(3). HIV-1 specific immune responses were monitored by INF-γ enzyme linked immunospot (Elispot) and intracellular cytokine staining (ICS) assay after vaccination. Following the randomized placebo-controlled vaccination phase, subjects who received HIVAX vaccine and who met eligibility underwent a 12-week analytical antiretroviral treatment interruption (ATI). Viral load was monitored throughout the study.HIVAX was well tolerated in trial participants. Transient grade 1 to 2 (mild to moderate) injection site reactions occurred in 8 of 10 vaccinated participants. HIVAX was immunogenic in all vaccinated participants. The functionality of T cells was significantly enhanced after vaccination. Median viral load (3.45 log10 copies/ml, range of 96-12,830 copies/ml) at the end of the 12-week treatment interruption in HIVAX vaccinated group was significantly lower than the pre-treatment levels. Three vaccinated participants extended ATI for up to 2 years with stable CD4 cells and low viral loads.HIVAX vaccine is generally safe, elicits strong anti-HIV-1 immune responses, and may play an important role in controlling viral load during treatment interruption in HIV-1 infected participants.
View details for DOI 10.1016/j.vaccine.2016.03.021
View details for PubMedID 27002500
Bioluminescence imaging in live cells and animals.
2016; 3 (2): 025001
The use of bioluminescent reporters in neuroscience research continues to grow at a rapid pace as their applications and unique advantages over conventional fluorescent reporters become more appreciated. Here, we describe practical methods and principles for detecting and imaging bioluminescence from live cells and animals. We systematically tested various components of our conventional fluorescence microscope to optimize it for long-term bioluminescence imaging. High-resolution bioluminescence images from live neurons were obtained with our microscope setup, which could be continuously captured for several hours with no signs of phototoxicity. Bioluminescence from the mouse brain was also imaged noninvasively through the intact skull with a conventional luminescence imager. These methods demonstrate how bioluminescence can be routinely detected and measured from live cells and animals in a cost-effective way with common reagents and equipment.
View details for DOI 10.1117/1.NPh.3.2.025001
View details for PubMedID 27226972
View details for PubMedCentralID PMC4874058
Combined Optogenetic and Chemogenetic Control of Neurons.
Methods in molecular biology (Clifton, N.J.)
2016; 1408: 207-25
Optogenetics provides an array of elements for specific biophysical control, while designer chemogenetic receptors provide a minimally invasive method to control circuits in vivo by peripheral injection. We developed a strategy for selective regulation of activity in specific cells that integrates opto- and chemogenetic approaches, and thus allows manipulation of neuronal activity over a range of spatial and temporal scales in the same experimental animal. Light-sensing molecules (opsins) are activated by biologically produced light through luciferases upon peripheral injection of a small molecule substrate. Such luminescent opsins, luminopsins, allow conventional fiber optic use of optogenetic sensors, while at the same time providing chemogenetic access to the same sensors. We describe applications of this approach in cultured neurons in vitro, in brain slices ex vivo, and in awake and anesthetized animals in vivo.
View details for DOI 10.1007/978-1-4939-3512-3_14
View details for PubMedID 26965125
View details for PubMedCentralID PMC5149414
Inhibitory luminopsins: genetically-encoded bioluminescent opsins for versatile, scalable, and hardware-independent optogenetic inhibition.
2015; 5: 14366
Optogenetic techniques provide an unprecedented ability to precisely manipulate neural activity in the context of complex neural circuitry. Although the toolbox of optogenetic probes continues to expand at a rapid pace with more efficient and responsive reagents, hardware-based light delivery is still a major hurdle that limits its practical use in vivo. We have bypassed the challenges of external light delivery by directly coupling a bioluminescent light source (a genetically encoded luciferase) to an inhibitory opsin, which we term an inhibitory luminopsin (iLMO). iLMO was shown to suppress action potential firing and synchronous bursting activity in vitro in response to both external light and luciferase substrate. iLMO was further shown to suppress single-unit firing rate and local field potentials in the hippocampus of anesthetized rats. Finally, expression of iLMO was scaled up to multiple structures of the basal ganglia to modulate rotational behavior of freely moving animals in a hardware-independent fashion. This novel class of optogenetic probes demonstrates how non-invasive inhibition of neural activity can be achieved, which adds to the versatility, scalability, and practicality of optogenetic applications in freely behaving animals.
View details for DOI 10.1038/srep14366
View details for PubMedID 26399324
View details for PubMedCentralID PMC4585826
Decreasing lactate level and increasing antibody production in Chinese Hamster Ovary cells (CHO) by reducing the expression of lactate dehydrogenase and pyruvate dehydrogenase kinases.
Journal of biotechnology
2011; 153 (1-2): 27-34
Large-scale fed-batch cell culture processes of CHO cells are the standard platform for the clinical and commercial production of monoclonal antibodies. Lactate is one of the major by-products of CHO fed-batch culture. In pH-controlled bioreactors, accumulation of high levels of lactate is accompanied by high osmolality due to the addition of base to control pH of the cell culture medium, potentially leading to lower cell growth and lower therapeutic protein production during manufacturing. Lactate dehydrogenase (LDH) is an enzyme that catalyzes the conversion of the substrate, pyruvate, into lactate and many factors including pyruvate concentration modulate LDH activity. Alternately, pyruvate can be converted to acetyl-CoA by pyruvate dehydrogenases (PDHs), to be metabolized in the TCA cycle. PDH activity is inhibited when phosphorylated by pyruvate dehydrogenase kinases (PDHKs). In this study, we knocked down the gene expression of lactate dehydrogenase A (LDHa) and PDHKs to investigate the effect on lactate metabolism and protein production. We found that LDHa and PDHKs can be successfully downregulated simultaneously using a single targeting vector carrying small inhibitory RNAs (siRNA) for LDHa and PDHKs. Moreover, our fed-batch shake flask evaluation data using siRNA-mediated LDHa/PDHKs knockdown clones showed that downregulating LDHa and PDHKs in CHO cells expressing a therapeutic monoclonal antibody reduced lactate production, increased specific productivity and volumetric antibody production by approximately 90%, 75% and 68%, respectively, without appreciable impact on cell growth. Similar trends of lower lactate level and higher antibody productivity on average in siRNA clones were also observed from evaluations performed in bioreactors.
View details for DOI 10.1016/j.jbiotec.2011.03.003
View details for PubMedID 21392546