Assessment of Pyrogenic Response of Medical Devices and Biomaterials by the Monocyte Activation Test (MAT): A Systematic Review

Pyrogens are fever-inducing substances routinely investigated in health products through tests such as the Rabbit Pyrogen Test (RPT), the Limulus Amebocyte Lysate (LAL), and the Monocyte Activation Test (MAT). However, the applications of the MAT for medical devices and biomaterials remain limited. This work aimed to overview the studies evaluating the pyrogenicity of medical devices and biomaterials using the MAT, highlighting its successes and potential challenges. An electronic search was performed by December 2023 in PubMed, Scopus, and Web of Science, identifying 321 records which resulted in ten selected studies. Data were extracted detailing the tested materials, MAT variants, interferences, and comparisons between methods. Methodological quality was assessed using the ToxRTool, and the results were synthesized descriptively. The selected studies investigated various materials, including polymers, metals, and natural compounds, employing the different biological matrices of the MAT. Results showed the MAT's versatility, with successful detection of pyrogens in most materials tested, though variability in sensitivity was noted based on the material and testing conditions. Challenges remain in optimizing protocols for different material properties, such as determining the best methods for direct contact versus eluate testing and addressing the incubation conditions. In conclusion, the MAT demonstrates significant potential as a pyrogen detection method for medical devices and biomaterials. However, continued research is essential to address existing gaps, optimize protocols, and validate the test across a broader range of materials.

A novel alternative for pyrogen detection based on a transgenic cell line

Pyrogen, often as a contaminant, is a key indicator affecting the safety of almost all parenteral drugs (including biologicals, chemicals, traditional Chinese medicines and medical devices). It has become a goal to completely replace the in vivo rabbit pyrogen test by using the in vitro pyrogen test based on the promoted 'reduction, replacement and refinement' principle, which has been highly considered by regulatory agencies from different countries. We used NF-κB, a central signalling molecule mediating inflammatory responses, as a pyrogenic marker and the monocyte line THP-1 transfected with a luciferase reporter gene regulated by NF-κB as an in vitro model to detect pyrogens by measuring the intensity of a fluorescence signal. Here, we show that this test can quantitatively and sensitively detect endotoxin (lipopolysaccharide from different strains) and nonendotoxin (lipoteichoic acid, zymosan, peptidoglycan, lectin and glucan), has good stability in terms of NF-κB activity and cell phenotypes at 39 cell passages and can be applied to detect pyrogens in biologicals (group A & C meningococcal polysaccharide vaccine; basiliximab; rabies vaccine (Vero cells) for human use, freeze-dried; Japanese encephalitis vaccine (Vero cells), inactivated; insulin aspart injection; human albumin; recombinant human erythropoietin injection (CHO Cell)). The within-laboratory reproducibility of the test in three independent laboratories was 85%, 80% and 80% and the interlaboratory reproducibility among laboratories was 83.3%, 95.6% and 86.7%. The sensitivity (true positive rate) and specificity (true negative rate) of the test were 89.9% and 90.9%, respectively. In summary, the test provides a novel alternative for pyrogen detection.

Safety Assessment: a Comparative Analysis of Quantitative Content of Bacterial Endotoxins and Evaluation of Pyrogenicity of the Kazakhstan Vaccine QazCovid-in® against COVID-19

We measured the levels of bacterial endotoxins in the bulk vaccine product (BVP) and finished vaccine QazCovid-in® and evaluated the effect of aluminum hydroxide (adjuvant) on the results of LAL test and pyrogenicity of samples in vivo (in rabbits receiving intravenous injection into the marginal ear vein). Administration of BVP with LPS resulted in a dose-dependent increase in body temperature in rabbits similar to that caused by LPS alone, which suggests that aluminum hydroxide in the vaccine did not affect the pyrogenic response in rabbits. Moreover, the LAL test showed that the aluminum hydroxide did not hinder LPS activity after serial dilution of samples.

Pre-Clinical Safety and Immunogenicity Study of a Coronavirus Protein-Based Subunit Vaccine for COVID-19

Creating an effective and safe vaccine is critical to fighting the coronavirus infection successfully. Several types of COVID-19 vaccines exist, including inactivated, live attenuated, recombinant, synthetic peptide, virus-like particle-based, DNA and mRNA-based, and sub-unit vaccines containing purified immunogenic viral proteins. However, the scale and speed at which COVID-19 is spreading demonstrate a global public demand for an effective prophylaxis that must be supplied more. The developed products promise a bright future for SARS-CoV-2 prevention; however, evidence of safety and immunogenicity is mandatory before any vaccine can be produced. In this paper, we report on the results of our work examining the safety, toxicity, immunizing dose choice, and immunogenicity of QazCoVac-P, a Kazakhstan-made sub-unit vaccine for COVID-19. First, we looked into the product's safety profile by assessing its pyrogenicity in vaccinated rabbit models and using the LAL (limulus amebocyte lysate) test. We examined the vaccine's acute and sub-chronic toxicity on BALB/c mice and rats. The vaccine did not cause clinically significant toxicity-related changes or symptoms in our toxicity experiments. Finally, we performed a double immunization of mice, ferrets, Syrian hamsters, and rhesus macaques (Macaca mulatta). We used ELISA to measure antibody titers with the maximum mean geometric titer of antibodies in the animals' blood sera totaling approximately 8 log2. The results of this and other studies warrant recommending the QazCoVac-P vaccine for clinical trials.

The future of pyrogenicity testing: Phasing out the rabbit pyrogen test. A meeting report

The rabbit pyrogen test (RPT) was the benchmark for pyrogenicity testing, but scientific advancements have provided innovative and humane methods, such as the in vitro monocyte-activation test (MAT). However, transitioning from the RPT to the MAT has been challenging. The European Directorate for the Quality of Medicines & HealthCare, the Council of Europe, and the European Partnership for Alternative Approaches to Animal Testing jointly hosted an international conference entitled "The future of pyrogenicity testing: phasing out the rabbit pyrogen test". The conference aimed to show how the European Pharmacopoeia intends to remove the RPT from its texts by 2026, facilitate the use of MAT, and identify gaps in the suppression of RPT. The events contributed to a better understanding of the barriers to RPT replacement and acceptance of in vitro alternatives. Participants comprised stakeholders from Asia, Europe, and North America, including vaccine developers, contract laboratories, and regulators. Participants shared their replacement strategies and experiences with MAT implementation. They emphasised the need for continued cooperation between stakeholders and stressed the importance of international harmonisation of regulatory requirements to help accelerate MAT acceptance outside Europe. Despite the challenges, the willingness to eliminate the unnecessary use of RPT was common across all participants.

Development and application of potency assays based on genetically modified cells for biological products

Potency assays are key to the development, registration, and quality control of biological products. Although previously preferred for clinical relevance, in vivo bioassays have greatly diminished with the advent of dependent cell lines as well as due to ethical concerns. However, for some products, the development of in vitro cell-based assay is challenging, or existing method has limitations such as tedious procedure or low sensitivity. The generation of genetically modified (GM) cell line with improved response to the analyte provides a scientific and promising solution. Potency assays based on GM cell lines are currently used for the quality control of biological products including cytokines, hormones, therapeutic antibodies, vaccines and gene therapy products. In this review, we have discussed the general principles of designing and developing GM cells-based potency assays, including identification of cellular signaling pathways and detectable biological effects, generation of responsive cell lines and constitution of test systems, based on the current research progress. In addition, the applications of some novel technologies and the common concerns regarding GM cells have also been discussed. The research presented in this review provides insights for the development and application of novel GM cells-based potency assays for biological products.

A worldwide survey on the use of animal‐derived materials and reagents in scientific experimentation

The use of cell and tissue‐based methods in basic, applied and regulatory science has been increasing exponentially. Animal‐derived components, including serum, coating materials, growth factors and antibodies are routinely used in cell/tissue cultures and in general laboratory practices. In addition to ethical issues, the use and production of animal‐derived materials and reagents raises many scientific concerns, generally associated with presence of undefined components and batch‐to‐batch variability, which may compromise experimental reproducibility. On the other hand, non‐animal materials and reagents, such as human cells, alternatives to animal sera or non‐animal recombinant antibodies, are becoming increasingly available, and their use is encouraged by the EU Directive 2010/63 and the Guidance Document on Good In vitro Method Practices (GIVIMP), published by the Organization for Economic Cooperation and Development (OECD). In an effort to map the current state of use of animal‐derived reagents across different sectors and to identify the obstacles possibly hampering the implementation of non‐animal derived alternatives, a global online survey addressed to scientists working on in vivo, in vitro, in silico methods, in academia as well as pharmaceutical or cosmetic companies, was conducted with the goal to understand: 1) the most commonly used animal‐derived materials and reagents, 2) the main issues associated with the production and use of animal‐derived materials and reagents, 3) the current level of knowledge on available non‐animal alternative materials and reagents, and 4) what educational and information sources could be most useful or impactful to disseminate knowledge on non‐animal alternatives. This paper provides an overview of the survey replies and discusses possible proposals to increase awareness, acceptance and use of non‐animal ingredients.

The monocyte activation test detects potentiated cytokine release resulting from the synergistic effect of endotoxin and non-endotoxin pyrogens

Pyrogens are classified in two groups, endotoxin pyrogens and non-endotoxin pyrogens (NEPs). The presence of either in parenteral pharmaceuticals or medical devices can cause severe harm to subjects, and when occurring in combination, synergistic potentiation effects can occur. As the standard in vitro pyrogen test, the Limulus Amebocyte Lysate (LAL) assay can detect LPS only, an endotoxin, but not NEPs. We tested whether the Monocyte Activation Test (MAT) that measures IL-6 induction, is suited for detecting synergistic pyrogen effects. Here we show that MAT reliably detects the NEPs heat-killed Staphylococcus aureus, R848 and lipoteichoic acid, in addition to LPS. When combinations of these pyrogens were tested, a potentiation of IL-6 production was seen beyond an additive effect, apparently reflecting on in-vivo synergisms. The current study therefore demonstrates that MAT not only is a reliable and reproducible assay for the sensitive detection of both endotoxin and non-endotoxin pyrogens, but also for identifying synergistic effects when parenteral drugs are contaminated with multiple pyrogens.

Innate Immunity Modulating Impurities and the Immunotoxicity of Nanobiotechnology-Based Drug Products

Innate immunity can be triggered by the presence of microbial antigens and other contaminants inadvertently introduced during the manufacture and purification of bionanopharmaceutical products. Activation of these innate immune responses, including cytokine secretion, complement, and immune cell activation, can result in unexpected and undesirable host immune responses. These innate modulators can also potentially stimulate the activation of adaptive immune responses, including the formation of anti-drug antibodies which can impact drug effectiveness. To prevent induction of these adverse responses, it is important to detect and quantify levels of these innate immunity modulating impurities (IIMIs) that may be present in drug products. However, while it is universally agreed that removal of IIMIs from drug products is crucial for patient safety and to prevent long-term immunogenicity, there is no single assay capable of directly detecting all potential IIMIs or indirectly quantifying downstream biomarkers. Additionally, there is a lack of agreement as to which of the many analytical assays currently employed should be standardized for general IIMI screening. Herein, we review the available literature to highlight cellular and molecular mechanisms underlying IIMI-mediated inflammation and its relevance to the safety and efficacy of pharmaceutical products. We further discuss methodologies used for direct and indirect IIMI identification and quantification.

Synthetic Material Abdominal Swabs Reduce Activation of Platelets and Leukocytes Compared to Cotton Materials

During surgical procedures, cotton abdominal swabs with their high absorptive capacity and malleability are used to retain organs and absorb blood or other body fluids. Such properties of the natural material cotton are advantageous for most operations, but in cardiopulmonary bypass (CPB) surgery, a high blood volume can accumulate in the thoracic cavity that is quickly retransfused via the heart-lung machine (HLM). This common practice is supposed to be safe due to the high anticoagulation. However, in vitro analyses showed that blood cells and plasma proteins were activated despite a high anticoagulation, which can propagate especially an inflammatory response in the patient. Thus, we investigated patients' blood during CPB surgery for inflammatory and coagulation-associated activation after contact to the HLM and either cotton or synthetic abdominal swabs. Contact with cotton significantly increased thrombocyte and neutrophil activation measured as β-thromboglobulin and PMN-elastase secretion, respectively, compared to synthetic abdominal swabs. Both inflammatory cytokines, interleukin (IL) 1β and IL6, were also significantly increased in the cotton over the synthetic patient group, while SDF-1α was significantly lower in the synthetic group. Our data show for the first time that cotton materials can activate platelets and leukocytes despite a high anticoagulation and that this activation is lower with synthetic materials. This additional activation due to the material on top of the activation exerted by the tissue contact that blood is exposed to during CPB surgery can propagate further reactions in patients after surgery, which poses a risk for this already vulnerable patient group.

Endotoxin contamination of engineered nanomaterials: Overcoming the hurdles associated with endotoxin testing

Nanomaterials are highly susceptible to endotoxin contamination due their large surface-to-volume ratios and endotoxins propensity to associate readily to hydrophobic and cationic surfaces. Additionally, the stability of endotoxin ensures it cannot be removed efficiently through conventional sterilization techniques such as autoclaving and ionizing radiation. In recent times, the true significance of this hurdle has come to light with multiple reports from the United States Nanotechnology Characterization Laboratory, in particular, along with our own experiences of endotoxin testing from multiple Horizon 2020-funded projects which highlight the importance of this issue for the clinical translation of nanomaterials. Herein, we provide an overview on the topic of endotoxin contamination of nanomaterials intended for biomedical applications. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Toxicology and Regulatory Issues in Nanomedicine > Regulatory and Policy Issues in Nanomedicine.

Recombinant bacterial endotoxin testing: a proven solution

Testing of parenteral pharmaceuticals and medical devices for pyrogens (fever-inducing substances) is critical to patient safety. The original rabbit pyrogen test has largely been replaced by different bacterial endotoxin tests based on Limulus amebocyte lysate (LAL), sourced from the blood equivalent of horseshoe crabs after comparative studies to the rabbit pyrogen test. Since 2004 a bacterial endotoxin test based on recombinant factor C (rFC), the endotoxin sensor protein inside of LAL, has been used as an animal-free alternative to LAL. Likewise, numerous studies compared LAL and rFC. Here we describe the history of pyrogen and bacterial endotoxin testing and summarize the evidence presented by those studies. We demonstrate that rFC and LAL are equivalent and comparable.

Standardized pyrogen testing of medical products with the bacterial endotoxin test (BET) as a substitute for rabbit Pyrogen testing (RPT): A scoping review

The Bacterial Endotoxin Test (BET) is a method for exclusion of endotoxin-related pyrogen contamination in pharmaceutical products, as an alternative to the Rabbit Pyrogen Test (RPT). However, BET does not detect a broad range of biologically relevant pyrogens, and interferences can limit its practical use for different medical products. This work aimed to scope the evidence in the scientific literature for case-by-case validity assessments of BET in different uses for medical products. A search strategy was conducted in PubMed, Scopus, and Web of Science in April 2020, according to the PRISMA-ScR statement. Twenty-two references were included, evaluating medical products for endotoxin contamination through both BET and RPT according to standardized protocols. A critical appraisal was performed through ToxRTool, followed by data extraction and qualitative synthesis of outcomes and methodological issues. Four classes of products assessed by BET were identified, including nanoparticles, drugs, blood and biological products. A considerable variation was observed on the BET methods used. Collectively, the evidence indicates different factors influencing the outcome of BET, including the chemical nature of samples that may cause interference depending on the selected method. While some applications to medical products appear adequate, others, such as nanoparticles, may require the use of different in vitro pyrogen testing methods, reinforcing the need for case-by-case validation for each BET method and type of medical product.

Bacterial Endotoxin Testing-Fast Endotoxin Masking Kinetics in the Presence of Lauryldimethylamine Oxide

For release of parenteral drug products, bacterial endotoxin testing is one of a panel of necessary tests. In order to ensure the validity of such tests, various controls are performed, including demonstration of compendial method suitability or method qualification. In addition to compendial suitability testing, quality control (QC) sample hold-time studies are requested by authorities like the Food and Drug Administration (FDA) as described in “Guidance for Industry: Pyrogen and Endotoxins Testing.” It is requested to be determine whether the ability to detect endotoxins can be affected by storage and handling of the sample to be tested. To accomplish these studies, endotoxin is introduced or spiked into the undiluted product and held for a certain period of time in process-representative containers. This time period reflects procedural maximum QC sample hold time from sampling until analysis. Inadequate detection of endotoxin can be caused by adsorption of endotoxin to container surfaces or molecular masking effects, in which the binding sites on the endotoxin molecules are prevented from triggering the enzymatic cascade necessary in the assay, are obscured. The endotoxin may form macromolecular structures, such as sheets or blebs, or the binding sites may otherwise be rendered unavailable due to the sample matrix composition. In either case, the endotoxin assay may yield falsely low results if and when masking occurs. In this work, the QC sample hold times of different in-process controls within the production process of a biopharmaceutical product were analyzed. One out of eight different samples showed a strong masking of endotoxin. Analysis of the sample composition revealed that either kifunensine, mycophenolic acid (MPA), or lauryl-N, N-dimethylamine oxide (LDAO) was responsible for masking. Further analysis clearly identified LDAO as the root cause for masking. A novel one-step mechanism for LDAO-induced endotoxin masking is proposed. The principle is similar to an already-proposed two-step mechanism for endotoxin masking, but the LDAO case combines these two steps: the disturbance of the salt bridges and hydrophobic interactions with LPS in one molecule. These molecular interactions occur quickly when both endotoxin and LDAO are present in the same matrix. Thus, depending on the masking agents, low endotoxin recovery (LER) can occur regardless of the QC sample hold duration.

Decoding inflammation, its causes, genomic responses, and emerging countermeasures

Inflammation is the mechanism of diseases caused by microbial, autoimmune, allergic, metabolic and physical insults that produce distinct types of inflammatory responses. This aetiologic view of inflammation informs its classification based on a cause‐dependent mechanism as well as a cause‐directed therapy and prevention. The genomic era ushered in a new understanding of inflammation by highlighting the cell's nucleus as the centre of the inflammatory response. Exogenous or endogenous inflammatory insults evoke genomic responses in immune and non‐immune cells. These genomic responses depend on transcription factors, which switch on and off a myriad of inflammatory genes through their regulatory networks. We discuss the transcriptional paradigm of inflammation based on denying transcription factors’ access to the nucleus. We present two approaches that control proinflammatory signalling to the nucleus. The first approach constitutes a novel intracellular protein therapy with bioengineered physiologic suppressors of cytokine signalling. The second approach entails control of proinflammatory transcriptional cascades by targeting nuclear transport with a cell‐penetrating peptide that inhibits the expression of 23 out of the 26 mediators of inflammation along with the nine genes required for metabolic responses. We compare these emerging anti‐inflammatory countermeasures to current therapies. The transcriptional paradigm of inflammation offers nucleocentric strategies for microbial, autoimmune, metabolic, physical and other types of inflammation afflicting millions of people worldwide.

Construction of a sensitive pyrogen-testing cell model by site-specific knock-in of multiple genes

A pyrogen test is crucial for evaluating the safety of drugs and medical equipment, especially those involved in injections. As existing pyrogen tests, including the rabbit pyrogen test, the limulus amoebocyte lysate (LAL) test and the monocyte activation test have limitations, development of new models for pyrogen testing is necessary. Here we develop a sensitive cell model for pyrogen test based on the lipopolysaccharides (LPS) signal pathway. TLR4, MD2, and CD14 play key roles in the LPS-mediated pyrogen reaction. We established a new TLR4/MD2/CD14-specific overexpressing knock-in cell model using the CRISPR/CAS9 technology and homologous recombination to detect LPS. Stimulation of our TLR4/CD14/MD2 knock-in cell line model with LPS leads to the release of the cytokines IL-6 and TNF-alpha, with a detection limit of 0.005 EU/ml, which is greatly lower than the lower limit of 0.015 EU/ml detected by the Tachypleus amebocyte lysate (TAL) assay.

Application of a TLR overexpression cell model in pyrogen detection

Pyrogens are components derived from microorganisms that induce complex inflammatory responses. Current approaches to detect pyrogens are complex and difficult to replicate, thus there is a need for new methods to detect pyrogens. We successfully constructed a pyrogen-sensitive cell model by overexpressing Toll-like receptor (TLR)2, TLR4, MD2, and CD14 in HEK293 cells. Since the cytokine IL-6 is specifically released upon stimulation of the TLR2 and TLR4 signaling pathways in response to pyrogen stimulation, we used it as a read out for our assay. Our results show that IL-6 is released in response to trace amounts of pyrogens in our cell model. Pyrogen incubation times and concentrations were explored to determine the sensitivity of our cell model, and was found to be sensitive to 0.05 EU/ml of LPS and 0.05 ug/ml of LTA after stimulation for 5 hr. Our TLR overexpressing cell model, with IL-6 as readout, could be a new method for in vitro testing of pyrogens and applicable for evaluating the safety of drugs.

Inflammatory potential of cotton-based surgically invasive devices: Implications for cardiac surgery

Cotton-based surgical invasive devices with their desired hemostyptic properties have been used for decades in the surgical field. However, in cardiac surgery using the heart-lung machine with direct retransfusion of suction blood, activated blood may re-enter the circulation without filtration and may trigger a cascade reaction leading to systemic inflammation and thrombosis. We therefore set out to evaluate the inflammatory potential of untreated and pyrogen-impregnated cotton-based surgical invasive medical devices. After incubation of the swabs with whole blood or PBMC, the cell-free supernatant was investigated for IL1β and IL6. While the reaction of human whole blood toward cotton swabs could not be influenced by any sterilization technique, dry heat and gamma-irradiation were able to diminish the inflammatory reaction of PBMC toward the material and the used pyrogens. In conclusion, using PBMC in direct contact to cotton we are the first to establish a suitable test method for quantification of the pyrogenic/inflammatory activity of this material. The unaltered reaction of whole blood, however, suggests a crosstalk of cells and plasma proteins in the inflammation activation that is not prevented by sterilization of the swabs. This new in vitro testing methodology may help to better display the clinical situation during development of new materials. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1877-1888, 2019.

Monocyte-activation test to reliably measure the pyrogenic content of a vaccine: An in vitro pyrogen test to overcome in vivo limitations

Pyrogen content is one of the critical quality attributes impacting the safety of a product, and there is an increasing need for assays that can reliably measure this attribute in vaccines. The Limulus amebocyte lysate (LAL) assay and the rabbit pyrogen test (RPT) are the canonical animal-based pyrogen tests currently used to release vaccines; however, there are several drawbacks associated with these tests when applied to Bexsero, intrinsically pyrogenic product, containing a meningococcal Outer Membrane Vesicle component. While the RPT, as applied to Bexsero at its given dilution, ensures safe vaccine, it is highly variable and prone to false positive results. On the other hand, the LAL assay although quantitative, can detect only endotoxin pyrogens and is not sufficient for monitoring the safety of Bexsero, which contains both LPS and non-endotoxin pyrogens. Being aware of these limitations of the RPT and LAL when applied to Bexsero, the Monocyte Activation Test (MAT) which is sensitive to both endotoxin and non-endotoxin based pyrogens has been developed as an alternative pyrogen test. Here, the development and the validation of a MAT assay adapted from the European pharmacopoeia for Bexsero, is described. The MAT assay is then used for monitoring the safety and consistency of Bexsero vaccines at release, providing great advantages in terms of reduced variability with respect to RPT, reduction of animal use, in line with the 3Rs principle concerning the protection of animals and faster time to market. In addition the correlation of the MAT to the RPT has been demonstrated supporting the replacement of the in vivo method and the potential application of the assay to other intrinsically pyrogenic vaccines.

Lipopolysaccharides in Food, Food Supplements, and Probiotics: Should We be Worried?

The fever-inducing effect of lipopolysaccharides (LPS) is well known, and human blood is extremely responsive to this pyrogen. Recently, the safety of LPS-containing food supplements and probiotic drugs as immune-stimulants has been questioned, although these products are orally taken and do not reach the bloodstream undigested. The concerns are understandable, as endotoxaemia is a pathological condition, but the oral uptake of probiotic products containing LPS or Gram-negative bacteria does not pose a health risk, based on the available scientific evidence, as is reviewed here. The available methods developed to detect LPS and other pyrogens are mostly used for quality control of parentally applied therapeuticals. Their outcome varies considerably when applied to food supplements, as demonstrated in a simple comparative experiment. Products containing different Escherichia coli strains can result in vastly different results on their LPS content, depending on the method of testing. This is an inherent complication to pyrogen testing, which hampers the communication that the LPS content of food supplements is not a safety concern.

Chemical Modification of CRISPR gRNAs Eliminate type I Interferon Responses in Human Peripheral Blood Mononuclear Cells

OBJECTIVES

CRISPR/Cas9 is currently the primary tool used for genome editing in mammalian cells. To cleave and alter genomic DNA, both the Cas9 nuclease and a guide RNA (gRNA) must be present in the nucleus. One preferred method of introducing these reagents is direct transfection of a recombinant Cas9 protein complexed with a synthetic gRNA as a ribonucleoprotein (RNP) complex. It is well established from prior work in RNA interference that synthetic RNAs can induce a type I interferon (IFN) response that can limit the application of such methods both in vitro and in vivo. While the immunological properties of short siRNAs are well understood, little is known about the immune recognition of longer CRISPR gRNAs. The objective of our in vitro study was to investigate how the composition of the gRNA influences its recognition by human immune cells.

METHODS

The study was performed in vitro in human peripheral blood mononuclear cells (PBMCs). The PBMCs from healthy donor volunteers were treated with gRNA for 24 h, and the levels of type I IFNs in culture supernatants were measured by a multiplex enzyme-linked immunosorbent chemiluminescent assay. Prior to the analysis in PBMCs, the physicochemical parameters and functionality of all nucleic acid constructs were confirmed by electrospray-ionization mass spectrometry and CRISPR/Cas9 gene editing assessment in HEK293-Cas9 cells, respectively.

RESULTS

We found that unmodified synthetic CRISPR gRNAs triggered a strong IFN response in PBMC cultures in vitro that could be prevented with chemical modification. Likewise, in vitro-transcribed single-guide RNAs (sgRNAs) also triggered a strong IFN response that could only be partially suppressed by phosphatase removal of the 5'-triphosphate group. However, the process by which the gRNA is prepared (i.e., chemically synthesized as a two-part crRNA:tracrRNA complex or in vitro-transcribed as an sgRNA) does not directly influence the immune response to an unmodified gRNA. When experiments were performed in the HEK293 cells, only in vitro-transcribed sgRNA containing 5'-triphosphate induced IFN secretion.

CONCLUSION

The results of our structure-activity relationship study, therefore, suggest that chemical modifications commonly used to reduce the immunostimulation of traditional RNA therapeutics can also be used as effective tools to eliminate undesirable IFN responses to gRNAs.

Platelets: an outlook from biology through evidence-based achievements in critical care

Since the original observations by Bizzozero and Osler, we have seen tremendous advances in the understanding of platelets far beyond haemostasis and the restoration of injured endothelium. In this mini-review on platelets, we will briefly outline their historical description and the importance of their evolution, focusing on a 450 million years old living fossil of Limulus polyphemus, a marine chelicerate arthropod, which helped researchers explain the basis for the immunity role of platelets and make correlations with platelet ultrastructure and function. In addition, the impact of the Limulus Amoebocyte Lysate (LAL) test for modern medicine is highlighted. The role of platelets in cardiovascular diseases, their relevance in arterial and venous thrombosis, and the utilization of antithrombotic drugs as therapeutic agents are also reported. Furthermore, platelet receptors are crucial in aggravating or mitigating other diseases, such as cancer and infections, which can recruit cells and have numerous interactions in a process recently coined "NETosis formation", which is also briefly depicted.