Cryopreservation of human monocytes for pharmacopeial monocyte activation test

Monocyte activation test (MAT) as an ethical alternative to animal testing

Ethical considerations surrounding the utilization of animals in scientific research have prompted a widespread search for alternative methodologies. This review explores the historical context and ethical dilemmas associated with traditional animal testing methods, before introducing the Monocyte Activation Test (MAT) as a promising alternative, and outlining its basic principles, historical development, and advantages over conventional animal testing. The role of monocytes in the immune system and the activation pathways utilized in MAT are elucidated, while regulatory acceptance and guidelines for MAT validation are introduced, alongside case studies proving its reliability and reproducibility. The applications of MAT in pharmaceutical and medical device testing are summarized, together with its potential future uses. Although the MAT faces limitations and challenges, the global perspective to reduce unnecessary animal tests has become a general concept in animal welfare and scientific research. [BMB Reports 2025; 58(3): 105-115].

Research progress of implantation materials and its biological evaluation

With the development of modern material science, life science and medical science, implantation materials are widely employed in clinical fields. In recent years, these materials have also evolved from inert supports or functional substitutes to bioactive materials able to trigger or promote the regenerative potential of tissues. Reasonable biological evaluation of implantation materials is the premise to make sure their safe application in clinical practice. With the continual development of implantation materials and the emergence of new implantation materials, new challenges to biological evaluation have been presented. In this paper, the research progress of implantation materials, the progress of biological evaluation methods, and also the characteristics of biocompatibility evaluation for novel implantation materials, like animal-derived implantation materials, nerve contact implantation materials, nanomaterials and tissue-engineered medical products were reviewed in order to provide references for the rational biological evaluation of implantable materials.

Current challenges in the manufacture of clinical-grade autologous whole cell vaccines for hematological malignancies

Autologous whole cell vaccines use a patient's own tumor cells as a source of antigen to elicit an anti-tumor immune response in vivo. Recently, the authors conducted a systematic review of clinical trials employing these products in hematological cancers that showed a favorable safety profile and trend toward efficacy. However, it was noted that manufacturing challenges limit both the efficacy and clinical implementation of these vaccine products. In the current literature review, the authors sought to define the issues surrounding the manufacture of autologous whole cell products for hematological cancers. The authors describe key factors, including the acquisition, culture, cryopreservation and transduction of malignant cells, that require optimization for further advancement of the field. Furthermore, the authors provide a summary of pre-clinical work that informs how the identified challenges may be overcome. The authors also highlight areas in which future basic research would be of benefit to the field. The goal of this review is to provide a roadmap for investigators seeking to advance the field of autologous cell vaccines as it applies to hematological malignancies.

Development of the general chapters of the Chinese Pharmacopoeia 2020 edition: A review

The Chinese Pharmacopoeia 2020 edition was reviewed and approved by the National Medical Products Administration and the National Health Commission of the People's Republic of China in July 2020. The current edition was officially implemented on December 30, 2020. The general chapters of the Chinese Pharmacopoeia discuss the general testing methods and guidelines, which are the common requirements and basis for the implementation of drug standards in the Chinese Pharmacopoeia. Owing to adherence to the principles of scientificity, versatility, operability, and sustainable development, there is an improvement in the general chapters of the 2020 edition over those of the previous editions. Further, the application of advanced and mature analytical techniques has expanded, the development of testing methods for exogenous pollutants in traditional Chinese medicines has been strengthened, and technical requirements are now better harmonized with international standards. The updated edition provides technical and methodological support to ensure safety, effectiveness, and control of pharmaceuticals in China and will play an important and active role in encouraging the application of advanced technologies, improving the quality control of medicines, and strengthening the means of drug regulation in China. This review provides a comprehensive introduction of the main features of and changes to the general chapters in the Chinese Pharmacopoeia 2020 edition and aims to provide reference for its correct understanding and accurate implementation.

Cryopreservation of peripheral blood mononuclear cells for use in proliferation assays: First step towards potency assays

Investigational cell-based therapeutics are rapidly heading towards pivotal clinical trials. The premise is that the scientific rationale is well defined, and that product quality reflects exactly this. In vitro potency assays are necessary tools for evaluating cell products, and with potency assays comes high demands for standardization and reproducibility of the methods involved. For demonstrating principles of cell therapeutics for allogeneic use or with claimed immunosuppressive efficacies, assays involving peripheral blood mononuclear cells (PBMC) are critical. Establishment of a cryopreserved bank of PBMC favors standardization, as it allows repeated use of a single donor and simultaneous testing of several donors. The first step to fulfil such potential is to ensure optimum conditions for preservation of PBMC function, and secondly to design assays which heightens the reproducibility. Emphasis should be put on application of the assay. The objective of the present study was to establish a methodological foundation for cell therapeutics to be tested, and several aspects were factored in, including cell concentrations and partial changes of medium. PBMC were isolated and cryopreserved in six formulations of cryoprotective medium consisting of fetal bovine serum (90%, 60%, and 30%) in combination with dimethyl sulfoxide (10% or 5%). The proliferative capacity of the cryopreserved cells was assayed by labeling with carboxyfluorescein succinimidyl ester and stimulation by phytohemagglutinin or in mixed lymphocyte reactions, analyzed by flow cytometry. To counter an eventual lag phase post thaw, the assays were designed to include two durations and to explore the possibility of reducing cell numbers, two cell concentrations. Qualitative and quantitative aspects of the staining were affected by formulation as well as design, stressing the importance of basic optimization for assay development. We conclude that the established methods allow for optimized preservation of function and will serve as a platform for further development of robust functional assays.

Current technologies to endotoxin detection and removal for biopharmaceutical purification

Endotoxins are the major contributors to the pyrogenic response caused by contaminated pharmaceutical products, formulation ingredients, and medical devices. Recombinant biopharmaceutical products are manufactured using living organisms, including Gram-negative bacteria. Upon the death of a Gram-negative bacterium, endotoxins (also known as lipopolysaccharides) in the outer cell membrane are released into the lysate where they can interact with and form bonds with biomolecules, including target therapeutic compounds. Endotoxin contamination of biologic products may also occur through water, raw materials such as excipients, media, additives, sera, equipment, containers closure systems, and expression systems used in manufacturing. The manufacturing process is, therefore, in critical need of methods to reduce and remove endotoxins by monitoring raw materials and in-process intermediates at critical steps, in addition to final drug product release testing. This review paper highlights a discussion on three major topics about endotoxin detection techniques, upstream processes for the production of therapeutic molecules, and downstream processes to eliminate endotoxins during product purification. Finally, we have evaluated the effectiveness of endotoxin removal processes from a perspective of high purity and low cost.

The Optimization of HL60-IL6 Assay and its Application in the Pyrogen Detection of Monoclonal Antibody

Background:

The HL60-IL6 assay has been initially established, but the process of the assay and calculation was not simplified. And there are no reports on whether it can be applied to detect pyrogen contamination in the monoclonal antibody.

Objective:

The study aimed to improve the HL60/IL-6 assay and detect the pyrogens in the monoclonal antibody drug by HL60-IL6 assay.

Methods:

The human promyelocytic leukemia cell line (HL-60) was incubated with pyrogen standard solution, such as lipopolysaccharide (LPS), zymosan and lipoteichoic acid (LTA),or monoclonal antibody sample solution for 48 hours, and then cytokines interleukin-6 (IL-6),secreted from HL-60, were measured by ELISA. The study further described the standard curves on OD (Optical Density) value of IL-6 responding to pyrogen stimulation, and determined the content of pyrogen in the monoclonal antibody production after validation. In addition, the sensitivity of HL60 to three pyrogens was evaluated to establish one standard curve to determine endotoxin and non-endotoxin level. Then, the credibility of standard curves was evaluated. After improvement of the assay, 9 monoclonal antibody batches were assayed for pyrogens in parallel with the Rabbit Pyrogen Test (RPT) and HL60/IL-6 assay.

Results:

It was achieved that the standard curve between OD value of IL-6 and pyrogen concentration was established. Then, it was found that the sensitivity of HL60 responding to LPS was the weakest, as a result of which, only LPS standard curve needs to be described in each test for detection of pyrogens. Besides, to evaluate the credibility of standard curve, the parameters of the standard curve were restricted and the resulting interpretation was also specified. 3 Bevacizumab batches failed the RPT, which also showed pyrogenic contamination by the HL60/IL-6 assay.

Conclusion:

HL60-IL6 assay was improved and can be applied to pyrogen detection of monoclonal antibody.

A Novel Reporter Gene Assay for Pyrogen Detection

Fever is a systemic inflammatory response of the body to pyrogens. Nuclear factor κB (NF-κB) is a central signaling molecule that causes the excessive secretion of various pyrogen-induced pro-inflammatory factors. This study explored the feasibility of a novel reporter gene assay (RGA) for pyrogen detection using RAW264.7 cells stably transfected with the NF-κB reporter gene as a pyrogenic marker. The RGA could detect different types of pyrogens, including the lipopolysaccharide of gram-negative bacteria, the lipoteichoic acid of gram-positive bacteria, and the zymosan of fungi, and a good dose-effect relationship was observed in terms of NF-κB activity. The limits of detection of the RGA to those pyrogens were 0.03 EU/ml, 0.001 μg/ml, and 1 μg/ml, respectively. The method had good precision and accuracy and could be applied to many molecules (e.g., nivolumab, rituximab, bevacizumab, etanercept, basiliximab, Haemophilus influenzae type b conjugate vaccine, 23-valent pneumococcal polysaccharide vaccine, group A and group C meningococcal conjugate vaccine, diphtheria, tetanus, pertussis [acellular, component], poliomyelitis [inactivated] vaccine, and imject alum adjuvant). The results of this study suggest that the novel RGA has a wide pyrogen detection spectrum and is sufficiently sensitive, stable, and accurate for various applications.

Evaluation of the monocyte activation test for the safety testing of meningococcal B vaccine Bexsero: A collaborative study

The aim of this collaborative study was to evaluate the robustness of the monocyte activation test (MAT) for quantifying the pyrogenic content in the outer membrane vesicle (OMV)-containing vaccine Bexsero: the first meningococcal B vaccine to be licenced. We analysed datasets from 9 laboratories covering 15 test systems for 3 batches of Bexsero with higher, equivalent and lower activity relative to a reference lot in the MAT. Activity was measured in terms of relative pyrogen units (RPU) based on European Pharmacopoeia (Ph. Eur.) MAT Chapter 2.6.30 Method C: Reference Lot Comparison Test. We report that all 15 test systems were consistent in that they showed sample A to be the most active in the MAT; that 13 of 15 test systems had an accuracy of more than 80% and an overall geometric mean RPU of 1.03 with lower and upper 95% confidence limits of 0.97 and 1.09 respectively for a sample with an expected value of 1.00 RPU. We also report larger variability in the results for test systems involving cells from individual blood donations for sample A suggesting that there could be donor to donor differences in sensitivity to the vaccine constituents responsible for the higher activity of this batch. Overall, the consistency and accuracy of the MAT was remarkable given the range of test systems used by participants, all of which are permitted by the Ph. Eur. General MAT Chapter. This is important given the limitations of the rabbit pyrogen test for the control of pyrogenicity in general and particularly with products with intrinsic pyrogenicity such as Bexsero.

A Comparison of Pyrogen Detection Tests in the Quality Control of Meningococcal Conjugate Vaccines: The Applicability of the Monocyte Activation Test

The meningococcal C conjugate vaccine (MenCC) is an interesting model with which to test the efficacy of the Monocyte Activation Test (MAT) as an alternative method of pyrogen testing in the quality control of vaccines. The MenCC that has been produced by Bio-Manguinhos in Brazil is in the final development stage, and, as recommended in the guidelines for MenCC production, its pyrogen content must be determined by using the Limulus Amoebocyte Lysate (LAL) assay and the Rabbit Pyrogen Test (RPT). This represents an ideal opportunity to compare LAL and RPT data with data obtained by using a MAT system with cryopreserved whole blood and IL-6/IL-1β as marker readouts. In order to assess the compatibility of the MAT with MenCC, endotoxin and non-endotoxin pyrogen content was quantified by using MenCC samples spiked with lipopolysaccharide (LPS), lipoteichoic acid or zymosan standards. The presence of the aluminium-based adjuvant interfered with the MAT, increasing the readout of IL-1β in LPS-spiked MenCC batches. This infringed the product-specific validation criteria of the test, and led to IL-6 being chosen as the more suitable marker readout. No pyrogenic contaminants were identified in the MenCC batches tested, demonstrating consistency among the different systems (MAT, RPT and the LAL assay). In conclusion, the introduction of the MAT during MenCC development could contribute to the elimination of animal tests post-licensing, ensuring human protection based on an effective non-animal based method of quality control.

Development and characterization of stable reporter cells for fast and sensitive detection of pyrogen

Pyrogens are a class of heterogeneous compounds that cause fever and induce inflammatory responses in the host. Lipopolysaccharides (LPS, also known as endotoxin) is the major pyrogen in the category of drug quality control. Accurate and fast quantification of pyrogens is crucial for drug safety. In the present study, we aimed to develop a sensitive and reliable method for rapid detection of pyrogens using luciferase reporter assay. Stable human A549 luciferase reporter cells were constructed under the control of a NF-κB-responsive element or IFN-β promoter. Our results showed that several monoclonal stable cell clones responded to 0.1 EU/ml endotoxin, which was less than human fever threshold at 0.3 EU/ml of endotoxin. Further, compared with original A549 cells, TLR4 expression on the reporter cells were significantly increased after low amount LPS stimulation. In addition, reporter cells also responded to zymosan stimulation. Therefore, these results indicated that the stable luciferase reporter cells respond to endotoxin and non-endotoxin pyrogens and have the potential to further develop into a sensitive and fast pyrogen evaluation method.

Applicability of the Monocyte Activation Test (MAT) in the quality control of the 17DD yellow fever vaccine

The need for alternatives to animal use in pyrogen testing has been driven by the Three Rs concept. This has resulted in the inclusion of the monocyte activation test (MAT) in the European Pharmacopoeia, 2010. However, some technical and regulatory obstacles must be overcome to ensure the effective implementation of the MAT by the industry, especially for the testing of biological products. The yellow fever (YF) vaccine (17DD-YFV) was chosen for evaluation in this study, in view of: a) the 2016-2018 outbreak of YF in Brazil; b) the increase in demand for 17DD-YFV doses; c) the complex production process with live attenuated virus; d) the presence of possible test interference factors, such as residual process components (e.g. ovalbumin); and e) the need for the investigation of other pyrogens that are not detectable by the methods prescribed in the YF vaccine monograph. The product-specific testing was carried out by using cryopreserved and fresh whole blood, and IL-6 and IL-1β levels were used as the marker readouts. After assessing the applicability of the MAT on a 1:10 dilution of 17DD-YFV, endotoxin and non-endotoxin pyrogens were quantified in spiked batches, by using the lipopolysaccharide and lipoteichoic acid standards, respectively. The quantitative analysis demonstrated the correlation between the MAT and the Limulus amoebocyte lysate (LAL) assays, with respect to the limits of endotoxin recovery in spiked batches and the detection of no pyrogenic contamination in commercial batches of 17DD-YFV. The data demonstrated the applicability of the MAT for 17DD-YFV pyrogen testing, and as an alternative method that can contribute to biological quality control studies.

Analysis of IL-6 and IL-1β release in cryopreserved pooled human whole blood stimulated with endotoxin

To overcome the lack of availability of fresh human whole blood for pyrogen detection, we explored the feasibility of utilizing cryopreserved pooled human blood to detect the responses of the pro-inflammatory cytokines IL-6 and IL-1β to LPS. Whole blood was obtained from five donors and incubated with LPS. The quantities of pro-inflammatory cytokines were measured using ELISA, and the results were compared among the samples. After the blood was cryopreserved with Dimethyl sulfoxide (DMSO) (10% v/v) and stored for 4 mo at –196℃, the detection limits of the IL-6/IL-1β responses to LPS were 0.2/0.4 endotoxin units (EU)/ml, respectively, and IL-6/IL-1β release increased in response to LPS in a dose-dependent manner. When these experiments were performed in three separate laboratories, the within-laboratory reproducibility of the IL-6/IL-1β responses was 100%/86.7%, 93.3%/100%, and 86.7%/80%, and the inter-laboratory reproducibility was 92.9%/85.7%, 64.3%/63.6%, and 57.1%/66.7%, respectively. The sensitivity (the probability of correctly classifying positive samples) and specificity (the probability of correctly classifying negative samples) of the IL-6/IL-1β tests were 81.7%/82.5% and 100%/100%, respectively. The results of this study suggest that cryopreserved pooled blood is a convenient and viable alternative for evaluating in vitro pyrogenicity. Additionally, maintaining cryopreserved pooled blood promotes safety for the user because it is released only after pretesting for infection parameters and has lower variation than fresh donations from a variety of donors.

Validation of biomarkers to predict response to immunotherapy in cancer: Volume I - pre-analytical and analytical validation

Immunotherapies have emerged as one of the most promising approaches to treat patients with cancer. Recently, there have been many clinical successes using checkpoint receptor blockade, including T cell inhibitory receptors such as cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) and programmed cell death-1 (PD-1). Despite demonstrated successes in a variety of malignancies, responses only typically occur in a minority of patients in any given histology. Additionally, treatment is associated with inflammatory toxicity and high cost. Therefore, determining which patients would derive clinical benefit from immunotherapy is a compelling clinical question.

Although numerous candidate biomarkers have been described, there are currently three FDA-approved assays based on PD-1 ligand expression (PD-L1) that have been clinically validated to identify patients who are more likely to benefit from a single-agent anti-PD-1/PD-L1 therapy. Because of the complexity of the immune response and tumor biology, it is unlikely that a single biomarker will be sufficient to predict clinical outcomes in response to immune-targeted therapy. Rather, the integration of multiple tumor and immune response parameters, such as protein expression, genomics, and transcriptomics, may be necessary for accurate prediction of clinical benefit. Before a candidate biomarker and/or new technology can be used in a clinical setting, several steps are necessary to demonstrate its clinical validity. Although regulatory guidelines provide general roadmaps for the validation process, their applicability to biomarkers in the cancer immunotherapy field is somewhat limited. Thus, Working Group 1 (WG1) of the Society for Immunotherapy of Cancer (SITC) Immune Biomarkers Task Force convened to address this need. In this two volume series, we discuss pre-analytical and analytical (Volume I) as well as clinical and regulatory (Volume II) aspects of the validation process as applied to predictive biomarkers for cancer immunotherapy. To illustrate the requirements for validation, we discuss examples of biomarker assays that have shown preliminary evidence of an association with clinical benefit from immunotherapeutic interventions. The scope includes only those assays and technologies that have established a certain level of validation for clinical use (fit-for-purpose). Recommendations to meet challenges and strategies to guide the choice of analytical and clinical validation design for specific assays are also provided.

Cryopreservation of primary human monocytes does not negatively affect their functionality or their ability to be labelled with radionuclides: basis for molecular imaging and cell therapy

Background

Circulating white blood cells crucially contribute to maintenance and repair of solid organs. Therefore, certain cell populations such as monocytes are attractive targets for use in molecular imaging and cell imaging, e.g. after labelling with radionuclides, as well as for cell therapies. However, the preparation of monocytes may require freezing and thawing to preserve cells for timely and standardised applications. Additional modifications of these cells such as radioisotope labelling are necessary prior to their application in vivo. We therefore tested the hypothesis whether cryopreservation of freshly isolated circulating human monocytes affects their functional phenotype or their suitability for radionuclide labelling.

Results

CD14+CD16− monocytes were isolated from human peripheral blood. They were either directly used for cellular assays and labelling or frozen down using cryoprotectants. In the latter case, cells were thawed prior to further use and analysed for survival, chemotactic responses to various growth factors and adhesion on endothelial cells. In addition, both fresh and cryopreserved monocytes were labelled with radiotracers followed by assessment of survival and chemotactic responses. In all functional assays performed, cryopreserved monocytes did not significantly differ from freshly isolated monocytes with regard to their functionality. Cryopreservation did not affect cell survival. There was no effect on the chemotactic response of monocytes towards different growth factors. Likewise, adhesion properties remained unchanged following cryopreservation. Moreover, the labelling efficiency was similar for freshly isolated and cryopreserved monocytes. Labelling did not negatively affect monocyte survival and function.

Conclusions

Our data indicate that cryopreservation of freshly isolated human primary monocytes is feasible and does not negatively affect their functionality when used for labelling and functional assessment.

Leukoreduction system chambers provide a valuable source of functional monocytes for the monocyte activation test by comparison with internationally validated methods

Despite being added to the European Pharmacopoeia in 2010 and strongly supported by the European directive enforcing the "3R's" - Replace, Reduce and Refine, uptake of the monocyte activation test (MAT) in preference over the rabbit pyrogen test for the detection of pyrogens has been limited. This has been attributed to the difficulty in sourcing human monocytes due to the necessity of phlebotomy. This study has attempted to address this issue by evaluating cryopreserved peripheral blood mononuclear cells (PBMCs) isolated from leukoreduction system chambers (LRSCs), a readily available by-product of platelet apheresis, as a source of monocytes for the MAT. Validation was performed by direct comparison with the two most commonly employed primary monocyte sources: fresh whole blood (WB) and PBMCs from fresh blood, assessing their ability to detect a panel of toll-like receptor (TLR) ligands including Pam3CSK4, Lipoteichoic acid, Peptidoglycan, Poly(I:C) and Flagellin, as well as two different endotoxin sources, with IL-1β and IL-6 as the readouts. All three cell sources were able to detect the pyrogens included in the study with comparable sensitivities, with the exception of TLR3 ligand Poly(I:C). The WB assay produced quantifiable, but significantly lower cytokine levels with every pyrogen tested than either of the PBMCs sources used. LRSCs provided an ample and convenient source of PBMCs which were successfully cryopreserved, providing cell banks for each donor, shown to maintain stability for at least a year. The use of cryopreserved PBMCs reduced the time and effort required to set up an assay, and the availability of single donor cell banks will allow investigations into assay variables in the absence of inter-donor variability. Significantly higher sensitivity to Pam3CSK4 was observed with a proportion of donors. This was found to correlate to single nucleotide polymorphisms rs4833095 and rs5743618 of TLR1. This evidence, along with the wide range of other SNPs identified in TLR regions without known biological function, supports caution in the practice of pooling donor cells in order to overcome donor-to-donor variation.

An improved monocyte activation test using cryopreserved pooled human mononuclear cells

The monocyte activation test (MAT) is a promising replacement of the currently used rabbit pyrogen test to detect the presence of pyrogens in injectable drugs. In the MAT, drugs are incubated with a source of human monocytes and production of pyrogenic cytokines used as readout. The best results are obtained with human mononuclear cells (MNC). However, donor variation requires testing on four different donors, and for most laboratories access to fresh MNCs is a problem. The current study shows how to overcome these problems using frozen pooled MNCs. The MAT is performed by thawing pooled MNC and co-culture overnight with a test substance, LPS or non-endotoxin pyrogens, with IL-6 production as the readout. The study demonstrates that fresh and frozen pooled MNC have comparable sensitivity. The reproducibility of the MAT performed with different batches of frozen pooled MNC was excellent. Different non-endotoxin pyrogens induce IL-6, confirming the ability of the MAT to detect a variety of pyrogens. In conclusion, the MAT using frozen pooled MNC is a highly sensitive, specific and reproducible pyrogen test, able to detect and quantify endotoxin and non-endotoxin pyrogenic contaminations in parenteral pharmaceuticals.