The European Bioanalysis Forum recommendation on establishing appropriate drug tolerance levels in antidrug antibody assays.

The European Bioanalysis Forum, in collaboration with several key industry stakeholders, has recently led discussions that address international immunogenicity guidance documents, specifically the three tier approach for immunogenicity testing strategies, after more than 20 years of experience with biotherapeutics. As part of this, the strategy and methods used to assess drug tolerance across all immunogenicity assays are challenged, emphasizing that bioanalytical scientists need to consider the context-of-use of each assay. Here, recommendations for drug tolerance assessments, driven by strong scientific rationale and subject to reevaluation as needed, are provided. This includes carefully considering the drug and positive control concentrations considered to be appropriate and which tiers are most relevant for performing drug tolerance assessments.

Proceedings of the 14th European immunogenicity platform open symposium on immunogenicity of biopharmaceuticals.

Biologics have revolutionized disease management in many therapeutic areas by addressing unmet medical needs and overcoming resistance to standard-of-care treatment in numerous patients. However, the development of unwanted immune responses directed against these drugs, humoral and/or cellular, can hinder their efficacy and have safety consequences with various degrees of severity. Health authorities ask that a thorough immunogenicity risk assessment be conducted during drug development to incorporate an appropriate monitoring and mitigation plan in clinical studies. With the rapid diversification and complexification of biologics, which today include modalities such as multi-domain antibodies, cell-based products, AAV delivery vectors, and nucleic acids, developers are faced with the challenge of establishing a risk assessment strategy sometimes in the absence of specific regulatory guidelines. The European Immunogenicity Platform (EIP) Open Symposium on Immunogenicity of Biopharmaceuticals and its one-day training course gives experts and newcomers across academia, industry, and regulatory agencies an opportunity to share experience and knowledge to overcome these challenges. Here, we report the discussions that took place at the EIP's 14th Symposium, held in April 2023. The topics covered included immunogenicity monitoring and clinical relevance, non-clinical immunogenicity risk assessment, regulatory aspects of immunogenicity assessment and reporting, and the challenges associated with new modalities, which were discussed in a dedicated session.

Pharmacokinetic and pharmacodynamic similarity of biosimilar natalizumab (PB006) to its reference medicine: a randomized controlled trial.

BACKGROUND: PB006 (Polpharma Biologics S.A; marketed as Tyruko®, Sandoz) is an approved biosimilar to natalizumab (Tysabri®; Biogen [ref-NTZ]). This multicenter, double-blind, randomized, single-dose study was conducted to demonstrate pharmacokinetic/pharmacodynamic (PK/PD) similarity between PB006 and ref-NTZ. RESEARCH DESIGN AND METHODS: Healthy participants (N = 453) were randomized to receive 3 mg/kg infusion of PB006, US-licensed, or EU-approved ref-NTZ before an 85-day follow-up. Primary PK endpoint was total natalizumab serum concentration over time; secondary PK endpoints explored concentration changes. Primary PD endpoints compared CD19+ cell counts and percentage α4-integrin receptor saturation, per natalizumab's mechanism of action. Secondary PD endpoints explored serum changes in sVCAM-1 and sMAdCAM-1, CD34+, and CD19+ cells. Safety, tolerability, and immunogenicity were assessed. RESULTS: The primary PK endpoint was met, with 90% confidence intervals (CIs) of the geometric mean for serum test/reference ratios contained within a prespecified margin (0.8-1.25). All primary PD endpoints were met, with 90% and 95% CIs within this similarity margin for baseline-adjusted CD19+ cell counts and percentage α4-integrin receptor saturation. All secondary endpoints were similarly contained, except sVCAM. No notable differences in safety, tolerability, or immunogenicity were observed. CONCLUSION: Similarity was confirmed, with PB006 demonstrating PK/PD behavior consistent with that of ref-NTZ. CLINICAL TRIAL REGISTRATION: EudraCT number 2019-003874-15.

PB006 (developed by Polpharma Biologics S.A; and marketed as Tyruko® by Sandoz) is an approved biosimilar to the reference medicine, natalizumab (Tysabri®, Biogen [ref-NTZ]) used to treat relapsing forms of multiple sclerosis. Approved biosimilar medicines have been shown to be as safe and effective as their reference medicines via different types of comparisons to the reference medicine, confirming that physicians and patients can expect the same clinical outcome.This study was conducted to confirm that PB006 acts the same way in the body as ref-NTZ. Healthy participants received one dose of either PB006, ref-NTZ from the US or ref-NTZ from Europe. During the study, blood samples were tested to confirm how much of each medicine was present in participants' blood, as well as to assess changes in immune cells or proteins related to how natalizumab works. The study also measured whether any treatment caused unwanted side effects or caused any changes in the immune system that may stop the medicine working.The results showed that PB006 behaved in the same way as ref-NTZ in the blood. All reported side effects were similar between groups and were as expected for this medicine, and neither PB006 nor ref-NTZ caused any important or unexpected changes to the immune system. This study showed that biosimilar natalizumab, PB006, behaves in the same way as ref-NTZ, and the same treatment outcomes can be expected.

When to Extend Monitoring of Anti-drug Antibodies for High-risk Biotherapeutics in Clinical Trials: an Opinion from the European Immunogenicity Platform.

The determination of a tailored anti-drug antibody (ADA) testing strategy is based on the immunogenicity risk assessment to allow a correlation of ADAs with changes to pharmacokinetics, efficacy, and safety. The clinical impact of ADA formation refines the immunogenicity risk assessment and defines appropriate risk mitigation strategies. Health agencies request for high-risk biotherapeutics to extend ADA monitoring for patients that developed an ADA response to the drug until ADAs return to baseline levels. However, there is no common understanding in which cases an extension of ADA follow-up sampling beyond the end of study (EOS) defined in the clinical study protocol is required. Here, the Immunogenicity Strategy Working Group of the European Immunogenicity Platform (EIP) provides recommendations on requirements for an extension of ADA follow-up sampling in clinical studies where there is a high risk of serious consequences from ADAs. The importance of ADA evaluation during a treatment-free period is recognized but the decision whether to extend ADA monitoring at a predefined EOS should be based on evaluation of ADA data in the context of corresponding clinical signals. If the clinical data set shows that safety consequences are minor, mitigated, or resolved, further ADA monitoring may not be required despite potentially detectable ADAs above baseline. Extended ADA monitoring should be centered on individual patient benefit.

Autoimmune Diseases Are Linked to Type IIb Autoimmune Chronic Spontaneous Urticaria.

PURPOSE: Patients with chronic spontaneous urticaria (CSU) have an increased risk for comorbid autoimmune diseases. In this retrospective multicenter study of CSU patients, we evaluated clinical and laboratory features of CSU associated with a higher risk of comorbid autoimmune diseases. METHODS: We analyzed records of CSU patients (n = 1,199) for a history or presence of autoimmune diseases. Patients were diagnosed with type IIb autoimmune CSU (aiCSU) if all 3 tests were positive: autologous serum skin test (ASST), basophil histamine release assay (BHRA) and/or basophil activation test (BAT), and IgG autoantibodies against FcεRIα/IgE detected by immunoassay. RESULTS: Twenty-eight percent of CSU patients had at least 1 autoimmune disease. The most prevalent autoimmune diseases were Hashimoto's thyroiditis (HT) (≥ 21%) and vitiligo (2%). Two percent of CSU patients had ≥ 2 autoimmune diseases, most frequently HT plus vitiligo. Comorbid autoimmune diseases, in patients with CSU, were associated with female sex, a family history of autoimmune diseases, and higher rates of hypothyroidism and hyperthyroidism (P < 0.001). Presence of autoimmune diseases was linked to aiCSU (P = 0.02). The risks of having autoimmune diseases were 1.7, 2.9 and 3.3 times higher for CSU patients with a positive ASST, BHRA and BAT, respectively. In CSU patients, markers for autoimmune diseases, antinuclear antibodies and/or IgG anti-thyroid antibodies were associated with non-response to omalizumab treatment (P = 0.013). CONCLUSIONS: In CSU, autoimmune diseases are common and linked to type IIb autoimmune CSU. Our results suggest that physicians assess and monitor all adult patients with CSU for signs and symptoms of common autoimmune diseases, especially HT and vitiligo.

2020 White Paper on Recent Issues in Bioanalysis: Vaccine Assay Validation, qPCR Assay Validation, QC for CAR-T Flow Cytometry, NAb Assay Harmonization and ELISpot Validation (Part 3 - Recommendations on Immunogenicity Assay Strategies, NAb Assays, Biosimilars and FDA/EMA Immunogenicity Guidance/Guideline, Gene & Cell Therapy and Vaccine Assays).

The 14th edition of the Workshop on Recent Issues in Bioanalysis (14th WRIB) was held virtually on June 15-29, 2020 with an attendance of over 1000 representatives from pharmaceutical/biopharmaceutical companies, biotechnology companies, contract research organizations, and regulatory agencies worldwide. The 14th WRIB included three Main Workshops, seven Specialized Workshops that together spanned 11 days in order to allow exhaustive and thorough coverage of all major issues in bioanalysis, biomarkers, immunogenicity, gene therapy and vaccine. Moreover, a comprehensive vaccine assays track; an enhanced cytometry track and updated Industry/Regulators consensus on BMV of biotherapeutics by LCMS were special features in 2020. As in previous years, this year's WRIB continued to gather a wide diversity of international industry opinion leaders and regulatory authority experts working on both small and large molecules to facilitate sharing and discussions focused on improving quality, increasing regulatory compliance and achieving scientific excellence on bioanalytical issues. This 2020 White Paper encompasses recommendations emerging from the extensive discussions held during the workshop and is aimed to provide the Global Bioanalytical Community with key information and practical solutions on topics and issues addressed, in an effort to enable advances in scientific excellence, improved quality and better regulatory compliance. Due to its length, the 2020 edition of this comprehensive White Paper has been divided into three parts for editorial reasons. This publication (Part 3) covers the recommendations on Vaccine, Gene/Cell Therapy, NAb Harmonization and Immunogenicity). Part 1 (Innovation in Small Molecules, Hybrid LBA/LCMS & Regulated Bioanalysis), Part 2A (BAV, PK LBA, Flow Cytometry Validation and Cytometry Innovation) and Part 2B (Regulatory Input) are published in volume 13 of Bioanalysis, issues 4 and 5 (2020), respectively.

European Immunogenicity Platform 11th Open Scientific Symposium on immunogenicity of biopharmaceuticals.

Given the expanding number of complex therapeutic protein drugs and advanced therapy medicinal products that are being developed, improving our ability to assess the potential immunogenicity of biologics is critical to ensuring treatment efficacy and patient safety. In this context, the European Immunogenicity Platform annual meeting provides opportunities for experts from industry and academia, regulators and clinicians to convene and discuss immunogenicity assessment methods and tools. This report summarizes the key messages on immunogenicity testing, prediction, clinical relevance and advanced therapy medicinal products discussed at the 11th Open Scientific European Immunogenicity Platform Symposium on Immunogenicity of Biopharmaceuticals, Lisbon, Portugal, 17-19 February 2020.

Current Considerations on Characterization of Immune Response to Multi-Domain Biotherapeutics.

Compounds containing two or more structural domains with a distinct mode of action relevant to functionality have been defined as multi-domain biotherapeutics (MDBs). Several modalities, including endogenous protein fusions with an antibody Fc fragment or another polypeptide, bispecific antibodies, antibody-drug conjugates, as well as polyethylene glycol conjugates have been viewed as examples of MDBs. Similar to other biotherapeutics, MDBs have the potential to induce a host immune response, commonly detected in the form of anti-drug antibodies (ADAs). The need to characterize ADA specificity to a particular domain of the MDB has been identified as a potential regulatory requirement based on the compound nature of the drug and associated immunogenicity risk factors. MDB-related immunogenicity risk factors are discussed herein. The relative risk level of each of the immunogenicity factors was analyzed based on publicly available information. It is proposed that MDB-related immunogenicity risk factors can be divided into major and minor categories. Major risk category factors include (a) presence of immunogenic structural or linear epitopes of either non-human or human sequence origin and (b) significant homology of an MDB domain to an endogenous protein with a specific and unique function. Proposed minor risk category factors include (a) epitope spread, (b) repetitive antigenic structure of MDB, and (c) hapten-like effect due to chemical conjugation or fusion with a larger protein. Detailed modality-based information on several examples of MDBs is presented to support this proposal.

Biomarkers and clinical characteristics of autoimmune chronic spontaneous urticaria: Results of the PURIST Study.

BACKGROUND: Autoimmune chronic spontaneous urticaria (aiCSU) is an important subtype of chronic spontaneous urticaria (CSU) in which functional IgG autoantibodies to IgE or its high-affinity receptor (FcεRI) induces mast cell degranulation and subsequent symptom development. However, it has not been tightly characterized. This study aimed to better define the clinical and immunological features and to explore potential biomarkers of aiCSU. METHODS: This was a multinational, multicenter study of 182 CSU patients. The clinical features studied included: urticaria activity and impact (UAS7 and quality of life); autologous serum skin test (ASST); IgG anti-FcεRI and IgG anti-IgE; IgG-anti-thyroperoxidase (IgG anti-TPO); total serum IgE; and basophil reactivity (BASO) using the basophil activation test (BAT) and basophil histamine release assay (BHRA). RESULTS: Of the 182 patients, 107 (59%) were ASST+, 46 (25%) were BASO+, and 105 (58%) were IgG anti-FcεRI+/IgE+. Fifteen patients (8%) fulfilled all three criteria of aiCSU. aiCSU patients appeared more severe (UAS7 21 vs 9 P < 0.016) but showed no other clinical or demographic differences from non-aiCSU patients. aiCSU patients also had markedly lower total IgE levels (P < 0.0001) and higher IgG anti-TPO levels (P < 0.001). Of biomarkers, positive BAT and BHRA tests were 69% and 88% predictive of aiCSU, respectively. CONCLUSIONS: aiCSU is a relatively small but immunologically distinct subtype of CSU that cannot be identified by routine clinical parameters. Inclusion of BHRA or BAT in the diagnostic workup of CSU patients may aid identification of aiCSU patients, who may have a different prognosis and benefit from specific management.

Glycan and Peptide IgE Epitopes of the TNF-alpha Blockers Infliximab and Adalimumab - Precision Diagnostics by Cross-Reactivity Immune Profiling of Patient Sera.

Biological drugs like therapeutic antibodies are widely used for the treatment of various diseases like inflammatory disorders and cancer. A drawback of these novel treatments is the substantial proportion of patients experiencing adverse reactions such as loss-of-drug effect or hypersensitivity reactions. These reactions are associated with pre-existing and/or developing anti-drug antibodies. Especially IgE development is a risk factor for life-threatening systemic anaphylaxis. METHODS: In order to characterize the individual drug-specific serum IgE, an IgE cross-reactivity immune profiling (ICRIP) assay was developed. Individual IgG epitopes of anti-drug antibodies against adalimumab were identified by epitope mapping via peptide microarray. RESULTS: ICRIP analyses of sera from patients treated with the therapeutic antibodies adalimumab (ADL) and infliximab (IFX) reveal individual, distinct IgE binding patterns. IgG epitopes were identified mostly located in the variable region of ADL. CONCLUSIONS: Using ICRIP and peptide microarrays for pharmacovigilance of the TNF-α blockers IFX and ADL, risk factors and biomarkers before and during therapy shall be identified. These diagnostic systems provide the basis for a safe and efficacious therapy decision for each patient in cases of adverse drug reactions mediated by different types of anti-drug antibodies.

Establishment of the first WHO Erythropoietin antibody reference panel: Report of an international collaborative study.

A panel of 9 fully human monoclonal antibodies against human erythropoietin (EPO) with defined characteristics (non-neutralizing, neutralizing, various isotypes, affinities) representative of those evident in antibody-mediated pure red cell aplasia (PRCA) and non-PRCA patients were formulated and lyophilized. The panel was evaluated in a multi-centre international collaborative study comprising eighteen different laboratories using different assay platforms including those in routine use. These included binding assays, some based on use of novel technologies and neutralization assays predominantly employing EPO responsive cell-lines. Results showed that detection and titre varied depending on antibody characteristics and the method used. Only selective assay platforms were capable of detecting the diverse repertoire of EPO antibodies in the panel indicating that some clinically relevant antibodies are likely to be missed in some assays. Importantly, the clinical samples from PRCA patients were distinguished as antibody-positive and the healthy donor serum as antibody negative across all different platforms tested. For neutralization, data was generally consistent across the assays for the different samples regardless of the cell-line and the assay conditions. The heterogeneity in data from the study clearly indicated the need for reference standards for consistency in detecting and measuring EPO antibodies across different assay platforms for monitoring the safety and efficacy of erythropoiesis stimulating agents. Therefore, the WHO ECBS at its meeting in October'15 established the EPO antibody panel, available from NIBSC, to facilitate decision-making on assay selection for testing antibodies against human EPO, for evaluating assay performance of antibody assays for clinical use, for assay validation and for standardization.

Serum pharmacokinetics and cerebrospinal fluid concentration analysis of the new IgG4 monoclonal antibody GNbAC1 to treat multiple sclerosis: A Phase 1 study.

GNbAC1 is a humanized IgG4 monoclonal antibody antagonist of Mulitple Sclerosis Retrovirus Envelope (MSRV-Env), a protein that could play a critical role in multiple sclerosis. This randomized placebo-controlled dose-escalation study evaluated the safety and pharmacokinetics of GNbAC1 in 21 healthy volunteers after single intravenous infusion at doses of 6, 18 and 36 mg/kg. Lumbar punctures were performed at days 2, 15 or 29 to measure GNbAC1 concentrations in cerebrospinal fluid (CSF). GNbAC1 was well tolerated. Serum data show a dose-linear pharmacokinetics. A mean CSF/serum ratio of 0.12% was observed at Day 2, increasing to 0.39% at Day 15 and 0.42% at Day 29. Linear regression analysis shows a relationship between GNbAC1 CSF/serum ratio and albumin CSF/serum ratio and a relationship at the limit of statistical significance with the timing of CSF sampling.

B cell epitopes on infliximab identified by oligopeptide microarray with unprocessed patient sera.

BACKGROUND: Autoimmune diseases like rheumatoid arthritis and inflammatory bowel disease are treated with TNF-alpha-blocking antibodies such as infliximab and adalimumab. A common side effect of therapeutic antibodies is the induction of anti-drug antibodies, which may reduce therapeutic efficacy. METHODS: In order to reveal immunogenic epitopes on infliximab which are responsible for the adverse effects, sera from patients treated with infliximab were screened by ELISA for anti-infliximab antibodies. Sera containing high levels of anti-drug-antibodies (>1.25 µg/ml) were analyzed in an oligopeptide microarray system containing immobilized 15-meric oligopeptides from the infliximab amino acid sequence. Immunogenic infliximab IgG-epitopes were identified by infrared fluorescence scanning and comparison of infliximab-treated patients versus untreated controls. RESULTS: Six relevant epitopes on infliximab were recognized by the majority of all patient sera: 4 in the variable and 2 in the constant region. Three of the epitopes in the variable region are located in the TNF-alpha binding region of infliximab. The fourth epitope of the variable part of infliximab is located close to the TNF-alpha binding region and contains an N-glycosylation sequon. The sera positive for anti-infliximab antibodies do not contain antibodies against adalimumab as determined by ELISA. Thus, there is no infliximab-adalimumab cross-reactivity as determined by these systems. CONCLUSIONS: Our data shall contribute to a knowledge-based recommendation for a potentially necessary therapy switch from infliximab to another type of TNF-alpha-blocker. The characterization of immunogenic epitopes on therapeutic monoclonal antibodies using unprocessed patient sera shall lead to direct translational aspects for the development of less immunogenic therapeutic antibodies. Patients benefit from less adverse events and longer lasting drug effects.

Managing unwanted immunogenicity of biologicals.

All protein drugs (biologicals) have an immunogenic potential and we are armed with multiple guidelines, regulatory documents and white papers to assist us in assessing the level of risk for unwanted immunogenicity of new biologicals. However, for certain biologicals, significant immunogenicity becomes only apparent after their use in patients. Causes of immunogenicity are multifactorial but not yet fully understood. Within the pharmaceutical industry there are only a few opportunities to openly discuss the causes and consequences of immunogenicity with regard to the development of new biologicals. The annual Open Scientific Symposium of the European Immunogenicity Platform (EIP) is one such meeting that brings together scientists and clinicians from academia and industry to build know-how and expertise in the field of immunogenicity. The critical topics discussed at the last EIP meeting (February 2014) will be reviewed here. The current opinion of this expert group is that the assessment of unwanted immunogenicity can be improved by using prediction tools, optimizing the performance of immunogenicity assays and learning from the clinical impact of other biologicals that have already been administered to patients. A multidisciplinary approach is warranted to better understand and minimize drug immunogenicity and its clinical consequences.

Preclinical and early clinical development of GNbAC1, a humanized IgG4 monoclonal antibody targeting endogenous retroviral MSRV-Env protein.

Monoclonal antibodies (mAbs) play an increasing important role in the therapeutic armamentarium against multiple sclerosis (MS), an inflammatory and degenerative disorder of the central nervous system. Most of the mAbs currently developed for MS are immunomodulators blocking the inflammatory immune process. In contrast with mAbs targeting immune function, GNbAC1, a humanized IgG4 mAb, targets the multiple sclerosis associated retrovirus envelope (MSRV-Env) protein, an upstream factor in the pathophysiology of MS. MSRV-Env protein is of endogenous retroviral origin, expressed in MS brain lesions, and it is pro-inflammatory and toxic to the remyelination process, by preventing the differentiation of oligodendrocyte precursor cells. We present the preclinical and early clinical development results of GNbAC1. The specificity of GNbAC1 for its endogenous retroviral target is described. Efficacy of different mAb versions of GNbAC1 were assessed in MSRV-Env induced experimental allergic encephalitis (EAE), an animal model of MS. Because the target MSRV-Env is not expressed in animals, no relevant animal model exists for a proper in vivo toxicological program. An off-target 2-week toxicity study in mice was thus performed, and it showed an absence of safety risk. Additional in vitro analyses showed an absence of complement or antibody-dependent cytotoxicity as well as a low level of cross-reactivity to human tissues. The first-in-man clinical study in 33 healthy subjects and a long-term clinical study in 10 MS patients showed that GNbAC1 is well tolerated in humans without induction of immunogenicity and that it induces a pharmacodynamic response on MSRV biomarkers. These initial results suggest that the mAb GNbAC1 could be a safe long-term treatment for patients with MS with a unique therapeutic mechanism of action.

Targeting aurora kinases with danusertib (PHA-739358) inhibits growth of liver metastases from gastroenteropancreatic neuroendocrine tumors in an orthotopic xenograft model.

PURPOSE: Aurora kinases play a crucial role in cell-cycle control. Uncontrolled expression of aurora kinases causes aneuploidy and tumor growth. As conservative treatment options for advanced gastroenteropancreatic neuroendocrine tumors (GEP-NET) are disappointing, aurora kinases may be an interesting target for novel therapeutic strategies. EXPERIMENTAL DESIGN: Human GEP-NETs were tested for aurora kinase expression. The efficacy of the new aurora kinase inhibitor danusertib was evaluated in two human GEP-NET cell lines (BON1 and QGP) in vitro and in vivo. RESULTS: The majority of ten insulinomas and all 33 nonfunctional pancreatic or midgut GEP-NETs expressed aurora A despite a mostly high degree of cell differentiation. Both human GEP-NET cell lines expressed aurora kinase A and B, and high Ser10 phosphorylation of histone H3 revealed increased aurora B activity. Remarkably, danusertib led to cell-cycle arrest and completely inhibited cell proliferation of the GEP-NET cells in vitro. Decreased phosphorylation of histone H3 indicated effective aurora B inhibition. In a subcutaneous murine xenograft model, danusertib significantly reduced tumor growth in vivo compared with controls or mice treated with streptozotocine/5-fluorouracil. As a consequence, decreased levels of tumor marker chromogranin A were found in mouse serum samples. In a newly developed orthotopic model for GEP-NET liver metastases by intrasplenic tumor cell transplantation, dynamic MRI proved significant growth inhibition of BON1- and QGP-derived liver metastases. CONCLUSIONS: These results show that danusertib may impose a new therapeutic strategy for aurora kinase expressing metastasized GEP-NETs.

Endocannabinoids limit excessive mast cell maturation and activation in human skin.

BACKGROUND: Mast cells (MCs) crucially contribute to many inflammatory diseases. However, the physiological controls preventing excessive activities of MCs in human skin are incompletely understood. OBJECTIVE: Since endocannabinoids are important neuroendocrine MC modifiers, we investigated how stimulation/inhibition of cannabinoid 1 (CB1) receptors affect the biology of human skin MCs in situ. METHODS: This was investigated in the MC-rich connective tissue sheath of organ-cultured human scalp hair follicles by quantitative (immuno)histomorphometry, ultrastructural, and quantitative PCR techniques with the use of CB1 agonists or antagonists, CB1 knockdown, or CB1 knockout mice. RESULTS: Kit+ MCs within the connective tissue sheath of human hair follicles express functional CB1 receptors, whose pharmacological blockade or gene silencing significantly stimulated both the degranulation and the maturation of MCs from resident progenitor cells in situ (ie, enhanced the number of tryptase+, FcεRIα, or chymase+ connective tissue sheath-MCs). This was, at least in part, stem cell factor-dependent. CB1 agonists counteracted the MC-activating effects of classical MC secretagogues. Similar phenomena were observed in CB1 knockout mice, attesting to the in vivo relevance of this novel MC-inhibitory mechanism. CONCLUSION: By using human hair follicle organ culture as an unconventional, but clinically relevant model system for studying the biology of MCs in situ, we show that normal skin MCs are tightly controlled by the endocannabinoid system. This limits excessive activation and maturation of MCs from resident progenitors via "tonic" CB1 stimulation by locally synthesized endocannabinoids. The excessive numbers and activation of MCs in allergic and other chronic inflammatory skin diseases may partially arise from resident intracutaneous MC progenitors, for example, because of insufficient CB1 stimulation. Therefore, CB1 stimulation is a promising strategy for the future management of allergy and MC-dependent skin diseases.

Erythropoietin and amyotrophic lateral sclerosis: Plasma level determination.

In amyotrophic lateral sclerosis (ALS), respiratory muscle weakness causes ventilatory insufficiency and tissue hypoxia, which induces a number of metabolic pathways, and in particular increases erythropoietin (EPO) synthesis. EPO is a glycoprotein with neuroprotective properties that stimulates erythropoiesis. Here, EPO plasma level in a large population of ALS patients, with and without respiratory failure, was measured. Plasma EPO level of patients with ALS (n = 98), controls with other neuromuscular diseases (n = 58) and healthy controls (n = 20) has been quantified by ELISA. No significant difference was found between ALS patients and the two control groups. EPO level was not different between bulbar- and spinal-onset patients and was not correlated with disease duration or functional impairment. However, in the ALS group EPO level was higher in females (p = 0.0006) and correlated positively with age (p = 0.006). The subgroup of ALS patients with respiratory failure had higher plasma levels of EPO compared with ALS patients with preserved respiratory function (p = 0.016), but short-term non-invasive ventilation did not change EPO level. In conclusion, EPO levels were found to be significantly higher in ALS patients with respiratory impairment representing preservation of this homeostatic mechanism.