Regulatory perspective on in vitro potency assays for human dendritic cells used in anti-tumor immunotherapy.

Dendritic cells (DCs) are key connectors between the innate and adaptive immune system and have an important role in modulating other immune cells. Therefore, their therapeutic application to steer immune responses is considered in various disorders, including cancer. Due to differences in the cell source and manufacturing process, each DC medicinal product is unique. Consequently, release tests to ensure consistent quality need to be product-specific. Although general guidance concerning quality control testing of cell-based therapies is available, cell type-specific regulation is still limited. Especially guidance related to potency testing is needed, because developing an in vitro assay measuring cell properties relevant for in vivo functionality is challenging. In this review, we provide DC-specific guidance for development of in vitro potency assays for characterisation and release. We present a broad overview of in vitro potency assays suggested for DC products to determine their anti-tumor functionality. Several advantages and limitations of these assays are discussed. Also, we provide some points to consider for selection and design of a potency test. The ideal functionality assay for anti-tumor products evaluates the capacity of DCs to stimulate antigen-specific T cells. Because this approach may not be feasible for release, use of surrogate potency markers could be considered, provided that these markers are sufficiently linked to the in vivo DC biological activity and clinical response. Further elucidation of the involvement of specific DC subsets in anti-tumor responses will result in improved manufacturing processes for DC-based products and should be considered during potency assay development.

Regulatory perspective on in vitro potency assays for human T cells used in anti-tumor immunotherapy.

The adaptive immune system is known to play an important role in anti-neoplastic responses via induction of several effector pathways, resulting in tumor cell death. Because of their ability to specifically recognize and kill tumor cells, the potential use of autologous tumor-derived and genetically engineered T cells as adoptive immunotherapy for cancer is currently being explored. Because of the variety of potential T cell-based medicinal products at the level of starting material and manufacturing process, product-specific functionality assays are needed to ensure quality for individual products. In this review, we provide an overview of in vitro potency assays suggested for characterization and release of different T cell-based anti-tumor products. We discuss functional assays, as presented in scientific advices and literature, highlighting specific advantages and limitations of the various assays. Because the anticipated in vivo mechanism of action for anti-tumor T cells involves tumor recognition and cell death, in vitro potency assays based on the cytotoxic potential of antigen-specific T cells are most evident. However, assays based on other T cell properties may be appropriate as surrogates for cytotoxicity. For all proposed assays, biological relevance of the tests and correlation of the read-outs with in vivo functionality need to be substantiated with sufficient product-specific (non-)clinical data. Moreover, further unraveling the complex interaction of immune cells with and within the tumor environment is expected to lead to further improvement of the T cell-based products. Consequently, increased knowledge will allow further optimized guidance for potency assay development.

Regulatory perspective on in vitro potency assays for human mesenchymal stromal cells used in immunotherapy.

Mesenchymal stromal cells (MSCs) are multipotent cells derived from various tissues that can differentiate into several cell types. MSCs are able to modulate the response of immune cells of the innate and adaptive immune system. Because of these multimodal properties, the potential use of MSCs for immunotherapies is currently explored in various clinical indications. Due to the diversity of potential MSC medicinal products at the level of cell source, manufacturing process and indication, distinct functionality tests may be needed to ensure the quality for each of the different products. In this review, we focus on in vitro potency assays proposed for characterization and release of different MSC medicinal products. We discuss the most used functional assays, as presented in scientific advices and literature, highlighting specific advantages and limitations of the various assays. Currently, the most proposed and accepted potency assay for release is based on in vitro inhibition of T cell proliferation or other functionalities. However, for some products, assays based on other MSC or responder cell properties may be more appropriate. In all cases, the biological relevance of the proposed assay for the intended clinical activity should be substantiated with appropriate product-specific (non-)clinical data. In case practical considerations prevent the use of the ideal potency assay at release, use of a surrogate marker or test could be considered if correlation with functionality has been demonstrated. Nevertheless, as the field of MSC immunology is evolving, improvements can be expected in relevant assays and consequently in guidance related to potency testing.

A structured approach to Exposure Based Waiving of human health endpoints under REACH developed in the OSIRIS project.

Exposure Based Waiving (EBW) is one of the options in REACH when there is insufficient hazard data on a specific endpoint. Rules for adaptation of test requirements are specified and a general option for EBW is given via Appendix XI of REACH, allowing waiving of repeated dose toxicity studies, reproductive toxicity studies and carcinogenicity studies under a number of conditions if exposure is very low. A decision tree is described that was developed in the European project OSIRIS (Optimised Strategies for Risk Assessment of Industrial Chemicals through Integration of Non-Test and Test Information) to help decide in what cases EBW can be justified. The decision tree uses specific criteria as well as more general questions. For the latter, guidance on interpretation and resulting conclusions is provided. Criteria and guidance are partly based on an expert elicitation process. Among the specific criteria a number of proposed Thresholds of Toxicological Concern are used. The decision tree, expanded with specific parts on absorption, distribution, metabolism and excretion that are not described in this paper, is implemented in the OSIRIS webtool on integrated testing strategies.

Exposure-based waiving under REACH.

Within the REACH framework, but also within OECD, there is understanding that for reasons of animal welfare, costs and logistics, it is important to limit the number of tests to be conducted. Exposure-based waiving (EBW) is a potentially important element in testing strategies. This publication describes criteria for exposure-based waiving as foreseen in the REACH regulation and gives more detail to the REACH requirements for exposure-based waiving The principle behind any EBW is that there are situations when human or environmental exposures are so low or infrequent that there is a very low probability that the acquisition of additional effect information may lead to an improvement in the ability to manage risk. EBW therefore is risk-based and needs thorough knowledge on exposure as well as on effects criteria. Both elements are discussed: exposure models are analysed and the uncertainty in their predictions discussed as well as no-effect criteria such as the threshold of toxicological concern. Examples of EBW are provided for environmental, consumer and worker exposure. REACH only allows EBW in a limited number of cases with constraints on tonnage levels, types of tests to be waived and the need for a thorough ES and exposure assessment throughout the life cycle of a chemical and for all human exposure routes and environmental pathways. EBW will only be considered a real option by industry if a cost-benefit analysis shows an advantage, which may heavily depend on the weighing factor one applies for the non-use of experimental animals.

Local inhibition of liver fibrosis by specific delivery of a platelet-derived growth factor kinase inhibitor to hepatic stellate cells.

Liver fibrosis is characterized by excessive proliferation and activation of hepatic stellate cells (HSC), a process in which platelet-derived growth factor (PDGF) plays an important role. Inhibition of liver fibrosis via specific delivery of a PDGF kinase inhibitor to HSC might therefore be an attractive strategy. The HSC-selective carrier mannose-6-phosphate modified human serum albumin (M6PHSA) was equipped with a tyrosine kinase inhibitor, 4-chloro-N-[4-methyl-3-(4-pyridin-3-yl-pyrimidin-2-ylamino)-phenyl]-benzamide (PAP19) (an imatinib derivative), by means of the platinum-based universal linkage system (ULS). The antifibrotic activity of PAP19-M6PHSA was evaluated in culture-activated rat HSC and precision-cut liver slices from fibrotic rats. After 24-h incubation, both free inhibitor PAP19 and PAP19-M6PHSA showed potent activity, as determined by quantitative reverse transcription-polymerase chain reaction analysis of alpha-smooth muscle actin (alphaSMA) and procollagen 1a1. Next, we examined the organ distribution and antifibrotic activity of PAP19-M6PHSA in bile duct-ligated (BDL) rats. Male Wistar rats at day 10 after BDL were administered a single dose of PAP19-M6PHSA and sacrificed at 2 h, 1 day, or 2 days afterward. The accumulation of PAP19-M6PHSA in the liver was quantified by high-performance liquid chromatography analysis (30% of the injected dose at 2 h) and detected in the liver by staining of the carrier. Liver drug levels were sustained at 24 and 48 h after the single dose. Furthermore, PAP19-M6PHSA reduced collagen deposition (Sirius red staining) and alphaSMA staining of activated HSC at these time points in comparison with saline-treated rats. We therefore conclude that delivery of a PDGF-kinase inhibitor to HSC is a promising technology to attenuate liver fibrogenesis.

Precision-cut fibrotic rat liver slices as a new model to test the effects of anti-fibrotic drugs in vitro.

BACKGROUND/AIMS: Current cell culture models contributed significantly to the study of liver fibrosis and the testing of anti-fibrotic drugs but mimic the complex in vivo milieu poorly. Therefore, we evaluated fibrotic rat liver slices as a new, more physiologic in vitro model to test anti-fibrotic compounds. METHODS: Precision-cut slices (8 mm diameter, 250 microm thickness) were prepared from fibrotic rat livers three weeks after bile-duct ligation and incubated for 0-48 h, during which viability and progression of the fibrotic process was evaluated. In addition, the effects of pentoxifylline, gleevec, and dexamethasone on mRNA expression of markers for fibrosis were determined. RESULTS: Fibrotic liver slices remained viable during 48 h of incubation, with increasing alphaSMA and pro-collagen 1a1 mRNA expression, and alphaSMA and collagen protein content after prolonged incubation. Addition of pentoxifylline, gleevec, or dexamethasone during incubation dose-dependently inhibited pro-collagen-1a1 and alphaSMA mRNA expression after 24h of incubation without influencing slice viability. CONCLUSIONS: Fibrotic liver slices are a promising tool to test anti-fibrotic drugs in vitro in a multicellular, fibrotic milieu, which cannot be achieved in vitro using other models. Importantly, this method may provide the opportunity to study anti-fibrotic compounds not only in animal but also in fibrotic human liver tissue.

Precision-cut liver slices as a new model to study toxicity-induced hepatic stellate cell activation in a physiologic milieu.

Hepatic stellate cell (HSC) activation is a key event in the natural process of wound healing as well as in fibrosis development in liver. Current in vitro models for HSC activation contribute significantly to the understanding of HSC biology and fibrogenesis but still fall far short of recapitulating in vivo intercellular functional and anatomic relationships. In addition, when cultured on uncoated plastic, HSC spontaneously activate, which makes HSC activation difficult to regulate or analyze. We have examined whether the use of precision-cut liver slices might overcome these limitations. Liver slices (8 mm diameter, 250 microm thickness) were generated from normal rat liver and incubated for 3 or 16 h with increasing doses of carbon tetrachloride (CCl4). Rat liver slices remained viable during incubation, as shown by minimal enzyme leakage. Expression of markers for HSC activation and the onset of fibrogenesis in the liver slices was studied using real-time PCR and Western blotting. In unstimulated liver slices, mRNA and protein levels of desmin, heat shock protein 47, and alpha B-crystallin remained constant, indicating quiescence of HSC, whereas Krüppel-like factor 6 expression was increased. In contrast, incubation with CCl4 led to a time- and dose-dependent increase in mRNA expression of all markers and an increased alpha B-crystallin protein expression. In conclusion, we have developed a technique to induce activation of quiescent HSC in rat liver slices. This model permits the study of toxicity-induced HSC activation within a physiological milieu, not only in animal but ultimately also in human tissue, and could contribute to the reduction of animal experiments.

Aspirin-like molecules that inhibit human immunodeficiency virus 1 replication.

Some anti-inflammatory molecules are also known to possess anti-human immunodeficiency virus (HIV) activity. We found that o-(acetoxyphenyl)hept-2-ynyl sulfide (APHS), a recently synthesized non-steroidal anti-inflammatory molecule can inhibit HIV-1 replication. The aim of this study was to clarify the mechanism of action of APHS. When administered during the first steps of the infection, APHS was capable of inhibiting the replication of several HIV-1 strains (macrophage-tropic and/or lymphocytotropic) in a dose-dependent manner in both peripheral blood mononuclear cells (PBMC), monocyte-derived macrophages and peripheral blood lymphocytes with 50% inhibitory concentration values of approximately 10 microM. The 50% toxic concentration of APHS varied between 100 and 200 microM in the different primary cells tested. APHS did not affect HIV-1 replication once the provirus was already inserted into the cellular genome. APHS also did not inhibit HIV-1 entry into the host cells as determined by quantification of gag RNA inside PBMC 2h after infection. However, APHS did inhibit gag DNA synthesis during reverse transcription in primary cells, which indicates that APHS may target the reverse transcription process.

APHS can act synergically with clinically available HIV-1 reverse transcriptase and protease inhibitors and is active against several drug-resistant HIV-1 strains in vitro.

OBJECTIVES: The use of multiple drug combinations in current anti-human immunodeficiency virus (HIV) therapy allows lower dosages of individual drugs and results in enhancement of the therapeutic effect due to synergic interactions between different drugs. We have shown that o-(acetoxyphenyl)hept-2-ynyl sulphide (APHS), a recently developed non-steroidal anti-inflammatory drug, shows anti-HIV activity in a dose-dependent manner. The first aim of this study was to investigate whether APHS can act synergically with the clinically available reverse transcriptase and protease inhibitors (RTIs and PIs, respectively) in vitro. Because of the increasing prevalence of RTI- and PI-resistant HIV-1 strains, the second aim of this study was to assess the antiviral activity of APHS against drug-resistant HIV-1 strains in vitro. MATERIALS AND METHODS: HIV-infected peripheral blood mononuclear cells (PBMC) were treated for 7 days with different combinations of APHS and RTIs or PIs. The MT-2 cell line was infected with different HIV-1 strains and treated with APHS for 5 days. RESULTS: APHS showed synergic interactions with the RTIs zidovudine, lamivudine and efavirenz and with the PIs indinavir and ritonavir. The 50% inhibitory concentration (IC50) of APHS in this assay dropped from 13 microM when used alone, to 5 micro M after combination with an RTI or PI. In combination with APHS the IC50 of the RTI and PI drugs tested also dropped. APHS inhibits the replication of HIV-1 strains resistant to zidovudine, lamivudine, stavudine, didanosine, zalcitabine and ritonavir. CONCLUSIONS: These results indicate that APHS can be combined with RTIs and PIs and can inhibit several NRTI and PI-resistant HIV-1 strains.