Preclinical development of keliximab, a Primatized anti-CD4 monoclonal antibody, in human CD4 transgenic mice: characterization of the model and safety studies

FDA and industry collaboration: Identifying opportunities to further reduce reliance on nonhuman primates for nonclinical safety evaluations

The nonhuman primate (NHP) has always been a limited resource for pharmaceutical research with ongoing efforts to conserve. This is due to their inherent biological properties, the growth in biotherapeutics and other modalities, and their use in small molecule drug development. The SARS-CoV-2 pandemic has significantly impacted the availability of NHPs due to the immediate need for NHPs to develop COVID-19 vaccines and treatments and the China NHP export ban; thus, accelerating the need to further replace, reduce and refine (3Rs) NHP use. The impact of the NHP shortage on drug development led DruSafe, BioSafe, and the United States (U.S.) Food and Drug Administration (FDA) Center for Drug Evaluation and Research (CDER) to discuss this issue at their 2021 annual meeting. This meeting identified areas to further the 3Rs in NHP use within the current nonclinical safety evaluation regulatory framework and highlighted the need to continue advancing alternative methods towards the aspirational goal to replace use of NHPs in the long term. Alignment across global health authorities is necessary for implementation of approaches that fall outside existing guidelines. This article captures the proceedings from this meeting highlighting current best practices and areas for 3Rs in NHP use.

PDGFRα monoclonal antibody: Assessment of embryo-fetal toxicity and time-dependent placental transfer of a murine surrogate antibody of olaratumab in mice

BACKGROUND

Olaratumab (Lartruvo™) is a recombinant human IgG₁ monoclonal antibody that specifically binds PDGFRα. The maternal and in utero embryo-fetal toxicity and toxicokinetics of a human anti-mouse PDGFRα antibody (LSN3338786) were investigated in pregnant mice.

METHODS

A pilot study was used to set doses for the definitive study. In the definitive study, mice were administered vehicle, 5, 50, or 150 mg/kg LSN3338786 by intravenous injection on gestation days (GD) 6, 9, 12, and 15. Fetal tissues and/or serum samples were collected on GD 10, 12, 15, and 18 to evaluate exposure of antibody.

RESULTS

There were no adverse maternal effects at 50 and 150 mg/kg although maternal deaths and adverse clinical signs were observed at 5 mg/kg. LSN3338786 crossed the placenta as early as GD 10 during organogenesis. Elimination half-life of LSN3338786 in dams decreased between GD 6 and 15. On GD 18, fetal serum concentrations of antibody were substantially higher than maternal serum concentrations at all doses. Increased incidences of malformations consisting of open and partially open eye and increased incidences of skeletal variation frontal/parietal additional ossification site occurred in fetuses from mid- and high-dose groups.

CONCLUSIONS

The majority of transplacental migration of antibody occurred in concert with rapid maternal serum clearance before parturition. The no-observed effect level for teratogenicity of 5 mg/kg was associated with GD 15 maternal serum concentrations 3-11 times lower than clinical exposure of olaratumab, suggesting that olaratumab may cause fetal harm when administered to pregnant women.

Construction of Macaque Immune-Libraries

Rapidly after the clinical success of the first murine therapeutic antibody licensed in 1985 (muromomab-CD3), the first limits of the therapeutic use of antibodies deriving from hybridoma technology appeared. Indeed, the nonhuman nature of these therapeutic antibodies makes them immunogenic when administrated to patients, which develop anti-drug antibodies (ADA). If repeated drug-administrations are needed, the immune response will accelerate the elimination of the drug, leading to a therapeutic failure, or in the worst case to an anaphylactic reaction against the murine protein. Several antibody generations were then developed to obtain better-tolerated molecules: chimeric, humanized, and fully human antibodies. The first antibody generation is fully based on cellular technology (mice hybridoma technology), but the next generations are improved by molecular engineering. Immune antibody phage-display libraries are one successful approach to isolating such engineered antibodies. One strategy to isolate high-affinity and well-tolerated antibodies when no immunized patients are available is based on the phage-display-screening of immune libraries deriving from immunized nonhuman primates, which are phylogenetically close to humans. This chapter presents the strategy for the construction of macaque antibody immune-libraries.

Optimized nonclinical safety assessment strategies supporting clinical development of therapeutic monoclonal antibodies targeting inflammatory diseases

An increasing number of immunomodulatory monoclonal antibodies (mAbs) and IgG Fc fusion proteins are either approved or in early-to-late stage clinical trials for the treatment of chronic inflammatory conditions, autoimmune diseases and organ transplant rejection. The exquisite specificity of mAbs, in combination with their multi-functional properties, high potency, long half-life (permitting intermittent dosing and prolonged pharamcological effects), and general lack of off-target toxicity makes them ideal therapeutics. Dosing with mAbs for these severe and debilitating but often non life-threatening diseases is usually prolonged, for several months or years, and not only affects adults, including sensitive populations such as woman of child-bearing potential (WoCBP) and the elderly, but also children. Immunosuppression is usually a therapeutic goal of these mAbs and when administered to patients whose treatment program often involves other immunosuppressive therapies, there is an inherent risk for frank immunosuppression and reduced host defence which when prolonged increases the risk of infection and cancer. In addition when mAbs interact with the immune system they can induce other adverse immune-mediated drug reactions such as infusion reactions, cytokine release syndrome, anaphylaxis, immune-complex-mediated pathology and autoimmunity. An overview of the nonclinical safety assessment and risk mitigation strategies utilized to characterize these immunomodulatory mAbs and Fc fusion proteins to support first-in human (FIH) studies and futher clinical development in inflammatory disease indications is provided. Specific emphasis is placed on the design of studies to qualify animal species for toxicology studies, early studies to investigate safety and define PK/PD relationships, FIH-enabling and chronic toxicology studies, immunotoxicity, developmental, reproductive and juvenile toxicity studies and studies to determine the potential for immunosuppression and reduced host defence against infection and cancer. Nonclinical strategies to facilitate clinical and market entry in the most efficient timeframe are presented.

Therapeutic targets for rheumatoid arthritis: Progress and promises

Recent therapeutic advancements in understanding of molecular and cellular mechanisms of rheumatoid arthritis (RA) have highlighted the strategies that aim to inhibit the harmful effects of up-regulated cytokines or other inflammatory mediators and to inhibit their associated signaling events. The utility of cytokine as therapeutic targets in RA has been unequivocally demonstrated by the success of tumor necrosis factor (TNF)-α blockade in clinical practice. Partial and non-responses to TNF-α blocking agents, however, together with the increasing clinical drive to remission induction, requires that further therapeutic targets be identified. Numerous proinflammatory mediators with their associated cell signaling events have now been demonstrated in RA, including interleukin (IL)-1 and IL-12 superfamilies. Continued efforts are ongoing to target IL-6, IL-15 and IL-17 in clinical trials with promising data emerging. In the present review, we focus on IL-7, IL-18, IL-32 and IL-10 family of cytokines (IL-19, IL-20 and IL-22) as they are implicated in contributing to the pathogenesis of RA, which could be targeted and offer new therapeutic options for RA therapy. Recent evidences also suggest that multiligand receptor for advanced glycation end products (RAGE), several adipokines and various components of immune system play a critical role in the pathophysiology of RA; therefore we have also highlighted them as therapeutic targets for RA therapy. Components of subcellular pathways, involve in nuclear transcription factor (NF)-κB, mitogen-activated protein kinases (MAPKs) and the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway have also been discussed and offer several novel potential therapeutic opportunities for RA.

Pre-clinical strategies and safety issues in developing therapeutic monoclonal antibodies

Although mAbs present a different set of challenges from other product classes, and the pre-clinical safety evaluation may need to be more extensive than for other medicinal products to overcome the limited predictive value of conventional pre-clinical test systems, the level of risk associated with first administration to human subjects can be effectively mitigated. This article seeks to provide a systematic approach to identifying and addressing the pertinent risks relative to the characteristics of the particular mAb product before the first administration to human subjects.

Monoclonal antibody-induced cytokine-release syndrome

Monoclonal antibodies (mAbs) are widely used in anti-inflammatory and tumor therapy. Although effective, mAbs can cause a variety of adverse effects. An important toxicity seen with a few mAbs is cytokine-release syndrome (CRS). These mAbs include: alemtuzumab, muromonab-CD3, rituximab, tosituzumab, CP-870,893, LO-CD2a/BTI-322 and TGN1412. By contrast, over 30 mAbs used clinically are not associated with CRS. In this review, the clinical aspects of CRS, the mAbs associated with CRS, the cytokines involved and putative mechanisms mediating cytokine release will be discussed. This will be followed by a discussion of the poor predictive value of studies in animals and the prospects for creating in vitro screens. Finally, approaches to decreasing the probability of CRS, decreasing the severity or treating CRS, should it occur, will be described.

Safety and immunotoxicity assessment of immunomodulatory monoclonal antibodies

Most therapeutic monoclonal antibodies (mAbs) licensed for human use or in clinical development are indicated for treatment of patients with cancer and inflammatory/autoimmune disease and as such, are designed to directly interact with the immune system. A major hurdle for the development and early clinical investigation of many of these immunomodulatory mAbs is their inherent risk for adverse immune-mediated drug reactions in humans such as infusion reactions, cytokine storms, immunosuppression and autoimmunity. A thorough understanding of the immunopharmacology of a mAb in humans and animals is required to both anticipate the clinical risk of adverse immunotoxicological events and to select a safe starting dose for first-in-human (FIH) clinical studies. This review summarizes the most common adverse immunotoxicological events occurring in humans with immunomodulatory mAbs and outlines non-clinical strategies to define their immunopharmacology and assess their immunotoxic potential, as well as reduce the risk of immunotoxicity through rational mAb design. Tests to assess the relative risk of mAb candidates for cytokine release syndrome, innate immune system (dendritic cell) activation and immunogenicity in humans are also described. The importance of selecting a relevant and sensitive toxicity species for human safety assessment in which the immunopharmacology of the mAb is similar to that expected in humans is highlighted, as is the importance of understanding the limitations of the species selected for human safety assessment and supplementation of in vivo safety assessment with appropriate in vitro human assays. A tiered approach to assess effects on immune status, immune function and risk of infection and cancer, governed by the mechanism of action and structural features of the mAb, is described. Finally, the use of immunopharmacology and immunotoxicity data in determining a minimum anticipated biologic effect Level (MABEL) and in the selection of safe human starting dose is discussed.

Preclinical development of monoclonal antibodies: considerations for the use of non-human primates

The development of mAbs remains high on the therapeutic agenda for the majority of pharmaceutical and biotechnology companies. Often, the only relevant species for preclinical safety assessment of mAbs are non-human primates (NHPs), and this raises important scientific, ethical and economic issues. To investigate evidence-based opportunities to minimize the use of NHPs, an expert working group with representatives from leading pharmaceutical and biotechnology companies, contract research organizations and institutes from Europe and the USA, has shared and analyzed data on mAbs for a range of therapeutic areas. This information has been applied to hypothetical examples to recommend scientifically appropriate development pathways and study designs for a variety of potential mAbs. The addendum of ICHS6 provides a timely opportunity for the scientific and regulatory community to embrace strategies which minimize primate use and increase efficiency of mAb development.

Alternative Strategies for Toxicity Testing of Species-Specific Biopharmaceuticals

Although toxicology studies should always be conducted in pharmacologically relevant species, the specificity of many biopharmaceuticals can present challenges in identification of a relevant species. In certain cases, that is, when the clinical product is active only in humans or chimpanzees, or if the clinical candidate is active in other species but immunogenicity limits the ability to conduct a thorough safety assessment, alternative approaches to evaluating the safety of a biopharmaceutical must be considered. Alternative approaches, including animal models of disease, genetically modified mice, or use of surrogate molecules, may improve the predictive value of preclinical safety assessments of species-specific biopharmaceuticals, although many caveats associated with these models must be considered. Because of the many caveats that are discussed in this article, alternative approaches should only be used to evaluate safety when the clinical candidate cannot be readily tested in at least one relevant species to identify potential hazards.

Immunogenicity of biologically-derived therapeutics: assessment and interpretation of nonclinical safety studies

An evaluation of potential antibody formation to biologic therapeutics during the course of nonclinical safety studies and its impact on the toxicity profile is expected under current regulatory guidance and is accepted standard practice. However, approaches for incorporating this information in the interpretation of nonclinical safety studies are not clearly established. Described here are the immunological basis of anti-drug antibody formation to biopharmaceuticals (immunogenicity) in laboratory animals, and approaches for generating and interpreting immunogenicity data from nonclinical safety studies of biotechnology-derived therapeutics to support their progression to clinical evaluation. We subscribe that immunogenicity testing strategies should be adapted to the specific needs of each therapeutic development program, and data generated from such analyses should be integrated with available clinical and anatomic pathology, pharmacokinetic, and pharmacodynamic data to properly interpret nonclinical studies.

[Are non-clinical studies predictive of adverse events in humans?]

The predictibility of adverse events induced by drugs in non-clinical safety studies performed on in vitro and/or in vivo models is a key point for the safety of humans exposed to pharmaceuticals. The strength and the weakness of animal studies to predict human toxicity were assessed by an international study on the concordance of the toxicity of 150 pharmaceuticals observed in humans with that observed in experimental animals. The results showed a good correlation (70% of the adverse events in humans were detected in animal studies) and an early time to first appearance of concordant animal toxicity: 94% were first observed in studies of 1 month or less in duration. The highest incidence of overall concordance was seen in hematological and cardiovascular adverse effects and the least was seen in cutaneous and ophthalmological adverse effects. These studies, scientifically and regulatory standardized, need, in some cases to be adapted to specific problems linked to sensitive populations (young, old or with a pathology which could be worsened by the drug), or specific pharmaceuticals (produced by biotechnology). Some severe adverse events are not detected in conventional animal models (immuno-allergy, idiosyncrasy). Taken together, these elements support the value of toxicology studies to predict many human toxic events associated with pharmaceuticals. Nevertheless, a part of human toxicity is not detected by these experimental approaches, and new tools developed through progress in biology and bio-informatics should reduce this uncertainly margin.

Duration of chronic toxicity studies for biotechnology-derived pharmaceuticals: is 6 months still appropriate?

For chronic use biotechnology-derived pharmaceuticals, toxicity studies of 6 months have generally been accepted for regulatory approval. This review assessed the data for 23 approved biotechnology-derived pharmaceuticals to determine whether the studies conducted were predictive of human safety and whether there is new data from approved products indicating that longer than 6 months is necessary. This assessment involved three approaches; whether new toxicities were identified at >6 months, similarity of findings between 6 months and shorter studies and predictivity of clinical adverse events. In two cases there were apparently new findings in studies >6 months. On examination however, one of these cases was a well established risk with foreign protein administration to animals (adalimumab). For insulin aspart, the 12 month study identified tumors not seen in shorter term studies, however, determination of carcinogenic potential is not a goal of chronic toxicity studies and is addressed by separate studies. In most cases the toxicology studies were predictive of common clinical adverse reactions, but were poorly predictive of rare clinical events or some serious adverse reactions. Although specific circumstances may require a longer study, this review indicates no new data is available to refute the utility of 6 month studies to support chronic clinical dosing with biotechnology-derived pharmaceuticals.

High-affinity, human antibody-like antibody fragment (single-chain variable fragment) neutralizing the lethal factor (LF) of Bacillus anthracis by inhibiting protective antigen-LF complex formation

The anthrax lethal toxin (LT) consists of two subunits, the protective antigen (PA) and the lethal factor (LF), and is essential for anthrax pathogenesis. Several recombinant antibodies directed against PA and intended for medical use have been obtained, but none against LF, despite the recommendations of anthrax experts. Here we describe an anti-LF single-chain variable fragment (scFv) that originated from an immunized macaque (Macaca fascicularis) and was obtained by phage display. Panning of the library of 1.8 x 10(8) clones allowed the isolation of 2LF, a high-affinity (equilibrium dissociation constant, 1.02 nM) scFv, which is highly neutralizing in the standardized in vitro assay (50% inhibitory concentration, 1.20 +/- 0.06 nM) and in an in vivo assay. The scFv neutralizes anthrax LT by inhibiting the formation of the LF-PA complex. The genes encoding 2LF are very similar to those of human immunoglobulin germ line genes, sharing substantial (84.2%) identity with their most similar, germinally encoded counterparts; this feature favors medical applications. These results, and others formerly published, demonstrate that our approach can generate antibody fragments suitable for prophylaxis and therapeutics.

Selection of a macaque Fab with framework regions like those in humans, high affinity, and ability to neutralize the protective antigen (PA) of Bacillus anthracis by binding to the segment of PA between residues 686 and 694

Human anthrax infection cannot always be treated successfully by antibiotics, as highlighted by recent bioterrorist attacks; thus, adjunct therapies are clearly needed for the future. There is a particular need to further develop adjunct therapies that can neutralize secreted toxins, such as antibodies directed towards the 83-kDa protective antigen (PA(83)). In the absence of human donors, we immunized a macaque (Macaca fascicularis) with PA(83) to obtain such antibodies suitable as an adjunct therapy for human anthrax infection. By using bone marrow as a template, we PCR amplified specific Fab-encoding genes and cloned them as an immune library (10(7) clones). We isolated a high-affinity (equilibrium dissociation constant [K(D)], 3.4 nM), highly neutralizing (50% inhibitory concentration, 5.6 +/- 0.13 nM) Fab (designated 35PA(83)) from this library by panning. Its epitope was localized by Pepscan analysis between residues 686 and 694 of PA(83) and is part of the region which directly interacts with the cell receptor. 35PA(83) may thus neutralize the anthrax toxin by competing directly for its receptor. The genes encoding 35PA(83) were similar to those of a human immunoglobulin germ line and were assigned to subgroups of human V, (D), or J genes by IMGT/V-QUEST analysis. The 35PA(83) framework regions were 92% identical to a representative allele of each subgroup. When compared to framework regions coded by related human germ line genes, only 2 of 74 (VH) or 75 (VK) analyzed amino acids of 35PA(83) have different chemical characteristics. A very high degree of identity with human framework regions makes 35PA(83) well suited for expression as a whole primatized immunoglobulin G and demonstrates the practicality of using macaque Fabs when immunized human plasma cell donors are not available.

Immunotoxicology: role in the safety assessment of drugs

The immunotoxic effects of drugs are divided into immunosuppression, immunostimulation, hypersensitivity and autoimmunity. The major adverse consequences of immunosuppression are infectious complications and virus-induced malignancies. Flu-like reactions, more frequent autoimmune diseases and hypersensitivity reactions to unrelated allergens, and inhibition of drug-metabolising enzymes are the adverse effects related to immunostimulation. Hypersensitivity reactions are the most frequent immunotoxic effects of drugs. They include immune-mediated ('allergic') and non immune-mediated ('pseudoallergic') reactions. Drug-induced autoimmune reactions, either systemic or organ-specific, are seemingly rare. A review of drug-induced immunotoxic effects demonstrates that immunotoxicity is a significant cause of morbidity and even mortality. As immunotoxicologists have long focused on immunosuppression, the nonclinical immunotoxicity safety assessment of unexpected immunosuppression is based on a number of relatively well standardised and validated animal models and assays. However, there is no general consensus regarding the minimal requirement for this assessment. Many different assays can be used to extend the assessment case by case. Few animal models and assays have been validated for use in the nonclinical safety assessment of unexpected immunostimulation. The situation is worse regarding the prediction of hypersensitivity and autoimmune reactions. Our limited understanding of the molecular and cellular mechanisms of immunotoxicity accounts, at least partly, for this situation. Recent guidelines for the immunotoxicity safety assessment of drugs, even though conflicting on several points, will serve as an impetus not only to refine current animal models and assays, but also to search for better alternatives. The new data generated will have to be interpreted and extended to animal species other than just rodents. Likewise, animal results will have to be compared with findings in humans. The search for immunological endpoints that can be used in several animal species and in humans will therefore become essential. Specific endpoints and clinical criteria that can be included in clinical trials to further investigate the potential for immunotoxicity of new drugs will have to be defined. Because immunotoxicity plays a key role in drug-induced adverse effects, the role of immunotoxicology in drug safety assessment is indisputable and the systematic nonclinical as well as clinical immunotoxicity assessment of every new drug is deemed essential.

Genetic aspects of immune-mediated adverse drug effects

Adverse drug effects (ADEs) are of great importance in medicine and account for up to 5% of all hospital admissions. ADEs can arise from several mechanisms and a wide range of drugs can cause immune-mediated ADEs (IMADEs). For a drug to elicit an IMADE, it must be both immunogenic (that is, able to sensitize the immune system) and antigenic (that is, able to evoke a response from a sensitized immune system). Unlike protein therapeutics, small-molecule drugs (or xenobiotics) are usually neither immunogenic nor antigenic. IMADEs are therefore the result of complex interactions between drug-metabolizing enzymes, immune sensitization and immune effectors. The genetic aspects of this interplay are discussed in this review.

Preclinical safety testing of biotechnology-derived pharmaceuticals: understanding the issues and addressing the challenges

The unique and complex nature of biotechnology-derived pharmaceuticals has meant that it is often not possible to follow the conventional safety testing programs used for chemicals, and hence they are evaluated on a case-by-case basis. Nonclinical safety testing programs must be rationally designed with a strong scientific understanding of the product, including its method of manufacture, purity, sequence, structure, species specificity, pharmacological and immunological effects, and intended clinical use. This knowledge, coupled with a firm understanding of the regulatory requirements for particular product types, will ensure that the most sensitive and regulatory-compliant test systems are used to optimize the chances of gaining regulatory approval for clinical testing or marketing authorization in the shortest possible time frame.

Evaluation of a surrogate antibody for preclinical safety testing of an anti-CD11a monoclonal antibody

Surrogate antibodies are a potential solution to the limited safety testing possible with humanized monoclonal antibodies with restricted species cross-reactivity. However, there are currently no defined criteria by which a potential surrogate antibody should be judged prior to its use in determining safety issues for the clinical agent. We propose that, potential surrogates should undergo rigorous evaluation to assess pharmacological and toxicological activities in comparison to the clinical agent. The current studies evaluated a chimeric mouse/rat anti-mouse CD11a monoclonal antibody (muM17) as a potential surrogate for efalizumab, a humanized anti-CD11a antibody in development for psoriasis. CD11a is a subunit of lymphocyte function associated antigen-1, an integrin involved in cell-cell interactions important to immune responses and inflammation. In vitro pharmacology studies included binding affinity to whole mouse blood and inhibitory activity of muM17 in a mixed lymphocyte response assay. In vivo pharmacology was examined using a delayed type hypersensitivity assay in female CD-1 mice. The toxicology evaluation included a murine tissue cross-reactivity study and in vivo multiple dose studies in female CD-1 mice which were administered muM17 (0.1-30 mg/kg) via subcutaneous injections once a week for 4 weeks. Clinical observations, body weight, clinical pathology, T cell CD11a expression, immunogenicity, toxicokinetics, and lymphoid organ histopathology were evaluated. Finally, since reproductive safety testing would be an important application of the proposed surrogate antibody, a pilot study in pregnant mice was conducted that demonstrated proportional transfer of muM17 into the fetus. These studies demonstrated that muM17 has pharmacological and toxicological activities similar to efalizumab. The selection of dose and regimen for GLP (Good Laboratory Practice) toxicology studies and extrapolation to clinical dose levels was based on pharmacodynamic activity (CD11a downmodulation on T cells).

[Preclinical evaluation of the safety of biotechnology products: specific aspects]

Biotechnology-derived products represent a class of increasingly numerous drugs. One of their major characteristics is extreme diversity, which requires specific approaches for the preclinical evaluation of their safety. The selection of relevant animal species is not easy, as most of these products are human-specific. Thus, only one species will often be used, i.e. primates. As most of these products are large molecules, they can be directly immunogenic. When they are human-specific, no animal model is available to predict the risk. Many biotechnology-derived products have an expected influence on the immune system. This must be taken into account in the preclinical strategy of immunotoxicity evaluation that is now required for every new drug. As conventional toxicity testing is generally limited, safety pharmacology studies should include more than the core battery of assays required by current guidelines in order to complement missing data as much as possible. Because of these particularities, a comprehensive investigation of metabolism and pharmacokinetics is not usually needed. Some products can cross-react with cellular components not intended as therapeutic targets. It is, therefore, essential to rule out the risk of possible cross-reactions that can result in adverse effects. Finally, viral safety is a crucial component of the preclinical safety evaluation of these products. Overall, biotechnology-derived products raise specific issues because of their innovative and original characteristics, and it is difficult to address all these issues if not by using a case-by-case approach.

Practical aspects of including functional endpoints in developmental toxicity studies. Case study: immune function in HuCD4 transgenic mice exposed to anti-CD4 MAb in utero

Keliximab is a human-cynomolgus monkey chimeric (Primatized) monoclonal antibody with specificity for human and chimpanzee CD4. As the preclinical safety assessment of biopharmaceuticals requires evaluation in pharmacologically responsive species, comprehensive toxicology studies, including reproductive toxicity, of this antibody were conducted in a human CD4 transgenic mouse model. The reproductive toxicology studies included a pre- and postnatal development study that incorporated immunotoxicological evaluation of offspring (F1) mice. The potential effects of exposure to treating maternal mice (F0) with keliximab during pregnancy and lactation on offspring viability, physical growth, neurobehavioral development, reproductive function, lymphoid tissue morphological structure, lymphocyte subsets and host resistance to Candida albicans infection were assessed. The results showed no impairment of these functions. The use of F1 transgenic mice in study with keliximab provides an example of a novel practical approach to assess developmental immunotoxicity within a study of pre- and postnatal development designed in accordance with ICH Guidelines.

Preclinical safety evaluation of monoclonal antibodies

Monoclonal antibodies (mAbs) can be potent and specific therapeutics with long plasma half-lives and therefore long exposure times, which are now being clinically used to treat chronic disorders. Their recombinant design means some of their behaviours in the clinic can be determined at the design stage. However, their specific nature means a flexible approach often is required for preclinical studies and the use of novel approaches including parallel reagents and specific transgenic mice are being used. The key aspects at this level to consider are the effects on safety pharmacology and long-term immune status in the preclinical species used in order to predict to people the likely result of chronic clinical usage.

Differential clinical efficacy of anti-CD4 monoclonal antibodies in rat adjuvant arthritis is paralleled by differential influence on NF-kappaB binding activity and TNF-alpha secretion of T cells

The aim of this study was to analyze the differential effects of three anti-CD4 monoclonal antibodies (mAbs) (with distinct epitope specifities) in the treatment of rat adjuvant arthritis (AA) and on T-cell function and signal transduction. Rat AA was preventively treated by intraperitoneal injection of the anti-CD4 mAbs W3/25, OX35, and RIB5/2 (on days -1, 0, 3, and 6, i.e. 1 day before AA induction, on the day of induction [day 0], and thereafter). The effects on T-cell reactivity in vivo (delayed-type hypersensitivity), ex vivo (ConA-induced proliferation), and in vitro (mixed lymphocyte culture) were assessed. The in vitro effects of anti-CD4 preincubation on T-cell receptor (TCR)/CD3-induced cytokine production and signal transduction were also analyzed. While preventive treatment with OX35 and W3/25 significantly ameliorated AA from the onset, treatment with RIB5/2 even accelerated the onset of AA by approximately 2 days (day 10), and ameliorated the arthritis only in the late phase (day 27). Differential clinical effects at the onset of AA were paralleled by a differential influence of the mAbs on T-cell functions, i.e. in comparison with OX35 and W3/25, the 'accelerating' mAb RIB5/2 failed to increase the delayed-type hypersentivity (DTH) to Mycobacterium tuberculosis, increased the in vitro tumor necrosis factor (TNF)-alpha secretion, and more strongly induced NF-kappaB binding activity after anti-CD4 preincubation and subsequent TCR/CD3-stimulation. Depending on their epitope specificity, different anti-CD4 mAbs differentially influence individual proinflammatory functions of T cells. This fine regulation may explain the differential efficacy in the treatment of AA and may contribute to the understanding of such treatments in other immunopathologies.

The functions of cytokines and their uses in toxicology

Cytokines are critical controllers of cell, and hence tissue, growth, migration, development and differentiation. The family includes the inflammatory cytokines such as the interleukins and interferons, growth factors such as epidermal and hepatocyte growth factor and chemokines such as the macrophage inflammatory proteins, MIP-1alpha and MIP-1beta. They do not include the peptide and steroid hormones of the endocrine system. Cytokines have important roles in chemically induced tissue damage repair, in cancer development and progression, in the control of cell replication and apoptosis, and in the modulation of immune reactions such as sensitization. They have the potential for being sensitive markers of chemically induced perturbations in function but from a toxicological point of view, the detection of cytokine changes in the whole animal is limited by the fact that they are locally released, with plasma measures being generally unreliable or irrelevant, and they have short half lives which require precise timing to detect. Even where methodology is adequate the interpretation of the downstream effects of high, local concentrations of a particular cytokine is problematic because of their interdependence and the pleiotropism of their action. A range of techniques exist for their measurement including those dependent upon antibodies specific for the respective cytokines, but with the introduction of genomic and proteomic technology, a more complete study of cytokine changes occurring under the influence of chemical toxicity should be possible. Their further study, as markers of chemical toxicity, will undoubtedly lead to a greater understanding of how synthetic molecules perturb normal cell biology and if, and how, this can be avoided by more intuitive molecular design in the future.

Assessment of biotechnology products for therapeutic use

Biotechnology products for therapeutic use include a very diverse range of products, including growth factors, cytokines, hormones, receptors, enzymes, clotting factors, monoclonal antibodies, vaccines, DNA vaccines, gene transfer products, cell therapies and tissue/organ grafts. While some of these products are regulated as medicinal products, the regulatory status of others such as some cell therapies and tissue/organ-based products differs globally and falls within the borderline between the practice of medicine, medical devices and medicinal products. The unclear regulatory status of some products can add to the complexity of the safety assessment of such products. Conventional non-clinical testing paradigms and guidelines for small molecule development are often not relevant for biotechnology products. Guidelines relating to the non-clinical safety evaluation of biotechnology products, gene transfer products and cell therapy products are available and represent a set of general guiding principals to be applied on a case-by-case basis. The quality, safety and efficacy of biotechnology products for therapeutic use are intricately linked, far more so than for conventional medicinal products, leading to the need for increased communication between those responsible for ensuring product quality and those responsible for non-clinical safety testing. Safety issues include microbiological safety (due to the use of biological materials either during the manufacturing process or as an integral part of the products), pharmacological/ biological toxicity (due to excessive primary pharmacology or undesirable secondary pharmacology), immunogenicity and potential tumourigenicity (for example, for growth factors, immunosuppressive monoclonal antibodies and cell therapy products). Genotoxicity and intrinsic chemical toxicity are less of a problem for biotechnology products.