Drug hypersensitivity reactions: review of the state of the science for prediction and diagnosis.

Drug hypersensitivity reactions (DHRs) are a type of adverse drug reaction that can occur with different classes of drugs and affect multiple organ systems and patient populations. DHRs can be classified as allergic or non-allergic based on the cellular mechanisms involved. Whereas nonallergic reactions rely mainly on the innate immune system, allergic reactions involve the generation of an adaptive immune response. Consequently, drug allergies are DHRs for which an immunological mechanism, with antibody and/or T cell, is demonstrated. Despite decades of research, methods to predict the potential for a new chemical entity to cause DHRs or to correctly attribute DHRs to a specific mechanism and a specific molecule are not well-established. This review will focus on allergic reactions induced by systemically administered low-molecular weight drugs with an emphasis on drug- and patient-specific factors that could influence the development of DHRs. Strategies for predicting and diagnosing DHRs, including potential tools based on the current state of the science, will also be discussed.

Re-evaluating the need for chronic toxicity studies with therapeutic monoclonal antibodies, using a weight of evidence approach.

To support registration of monoclonal antibodies (mAbs) for chronic indications, 6-month toxicity studies have historically been conducted. Experience with mAb development has shown a relatively benign and well-understood safety profile for this class, with most toxicity findings anticipated based on pharmacology. We evaluated whether a 6-month toxicity study is necessary to assess the long-term safety of mAbs. Data on First-in-Human (FIH)-enabling and chronic toxicity studies were shared for 142 mAbs submitted by 11 companies. Opportunities to further optimize study designs to reduce animal usage were identified. For 71% of mAbs, no toxicities or no new toxicities were noted in chronic studies compared to FIH-enabling study findings. New toxicities of potential concern for human safety or that changed trial design were identified in 13.5% of cases, with 7% being considered critical and 2% leading to program termination. An iterative, weight-of-evidence model which considers factors that influence the overall risk for a mAb to cause toxicity was developed. This model enables an evidence-based justification, suggesting when 3-month toxicity studies are likely sufficient to support late-stage clinical development and registration for some mAbs.

The use of recovery animals in nonclinical safety assessment studies with monoclonal antibodies: further 3Rs opportunities remain.

Assessment of reversibility from nonclinical toxicity findings in animals with potential adverse clinical impact is required during pharmaceutical development, but there is flexibility around how and when this is performed and if recovery animals are necessary. For monoclonal antibodies (mAbs) and in accordance with ICH S6(R1) if inclusion of recovery animals is warranted, this need only occur in one study. Data on study designs for first-in-human (FIH)-enabling and later-development toxicity studies were shared from a recent collaboration between the NC3Rs, EPAA, Netherlands Medicines Evaluation Board (MEB) and 14 pharmaceutical companies. This enabled a review of practices on recovery animal use during mAb development and identification of opportunities to reduce research animal use. Recovery animals were included in 68% of FIH-enabling and 69% of later-development studies, often in multiple studies in the same program. Recovery groups were commonly in control plus one test article-dosed group or in all dose groups (45% of studies, each design). Based on the shared data review and conclusions, limiting inclusion of recovery to a single nonclinical toxicology study and species, study design optimisation and use of existing knowledge instead of additional recovery groups provide opportunities to further reduce animal use within mAb development programs.

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.

Industry experiences with immune-mediated findings in biotherapeutic nonclinical toxicology studies.

With the growth of monoclonal antibodies and other proteins as major modalities in the pharmaceutical industry, there has been an increase in pharmacology and toxicity testing of biotherapeutics in animals. Animals frequently mount an immune response to human therapeutic proteins. This can result in asymptomatic anti-drug antibody formation, immune complexes that affect drug disposition and/or organ function such as kidney, cytokine release responses, fatal hypersensitivity, or a range of reactions in between. In addition, an increasing number of oncology therapeutics are being developed that enhance or directly stimulate immune responses by a variety of mechanisms, which could increase the risk of autoreactivity and an autoimmune-like syndrome in animals and humans. When evaluating the risk of biotherapeutics prior to entering the clinic, the nonclinical safety data may include any of these responses and it is critical to understand whether they represent a safety liability for humans. The DruSafe Leadership group of the IQ Consortium conducted a survey of industry to understand sponsors' experiences with these immune reactions in nonclinical studies related to both immunogenicity and pharmacologically-mediated immune perturbations. The survey covered what pathways were affected, how the immune responses were presented, how the company and health authorities interpreted the data and whether the immune responses were observed in the clinic. Additionally, the survey gathered information on association of these findings with anti-drug antibodies as well as sponsor's use of immunogenicity predictive tools. The data suggests that the ability of a biotherapeutic to activate the immune system, intended or not, plays a significant role on characteristics of the response and whether theys are translatable.

A T-cell-dependent antibody response study using a murine surrogate anti-PD-1 monoclonal antibody as an alternative to a non-human primate model.

The programmed cell death 1 (PD-1) pathway represents a major immune checkpoint which may be engaged by cells in a tumor microenvironment to overcome active T-cell immune surveillance. Pembrolizumab (Keytruda®) is a potent and highly selective humanized monoclonal antibody (mAb) of the IgG4/κ isotype designed to directly block the interaction between PD-1 and its ligands, PD-L1 and PD-L2. The current work was focused on developing a mouse T-Dependent Antibody Response (TDAR) model using a murinized rat anti-mouse PD-1 antibody (muDX400; a rodent surrogate for pembrolizumab) to evaluate the potential impact of treatment with a PD-1 inhibitor on immune responses to an antigen challenge (e.g. HBsAg in Hepatitis B vaccine). Despite the lower binding affinity and T1/2 compared to pembrolizumab, ligand blocking data indicated muDX400 had appropriate pharmacological activity and demonstrated efficacy in mouse tumor models, thus was suitable for pharmacodynamic and vaccination studies in mice. In a vaccination study in which mice were concomitantly administered muDX400 and the Hepatitis B vaccine, muDX400 was well-tolerated and did not result in any immune-mediated adverse effects. The treatment with muDX400 was associated with a shift in the ratio between naive and memory cells in both CD4+ and CD8+ T-lymphocytes in the spleen but did not affect anti-HBsAg antibody response profile. The mouse TDAR model using the Hepatitis B vaccine and the surrogate anti-PD1 monoclonal antibody was a useful tool in the evaluation of the potential immune-mediated effects of pembrolizumab following vaccination and appears to be a suitable alternative for the nonhuman primate TDAR models utilized for other checkpoint inhibitors.

Biophysical and Immunological Characterization and In Vivo Pharmacokinetics and Toxicology in Nonhuman Primates of the Anti-PD-1 Antibody Pembrolizumab.

The programmed cell death 1 (PD-1) pathway represents a major immune checkpoint, which may be engaged by cells in the tumor microenvironment to overcome active T-cell immune surveillance. Pembrolizumab (Keytruda®, MK-3475) is a potent and highly selective humanized mAb of the IgG4/kappa isotype designed to directly block the interaction between PD-1 and its ligands, PD-L1 and PD-L2. This blockade enhances the functional activity of T cells to facilitate tumor regression and ultimately immune rejection. Pembrolizumab binds to human and cynomolgus monkey PD-1 with picomolar affinity and blocks the binding of human and cynomolgus monkey PD-1 to PD-L1 and PD-L2 with comparable potency. Pembrolizumab binds both the C'D and FG loops of PD-1. Pembrolizumab overcomes human and cynomolgus monkey PD-L1-mediated immune suppression in T-cell cultures by enhancing IL2 production following staphylococcal enterotoxin B stimulation of healthy donor and cancer patient cells, and IFNγ production in human primary tumor histoculture. Ex vivo and in vitro studies with human and primate T cells show that pembrolizumab enhances antigen-specific T-cell IFNγ and IL2 production. Pembrolizumab does not mediate FcR or complement-driven effector function against PD-1-expressing cells. Pembrolizumab displays dose-dependent clearance and half-life in cynomolgus monkey pharmacokinetic and toxicokinetic studies typical for human IgG4 antibodies. In nonhuman primate toxicology studies, no findings of toxicologic significance were observed. The preclinical data for pembrolizumab are consistent with the clinical anticancer activity and safety that has been demonstrated in human clinical trials.

Nonclinical safety of tildrakizumab, a humanized anti-IL-23p19 monoclonal antibody, in nonhuman primates.

Tildrakizumab (also known as MK-3222), is a high-affinity, humanized, immunoglobin G1κ monoclonal antibody targeting the p19 subunit of interleukin-23 recently approved for the treatment of moderate to severe plaque psoriasis in the US, Europe, and Australia. The safety profile of tildrakizumab was characterized in nonclinical studies using a pharmacologically relevant cynomolgus monkey model. In repeat-dose toxicity studies, cynomolgus monkeys were chronically treated with subcutaneous (SC) injections of 100 mg/kg of tildrakizumab every 2 weeks up to 9 months. Tildrakizumab was well tolerated, with no toxicological findings (including assessment of reproductive organs; hormonal effects; and cardiovascular, respiratory, and central nervous system function) at systemic exposures approximately 90 times higher than the recommended human dose of 100 mg. An embryofetal developmental study conducted in pregnant monkeys revealed no treatment-related effects to the developing fetus following SC administration of tildrakizumab 100 mg/kg. In a pre- and postnatal development study, 2 neonatal deaths due to potential viral infection at 100 mg/kg were considered of uncertain relationship to the treatment based on a lack of historical data on the occurrence of viral infection in neonate cynomolgus monkeys. The results of this comprehensive nonclinical safety program support the safe use of tildrakizumab.

Drug safety Africa: An overview of safety pharmacology & toxicology in South Africa.

This meeting report is based on presentations given at the first Drug Safety Africa Meeting in Potchefstroom, South Africa from November 20-22, 2018 at the North-West University campus. There were 134 attendees (including 26 speakers and 34 students) from the pharmaceutical industry, academia, regulatory agencies as well as 6 exhibitors. These meeting proceedings are designed to inform the content that was presented in terms of Safety Pharmacology (SP) and Toxicology methods and models that are used by the pharmaceutical industry to characterize the safety profile of novel small chemical or biological molecules. The first part of this report includes an overview of the core battery studies defined by cardiovascular, central nervous system (CNS) and respiratory studies. Approaches to evaluating drug effects on the renal and gastrointestinal systems and murine phenotyping were also discussed. Subsequently, toxicological approaches were presented including standard strategies and options for early identification and characterization of risks associated with a novel therapeutic, the types of toxicology studies conducted and relevance to risk assessment supporting first-in-human (FIH) clinical trials and target organ toxicity. Biopharmaceutical development and principles of immunotoxicology were discussed as well as emerging technologies. An additional poster session was held that included 18 posters on advanced studies and topics by South African researchers, postgraduate students and postdoctoral fellows.

Cancer Immunotherapy: Factors Important for the Evaluation of Safety in Nonclinical Studies.

The development of novel therapies that can harnass the immune system to eradicate cancer is an area of intensive research. Several new biopharmaceuticals that target the immune system rather than the tumor itself have recently been approved and fundamentally transformed treatment of many cancer diseases. This success has intensified the search for new targets and modalities that could be developed as even more effective therapeutic agents either as monotherapy or in combination. While great benefits of novel immunotherapies in oncology are evident, the safety of these therapies has to also be addressed as their desired pharmacology, immune activation, can lead to "exaggerated" effects and toxicity. This review is focused on the unique challenges of the nonclinical safety assessment of monoclonal antibodies that target immune checkpoint inhibitors and costimulatory molecules. This class of molecules represents several approved drugs and many more drug candidates in clinical development, for which significant experience has been gained. Their development illustrates challenges regarding the predictivity of the animal models for assessing safety and setting starting doses for first-in-human trials as well as the translatability of nonclinical in vitro and in vivo data to the human findings. Based on learnings from the experience to date, factors to consider and novel approaches to explore are discussed to help address the unique safety issues of immuno-oncology drug development.

Characterization of MK-4166, a Clinical Agonistic Antibody That Targets Human GITR and Inhibits the Generation and Suppressive Effects of T Regulatory Cells.

GITR is a T-cell costimulatory receptor that enhances cellular and humoral immunity. The agonist anti-mouse GITR antibody DTA-1 has demonstrated efficacy in murine models of cancer primarily by attenuation of Treg-mediated immune suppression, but the translatability to human GITR biology has not been fully explored. Here, we report the potential utility of MK-4166, a humanized GITR mAb selected to bind to an epitope analogous to the DTA-1 epitope, which enhances the proliferation of both naïve and tumor-infiltrating T lymphocytes (TIL). We also investigated the role of GITR agonism in human antitumor immune responses and report here the preclinical characterization and toxicity assessment of MK-4166, which is currently being evaluated in a phase I clinical study. Expression of human GITR was comparable with that of mouse GITR in tumor-infiltrating Tregs despite being drastically lower in other human TILs and in many human peripheral blood populations. MK-4166 decreased induction and suppressive effects of Tregsin vitro In human TIL cultures, MK-4166 induced phosphorylation of NFκB and increased expression of dual specificity phosphatase 6 (DUSP6), indicating that MK-4166 activated downstream NFκB and Erk signaling pathways. Furthermore, MK-4166 downregulated FOXP3 mRNA in human tumor infiltrating Tregs, suggesting that, in addition to enhancing the activation of TILs, MK-4166 may attenuate the Treg-mediated suppressive tumor microenvironment. Cancer Res; 77(16); 4378-88. ©2017 AACR.

An Evaluation of the Impact of PD-1 Pathway Blockade on Reproductive Safety of Therapeutic PD-1 Inhibitors.

This report discusses the principles of reproductive toxicity risk assessment for biopharmaceuticals blocking the PD-1/programmed cell death ligand 1 (PD-L1) pathway, which have been developed for the treatment of patients with advanced malignancies. The PD-1/PD-L1 pathway is a T-cell co-inhibitory pathway that normally maintains immune tolerance to self. Its role in pregnancy is to maintain immune tolerance to the fetal allograft. In cancer patients, this signaling pathway is hijacked by some neoplasms to avoid immune destruction. PD-1/PD-L1-blocking agents enhance functional activity of the target lymphocytes to eventually cause immune rejection of the tumor. A therapeutic blockade of PD-1/PD-L1 pathway that occurs at full target engagement provides a unique challenge to address the risk to pregnancy because disruption of the same pathway may also reduce or abrogate maternal immune tolerance to the fetal alloantigens inherited through the father. Typically, nonclinical reproductive and developmental toxicity (DART) studies in animals (rats and rabbits) with clinical drug candidates are conducted to identify potential risk in humans and to determine exposure margin for the effects on reproduction as part of the risk assessment. However, for biopharmaceuticals for which the desired mechanism of action cannot be separated from potential deleterious effects to the fetus and when the only relevant toxicology species is nonhuman primate (NHP), the risk to reproduction can be predicted by a mechanism-based assessment using data generated from murine surrogate models as supportive information without conducting DART in NHPs. Such an approach has been used in the evaluation of pregnancy risk of anti-PD-1 agent, pembrolizumab, and has been demonstrated as an important alternative to performing DART studies in NHPs.

The T-dependent antibody response to keyhole limpet hemocyanin in rodents.

Central to the evaluation of potential immunotoxicants is the concept that measurement of multiple parameters is required for the determination of toxicity toward the immune system. A carefully considered integration of endpoints involved in the immune response should be used to determine an immunotoxic effect. A functional evaluation, specifically the rodent T-cell-dependent antibody response (TDAR) model developed for regulated immunotoxicity evaluations, has been established to detect potential immunotoxicity, especially immunosuppression, caused by chemicals and novel pharmaceuticals in development. This chapter provides an overview and detailed procedures involved in the TDAR assay that measures the immune response (i.e., antibody production) to an introduced antigen (i.e., keyhole limpet hemocyanin (KLH)) in rats or mice treated with a chemical (e.g., a known immunotoxicant and/or a new drug candidate). The TDAR model of competent immune function requires the participation of multiple effector cells such as antigen presenting cells, T lymphocytes, and B lymphocytes to produce the final product, the antigen-specific antibody response. Thus, alterations in the level of antibody production to the specific antigen may reflect effects on any or all of the cell populations involved in TDAR.

Summary of a workshop on nonclinical and clinical immunotoxicity assessment of immunomodulatory drugs.

The number of anti-inflammatory and immunomodulatory drugs being developed in the pharmaceutical industry has increased considerably in the past decade. This increase in research and development has been paralleled by questions from both regulatory agencies and industry on how best to assess decreased host resistance to infections or adverse immunostimulation caused by immunomodulatory agents such as anti-cytokine antibodies (e.g., the tumor necrosis factor-alpha inhibitors), anti-adhesion molecule antibodies (e.g., anti-alpha-4 integrin inhibitors) and immunostimulatory molecules (e.g., anti-CD28 antibodies). Although several methods have been developed for nonclinical assessment of immunotoxicity, highly publicized adverse events have brought to light significant gaps in the application of nonclinical immunotoxicity testing in assessing potential risk in humans. Confounding this problem is inconsistent application of immunotoxicology methods for risk assessment within the scientific community, limited understanding of appropriate immunotoxicity testing strategy for immunomodulators and inconsistent testing requests by regulatory agencies. To address these concerns, The Immunotoxicology Technical Committee (ITC) of the International Life Science Institute (ILSI) Health and Environmental Sciences Institute (HESI) organized a workshop on Immunomodulators and Clinical Immunotoxicology in May 2007. The Workshop was convened to identify key gaps in nonclinical and clinical immunotoxicity testing of anti-inflammatory and immunomodulatory agents and to begin to develop consistent approaches for immunotoxicity testing and risk assessment. This paper summarizes the outcome of the HESI ITC Immunomodulators and Clinical Immunotoxicology Workshop. Topics not discussed at the Workshop were outside the scope of this report. Although more work is needed to develop consistent approaches for immunotoxicity assessment of immunomodulators, this Workshop provided the foundation for future discussion.

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.

Immunotoxicity evaluation by immune function tests: focus on the T-dependent antibody response (TDAR) [Overview of a Workshop Session at the 45th Annual Meeting of the Society of Toxicology (SOT) March 5-9, 2006 San Diego, CA].

Increased expectations from a number of regulatory agencies, e.g., Environmental Protection Agency (EPA), Food and Drug Administration (FDA), European Medicines Agency (EMEA), and the Ministry of Health, Labour and Welfare (MHLW) of Japan, call for the evaluation of potential adverse effects on the immune system. As recently summarized in the ICH S8 guideline, the T-cell-dependent antibody response (TDAR) has been identified in a regulatory context as a main functional test of immunotoxicity. While the characterization of immunotoxic potential is pertinent to both the chemical and pharmaceutical industries, the use of immunotoxicology data for hazard identification and/or risk assessment in each case is different. Therefore, multiple approaches to immunotoxicity testing have evolved. The assays that evaluate TDAR function include both well-established tests, e.g., anti-sheep red blood cell plaque-forming cell (PFC) assay, and newer models, e.g., anti-keyhole limpet hemocyanin (KLH) antibody ELISA. These tests vary in the study design, antigen application and analytical methods. However, they all evaluate the same endpoint-a competent immune (e.g., antibody) response to an antigen. Numerous issues have been identified in the application of TDAR tests, including high animal to animal variability; differences in antigen source and potency; a lack of established "normal range" of the immune response and uncertainty about the degree of inhibition of the TDAR to be considered toxicologically important. As such, the need for a forum to discuss these issues was recognized by the immunotoxicology community, and was addressed at the 2006 Society of Toxicology (SOT) Workshop. A series of papers will summarize that forum with the ultimate objectives being to build a consensus among immunotoxicologists on the implications of these factors on using TDAR results in hazard identification and/or risk assessment, and to establish a criteria to classify compounds as immunotoxicants.

Adequate immunotoxicity testing in drug development.

Modulation of the immune system can lead to either immunostimulation or immunosuppression and can be either intended or unintended. While many effects on the immune system's components can be found as a result of a drug treatment or chemical exposure, true immunotoxicity occurs when such treatment results in adverse effects or defects in the immune response. Regulatory expectations to evaluate potential adverse effects of pharmaceuticals warrants a need for reliable and readily standardized methods. Moreover, criteria to classify a drug as an "immunotoxicant" need to be established. Examples of studies using a modified approach to measure T-cell-dependent antibody responses (the rat KLH model) and interpretation of the results in the context of immunotoxicity evaluation are discussed in this paper.

Primary antibody response to keyhole limpet hemocyanin in rat as a model for immunotoxicity evaluation.

To address current regulatory expectations on immunotoxicity testing of new chemicals, we describe an animal model that measures the primary antibody response to the T-cell dependent antigen, keyhole limpet hemocyanin (KLH). Single immunization with KLH by either footpad (300microg/rat) or intravenous (300microg/kg) route in Sprague Dawley rats resulted in increased germinal center formation in the spleen and a robust anti-KLH IgM (70-388microg/ml) and IgG (230-470microg/ml) antibody response with peak detection on Days 5 and 14 post-immunization, respectively. Subcutaneous immunization with KLH (300microg/kg) resulted in a much weaker anti-KLH IgM and IgG (< or =20microg/ml) antibody response with no detectable increase in splenic germinal center formation. The utility of a rat KLH immunization model in detecting immunosuppression was evaluated with the known immunosuppressive drugs: cyclosporin, azathioprine and prednisolone. Rats, treated with drug at a maximum tolerated dose, were immunized with KLH by footpad or intravenous injection and serum samples were collected at various intervals up to 2 weeks post-immunization. Additional study parameters included terminal body weight, hematology and/or histopathology. All three drugs inhibited the IgM (60%) and IgG (> or =90%) antibody responses in the absence of overt toxicity based on evaluation of the standard toxicology parameters. In conclusion, measurement of a rat primary antibody response to KLH by ELISA is a reliable and readily standardized method for assessing immunotoxicity of pharmaceuticals.

Preclinical safety of recombinant human interleukin-18.

Recombinant human interleukin-18 (rHuIL-18) is currently in clinical trials for treatment of cancer. This report presents results of preclinical toxicity studies with rHuIL-18 in cynomolgus monkeys and recombinant murine IL-18 (rMuIL-18) in mice. The rHuIL-18 was administered intravenously in 1 or 2 different 5-day cycles at doses 0.3 to 75 mg/kg/day in monkeys. Decreases in red cell mass, neutrophil, and platelet counts, increases in monocyte and large unstained cell counts, and lymphoid hyperplasia in spleen and lymph nodes were mild, reversible, and likely related to the pharmacologic activity of IL-18. The only toxic effect was protein cast nephropathy, secondary to coprecipitation of administered IL-18 and Tamm-Horsfall protein in the distal nephron, that only occurred at 75 mg/kg/day. Other adverse effects of rHuIL-18 were related to strong immunogenicity in monkeys and were manifest only during a second dosing cycle. The rMuIL-18, at similar dosing levels and cycles in mice, resulted in reduced red cell mass, increased white blood cell counts, spleen and lymph node hyperplasia, and mild, reversible changes in intestine, liver, and lungs. Protein cast nephropathy occurred in mice at doses > or = 30 mg/kg/day. In conclusion, preclinical safety studies showed that rIL-18 was well tolerated at pharmacologically active doses in both monkeys and mice.