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.

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.

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.

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.

Identification of natural antibodies to interleukin-18 in the sera of normal humans and three nonhuman primate species.

Natural antibodies to cytokines can be found in the sera of normal healthy individuals in the absence of specific immunostimulation. However, the function, impact, and purpose of natural antibody development have yet to be fully elucidated. Interleukin (IL)-18 is a cytokine that exerts proinflammatory activities and induces natural killer (NK) cell activity. Recombinant human IL-18 (rHuIL-18) is currently in development as a cancer immunotherapy. In this study, the presence of natural antibodies to IL-18 in the sera of normal humans and three nonhuman primate species was evaluated by electrochemiluminescence immunoassay (ECLIA). Of the human sera tested, 6 of 47 samples were positive for natural antibodies to IL-18. Of the nonhuman primate sera tested, 22 of 80 cynomolgus monkey samples, 4 of 31 rhesus monkey samples, and 2 of 20 chimpanzee samples were positive for natural antibodies to IL-18. Natural anti-IL-18 antibodies were neutralizing in 5 of 22 cynomolgus and 2 of 4 rhesus sera. None of the chimpanzee or human sera were able to neutralize IL-18 induction of interferon (IFN)-gamma in vitro. In vivo activity of rHuIL-18 was compared in IL-18 natural antibody-positive and -negative cynomolgus monkeys. The presence of natural antibodies to IL-18 did not alter rHuIL-18 systemic exposure levels, induction of neopterin, or induction of treatment-induced antibodies following intravenous administration of rHuIL-18. In conclusion, our data indicate that, as has been found with other cytokines, natural anti-IL-18 antibodies are relatively common. Moreover, natural anti-IL-18 antibodies do not appear to influence rHuIL-18 activity in vivo and are not predictive of a heightened immune response, suggesting that natural anti-IL-18 antibodies do not impact IL-18 therapy. Finally, our data suggest that the ability to detect natural anti-cytokine antibodies may be a useful measure of the adequacy of an assay for deployment in clinical trials.

The immunogenicity of therapeutic cytokines.

Therapeutic cytokines that modulate immune responses are designed to enhance host defense to combat tumors and chronic infections. In general, cytokines are pleiotropic molecules and mediate both systemic and local immune activities. Therapeutic recombinant human cytokines currently in clinical use include interferons (IFN alpha, IFN beta and IFN gamma), interleukins (IL-2 and IL-12) and hematopoietic factors such as granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, erythropoietin and thrombopoietin. Their use as therapeutic agents has been challenging since the safety and efficacy of these products are complicated by immunogenicity issues.

Immunopharmacology of recombinant human interleukin-18 in non-human primates.

Recombinant human interleukin (IL)-18 (rHuIL-18) has a potential as a therapeutic agent in cancer and is currently in drug development. Since human IL-18 displays 96% and 100% amino acid sequence homology with cynomolgus monkey and chimpanzee IL-18, respectively, the biological responses to rHuIL-18 were evaluated in these species. A single intravenous dose of rHuIL-18 at 1 or 10mg/kg in cymonolgus monkeys caused a transient reduction in lymphocyte counts, induction of IL-1alpha and tumour necrosis factor alpha (TNF-alpha) mRNA in whole blood cells and a marked increase in plasma neopterin. rHuIL-18 administered to cynomolgus monkeys at doses of 0.3 or 3mg/kg for two 5-day cycles (Days 1-5 and 15-19) resulted in increased monocyte counts, induction of NK cells and concomitant increases in plasma IL-12 and neopterin. Administration of repeat doses of rHuIL-18 at 10mg/kg to chimpanzees was associated with increased monocyte counts, upregulation of FcgammaRI surface expression on monocytes, and increased IL-8, IL-12 and neopterin in plasma. These studies demonstrate, for the first time, the immunostimulatory activity of rHuIL-18 in vivo. The described pharmacological profile of rHuIL-18 in both cynomolgus monkeys and chimpanzees is indicative of the immunotherapeutic potential of rHuIL-18 in the treatment of cancer.