Methodologies and Emerging Technologies for the Evaluation of the Hematopoietic System.

Hematology and bone marrow analysis is central to our understanding of the hematopoietic system and how it responds to insults, and this session presented during the 2022 STP symposium provided a review of current and novel approaches for the evaluation of the hematopoietic system in the context of nonclinical investigations. This publication summarizes the information presented on novel approaches for evaluation of the hematopoietic system using automated hematology analyzers, including details around the quantitative assessment of bone marrow cell suspensions as well as introducing several newly available hematology parameters. It was followed by a discussion on intravital microscopy and live cell imaging and how these methods can assist with de-risking hematopoiesis-associated safety concerns, and a review of recent assays using artificial intelligence for the evaluation of bone marrow.

Development of a nonhuman primate challenge model to evaluate CD8+ T cell responses to an adenovirus-based vaccine expressing SIV proteins upon repeat-dose treatment with checkpoint inhibitors.

Targeting immune checkpoint receptors expressed in the T cell synapse induces active and long-lasting antitumor immunity in preclinical tumor models and oncology patients. However, traditional nonhuman primate (NHP) studies in healthy animals have thus far demonstrated little to no pharmacological activity or toxicity for checkpoint inhibitors (CPIs), likely due to a quiescent immune system. We developed a NHP vaccine challenge model in Mauritius cynomolgus monkey (MCMs) that elicits a strong CD8+ T cell response to assess both pharmacology and safety within the same animal. MHC I-genotyped MCMs were immunized with three replication incompetent adenovirus serotype 5 (Adv5) encoding Gag, Nef and Pol simian immunodeficiency virus (SIV) proteins administered 4 weeks apart. Immunized animals received the anti-PD-L1 atezolizumab or an immune checkpoint-targeting bispecific antibody (mAbX) in early development. After a single immunization, Adv5-SIVs induced T-cell activation as assessed by the expression of several co-stimulatory and co-inhibitory molecules, proliferation, and antigen-specific T-cell response as measured by a Nef-dependent interferon-γ ELIspot and tetramer analysis. Administration of atezolizumab increased the number of Ki67+ CD8+ T cells, CD8+ T cells co-expressing TIM3 and LAG3 and the number of CD4+ T cells co-expressing 4-1BB, BTLA, and TIM3 two weeks after vaccination. Both atezolizumab and mAbX extended the cytolytic activity of the SIV antigen-specific CD8+ T cell up to 8 weeks. Taken together, this vaccine challenge model allowed the combined study of pharmacology and safety parameters for a new immunomodulatory protein-based therapeutic targeting CD8+ T cells in an NHP model.

Aspiration and Inspiration: Using Bronchoalveolar Lavage for Toxicity Assessment.

Bronchoalveolar lavage (BAL) is a simple procedure that is used to investigate drug efficacy or lung toxicity. It is sensitive to lung changes and less invasive than histological evaluation. It can be performed repeatedly at interim time points or as a terminal procedure. Airborne contaminants and purposely inhaled compounds, resident and inflammatory cells, as well as different cellular soluble products can be harvested in bronchoalveolar fluid (BALF) and measured. Bronchoalveolar lavage can also be an important tool to understand drug exposure and its metabolism in the lung, although it should be rigorously performed and interpreted with caution, especially in the context of regulated toxicology studies. This review focuses on the methods and uses of BAL in animal research, primarily in the pharmaceutical industry, as well as for the assessment of drugs, pollutants, and chemical lung toxicity. Methods of collecting and analyzing BALF and parameters affecting variability are discussed in detail. Improved automated methods for cell counting and analysis of the inflammatory cellular differential using hematology analyzers, common markers of lung injury, and new methodologies are described. Correlation between BALF and histological evaluation should not be considered as repetitive but as complementary assessments in the context of efficacy and toxicity studies.

Salt Selection Matters: Differential Renal Toxicity With MDV1634.Maleate Versus MDV1634.2HCl.

Salt forms of pharmaceutical compounds can have unique pharmacokinetic and toxicity properties. MDV1634 was evaluated for neurology indication and also demonstrated blood pressure (BP)-lowering effects in nonclinical studies. During the chemistry manufacturing campaign, 2 salt forms, dihydrochloride (2HCl) and maleate (MAL), which improved chemical stability and water solubility of the free base were identified. MDV1634.MAL showed better chemical attributes and was evaluated in toxicology studies for further development. A 28-day oral toxicity study in dogs with MDV1634.MAL demonstrated partially reversible renal toxicity. Although MAL salt is generally regarded as safe, renal toxicity is sometimes observed in rats and dogs. To evaluate contribution of each salt form to renal toxicity and BP lowering, an additional 28-day study was conducted with MDV1634.2HCL and MDV1634.MAL, which included toxicokinetics, continuous BP measurement in a subset of dogs, and sensitive urinary biomarker evaluation for temporal monitorability and reversibility of potential renal findings. In the repeat study, both salt forms showed similar exposures during the dosing period, but renal tubular toxicity was observed only with MDV1634.MAL and not with MDV1634.2HCl. The renal findings with MDV1634.MAL included early urinary biomarker changes (increase in albumin, clusterin, ß2 microglobulin, and neutrophil gelatinase-associated lipocalin); elevations in serum blood urea nitrogen and creatinine; and microscopic findings of partially reversible tubular basophilia, single cell necrosis, pigmentation, and mineralization. The renal findings in contrast to the BP findings were MAL-specific and considered not related to MDV1634, thereby under scoring the importance of salt forms in pharmaceutical development.

Reducing blood volume requirements for clinical pathology testing in toxicologic studies-points to consider.

In preclinical safety assessment, blood volume requirements for various endpoints pose a major challenge. The goal of this working group was to review current practices for clinical pathology (CP) testing in preclinical toxicologic studies, and to discuss advantages and disadvantages of methods for reducing blood volume requirements. An industry-wide survey was conducted to gather information on CP instrumentation and blood collection practices for hematology, clinical biochemistry, and coagulation evaluation in laboratory animals involved in preclinical studies. Based on the survey results and collective experience of the authors, the working group proposes the following "points to consider" for CP testing: (1) For most commercial analyzers, 0.5 mL and 0.8 mL of whole blood are sufficient for hematology and biochemistry evaluation, respectively. (2) Small analyzers with low volume requirements and low throughput have limited utility in preclinical studies. (3) Sample pooling or dilution is inappropriate for many CP methods. (4) Appropriate collection sites should be determined based on blood volume requirements and technical expertise. (5) Microsampling does not provide sufficient volume given current analyzer and quality assurance requirements. (6) Study design considerations include: the use of older/larger animals (rodents), collection of CP samples before toxicokinetic samples, use of separate subsets of mice for hematology and clinical biochemistry testing, use of a priority list for clinical biochemistry, and when possible, eliminating coagulation testing.

STP Best Practices for Evaluating Clinical Pathology in Pharmaceutical Recovery Studies.

The Society of Toxicologic Pathology formed a working group in collaboration with the American Society for Veterinary Clinical Pathology to provide recommendations for the appropriate inclusion of clinical pathology evaluation in recovery arms of nonclinical toxicity studies but not on when to perform recovery studies. Evaluation of the recovery of clinical pathology findings is not required routinely but provides useful information on risk assessment in nonclinical toxicity studies and is recommended when the ability of the organ to recover is uncertain. The study design generally requires inclusion of concurrent controls to separate procedure-related changes from test article-related changes, but return of clinical pathology values toward baseline may be sufficient in some cases. Evaluation of either a select or full panel of standard hematology, coagulation, and serum and urine chemistry biomarkers can be scientifically justified. It is also acceptable to redesignate dosing phase animals to the recovery phase or vice versa to optimize data interpretation. Assessment of delayed toxicity during the recovery phase is not required but may be appropriate in development programs with unique concerns. Evaluation of the recovery of clinical pathology data for vaccine development is required and, for efficacy markers, is recommended if it furthers pharmacologic understanding.

An Investigative Study of Pancreatic Exocrine Biomarkers, Histology, and Histomorphometry in Male Zucker Diabetic Fatty (ZDF) Rats Given Dulaglutide by Subcutaneous Injection Twice Weekly for 13 Weeks.

Glucagon-like peptide-1 (GLP-1) receptor agonist therapy has been implicated as a possible risk factor for acute pancreatitis in patients with type 2 diabetes. Dulaglutide is a long-acting GLP-1 receptor agonist in development for treatment of type 2 diabetes. The effects of dulaglutide were evaluated in male Zucker diabetic fatty (ZDF) rats to examine whether dulaglutide may induce or modulate pancreatitis. Rats were randomized to dose groups receiving twice-weekly subcutaneously administered dulaglutide 0.5, 1.5, and 5.0 mg/kg/dose (corresponding human plasma exposures following twice-weekly dosing are 3-, 8-, and 30-fold, respectively) for 13 weeks or to vehicle control. Following termination, serially trimmed sections of pancreases were stained with hematoxylin and eosin or co-stained with an epithelial marker and a marker of either proliferation or apoptosis. Efficacious reductions in glucose and hemoglobin A1c occurred at all dulaglutide doses. Lipase activity was unaffected, and there were modest increases in total and pancreatic amylase activities at all doses without individual microscopic inflammatory correlates. Microscopic dulaglutide-related pancreatic changes included increased interlobular ductal epithelium without ductal cell proliferation (≥0.5 mg/kg), increased acinar atrophy with/without inflammation (≥1.5 mg/kg), and increased incidence/severity of neutrophilic acinar pancreatic inflammation (5.0 mg/kg). In summary, dulaglutide treatment was associated with mild alterations in ductal epithelium and modest exacerbation of spontaneous lesions of the exocrine pancreas typically found in the ZDF rat model.

Best practices for veterinary toxicologic clinical pathology, with emphasis on the pharmaceutical and biotechnology industries.

The purpose of this paper by the Regulatory Affairs Committee (RAC) of the American Society for Veterinary Clinical Pathology (ASVCP) is to review the current regulatory guidances (eg, guidelines) and published recommendations for best practices in veterinary toxicologic clinical pathology, particularly in the pharmaceutical and biotechnology industries, and to utilize the combined experience of ASVCP RAC to provide updated recommendations. Discussion points include (1) instrumentation, validation, and sample collection, (2) routine laboratory variables, (3) cytologic laboratory variables, (4) data interpretation and reporting (including peer review, reference intervals and statistics), and (5) roles and responsibilities of clinical pathologists and laboratory personnel. Revision and improvement of current practices should be in alignment with evolving regulatory guidance documents, new technology, and expanding understanding and utility of clinical pathology. These recommendations provide a contemporary guide for the refinement of veterinary toxicologic clinical pathology best practices.

Unexpected thrombocytopenia and anemia in cynomolgus monkeys induced by a therapeutic human monoclonal antibody.

Cynomolgus monkeys dosed with a therapeutic monoclonal antibody (mAbY.1) at ≥ 50 mg/kg had unexpected acute thrombocytopenia (nadir ~3,000 platelets/µl), sometimes with decreases in red cell mass. Increased activated macrophages, mitotic figures, and erythrophagocytosis were observed in the spleen. Binding of mAbY.1 to cynomolgus peripheral blood cells could not be detected in vitro. mAbY.1 induced phagocytosis of platelets by peripheral blood monocytes from cynomolgus monkeys, but not from humans. mAbs sharing the same constant domain (Fc) sequences, but differing from mAbY.1 in their variable domains, bound competitively to and had similar biological activity against the intended target. None of these antibodies had hematologic liabilities in vitro or in vivo. Neither the F(ab')2 portion of mAbY.1 nor the F(ab')2 portion on an aglycosylated Fc (IgG1) framework caused phagocytosis of platelets in vitro. These data suggest that the hematologic effects of mAbY.1 in cynomolgus monkeys likely occurred through an off-target mechanism, shown to be driven by 1 to 3 amino acid differences in the light chain. The hematologic effects made mAbY.1 an unsuitable candidate for further development as a therapeutic agent. This example demonstrates that nonclinical safety studies may be essential for understanding off-target effects of mAbs prior to clinical trials.

Best practices for evaluation of bone marrow in nonclinical toxicity studies.

This manuscript is intended to provide a best practice approach to accurately and consistently assess toxicant-induced bone marrow effects of test articles. In nonclinical toxicity studies, complete blood count data in conjunction with the histological examination of the bone marrow are recommended as the foundation for assessing the effect of test articles on the hematopoietic system. This approach alone can be used successfully in many studies. However, in some situations it may be necessary to further characterize effects on the different hematopoietic lineages, either by cytological or flow cytometric evaluation of the bone marrow. Both modalities can be used successfully, and which one is selected will depend on the expertise, preference of the facility, and the nature of the change in the bone marrow. Other specialized techniques such as clonogenic assays or electron microscopy are used rarely to further characterize hematotoxicity. The indications and techniques to successfully employ histological, cytological, or flow cytometric evaluation as well as clonogenic assays and electron microscopy are reviewed.

Best practices for evaluation of bone marrow in nonclinical toxicity studies.

This manuscript is intended to provide a best practice approach to accurately and consistently assess toxicant-induced bone marrow effects of test articles. In nonclinical toxicity studies, complete blood count data in conjunction with the histological examination of the bone marrow are recommended as the foundation for assessing the effect of test articles on the hematopoietic system. This approach alone can be used successfully in many studies. However, in some situations it may be necessary to further characterize effects on the different hematopoietic lineages, either by cytological or flow cytometric evaluation of the bone marrow. Both modalities can be used successfully, and which one is selected will depend on the expertise, preference of the facility, and the nature of the change in the bone marrow. Other specialized techniques such as clonogenic assays or electron microscopy are used rarely to further characterize hematotoxicity. The indications and techniques to successfully employ histological, cytological, or flow cytometric evaluation as well as clonogenic assays and electron microscopy are reviewed.