International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Non-proliferative and Proliferative Lesions of the Non-human Primate (M. fascicularis)

Neuropathological Findings in Nonclinical Species Following Administration of Adeno-Associated Virus (AAV)-Based Gene Therapy Vectors

Adeno-associated virus (AAV) gene therapy vectors are an accepted platform for treating severe neurological diseases. Test article (TA)-related and procedure-related neuropathological effects following administration of AAV-based vectors are observed in the central nervous system (CNS) and peripheral nervous system (PNS). Leukocyte accumulation (mononuclear cell infiltration > inflammation) may occur in brain, spinal cord, spinal nerve roots (SNRs), sensory and autonomic ganglia, and rarely nerves. Leukocyte accumulation may be associated with neuron necrosis (sensory ganglia > CNS) and/or glial changes (microgliosis and/or astrocytosis in the CNS, increased satellite glial cellularity in ganglia and/or Schwann cellularity in nerves). Axonal degeneration secondary to neuronal injury may occur in the SNR (dorsal > ventral), spinal cord (dorsal and occasionally lateral funiculi), and brainstem centrally and in nerves peripherally. Patterns of AAV-associated microscopic findings in the CNS and PNS differ for TAs administered into brain parenchyma (where tissue at the injection site is affected most) versus TAs delivered into cerebrospinal fluid (CSF) or systemically (which primarily impacts sensory ganglion neurons and their processes in SNR and spinal cord). Changes related to the TA and procedure may overlap. While often interpreted as adverse, AAV-associated neuronal necrosis and axonal degeneration of limited severity generally do not preclude clinical testing.

Hepatitis A Virus Infection in Cynomolgus Monkeys Confounds the Safety Evaluation of a Drug Candidate

In a 3-month toxicity study in cynomolgus monkeys at a European contract laboratory, animals were infected with HAV, initially resulting in hepatic injury being incorrectly attributed to the test compound. Elevated serum ALT/AST/GLDH (5- to 10-fold) were noted in individual animals from all groups including controls, with no apparent dose, exposure, or time-related relationship. Liver histopathology revealed minimal to slight inflammatory cell accumulation in periportal zones of most animals, and minimal to slight hepatocyte degeneration/necrosis in 10/42 animals from all groups. As these findings were more pronounced in 6 drug-treated animals, including 2/6 in the low dose group, the draft report concluded: "treatment-related hepatotoxicity at all dose levels precluded determination of a NOAEL." However, the unusual pattern of hepatotoxicity suggested a factor other than drug exposure might have caused the hepatic effects. Therefore, snap-frozen liver samples were tested for hepatitis viruses using a PCR method. Tests for hepatitis B, C, and E virus were negative; however, 20/42 samples were positive for hepatitis A virus (HAV). Infection was strongly associated with increased serum ALT/GLDH, and/or hepatocyte degeneration/necrosis. Re-evaluation of the study in light of these data concluded that the hepatic injury was not drug-related. A subsequent 6-month toxicology study in HAV-vaccinated cynomolgus monkeys confirmed the absence of hepatotoxicity. Identification of HAV infection supported progression of the drug candidate into later clinical trials. Although rarely investigated, subclinical HAV infection has occasionally been reported in laboratory primates, including those used for toxicology studies and it may be more prevalent than the literature indicates.

Effects of two weeks of food restriction on toxicological parameters in cynomolgus monkeys

Animals frequently eat less after a test-article treatment in nonclinical toxicological studies, and it can be difficult to distinguish test article-derived toxicities from secondary changes related to this reduced food intake. Therefore, in this study, we restricted the food intake of cynomolgus monkeys (Cambodian, male, n=2 or 3, 48 ± 3 months old) to 25% of the control for two weeks and evaluated the effects on toxicological parameters (general conditions, body weight, electrocardiography, urinalysis, hematology, blood chemistry, bone marrow analysis, pathological examination). After 2 weeks, the monkeys exhibited decreases in bone marrow erythropoiesis (e.g., decreases in reticulocytes and bone marrow erythrocytes), as well as glycogenesis induction (e.g., increase in aspartate aminotransferase (AST)) and malnutrition (e.g., decrease in triglyceride and systemic adipocytes atrophy). Additionally, histopathological analysis revealed granuloma and inflammatory cell infiltration in coronary fat, which had never been found in previous food restriction studies using other animal species. These findings will enable researchers to more accurately evaluate the toxicological risks of test articles that simultaneously induce food intake reduction.

Evaluation of Oromucosal Natural Gum-Based Emulgels as Novel Strategy for Photodynamic Therapy of Oral Premalignant Lesions

Photodynamic therapy (PDT) recently has been shown as a promising option in the treatment of premalignant lesions of the soft oral tissues. Effective delivery of photosensitizer is challenging due to poor drug adherence to the oromucosal epithelium. In the present work, emulgels composed of natural polysaccharide gums (tragacanth, xanthan and gellan) were evaluated as novel oromucosal platforms of delta-aminolevulinic acid (ALA) for PDT. Apart from mucoadhesive and textural analysis, the specific steps involved studies on drug penetration behavior and safety profile using a three-dimensional human oral epithelium model (HOE). All designed emulgels presented greater mucoadhesiveness when compared to commercial oromucosal gel. Incorporation of ALA affected textural properties of emulgels, and tragacanth/xanthan formulation with greater hardness and cohesiveness exhibited a protective function against the mechanical tongue stress. Permeability studies revealed that ALA is capable of penetrating across oromucosal epithelium by passive transport and all formulations promoted its absorption rate when compared to a commercial topical product with ALA. Importantly, the combination of tragacanth and xanthan profoundly enhanced photosensitizer retention in the buccal epithelium. Tested samples performed negligible reduction in cell viability and moderately low IL-1β release, confirming their non-irritancy and compatibility with HOE. Overall, the presented findings indicate that tragacanth/xanthan emulgel holds promise as an oromucosal ALA-carrier for PDT strategy.

Assessment of Safety and Biodistribution of AAVrh.10hCLN2 Following Intracisternal Administration in Nonhuman Primates for the Treatment of CLN2 Batten Disease

CLN2 disease is a fatal, childhood autosomal recessive disorder caused by mutations in ceroid lipofuscinosis type 2 (CLN2) gene, encoding tripeptidyl peptidase 1 (TPP-1). Loss of TPP-1 activity leads to accumulation of storage material in lysosomes and resultant neuronal cell death with neurodegeneration. Genotype/phenotype comparisons suggest that the phenotype should be ameliorated with increase of TPP-1 levels to 5-10% of normal with wide central nervous system (CNS) distribution. Our previous clinical study showed that intraparenchymal (IPC) administration of AAVrh.10hCLN2, an adeno-associated vector serotype rh.10 encoding human CLN2, slowed, but did not stop disease progression, suggesting that this may be insufficient to distribute the therapy throughout the CNS (Sondhi 2020). In this study, we assessed whether the less invasive intracisternal delivery route would be safe and provide a wider distribution of TPP-1. A study was conducted in nonhuman primates (NHPs) with intracisternal delivery to cerebrospinal fluid (CSF) of AAVrh.10hCLN2 (5 × 1013 genome copies) or phosphate buffered saline (PBS). No abnormal behavior was noted. CNS magnetic resonance imaging and clinical chemistry data were all unremarkable. Histopathology of major organs had no abnormal finding attributable to the intervention or the vector, except that in one out of two animals treated with AAVrh.10hCLN2, dorsal root ganglia showed mild-to-moderate mononuclear cell infiltrates and neuronal degeneration. In contrast to our previous NHP study (Sondhi 2012) with IPC administration where TPP-1 activity was >2 × above controls in 30% of treated brains, in the two intracisternal treated NHPs, the TPP-1 activity was >2 × above controls in 50% and 41% of treated brains, and 52% and 84% of brain had >1,000 vector genomes/μg DNA, compared to 0% in the two PBS NHP. CSF TPP1 levels in treated animals were 43-62% of normal human levels. Collectively, these data indicate that AAVrh.10hCLN2 delivered by intracisternal route is safe and widely distributes TPP-1 in brain and CSF at levels that are potentially therapeutic. Clinical Trial Registration: NCT02893826, NCT04669535, NCT04273269, NCT03580083, NCT04408625, NCT04127578, and NCT04792944.

Toxicologic Pathology Forum: Opinion on Interpretive Challenges for Procedure-Related Effects Associated With Direct Central Nervous System Delivery of Oligonucleotides to Rodents, Dogs, and Nonhuman Primates

Direct delivery of therapeutics to the central nervous system (CNS) greatly expands opportunities to treat neurological diseases but is technically challenging. This opinion outlines principal technical aspects of direct CNS delivery via intracerebroventricular (ICV) or intrathecal (IT) injection to common nonclinical test species (rodents, dogs, and nonhuman primates) and describes procedure-related clinical and histopathological effects that confound interpretation of test article-related effects. Direct dosing is by ICV injection in mice due to their small body size, while other species are dosed IT in the lumbar cistern. The most frequent procedure-related functional effects are transient absence of lower spinal reflexes after IT injection or death soon after ICV dosing. Common procedure-related microscopic findings in all species include leukocyte infiltrates in CNS meninges or perivascular (Virchow-Robin) spaces; nerve fiber degeneration in the spinal cord white matter (especially dorsal and lateral tracts compressed by dosing needles or indwelling catheters), spinal nerve roots, and sciatic nerve; meningeal fibrosis at or near IT injection sites; hemorrhage; and gliosis. Findings typically are minimal to occasionally mild. Findings tend to be more severe and/or have a higher incidence in the spinal cord segments and spinal nerve roots at or close to the site of administration.

Scientific and Regulatory Policy Committee Points to Consider: Sampling, Processing, Evaluation, Interpretation, and Reporting of Test Article-Related Ganglion Pathology for Nonclinical Toxicity Studies

Certain biopharmaceutical products consistently affect dorsal root ganglia, trigeminal ganglia, and/or autonomic ganglia. Product classes targeting ganglia include antineoplastic chemotherapeutics, adeno-associated virus-based gene therapies, antisense oligonucleotides, and anti-nerve growth factor agents. This article outlines "points to consider" for sample collection, processing, evaluation, interpretation, and reporting of ganglion findings; these points are consistent with published best practices for peripheral nervous system evaluation in nonclinical toxicity studies. Ganglion findings often occur as a combination of neuronal injury (e.g., degeneration, necrosis, and/or loss) and/or glial effects (e.g., increased satellite glial cell cellularity) with leukocyte accumulation (e.g., mononuclear cell infiltration or inflammation). Nerve fiber degeneration and/or glial reactions may be seen in nerves, dorsal spinal nerve roots, spinal cord, and occasionally brainstem. Interpretation of test article (TA)-associated effects may be confounded by incidental background changes or experimental procedure-related changes and limited historical control data. Reports should describe findings at these sites, any TA relationship, and the criteria used for assigning severity grades. Contextualizing adversity of ganglia findings can require a weight-of-evidence approach because morphologic changes of variable severity occur in ganglia but often are not accompanied by observable overt in-life functional alterations detectable by conventional behavioral and neurological testing techniques.

Comparison of Cardiovascular Pathology In Animal Models of SARS-CoV-2 Infection: Recommendations Regarding Standardization of Research Methods

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged as the viral pathogen that led to the global COVID-19 pandemic that began in late 2019. Because SARS-CoV-2 primarily causes a respiratory disease, much research conducted to date has focused on the respiratory system. However, SARS-CoV-2 infection also affects other organ systems, including the cardiovascular system. In this critical analysis of published data, we evaluate the evidence of cardiovascular pathology in human patients and animals. Overall, we find that the presence or absence of cardiovascular pathology is reported infrequently in both human autopsy studies and animal models of SARS-CoV-2 infection. Moreover, in those studies that have reported cardiovascular pathology, we identified issues in their design and execution that reduce confidence in the conclusions regarding SARS-CoV-2 infection as a cause of significant cardiovascular pathology. Throughout this overview, we expand on these limitations and provide recommendations to ensure a high level of scientific rigor and reproducibility.

Proceedings of the 2022 National Toxicology Program Satellite Symposium

The 2022 annual National Toxicology Program Satellite Symposium, entitled "Pathology Potpourri," was held in Austin, Texas at the Society of Toxicologic Pathology's 40th annual meeting during a half-day session on Sunday, June 19. The goal of this symposium was to present and discuss challenging diagnostic pathology and/or nomenclature issues. This article presents summaries of the speakers' talks along with select images that were used by the audience for voting and discussion. Various lesions and topics covered during the symposium included induced and spontaneous neoplastic and nonneoplastic lesions in the mouse lung, spontaneous lesions in the reproductive tract of a female cynomolgus macaque, induced vascular lesions in a mouse asthma model and interesting case studies in a rhesus macaque, dog and genetically engineered mouse model.

A Comparison of Historical Control Data From Cynomolgus Macaques (Macaca Fascicularis) of Chinese, Cambodian, and Vietnamese Origin

Cynomolgus macaques, the most commonly utilized nonhuman primate in nonclinical toxicology studies, are acquired from purpose-bred colonies across various geographic locations, including China, Cambodia, and Vietnam. Importation challenges and limited availability have restricted animals suitable for inclusion in nonclinical studies. The coronavirus disease 2019 (COVID-19) outbreak further stressed supply chains, reducing the ability to source animals from a singular location to complete a drug development program. These challenges raised concerns of increased variability in study endpoints due to heterogeneity of animals and that this could subsequently impact historical control data and toxicology study interpretation. To investigate the impact of Chinese, Vietnamese, or Cambodian geographic origin on standard nonclinical toxicology study endpoints, historical control data from studies conducted at a single facility from 2005 to 2020 were compiled and evaluated for the following: clinical observations, body weight, ophthalmoscopic examinations, and clinical and anatomic pathology data. Study populations consisted of 2- to 5-year-old cynomolgus macaques sourced from China (n = 750 males/741 females), Cambodia (n = 282 males/271 females), and Vietnam (n = 122 males/120 females). Interpretation of the various data demonstrated no notable differences in standard toxicology study endpoints or background findings among cynomolgus macaques originating from China, Cambodia, or Vietnam.

Society of Toxicologic Pathology Neuropathology Interest Group Article: Neuropathologic Findings in Nonhuman Primates Associated With Administration of Biomolecule-Based Test Articles

The increasing specificity of novel druggable targets coupled with the complexity of emerging therapeutic modalities for treating human diseases has created a growing need for nonhuman primates (NHPs) as models for translational drug discovery and nonclinical safety assessment. In particular, NHPs are critical for investigating potential unexpected/undesired on-target and off-target liabilities associated with administration of candidate biotherapeutics (nucleic acids, proteins, viral gene therapy vectors, etc.) to treat nervous system disorders. Nervous system findings unique to or overrepresented in NHPs administered biomolecule-based ("biologic") test articles include mononuclear cell infiltration in most neural tissues for all biomolecule classes as well as neuronal necrosis with glial cell proliferation in sensory ganglia for certain viral vectors. Such test article-related findings in NHPs often must be differentiated from procedural effects (e.g., local parenchymal or meningeal reactions associated with an injection site or implanted catheter to administer a test article directly into the central nervous system) or spontaneous background findings (e.g., neuronal autophagy in sensory ganglia).

Selected Resources for Pathology Evaluation of Nonhuman Primates in Nonclinical Safety Assessment

Humans and nonhuman primates (NHPs) share numerous anatomical and physiological characteristics, thereby explaining the importance of NHPs as essential animal models for translational medicine and nonclinical toxicity testing. Researchers, toxicologic pathologists, toxicologists, and regulatory reviewers must be familiar with normal and abnormal NHP biological traits when designing, performing, and interpreting data sets from NHP studies. The current compilation presents a list of essential books, journal articles, and websites that provide context to safety assessment and research scientists working with NHP models. The resources used most frequently by the authors have been briefly annotated to permit readers to rapidly ascertain their applicability to particular research endeavors. The references are aimed primarily for toxicologic pathologists working with cynomolgus and rhesus macaques and common marmosets in efficacy and safety assessment studies.

Spontaneous Findings in the Reproductive System of Sexually Mature Male Cynomolgus Macaques

Sexually mature nonhuman primates are often used in nonclinical safety testing when evaluating biopharmaceuticals; however, there is limited information in historical control databases or in the published literature on the spontaneous findings in the male reproductive system. This review evaluated digital slides from the male reproductive tract (testes, epididymides, prostate, and seminal vesicles) in sexually mature cynomolgus macaques ( Macaca fascicularis; n = 255) from vehicle control groups in nonclinical toxicology studies and compared the observations with body weight, organ weight, and geographical origin. The most common microscopic findings were hypospermatogenesis and tubular dilatation in the testes; inflammatory cell infiltrate, cellular debris, and decreased sperm in the epididymides; inflammatory cell infiltrate and acinar dilatation in the prostate; and corpora amylacea and atrophy in the seminal vesicles. There were a few correlative observations in animals when grouped by weight or geographical origin: animals with lower terminal body weights (<5 kg) often displayed features of late puberty despite having sperm in the epididymis, while animals originating from Mauritius had a lower incidence of inflammatory cell infiltrates than those from Southeast Asia/China. This review provides incidence, descriptions, and photomicrographs of the common spontaneous microscopic findings in the reproductive system of mature male cynomolgus macaques.