Replacement of concurrent control groups (CCG) with virtual control groups (VCG) has been advocated as a strategy to reduce animal use in nonclinical toxicity testing. This “Points to Consider” paper examines VCG utility as it impacts toxicologic pathology endpoints and identifies the following points. (1) The CCG remains the gold standard, as it best controls for extrinsic and intrinsic study variables in discriminating subtle effects. (2) Pure VCG are unlikely to provide the same discernment since historical control data (HCD) from which VCG are assembled do not share all biological, environmental, husbandry, and procedural attributes of animals in the current study. (3) Clinical pathology endpoints are particularly vulnerable to VCG distortion given their dynamic range and sensitivity to preanalytical variables, with proof-of-concept studies demonstrating nonreproducibility rates for data interpretation of 31% to 49%. (4) Hybrid control groups combining reduced CCG with VCG are the most rational implementation strategy, balancing 3Rs (reduction, refinement, replacement) goals with scientific rigor and ongoing HCD refreshment. (5) The HCD pools require major upgrades, including comprehensive individual animal metadata, particularly for preanalytical and analytical variables, and (6) access to archived tissues as whole-slide scanned images, permitting reevaluation by the study pathologist using consistent nomenclature and grading criteria. (7) No major regulatory authority currently accepts VCG as a replacement for CCG in Good Laboratory Practice studies, and (8) proprietary data and data-sharing barriers to building sufficiently large multi-institutional HCD databases remain unresolved. (9) The VCG feasibility is highly species-dependent. (10) Multiple other new approach methodologies and modified study designs can support reduced animal use when VCG are not an optimal approach.
In April 2025, the US Food and Drug Administration (FDA) introduced a bold roadmap to phase out animal testing in drug development by promoting the integration of New Approach Methodologies (NAMs), beginning with monoclonal antibodies (mAbs). Similar roadmaps have also been created by European health authorities and chemical safety agencies around the globe. This opinion paper from the European Society of Toxicologic Pathology and US Society of Toxicologic Pathology complex in vitro model and pathology working groups provides a balanced and expert perspective on the promise and limitations of these initiatives. NAMs, including in vitro, in silico, and refined in vivo models, offer exciting opportunities to improve human relevance, efficiency, and ethical standards in nonclinical safety assessment. While these approaches are already making meaningful contributions, current scientific and technical limitations prevent them from fully replacing animal studies in all contexts. At this time, NAMs should be viewed as powerful complementary tools whose appropriate integration depends on the context of use, validation, and continued collaboration across disciplines. Pathologists and investigative molecular pathology leaders are uniquely positioned to support this transition by bridging traditional methods with emerging technologies to enhance the safety and effectiveness of future therapeutics.
Intraocular inflammation (IOI) following intravitreal (IVT) administration of large molecules (LM) is commonly seen in preclinical species and often relates to the presence of systemic anti-drug antibodies (ADA) as a reaction to the application of human proteins into a non-human species. This retrospective study aimed to characterize histopathological findings of IOI after IVT administration of LMs to non-human primates (NHP) and minipigs. Three independent safety studies were analyzed using immunohistochemical and special stains for inflammatory cell markers (CD68, Iba1, CD163, CD3, CD20, CD138), glial cell markers (glial fibrillary acidic protein [GFAP], vimentin, glutamine synthetase [GS]), and extracellular matrix (ECM) (fibronectin, collagen I, trichrome staining). Mononuclear cell infiltrates, membrane formation, and retinal degeneration were assessed. Infiltrates in various ocular compartments consisted mainly of monocytes/macrophages, T cells, and plasma cells, indicating an ongoing adaptive immune response. Membranes were primarily composed of glial cells (GFAP, vimentin positive) with a lack of substantial ECM deposition. Retinal degeneration correlated with increased GFAP/vimentin and decreased GS staining in the retina. Overall, these results correlated with the presence, location, and severity of the histopathologic diagnoses and were consistent between the two species. This study provides a detailed characterization of IOI consistent with an adaptive immune response following IVT administration of LM, enhancing our understanding of the ongoing immunological processes.
Drug-induced taste dysfunctions are an underrecognized yet clinically significant class of adverse effects that can substantially impair patients’ quality of life and compromise adherence to therapeutic regimens. Despite the potential for many pharmacologic agents to alter taste perception, these effects are frequently overlooked in both clinical practice and drug development. Gustatory disorders are rarely assessed in toxicology studies, and current knowledge regarding the pathophysiology of dysgeusia, the relevant organ systems involved, and nonclinical evaluation methods remains limited. This review details the anatomy of the gustatory system including taste buds and papillae, the functional characteristics of taste cells, the molecular mechanisms of taste transduction, and the neural components (peripheral and central). We emphasize the multimodal nature of flavor perception encompassing gustatory, olfactory and somatosensory systems, including the role of saliva in modulating flavor. Furthermore, we propose a comprehensive framework for nonclinical histopathological assessment of the key organ systems involved in flavor perception, with relevant case examples. By advancing awareness and providing optimized approaches for gustatory system evaluation in nonclinical toxicology studies, we aim to enable earlier detection and mechanistic investigation of taste-related adverse effects and improve safety profiling during drug development.
