Scientific and Regulatory Policy Committee Points to Consider for Medical Device Implant Site Evaluation in Nonclinical Studies.

Nonclinical implantation studies are a common and often critical step for medical device safety assessment in the bench-to-market pathway. Nonclinical implanted medical devices or drug-device combination products require complex macroscopic and microscopic pathology evaluations due to the physical presence of the device itself and unique tissue responses to device materials. The Medical Device Implant Site Evaluation working group of the Society of Toxicologic Pathology's (STP) Scientific and Regulatory Policy Committee (SRPC) was tasked with reviewing scientific, technical, and regulatory considerations for these studies. Implant site evaluations require highly specialized methods and analytical schemes that should be designed on a case-by-case basis to address specific study objectives. Existing STP best practice recommendations can serve as a framework when performing nonclinical studies under Good Laboratory Practices and help mitigate limitations in standards and guidances for implant evaluations (e.g., those from the International Organization for Standardization [ISO], ASTM International). This article integrates standards referenced by sponsors and regulatory bodies with practical pathology evaluation methods for implantable medical devices and combination products. The goal is to ensure the maximum accuracy and scientific relevance of pathology data acquired during a medical device or combination drug-device implantation study.

Corneal Dystrophy in Dutch Belted Rabbits as a Possible Model of Thiel-Behnke Subtype of Epithelial-Stromal TGFß-Induced Corneal Dystrophy.

The International Committee for Classification of Corneal Dystrophies (IC3D) categorized corneal dystrophies in humans using anatomic, genotypic, and clinicopathologic phenotypic features. Relative to the IC3D classification, a review of the veterinary literature confirmed that corneal dystrophy is imprecisely applied to any corneal opacity and to multiple poorly characterized histologic abnormalities of the cornea in animals. True corneal dystrophy occurs in mice with targeted mutations and spontaneously in pet dogs and cats and in Dutch belted (DB) rabbits, but these instances lack complete phenotyping or genotyping. Corneal dystrophy in DB rabbits can be an important confounding finding in ocular toxicology studies but has only been described once. Therefore, the ophthalmology and pathology of corneal dystrophy in 13 DB rabbits were characterized to determine whether the findings were consistent with or a possible model of any corneal dystrophy subtypes in humans. Slit lamp and optical coherence tomography (OCT) imaging were used to characterize corneal dystrophy over 4 months in young DB rabbits. The hyperechoic OCT changes correlated with light microscopic findings in the anterior stroma, consisting of highly disordered collagen fibers and enlarged keratocytes. Histochemical stains did not reveal abnormal deposits. Small clusters of 8 to 16 nm diameter curly fibers identified by transmission electron microscopy were consistent with Thiel-Behnke (TBCD) subtype of epithelial-stromal transforming growth factor ß-induced dystrophies. Sporadic corneal dystrophy in DB rabbits appears to be a potential animal model of TBCD, but genotypic characterization will be required to confirm this categorization.

Mucosa-Associated Lymphoid Tissue and Tertiary Lymphoid Structures of the Eye and Ear in Laboratory Animals.

Mucosa-associated lymphoid tissue (MALT) of special senses is poorly described and can be confused with nonspecific mononuclear cell infiltrates and tertiary lymphoid structures (TLS). In the eye, MALT consists mostly of conjunctiva-associated lymphoid tissue (CALT) and lacrimal drainage-associated lymphoid tissue (LDALT). In humans, CALT and LDALT are important components of the normal eye-associated lymphoid tissue (EALT), but EALT is less frequently described in ocular tissues of animals. The EALT are acquired postnatally in preferential mucosal sites, expand with antigenic exposure, form well-developed lymphoid follicles, and are reported to senesce. Lymphoid follicles that are induced concurrently with chronic inflammation are more appropriately considered TLS but must be differentiated from inflammation in MALT. Less understood is the etiology for formation of lymphoid tissue aggregates in the ciliary body, limbus, or choroid of healthy eyes in animals and humans. In the healthy eustachian tube and middle ear of animals and humans, MALT may be present but is infrequently described. Concurrent with otitis media, lymphoid follicles in the eustachian tube are probably expanded MALT, but lymphoid follicles in the middle ear may be TLS. The purpose of this comparative review is to familiarize toxicologic pathologists with MALT in the special senses and to provide considerations for differentiating and reporting eye and ear MALT from immune or inflammatory cell infiltrates or inflammation in nonclinical studies, and the circumstances for reporting TLS in compartments of the eye and ear.

Compilation of International Standards and Regulatory Guidance Documents for Evaluation of Biomaterials, Medical Devices, and 3-D Printed and Regenerative Medicine Products.

The development of biomaterials, medical device components, finished medical products, and 3-D printed and regenerative medicine products is governed by a variety of international and country-specific standards and guidelines. Of greatest importance to planning, executing, and reporting biocompatibility, safety and efficacy studies for most biomaterials and medical components or products are the International Organization for Standardization guidelines, U.S. Pharmacopeial Convention, ASTM International, and Conformité Européenne (European Conformity) marking. The International Medical Device Regulators Forum publishes harmonized standards similar to the International Council for Harmonization. Good Laboratory Practices are applicable and guidance documents for the development of drugs and biologics can also be relevant to biomaterials, medical device components, and medical products and more recently to products produced by 3-D printing or additive manufacturing. Regenerative products may have medical device-based scaffolding and may be treated as biologics, reflecting the cell and tissue components. This compilation of international standards and guidelines provides toxicologic pathologists, toxicologists, bioengineers, and allied professionals with an overview of and source for important regulatory documents that may apply to the nonclinical development of their products.

Toxicologic Pathology Forum Opinion Paper: Considerations for Toxicologic Pathologists Evaluating the Safety of Biomaterials and Finished Medical Devices.

Safety ("biocompatibility") assessment of medical devices has evolved along a different path than that of drugs, being historically governed more by the considerations and needs of engineers rather than chemists and biologists. As a result, the involvement of veterinary pathologists has been much more limited-almost entirely to evaluating tissue responses in tissues in direct contact with implanted devices. As devices have become more complex in composition, structure, placement, and use, concerns as to adverse systemic responses in patients have called for more comprehensive and thoughtful evaluations of effects throughout the body. Further complexities arise from the increasing marriage of devices and drug/biologic therapeutics to achieve either better dose control and, specifically, in delivery to target organs/tissues or better tolerance of the body to medical devices (i.e., minimization of the foreign body response). The challenge to pathologists is to integrate in new technologies (such as in vivo imaging and immunology) and ways of viewing interactions with patient bodies. To fail to do so will allow the methods and standards for medical device safety evaluation to be based on chemical analysis and then the limited details inherent in literature-based risk assessments.

The First Cut Is the Deepest: The History and Development of Safe Treatments for Wound Healing and Tissue Repair.

As the skin is the primary barrier to infection, the importance of wound healing has been understood since ancient times. This article provides a synopsis on the symposium presentations focusing on how wounds were traditionally treated, what models and pathology endpoints exist to study wound healing, special considerations for wound healing studies, an overview of regulatory aspects of new pharmaceutical and medical device development, and the clinical relevance of such models. The clinical treatment of small and large wounds is also considered.

General session 3: acquired immunity.

Session 3 of the Toxicologic Pathology and the Immune System Symposium, presented as part of the 30th Annual Symposium of the Society of Toxicologic Pathology in 2011, focused on the biological advances in control of selected cellular and secretory components of acquired immunity. Acquired immunity goes beyond innate immunity to provide controlled recognition and memory for specific antigenic challenges. Predominately involving activation of T and B lymphocytes, the resulting cellular- and secretory-mediated activity provides immediate and long-term host defenses to antigenic challenge. This session highlighted the biological advances in function and dysfunction of acquired immunity through regulatory T cells, the pathophysiology of effector cells and secretory molecules in immunosuppression, allergic inflammatory disease, and dysregulation that leads to loss of tolerance and autoimmune disease. A brief overview of major concepts in acquired immunity and summaries of the above themes are covered herein, and discussions of these themes are covered in greater detail in this issue of Toxicologic Pathology.

Medical device regulations and testing for toxicologic pathologists.

Awareness of the regulatory environment is fundamental to understanding the biological assessment of biomaterials and medical devices. Medical devices are a diverse and heterogeneous group of medical products and technologies defined by the lack of chemical action or requirement for metabolism. Regional activity and the Global Harmonization Task Force are now working on harmonizing the categorization and testing of medical devices. The International Organization for Standardization (ISO) has published 19 standards for biological evaluation. ISO 10993 standards are generally accepted outright or as an alternative to most national regulatory directives or acts, although Japan and the United States require more stringency in some tests. Type of materials, intended use, and risk are the basis for drafting testing programs for biomaterials and medical devices. With growth of the medical device industry and advent of new biomaterials and technologies, the need for toxicologic pathologists in safety (biocompatibility) and efficacy (conditions of use) evaluation of moderate- to high-risk devices is expanding. Preclinical evaluation of biomaterials and medical devices increasingly requires a basic understanding of materials science and bioengineering to facilitate interpretation of complex interface reactions between biomaterials, cellular and secretory factors, and vascular and tissue responses that modulate success or failure of medical devices.

Trials, tribulations, and trends in tumor modeling in mice.

Selection of mouse models of cancer is often based simply on availability of a mouse strain and a known compatible tumor. Frequently this results in use of tumor models long on history but short on homology and quality control. Other factors including genetics, sex, immunological status, method and site of tumor implantation, technical competence, biological activity of the tumor, protocol sequence and timing, and selection of endpoints interact to produce outcomes in tumor models. Common reliance on survival and tumor burden data in a single mouse model often skews expectations towards high remission and cure rates; a finding seldom duplicated in clinical trials. Inherent limitations of tumor models coupled with the advent of new therapeutic targets reinforce need for careful attention to design, conduct, and stringent selection of in vivo and ex vivo endpoints. Preclinical efficacy testing for anti-tumor therapies should progress through a series of models of increasing sophistication that includes incorporation of genetically engineered animals, and orthotopic and combination therapy models. Pharmacology and safety testing in tumor-bearing animals may also help to improve predictive value of these models for clinical efficacy. Trends in bioinformatics, genetic refinements, and specialized imaging techniques are helping to maintain mice as the most scientifically and economically powerful model of malignant neoplasms.

Characterization of the in vivo function of TNF-alpha-related apoptosis-inducing ligand, TRAIL/Apo2L, using TRAIL/Apo2L gene-deficient mice.

To define the normal physiological role for the TRAIL/Apo2L in vivo, we generated TRAIL/Apo2L gene-targeted mice. These mice develop normally and show no defects in lymphoid or myeloid cell homeostasis or function. Although TRAIL/Apo2L kills transformed cells in vitro, TRAIL/Apo2L(-/-) mice do not spontaneously develop overt tumors at an early age. However, in the A20 B cell lymphoma-transferred tumor model, TRAIL/Apo2L(-/-) mice are clearly more susceptible to death from overwhelming tumor burden, due to increased lymphoma load in the liver. A20 tumors are susceptible to TRAIL/Apo2L killing in vitro, indicating that TRAIL/Apo2L may act directly to control A20 cells in vivo. Despite the fact that TRAIL binds osteoprotegerin and osteoprotegerin-transgenic mice are osteopetrotic, TRAIL/Apo2L(-/-) mice show no evidence of altered gross bone density, and no alterations in frequency or in vitro differentiation of bone marrow precursor osteoclasts. Moreover, leucine zipper TRAIL has no toxicity when repeatedly administered to osteoprotegerin(-/-) mice. Thus, TRAIL/Apo2L is important in controlling tumors in vivo, but is not an essential regulator of osteoprotegerin-mediated biology, under normal physiological conditions.

Periosteal hyperostosis (exostosis) in DBA/1 male mice.

Periosteal hyperostosis (exostosis) was identified in 5.9% (11/188) of DBA/1 male mice 10-14 weeks old used for collagen-induced arthritis (CIA) efficacy testing of immunomodulatory biologics. Mice with and without CIA in the affected limb, and also control and treated groups, were involved, with bilateral lesions in one mouse. Hyperostosis was characterized by circumferential and raised masses of variable location, length, and laterality, generally external to but occasionally breaching the periosteum of the metatarsals, metacarpals, tibia, femur, and humerus. Proportionally, the hyperostotic foci consisted of cancellous and woven bone, followed by osteoid, cartilage, and fibrous connective tissue and rarely inflammatory cells. A displaced, presumably pathological fracture with callus formation was a concurrent lesion in only one case. Tartrate-resistant acid phosphatase-positive cells were frequent at bony interfaces, indicating an active resorptive process. Periosteal hyperostosis is an incidental and potentially common finding in DBA/1 mice. Underreporting may occur due to the male bias in disease expression of this CIA model, sampling bias (generally paws only), tissue obliteration in the presence of CIA, and lack of comprehensive historical data on the background and aging lesions in this strain of mouse. Identification of such confounding bony lesions is important to the interpretation of efficacy studies, and suggests the need to further examine the biology of bone development in this strain of mouse.