We read with great interest the review by Johnson,1 which discloses the current and potential applications of mesenchymal stem cells (MSCs) in exotic animal species, and we were particularly intrigued by the discussion of the use of MSCs for the treatment of arthritis and wound healing. As researchers with a keen interest in the application of regenerative medicine to exotic animal species, we believe that the potential of MSCs extends beyond the aforementioned conditions and could be particularly beneficial in the area of fracture healing. Based on our experience in cell technologies, we will venture to affirm that cell processing of exotic animals will not be easy.
The challenges associated with isolating and culturing cells for the treatment of exotic animal species are multifaceted and complex. These difficulties stem from not only a lack of specific knowledge about the anatomy and physiology of these animals but also uncertainties about the suitability of standard culture methods and the effectiveness of cell injection protocols.
Each exotic animal species may have unique healing processes influenced by factors such as metabolism, immune response, and habitat.2 Without a deep understanding of these processes, it’s challenging to tailor cell-based therapies that align with the natural healing mechanisms of these animals. For example, the endogenous presence of specific immune cells in epithelial tissues could compromise the efficacy of MSC-based cell therapies.
The scarcity of baseline data on how cells from exotic animals behave in vitro, including growth rates, differentiation potential, and senescence triggers, complicates the establishment of optimized culture conditions. This lack of data makes it difficult to predict how these cells will respond to standard culturing practices. For example, the standard medium containing Dulbecco modified Eagle medium with 10% fetal bovine serum is universally suitable for culturing stromal cells from all animal species but may not hold true for exotic animals. Some animals may require specific growth factors, nutrients, or environmental conditions (eg, oxygen levels, CO2 concentration, gas compositions, and temperature) that differ significantly from those provided by standard media conditions. The use of minimally manipulated cells without cell culture requires a large amount of cell-containing bone marrow biopsy.3 In addition, ethical considerations and the development of protocols that minimize stress and discomfort during cell collection and administration are paramount.
The derivation of primary cells from endangered or protected exotic animal species raises ethical and legal concerns. This requires the development of noninvasive or minimally invasive methods of cell collection, such as using blood separation, shed skin, hair follicles, or other tissues that do not harm the animal. The use of donor cells, especially those derived from biobanks, introduces additional complexities related to immune compatibility and the risk of disease transmission.
The absence of species-specific protocols for the injection or implantation of cultured cells into bone defects is a significant hurdle. Factors such as the choice of delivery vehicle (eg, hydrogels, scaffolds), timing of intervention (acute vs chronic defects), and method of securing the cells at the defect site require careful consideration and optimization. Traditional treatment methods in veterinary medicine, such as immobilization and surgery, can be particularly stressful and may not always produce satisfactory outcomes due to the unique anatomy and behavior of the animal.
Addressing these issues requires a multidisciplinary approach that combines expertise in veterinary medicine, cell biology, tissue engineering, and immunology. Collaborative efforts are essential to developing safe, effective, and ethically responsible cell-based therapies. Researchers and conservationists should work together to expand our knowledge of regenerative medicine for exotic animals to meet these challenges.
- 1.↑
Johnson VA. Review of current and potential applications of mesenchymal stem cells in exotic animal species. J Am Vet Med Assoc. 2024;262(suppl 1):S131-S140. doi:10.2460/javma.24.01.0034
- 2.↑
Latney LV. Nutritive support for critical exotic patients. Vet Clin North Am Exot Anim Pract. 2023;26(3):711-735. doi:10.1016/j.cvex.2023.05.009
- 3.↑
Krasilnikova OA, Baranovskii DS, Yakimova AO, et al. Intraoperative creation of tissue-engineered grafts with minimally manipulated cells: new concept of bone tissue engineering in situ. Bioengineering (Basel). 2022;9(11):704 doi:10.3390/bioengineering9110704
The author responds:
I greatly appreciate the comments provided by Klabukov and Skornyakova concerning the review article, “Review of current and potential applications of mesenchymal stem cells in exotic animal species.”1 I agree there are many potential applications of these cells in exotic species in addition to the conditions I reviewed. Fracture healing is certainly an area where these cells have been demonstrated to be of benefit, and indeed many of the studies on fracture healing have been performed on veterinary species such as rabbits.2 Other conditions where mesenchymal stem cell (MSC) therapy could be extravasated to other species include inflammatory conditions such as inflammatory bowel disease and pancreatitis or immune-mediated disease.3 Biologic therapies are a novel treatment modality, and the potential applications are the subject of many other reviews.4 In my limited review, I attempted to focus on conditions where I currently have clinical trials open to assess the safety and efficacy of this therapy in exotic animals. My review was not meant to be an exhaustive review of all potential therapeutic possibilities for which MSCs may be used, although much has been written on the subject for those in search of further information.
Your point is well taken regarding the complexities in dealing with such a large variety of animals each with various physiological differences and environmental adaptations. In my laboratory, we have grown MSCs from over 30 different species and have often noted the differences in nutrient requirements and phenotypical characteristics of the cells from various species. Through trial and error, we have discerned the various media, temperatures, and cell seeding numbers preferred by a variety of mammals, birds, and reptiles but also have species for which we were not able to find the optimal growth conditions at the time of this writing. Indeed, we are in the process of writing up the findings of a comparative study utilizing MSCs from multiple species and have plans to perform genetic comparisons of the MSCs from these same species to examine the immunomodulatory pathways utilized in various species. I have worked and continue to work with multiple collaborators to seek the answers to the very questions you pose, although it is an undertaking that likely will require multiple groups working together and separately to even begin to delve into the complexities of cells derived from multiple species.
I appreciate your consideration of the ethics of working with and treating these species. To overcome some of the hurdles of the ethical concerns of taking samples through invasive procedures, our laboratory has developed a technique for isolating MSCs from blood and we have employed that technique in multiple species for which blood is readily available through training for blood draws. In addition, for the conditions of osteoarthritis and wounds, we inject the cells intravenously for multiple reasons, one of which is the ease and lower complication rate of an intravenous injection. Another reason is that the cells can then track to areas of inflammation that may not be detectable with the current tools we have to detect inflammation, such as radiographs and thermography. This is of particular benefit in older animals with arthritis in multiple joints.5
I fully concur with the authors’ conclusion that multiple groups should collaborate to investigate this promising new therapeutic. Furthermore, an approach that encompasses animal welfare, conservation, and scientific research is critical to this effort. I greatly look forward to future collaborations and investigations into this new and exciting realm of biologic therapies.
Valerie Johnson, DVM, PhD, DACVECC
Michigan State University
- 1.↑
Johnson VA. Review of current and potential applications of mesenchymal stem cells in exotic animal species. J Am Vet Med Assoc. 2024;262(suppl 1):S131-S140. doi:10.2460/javma.24.01.0034
- 2.↑
Sabater González M, Calvo Carrasco D. Advances in exotic animal osteosynthesis. Vet Clin North Am Exot Anim Pract. 2019;22(3):441-450. doi:10.1016/j.cvex.2019.06.006
- 3.↑
Soontararak S, Chow L, Johnson V, et al. Humoral immune responses against gut bacteria in dogs with inflammatory bowel disease. PLoS One. 2019;14(8):e0220522. doi:10.1371/journal.pone.0220522
- 4.↑
Andrzejewska A, Lukomska B, Janowski M. Concise review: mesenchymal stem cells: from roots to boost. Stem Cells. 2019;37(7):855-864. doi:10.1002/stem.3016
- 5.↑
Olsen A, Johnson V, Webb T, Santangelo KS, Dow S, Duerr FM. Evaluation of intravenously delivered allogeneic mesenchymal stem cells for treatment of elbow osteoarthritis in dogs: a pilot study. Vet Comp Orthop Traumatol. 2019;32(3):173-181. doi:10.1055/s-0039-1678547
