Somatic Cell Therapies utilize mature, differentiated cells—such as CAR-T and CAR-M—which are strictly autologous and genetically modified to target specific antigens, whereas CAR-NK cells provide an allogeneic alternative that reduces the risk of cytokine release syndrome (CRS).
Non-genetically engineered somatic therapies, such as Tumor-Infiltrating Lymphocytes (TILs) like FDA-approved lifileucel (Amtagvi) and Virus-Specific Cytotoxic T Lymphocytes (CTLs), target metastatic cancer and latent viral infections like Epstein-Barr virus (EBV) by expanding naturally occurring target-recognizing immune cells.
Mesenchymal Stem Cells (MSCs) harvested from adipose tissue or bone marrow demonstrate superior therapeutic efficacy in treating orthopedic conditions like osteoarthritis and tendon injuries by migrating directly to damaged sites, responding dynamically to environmental cues, and modulating immune responses.
Veterinary medicine serves as an essential translational bridge under the One Health paradigm, where naturally occurring animal diseases closely mirror complex human conditions, significantly reducing late-stage clinical failures in human trials.
Induced Pluripotent Stem Cells (iPSCs), pioneered via reprogramming techniques from adult fibroblasts or peripheral blood, circumvent the ethical limitations of Human Embryonic Stem Cells (hESCs), though no iPSC-based therapeutic has received FDA approval to date.
1. The Expanding Role of Living Cell Treatments
1.1. Cell therapy is an innovative approach that uses living cells to heal the body by repairing or replacing damaged cells, or, in the case of immune cell therapies, targeting and destroying cancerous and other harmful cells. Over the years, a range of cell types has been developed into effective therapies, including hematopoietic (blood-forming) stem cells (HSCs), embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and adult stem cells like mesenchymal stem cells (MSCs). In addition, immune cells have shown promise in various therapeutic applications, including CAR-T (T cells), TIL (tumor-infiltrating lymphocytes), and CAR-NK (natural killer cells), among others.
1.2. The most established form of cell therapy is the transplantation of HSCs, commonly known as bone marrow transplants, primarily used to treat blood cancers and other hematologic conditions. Cell therapies have expanded beyond this application in recent years, however, and they are now approved or being developed for a wide array of indications, including solid tumors, autoimmune and infectious diseases, spinal cord injuries, neurological disorders, and other critical health issues.[1] This broadening scope highlights the transformative potential of cell-based treatments in modern medicine.
2. Why Cell Therapies Stand Out
2.1. Cell therapies have attracted significant attention as promising treatment options, offering potential improvements in safety and efficacy compared with traditional drug substances. Unlike conventional biologics or small molecule drugs, certain types of cells have the unique ability to migrate to targeted tissues and then multiply, bypassing some of the pharmacokinetic challenges often encountered with standard treatments.
2.2. Additionally, many therapeutic cells can sense and respond dynamically to environmental cues, such as cell surface receptors or bioactive molecules. This capability enables them to activate specific biological pathways and produce or secrete essential biomolecules, leading to more targeted and adaptable therapeutic effects.
3. Veterinary Applications of Mesenchymal Stem Cell Therapies
3.1. In 1991, Dr. Arnold Caplan described the role of MSCs in embryonic bone and cartilage formation, and in tissue regeneration and repair in adults. He further hypothesized that these cells could be used therapeutically as a form of regenerative medicine.[2] The lack of effective treatment alternatives, combined with a tolerant regulatory framework, resulted in a rapid transition from research to veterinary clinical practice. In 2001, Douglas Herthel published a retrospective study of 100 horses he had treated with intralesional injections of autologous bone marrow over the preceding six years. Of those 100 horses, 84 returned to full work and soundness after 6 months.[3] Shortly afterwards, researchers at the Royal Veterinary College in London published a case study outlining the isolation, characterization, expansion, and reimplantation of autologous MSCs into an 11-year-old polo pony with superficial digital flexor tendon (SDFT) damage.[4]
3.2. MSCs are multipotent adult stem cells that can both self-renew and differentiate into specialist cell types including bone, cartilage, ligaments, tendons, fat, skin, muscle, and connective tissue.[2] Proliferation and differentiation are activated through cell signaling, and MSC behavior and function are influenced by interactions with other stem cells, neighboring differentiated cells, adhesion molecules, the extracellular matrix, growth factors, cytokines, and other components of the stem cell “niche.”[5][6] Initial research postulated that the therapeutic potential of MSCs was a direct result of differentiation into new tissue cells. However, more recent studies indicate that the regenerative power of MSCs in fact stems from their ability to influence the immune system, sense tissue damage, and migrate to the source and promote tissue repair.[7][8]
3.3. MSCs are found in all adult tissues, are relatively easy to isolate, yield a high number of cells upon harvesting, and have no ethical barriers to use, making them especially promising for stem cell therapies. In veterinary medicine, preferred tissue sources for MSCs are adipose tissue and bone marrow, both of which yield high numbers of stem cells. In addition, MSC isolation from adipose tissue is minimally invasive.[7]
3.4. Since its initial application in horses, veterinary stem cell therapy has since expanded to companion animals, predominantly dogs and cats. In dogs, for example, several studies have reported beneficial effects of MSC therapies to treat cranial cruciate ligament injuries.[9][10][11]
3.5. Following early successes with stem cell therapies in orthopedic conditions in horses and dogs, MSC therapies have been further investigated in numerous other veterinary diseases. However, despite positive findings in several indications — including severe refractory gingivostomatitis in cats,[12] inflammatory bowel disease in dogs,[13] enteropathy in cats,[14] degenerative hepatopathy in dogs,[15] and wound healing and eye disease in horses (reviewed in Voga et al.[7]) — the study sizes have been too small, the protocols insufficiently optimized, and the research insufficiently systematic to make a definitive conclusion as to the efficacy of stem cell therapies in any of these indications.
4. Veterinary Applications for Cell Therapies
4.1. The human cell therapy landscape for both approved and pipeline therapeutics is dominated by oncology treatments.[16] In veterinary medicine, however, the development of cell therapies has been driven primarily by the desire to achieve full functional restoration following orthopedic injuries.
4.2. Horses and dogs are both prone to tendon, ligament, and joint injuries, which have similar characteristics to those experienced by humans. Similarly to human athletes, competitive horses, such as racehorses, event horses, show jumpers or polo ponies, are at particularly high risk of sports-related stress or repetitive strain injuries. Competitive horses frequently experience equine SDFT strains, and distal deep digital flexor tendon (DDFT) injuries are common in elite showjumping.[17]
4.3. As tendon and ligament injuries heal, the formation of scar tissue, which is functionally deficient compared to healthy tissue, leads to reduced flexibility and increased risk of reinjury. These types of injuries are traditionally treated by cooling, bandaging, and a period of rehabilitation exercises. They can also be treated with systemic or local corticosteroid or anti-inflammatory drugs, but often require surgical intervention. However, none of these measures allow for complete tissue healing.[7] Orthopedic problems are the cause of 70% of days-lost to training in showjumpers and racehorses, and in many cases, the horse will never return to its preinjury performance.[18][19] In fact, osteoarthritis is the leading career-ending condition and cause of chronic lameness in horses.[20]
5. Veterinary Stem Cell Therapies are Commercially Available Without Regulatory Approval
5.1. Perhaps unsurprisingly, particularly in the U.S., commercial interest in veterinary applications of stem cell therapies rapidly outpaced regulatory control. While the first companies supplying allogeneic MSCs or services to support the isolation and expansion of autologous MSCs were established in the early 2000s, the FDA guidance for developing cell-based products for animal use wasn’t published until 2015.[21]
5.2. To date, no cell therapy products for veterinary medicine have been approved by the FDA, which is likely because published peer-reviewed studies demonstrating conclusive benefits are still lacking for many diseases, despite a growing body of data suggesting that stem cell therapies are effective, particularly for orthopedic injury. The American Veterinary Medical Association takes a similarly conservative policy position.[22] Despite muted regulatory enthusiasm, stem cell therapies are reasonably accessible for both horses and pets for osteoarthritis and some tendon and cartilage joint injuries. MSC therapies for dogs cost somewhere in the range of $2,000–$3,000, but this is now covered under some pet insurance policies.[23]
5.3. In Europe, the European Medicines Agency (EMA) has approved two MSC products for commercial use. Arti-Cell Forte is given as a single injection into an affected joint for the treatment of mild to moderate lameness resulting from joint inflammation in horses, while HorStem is approved for the treatment of mild to moderate osteoarthritis in horses.[24] In the UK, veterinary medicines are regulated by the Veterinary Medicines Directorate, and specialist centers such as the Royal Veterinary College are approved to carry out stem cell therapies in horses and dogs for certain indications or to supply cell products to veterinarians.[25]
6. Potential for Veterinary Research to Inform Human Trials
6.1. Under the One Health Initiative, which is defined by the World Health Organization (WHO) as an integrated, unifying approach to balance and optimize the health of people, animals, and the environment, some veterinarians suggest that the body of data supporting the use of MSCs for orthopedic indications in animals can and should be considered in the assessment of novel human therapies. In particular, they argue that the lack of fidelity in traditional animal models leads to later clinical failures, and that treatment of naturally occurring diseases in companion animals may therefore provide a better indication of human clinical success. Companion animal models more closely resemble human conditions because their naturally occurring diseases arise from complex interactions between multiple genes and environmental factors. In addition, their longer lifespans and larger size allow for diagnostic and treatment procedures that are more directly translatable to humans.[12]
6.2. On the other hand, there is no central, searchable database for veterinary clinical trials, and, as discussed above, veterinary clinical trials are often small, sporadic, and not completed in a systematic phased manner, as human trials are. Therefore, while it may be possible to amass sufficient data to support a general suggestion of efficacy in certain indications, it is harder to argue that there would routinely be sufficient veterinary trial data available to directly inform in-human clinical studies. Nevertheless, based on its experience delivering veterinary stem cell therapies, cell therapy company VetStem has spun out a sister company, Personalized Stem Cells, to conduct human clinical trials so that you can also be “treated like a dog.”[26] They received FDA approval of their investigational new drug (IND) to launch a clinical trial for use of autologous MSCs to treat osteoarthritis in 2019.[27]
7. Veterinary Research iPSC and CAR-T Cell Therapy
7.1. Understanding of veterinary species-specific iPSCs and their corresponding regulators of pluripotency lags behind that of human iPSCs, which has delayed their evaluation in veterinary clinical trials.[12] To date, one pilot study has aimed to optimize the generation of neural progenitor cells (NPCs) from canine iPSCs and test their safety in dogs with spinal cord injuries. This study found that, although NPCs derived from canine iPSCs could differentiate into mature neural cells, neither of the two dogs that were injected with canine NPCs experienced any meaningful improvement in their condition.[28]
7.2. Veterinary research into CAR-T cell therapies is still in its infancy. A first-in-species trial investigated the use of CAR-T cell therapies in dogs with spontaneous diffuse large B cell lymphoma (DLBCL). However, this trial injected only low numbers of CAR-T cells into each dog. Its primary objective was to assess whether dogs might provide a more faithful representation than rodents of the clinical challenges observed in human CAR-T therapy trials, as well as to establish their feasibility as a model for addressing manufacturing issues.[29]
7.3. More recently, the Gates Institute in Colorado has launched a clinical trial of CAR-T cell therapies in dogs with osteosarcoma, with the hope that this research might inform future human clinical trials into use of CAR-Ts for solid tumors.[30] Current CAR-T cell manufacturing platforms are likely to prove cost prohibitive for veterinary use, so if these cell therapies are to progress beyond improved preclinical models to inform human trials, it will be essential to establish alternative reagents, manufacturing processes, and product profiles that can deliver CAR-based therapeutics to animal patients at a significantly lower cost.[31]
FAQs
What is the difference between autologous CAR-T and allogeneic CAR-NK therapies?
Autologous CAR-T therapy relies on isolating and genetically modifying a patient’s own cytotoxic T cells, creating logistical complexity. Conversely, CAR-NK therapies utilize donor natural killer cells that are not host-specific, enabling off-the-shelf allogeneic administration with reduced risks of cytokine release syndrome (CRS) and graft-versus-host disease (GvHD).
How do Tumor-Infiltrating Lymphocytes (TILs) treat metastasized melanoma without genetic modification?
TIL therapies, such as FDA-approved lifileucel (Amtagvi), extract naturally occurring lymphocytes from a patient's tumor biopsy. Because these cells already express receptors for tumor-associated antigens (TAAs), they are expanded and activated in vitro without genetic engineering, enabling reinfused cells to target systemic metastasized melanoma.
Why is veterinary cell therapy research vital to the One Health initiative?
Veterinary cell research supports One Health by evaluating naturally occurring diseases in companion animals like dogs and horses. These animals share environmental exposures and complex genetic interactions with humans, offering a realistic, highly translatable model that predicts human clinical trial success better than traditional rodent models.
Why are induced pluripotent stem cells (iPSCs) preferred over human embryonic stem cells (hESCs)?
Induced pluripotent stem cells (iPSCs) are reprogrammed from adult differentiated somatic cells—such as fibroblasts or keratinocytes—offering pluripotency without the ethical and regulatory constraints surrounding human embryonic stem cells (hESCs) derived from fetal tissue. Additionally, iPSCs enable patient-matched autologous applications.
What chronic indications are best suited for Mesenchymal Stem Cell (MSC) therapies?
Mesenchymal Stem Cells (MSCs) are multipotent adult stem cells derived from bone marrow, cord blood, or adipose tissue. Because their differentiation process requires time in vivo, MSCs are clinically optimal for long-term degenerative conditions, including amyotrophic lateral sclerosis (ALS), Parkinson's disease, osteoarthritis, stroke, and chronic kidney disease.
What therapeutic challenges limit non-stem islet cell transplants for type 1 diabetes?
Non-stem islet cell transplants isolate insulin-producing pancreatic cells from cadaveric or living donors to restore endogenous glucose regulation. However, because donor and recipient HLA epitopes are typically mismatched, commercialization is constrained by the strict trade-off between chronic insulin dependence and lifelong immunosuppressive therapy.
