Feline chronic gingivostomatitis (FCGS) is a painful and debilitating disorder that has no treatments that are both easy and effective. Affected cats experience moderate to severe oral pain and discomfort that leads to anorexia, weight loss, inability to groom, hypersalivation, and in some cases, euthanasia for medical or economic reasons. Estimates of the number of cats affected with this idiopathic, inflammatory disease range between 0.7%-10% of the feline population.
The current standard of care for FCGS is full- or near full-mouth tooth extraction; approximately 70% of cats so treated will respond well. In the remaining 30%, there is little to no response to extensive dental extractions, and medical therapy with anti-inflammatory drugs, antibiotics, and analgesics may only partially ameliorate the residual pain and disability. This subpopulation of affected cats are considered to have refractory FGCS.
Mesenchymal stem cells (MSCs) are adult multipotent stem cells that can be derived from a variety of tissues, including adipose tissue (adipose-derived MSCs, or ASCs), that have potent immunomodulatory properties. Treatment with autologous ASCs is safe and well tolerated in both humans and animals. The immunomodulatory and regenerative capacity of MSCs derives from their ability to inhibit T-cell proliferation, alter B-cell function, inhibit dendritic cell maturation and differentiation, and downregulate MHC (major histocompatibility complex) II on antigen-presenting cells. As CD-8 T-cell inflammation and a dysregulated immune response are hallmarks of FCGS and similar immune-mediated, oral mucosal inflammatory diseases of humans, these investigators hypothesized that ASCs, with their ability to inhibit T-cell proliferation and induce T-cell anergy, might be useful in treating FCGS.
Nine client-owned cats with refractory FCGS, which was nonresponsive to full-mouth dental extractions (performed at least 6 months prior to enrollment) and immunosuppressive medical therapies, were enrolled in the study. If the cat was receiving immunosuppressive medications, this therapy was discontinued 2 weeks prior to the trial and for the entire 6-month duration of the study. The cats were allowed to receive only opioid analgesics for the duration of the trial. All patients had full-mouth dental radiographs to rule out the presence of retained roots, and all patients tested negative for both the feline immunodeficiency virus (FIV) and the feline leukemia virus. The cats also underwent a clinical examination, oral biopsy, and blood sample collection prior to treatment. Subcutaneous abdominal fat was then collected from each patient under general anesthesia, and then each cat’s ASCs were isolated, cultured, expanded and passaged.
The first intravenous autologous ASC transfusion was given to the patients 10-14 days after fat harvest. The second intravenous ASC injection was given one month later. Two patients left the study because the owners chose to administer corticosteroids to these animals. Of the seven cats that completed the study, five males and two females, two had immediate transfusion reactions which resolved rapidly and spontaneously when the transfusion rate was reduced, and the occurrence of a transfusion reaction did not influence the cat’s potential to respond to the ASC treatment. No other short- or long-term adverse reactions occurred in any of the patients.
Five of the seven cats responded to the ASC treatment; three had complete clinical remission and two demonstrated substantial clinical improvement within 1-4 months of the first ASC injection. Post-treatment oral biopsies were evaluated from one patient that had complete clinical remission, one that had substantial clinical improvement, and one non-responder. In the cat with complete clinical remission, the biopsy showed a complete return to normal tissue architecture; in the cat with significant clinical improvement, the biopsy demonstrated reduction in lymphoplasmacytic infiltration of the epithelium and subepithelial stroma, resolution of neutrophilic inflammation and ulceration, and clearing of CD3+ T cells and CD20+ B cells. Findings in the non-responder’s oral biopsy were identical to those of the pre-treatment biopsy.
Evaluation of peripheral blood samples prior to and following treatment also revealed differences between responders and non-responders. Most cats with FCGS have neutrophilia, polyclonal hypergammaglobulinemia, and increased levels of proinflammatory cytokines. In the responders, neutrophil counts returned to normal or near-normal levels within 6 months after the first injection; non-responders’ neutrophil counts did not change. In addition, responders had decreased circulating numbers of CD8+ T cells, a normalization of the CD4/CD8 ratio, decreased interferon-γ and interleukin-1β concentration (both proinflammatory cytokines), and a temporary increase in serum interleukin-6 and tumor necrosis factor-α concentration. Response to the ASC therapy was relatively slow, up to 4 months after the first injection, even in complete responders.
Cats in which CD8lo cells constituted less than 15% of the total CD8+ T cells, a lower percentage than is found in normal cats or nonresponders, were the ones that responded to the ASC therapy. A CD8lo cell is a cytotoxic CD8 cell with low expression of CD8, and low expression of CD8 shifts the function of these cells towards a suppressive rather than a cytotoxic phenotype. These cells are associated with chronic viral infections such as Epstein-Barr virus and HIV in humans, FIV in cats, and in chronic antigen stimulation in a mouse skin graft model. In cats CD8lo cells have very strong anti-FIV suppressor activity. The increased numbers of CD8+ cells in the peripheral blood of cats with FCGS suggests that this disease is an inappropriate response to chronic oral antigenic stimulation from clinical or subclinical viral infections. Given that there is a decreased percentage of CD8lo cells in cats that responded to the ASC therapy, it is possible that treatment with ASCs supports the expansion of CD8lo cells, which in turn help to resolve the inflammatory oral response. At least in this small cohort, a predominance of CD8+ T cells along with <15% CD8lo in peripheral blood was 100% predictive of response to autologous ASC therapy, so these cell counts are a potentially useful biomarker for identification of patients who are probable responders to autologous ASC therapy for FCGS. Stem cell therapy may therefore hold a great deal of promise for a population of feline patients who suffer significantly from the difficult and enigmatic disease that is FCGS. [PJS]