For many puppies, infection with canine papillomavirus is a rite of passage along the road to adulthood. But for some dogs, latent infection with the virus can re-emerge later in life and be particularly resistant to treatment (in some cases, even becoming malignant). At the Colorado State University Veterinary Teaching Hospital, veterinarians are showing good results in treating persistent canine papillomavirus using liposome-based immune therapeutics.
"Most dogs get infected as puppies through exposure to papillomavirus in their environment," said Dr. Steven Dow
, a Professor in the Department of Clinical Sciences and Director of the Center for Immune and Regenerative Medicine. "The condition tends to be mild, and most dogs never develop the characteristic lesions. Lesions that do develop tend to regress spontaneously after a few months. In older dogs, however, because of a lack of immune control, the disease can recur and the lesions don't go away.
The severe mouth lesions in this dog completely disappeared after several weeks of immunotherapy.
The papillomas, or wart-like lesions, caused by canine papillomavirus often have a jagged surface and may have a cauliflower-like appearance. They most often occur on the lips and muzzle of the dog and can become quite large, causing quite a bit of concern among new puppy owners unfamiliar with this common virus. Less frequently, these growths may be seen on the eyelids or even on the eyes themselves. On occasion, they can also be found on the feet, between the toes and, less commonly, on other parts of the body.
As a dog ages, its immune system may not be as robust or the dog may be on immunosuppressants for other conditions, and papillomavirus can re-emerge. A lack of immune control, notes Dr. Dow, allows the virus the opportunity to strike again.
"For these dogs, there are really no effective treatment options," said Dr. Dow, who collaborated on the project with Dr. Jessica Quimby, a DVM Postdoctoral Fellow in the Department of Clinical Sciences. "With liposome-based immunotherapy developed at CIRM, we applied an established treatment modality to a novel disease. We recently completed a study of nine older dogs with lesions that didn't respond to conventional therapy, and we are submitting the results for publication. Using liposome-based therapy, we were able to show a partial or complete regression in all the dogs, with durable responses. We believe the therapy activates the immune system in such a way that the virus stops replicating, which in turn leads to lesion regression."
Researchers believe that liposome-based immune therapy activates natural killer cells (also known as NK cells, a key component of the innate immune system) and T-cells (lymphocytes that also play a central role in cell-mediated immunity). Dr. Dow said that researchers at CIRM are not only excited about the outcomes of liposome-based immunotherapy with regards to canine papillomavirus, but also to other applications in veterinary medicine. In human medicine, the therapy already is in clinical trials targeting cancer.
"Veterinary medicine is in need of a non-specific immune stimulant that we can use for a variety of diseases from cancer to infectious diseases, as well as in vaccine development programs, and liposome-based immunotherapy shows real promise," said Dr. Dow.