Currently there is no universally effective treatment for sarcoids and if treatment fails, the sarcoids will often come back worse than they were in the first place. Although the disease is rarely life threatening, many horses with sarcoids are euthanased because the condition is untreatable or because the horse is unsellable.
A study by Johanna Loschelder-Ostrowski and colleagues assessed the use of canarypox expressing feline Interleukin-2 (IL-2) in the treatment of equine sarcoids.
Interleukin (IL)-2 is one of the key cytokines (proteins involved in cell signalling). It stimulates cell mediated immunity, activating a range of T-cells. IL-2 is used in human medicine, including for treating cancerous conditions such as metastatic renal cell carcinomas and metastatic melanoma.
A canarypox virus vector, which has been genetically modified to contain a gene to make it produce IL-2, was used in the study. (A licenced product is available for use in the treatment of fibrosarcoma in cats.) The canarypox virus does not spread or multiply in cats or other mammals.
The technology is widely used in the production of vaccines for horses and other species (such as some equine influenza and West Nile virus vaccines).
Firstly, the research team carried out a safety trial in four healthy horses. None of the horses showed significant adverse effects after two treatments.
They then assessed its use to treat 20 horses with sarcoids. The sarcoids were injected twice seven days apart, using the recombinant canarypox virus expressing feline IL-2.
None of the horses with equine sarcoids showed significant adverse effects after intratumoural treatment.
The researchers report that “complete regression was achieved in eight horses (40%) and partial regression in two horses (10%). No change in sarcoid size was observed in two horses (10%) and the disease progressed in five horses (25%). Sarcoids of three horses (15%) showed initial response followed by tumour growth.”
However, they noticed a long delay between the first injection and the beginning of tumour remission. “Of the 68% of sarcoids that did show remission after 23 months, remission started after a median time of 30.4 ± 5.4 weeks.”
Reporting their work in the journal Veterinary Dermatology, the authors conclude: “In summary, in this clinical pilot study, the treatment of equine sarcoids with canarypox virus locally expressing IL-2 was easy and safe for both user and horse. Equine sarcoids injected with canarypox virus expressing feline IL-2 showed a reduction in tumour size or a complete remission of the tumour in 50% of cases.”
They add: “Further studies are necessary to research vector and feline IL-2 effects in horses, establish an optimal treatment regime for equines and verify the results in a larger population of patients.”
For more details, see:
Treatment of equine sarcoids using recombinant poxviruses expressing feline interleukin-2
Johanna Loschelder-Ostrowski, Judith Christine Winter, Roswitha Merle, Robert Klopfleisch, Heidrun Gehlen
Veterinary Dermatology (2021)
https://doi.org/10.1111/vde.12941
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