Treatment of equine sarcoids using recombinant poxviruses expressing feline interleukin-2

Abstract

Background Interleukin (IL)‐2 stimulates antitumour immunity and is successfully used for the treatment of different neoplasias.

Hypothesis/Objectives Canarypox virus locally expressing feline IL‐2 is safe and can be used to treat equine sarcoids.

Animals Twenty horses of different breeds with a median age of eight years (interquartile range 6.0–13.3 years) and a total number of 59 sarcoids were included in the study.

Methods In this prospective clinical trial, sarcoids were injected twice seven days apart, with a recombinant canarypox virus expressing feline IL‐2. Complete blood counts (CBC) and fibrinogen levels were measured before treatment and on days 1, 2, 7 and 8.

Results 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. There were no significant changes in CBC and fibrinogen levels after either injection. One horse developed a mild fever the day after each injection, which subsided without treatment the following day.

Conclusions Treatment of equine sarcoids with recombinant canarypox virus expressing feline IL‐2 seems to be a safe therapy option. Although the expression of IL‐2 after vector injection and its biological activity in horses were not proven in this study, the treatment resulted in regression and partial regression in 50% of the cases. Further studies are necessary to verify these findings and to establish a treatment protocol.