Sarcoids tumors develop in many forms in horses, ranging from mild to locally aggressive, and they have various causes. One common cause, especially in Europe, is due to bovine papillomaviruses types 1 and 2 (BPV1, BPV2).
An Austrian study looked at the use of immunotherapy of sarcoids based on influenza A and B virus vectors containing a truncated NS1 gene (iNS)—this gene induces interferon and expression of specific antigens to target sarcoids caused by BPV1 or BPV2 [Jindra, C.; Hainisch, E.K.; Rummele, A.; et al. Influenza virus vector iNS1 expressing bovine papillomavirus 1 (BPV1) antigens efficiently induces tumor regression in equine sarcoid patients. PLoS ONE Nov 2021; 16(11): e0260155; https://doi.org/10.1371/journal.pone.0260155].
A safety trial was based on induction of bovine papillomavirus virions to create “pseudo-sarcoids” on both sides of the neck of 12 healthy horses. Once the lesions grew to more than 2 cm, those on the left neck of six horses were injected with the influenza vector containing the specific targeting genes and antigens, while the other six horse necks served as controls and were only injected with the virus carrier solution. The right neck lesions were left untreated. The treated and control lesions received their specific injections on Days 0, 2 and 4, or on Days 7, 9 and 11. Sarcoid diameters were measured twice weekly until week 10. No viral shedding was identified in nasal secretions or feces during the trial.
A second part of the study evaluated 29 sarcoid-affected horses in otherwise good health. Sarcoids were graded as mild (n=5), moderate (n=5), or severe (n=19). Lesions were injected with influenza vector material iNSA/E6E7equ and/or iNSB/E6E7equ. Injections were done on Days 0, 2, 4, 7, 9 and 11 or on Days 0, 28 and 86. One tumor remained untreated as a control in horses with more than one lesion. Monthly diameter measurements and photographs were taken, and the horses were monitored for local or systemic adverse effects. A few individuals developed a low-grade fever for less than 24 hours, and about half developed edema at the injection site and/or the non-injected tumor site, with most resolving within 12 hours.
Complete tumor regression was achieved in 10 patients while in 10 other horses, sarcoid regression continued. Tumor regression also occurred in non-injected lesions, indicating a systemic, sarcoid-specific immune response. Six horses did not respond at all while three responded only transiently—this set of horses that was non-responsive to treatment had severe, multiple, aggressive fibroblastic sarcoids that had also failed to respond in previous treatment efforts.
The standard protocol adopted for the best success uses a treatment schedule on Days 0, 28 and 86. This protocol is preferable also because of stabling logistics following injection. The Days 0, 2, 4, 7, 8 and 11 protocol required stabling of horse patients at a facility for two weeks whereas the 0, 28 and 86 day treatment protocol only required three overnight stays.