Working towards a sarcoid vaccine

Equine sarcoids are the most frequently diagnosed skin tumours in horses. Although they are generally non-malignant, they can be highly problematic. 

Sarcoids are believed to be associated with bovine papillomavirus type 1 (BPV1). The virus is implicated in the transformation of equine skin cells, resulting in tumour development. Although the exact transmission route is not fully understood, BPV1 DNA has been detected in many equine sarcoid lesions, strengthening the link between the virus and the disease.

Currently there is no universally effective treatment, 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.  

Various treatment options are available for equine sarcoids, including:  surgical removal, laser excision, cryotherapy (freezing the tumour), topical and intralesional chemotherapy and immunotherapy.

However, treating sarcoids is challenging due to their high recurrence rates, especially following surgical removal. Residual tumour cells left behind during surgery often lead to regrowth, making long-term management difficult.

Currently, there is no approved vaccine available to prevent or treat equine sarcoids. However, given the association with BPV1, the development of a vaccine could potentially offer protection against the disease.

Researchers at the Maxwell H. Gluck Equine Research Center, University of Kentucky, Lexington, have made a significant step toward developing a sarcoid vaccine.

A team led by Olivia Jacob and colleagues has developed an experimental vaccine using a recombinant baculovirus vector. This vaccine expresses the L1 protein of BPV1.

(The L1 protein is a major structural component of the BPV1 viral capsid. It plays a key role in triggering the immune system to recognize and neutralize the virus, making it a prime target for vaccine development.)

The researchers conducted a trial involving 15 horses. Ten healthy, sarcoid-free horses received two doses of the experimental vaccine, administered three weeks apart. Five control horses were injected with a placebo vaccine containing only the culture medium.

Blood samples were collected before and after vaccination to assess the immune response.

Vaccinated horses produced strong neutralising antibody responses, with antibody titres ranging from 40 to over 1280. In contrast, the control horses showed no detectable immune response.

The researchers concluded that since neutralising antibodies are recognised as an indicator of protection against BPV1, this experimental vaccine has the potential to protect horses from developing sarcoids.

The study offers promising evidence that a BPV1-based vaccine could provide immunity against equine sarcoids. Although still in the experimental stage, the vaccine demonstrated a good safety profile and the ability to elicit a strong immune response in horses. If further trials confirm its effectiveness, this vaccine could provide a novel tool in preventing and managing equine sarcoids, significantly improving equine health and welfare.

For more details, see:

 

O. Jacob, B. Hause, K. Peters-Smith, E.N. Adam, A.E. Page, C. Floyd, C. Tucker, L.G. Eertink, D. Wang, F. Li,

Safety and immunogenicity of a sarcoid vaccine in horses,

Journal of Equine Veterinary Science,(2025) 146, 105381,

https://doi.org/10.1016/j.jevs.2025.105381

Effect of punch biopsy on sarcoid growth

 The common belief that taking biopsies of suspected sarcoids could make them worse may not be justified.

 Sarcoids, are the most common skin tumour of horses. Although typically benign, they can be locally aggressive and difficult to manage. They appear in various forms, including flat, nodular, verrucous, fibroblastic, and occult types. Bovine papillomavirus (BPV) has been implicated in the development of sarcoids, although the exact mechanism is not fully understood.

 

In standard veterinary practice, biopsies are a useful diagnostic tool for identifying the nature of swellings and masses. However, the fear of inadvertently worsening the condition has led many veterinarians to avoid biopsy procedures for sarcoids.

 

A recent small-scale study investigating the impact of punch biopsies on the growth of equine sarcoids challenges this assumption. The study failed to confirm the notion that biopsies could exacerbate the aggressiveness or spread of sarcoids.

 

Lien Gysens carried out the study with her colleagues at the Department of Large Animal Surgery, Anaesthesia and Orthopaedics of Domestic Animals, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium. A full rereport of tth research is published in Veterinary Dermatology.

 

The study included six client-owned horses with a total of 11 sarcoids. These horses, all Belgian Warmbloods, presented with a range of clinical types: three occult, four nodular, two verrucous, and two fibroblastic sarcoids.

 

To qualify for inclusion in the study, the horses had to test positive for BPV-1/-2. This was determined using superficial swabs, scrapings, or fine needle aspirates (FNA), which were then subjected to quantitative PCR (qPCR).

 

 The research team examined the dynamics of tumour growth, focusing on factors such as thickness, area, and circumference, as well as viral load (VL) and Visual Analog Scale (VAS) scores in horses affected by sarcoids who underwent a single diagnostic punch biopsy.

 

The growth of each sarcoid was closely monitored on a weekly basis for nine months: from 12 weeks prior to the punch biopsy to 24 weeks following the procedure.

 

In this preliminary study, the researchers didn't find any clear trend in how sarcoids grew after a single punch biopsy. 

 

They observed significant changes in all growth parameters after the biopsy, but there wasn't a consistent direction of change – some grew larger, some smaller, and some stayed the same.

Drawing definite conclusions is challenging due to the limited number of tumours (11 in total) from only six horses with four different types of clinical sarcoids.

 

They conclude: “Our results indicate that post-biopsy lesion deterioration is not a general concept that applies to all sarcoids, and both deterioration or improvement are possible outcomes over a 24-week period. Further clinical studies with a larger sample size are needed before a definitive conclusion can be made.”

 

 

For more details, see:

 

Gysens L,  Martens A,  Haspeslagh M.  

Longitudinal pilot study examining the effect of punch biopsy on equine sarcoid growth dynamics. 

Vet Dermatol.  2024; 35: 148–155.

https://doi.org/10.1111/vde.13236

Pilot study suggests role for IL-2 in sarcoid treatment.

 Sarcoids are the most common skin tumour in horses. It is estimated that 6-7% of horses in the United Kingdom are affected. 

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