ALVAC-fIL2, a feline interleukin-2 immunomodulator, as a treatment for sarcoids in horses: A pilot study.
Authors: Saba Corey, Eggleston Randall, Parks Andrew, Peroni John, Sjoberg Eric, Rice Shelbe, Tyma Jesse, Williams Jarred, Grosenbaugh Deborah, Leard A Timothy
Journal: Journal of veterinary internal medicine
Summary
# ALVAC-fIL2 Immunotherapy for Equine Sarcoids: Promising Early Results Equine sarcoids represent a significant clinical challenge, as these common neoplasms currently lack a reliably effective treatment despite their impact on performance and economic value. Researchers conducted a prospective pilot study injecting ALVAC-fIL2 (a modified vaccinia virus expressing feline interleukin-2) directly into sarcoid tumours at weeks 0, 1, 3, and 7 across 14 client-owned horses, with tumour measurements and response assessment continued for a minimum of 12 months post-treatment. Tumour regression occurred in 86% of treated horses, with a median time to initial response of 89 days and best response achieved by day 211, though three sarcoids continued shrinking beyond the study endpoint; critically, the median progression-free interval was not reached during follow-up, indicating durable responses in the cohort. Tolerability was excellent, with only transient focal inflammation noted in two horses, suggesting this intratumoral immunomodulatory approach avoids the tissue damage associated with conventional treatments. For practitioners managing sarcoid cases, ALVAC-fIL2 represents a tissue-sparing alternative worthy of further investigation, particularly as owners and veterinarians seek treatments that preserve function and cosmetic outcome—though larger, controlled trials are needed to establish efficacy benchmarks and identify which sarcoid presentations respond most favourably.
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Practical Takeaways
- •ALVAC-fIL2 intratumoral injection offers a well-tolerated alternative for sarcoid treatment with 86% response rate and minimal side effects, potentially useful for horses where surgery or other treatments are contraindicated or have failed
- •Treatment requires a 7-week injection protocol with reassessment over 12+ months; practitioners should counsel clients on this extended timeline and need for serial measurements to assess response
- •This pilot study shows promise but is limited to 14 horses; larger controlled trials are needed before widespread clinical adoption, and current evidence does not yet establish this as a first-line therapy
Key Findings
- •Tumor size decreased in 86% of treated horses (12/14 horses)
- •Median time to first response was 89 days with a range of 34-406 days
- •Median time to best response was 211 days, with 3 sarcoids still decreasing at final evaluation
- •Adverse events were minimal, limited to transient focal inflammation in 2 horses