Vaccine shows promise against equine melanomas

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A melanoma on a horse's dock.
A melanoma on a horse’s dock.

A vaccine designed to target equine melanomas has shown promise in a German study.

The research involved 27 grey horses suffering from melanomas. The horses were not treated with any medication at least two weeks prior to immunisation.

Jessika Cavalleri and her colleagues said a DNA-based vaccination may represent a promising therapeutic approach against equine melanomas as such treatments had successfully induced an immunological response in other affected species and in healthy horses.

The melanoma-affected horses were divided into three groups in order to receive different therapy protocols, all of which contained DNA vectors encoding for equine (eq) IL-12 and IL-18.

Depending on the group, they received these alone or in combination with either human glycoprotein (hgp) 100 or human tyrosinase (htyr). Neither hgp or htyr were ultimately found to increase the effect of the vaccine.

The horses were vaccinated into muscle on days 1, 22, and 78. One selected melanoma on each horse was also treated with injection straight into the tumour.

Up to nine melanomas were monitored on each horse.

The researchers, whose findings have been reported in the journal, BMC Veterinary Research, found a significant reduction in the relative tumor volume in the horses after 120 days.

They described it as the first clinical report on a systemic effect against equine melanoma following treatment with DNA vectors encoding eqIL12 and eqIL18 and formulated with a transfection reagent.

A vector is a DNA molecule used as a vehicle to artificially carry foreign genetic material into another cell, in this case to target the melanomas.

The horses were hospitalized for three days after each injection. Based on the clinical examinations of the horses, the vaccine was safe and well tolerated. The only consistent abnormal finding was a significant increase in body temperature on the day after injection.

The melanomas were monitored before each injection and on day 120 using calipers and by two independent ultrasound examiners. All measurements were performed three times.

The relative volumes of the tumors were calculated in reference to the volume on day one, before the first immunisation, which was defined as 100 percent.

In total, 136 melanomas were measured in the study. Over the course of the study they found a reduction equivalent to 28.5 percent of tumor volume as measured by calipers. One ultrasound operator reported a 13 percent tumor volume reduction and the second operator recorded 17.9 percent.

The research team said the findings represented a measurable systemic anti-tumoral effect on equine melanomas.

“Because no specific immune response was detected, it remains to be elucidated whether this systemic anti-tumoral effect was caused by interleukins expressed from the DNA vectors, or an unspecific immune reaction to the combination of DNA and transfection reagent.”

Local and systemic effect of transfection-reagent formulated DNA vectors on equine melanoma.
Kathrin Mählmann, Karsten Feige, Christiane Juhls, Anne Endmann, Hans-Joachim Schuberth, Detlef Oswald, Mareu Hellige, Marcus Doherr and Jessika-MV Cavalleri.
BMC Veterinary Research 2015, 11:107 doi:10.1186/s12917-015-0414-9
The full study can be read here

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