Prospect for immunological therapies of the equine malignant melanoma

Abstract

Although equine melanocytic neoplasms occur frequently, at least in grey horses, their existence is neglected frequently, despite their potentially severe clinical consequences. Immune-based therapies have been investigated in human metastatic melanoma and offer encouraging results. Researchers have recently begun to explore the immunological approach in equine malignant melanoma (EMM) with some success. Therefore, this review aims at giving a short overview of the nature of EMM and providing insight into the immunological basis of melanocytic neoplasms in general. Equine malignant melanoma is a true neoplasm with a genetic basis. Initially they show a slow invasive growth, but they have the potential to metastasize. EMM and human malignant melanomas share various common histopathologic features. For the immune system eradication of the tumor is a challenge. Although solid tumors are often infiltrated with immune cells, they usually do not induce a significant tumor remission. The antitumoral immune response depends on factors of the innate immune system interacting in a coordinated fashion with the adaptive immune system. Antigen-presenting cells, neutrophilic granulocytes, and lymphoid cells may elicit antitumoral effects. This innate response precedes a downstream antigen-specific response. In the tumor microenvironment of solid tumors immune suppressive factors can induce immune escape mechanisms of the tumors. Immunological therapies of EMM include blockage of histamine 2 receptors on melanoma cells and lymphocytes, cancer vaccines and gene therapeutic approaches. This article focuses on the immunological therapeutic approach of EMM and gives an outlook on future implications.