CD47 expression in cryopreserved equine cutaneous masses and normal skin.

We investigated CD47 expression in cryopreserved sections of equine cutaneous masses and normal skin. CD47 is a cell surface protein expressed on many cell types and overexpressed in some tumors. Interaction of CD47 and signal regulatory protein-alpha (SIRPα) inhibits phagocytosis by macrophages. Formalin-fixed tissues from horses prospectively enrolled in the study were used to establish a histologic diagnosis. Immunohistochemical assays were performed on cryopreserved tissues using anti-CD47 antibodies or IgG control antibodies. CD47 was not expressed on equine normal skin but positivity to CD47 was present in 13 of 24 (54%) masses. Immunotherapy with anti-CD47 antibodies for equine cutaneous tumors that express CD47 warrants further investigation.