CTLA4 and cancer: Soluble CTLA-4 is derived from an alternatively spliced isoform of full-length CTLA-4 and is secreted by several cell types including Treg [25], monocytes [27], melanoma cell lines [28], and pituitary gland cells [29], but its effects remain largely unexplored despite the clinical relevance of CTLA-4 both in autoimmune disease and cancer.