CTLA4 and melanoma: While Wnt-3a is thought to function to promote self-renewal of hematopoietic stem cells, neural stem cells and embryonic stem cells, the addition of Wnt-3a to human melanoma cell lines and primary melanoma tumors upregulated the expression of CTLA-4 on the melanoma cells, likely due to CTLA-4 being a direct target of the Wnt/β-catenin signaling pathway (Figure 1) [101].