MCAM and melanoma: However, in severe combined immunodeficiency (SCID) mice, CD146 expression minimally affected the tumourigenicity of melanoma cells, as CD146 transfection into both human melanoma SK-2 and XP44RO(Mel) cell lines (which are normally CD146-negative) resulted in tumour formation comparable to, or even smaller, than their respective vector controls in SCID mice [42].