C3a plays a pivotal role in inducing retinal stem and progenitor cell activation, independent of fibroblast growth factor.27 Another complement anaphylatoxin C5a and its receptor C5aR are expressed in human pluripotent stem cells, and they promote pluripotency of stem cells.37 Stemness factors Sox‐2, Nanog, Oct‐4 and c‐Myc control the self‐renewal and pluripotency of human pluripotent stem cells, suggesting that they are correlated with cancer stem cells.38 In this study, C3a exposure promoted the expression of Sox‐2, Nanog, Oct‐4, c‐Myc and CD‐44. Here, SOX2 is linked to cancer.