An object of the present invention is to provide a method capable of easily and inexpensively preparing cells having pluripotency and extremely low risk of tumorigenesis. Human bone marrow mesenchymal stem cells (HMSC-BM), human adipose tissue-derived mesenchymal stem cells (hAT-MSC) (“human adipocyte-derived stem cells [ Mammalian mesenchymal stem cells such as Human Adipose-derived Stem Cells (hADSC)), 7 types of human adherent mature cells (human hepatocyte cells [hHEP cells], human umbilical vein endothelial cells [HUVEC cells] Human skin microlymphatic endothelial cells [HMVEC cells], human epidermal keratinocytes [NHEK cells], human bronchial epithelial cells [NHBE cells], human melanocyte cells [NHEM cells], and human smooth muscle cells [UASMC cells]) And three types of human adherent progenitor cells (human skin fibroblasts [NHDF cells], human skeletal muscle myoblasts [HSMM cells], and human osteoblasts Suspended cultured cells [NHOst cells]) and to form a cell mass (spheroids [Spheroid]), have pluripotency and can tumorigenic risk to prepare very low cell.本発明は、多能性を有し、かつ腫瘍化リスクが極めて低い細胞を、安価に且つ簡便に調製できる方法を提供することを課題とする。ヒト骨髄間葉系幹細胞（Human Mesenchymal Stem Cells from Bone Marrow；ｈＭＳＣ-ＢＭ）、ヒト脂肪組織由来間葉系幹細胞（Human Adipose Tissue-derived Mesenchymal Stem Cell；ｈＡＴ－ＭＳＣ）（「ヒト脂肪細胞由来幹細胞［Human Adipose-derived Stem Cells；ｈＡＤＳＣ］」ともいう。）等の哺乳動物間葉系幹細胞や、ヒト接着性成熟細胞７種（ヒトヘパトサイト細胞［ｈＨＥＰ細胞］、ヒト臍帯静脈内皮細胞［ＨＵＶＥＣ細胞］、ヒト皮膚微小リンパ管内皮細胞［ＨＭＶＥＣ細胞］、ヒト表皮角化細胞［ＮＨＥＫ細胞］、ヒト気管支上皮細胞［ＮＨＢＥ細胞］、ヒトメラノサイト細胞［ＮＨＥＭ細胞］、及びヒト平滑筋細胞［ＵＡＳＭＣ細胞］）及びヒト接着性前駆細胞３種（ヒト皮膚線維芽細胞［ＮＨＤＦ細胞］、ヒト骨格筋筋芽細胞［ＨＳＭＭ細胞］、及びヒト骨芽細胞［ＮＨＯｓｔ細胞］）を浮遊培養し、細胞塊（スフェロイド［Spheroid］）を形成させると、多能性を有し、かつ腫瘍化リスクが極めて低い細胞を調製することができる。
