This invention addresses the problem of providing: a mammalian cell suspension capable of preventing the formation of pulmonary embolisms when mammalian stem cells or other mammalian cells are administered intravenously； or a prophylactic agent against the formation of pulmonary embolisms when mammalian cells are administered intravenously. This invention is characterized by the suspension of mammalian stem cells or other mammalian cells in a physiological aqueous solution including as an effective component thereof trehalose, a derivative thereof, or a salt of either, and the preparation of a mammalian cell suspension for the prevention of pulmonary embolism formation when administering mammalian cells intravenously, said suspension containing as an effective component thereof: mammalian cells； and trehalose, a derivative thereof, or a salt of either. In addition to mammalian stem cells, islet cells, dendritic cells, natural killer cells, alpha-beta T cells, gamma-delta T cells, and cytotoxic T lymphocytes, etc., can be used as the mammalian cells. Mammalian mesenchymal stem cells and mammalian pluripotent stem cells are suitable examples of mammalian stem cells.本發明係以提供在經由血管投予哺乳動物幹細胞等之哺乳動物細胞時能預防肺栓塞形成的哺乳動物細胞懸浮液，以及在經由血管投予哺乳動物細胞時的肺栓塞形成預防劑作為課題。本發明之特徵係將哺乳動物幹細胞等之哺乳動物細胞懸浮於含有以海藻糖或其衍生物或該等之鹽作為有效成分的生理性水溶液中，以製作含有哺乳動物細胞及海藻糖或其衍生物或該等之鹽作為有效成分之為了預防在經由血管投予哺乳動物細胞時形成肺栓塞的哺乳動物細胞懸浮液。作為該哺乳動物細胞，哺乳動物幹細胞以外可舉出胰島細胞、樹狀細胞、自然殺手細胞、阿爾發．貝塔T細胞、伽瑪．德爾塔T細胞、細胞毒性T細胞等，此外，作為上述哺乳動物幹細胞可合適地舉例哺乳動物間葉系幹細胞或哺乳動物多能性幹細胞。
