A method of culturing human or mammalian mesenchymal stem cells (MSC) or osteoblastic cells to form corresponding cell aggregates evenly distributed in the culturing medium having a reduced content of cells with fibroblast morphology comprises contacting MSC or OC with a water-soluble cellulose derivative over a period of from 1 day to one or two weeks. Also disclosed are a corresponding aggregates, a culture medium and a pharmaceutical composition, and uses of the aggregate, the culturing medium and the composition.