Most reported human studies of stem cell-based bone regeneration are cohort outcome studies or case reports, because of the practical and ethical issues involved in conducting a randomised controlled trial. Published human clinical studies  or case reports used autologous, culture-expanded, non-genetically modified human mesenchymal stem cells for bone regeneration. While the absence of controls is a major drawback, these preliminary cohort studies hint at the safety and potential therapeutic effects of autologous stem cell treatment.