INTRODUCTION: Breast reconstruction using fat grafts presents challenges; for example, fat necrosis owing to inadequate blood flow results in reduced engraftment rates. Supplementation of adipose tissue with adipose-derived mesenchymal stem cells (ADSCs) to promote the rapid vascularization of transplanted tissue has been investigated. However, the vascularization of fat-grafted tissues using only ADSC transplantation is limited. cultured mononuclear cells (RE-01) are a cell population with highly vascular and tissue-regenerative properties. This study aimed to evaluate the effect of combining RE-01 cells and ADSCs on the engraftment rate of fat grafts and explore the potential of this approach as a new option for breast reconstruction surgery. We hypothesized that combining RE-01 with ADSCs might promote angiogenesis and improve the fat grafting rate, consequently reducing the number of ADSCs required. METHODS: ADSCs cultured from human adipose tissue discarded during liposuction were co-cultured with RE-01 cells produced from the peripheral blood of healthy volunteers. vascular regeneration and adipogenic differentiation potential were analyzed. In addition, fat grafting experiments were conducted using nude mice to verify the fat grafting efficacy of ADSCs after co-cultivation with RE-01. RESULTS: ADSCs co-cultured with RE-01 cells promoted angiogenesis and adipogenesis . This was evidenced by a significant increase in the expression of adipogenic markers and , as well as enhanced lipid droplet formation observed through Oil Red O staining. The results demonstrated that the fat engraftment rate was significantly improved in the mixed group of ADSCs co-cultured with RE-01 cells. The number of blood vessels and fat quality of the transplanted adipose tissue were also increased in this group, suggesting that ADSCs co-cultured with RE-01 cells were highly effective in fat transplantation. CONCLUSIONS: ADSCs co-cultured with RE-01 cells may be useful for improving the engraftment rate of fat grafts. However, further studies are required to verify the mechanisms.