Abstract
Adult stem cells have been intensively studied for their cell-therapeutic potential to renew and replace lost cells in any damaged tissue or organ. Yet, the origin of adult stem cells remains an important question to be resolved. On the other hand, microcells have been used for cell fusion in cancer research. A microcell contains a micronucleus that has one or a few chromosomes with a small amount of cytoplasm. Recently it was reported that microcells can transform into undifferentiated cells, which suggests microcells are a possible origin of adult stem cells. In the early 1960's Bonghan Kim claimed that anatomical structures corresponding to acupuncture meridians had been observed and that they formed a circulatory network distributed throughout a body which was entirely different from the blood, lymph, or neural systems. A liquid whose most important component was microcell-like bodies called "Bonghan granules" flowed in this new circulatory system. Granule sizes, shapes, structures and DNA-content were similar to those of microcells. Furthermore, Kim observed that the Bonghan granules grew and regenerated or repaired damaged cells. Recently, after decades of neglect, Kim's studies are being considered again, and some of his findings, including Bonghan granules, have been reconfirmed. We put forward a hypothesis on a possible origin of adult stem cells : The Bonghan granules that flow in the Bonghan circulatory network are naturally generated microcells and they are capable of growing and differentiating into tissue cells and also regenerating the tissues of injured organs. Any differentiated tissue cells in mammalian organisms may have a capacity for self-reproduction and self-renewal by specific "microcell-like Bonghan granules". Understanding of the origin of adult stem cells in animals is one of the most fundamental tasks in modern biomedicine and may result in new approaches to the treatment of many diseases in the future.
