mixedchimerism

Mixedchimerism is a biological phenomenon in which an individual harbors two or more genetically distinct cell populations that coexist within the same organism. The term is most commonly used in the context of hematopoietic (blood-forming) cell transplants, where the recipient’s immune system is partially replaced by donor stem cells. During a successful bone‑marrow or stem‑cell transplantation, donor cells engraft in the recipient’s bone marrow and give rise to blood cells that express the donor’s DNA. However, due to incomplete ablation of the host immune system or residual host hematopoiesis, some host immune cells may persist, resulting in a mixed population of host and donor cells.

Detection of mixedchimerism is generally performed with molecular techniques that distinguish donor and recipient DNA, such as short tandem repeat (STR) analysis or quantitative polymerase chain reaction (qPCR). The proportion of donor versus recipient cells is monitored to assess engraftment success, predict graft‑versus‑host disease (GVHD) risk, and detect early signs of relapse in malignant conditions such as acute myeloid leukemia.

Clinically, the presence of mixedchimerism can be an intermediate state. In transplantation for hematologic disorders, a gradual decline of recipient cells toward complete donor chimerism is often desired, whereas persistent donor dominance may be associated with reduced GVHD but may also indicate insufficient graft‑versus‑tumor effect. Conversely, high levels of host cells can signal incomplete engraftment, increased infection risk, or imminent graft rejection. In autoimmune disease treatment, mixed chimerism has been explored as a strategy to induce immune tolerance, potentially allowing the discontinuation of immunosuppressive drugs.