When a human body detects cells with non-matching tissue antigens, i.e., protein structures, the default reaction of the immune system is to attack those cells, leading the body to reject the new organ. Traditionally, this problem has been overcome with the use of immunosuppressant drugs to keep that immune response in check, but there are side effects to long-term, often indefinite, immunosuppression.

The cells produced by the bone marrow form a vital component of the human immune system. 

A new technique, now in the clinical trial stage, is providing an alternative. The procedure is called “mixed bone marrow and solid organ transplantation” and, as the name suggests, it involves transplanting bone marrow simultaneously with other organs like kidneys or lungs. Bone marrow is one of the body’s main sources of stem cells – cells that can multiply and transform into many different types of specialized cells, from white blood cells to neural cells. The cells produced by the bone marrow form a vital component of the human immune system.

This new procedure of transplanting bone marrow, containing stem cells from the donor, simultaneously with transplantation of the required organ, allows the recipient’s immune system to become a hybrid of their own stem cells and the donor stem cells. The result is that, over time, their body comes to recognize the transplanted organ as a genetic match rather than a foreign object. Once this ‘immune education’ happens, the body stops trying to reject the transplanted organ and the recipient may be able to dramatically reduce their regimen of immunosuppressant drugs, or even go off them entirely.

This is only one of several new techniques being developed to prevent organ rejection, but it is a very promising one. In cases where this procedure is identified by doctors as a good option, mixed bone marrow and solid organ transplantation has the potential to substantially improve the post-operative standard of living for transplant patients.