Red blood cells are crucial to carry oxygen from the lungs to cells and to take away carbon dioxide. They are formed in the red bone marrow, but new research implies that this might not be the full picture. New evidence suggests that a small fraction of blood cells can form in the gut too.

The research, published in the journal Cell Stem Cell, comes from the discovery that patients who received an intestinal transplant also received stem cells that can mature into full blood cells. This leads to episodes of blood chimerism in the recipient, where different blood types co-exist for a while. This surprising fact could have an important benefit. 

Intestinal transplantation is the only long-term option for patients whose intestines have failed, such as people who have Crohn’s disease. Unfortunately, this type of transplant has high rejection rates and life-threatening complications due to the immunosuppression medications required. Those drugs help to stop the immune system of the transplant receiver from destroying the transplanted organ.

But the presence of these hematopoietic stem cells seems to change things a bit. The matured cells from the intestine seem to be tolerant of the recipient’s own tissue. And the immune system of the recipient seems to be educated by the donor cells in being tolerant of the transplanted organ.

"We are clearly showing that there's immunological cross-talk between the two sets of blood cells that protects the transplant from the patient's immune system and protects the patient from the transplant," senior author Dr Megan Sykes, director of the Columbia Center for Translational Immunology, said in a statement. "It's possible that patients with a high level of donor cells may not require as much immunosuppression as they are currently getting and reducing immunosuppression could improve outcomes."

The study analyzed 21 patients who received an intestinal transplant. If these findings are confirmed, the use of hematopoietic stem cells could be a new weapon in our medical arsenal. This approach could improve the chances of many transplant receivers.

"That could improve the lives of transplant patients dramatically," Sykes explained. "Our ultimate goal is to get immune tolerance, which would allow us to remove immunosuppression altogether and have the graft treated as self by the patient. That's really the Holy Grail."

The team plans to investigate if boosting hematopoietic stem cells during intestinal transplants leads to more immune tolerance.