[...] Years later, "he is completely off all medication and shows no psychiatric symptoms," Dr. Miyaoka told me in an email. Somehow the transplant cured the man's schizophrenia.
A bone-marrow transplant essentially reboots the immune system. Chemotherapy kills off your old white blood cells, and new ones sprout from the donor's transplanted blood stem cells. It's unwise to extrapolate too much from a single case study, and it's possible it was the drugs the man took as part of the transplant procedure that helped him. But his recovery suggests that his immune system was somehow driving his psychiatric symptoms.
At first glance, the idea seems bizarre — what does the immune system have to do with the brain? — but it jibes with a growing body of literature suggesting that the immune system is involved in psychiatric disorders from depression to bipolar disorder.
He Got Schizophrenia. He Got Cancer. And Then He Got Cured.
(Score: 1, Interesting) by Anonymous Coward on Tuesday October 02 2018, @09:24AM
It's also known that cells from babies can end up in their mother's brains: https://www.scientificamerican.com/article/scientists-discover-childrens-cells-living-in-mothers-brain/ [scientificamerican.com]
So I wouldn't be surprised that in some cases stem cells from a transplanted organ could end up in the recipient's brain and change stuff.
See also: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3518667/ [nih.gov]
On a vaguely related note: https://www.livescience.com/63596-organ-donation-transmitted-breast-cancer.html [livescience.com]