Pregnancy presents a similar situation, and fetal microchimerism among parous women is not uncommon. This also includes, supposedly, brain tissue: https://www.science.org/content/article/bearing-sons-can-alt...

I think the relevant transplant is bone marrow, since that produces Red Blood Cells. Here is an article about it:https://www.nytimes.com/2019/12/07/us/dna-bone-marrow-transp...

A founder I worked with had both a bone marrow transplant and a lung transplant. He named his company 3dna to commemorate having three sets of DNA in his body