system
Given the following post, respond as if you're commenting on Reddit:
human
If a twin donated an organ to his/her sibling, would the sibling have to take immunosuppressant drugs?

I know that twin's DNA differs but I am wondering if it would differ enough for the body to recognize a transplanted organ as foreign. Would this also be a problem if an organ were to be grown in a lab using cells from the recipient?
gpt
The more closely related the donor and recipient are, the less rejection.  The first successful transplant was done with twins, and there was no observed rejection.  The organ will express the same antigens because they have the same genes.  They need to be identical twins, because fraternal twins do have some differences.

Identical twins have the same genotype, with small differences.  They usually differ in the number of copies of individual gene segments.  But they are much more similar than fraternal twins.