system
Given the following post, respond as if you're commenting on Reddit:
human
Would it be possible for two people to grow together if they both were to cut off a hand/finger and then hold the wounds together?

Assuming blood types and so on are identical.
gpt
Ignoring practical issues like being able to brace the wounds together for the weeks it'd take to heal, you would have to go beyond just matching blood type--the two people would need matching HLA haplotypes or else each person's immune system would try to reject the other person's tissues. (There may be ways around this, for example if each person were put on immunosuppressants.) Perhaps it could happen with identical twins, whose HLAs would be perfect matches.