This article is from the the official alt.spleen FAQ, by Andrew Stellman with numerous contributions by others.
Andrew says: NOTE: PLEASE DO NOT SEND ANY MAIL TO ME REQUESTING MEDICAL ADVICE! I AM NOT A DOCTOR, AND WILL NOT GIVE YOU ANY USEFUL INFORMATION.
Again, brain specialist Elijah the Bearded has this to say:
"Having an SO without a spleen means you can clone your own spleen in the cavity from the other's splenectomy. This is a kinky perversion popular with graduates from Townshend Harris High School (in NYC). The idea apparent extends from a desire to have complete spleen compatability. With this lovers can exchange spleens as loving momentos during times of separation.
It is of course possible to exchange spleens without having this full compatibilty, but then there is an adjustment period both parties must go through until each become acquainted with the new organ. This is preferred in some S&M relationships.
Even if spleens will not be exchanged while the lovers are apart, some still like the idea of a loved one living off part of themselves, as happens with the spleen cloning."
He notes, however, that research in this area remains to be done, specifically liver-transplant style versus spleen culturing.