tamei tahor ritual purity - Is a Kohen Allowed to Receive an Organ Donation?

A Kohen is forbidden from becoming Tamei Meis (coming in contact with a dead body) (Vayikra-21)

Aside from being allowed for Pikuach Nefesh reasons (life threatening situation). What other reasons can be found to allow a Kohen to receive an organ donation from a deceased person?

Answer

Quoted from the book Healing in Halacha By Rabbi Micha Cohn (page. 245-247 Mosaica Press 2016)

Rav Moshe Feinstein (Iggros Moshe Yoreh Deah 1:230), wrote on the opinions of a contemporary Rabbi Yitzchok Isaac Leibes, who wrote a Kuntres called Rofe Kol Bassar where he asks this very question.

One of the issues that Rabbi Leibes and Rabbi Feinstein discussed was our question about the permissibility of a Kohen to receive an organ transplant. Rabbi Leibes pointed out that if the size of the tissue being transplanted is more than an olive, it could give off tumah ritual impurity, and a Kohen would be prohibited from coming in contact with it even in today's times. Rabbi Leibes offered a number of possible arguments to permit a Kohen to accept a transplant, such as relying on less mainstream opinions that maintain that there is not a Torah prohibition for a Kohen to defile himself in contemporary times when he is already ritually impure, as well as the opinion of the Maharashdam that questions the reliability of a Kohen's tradition on his lineage. Rabbi Feinstein did not view these reasons as being substantial, and offered a perspective of his own

Firstly, Rabbi Feinstein pointed out that if the tissue will be put inside the body, there is a concept of tumah balu'ah that ritual impurity is not transferred from inside the body. The commentary of Rabbeinu Shimshon explains that since it is inside the body, it loses its own significance and is considered a part of the body. Based on this idea, if the tissue is transplanted Based on will beneath the skin, the patient not become tamei since it is not in contact with external part of the the recipient's body. This would be a significant argument to permit a Kohen to receive a transplant since most transplanted organs ar visible externally.

Furthermore, the Rambam writes that although human skin from a deceased person is ritually impure, if it is chemically treated it lose its tumah. The reason seems to be because when an item takes on a new form, it loses its previous status. Based on this concept, Rabbi Feinstein understands that if tissue from the deceased takes on a new role, like being used in a transplant, it removes the tumah status from it. As such, a Kohen would be allowed to a accept a transplant (given certain provisions) even if it is not beneath the skin, the very fact that it is now part of a living person gives it a new status and removes the tumah.