Genetic compatibility: family and unrelated donors

Who can donate bone marrow? Where do we get the stem cells that will save the patient’s life? The answers to these questions have decades of history, constant processes of trial and error to understand a complex biology, which at its center comprises our immune system. This gives us a precise identity and allows us to protect ourselves from others, mainly germs. The complexity and variability of this system has been the highest wall that the doctors and scientists who developed the transplant had to overcome.
The genes that decide the match in the transplant are called HLA. Like any gene, we all have two copies, inherited from our parents, in half and half, which can be combined in four different ways. Two brothers are 100% compatible when they inherit the same halves, like two drops of water. That is the perfect donor, no matter if they are of different gender, blood group or age, the stem cells of one will be felt at home within the other.
However, the chances of two brothers or sisters being compatible are one in four. And not by having three brothers a person claims to have a 100% compatible donor. This possibility depends on the size of families in a specific population. In Chile, 1 in 5 people has that perfect donor, for the other four you have to look for a person outside the family. That’s where the hard part begins.
HLA genes are among the most diverse in the human organism, where hundreds of them come together in thousands of combinations. Some genes are more prevalent than others and so the chance of two unrelated people being compatible can range from 1 in 40,000 to one in a million. A needle in a haystack. Even within a family, that possibility is very low because while everyone shares halves, the uns shared ones are infinitely variable.
The first transplants with sister donors were made in the 60s, when the effectiveness of the procedure and the need for an almost identical match between donor and patient were confirmed. Every time an attempt was made to get out of that genetic equality, the donor’s immune system attacked the patient mercilessly, transforming the bone marrow transplant into a nightmare: the graft-versus-host reaction, a reverse rejection with serious consequences for the patient’s health, to the point of attempting against his life.
Until the 70s the transplant did not reach beyond the brother or sister. I lived the years when, for a child with cancer in search of a transplant, the door to life was opened or closed on a piece of paper where the results of his brothers were. At that time, the medical community, which saw how this procedure was a salvation, considered looking for strength in numbers as the only solution.
Thus began the first timid efforts, often led by patients, mothers and fathers of sick children, to seek in the generosity of their community people who were willing to donate stem cells for a patient who, having no family relationship, had the right combination of compatibility genes.
Today we have many organizations like DKMS that are in this precise task. Together we add up to about 30 million people registered as potential donors around the world, which for me is the most amazing miracle in contemporary medicine, something that makes us believe in the innate goodness of people. With this panorama we can begin the search for the ideal donor.
The content expressed in this opinion column is the sole responsibility of its author, and does not necessarily reflect the editorial line or position of El Mostrador.

Original source in Spanish

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