What are the different types of bone marrow transplants, and how is a donor selected?

What are the different types of bone marrow transplants and how is a donor selected?

Three major flavors of transplants. There are what we call autologous transplants. Now, these are transplants where we give patients their own stem cells back. This is something that we use for some high risk solid tumors and some lymphomas that we don't use for AML, with one rare exception called APML.

There's the syngenetic transplant where somebody with an identical twin gets a transplant from their identical twin. This is not something we routinely do, first off, because identical twins are rare and second off, identical twins will not give that GvL because their immune system is too, like, between the donor and the recipient from a transplant like that. So it's very rare that we would do that type of transplant and very unique situations that have nothing to do with cancer.

The third type of transplants, an allogeneic transplant where somebody gets cells from another person that's not an identical twin. And this allows for that immune system to be able to help identify and fight the cancer. When we do these transplants from allogeneic donors, which is what we always use for AML, with that one exemption that I spoke about earlier, we have different options for grafts that we can use.

We can use bone marrow stem cells. We can use peripheral blood stem cells, or we can use umbilical cord blood units as a source of stem cells. And they all have their own pros and cons. Generally in pediatrics, if we're using a standard what we call unmanipulated, stem cell product, we prefer bone marrow. It is a bit more invasive to the donor to harvest bone marrow than it is to harvest peripheral blood stem cells, but we know that it does have a lower risk for some of the later immune mediated complications of transplant.

And we will use peripheral blood stem cells if we we're doing manipulations of the graph, things like doing what we call an alpha beta T-cell B-cell depleted graft, which we will sometimes do with a half identical donor or like a parent or a half match sibling. We'll also sometimes do it with slightly mismatched, unrelated donors. But there's also other ways of doing these types of transplants, where we also use different medicines after transplant to make them safe.

And then cord blood units we will use for patients in some centers where they don't have a fully matched donor. And there are some emerging, medical science that's showing that perhaps with cord blood units for very high risk myeloid diseases, they may have a different form of GvL that's more robust than if we use a fully matched donor that may lower our risk for relapse. So some centers are now preferentially using cord blood transplants.

The problems with these cord blood units is, it's roughly 10% of the amount of cells. And we would give if we were to give a peripheral blood stem cell transplant or a bone marrow transplant. And the immune system that comes with it is very naive. So that has some additional risk for slower recovery and immune reconstitution. But despite that, we have seen that relapse risks may be lower with this. And this is something that we're doing ongoing future studies to confirm these findings that we're seeing from single centers.