Outcomes are comparable between half-match and full-match bone marrow transplant recipients

In the first comparison using the same protocol, researchers have shown that haploidentical (half-match) bone marrow stem cell transplant recipients do just as well as matched related (full-match) transplant recipients. If verified, this development could be a major advance for minorities and others with inadequate access to full-match donors, the researchers suggested.

The study was published online September 25, 2015 in Biology of Blood and Marrow Transplantation.

Only 30% of patients have a family member whose cells are a full match, according to the National Marrow Donor Program. Half-match donors are much easier to find among a patient’s relatives, and can be ready to donate within days.

“This is the first study to compare the gold standard to a half-match using an identical protocol,” said the study’s senior author Neal Flomenberg, MD, Chair of the Department of Medical Oncology at Thomas Jefferson University, in Philadelphia, PA.

He explained, “The field has debated whether the differences in outcomes between full and partial matches were caused by the quality of the match or by all the procedures the patient goes through before and after the donor cells are administered. We haven’t had a clear answer.”

To that end, the study researchers gathered 3-year outcomes data from 50 haploidentical donor recipients, who had been transplanted using the Jefferson Two-Step protocol, and compared them with 27 matched related donors who had received the same two-step approach.

Three years after transplantation, approximately 70% of the patients in both groups were still alive and cancer free. Serious cases of acute graft-vs-host disease were comparable in both groups (haploidentical: 6%, matched related: 4%).

In the two-step protocol, donor T-cells and stem cells are given in two separate stages. Cyclophosphamide (CY) is administered after the introduction of T-cells but before stem cells are infused. In preliminary results presented at the 2014 American Society of Bone and Marrow Transplantation meeting, the two-step protocol resulted in engraftment of donor cells 3 to 4 days earlier than with a one-step procedure.

“There are some major advantages to the two-step approach,” said first author Sameh Gaballa, MD, Assistant Professor in the Department of Medical Oncology and a researcher at the Sidney Kimmel Cancer Center at Thomas Jefferson University.

First, he explained, rather than extracting stem cells from the bone marrow, the two-step method uses stem cells harvested from the blood. This is not only easier for the donor, but it gives physicians the ability to control the exact number of T cells and donor stem cells.

“Making sure we have just the right amount of T cells makes a difference,” Dr. Gaballa said. “Too few and you might not control the cancer, resulting in a relapse or rejection of the transplant. Too many and you run the risk of severe graft-versus host disease, which can endanger the patient.”

The results of the study indicate that outcomes from half-matched related donors are similar to fully-matched donors. Thus, “it might be time to reassess whether half-matched related transplants can be considered the best alternative donor source for patients lacking a fully-matched family member donor,” Dr. Gaballa said. “For that, we’ll need more evidence from a randomly controlled prospective trial, rather than studies that look at patient data retrospectively, to help solidify our findings here.”