Stem Cell Transplant Recipients – Rabbit Antibodies Help Leukemia Patients


A recent study performed by researchers at the Virginia Commonwealth University found that the use of rabbit antibodies can improve the survival and relapse outcomes of leukemia and myelodysplasia patients receiving a stem cell transplant from an unrelated donor.

During the study, led by Amir Toor, M.D., hematologist-oncologist in the Bone Marrow Transplant Program and member of the Developmental Therapeutics program at VCU Massey Cancer Center, researchers viewed the outcomes of 48 patients who received a transplant of stem cells from a related donor to the outcomes of 50 patients who alternatively received rabbit anti-thymocyte globulin (ATG) before being given a transplant of stem cells from an unrelated donor.

This study has been published in Bone Marrow Transplantation

The results showed similar outcomes for both groups in terms of relapse, mortality, and development of graft-versus-host disease (GVHD), a common occurrence that can happen when a transplant is inserted and the new material clashes with the recipient’s body.

When the patients were followed up at 35 months, 50% of the ATG group and 63% of the no ATG group were still alive. Generally, unrelated stem cell transplants typically have significantly poorer outcomes.

Toor says:

“Unfortunately, we can’t always find a related (genetically similar) donor for patients in need of stem cell transplantation.”

Thus, being able to provide improved outcomes using stem cell transplants from unrelated donors offers many blood cancer patients the chance of longer survival.

The results of this particular study showed no survival differences between the two groups, regardless of diagnosis or age.

Incidences of GVHD and relapse rates were also seen to be similar. Transplants using unrelated stem cell donors are generally considered high-risk treatments because of previous reports of disease relapse and GVHD. Also noticed were the higher rate of infections in patients who received the highest rate of ATG, but that risk disappeared in patients with a lower level of ATG.

Overall, those receiving ATG were diagnosed with chronic GVHD less often.

Doctors are currently using two types of ATG:

ATG made from rabbit antibodies. It is known by the brand name Thymoglobulin, and is produced and marketed by Genzyme Corporation, a Sanofi company.

ATG made form horse antibodies. It is known by the brand name Atgam, and is produced and marketed by Pfizer Inc.

Both forms of ATG are licensed for the treatment of renal allograft rejection. Traditionally, Atgam is used in the treatment of aplastic anemia. Both medications are used off-label as immunosuppression induction agents before or during a kidney transplant.

ATG works by reducing the number of circulating T-lymphocytes, which remain a crucial component of the immune system..

This study was one of the first to use ATG in a stem cell transplant. Toor goes on to say the outcomes of his study are extremely encouraging. If researchers continue observing the minimum of risk when using unrelated donor stem cell transplants, this therapy may become an excellent option when related stem cells are not available.