Umbilical Cord Blood Transplantation May Be Option for Adults with Hematologic Malignancies

DURHAM, North Carolina—Umbilical cord blood transplantation may be a viable option for adult patients with hematologic malignancies who do not have suitably matched donors as a source of stem cells, according to reports presented at the ASH meeting.

While allogeneic hematopoietic progenitor cell transplantation is curative for a number of hematologic malignancies, bone marrow failure syndromes, and inherited disorders, the application is hampered by the lack of HLA-matched donors. Stem cells from related and unrelated umbilical cord blood have been shown to successfully rescue patients after myeloablative therapy, but this procedure is generally limited to pediatric patients due to concerns that numbers of stem cells will be insufficient for engraftment in adult patients.

Successful Engraftment

Gwynn Long, MD, of Duke University Medical Center, reported on a study there involving 38 adults treated with myeloablative therapy followed by infusion of hematopoietic stem cells from unrelated umbilical cord blood. The patients’ median age was 30 (ranging from 18 to 58). Two patients had genetic disorders and the rest had hematologic malignancies. This was a high-risk group, as all patients with leukemia were beyond first remission or first chronic phase, except one patient with chronic myelogenous leukemia who had failed interferon. Four patients had relapsed after autologous transplant and two after allogeneic transplants.

Survival was related to number of cells cryopreserved and number of cells infused. The median nucleated cell dose was 1.37 x 10⁷/kg and the median CD34+ cell dose was 2.17 x 10⁵/kg. Analyses of 171 pediatric and adult patients at Duke had shown that cell dose is the strongest single predictor of engraftment, nonrelapse mortality, and long-term event-free survival.

The preparative regimen for most patients was total body irradiation, melphalan (Alkeran), and antithymocyte globulin. HLA matching was 3/6 in 3 patients, 4/6 in 27 patients, 5/6 in 6 patients, and 6/6 in 3 patients. All patients received graft-versus-host disease (GVHD) prophylaxis and G-CSF post-transplant until neutrophil recovery.

Dr. Long said that patients were selected for the protocol if they did not have a 6/6 unrelated donor match or there was “no time to look for one,” noting that their policy is to go directly to cord blood if there is no 6/6 unrelated donor match.

Neutrophil engraftment occurred in a median of 24 days, and median number of days to platelet transfusion independence was 58. The median survival was 175 days (range 19 to 1,409). Acute GVHD occurred in 13 patients out of 28 who engrafted, at a median onset of 30 days. Three patients died of acute GVHD and five patients now have chronic GVHD. The most common cause of death was bacterial infection, which occurred in eight patients. Overall survival at 1 year was about 40% and is 28% at 4 years.

The findings suggest that unrelated umbilical cord blood can be successfully engrafted in adult patients. This approach can result in a lower than expected incidence of acute GVHD compared to similarly HLA-matched unrelated donor marrow transplants but is associated with significant risk of bacterial infection. Relapse rate is no higher than expected for patients with advanced hematologic malignancies. ”The use of these transplants should be explored in patients with earlier stage disease in whom matched related or unrelated donors are not available or identified in a timely fashion,” Dr. Long proposed.

Immune System Role

The report was highlighted in a poster session moderated by John E. Wagner, MD, of the University of Minnesota, who suggested that the positive outcomes from cord blood transplantation may be somehow related to cord blood’s immune profile. With this approach, HLA matching becomes less crucial, he pointed out.

“We already know that there is a difference in the immune profile of cord blood lymphocytes. They don’t secrete IL-4, 5, and 10 to any significant amount. They do produce IL-2 but the numbers of T cells are small, which may partly account for the decreased alloreactive response. There may also be other factors less well described, for example, a suppressor cell activity. This could be playing a major role in reducing the risk of graft-versus-host disease,” he added.

A comparison of sibling donor cord blood to HLA-matched sibling donor bone marrow has found the risk of GVHD to be lower, indeed, in cord blood transplantation. This suggests there may be something biologically different about the neonatal immune system versus older donors, he said.

Ex Vivo Cell Expansion

Since cell dose is important to outcome, technology that will increase cell numbers should facilitate transplant efforts, especially in adults. In a separate report, Duke investigators from the Pediatric Bone Marrow Program described their automated, ex vivo expansion method, a continuous profusion culture device, known as the Replicell System.

Joanne Kurtzberg, MD, reiterated that cell dose greater than 2 x 10⁷ nucleated cells or 1 x 10⁵ CD34 cells/kg body weight is associated with superior outcome. Patients over 60 kg often receive insufficient numbers for engraftment.

The question of this phase I trial of 28 high-risk patients with malignant and nonmalignant diseases was whether umbilical cord blood cells could be expanded in the clinical transplant setting and safely infused. The patients were cytoreduced with one of three regimens. GVHD prophylaxis was given, plus G-CSF and additional supportive care. Patients were given 1.5-2 x 10⁷ nucleated cells/kg as a conventional unmanipulated graft, and 12 days later were given the expanded cells.

Expansion occurred in all cases, but the magnitude varied. The median fold increase in total nucleated cells was 2.4 and median CFU-GM increase was 70 fold. CD34 lineage negative cells did not expand, Dr. Kurtzberg reported.

The method was well tolerated. Compared to historical controls receiving similar doses of unmanipulated cells, recipients had superior 100-day survival, but time to myeloid, erythroid, or platelet engraftment was not altered. Randomized studies are underway to determine whether the improvement in survival was due to the augmentation of cell dose by infusion of the expanded cells or to another factor.

Ideally, cell expansion should occur prior to transplantation to allow for administration of expanded and unmanipulated cells on the same day. “Optimization of expansion conditions should allow for this in the future,” Dr. Kurtzberg said.