MONTREAL (FRONTLINE MEDICAL NEWS) – A combination of placenta-derived stem cells and umbilical cord blood was associated with early engraftment and high degrees of cord blood donor chimerism in the treatment of children with both malignant and nonmalignant hematologic conditions requiring stem cell transplantation, updated results of a pilot study show.

Among 16 children treated with the combination, the probability of neutrophil engraftment was 87.5%, and all patients who had neutrophil engraftment went on to have platelet engraftment. The probability of 12-month overall survival was 81.2%, reported Allyson Flower, MD , from Boston Children’s Health Physicians in Hawthorne, N.Y. “The probability of grade II-IV acute graft vs. host disease was 12.5%, compared with 32.5% seen with unrelated cord blood in our group’s previous studies. Cellular immune reconstitution was robust,” she said at the annual meeting of the American Society of Pediatric Hematology/Oncology.

Augmenting cord blood

Although unrelated donor cord blood transplantation expands the donor pool, is rapidly available, and is associated with decreases in both severe acute graft vs. host disease (GVHD) and chronic GVHD, compared with other stem cell sources, the technique is hampered by limited cell doses, prolonged immune reconstitution time, delays in hematopoietic recovery, and a higher incidence of graft failure.

Early studies of myeloablative conditioning followed by unrelated umbilical or placental blood transplantation showed a median of 22-24 days to neutrophil engraftment ( Blood 1996 88:795-802 ; N Engl J Med. 1996;335:157-66 ), Dr. Flower noted.

More recently, a multivariate analysis of patients who underwent reduced-intensity conditioning followed by hematopoietic stem cell transplant with unrelated cord blood showed that graft failure was an independent risk factor for worse overall survival ( Biol Blood Marrow Transplant. 2013 Apr;19:4;552-61 ).

Multiple groups have shown that adding human placenta–derived stem cells (HPDSC) to cord blood transplantation can facilitate more rapid hematopoietic engraftment by increasing the number of stem cells, increasing the proportion of hematopoietic progenitor cells, and providing additional, immature CD34+/CD45– progenitor cells.

In a single-arm, nonrandomized study, the investigators enrolled 16 patients ranging in age from 0.3 to 15.7 years with inborn errors of metabolism, marrow failure syndromes, severe immunodeficiency states, or hematologic malignancies.

Malignant conditions included B-cell precursor acute lymphoblastic leukemia (B-ALL; four patients), acute myeloid leukemia (AML; two), and T-cell ALL (one) in first complete remission, and T-cell lymphoblastic lymphoma following induction failure (one). Nonmalignant conditions included adrenoleukodystrophy (two patients), amegakaryotic thrombocytopenia (one), severe combined immunodeficiency (SCID; two), dyskeratosis congenita (one), chronic granulomatous disease (one), and severe congenital neutropenia (one).

The patients first underwent either myeloablative or reduced-intensity conditioning, followed 10 days later by infusion of unrelated cord blood and HPDSCs. Prior to HPDSC infusion, patients were medicated with diphenhydramine and hydrocortisone to prevent or reduce potential sensitivity reactions. HPDSCs were infused no sooner than 4 hours after the end of the cord blood infusion.

Patients received GVHD prophylaxis with either tacrolimus or cyclosporine, plus mycophenolate mofetil.

The combination appeared to be safe, with no cases of grade 3 or 4 toxicity secondary to HPDSC infusion.

The probability of neutrophil engraftment was 87.5%, with engraftment occurring at a median of 23 days (range 13-53). As noted before, all patients who had neutrophil engraftment had platelet engraftment, which was achieved at a median of 47 days (range, 20-98). In the group’s previous studies, median time to platelet engraftment was 53 days for patients who had undergone reduced-intensity conditioning, and 118 days for patients who had undergone myeloablation.

The probability of grade 2-4 acute GVHD within 100 days was 12.5%, and there were no cases of chronic GVHD.

Respective percentages of cord blood donor chimerism at days 30, 60, 100, and 180 were 88%, 98%, 99%, and 99%.

Immune reconstitution was strong, with normalization of mean CD3+, CD19+, and CD56+ cells occurring by day 100, CD8+ cells by day 180, and CD4+ cells by day 270.

There were three patient deaths: one from adenoviremia in a patient with B-ALL and CNS relapse, who had neutrophil engraftment at day 21; one in a patient with SCID, from adenoviremia and multiple system organ failure, who did not have engraftment before death; and one in a patient with severe congenital neutrophilia, who also did not have neutrophil engraftment.

None of the eight patients with malignant disease have experienced relapse to date, Dr. Flower noted.

The study was funded by a grant from Celgene Cellular Therapeutics. Dr. Flower reported having no conflicts of interest.


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