Treatment of Secondary Post-Transplant Engraftment Failure with Donor CD34+ Enriched, T-Cell Depleted Peripheral Blood Stem Cells Isolated By the Clinimacs® System

Introduction: Secondary engraftment failure after hematopoietic stem cell transplant (HSCT) is characterized by pancytopenia and 1-year mortality reported to reach as high as 75% (1) secondary to infectious and bleeding complications. It is frequently associated with treatment of CMV reactivation. Reinfusion of a second graft from the original donor is the preferred treatment but carries the risk of graft versus host disease (GVHD) given high T lymphocyte graft content. The CliniMACS® CD34 reagent system permits in vitro selection and enrichment of CD34+ cells from heterogeneous hematologic cell populations and is used for T cell depletion of HSCT. We report the results of a pilot study of infusion of CD34+ selected stem cell boost for treatment of post-transplant secondary engraftment failure.

Methods: Eligible patients were 0 - 80 years of age, treated with a prior HSCT and diagnosed with secondary engraftment failure (defined as a decrease in donor chimerism by ≥ 50%) or incomplete graft function (anemia ≤8g/dL or transfusion dependent; neutropenia ≤1000/mcl or requiring growth factor support; thrombocytopenia ≤20,000/mcl or transfusion dependent). Subjects were excluded if the original donor was not available or if they had reversible causes for engraftment failure, including active viral infections, continued use of myelosuppressive medications or uncontrolled acute or chronic GVHD. Once collected, peripheral blood stem cell (PBSC) donor grafts were processed using the CliniMACS® System and CD34 reagent to enrich CD34+ cell content and decrease CD3+ cell content. After enrichment, the product was considered acceptable for infusion if CD34+ cell content was ≥ 1x10⁶ cells/kg and CD3+ content was ≤ 5x10⁴ cells/kg. The CD34+ enriched stem cell boost was infused without a preceding conditioning regimen.

Results: 10 patients were enrolled; median age was 53.5 years (range 7 - 69), 6 patients were male. Diagnoses included: aplastic anemia (n=1), acute lymphoblastic leukemia (n=1), acute myeloid leukemia (n=3), myelodysplastic syndrome (n=2) and non-Hodgkin lymphoma (n=3). The original graft source was PBSC from a matched related donor (MRD) in 3 subjects, matched unrelated donor in 6 cases, and one haploidentical related donor. GVHD prophylaxis included tacrolimus and methotrexate (n=8), tacrolimus, methotrexate and mycophenolate (n=1); one subject did not receive GVHD prophylaxis as part of a T cell depleted transplant. Eight patients had resolved or controlled GVHD. Median donor chimerism before engraftment failure was 98% (range 96 - 100).

The cause of engraftment failure was known in 5 cases (irreversible medication toxicity [n=3], recurrence of aplastic anemia [n=1], viral infection [n=1]). Median time to diagnosis of secondary engraftment failure was 4 months (range 2-21). Median donor chimerism before boost was 2.5% (range 0-91%). Neutrophil engraftment failure was present in 6 patients; red blood cell (RBC) and platelet engraftment failure was present in 8 patients. Median time from transplant to boost infusion was 7.5 months (range 2-27)Median infused CD34+ cell dose was 3.15 x 10⁶ CD34+ cells/kg (range1.67-10.9); median CD3+ cell dose was 1.9 x 10³ CD3+ cells/kg (range 1.43 - 26.2). There were no infusion reactions and all patients tolerated the procedure without adverse events. Thirty days after boost infusion, 7 subjects (70%) had resolution of their cytopenias, 1 patient had platelet engraftment but remained dependent on RBC transfusions and 2 did not respond. We observed 2 cases of recurrence of GVHD; in both cases, the recurrence was at a lower grade than before the boost infusion. One responsive patient presented subsequent engraftment failure after boost (refractory aplastic anemia). Five patients remain alive at a median of 37 months after CD34+ enriched stem cell boost, with 1 - year estimated survival of 56%.

Conclusions: Secondary engraftment failure can be safely and effectively treated with infusion of a CD34-enriched boost using the CliniMACS® System.

Davies SM, Weisdorf DJ, Haake RJ, et al. Second infusion of bone marrow for treatment of graft failure after allogeneic bone marrow transplantation. Bone Marrow Transplant 1994;14:73-7.