RESUMO
BACKGROUND AND AIMS: High-dose chemotherapy (HDC) followed by autologous stem cell transplantation (ASCT) improves the prognosis in pediatric patients with several solid tumors and lymphomas. Little is known about the reconstitution of the immune system after ASCT and the influence of CD34+ cell selection on the reconstitution in pediatric patients. METHODS: Between 1990 and 2001, 94 pediatric patients with solid tumors and lymphomas received autologous CD34+ selected or unmanipulated peripheral stem cells after HDC. CD34+ selection was carried out with magnetic microbeads. The absolute numbers of T cells, B cells and natural killer (NK) cells were measured and compared in both groups at various time points post-transplant. RESULTS: Recovery of T cells was significantly faster in the unmanipulated group at day 30, with no significant difference later on. Reconstitution of B and NK cells was similar in both groups without significant differences at any time. The CD34+-selected group was divided into patients receiving less or more than 5.385 × 106/kg CD34+ cells. Patients in the CD34+ high-dose group displayed significantly faster reconstitutions of neutrophiles and lymphocyte subsets than the CD34+ low-dose group. CONCLUSIONS: Engraftment and reconstitution of leukocytes, B cells and NK cells after transplantation of CD34+ selected stem cells were comparable to that in patients receiving unmanipulated grafts. T-cell recovery was faster in the unmanipulated group only within the first month. However, this delay could be compensated by transplantation of >5.385 × 106 CD34+ cells/kg. Especially for patients receiving immunotherapy after HDC large numbers of immune effector cells such as NK and T cells are necessary to mediate antibody-dependent cellular cytotoxicity. Therefore, in patients receiving autologous CD34+-selected grafts, our data emphasize the need to administer high stem cell counts.
RESUMO
ABSTRACT: Anti-T lymphocyte globulin (ATLG) significantly reduces the risk of engraftment failure in allogeneic hematopoietic stem cell transplant (HSCT) but hampers posttransplant immune reconstitution. We hypothesized that in patients receiving haploidentical CD3/CD19-depleted grafts, these double-edged effects could be better balanced by attaining high ATLG serum concentrations before transplant but as low as possible on the day of transplant. Therefore, we moved the start of ATLG application to day -12 and determined serum concentrations of T-cell-specific ATLG in pediatric patients treated with 3 established dosing regimens (15, 30, or 60 mg/kg). Corresponding mean T-cell-specific ATLG serum concentrations at day 0 were 1.14, 2.99, or 12.10 µg/mL, respectively. Higher ATLG doses correlated with higher peak levels at days -8 and -7 and reduced graft rejection, whereas lower ATLG doses correlated with significantly faster posttransplant recovery of T and natural killer cells. The rate of graft-versus-host disease remained low, independent of ATLG doses. Moreover, in vitro assays showed that ATLG concentrations of 2.0 µg/mL and lower only slightly reduced the activity of natural killer cells, and therefore, the function of such effector cells might be preserved in the grafts. Pharmacokinetic analysis, compatible with linear first-order kinetics, revealed similar half-life values, independent of ATLG doses. Hence, the day on which a desired ATLG serum level is reached can be calculated before HSCT. Our retrospective study demonstrates the relevance of dosing and time of administration of ATLG on engraftment and immune recovery in ex vivo CD3/CD19-depleted haploidentical HSCT.