Superior GVHD-free, relapse-free survival for G-BM to G-PBSC grafts is associated with higher MDSCs content in allografting for patients with acute leukemia

Abstract

Background: Granulocyte colony-stimulating factor (G-CSF)-mobilized peripheral blood stem cells (G-PBSC) has largely replaced unstimulated bone marrow (un-BM) for allografting because of accelerated engraftment, but with a higher morbidity and mortality of graft-versus-host-disease (GVHD). Recent studies suggested that G-CSF-primed BM (G-BM) had similar engraftment but lower morbidity and mortality of GVHD comparing to G-PBSC. A prospective, randomized, multicenter study was conducted to compare G-BM with G-PBSC as the grafts in allogeneic hematopoietic stem cell transplantation (allo-HSCT) for acute leukemia in first complete remission (CR1).

Methods: Totally 101 adult leukemia in CR1 undergoing HLA-identical sibling transplants were randomized into G-BM or G-PBSC group. The primary study endpoint was GVHD-free/relapse-free survival (GRFS).

Results: Both the engraftment of neutrophil and platelet were 2 days later in G-BM than in G-PBSC group (P = 0.412, P = 0.39). G-BM group showed significantly lower II-IV acute GVHD (aGVHD) and similar III-IV aGVHD compared with G-PBSC group (12.2% vs 28.8% for II-IV, P = 0.048; 4.1% vs 9.6% for III-IV aGVHD, P = 0.267, respectively). The overall cumulative incidence of chronic GVHD (cGVHD) at 3 years were 22.3% ± 6.3% and 44.8% ± 7.6% (P = 0.026), respectively, and extensive cGHVD were 4.5% ± 3.1% and 15% ± 5.3% (P = 0.08), respectively, in G-BM and G-PBSC groups. Two groups had similar 3-year relapse, transplant-related mortality (TRM), overall survival (OS), and disease-free survival (DFS) (all P > 0.05). G-BM group showed significantly higher probability of GRFS than G-PBSC group (73.5% ± 6.3% vs 55.8% ± 6.9% at 1 year, P = 0.049; 69.0% ± 6.7% vs 49.7% ± 7.0% at 2 and 3 years, P = 0.03, respectively). Graft content analysis revealed statistically higher frequency of myeloid-derived suppressor cells (MDSCs) in the G-BM than in G-PBSC grafts (P < 0.01), and recipients received statistically higher numbers of MDSCs in G-BM than in G-PBSC group (P = 0.045). Numbers of MDSCs infused to patients were negatively correlated with the severity of aGVHD (P = 0.032, r = -0.214). Multivariate analysis showed that MDSC cell dose below the median (HR = 3.49, P < 0.001), recipient age (HR = 2.02, P = 0.039), and high risk of disease (HR = 2.14, P = 0.018) were independent risk factors for GRFS.

Conclusions: G-BM grafts lead a better GRFS and less GVHD associated with a higher MDSCs content compared with G-PBSC grafts.

Keywords: GVHD-free/relapse-free survival; Graft-versus-host disease; Granulocyte colony-stimulating factor (G-CSF)-primed bone marrow; Myeloid-derived suppressor cells.

Fig. 1

Expression of MDSCs in the BM and PB before and after G-CSF mobilization. a Sequential gating strategy for MDSC identification (Lin^low/negHLA-DR⁻CD11b⁺CD33⁺) using flow cytometry. b Cumulative dot plots showing MDSC frequencies from BM and PB of 20 donors before and after G-CSF mobilization (**P < 0.01, ***P < 0.001)

Fig. 2

Suppressive activity of MDSCs isolated from G-BM and G-PBSC grafts. a The proliferation of purified and CFSE-labled CD3+ T cells in the coculture with isolated MDSCs or not. b The inhibition rate of the proliferation of CD3+ T cells by MDSCs. Isolated MDSCs were added at a 1:1 and 1:5 ratio to purified CD3+ T cells in the presence of anti-CD2/CD3/CD28 biotin beads according to manufacturer instructions (Miltenyi Biotec). Data are representative of three independent experiments (NS P > 0.05, **P < 0.01)

Fig. 3

Box plots showing the absolute number of infused MDSCs with respect to II–IV aGVHD (a) and extensive cGVHD (b). Bars represent the median values, whereas whiskers represent the minimum and maximum. The severity of aGVHD (c) and cGVHD (d) were plotted against the number of infused MDSCs. The grade for severity of cGVHD included limited and extensive cGVHD (1 = limited, 2 = extensive, respectively). r and P values were calculated using Spearman’s correlation test

Fig. 4

Cumulative incidence of 3-year a relapse, b TRM, c OS, d DFS, and e GRFS. The 3-year cumulative incidence of relapse were 18.9% ± 5.8% and 19.6% ± 5.7% in G-BM and G-PBSC groups (P = 0.840), and TRM were 8.2% ± 4.0% and 11.5% ± 4.5%, respectively, in G-BM and G-PBSC groups (P = 0. 549). The 3-year cumulative OS were 75.5% ± 6.7% and 69.6% ± 7.1%, respectively, in the G-BM and G-PBSC group (P = 0.426), and DFS were 72.9% ± 6.4% and 67.1% ± 6.6%, respectively, in the G-BM and G-PBSC groups (P = 0.456). The 1-year cumulative GRFS were 73.5% ± 6.3% vs 55.8% ± 6.9%, respectively, in the G-BM and G-PBSC groups (P = 0.049), and 2- and 3-year cumulative GRFS were 69.0% ± 6.7% vs 49.7% ± 7.0%, respectively, in the G-BM and G-PBSC groups (P = 0.03)