High proportions of regulatory T cells in PBSC grafts predict improved survival after allogeneic haematopoietic SCT

Abstract

Regulatory T cells (Tregs) modulate immune responses and improve survival in murine transplant models. However, whether the Treg content of allogeneic cell grafts influences the outcome in human haematopoietic stem cell (HSC) transplantation is not well established. In a prospective study of 94 adult allogeneic PBSC transplants (60% unrelated; 85% reduced intensity conditioning), the median Treg (CD3(+)CD4(+)CD25(+)FOXP3(+)CD127(dim/-)) dose transplanted was 4.7 × 10(6)/kg, with Tregs accounting for a median of 2.96% of CD4(+) T cells. Patients transplanted with grafts containing a Treg/CD4(+) T-cell ratio above the median had a 3-year overall survival of 75%, compared with 49% in those receiving grafts with a Treg/CD4(+) T-cell ratio below the median (P=0.02), with a 3-year non-relapse mortality of 13% and 35%, respectively (P=0.02). In multivariate analysis, a high graft Treg/CD4(+) T-cell ratio was an independent predictor of lower non-relapse mortality (hazard ratio (HR), 0.30; P=0.02), improved overall survival (HR, 0.45; P=0.03) and improved sustained neutrophil (HR, 0.52; P=0.002), platelet (HR, 0.51; P<0.001) and lymphocyte (HR, 0.54; P=0.009) recovery. These data support the hypothesis that the proportion of Tregs in allogeneic HSC grafts influences clinical outcome and suggest that Treg therapies could improve allogeneic HSC transplantation.

Figure 1

Flow cytometry for Tregs. PBMCs were stained with anti-CD3 PE-Cy7, -CD4 FITC, -CD8 APC-AF750, -CD25 PE, -FOXP3 APC, -CD127 PerCP-Cy5.5 and analysed on an LSRII Flow Cytometer (BD Biosciences, Oxford, UK). CD3⁺ cells were gated by CD3/FSC/SSC; CD3⁺CD4⁺CD8⁻ cells analysed for FOXP3 and CD25 expression; CD3⁺CD4⁺CD25⁺FOXP3⁺ cells analysed for expression of CD127. FSC, forward scatter; SSC, side scatter; Tregs, regulatory T cells.

Figure 2

Haematopoietic recovery, CMV activation and GvHD. The cumulative incidence of (a) sustained neutrophil recovery (>0.5 × 10⁹/l), (b) sustained platelet recovery (>50 × 10⁹/l), (c) lymphocyte recovery (>1.0 × 10⁹/l), (d) CMV activation (CMV DNA detected by PCR), (e) acute GvHD (II–IV) and (f) chronic GvHD (all grades) according to the proportion of Tregs (Tregs/CD4⁺ T cells) in the graft. Low %Tregs, Tregs/CD4⁺ T cells below the median (dotted line); High %Tregs, Tregs/CD4⁺ T cells above the median (solid line); Tregs, regulatory T cells.

Figure 3

Relapse, NRM and overall survival. The cumulative incidence of (a) relapse and (b) NRM according to the proportion of Tregs (Tregs/CD4⁺ T cells) in the graft. (c and d) Overall survival according to the proportion of Tregs (Tregs/CD4⁺ T cells) in the graft. (c) Low %Tregs, Tregs/CD4⁺ T cells below the median (dotted line); High %Tregs, Tregs/CD4⁺ T cells above the median (solid line). (d) 1st Quartile, Tregs/CD4⁺ T cells <0.022; 2nd quartile, Tregs/CD4⁺ T cells 0.0223–0.0296; 3rd quartile, Tregs/CD4⁺ T cells 0.0297–0.0393; 4th quartile, Tregs/CD4⁺ T cells >0.0394; Tregs, regulatory T cells.