Regulatory T cells affect early relapse following high-dose chemotherapy with autologous hematopoietic stem cell transplantation in multiple myeloma patients

Summary

Introduction

Regulatory Т cells (Тregs) play an important role in pathogenesis of multiple myeloma (MM), providing tumor cell avoidance of immune surveillance. The latter, in turn, are able to induce the Treg expansion. However the data on their contents at different stages of disease and their relations to efficiency of the therapy performed are incomplete and controversial. The aim of this study was to investigate dynamics of CD4+FOXP3+ regulatory T cells (Treg) recovery following high-dose chemotherapy (HDCT) with autologous hematopoietic stem cell transplantation (AHSCT), and possible relationship between Tregs and clinical outcomes in multiple myeloma (MM) patients.

Patients and methods

Fifty-nine patients with MM (median age 49 years, range 32-64) underwent AHSCT in 2009-2015. For stem cell mobilization, patients were administered high-dose cyclophosphamide (4 g/m2) or another standard chemotherapy course + G-CSF, melfalan 140-200 mg/m was used as conditioning regimen. The average CD34+ hematopoietic stem cell dose was 5.9 ± 2.7 × 106 /kg (here and below data as М ± SD). The median observation time was 21 month. The counts of circulating CD4+FOXP3+ Tregs have been evaluated using flow cytometry (BD FACSCalibur, CellQuest Software) before HDCT with AHSCT at the day of engraftment, and following 6 and 12 months. The Mann-Whitney U test was used to calculate differences between groups of patients. ROC-analysis with area under the curve calculation was used to evaluate the predictive value. P < 0.05 was considered statistically significant confidence level.

Results

Pre-transplant count of CD4+FOXP3+ Tregs was 4.0±3.0 %. Percentage of Tregs restored rapidly, became higher than initial pre-transplant level (5.5 ± 3.3 %; pU=0.028) at the time of engraftment (~the 14th day following AHSCT) and then subsequently decreased for a year until it lowered to 2.3 ± 1.3 %. CD4+FOXP3+ Tregs at the time of engraftment were increased in patients with relapse of disease during 12 months following AHSCT (n=7) compared to non-relapsed patients (n=29): 7.9 ± 2.6 vs 4.6 ± 2.5 %; pU=0.0066. The prognostic value of CD4+FOXP3+ Treg relative counts at the day of engraftment was assessed for relapse rates at the 1st year post-transplant. Area under the curve (AUC) was 0.835 (95 % CI: 0.678-0.992; р=0.0066). CD4+FOXP3+ Treg relative count > 5.77 % allowed to predict early relapse (85.7 % sensitivity, 75.7 % specificity, with 3.55 likelihood ratio).

Conclusions

Relative counts of Tregs recovered rapidly following HDCT with AHSCT (at the day of engraftment), became higher than pre-transplant level and then subsequently decreased within a year to healthy donor values. The excess of Tregs at the time of engraftment is associated with early relapse.

Keywords

Multiple myeloma, autologous hematopoietic stem cell transplantation, regulatory t cells, early relapse