HR-02. Influence of various types of immunosuppressive therapy on the reconstitution of lymphocyte subpopulations in the long term after allogeneic hematopoietic stem cell transplantation

Summary

Introduction

Distinct regimens of immunosuppressive therapy (IST) have differential effects upon the immune cell reconstitution. Slow and/or incomplete recovery of lymphocyte subpopulations is one of the key obstacles to the successful outcome of allogeneic hematopoietic stem cell transplantation (allo-HSCT). The aim of present study was to evaluate the results of long-term (up to one year) monitoring of lymphocyte subpopulations in patients with various IST-regimens.

Materials and methods

The study included 105 patients who underwent allo-HSCT at the National Research Center for Hematology from 2017 to 2019. Three types of IST were applied: (1) classical IST (cIST), including anti-thymocyte immunoglobulin; (2) IST using combinations of post-transplant cyclophosphamide (PT-CP) and other drugs; (3) αβ-T-cell depletion (TCD). The cIST group included 66 HSCT patients with HLA-matched related and unrelated donors. PT-CP was used in 27 patients with unrelated mismatched donor. TCD was performed in 12 patients with HLA-haploidentical donors. The analysis of lymphocyte subpopulations in peripheral blood was carried out at 3, 6, 9 and 12 months after allo-HSCT. The absolute number of T-helpers (CD3⁺CD4⁺), T-cytotoxic lymphocytes – TCLs (CD3⁺CD8⁺), natural killers – NKs (CD3^-CD16⁺CD56⁺) and B-cells (CD3^-CD19⁺) was determined using the Multitest 6-Color TBNK (BD, USA), with a FACSCanto II flow cytometer (BD, USA). Previous data published by S. V. Khaidukov (2015) were used as reference intervals. Statistical analysis was performed using GraphPad Prism 6 software. Comparison of data was performed by ANOVA with Tukey’s correction for normally distributed values or using Kruskall-Wallis test with Dunn’s correction for data with abnormal distribution.

Results

The number of T-helpers showed gradual increase in all IST-groups, being significantly increased in the cIST group by +9 months (p=0.001) and in PT-CP by +12 months posttransplant (p=0.001), as compared to +3 months after allo-HSCT. In most patients, however, it remained below the reference interval. The number of TCLs in TCD-group was lower at all points compared with cIST and PT-CP. In the cIST and PT-CP groups, the TCL number increased by +9 months (p=0.0001, and p=0.01, respectively), and by +12 months (p=0.0002, and p=0.0002). T-helpers and TCL did not recover in the majority of patients with TCD even at +12 months after allo-HSCT (Fig. 1). The number of NKs in TCD-group was already within the normal interval in the early stages. In the cIST group, the number of NKs reached the reference interval only by +9 months, being significantly increased by +12 months (p=0.006). At +6 months in the cIST group, the NKs number was lower than that in the PT-CP group (p=0.044), as seen from Fig. 1. The number of B-cells at +9 and +12 months was higher, compared to +3 months in cIST (p=0.002 and p <0.0001) and PT-CP groups (p=0.002 and p <0.0001 ). At +12 months, the number of B-cells in PT-CP was higher than in that in cIST (p=0.014) (Fig. 1).

Conclusions

The IST-regimens have a significant effect upon the reconstitution of lymphocyte subpopulations, even at longer terms after allo-HSCT. T-helpers did not recover by +12 months. In the patients transplanted with T-cell depletion, TCL was less than that in cIST and PT-CP. In PT-CP, there are more B-cells and NK than that in cIST.

Keywords

Immunosuppressive therapy, posttransplant cyclophosphamide, αβ-T-cell depletion, lymphocyte subpopulations, flow cytometry.