Dysregulated T Cell Response in Bone Marrow Immune Micro-Environment of Patients with Poor Graft Function after Allogeneic Hematopoietic Stem Cell Transplantation

Background:Poor graft function (PGF), a kind of bone marrow (BM) failure syndrome, is a serious complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Nevertheless, the exact mechanisms underlying PGF remain unclear. The BM immune micro-environment is considered to be involved in the regulation of murine hematopoiesis. Dysregulated T cell response was found to suppress proliferation and induce apoptosis of hematopoietic progenitor cells in patients with aplastic anemia. Therefore, we conducted a study to analyze the alteration of T cell subpopulations in BM micro-environment of allotransplant patients.

Aims:To compare the cellular compositions and function of T cells in BM micro-environment between patients with PGF and good graft function (GGF) after allo-HSCT in Peking University Institute of Hematology.

Methods: Using a prospective nested case-control study, the active phenotype and memory phenotype of CD4⁺ T cells and CD8⁺ T cells in BM were analyzed by flow cytometry in 12 patients with PGF, 36 matched patients with GGF after allo-HSCT, and 15 healthy donors (HDs). Furthermore, the cytokine secretion function of CD4⁺ T cells and CD8⁺T cells were evaluated after simulation and the level of eight Th1 and Th2 cytokines in BM plasma were detection by cytometric beads assay.

Results: The demographic and clinical characteristics were similar between allo-HSCT patients with PGF and those with GGF. Although the PGF patients presented a significant lymphopenia, a notable increased percentage of activated CD8⁺ T cells was detected in the BM of PGF patients when compared to that in GGF patients (61.7% versus 35.0%, P=.02). Moreover, the in vitro cytokine stimulated tests demonstrated a significant higher proportion of Tc1 in PGF patients (46.1% versus 20.3% versus 28.4%, P<.005), an elevated percentage of Th1 in PGF compared with HDs (38.5% versus 21.7%, P<.005), a higher percentage of Th2 (4.5% versus 2.1% versus 2.3%, P<.005) and a dramatically decreased percentage of Tc2 in PGF (0.6% versus 2.0% versus 2.0%, P<.0001). Therefore, a significant elevation in the ratio of Th1/Th2 (19.73 versus 7.39 versus 6.91, P<.0001) and Tc1/Tc2 (67.25 versus 10.07 versus 14.57, P<.005) were observed in PGF when compared with those in GGF and HDs. The changes of IFN-gama and IL-4 levels in BM plasma detected by cytometric beads assay were in accordance with the intracellular cytokine results analyzed by flow cytometry.

Summary/Conclusion: Both the in vitro intracellular cytokine testing after stimulation and the BM plasma cytokine detection provides evidence that CD4⁺ and CD8⁺T cells were polarized towards a type-1 cytokine response in patients with PGF, suggesting that the dysfunction of T cell response in BM immune micro-environment may hamper the hematopoietic recovery after allo-HSCT.

Acknowledgement: Supported by the National Natural Science Foundation of China (grant nos. 81370638&81230013), and the Beijing Municipal Science and Technology Program (grant nos. Z141100000214011& Z151100004015164& Z151100001615020).