In vitro deprivation of CD8⁺CD57⁺T cells promotes the malignant growth of bone marrow colony cells in patients with lower-risk myelodysplastic syndrome

Objective

CD8⁺T lymphocytes have inhibitory effects on the proliferation of malignant clones in myelodysplastic syndrome (MDS). The exact CD8⁺T subset involved in the regulation of MDS and the target clones of CD8⁺T lymphocytes has not been studied. We investigated the effect of activated CD8⁺T (CD8⁺CD57⁺) lymphocytes on colony formation (in particular, malignant colony formation) during MDS in vitro.

Materials and Methods

Bone marrow mononuclear cells (BMNCs) from a total of 59 MDS patients were subjected to magnetic-activated cell sorting to separate CD8⁺CD57⁺T lymphocytes. BMNCs were cultured without CD8⁺CD57⁺T cells or cocultured with a 1:4 ratio of CD8⁺CD57⁺T cells to study the association between stem/progenitor cell colony formation and the existence of activated CD8⁺ T cells, as well as the polarization of T cells towards Tc1. In addition, the fluorescence in situ hybridization method was used to detect bone marrow cells carrying abnormal karyotypes, and the proportion of abnormal cells among BMNCs was calculated before and after T-cell deprivation culture in vitro. Crossing cultures between MDS patients and normal volunteer was performed. The impact of effector CD8⁺T cells on the malignant growth of BMNCs was closely examined.

Results

After deprivation of CD8⁺CD57⁺T cells, BMNCs from 33 MDS patients formed colonies in the culture media. The average number cells in the granulocyte and monocyte colony-forming units (CFU-GM) was 40.3/4 × 10⁵, and the average number of cells in the erythroid colony-forming unit (CFU) was 10.4/4 × 10⁵. These totals were significantly lower than those in the normal control group after deprivation of CD8⁺CD57⁺T cells (CFU-GM 83.4/4 × 10⁵ cells, erythroid CFU 32.8/4 × 10⁵ cells; p < 0.001). After add-back of CD8⁺CD57⁺ T cells (four times), none of the BMNCs cultures from any of the 59 MDS patients formed colonies in vitro. Additionally, in 33 MDS patients whose BMNCs formed colonies after T-cell deprivation, the bone marrow Tc1/Tc2 ratio was positively correlated with CFU-GM count (r = 0.443, p < 0.05). Crossing cultures indicated that CD8⁺CD57⁺ T cells from MDS patients cocultured with BMNC from normal donor did not show inhibition to colony-forming. In 15 MDS patients with abnormal karyotypes, deprivation of CD8⁺CD57⁺T cells significantly increased the proportion of abnormal cells from 43.8% to 56.3% in BMNC culture (p < 0.001).

Conclusion

Effector CD8⁺T lymphocytes inhibit bone marrow hematopoiesis in MDS patients; target cells were primarily cells with abnormal karyotypes.