Objective To investigate the role of the burden of abnormal hematopoietic clone in the development of myelodysplastic syndromes （MDS）. Methods The ratio of the bone marrow cells with abnormal chromosomes to the total counted bone marrow cells was regarded as the index of MDS clone burden. The disease severity related parameters including white blood cell count

hemoglobin

platelet count

lactate dehydrogenase level

bone marrow blast

myeloid differentiation index

micromegakaryocyte

transfusion

interleukin-2

tumor necrosis factor （TNF）

CD4

+

and CD8

+

T cells of MDS patients were assayed

and the correlations between those parameters and MDS clone burden were also analyzed. Results The clone burden of MDS patients was 67.4%±36.2%. MDS clone burden positively correlated with bone marrow blasts （r = 0.483

P

<

0.05）

negatively with hemoglobin level （r=-0.445

P

<

0.05）. The number of blasts

hemoglobin

and erythrocytes in high clone burden （

>

50%） and low clone burden （≤50%） groups were 7.78%±5.51% and 3.45%±3.34%

56.06±14.28 g/L and 76.40±24.44 g/L

（1.82±0.48）×10

12 /L and （2.32±0.66）×10

12 /L

respectively （all P

<

0.05）. CD4

+

T lymphocytes of MDS patients and normal controls were （0.274±0.719）×10

9 /L and （0.455±0.206）×10

9 /L

respectively （P

<

0.05）. CD8

+

T lymphocytes of MDS patients and normal controls were （0.240±0.150）×10

9 /L and （0.305±0.145）×10

9 /L

respectively. The serum level of interleukin-2 of MDS patients （6.29±3.58 ng/mL） was significantly higher than normal control （3.11±1.40 ng/mL

P

<

0.05）. The serum level of TNF of MDS patients and normal control group were 2.42±1.79 ng/mL and 1.68±0.69 ng/mL

respectively. The ratio of CD4 to CD8 was higher in high clone burden MDS patients （1.90±0.52） than that in low clone burden patients （0.97±0.44

P

<

0.05）. Conclusion The quantitive clonal karyotype abnormalities and deficient T cell immunity are important parameters for evaluating MDS severity and predicting its progression.