As early as 2014, the University of Texas MD cancer center in the United States found that the expression of PD-1, PD-L1 and PD-L2 in CD34+ cells of MDS patients was significantly increased, which was related to the risk stratification of disease and the drug resistance mechanism of hypomethylating agent (HMA) (24). The gene discussed is PDCD1LG2; the disease is myelodysplastic syndrome.