CD4 and cytomegalovirus infection: In order to understand the reconstitution and function of CMV immunity after allo-HSCT and obtain reliable predictive factors for CMV infection, multi-parameter cytokine flow cytometry is generally employed in this study to study the immune response levels of CD4+ and CD8+T cells to CMV-PP65 overlapping peptides in patients after allo-HSCT, and the CMV-specific cellular immune function of the allo-HSCT donor was also included.