3. Study design 3.1 Principle of design: prospective, randomized, control, open label 3.2 Subjects: patients with SAA undergoing allogeneic HSCT 3.3 Grouping: In this study, central randomization was used for random enrolment (1:1). After signing the informed consent, patients were randomized into rituximab conditioning group (test group) or non- rituximab conditioning group (control group). Treatment was assigned on a randomized basis according to a 1:1 ratio. The test group and the control group each will include 100 cases.~3.4 Study schedule: This clinical research is to be completed from September 2020 to September 2023.~Subject enrollment 36months~Transplantation to the end of follow-up 24months~Data collection and report writing 3months In total 63months
Objectives 2.1 Primary objectives~1) To observe and compare incidence and severity of aGVHD and cGVHD between the two arms within 2 years after transplantation.~2) To observe and compare the engraftment rate between the two arms. 3) To observe and compare the incidence of infections between the two arms. 2.2 Secondary objectives~To conduct pharmacogenomic assay in CD20 arm(treatment arm) before conditioning and monitor plasma concentration of CD20 dynamically（7d、14d、28d、56d、91d）.~To monitor levels of B cells in peripheral blood dynamically (+90d、+180d、+270d、+360d、+450d、+540d、+630d、+720d) in all patients.~To observe and compare the incidence of PTLD between the two arms.~To observe and compare immunoglobulin levels after transplantation in all patients.~To evaluate transplant-related mortality.~To evaluate the effect on hematopoietic reconstruction.