This study is a single center, prospective, single arm exploratory clinical trial that includes patients with hematological malignancies who are indicated for allogeneic hematopoietic stem cell transplantation (allo HSCT) but lack suitable donors. This project plans to use highly mismatched unrelated HLA mismatched donors. Ultimately, an unrelated human leukocyte antigen (HLA) mismatched allo HSCT transplantation plan will be established to improve the disease prognosis of this group of patients and truly enter the era of "everyone has a donor" for allo HSCT.