Microtransplantation

Microtransplantation(MST) is an advanced technology to treat malignant hematological diseases and tumors by infusing patients with granulocyte colony-stimulating factor (G-CSF) mobilized human leukocyte antigen (HLA)-mismatched allogeneic peripheral blood stem cells following a reduced-intensity chemotherapy or targeted therapy. The term "microtransplantation" comes from its mechanism of reaching donor cell microchimerism. Chemotherapy is used by lower doses only to destroy cancer and partially suppress patient’s immune system, which will be reinitiated by donor’s stem cells soon after transplantation, and will play a role as recipient-versus-tumor (RVT) effect combining donor cells’ graft-versus-tumor (GVT) effect. Donor’s stem cells, which have been processed, will also accelerate functional recovery of recipient’s hematopoietic stem cells, greatly reducing infections and transplant-related mortality. Practices of microtransplantation has shown none graft-versus-host disease (GVHD) till present, thus immunosuppressive drugs for relieving GVHD wouldn’t be necessary. Possible mechanisms of the successful avoidance of GVHD include donor cell microchimerism, less-toxic cells processed prior to transplantation, and the preservation of host immune system that is capable of resisting the GVH alloresponse. Moreover, as HLA-mismatched stem cells are employed, donor availability is extremely extended.

Indications for microtransplantation are as follows:

Hematologic Malignancies Tumors

The cells employed are allogeneic peripheral blood stem cells. Matched HLA between donor and recipient is not necessary. The stem cells are collected from donor’s blood through a process known as apheresis after a certain period of daily subcutaneous injections of Granulocyte-colony stimulating factor, serving to mobilize stem cells from the donor's bone marrow into the peripheral circulation. Fresh cells are infused to recipient for the first time, and then stored in a controlled-rate freezer.

Donor’s Requirements:

In a randomized controlled trial from 2004 to 2009, 58 AML patients aged 60–88 years were randomly assigned to receive chemotherapy (control group; n=28) or it plus HLA-mismatched G-CSF–mobilized donor peripheral blood stem cell (G-PBSC) (G-PBSC group/ Microtransplantation; n = 30). The complete remission rate was significantly higher in the G-PBSC group than in the control group (80.0% vs 42.8%); The median recovery times of neutrophils and platelets were 11 days and 14.5 days, respectively, in the G-PBSC group and 16 days and 20 days, respectively, in the control group after chemotherapy; The 2-year probability of disease-free survival (DFS) was significantly higher in the G-PBSC group than in the control group (38.9% vs 10.0%). No graft-versus-host disease was observed in any patient. Persistent donor microchimerism was successfully detected in all of the 4 female patients.

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