Effect of the microtransplantation of allogeneic hematopoietic stem cells as maintenance therapy for elderly patients with acute leukemia

Hematopoietic stem cell microtransplantation: current situation and challenges

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) stands as a cornerstone in the treatment of hematological malignancies, recognized for its remarkable efficacy. However, the persistent challenge of graft-versus-host disease (GVHD) continues to represent a significant barrier, often being the leading cause of nonrelapse mortality after allo-HSCT. To address this limitation, hematopoietic stem cell microtransplantation (MST) has emerged as a novel therapeutic strategy that synergistically combines chemotherapy, allo-HSCT, and cellular immunotherapy. This innovative approach is designed to retain the patient's immune function, promote the establishment of microchimerism, and achieve a potent graft-versus-tumor (GVT) response, all while significantly minimizing the risk of GVHD. MST has primarily been applied in the treatment of hematological malignancies, where it has demonstrated promising outcomes, including marked improvements in complete remission rates, overall survival rates, and progression-free survival rates. Moreover, MST facilitates hematopoietic recovery, decreases the likelihood of infections, and reduces the incidence of GVHD, thus contributing to an improved quality of life for patients. A deeper and more comprehensive understanding of MST's mechanisms could enhance its clinical utility and integration into standard treatment protocols. This review aims to explore the underlying mechanisms, current clinical applications, and challenges of MST, shedding light on its potential role in advancing the management of hematological malignancies.

Expert consensus on microtransplant for acute myeloid leukemia in elderly patients -report from the international microtransplant interest group

Recent studies have shown that microtransplant (MST) could improve outcome of patients with elderly acute myeloid leukemia (EAML). To further standardize the MST therapy and improve outcomes in EAML patients, based on analysis of the literature on MST, especially MST with EAML from January 1st, 2011 to November 30th, 2022, the International Microtransplant Interest Group provides recommendations and considerations for MST in the treatment of EAML. Four major issues related to MST for treating EAML were addressed: therapeutic principle of MST (1), candidates for MST (2), induction chemotherapy regimens (3), and post-remission therapy based on MST (4). Others included donor screening, infusion of donor cells, laboratory examinations, and complications of treatment.

Clinical Studies in Hematologic Microtransplantation

The anti-tumor effects of allogeneic hematopoietic stem cell transplantation depend upon engraftment of donor cells followed by a graft-versus-tumor (GVT) effect. However, pre-clinical and clinical studies have established that under certain circumstances, anti-tumor responses can occur despite the absence of high levels of durable donor cell engraftment. Tumor response with little or no donor engraftment has been termed "microtransplantation." It has been hard to define conditions leading to tumor responses without donor cell persistence in humans because the degree of engraftment depends very heavily upon many patient-specific factors, including immune status and degree of prior therapy. Likewise, it is unknown to what degree donor chimerism in the blood or tissue is required for an anti-tumor effect under conditions of microtransplantation. In this review, we summarize some key studies supporting the concept of microtransplantation and emphasize the importance of recent large studies of microtransplantation in patients with acute myelogenous leukemia (AML). These AML studies provide the first evidence of the efficacy of microtransplantation as a therapeutic strategy and lay the foundation for additional pre-clinical studies and clinical trials that will refine the understanding of the mechanisms involved and guide its further development as a treatment modality.