Post-Transplant Bendamustine Extends Survival and Reduces GvHD in a Xenogeneic NSG Transplant Model Compared to Post-Transplant Cyclophosphamide

Acute graft-versus-host disease (GvHD) is a significant complication following allogeneic hematopoietic stem cell transplantation. This process begins with the activation of donor T-cells that recognize host tissue antigens as foreign, resulting in an immune attack primarily targeting the skin, gastrointestinal tract and liver. Post-transplant cyclophosphamide (PT-CY) has significantly reduced GvHD in haploidentical and other allogeneic transplant settings, although relapse, viral reactivations, hemorrhagic cystitis and cardiotoxicity remain common. Our laboratory has investigated the use of bendamustine, another nitrogen mustard agent, as a post-transplant GvHD prophylaxis. The goal is to reduce GvHD while preserving graft-versus-leukemia (GvL) effects and avoiding the significant side effects associated with PT-CY.

Using a xenogeneic GvHD (xGvHD) model of irradiated NSG mice infused with human peripheral blood mononuclear cells (PBMCs), we found that a day +3 dose of 30 mg/kg of post-transplant bendamustine (PT-BEN) confers better survival and reduces xGvHD more effectively than PT-CY (50 mg/kg). These results were also maintained in a xGvHD model of NSG mice receiving PT-CY (25 mg/kg) on days +3 and +4 as compared to PT-BEN (15 mg/kg). Engraftment of human lymphocytes on days +7, +14, +21, +28, +42, and +70 was tracked using flow cytometric analysis of peripheral blood samples. Interestingly, we observed higher rates of human engraftment in PT-CY treated mice which was associated with a more pronounced reduction in murine CD45+ cells in the peripheral blood. Our findings indicate that a dose of 25 mg/kg PT-CY on days +3 and +4, previously reported to be optimal in mice, or a single PT-CY dose of 50 mg/kg on day +3 does not significantly extend survival in our xGvHD model. Additionally, PT-BEN can significantly prolong survival and reduce acute GvHD, although this may be partially attributed to a reduced circulating number of engrafted human lymphocytes. Ongoing experiments include investigation into the early deleterious effects of PT-CY on murine CD45+ populations and use of xenogeneic GvL models to examine whether the engrafted cells maintain a GvL effect in the presence of reduced GvHD. Additionally, single cell RNA-sequencing on engrafted hCD45+ cells will be performed to assess changes in gene expression across T-cell populations in xGvHD mice treated with either PT-CY or PT-BEN.

No relevant conflicts of interest to declare.