Background: Patients undergoing allogeneic hematopoietic stem cell transplantation (alloHSCT) frequently require red blood cell (RBC) transfusions. Immunomodulation by RBC transfusion is of great interest in the context of alloHSCT, as donor immune cells mediate tumor control, fight pathogens, but also cause graft-versus-host disease (GvHD), a potentially lethal complication of alloHSCT. Data linking RBC transfusion burden with relevant clinical outcome parameters after alloHSCT are scarce.

Methods: In this retrospective study, we examined the association between RBC transfusion burden and clinical outcomes in a cohort of 116 patients who underwent alloHSCT at a single transplant center. Therefore, we analyzed the impact of RBC transfusion burden on the following relevant outcomes after alloHSCT: overall survival, leukocyte engraftment, GvHD incidence, and infection rate.

Results: Reduced transfusion frequencies, both before (p = 0.003) and after (p = 0.002) alloHSCT, are associated with favorable survival rates 100 days after transplantation. In line, those patients showed an earlier leukocyte engraftment (p < 0.001). However, no significant association was found between the transfusion rate and the incidence of grade II–IV acute GvHD (aGvHD) (p = 0.87). Notably, it was not the frequency of pre-transplant RBC transfusions (p = 0.05), but rather an increased post-transplant transfusion rate (p < 0.001), that was significantly associated with a lower infection rate, particularly with infections within the first 21 days following alloHSCT (p < 0.001 for post-transplant transfusions).

Conclusion: In summary, our data support recent evidence that high RBC transfusion burden is associated with poor survival. GvHD incidence was not linked to RBC transfusion, but we were able to detect a negative association with infectious complications. Larger, multi-center trials are needed to confirm our findings, accompanied by molecular analysis of RBC–immune cell interactions.