Increased Risk of 100-Day and 1-Year Infection-Related Mortality in Haploidentical Stem Cell Transplantation Patients
Authors: Chang Jeremy , Vahdani Golnaz , Yaghmour George , Weissman Ashley , Lee Kum-Ja , Akhtari Mojtaba 
Published: October 2019

Abstract
Introduction:
Haploidentical hematopoietic stem cell transplantation (HSCT) is a potentially curative intervention for various malignant and non-malignant hematological conditions. Its use has led to the near universal availability of donors, but major challenges compared to HLA-matched related donor (MRD) and HLA-matched unrelated donor (MUD) transplants still exist. Although the most frequently discussed complication of haploidentical HSCT is graft rejection or severe/fatal graft-versus-host disease (GVHD), infection remains a significant cause of morbidity and mortality compared to other forms of transplant.
Methods:
This was a retrospective, single institution study that analyzed the outcomes of 187 patients with various hematological diseases who received allogeneic HSCT with haplo donor transplants, MRD transplants, or MUD transplants from 2011-2018. Conditioning regimens included combinations of fludarabine, busulfan, cyclophosphamide, melphalan, antithymocyte globulin, and total body irradiation. GVHD prophylaxis included either the combination of cyclosporine, tacrolimus, and mycophenolate mofetil (MMF) or tacrolimus and methotrexate (MTX). All patients received anti-viral prophylaxis with acyclovir, anti-fungal prophylaxis with either an azole or echinocandin, and anti-bacterial prophylaxis with trimethoprim-sulfamethoxazole or levofloxacin if the absolute neutrophil count (ANC) was <500 cell/mm3. Statistical analysis was performed using the Fisher Exact Probability Test with p-values <0.05 deemed significant.
Results:
Of the 187 patients who underwent allogeneic HSCT, 45 (24%) of the transplants were from haploidentical donors and 142 (76%) from non-haplo donors (MRD and MUD). Amongst all patients, median time to neutrophil engraftment (ANC >500 cells/mm3) was 16 days (range 13-25 days). Acute GVHD was present in 41% of haploidentical patients and 42% of non-haploidentical patients (p >0.05). Rates of chronic GVHD were also similar between the two groups at 45% in haplo patients and 48% in non-haplo patients (p >0.05). The 100-day infection-related mortality rate following transplant was significantly higher in the haploidentical group at 9% compared to 1% in the non-haploidentical group (p = 0.03, Figure 1). In addition, the 1-year rate of infection-related mortality after transplant was also significantly increased at 16% vs. 4% in the haplo vs. non-haplo groups, respectively (p = 0.01, Figure 2). The proportion of patients who experienced bacterial and fungal infections over this time period was comparable between the two groups (41% vs. 42% for bacterial infections and 18% vs. 12% for fungal infections in haploidentical patients vs. non-haploidentical patients, p >0.05 for both) while the incidence rate of viral infections was significantly higher in the haplo group at 72% vs. 38% in the non-haplo group (p < 0.001). However, all cases of infection-related mortality were due to bacterial and fungal infections rather than viral with 27% of bacterial or fungal infections leading to patient death in haploidentical patients compared to 7% in non-haploidentical patients (p = 0.02, Figure 3).
Conclusion:
The results of our study showed that compared to non-haplo transplant recipients, patients who underwent haplo transplants had significantly increased risks of 100-day and 1-year mortality secondary to infections. This finding is supported by prior data demonstrating that there is a longer time to immune reconstitution, specifically of the T-cell subset and dendritic cell subgroup, in the haploidentical population (Chang et. al. Journal of Clinical Immunology 2011). Furthermore, our results showed that the increased risk of infection-related mortality is not due to higher rates of acute or chronic GVHD, implying that the risk may be due to haploidentical transplantation itself as opposed to increased amounts of immunosuppressive therapy. While there was a greater incidence rate of viral infections amongst haploidentical patients, no viral infections led to mortality in either transplant group. In contrast, despite similar rates of bacterial and fungal infections between haploidentical and non-haploidentical patients, these infections led to death more often in the haplo population. These findings are important in considering future approaches to infection prophylaxis and treatment in haploidentical transplant recipients.

Disclosures
No relevant conflicts of interest to declare.