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Severe infections and their attributable mortality are major complications in recipients of allogeneic hematopoietic stem cell transplantation (alloSCT). We herein report 236 adult patients who received haploSCT with PTCy. The median follow-up for survivors was 37 months. The overall incidence of bloodstream infections by gram-positive and gram-negative bacteria at 37 months was 51% and 46%, respectively. The incidence of cytomegalovirus infection was 69%, while Epstein Barr virus infections occurred in 10% of patients and hemorrhagic cystitis in 35% of cases. Invasive fungal infections occurred in 11% at 17 months. The 3-year incidence of infection-related mortality was 19%. The median interval from transplant to IRM was 3 months (range 1–30), 53% of IRM occurred >100 days post-haploSCT. Risk factors for IRM included age >50 years, lymphoid malignancy, and developing grade III-IV acute GvHD. Bacterial infections were the most common causes of IRM (51%), mainly due to gram-negative bacilli BSI. In conclusion, severe infections are the most common causes of NRM after haploSCT with PTCy, with a reemergence of gram-negative bacilli as the most lethal pathogens. More studies focusing on the severe infections after haploSCT with PTCy and differences with other types of alloSCT in adults are clearly warranted.

Key Points PTCy with additional immunosuppression using mostly PBSCs grafts showed a reduction of acute GVHD rate in matched sibling donor HSCT. GRFS was improved after PTCy compared with CsA-MTX.

Cytokine release syndrome (CRS) is a systemic inflammatory response with aberrant immune activation and immune hyperstimulation, that leads to increased cytokine levels and inflammation. CRS has been described after antibody and cellular-based therapies. The use of posttransplant cyclophosphamide (PTCy) as graft-vs-host disease (GVHD) prophylaxis in haploidentical hematopoietic stem cell transplantation (haplo-HSCT) has led to the extension of allogeneic HSCT to patients without HLA-identical donors. Furthermore, PTCy has also been introduced in matched and unrelated donor HSCT. However, description of incidence and clinical impact of CRS on outcomes in these patients is scarce. We retrospectively analyzed 107 consecutive haplo-HSCT and 39 HLA-identical HSCT with PTCy from 2010 to 2017 in our institution. We used published CRS criteria to identify 76% and 14% of patients who developed CRS after haplo-HSCT and HLA-identical HSCT, respectively. Most patients presented CRS grades 1 and 2. Only one patient from the whole series presented grade 3 CRS and required tocilizumab therapy. The use of peripheral blood stem cells (PBSC), as well as total nucleated cells infused were associated with an increased risk of CRS. Patients who presented CRS developed grade II-IV acute GVHD more frequently than those who did not (60% vs 28.6% respectively, P = .012). The development of CRS was not significantly associated with nonrelapse mortality or overall survival. CRS is a frequent complication after PBSC haploidentical T-repleted HSCT, but significantly less frequent after HLA-identical HSCT. Most cases are mild. Prompt identification allows adequate management of severe forms. K E Y W O R D S cyclophosphamide, cytokine release syndrome, haploidentical stem cell transplantation, hematopoietic stem cell transplantation 1 | INTRODUCTION Cytokine release syndrome (CRS) is a systemic inflammatory response that occurs as a result of high-level immune activation. With the extended use of inmune-based therapies CRS has been increasingly recognized. 1 However, the pathophysiology of CRS is still incompletely understood. CRS is triggered by the massive release of IFN-γ by activated Tcells and / or tumor cells after the administration of antibody-based therapies, nonprotein-based cancer drugs such as oxaliplatin and lenalidomide and, recently, the new T-cell engaging immunotherapies including bispecific antibody constructs and chimeric antigen receptor (CAR) T cells. IFN-γ causes activation of different immune cells especially macrophages. Activated macrophages produce a cascade Jose Luis Díez-Martín and Mi Kwon contributed equally to this study.

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