Corticosteroids Impair Granulocyte Transfusion Therapy By Targeting NET Formation and Neutrophil Antifungal Functions Via ROS/Dectin1 Pathways

Introduction:

Invasive pulmonary Aspergillus fumigatus infections cause high morbidity and mortality in neutropenic patients. Granulocyte transfusions have been tested as an alternative therapy for the management of high-risk neutropenic patients with invasive A. fumigatus infections. To increase the granulocyte yield for transfusion, donors are treated with corticosteroids. Yet, the efficacy of granulocyte transfusion and functional defense mechanisms of granulocytes collected from corticosteroid treated donors remain largely elusive. Therefore, we investigated the efficacy of granulocyte transfusion and functional defense mechanisms of corticosteroid treated granulocytes using mouse models.

Methods:

To determine the effects of corticosteroids on granulocytes to control A. fumigatus infections, we performed granulocyte adoptive cell transfers using in vivo mouse models, in vitro human and mouse granulocyte and A. fumigatus functional co-culture experiments in combination with flow cytometry, cytokine analysis, fluorescence and electron microscopy.

Results:

Transfusion of granulocytes from corticosteroid treated mice did not protect cyclophosphamide immunosuppressed mice against lethal A. fumigatus infection in contrast to granulocytes from untreated mice. Upon infection increased levels of inflammatory cytokines helped to recruit granulocytes to the lungs without any recruitment defects in corticosteroid treated and infected mice or in cyclophosphamide immunosuppressed and infected mice that had received the granulocytes from corticosteroid treated mice. However, corticosteroid treated human or mouse neutrophils failed to form neutrophil extracellular traps (NETs) under in vitro and in vivo conditions. Furthermore, corticosteroid treated granulocytes exhibited impaired ROS production against A. fumigatus. Notably, corticosteroids impaired the β-glucan receptor Dectin-1 (CLEC7A) on mouse and human granulocytes to efficiently recognize and phagocytize A. fumigatus, which markedly impaired fungal killing.

Conclusions:

We conclude that corticosteroid treatment of granulocyte donors for increasing neutrophil yields or patients with ongoing corticosteroid treatment could result in deleterious effects on granulocyte antifungal functions, thereby limiting the benefit of granulocyte transfusion therapies against invasive fungal infections.