The immune system defends the body against certain tumor cells and against foreign agents such as fungi, parasites, bacteria, and viruses. One of its main roles is to distinguish endogenous components from non-self-components. An unproperly functioning immune system is prone to primary immune deficiencies caused by either primary immune deficiencies such as genetic defects or secondary immune deficiencies such as physical, chemical, and in some instances, psychological stressors. In the manuscript, we will provide a brief overview of the immune system and immunotoxicology. We will also describe the biochemical mechanisms of immunotoxicants and how to evaluate immunotoxicity.

Background: Invasive fungal infections (IFI) following allogeneic stem cell transplant (allo-HCT) are associated with high morbidity and mortality. Primary prophylaxis using voriconazole has been shown to decrease the incidence of IFI. Methods: We conducted a retrospective analysis at the Bone Marrow Transplant (BMT) unit of the American University of Beirut including 195 patients who underwent allo-HCT for hematological malignancies and received voriconazole as primary prophylaxis for IFI. The primary endpoints were based on the incidence of IFI at day 100 and day 180, and the secondary endpoint based on fungal-free survival. Results: For the study, 195 patients who underwent allo-HCT between January 2015 and March 2021 were included. The median age at transplant was 43 years. Of the patients, 63% were male, and the majority of patients were diagnosed with acute myeloid leukemia (AML) (60%). Voriconazole was given for a median of 90 days and was interrupted in 20 patients. The majority of IFI cases were probable invasive aspergillosis (8%). The incidence of IFI including proven, probable and possible IFI was 34%. The incidence of proven and probable IFI was 5% were 8%, respectively. The incidence of proven-probable (PP-IFI) was 5.1% at day 100 and 6.6% at day 180. The majority of PP-IFI cases were invasive aspergillosis (8%). A univariate analysis of patients, transplant characteristics and IFI showed a significant correlation between the type of donor, disease status before transplant, graft-versus-host disease prophylaxis used and incidence of IFI. Only disease status post-transplant showed a significant correlation with fungal-free survival in the multivariate analysis. Conclusion: Primary prophylaxis with voriconazole in allo-HCT is associated with a low incidence of IFI. More studies are required to compare various antifungal agents in this setting.