Functional characterization of the human dendritic cell immunodeficiency associated with the IRF8K108E mutation

Abstract

AbstractWe have previously reported on a unique patient in whom homozygosity for a mutation at IRF8 (IRF8K108E) causes a severe immunodeficiency. Laboratory evaluation revealed a highly unusual myeloid compartment, remarkable for the complete absence of CD14+ and CD16+ monocytes, absence of CD11c+ conventional dendritic cells (DCs) and CD11c+/CD123+ plasmacytoid DCs, and striking granulocytic hyperplasia. The patient initially presented with severe disseminated mycobacterial and mucocutaneous fungal infections and was ultimately cured by cord blood transplant. Sequencing RNA from the IRF8K108E patient’s primary blood cells prior to transplant shows not only depletion of IRF8-bound and IRF8-regulated transcriptional targets, in keeping with the distorted composition of the myeloid compartment, but also a paucity of transcripts associated with activated CD4+ and CD8+ T lymphocytes. This suggests that T cells reared in the absence of a functional antigen-presenting compartment in IRF8K108E are anergic. Biochemical characterization of the IRF8K108E mutant in vitro shows that loss of the positively charged side chain at K108 causes loss of nuclear localization and loss of transcriptional activity, which is concomitant with decreased protein stability, increased ubiquitination, increased small ubiquitin-like modification, and enhanced proteasomal degradation. These findings provide functional insight into the molecular basis of immunodeficiency associated with loss of IRF8.