Life-threatening influenza pneumonitis in a child with inherited IRF9 deficiency

Hernandez, Nicholas; Melki, Isabelle; Jing, Huie; Habib, Tanwir; Huang, Susie S.Y.; Danielson, Jeffrey; Kula, Tomasz; Drutman, Scott; Belkaya, Serkan; Rattina, Vimel; Lorenzo-Diaz, Lazaro; Boulai, Anais; Rose, Yoann; Kitabayashi, Naoki; Rodero, Mathieu P.; Dumaine, Cecile; Blanche, Stéphane; Lebras, Marie-Noëlle; Leung, Man Chun; Mathew, Lisa Sara; Boisson, Bertrand; Zhang, Shen-Ying; Boisson-Dupuis, Stephanie; Giliani, Silvia; Chaussabel, Damien; Notarangelo, Luigi D.; Elledge, Stephen J.; Ciancanelli, Michael J.; Abel, Laurent; Zhang, Qian; Marr, Nico; Crow, Yanick J.; Su, Helen C.; Casanova, Jean-Laurent

We investigated the impact of IRF9 deficiency on cell-intrinsic, nonhematopoietic immunity, using P's F-SV40 cells. We observed an ∼10-fold difference in IAV titer at 48 h after infection when compared with healthy controls and P's heterozygous mother (Fig. 5 A) . Pre-treatment with IFN-α2b substantially reduced viral replication in healthy control cells but not P's cells, which produced roughly 100-fold higher IAV titers than cells with an intact IFN signaling pathway (Fig. 5 A) . Similarly, P's F-SV40s were substantially more susceptible to vesicular stomatitis virus (VSV) at 12 h after infection in the absence of pretreatment with IFN-α2b, or at all time points beyond 8 h in cells that were pretreated with IFN, with roughly a 1,000-fold difference in titer between healthy controls and P (Fig. 5 B) . To demonstrate that these defects in IAV and VSV immunity were IRF9 dependent, we stably transfected P's F-SV40 cells with various IRF9 alleles or an empty vector and analyzed the ability of the transfected cells to control VSV and IAV infection (Fig. 5 , C and D). Expression of WT IRF9 was able to rescue the inability of P's cells to control of infection with either pathogen, while expression of K81R and IRF9-Δex7 alleles was unable to do so. Significantly, cells that expressed the Q127H mutation were also able to control infection with VSV or IAV, suggesting that this allele may not be deleterious in the context of type I IFN signaling and anti-viral immunity, consistent with the lack of overt viral infections experienced by the individual harboring this mutation. R292Q and R292C alleles were also somewhat able to control infection with VSV or IAV, although not at the level of the WT IRF9 allele, suggesting that a partial form of IRF9 deficiency may have contributed to the viral infections of the HOIL1-deficient patient . We further showed that cell-intrinsic anti-viral immunity was broadly impaired, by testing PIV and RSV (Fig. 5, E-H) . To further demonstrate that IRF9 mediates susceptibility to viral infection in vitro, we also knocked down IRF9 or mitochondrial anti-viral signaling protein (MAVS) expression in primary dermal fibroblasts from FC values of all ISGs that were found to be differentially regulated (≥1.5-fold) in all three control subjects relative to unstimulated cells. Bar graphs (C and D) quantify the number of ISGs that were differentially regulated (≥1.5-fold) compared with unstimulated cells in healthy controls or the IRF9-deficient patient.