Increased pulmonary monocyte infiltration and attenuated phagocytosis defines perinatal dysfunction of innate immunity in Cystic Fibrosis

In Cystic Fibrosis (CF) patients, cycles of infection and inflammation lead to fatal lung damage. While diminished mucus clearance is restored by highly effective CFTR modulator therapy, inflammation and infection persist in treated patients, suggesting alternative mechanisms may contribute to impaired immunity in CF. Here, we made use of a CF pig model to investigate the innate immune system at birth, before the onset of infection. We observed a substantial change in the composition of tissue resident immune cells towards emergency myelopoiesis, accompanied by increased infiltration of monocytes into CF lungs. A more immature status in the transcriptome profile of classical monocytes in CF pigs and preschool children with CF correlated with reduced phagocytic capacity, confirming a congenital and translationally conserved aberration of the immune system in CF. The lack of CFTR expression in circulating monocytes indicates an indirect etiology of these effects and suggests that additional immunological treatments are necessary for CF patients. One Sentence Summary Increased infiltration of lung tissue by monomyeloid cells and their impaired phagocytic potential cause dysfunctional imprinting of mucosal immunity in Cystic Fibrosis airways at birth and suggest early and specific treatment of the innate immune system in patients. ### Competing Interest Statement M.A.M. reports grants from Vertex Pharmaceuticals; personal fees for consulting or advisory board participation from Abbvie, Antabio, Arrowhead Pharmaceuticals, Boehringer Ingelheim, Enterprise Therapeutics, Kither Biotech, Pari, Prieris, Recode, Santhera, Splisense, Vertex Pharmaceuticals; lecture honoraria from Vertex Pharmaceuticals; travel support from Boehringer Ingelheim and Vertex Pharmaceuticals; patent on the Scnn1b-transgenic mouse as animal model for chronic obstructive pulmonary disease and cystic fibrosis, outside the submitted work.