The fact that pIHBoV1 did not replicate well in undifferentiated human airway epithelial cells (Figures 2B and 2C) indicates that polarization and differentiation of the HAE is critical for HBoV1 DNA replication. Nevertheless, polarized NuLi-HAE, which is derived from normal human airway epithelial cells, did not support HBoV1 infection, but the CuFi-HAE derived from airway epithelial cells isolated from a cystic fibrosis patient did. The CuFi-HAE is unique relative to the others in that it retains the capacity to develop epithelia that actively transport in Na + but not Cl 2 because of the mutation in the cystic fibrosis gene [44] . Given the high complexity of the airway epithelium, we speculate that the permissiveness of HBoV1 infection is dependent on various steps of virus infection, e.g. attachment, entry, intracellular trafficking, and DNA replication of the virus. Nevertheless, a polarized CuFi-HAE model derived from the CuFi-8 cell line represents a novel stable cell culture model that is providing unexpected insights into the infection characteristics of HBoV1. Although HBoV1 infection of CuFi-HAE reproduced disruption of the barrier tight junctions like that seen also in primary B-HAE, the absence of virus on the basolateral side implies that in HAE the secretion of HBoV1 is apically polarized. We speculate that the milder damage of tight junctions in these cells might prevent virus release from the basolateral side of infected CuFi-HAE. Further studies will focus on understanding the permissiveness of CuFi-HAE to HBoV1 infection and on the reason for the ease of infection of an HAE with a cystic fibrosis phenotype.