In Vivo Functions of Mouse Neutrophils Derived from HoxB8-Transduced Conditionally Immortalized Myeloid Progenitors

Although neutrophils play important roles in immunity and inflammation, their analysis is strongly hindered by their short-lived and terminally differentiated nature. Prior studies reported conditional immortalization of myeloid progenitors using retroviral expression of an estrogen-dependent fusion protein of the HoxB8 transcription factor. This approach allowed the long-term culture of mouse myeloid progenitors (HoxB8 progenitors) in estrogen-containing media, followed by differentiation toward neutrophils upon estrogen withdrawal. Although several reports confirmed the in vitro functional responsiveness of the resulting differentiated cells (HoxB8 neutrophils), little is known about their capacity to perform in vivo neutrophil functions. We have addressed this issue by an in vivo transplantation approach. In vitro-generated HoxB8 neutrophils showed a neutrophil-like phenotype and were able to perform conventional neutrophil functions, like respiratory burst, chemotaxis, and phagocytosis. The i.v. injection of HoxB8 progenitors into lethally irradiated recipients resulted in the appearance of circulating donor-derived HoxB8 neutrophils. In vivo-differentiated HoxB8 neutrophils were able to migrate to the inflamed peritoneum and to phagocytose heat-killed Candida particles. The reverse passive Arthus reaction could be induced in HoxB8 chimeras but not in irradiated, nontransplanted control animals. Repeated injection of HoxB8 progenitors also allowed us to maintain stable circulating HoxB8 neutrophil counts for several days. Injection of arthritogenic K/BxN serum triggered robust arthritis in HoxB8 chimeras, but not in irradiated, nontransplanted control mice. Taken together, our results indicate that HoxB8 progenitor-derived neutrophils are capable of performing various in vivo neutrophil functions, providing a framework for using the HoxB8 system for the in vivo analysis of neutrophil function.