Enhanced Protection by Recombinant Newcastle Disease Virus Expressing Infectious Bronchitis Virus Spike Ectodomain and Chicken Granulocyte-Macrophage Colony-Stimulating Factor

We previously reported that recombinant Newcastle disease virus LaSota (rLS) expressing infectious bronchitis virus (IBV) Arkansas (Ark)-type trimeric spike (S) ectodomain (Se; rLS/ArkSe) provides suboptimal protection against IBV challenge. We have now developed rLS expressing chicken granulocyte-macrophage colony-stimulating factor (GMCSF) and IBV Ark Se in an attempt to enhance vaccine effectiveness. In the current study, we first compared protection conferred by vaccination with rLS/ArkSe and rLS/ArkSe.GMCSF. Vaccinated chickens were challenged with virulent Ark, and protection was determined by clinical signs, viral load, and tracheal histomorphometry. Results showed that coexpression of GMCSF and the Se from rLS significantly reduced tracheal viral load and tracheal lesions compared with chickens vaccinated with rLS/ArkSe. In a second experiment, we evaluated enhancement of cross-protection of a Massachusetts (Mass) attenuated vaccine by priming or boosting with rLS/ArkSe.GMCSF. Vaccinated chickens were challenged with Ark, and protection was evaluated. Results show that priming or boosting with the recombinant virus significantly increased cross-protection conferred by Mass against Ark virulent challenge. Greater reductions of viral loads in both trachea and lachrymal fluids were observed in chickens primed with rLS/ArkSe.GMCSF and boosted with Mass. Consistently, Ark Se antibody levels measured with recombinant Ark Se protein-coated ELISA plates 14 days after boost were significantly higher in these chickens. Unexpectedly, the inverse vaccination scheme, that is, priming with Mass and boosting with the recombinant vaccine, proved somewhat less effective. We concluded that a prime and boost strategy by using rLS/ArkSe.GMCSF and the worldwide ubiquitous Mass attenuated vaccine provides enhanced cross-protection. Thus, rLS/GMCSF coexpressing the Se of regionally relevant IBV serotypes could be used in combination with live Mass to protect against regionally circulating IBV variant strains.