Infectious Bronchitis Virus S2 Expressed from Recombinant Virus to Confer Protection Across Serotypes in Chickens
PI: . Toro, Q. Yu, V.L. van Santen, F.W. van Ginkel and K. Joiner
Mono- and polyvalent vaccines covering multiple infectious bronchitis virus (IBV) serotypes have been developed to protect the poultry industry during the last 7 decades. In spite of extensive vaccination programs IBV continues to cause enormous economic losses from phenotypic diversity and continuing evolution of the causal coronavirus. Accumulating evidence indicates that attenuated IBV vaccines contribute to the emergence of virulent vaccine-like viruses from point mutations and recombination with other prevalent IBV. The S1 subunit of the spike (S) glycoprotein exhibits extensive variation among IBV populations and this variation is responsible for immunological escape. In contrast, the S2 subunit of S is more conserved among IBV. We have demonstrated that overexposing the chicken immune system to the more conserved S2 subunit of IBV S by expression from a vectored vaccine, followed by boosting with whole live attenuated virus, protects the host against IBV showing dissimilar S1. Specifically, we developed recombinant Newcastle disease virus (NDV) LaSota (rLS) expressing an IBV Arkansas-type S2 transgene (rLS/IBV.S2). Chickens primed ocularly with rLS/IBV.S2 and boosted with a Massachusetts-type (Mass) attenuated vaccine were protected against challenge with virulent IBV Ark-type. We will (1) evaluate immunity elicited by rLS encoding IBV S2 proteins and (2) optimize protection in chickens by rLS encoding distinct IBV S2 proteins. Summarized activities by year are as follows:
Yearly Goals:
Year 1:
(1) We will develop rLS vectoring the S2 gene of IBV UK4/91 (serotype 793/B). The S2 sequence of IBV 4/91 (GenBank accession #AEL97578.1) will be optimized to the chicken codons and synthesized. The rLS/IBV4/91.S2 will be developed as previously described. (2) The NDV biological properties of the rescued rLS/IBV4/91.S2 virus will be evaluated as accepted. (3) Evaluate protection conferred by previously constructed rLS/IBV.S2 followed by attenuated Mass against challenge with IBV PA/171/99 (also called GA13). Evaluation of protection conferred by vaccination against IBV challenge will be assessed in all experiments by clinical signs, relative viral load determined by RT-PCR, and histopathology
Year 2:
1) Evaluate protection conferred by newly developed rLS/IBV4/91.S2 followed by attenuated Ark against challenge with IBV PA/171/99. (2) Evaluate protection conferred by previously developed rLS/IBV.S2 followed by attenuated DE072 against challenge with virulent IBV PA/171/99.
Year 3:
(1) Characterize immune responses induced by priming with rLS/IBV.S2 followed by Mass boost (IBV-specific IgA and IgG spot-forming cells in the Harderian glands (HG) and spleen, relative abundance of T lymphocyte populations (CD3+, CD44+,CD4+, CD8+) in the HG and spleen by flow cytometry, IBV serum antibody by ELISA, and IFN-? levels in tears and serum by ELISA.
Year 4:
(1) Evaluate protection conferred by newly developed rLS/IBV4/91.S2 followed by attenuated Mass against challenge with virulent IBV Ark. (2) Evaluate protection conferred by rLS/IBV.S2 followed by attenuated Ark against challenge with virulent IBV PA/171/99.
Year 5:
1) Sera from chickens immunized with each rLS constructs rLS/IBV.S2 and rLS/IBV4/91.S2 will be tested in cross-neutralization tests against heterotypic IBV strains to determine S2 sequences displaying cross-immunodominant neutralizing B cell epitopes. (2) Evaluate protection conferred by newly developed rLS/IBV4/91.S2 followed by attenuated GA98 against challenge with virulent IBV Ark. (3) Evaluate protection conferred by previously developed rLS/IBV.S2 followed by attenuated GA98 against challenge with virulent IBV Ark.
