Low pathogenic avian influenza H9N2 is still circulating in the Middle East causing respiratory manifestations and severe economic losses in poultry. In the present study, an H9 plasmid-based DNA vaccine targeting the HA gene of H9N2 A/CK/Egypt/SCU8/2014 was developed and evaluated in turkeys. The full length of HA was cloned into vector plasmids under the control of a cytomegalovirus promoter. The in-vitro expression of the recombinant HA was demonstrated in HeLa cells transfected with the plasmids pVAX1-H9 or pCR-H9 using western blot and Immunofluorescent assay (IFA). The efficacy of pVAX-H9 and pCR- H9, naked or saponin-adjuvanted, was evaluated in turkey poults at 3 weeks and challenged with A/CK/Egypt/SCU8/2014 (10⁶ EID₅₀/bird at 3 weeks post-vaccination. The efficacy was assesses based on virus shedding, oropharyngeal and cloacal, as well as seroconversion using haemagglutination inhibition (HI) test. All immunized birds showed high HI antibody titers (7–8 log₂) at 3 weeks post-vaccination. None of the birds vaccinated with naked or saponin-adjuvanted pVAX-H9 or pCR-H9 showed any clinical signs. The pVAX-H9 and pCR-H9 alone did not prevent cloacal and oropharyngeal virus shedding, however, saponin-adjuvanted pVAX1-H9 and pCR-H9 prevented cloacal and oropharyngeal virus shedding at 3 and 5 days post challenge, respectively. In conclusion, DNA vaccination with pVAX1-H9 and pCR-H9 could protect turkey from the H9N2 virus, but vaccination regimes need to be improved.

低致病性禽流感H9N2仍在中东传播，导致呼吸道疾病和严重的家禽经济损失。在本研究中，针对火鸡的H9N2 A / CK / Egypt / SCU8 / 2014的HA基因开发了基于H9质粒的DNA疫苗。HA的全长在巨细胞病毒启动子的控制下被克隆到载体质粒中。在体外的重组HA的表达被证明在HeLa细胞用免疫印迹和免疫荧光测定法（IFA）的质粒pVAX1上-H9或PCR-H9转染的细胞。在3周时在火鸡家禽中评估了pVAX-H9和pCR-H9裸或皂苷佐剂的功效，并用A / CK / Egypt / SCU8 / 2014攻击（10 ⁶ EID ₅₀疫苗接种后3周/只/只鸟。根据病毒脱落，口咽和泄殖腔以及使用血细胞凝集抑制（HI）测试进行的血清转化评估疗效。接种后3周，所有免疫的禽类均显示高HI抗体滴度（7-8 log ₂）。接种裸露或皂苷佐剂的pVAX-H9或pCR-H9的家禽均未显示任何临床症状。单独使用pVAX-H9和pCR-H9并不能防止泄殖腔和口咽病毒脱落，但是，在攻击后3天和5天，皂苷佐剂的pVAX1-H9和pCR-H9分别可以防止泄殖腔和口咽病毒脱落。总之，用pVAX1-H9和pCR-H9进行DNA疫苗接种可以保护火鸡免受H9N2病毒的侵害，但是需要改进疫苗接种方法。