Comparison of different adjuvants for immune efficacy of recombinant PKF protein of Acinetobacter baumannii

To compare the immune effects of recombinant PKF protein of Acinetobacter baumannii with different immune modes and different adjuvants.

After recombinant PKF protein was obtained by plasmid expression and purification, the protein was then combined with aluminum hydroxide（Al）or with AS03 to immunize mice by intramuscular（im）injection. In another experiment, the combination of PKF and LTK63 or PKF and LP1-34 was adopted to intranasally（in）immunize mice, respectively. The total animals were thus divided into 7 groups: PBS group; PKF group（im）, PKF+Al group（im）, PKF+AS03 group（im）, PKF group（in）, PKF+LTK63 group（in）, and PKF+LP1-34 group（in）. The levels of serum specific IgG and mucosal sIgA in the immunized mice were detected by ELISA. Moreover, the sublethal model of Acinetobacter baumannii pulmonary infection was established, and then the bacterial colonization amount in blood and lung of mice after challenge was measured to evaluate the protective immune efficacy of the recombinant vaccine.

In the intramuscular immunization group, AS03-assisted PKF produced the highest specific IgG antibody level（P<0.01）, and in the nasal immunization group, LTK63 significantly increased the level of specific sIgA in the alveolar lavage fluid（P<0.01）. Bacterial challenge test showed that the bacterial colonization amount was similar in the PKF+AS03（im）group and PKF（im）alone group, while the PKF+LTK63 group（in）obtained remarkably reduced bacterial colonization amount（P<0.01）.

LTK63 assists PKF to better protect against Acinetobacter baumannii pulmonary infection, suggesting that vaccine-mediated mucosal immune response may play a more important role in the infection protection.