Study On The Protective Effect And The Mechanism Of Heterology Prime-boost Immunization With Streptococcus Pneumoniae Vaccines

Background:Streptococcus pneumoniae(S.pn)is a Gram-positive bacterium,frequently cause an infection among the pediatric,elderly,and immunocompromised populations,result in pneumonia,otitis media,meningitis,and bacteremia.There is about 138,000 children under 5-yearold,and more than 800,000 people died of disease caused by Streptococcus pneumoniae annually,the number keeps growing year by year.Due to the morbidity and mortality of this pathogen,it is a burden of economic worldwide.Over the past 30 years,health care has been focused on development and application of Streptococcus pneumoniae vaccine to prevent disease caused by Streptococcus pneumoniae.Our previous studies confirmed that mucosal immunization with live attenuated strain SPY1 can protect mice against nasopharyngeal colonization of Streptococcus pneumoniae and lethal pneumococcal infection,and the protective effects are comparable with those induced by commercially available 23-valent polysaccharide vaccine.However,live attenuated vaccine SPY1 needs four inoculations to get satisfactory protective effect,which may increase the risk of virulence recovery.The heat shock protein of Streptococcus pneumoniae DnaJ is a good vaccine candidate,which can elicit a protective effect in mice although lightly weaker than SPY1.It is reported that heterologous primeboost approach is more effective than homologous prime-boost approach,so we design a heterologous immunization strategy with live attenuated strain SPY1 and heat shock protein of S.pneumoniae DnaJ.Objective:In this study,we aim to achieve a better protective effect through heterology prime-boost immunization with two different types of vaccines.Method:The mice are vaccinated by heterology prime-boost immunization strategy with live attenuated strain SPY1/protein DnaJ or plasmid DNA pcDNA3-dnaJ/protein DnaJ.Results:In the first part(live attenuated strain SPY1/protein DnaJ): the recombinant protein were expressed successfully;the mice that heterologous prime-boost immunization with SPY1 and DnaJ protein could significantly reduced the colonization of Streptococcus pneumoniae in the respiratory tract of mice,can defense against lethal infection;and induce higher level of IFN-?and IL-17 A than others and a comparable antigen specific antibody titer IgG and subtypes.In the second part(plasmid DNA pcDNA3-dnaJ/protein DnaJ): we generated successfully the plasmid DNA and expressing the protein DnaJ,which can promote the activation and maturation of bone marrow dendritic cells(BMDCs)in vitro.The group DP induced antigen-specific antibody in serum and significantly reduced the pneumococcal colonization in the nasopharynx and better protect against lethal infection than group DNA.Furthermore,this group DP generated higher levels of DnaJ-specific IFN-? and IL-17 A positive CD4+T cells and increased secretion of these cytokines in spleens more than the group DNA.The memory CD4+T cells in cervical lymph nodes and spleens of vaccinated mice were obviously higher than the control mice received the empty plasmid vector.Conclusion:Our two parts of researches suggest that heterology prime-boost with live attenuated strain SPY1/protein DnaJ and plasmid DNA pcDNA3-dnaJ/protein DnaJ can reach a better protective effect against Streptococcus pneumoniae,is a promising vaccine strategy.