Short-Fragment DNA Residue from Vaccine Purification Processes Promotes Immune Response to the New Inactivated EV71 Vaccine by Upregulating TLR9 mRNA.

To reduce potential oncogenic long genomic DNA in vaccines, nuclease treatment has been applied in the purification processes. However, this action increased the residue of short-fragment DNA and its effect on vaccine potency was still elusive. In this study, we found residual sf-DNA in an inactivated EV71 vaccine could enhance humoral immune response in mice. Ag stimulation in vitro and vaccine injection in vivo revealed that TLR9 transcription level was elevated, indicating that sf-DNA could activate TLR9. These new findings will help us to understand the molecular mechanism induced by vero-cell culture-derived vaccines.