The culmination of 5.5yrs of research . . .

Mar 19, 2008

ABSTRACT

Replication and Persistence of VSV-based
Vaccine Vectors in an Animal Model


2008

Recombinant vesicular stomatitis virus vectors expressing foreign antigens are highly effective vaccines, protecting against disease in several animal models. Single-cycle (VSV∆G) or highly attenuated (VSV-CT1) vectors generate potent humoral and cellular immune responses comparable to recombinant wild-type (rwtVSV) vectors when administered to mice intramuscularly (i.m), but not intranasally (i.n.). Employing both infectious virus titer assay and a reverse transcription, real-time PCR assay for genomic RNA (gRNA), we showed that the ability of these vectors to generate strong immune responses when given i.n. correlates with replication competence and their capacity to spread to other organs, including lymph nodes. We also carried out a detailed analysis of rwtVSV, VSV-CT1, and VSV∆G vector spread following i.m. inoculation. We found that infectious rwtVSV and VSV-CT1 vectors spread from the muscle to lymph nodes to comparable extents, but did not spread to peripheral organs. In addition, gRNA from all vectors was detected at similar levels in the muscle and draining lymph nodes. These results suggest that even replication-competent VSVs are effectively single-cycle vectors when given i.m. and that viral dissemination to lymph nodes does not require more than a primary infection event. Following i.n. and i.m. inoculation, VSV gRNA was able to persist in draining lymph nodes as long as 60 days post inoculation. To determine if this persistence could be the result of ongoing replication, we developed a real-time assay that is specific for VSV N mRNA by using sequence-tagged primers. However, VSV N mRNA sequences did not persist beyond 10 days after i.m. inoculation and 20 days after i.n. inoculation, indicating that gRNA persists by some sequestration mechanism, rather than by ongoing replication. Finally, we examined the possibility that CD169+ lymph node macrophages, which bind VSV, were responsible for the sequestration of VSV gRNA. Although elimination of these cells reduced gRNA levels in the popliteal lymph node, our results indicate that resident macrophages are not the only cells harboring VSV gRNA in the lymph nodes. Overall, i.m. inoculation of single-cycle VSV-based vaccine vectors constitutes a promising development toward a safe and effective vaccine platform.