Finally, we questioned if the above changes in epitope-specific CTL would also be associated with changes in immunity to LCMV infections. We performed virus titration from the spleens at different days p.i. after initializing first cross-priming in the same protocol as shown in Fig. 7A. The data in Fig. 7B demonstrate that immunization with ADC encoding LCMV proteins caused significant reduction in virus titers 4 days p.i. with LCMV compared control mice. By day 7, this effect was unambiguous with no detectable virus in the cross-priming condition. These results suggest that initial cross-priming of LCMV proteins

prior to viral infection can enhance anti-viral immunity due to increased frequencies of CTL as shown in Fig. 7A. Induction of protective immune responses against viruses or tumors can be achieved via cross-priming 4–6. In this study, we employed the LCMV infection model OSI-906 ic50 to study how cross-presentation GSI-IX of multiple epitopes translates when studying cross-priming. We used LyUV treatment of the ADC because it fully inactivated the virus and allowed for efficient NP396 cross-presentation similar to HEK-NP cells 7, 8. We initially expected that GP33 would fail to cross-present because it is located in the signal peptide

of LCMV-GP 12, but it was cross-presented with low efficiency, probably due to its exceptional long half-life of 6 h 15. Although NP396, located in the long-lived nucleoprotein 21, was efficient at cross-presentation, NP205 was poor, possibly due to inefficient processing by the phagosomal/proteasomal machineries. GP276 is another epitope that cross-presented with low efficiency, probably due to its low binding affinity to MHC 22, which could be critical when the antigen supply is limited. Immunoproteasomes, which have been implicated in cross-presentation 23, could Interleukin-3 receptor also account for GP276 poor cross-presentation since it can downregulate GP276 presentation 24. We have

detected LMP7 expression in DC2.4 (unpublished data), which concurs with the previous data showing that immunoproteasomes are expressed in DC irrespective of their maturation states 25. Considering the direct presentation of the NP and GP-derived epitopes, it has been shown that NP epitopes can be detected as early as 2 h p.i., whereas GP epitopes were detected 4–6 h p.i. 20. Our results show that infected ADC can provide antigens for cross-presentation in a comparable time frame. Such kinetics would probably be dependent on the stress status of the infected cell 26 and would be sufficient to supply antigens for cross-presentation before the completion of the replication cycle. Thus far, one would expect that during cross-priming, NP396 will dominate the CTL response in vivo.