Evaluation of cellular immune responses induced in mice by alphavirus replicon particle vaccines for SARS-CoV (B190)

An RNA replicon vector system derived from an attenuated strain of VEE virus was used to produce virus-like replicon particles (VRP) expressing SARS-CoV genes. We previously showed in mouse studies that complete protection was conferred by SARS S VRP and partial protection with SARS M VRP. In this study, two assays for cellular immunity were used to characterize the T cell phenotypes and cytokine profiles induced after SARS VRP vaccination. Following SARS M, N, S or E VRP immunization of BALB/c mice, splenocytes were harvested for antigen specific ICS and ELISPOTs. The SARS S VRP induced both CD4 and CD8 responses with the latter being the dominant component as measured by ICS for IFN-γ or TNF-α. Polyfunctional CD8 cells secreting both IFN-γ and TNF-α were also detected. Following SARS N VRP immunization, T cells secreting IFN-γ or TNF-α were readily detected with cells secreting both predominately identified as CD4 cells. Th1 cytokine secretion was not detected in cells from SARS M VRP inoculated mice. SARS E VRP elicited a robust CD8 response as shown by cytokine expression in cells stimulated with a 9mer peptide. IL-4 was not detectable after any SARS VRP vaccination. The IFN-γ ELISPOT results paralleled those from ICS, indicating that the SARS VRP vaccines induced Th1 biased responses, although the cytokines elicited differed depending on the SARS gene expressed. This study was supported by NIH grant #UC1-AI62582