Assessment of the phenotype and functionality of porcine CD8 T cell responses following vaccination with live attenuated classical swine fever virus (CSFV) and virulent CSFV challenge

Vaccination with live attenuated classical swine fever virus (CSFV) induces solid protection after only 5 days, which has been associated with virus-specific T cell gamma interferon (IFN-gamma) responses. In this study, we employed flow cytometry to characterize T cell responses following vaccination and subsequent challenge infections with virulent CSFV. The CD3(+) CD4(-) CD8(hi) T cell population was the first and major source of CSFV-specific IFN-gamma. A proportion of these cells showed evidence for cytotoxicity, as evidenced by CD107a mobilization, and coexpressed tumor necrosis factor alpha (TNF-alpha). To assess the durability and recall of these responses, a second experiment was conducted where vaccinated animals were challenged with virulent CSFV after 5 days and again after a further 28 days. While virus-specific CD4 T cell (CD3(+) CD4(+) CD8 alpha(+)) responses were detected, the dominant response was again from the CD8 T cell population, with the highest numbers of these cells being detected 14 and 7 days after the primary and secondary challenges, respectively. These CD8 T cells were further characterized as CD44(hi) CD62L(-) and expressed variable levels of CD25 and CD27, indicative of a mixed effector and effector memory phenotype. The majority of virus-specific IFN-gamma(+) CD8 T cells isolated at the peaks of the response after each challenge displayed CD107a on their surface, and subpopulations that coexpressed TNF-alpha and interleukin 2 (IL-2) were identified. While it is hoped that these data will aid the rational design and/or evaluation of next-generation marker CSFV vaccines, the novel flow cytometric panels developed should also be of value in the study of porcine T cell responses to other pathogens/vaccines.