Study of the immunogenicity and virulence of replication-competent recombinant vaccinia virus in CD4＋T cell-depleted mice

Abstract

Objective To investigate the effects of CD4＋T cell depletion in BALB/c mice on the immunogenicity and virulence of replication-competent recombinant vaccinia virus. Methods Twelve BALB/c mice were inoculated with recombinant Tiantan vaccinia （ rTV, n=8 ） or vaccinia virus Tiantan strain （ VTT, n=4） by tail scarification after the depletion of CD4＋T cells with anti-CD4 monoclonal anti-body（ McAb） injected intraperitoneally for three days before virus inoculation.A control group without anti-body treatment was set up accordingly.Several parameters including the body weight, pocks on tail, viral shedding and the percentage of CD4＋T cells were monitored.In the fourth week after virus infection, ovaries were collected from mice and viral loads in the tissue were titrated by plaque forming assay on chick embryo fibroblast （ CEF） cells.The specific cellular immune responses against vaccinia virus and HIV induced by inoculation of VTT and rTV respectively were detected by intracellular cytokine staining （ ICS） assay.ELISA was used to detect antibodies against vaccinia virus and HIV-1 gp120.Results All mice with or without CD4 McAb treatment showed typical poxvirus pocks on tails after inoculation of vaccinia viruses, but none of them developed secondary or satellite lesions.It took a longer time for CD4＋T cell-depleted mice to heal from lesions, to regain body weights and to release viruses than the mice in control group.No vaccinia virus was detected in the ovaries of CD4＋T cell-depleted mice or mice in control group.The mean absorbance（ A） values for the detection of HIV-specific and vaccinia virus-specific antibodies in CD4＋T cell-depleted mice with ELISA were respectively 0.119 and 0.168, which were significantly lower than those in mice of control group.The titers of neutralizing antibodies against vaccinia virus in McAb/rTV treated mice （1 ∶321） were lower than those in rTV treated mice （1 ∶1286） （P〈0.05）.The percentages of CD4＋T cells secreting IFN-γ（0.654%） in McAb/rTV treated mice were significantly lower than those in rTV treated mice in the fourth week after immunization （P 〈0.0004）.No significant differences with the vaccinia virus-specificCD8＋ T cell responses were observed among mice with or without CD4＋T cells depletion.Conclusion Thereplication and dissemination of replication-competent recombinant vaccinia virus could be effectively controlledin the mice with CD4＋ T cell-depletion.The depletion of CD4＋ T cells significantly reduced the humoraland CD4＋ T cell responses, but had no effect on CD8＋ T cell responses. Key words: Replication-competent recombinant vaccinia virus CD4＋T cell CD8＋T cell Viral clearance Immunogenicity