Liposome-Coupled Peptides Induce Long-Lived Memory CD8(+) T Cells Without CD4(+) T Cells

CD8(+) T cells provide broad immunity to viruses, because they are able to recognize all types of viral proteins. Therefore, the development of vaccines capable of inducing long-lived memory CD8(+) T cells is desired to prevent diseases, especially those for which no vaccines currently exist. However, in designing CD8(+) T cell vaccines, the role of CD4(+) T cells in the induction and maintenance of memory CD8(+) T cells remains uncertain. In the present study, the necessity or not of CD4(+) T cells in the induction and maintenance of memory CD8(+) T cells was investigated in mice immunized with liposome-coupled CTL epitope peptides. When OVA-derived CTL epitope peptides were chemically coupled to the surfaces of liposomes and inoculated into mice, both primary and secondary CTL responses were successfully induced. The results were further confirmed in CD4(+) T cell-eliminated mice, suggesting that CD4(+) T cells were not required for the generation of memory CD8(+) T cells in the case of immunization with liposome-coupled peptides. Thus, surface-linked liposomal antigens, capable of inducing long-lived memory CD8(+) T cells without the contribution of CD4(+) T cells, might be applicable for the development of vaccines to prevent viral infection, especially for those viruses that evade humoral immunity by varying their surface proteins, such as influenza viruses, HIV, HCV, SARS coronaviruses, and Ebola viruses.