Protection against Vaccinia Virus Challenge by CD8 Memory T Cells Resolved by Molecular Mimicry

Abstract

Live vaccinia virus (VV) vaccination has been highly successful in eradicating smallpox. However, the mechanisms of immunity involved in mediating this protective effect are still poorly understood, and the roles of CD8 T-cell responses in primary and secondary VV infections are not clearly identified. By applying the concept of molecular mimicry to identify potential CD8 T-cell epitopes that stimulate cross-reactive T cells specific to lymphocytic choriomeningitis virus (LCMV) and VV, we identified after screening only 115 peptides two VV-specific immunogenic epitopes that mediated protective immunity against VV. An immunodominant epitope, VV-e7r 130 , did not generate cross-reactive T-cell responses to LCMV, and a subdominant epitope, VV-a11r 198 , did generate cross-reactive responses to LCMV. Infection with VV induced strong epitope-specific responses which were stable into long-term memory and peaked at the time virus was cleared, consistent with CD8 T cells assisting in the control of VV. Two different approaches, direct adoptive transfer of VV-e7r-specific CD8 T cells and prior immunization with a VV-e7r-expressing ubiquitinated minigene, demonstrated that memory CD8 T cells alone could play a significant role in protective immunity against VV. These studies suggest that exploiting cross-reactive responses between viruses may be a useful tool to complement existing technology in predicting immunogenic epitopes to large viruses, such as VV, leading to a better understanding of the role CD8 T cells play during these viral infections.

Vaccination and heterologous immunity: educating the immune system

“…LCMV and VACV share a complex matrix of CD8 T cell crossreactivity, which has been defined and studied molecularly. 28,52,57 Herein, adoptive transfer studies showed that T cell private specificity of crossreactive memory responses plays a major role in the protection and immunopathology. 32,33 The IAV+LCMV respiratory infection mouse model is noteworthy in that there are both higher titers of LCMV and much greater lung pathology in mice previously infected with IAV, both detrimental effects of heterologous immunity.…”

“…40,47 Clear networks of crossreactive epitopes and patterns of beneficial or detrimental heterologous immunity have been defined in specific virus sequences in mouse models (Supplementary Figure 1). [24][25][26][27][28][29][30][31][32][33][34][48][49][50][51][52][53] For example, in the C57BL/6 mouse (H2 b ), CD8 T cell crossreactive epitopes have been defined between LCMV and Pichinde virus (PICV), LCMV and vaccinia virus (VACV), LCMV and murine cytomegalovirus (MCMV), LCMV and IAV, IAV and MCMV, and PICV and VACV, and complex networks of mouse or human T cell crossreactivity can exist between two viruses. 23,24,27,28,34,[54][55][56] Furthermore, structural studies on crossreactivity between LCMV and VACV epitopes can pinpoint the target of crossreactivity and render the OVA SIINFEKL epitope crossreactive with LCMV by an amino acid substitution.…”

Bi-specific MHC Heterodimers for Characterization of Cross-reactive T Cells*

“…BL/6 mice were infected intraperitoneally with a non-lethal dose of 5 ϫ 10 4 plaque-forming units of LCMV as previously described (25). Mice were considered immune at greater than 6 weeks after infection (9). Splenocytes from LCMV immune mice were co-cultured with mouse RMA cells that were pulsed with 1 M GP34 peptide, washed, and then ␥-irradiated (3000 rads) as previously described (9).…”

“…Mice were considered immune at greater than 6 weeks after infection (9). Splenocytes from LCMV immune mice were co-cultured with mouse RMA cells that were pulsed with 1 M GP34 peptide, washed, and then ␥-irradiated (3000 rads) as previously described (9). RMA is a K b -positive, Rauscher virus-induced, T-lymphoma cell line of BL/6 origin.…”

“…T cell cross-reactivity has been observed in many systems (3)(4)(5)(6) and the structural basis for the phenomenon is beginning to be clarified (7,8). T cell cross-reactivity appears to provide a molecular basis for T cell heterologous immunity, in which exposure to one pathogen provides protection against another (9). For example, prior infection by lymphocytic choriomeningitis virus (LCMV) protects mice from a lethal dose of vaccinia virus (VV), with LCMV immune mice showing alterations in their T cell response to VV infection due to LCMV-specific T cells cross-reacting with VV (10,11).…”