Cutting edge: shift in antigen dependence by an antiviral MHC class Ib-restricted CD8 T cell response during persistent viral infection

Abstract

The requirement for Ag in maintaining memory CD8 T cells often differs between infections that are acutely resolved and those that persist. Using the mouse polyoma virus (PyV) persistent infection model, we recently described a novel CD8 T cell response directed to a PyV peptide presented by Q9, an MHC class Ib molecule. This antiviral Q9-restricted CD8 T cell response is characterized by a 3-mo expansion phase followed by a long-term plateau phase. In this study, we demonstrate that viral Ag is required for this protracted inflation phase but is dispensable for the maintenance of this Q9-restricted CD8 T cell response. Moreover, proliferation by memory T cells, not recruitment of naive PyV-specific T cells, is primarily responsible for Q9-restricted, anti-PyV CD8 T cell inflation. These data reveal a dynamic shift in Ag dependence by an MHC class Ib-restricted memory CD8 T cell response during a persistent viral infection.

FIGURE 1

VP2.139-specific CD8 T cell expansion is associated with persistent viral infection. Percentage of Q9/VP2.139 tetramer⁺ CD8 T cells in the blood of PyV or VV-VP2-infected K^b−/−D^b−/− mice ± SEM over time (n = 3 mice). Data are representative of two independent experiments.

FIGURE 2

De novo priming of VP2.139-specific CD8 T cells during persistent infection. Representative dot plots of lymphocytes isolated from indicated organs of Thy congenic mice 50 days after bone marrow transfer (n = 3–4 mice). Plots are gated on CD8 T cells and values indicate the percentage of donor tetramer⁺ cells of total tetramer⁺ population. Data is representative of two independent experiments.

FIGURE 3

Dynamic phenotype of VP2.139-specific cells over the course of persistent PyV infection. Splenic Q9/VP2.139 tetramer⁺ cells from PyV-infected K^b−/−D^b−/− mice were analyzed for (A) Ki67 or (B) Annexin V and 7-AAD coexpression at 1 mo and 3 mos p.i. A, Plots are gated on CD8⁺ cells and values indicate the percentage Ki67⁺tetramer⁺ cells. B, Plots are gated on tetramer⁺ cells and values indicate the percentage of cells in the indicated quadrant. Splenic D^b/LT359 tetramer⁺ cells from B6 mice at day 8 p.i. were analyzed for Annexin V and propidium iodide (PI) staining as a positive control. Dot plots in (A) and (B) are representative of mice in (C), which indicates the percentage of Ki67⁺ or Annexin V⁺7-AAD⁻ of tetramer⁺ CD8 T cells at the indicated timepoints (n = 5 mice). (D) TCR Vβ expression by splenic CD8 T cells from uninfected K^b−/−D^b−/− mice (left panel) and by Q9/VP2.139 tetramer⁺ CD8 T cells from K^b−/− D^b−/− mice day 35 p.i. (right panel). Each bar pattern represents an individual mouse. Two independent experiments were performed.

FIGURE 4

Inflation, but not survival, of memory VP2.139-specific CD8 T cells is Ag-dependent. A, B cell-depleted spleen cells from wild type PyV (A2 strain)-infected K^b−/−D^b−/−Thy1.1 mice at 1 mos or 3 mos p.i. were transferred to infection-matched K^b−/−D^b−/− Thy1.2 mice (1 mo 1 mo; 3 mo 3 mo) or cells from A2-infected K^b−/−D^b−/− Thy1.1 mice at 3 mo p.i were transferred into A2-infected K^b−/−D^b−/− Thy1.2 mice at 1 mo p.i. (3 mo 3 mo). PBLs were monitored over time and values indicate the percentage of donor Q9/VP2.139 tetramer⁺ CD8 T cells ± SEM normalized for input tetramer⁺ cells at day 4 after transfer (n = 3–6 mice). B, As in (A) except that cells were transferred from A2-infected K^b−/−D^b−/− mice at 1 mo p.i. to Thy congenic K^b−/−D^b−/−mice infected 1 mo previously by either A2 PyV or a VP2.139 epitope^null mutant PyV (A2.H145A). C, Representative CFSE profiles of donor VP2.139-specific CD8 T cell populations at the indicated timepoints after transfer for experiments in (A) and (B). Values indicate the percentage of cells in the marked regions. Two independent experiments were performed.