Control of T cell reactivation by regulatory Qa-1-restricted CD8 ⁺ T cells

Administration of attenuated pathogenic T cell clones, a procedure known as T cell vaccination, induces CD8⁺ T cells specific for peptides derived from the Vβ-chain of the TCR presented by the MHC class Ib molecule, Qa-1 expressed on the vaccine cells. These regulatory CD8⁺ T cells have the capacity to control the activation of endogenous T cells expressing the same TCR Vβ-chain as the vaccinating cells. We hypothesized that vaccination with NKT cells could also induce Qa-1-restricted CD8 ⁺ T cells that would control NKT cell activation. We tested this hypothesis in a murine model of Con A-induced hepatitis that is induced by NKT cells. Vaccination with NKT cells effectively induced protective Qa-1-restricted CD8⁺ T cells that prevented hepatitis. Surprisingly, upon vaccination with T cells expressing Vβ-chains irrelevant to NKT cells, we discovered that the specificity of vaccine-induced Qa-1-restricted CD8 ⁺ T cells was not limited to the Vβ-chain of the vaccinating cells. We further show that these regulatory Qa-1-restricted CD8⁺ T cells arise spontaneously upon polyclonal activation of T cells in the absence of deliberate T cell vaccination. These experiments provide new insight into a CD8⁺ T cell compartment that regulates the immediate reactivation of conventional T cells and NKT cells.