Abstract
We have identified a set of putative natural T regulatory epitopes (Tregitopes) which, when co-administered with an antigen, cause the expansion of antigen-specific adaptive Tregs in vitro and in vivo. They have the following characteristics:
they bind, in most cases, with high affinity to multiple MHC class II molecules and, when co-administered with antigen, they suppress effector T cell immune responses to the antigen and up-regulate Treg associated cytokines and chemokines.
T cells responding to Tregitopes exhibit a T regulatory phenotype (CD4+/CD25hiFoxP3+). To test whether Tregitopes derived from immunoglobulin (Ig) suppress immune responses to antigen co-administered in vivo, we performed two types of experiments. In the first, we dosed three groups of HLA DR4 mice every other week for six weeks with either
a peptide antigen (pAg) alone, pAg with murine Fc, or pAg with mTregitope289, the murine homolog of the human Tregitope289.
Mice were sacrificed and spleens harvested for assay. While the mice dosed with murine Fc demonstrated a reduced IL-4 ELIspot response to pAg, remarkably, the reduction was even greater in the mice treated with Tregitope. In a second model, C57Bl/6 mice were injected with LPS-stimulated B cells that were pulsed with either
ovalbumin (OVA) alone, mTregitopes 167 and 289 or with OVA together with the two mTregitopes.
One week later, mice were challenged with OVA 323–339 peptide in adjuvant. Two weeks after challenge, draining lymph nodes were harvested and LN cells stimulated with OVA 323–339 for measurement of T-cell proliferation by thymidine incorporation and by IFN-γ secretion by ELIspot. The mice receiving B cells previously pulsed with OVA alone demonstrated a robust IFN-gamma response to OVA re-stimulation. In contrast, the mice receiving B cells previously pulsed with OVA + Tregitopes demonstrated a comparatively reduced response. When sera were assayed for anti-OVA antibodies by ELISA, antibody response to OVA also declined following treatment with B cells co-administered with Tregitope. The mechanism of suppression appears to be due to the induction of antigen-specific adaptive tolerance induction (De Groot AS et al. Activation of natural regulatory T cells by IgG Fc-derived Peptide “Tregitopes” Blood112: in press, 2008).
In Vivo Instruction of Suppressor Commitment in Naive T Cells