Targeting the epitope spreader Pep19 by naïve human CD45RA regulatory T cells dictates a distinct suppressive T cell fate in a novel form of immunotherapy.

PURPOSE

Beyond the limited scope of non-specific polyclonal regulatory T cell (Treg)-based immunotherapy, which depends largely on serendipity, the present study explored a target Treg subset appropriate for the delivery of a novel epitope spreader Pep19 antigen as part of a sophisticated form of immunotherapy with defined antigen specificity that induces immune tolerance.

METHODS

Human polyclonal CD4CD25CD127 Tregs (127-Tregs) and naïve CD4CD25CD45RA Tregs (45RA-Tregs) were isolated and were stimulated with target peptide 19 (Pep19)-pulsed dendritic cells in a tolerogenic milieu followed by expansion. Low-dose interleukin-2 (IL-2) and rapamycin were added to selectively exclude the outgrowth of contaminating effector T cells (Teffs). The following parameters were investigated in the expanded antigen-specific Tregs: the distinct expression of the immunosuppressive Treg marker Foxp3, epigenetic stability (demethylation in the Treg-specific demethylated region), the suppression of Teffs, expression of the homing receptors CD62L/CCR7, and CD95L-mediated apoptosis. The expanded Tregs were adoptively transferred into an NOD/scid/IL-2Rγ mouse model of collagen-induced arthritis.

RESULTS

Epitope-spreader Pep19 targeting by 45RA-Tregs led to an outstanding suppressive T cell fate characterized by robust expansion, the salient expression of Foxp3, high epigenetic stability, enhanced T cell suppression, modest expression of CD62L/CCR7, and higher resistance to CD95L-mediated apoptosis. After adoptive transfer, the distinct fate of these T cells demonstrated a potent immunotherapeutic capability, as indicated by the complete elimination of footpad swelling, prolonged survival, minimal histopathological changes, and preferential localization of CD4CD25 Tregs at the articular joints in a mechanistic and orchestrated way.

CONCLUSIONS

We propose human naïve CD4CD25CD45RA Tregs and the epitope spreader Pep19 as cellular and molecular targets for a novel antigen-specific Treg-based vaccination against collagen-induced arthritis.