Enhancing in vivo antigen-specific Treg cells in murine model as combination therapy of anti-DEC205-OVA and FC-IL-2 Mutein

In mice, immune responses to antigen administered in the absence of adjuvant are typically tolerogenic through the induction of regulatory T cells (Treg) and the deletion/inactivation of conventional T cells (Tconv). Nevertheless, antigen-specific immunotherapy (ASI) approaches in autoimmune and allergic patients may be ineffective or unpredictable due to the heightened and variable activation state of immune cells in humans. Consequently, a method to reliably direct immune responses following ASI toward tolerogenic outcomes is warranted. Here, we present an approach to control immune responses by administering ASI during IL-2-mediated Treg-enrichment. Our “Treg-vaccination protocol” consists of a combination therapy leveraging a new Treg-selective Fc-fused IL-2 mutein (Fc.IL-2m) and OVA protein targeted to DC1 via fusion to anti-DEC205 (anti-DEC205-OVA). A single dose of Fc.IL-2m increases Treg to nearly 50% of CD4 T cells on day 4 post injection.

To enable detection of antigen-specific Treg and Tconv, we employed mice that had received lymph node cells from OT-II TCR transgenic mice, which contain OVA-responsive Treg. Mice harboring OT-II cells received Fc.IL-2m or PBS on day 0 and anti-DEC205-OVA or PBS on day 2. Following 3 weekly cycles of this regimen, OT-II T-cells were enriched via magnetic bead immuno-selection. Administration of PBS (n=5), Fc.IL-2m (n=5), or anti-DEC205-OVA alone (n=5) did not promote enrichment of OT-II-Treg cells. In contrast, the combination therapy (n=5) resulted in a 2 to 3-fold increase in Treg among total OT-II CD4 T cells (p≤0.02).

Our promising data demonstrates that pre-enrichment of Treg with half-life-extended Fc.IL-2m before ASI markedly increases the frequency of antigen-specific Treg. Ongoing studies are addressing the optimal time-point for ASI after Fc.IL-2m treatment, the number of dosing cycles required to reach a maximum antigen-specific Treg frequency, and the durability of enrichment after treatment cessation.