(340b) Engineering a Cytokine/Antibody Fusion Protein for Targeted Expansion of Regulatory T-Cells

Interleukin-2 (IL-2) is a pleiotropic cytokine that mediates key functions in immune homeostasis, particularly those pertaining to the regulation of T cells. IL-2 treatment has been clinically approved to treat cancer and has also proven beneficial for autoimmune disorder therapy and regenerative medicine applications. However, high toxicity, short serum half-life, and lack of specificity limit the current clinical potential of IL-2 treatment. Recent work has shown that complexing IL-2 with anti-IL-2 antibodies can increase efficacy and reduce toxicity of the cytokine by both extending its in vivo half-life and selectively targeting its functions toward particular immune cell subsets. Although this approach is promising, clinical translation of these complexes is complicated by the need for optimization of dosing ratios and by the instability of the complex, as dissociation will lead to toxicity and rapid clearance of the free cytokine.

To overcome challenges in translating anti-cytokine antibody approaches to the clinic, we have developed single-chain IL-2/antibody fusion proteins (known as immunocytokines) that stably and selectively deliver IL-2 to specific immune cell populations. In particular, we leveraged insights from structural biology to engineer a fusion protein that tethers human IL-2 to an anti-IL-2 antibody known as F5111 in order to achieve selective expansion of immunosuppressive regulatory T cells (T_Regs). We further applied crystallographic insights to rationally design a panel of immunocytokine variants with a range of potencies in activating human T_Regs. In vitro and in vivo studies identified the lead molecule, which shows optimal bias toward expanding T_Regs over immune effector cell populations (such as effector T cells and natural killer cells). We are currently testing our lead molecule in mouse models of autoimmune diseases, including colitis and graft-versus-host disease. Our innovative approach presents a translationally relevant and versatile therapy for selective T_Reg expansion, which can be used for a wide range of research and medical applications.