(462a) Engineered Immunocytokines Improve Delivery of IL-2 to Pro-Inflammatory Cells and Promote Anti-Tumor Activity

Interleukin 2 (IL-2) is a powerful cytokine that plays a pivotal role in the development, maintenance, activation and proliferation of T cells. Upon encountering their cognate antigen, effector T cells require IL-2 stimulation for effective activation and proliferation. T regulatory cells (T_regs)—which are responsible for suppressing inflammatory responses and maintaining tolerance to self—are even more sensitive to IL-2 levels than effector T cells. In tumors, this increased sensitivity to IL-2 allows T_regs to deplete the IL-2 levels within the tumor, which can prevent potentially tumor-reactive effector T cells from mounting an inflammatory immune response to clear the malignant cells.

Because IL-2 plays such an essential role in stimulating both pro- and anti-inflammatory responses, this cytokine has great potential for immune disease treatment. However, on its own it has an incredibly rapid clearance, and its indiscriminate activity on both effector and regulatory T cells limits its therapeutic performance.

To address these shortcomings, we have engineered an IL-2 specific antibody that biases cytokine activity toward immunostimulatory functions. By modulating the interactions between IL-2 and its receptor, the antibody can eliminate the sensitivity advantage of T_regs. Moreover, complexing IL-2 with an antibody simultaneously prolongs cytokine half-life. Previous work using an anti-mouse IL-2 antibody demonstrated that IL-2/antibody complexes stimulated potent preferential expansion of effector T cells compared to T_regs, leading to inhibition of tumor growth in vivo.

We first engineered an IL-2-specific antibody—602—to more effectively bias the interaction with the IL-2 receptor using a yeast surface display. We then tethered the improved variant, F10, and the parental 602 to IL-2 with an optimized Gly₄Ser linker that fused the C-terminus of IL-2 to the N-terminus of the antibody light chain. This tethered IL-2-antibody molecule, or immunocytokine (IC), will reduce potential off-target effects by preventing IL-2 from dissociating away from the antibody, and as a single molecule therapeutic, is streamlined for translation. We have shown that both the parental 602 IC and the engineered F10 IC vastly improve that bias towards stimulating effector T cells in primary human mononuclear cells, as compared to IL-2, the complex of IL-2 and 602 antibody, and a control IC in which an irrelevant antibody was used, and there is no intramolecular binding (Fig. a-e). The engineered F10 IC shows some additional improvement in bias. The IC also potently drives expansion of effector immune cells in vivo, resulting in increased therapeutic efficacy in the eradication of tumors.