Enhanced affinity for the IL-2 receptor β subunit potently increases antitumor efficacy of IL-2 across various tumor models by reshaping the tumor microenvironment

The main limitations of cancer treatment with high doses of recombinant interleukin 2 (IL-2) are high toxicity and the undesired expansion of regulatory T cells. The generation of IL-2 mutated variants (muteins) with changes in the affinity for different chains of the IL-2 receptor (IL-2R) allows selective stimulation of effector cells while overcoming its toxicity. As increasing the IL-2 affinity for the IL-2R beta chain leads to better antitumor effect, we generated a group of these muteins using phage display technology, in a previous work. Recombinant Fc-fusion proteins, including these variants, resulted in improved developability properties and better in vivo effect than variants containing the IL-2 (IL-2Fc). Here, we assessed one such improved mutein, named superbeta 834 (SB834Fc), and performed a comprehensive characterization of its properties. This mutein showed a stronger antitumor effect than IL-2Fc in 5 murine tumor models: 3LL-D122, B16F10, CT26, MC38, and 4T1 at very low doses. Different from other IL-2 variants, SB834Fc, as single therapy, shows antitumor effect in a therapeutic injection scheme. This antitumor effect was coincident with strong stimulation of effector T cells in the spleen and in the tumor microenvironment, far above that observed with IL-2Fc, despite maintaining the same level of Treg stimulation. Additionally, induction of proliferation was demonstrated in CD8+ T cells isolated from human healthy donors, highlighting its translational value. These results support the SB834Fc fusion protein as a suitable candidate to develop a new cancer immunotherapy based in IL-2.