Dual targeting OX40 and IL-2 receptor enhances antitumor activity through tumor-infiltrating Treg depletion and CD8⁺ T-cell proliferation

The strong regulatory T cell (Treg) inhibitory activity and dysfunctional cytotoxic T lymphocytes (CTLs) represent major barriers to effective antitumor immunity, particularly in late-stage cancer. Multiple anti-OX40 (aOX40) agonistic antibodies have been developed but exhibit limited antitumor efficacy. Interleukin-2 (IL-2) effectivity expands CTLs but has severe side effects. We construct an aOX40-mIL2-Fc bispecific antibody through Fab physical blocking and attenuated IL-2 with Rβ reducing N88D mutation. We also produced aOX40-Fc and IL-2/aOX40-Fc as a comparison using the 293F expression system. Single-cell and flow cytometry were used to analyze the change of T-cell subsets in the tumor microenvironment (TME). Mouse tumor models were used to assess the antitumor efficacy of aOX40-mIL2-Fc by tumor growth and survival, and toxicity by body weight loss, inflammatory cytokine production, and natural killer (NK) cell proliferation in the blood. The tumor-bearing mice were randomly assigned, and the average size was similar among various groups. aOX40-mIL2-Fc bispecific antibody-cytokine exhibited a synergistic therapeutic effect with limited toxicity, outperforming IL-2-Fc or aOX40 alone treatment, and conferring resistance to tumor rechallenge. On cellular mechanisms, aOX40-mIL2-Fc treatment showed great Treg depletion and increased both stem-like and effector functional terminal CD8+ T cells in the TME, while avoiding NK cells expansion in the periphery. Furthermore, this bispecific antibody remarkably improved the anti-programmed death-ligand 1 (PD-L1) therapeutic effect. Our study unveils a novel approach to IL-2 design that addresses several critical shortcomings of existing strategies and elucidates the cellular mechanisms underlying aOX40-mIL2-Fc therapy. Meanwhile, combining aOX40-mIL2-Fc with PD-L1 blockade represents a strategic approach to enhance tumor control and overcome resistance to immune checkpoint blockade therapies synergistically.