Background: AU-007 is a computationally designed mAb that binds to IL-2 on its CD25 binding epitope. AU-007 bound IL-2 (A/IL-2) cannot bind to trimeric (CD25, CD122, CD132) IL-2 receptors (IL-2R) on Tregs, vascular endothelium, or eosinophils, but IL-2’s binding to dimeric IL-2Rs (CD122, CD132) on T effector and NK cells is unhindered. AU-007 thus redirects endogenous or exogenous IL-2 (aldesleukin) towards T effector and NK cell activation, while diminishing immunosuppressive Treg activation and vascular leak. Unique in the IL-2 field, AU-007 can redirect endogenous IL-2 generated from A/IL-2 driven T effector cell expansion in vivo, converting a Treg-mediated autoinhibitory loop into an immune stimulating loop. A/IL-2 is expected to prolong the 85-minute T1/2 of IL-2, allowing endogenous IL-2 (as A/IL-2) or low dose aldesleukin to initiate an anti-tumor response. Methods: This first-in-human Phase 1 study consists of 3 dose escalation arms, each starting with one 1+2 cohort followed by 3+3 cohorts. Arm 1A evaluates escalating doses of monotherapy AU-007 (intravenous, every 2 weeks [Q2W]). Arm 1B evaluates AU-007 (Q2W) plus 1 loading dose of subcutaneous, low dose aldesleukin with the 1st AU-007 dose. The AU-007 dose will be fixed with escalating aldesleukin doses in sequential cohorts. Arm 1C evaluates AU-007 plus escalating doses of concomitant subcutaneous, low dose aldesleukin, both Q2W. The dose-limiting toxicity (DLT) evaluation period is the first 28 days of the 1st cycle. Tumor assessments by computed tomography scan occur with each 8-week cycle. The AU-007 and aldesleukin dose and schedule for Phase 2 expansion will be based on safety, efficacy, pharmacokinetics (PK), and pharmacodynamics (PD). Results: As of 01 February 2023, 8 patients have been enrolled into the first 3 Cohorts of Arm 1A (0.5, 1.5, and 4.5 mg/kg AU-007). AU-007 was well tolerated with no DLTs and all treatment-related adverse events were Grade 1. These occurred in 3 patients, 1 at each dose level. The 4th Cohort of Arm 1A (9 mg/kg AU-007) and the 1st Cohort of Arm 1B (4.5 mg/kg AU-007 + 1 aldesleukin dose of 15,000 IU/kg) are now being evaluated. Three of 4 tumor evaluable patients had a best response of stable disease and 2 continue treatment. Two patients discontinued with objective progression and one with clinical progression. Initial PK data (0.5 and 1.5 mg/kg) demonstrate dose proportional AU-007 serum concentrations with typical characteristics of an IgG1 human mAb. All 7 patients with available PD data demonstrate overall decreasing Tregs (% change and absolute) and eosinophils, which both express the trimeric IL-2 receptor. Conclusions: AU-007 monotherapy at doses up to 4.5 mg/kg Q2W is safe and well tolerated, with initial signs of immune modulation consistent with AU-007’s mechanism of action. These findings warrant continued escalation and combination with aldesleukin. Clinical trial information: NCT05267626.