BackgroundInterleukin-2 (IL-2) is a driver of T and NK cell proliferation and activation, and has produced remarkable clinical efficacy in a few cancer patients. However, its clinical use is limited by its narrow therapeutic index, and potentially by its preferential stimulation of immune suppressing Treg cells. TNRX-257, a novel multi-specific LAG3 antagonist with unique LAG3-conditional partial agonism of the IL2Rγ/β receptors, was developed using Tentarix’s propriety Tentacles™ platform, which is based on fully human, stabilized antibody VH domains. LAG3 expression is restricted to antigen-experienced and tumor-reactive immune cells with little expression on peripheral PBMC or immune cells in normal tissues. Thus, TNRX-257 is anticipated to drive the proliferation of this tumor-antigen positive pool of cells, while minimizing the dose limiting toxicity seen in the pre-clinical models and human clinical trials, as well as the bias towards Treg proliferation seen with WT IL-2.MethodsTNRX-257 was assessed for the affinity for human and cynomolgus LAG3, IL2Rγ and IL2Rβ affinities by Bio-Layer Interferometry, and by cytometry for binding and pSTAT5 induction on CD3/CD28 activated human and cynomolgus monkey PBMCs. To determine the pharmacokinetics and pharmacodynamics of TNRX-257, the molecule was dosed intravenously at 2 dose levels, 2.5mg/kg or 9mg/kg, to 2 cynomolgus monkeys each, and blood was harvested at multiple timepoints over 14 days for analysis. Pharmacokinetics was determined by ELISA, cytokine release by MSD assays, and Ki67 positivity of NK and T cells by cytometry.ResultsTNRX-257 was shown to have equivalent affinities for human and cynomolgus LAG3, IL2Rγ, IL2Rβ. The bioactivity of TNRX-257 on cynomolgus monkey PBMCs is highly similar to its human responses, retaining its unique IL2Rγ/β partial agonism and full antagonist activity for LAG3. At both dose levels, TNRX-257 was well tolerated and blood levels remained above the minimal concentration required for IL2Rγ/β agonism throughout the study period. TNRX-257 bioactivity was seen at both day 5 and day 7 post-dosing, as increases in the percentage of Ki67 positive NK cells, CD4 and CD8 T cells over the pre-dose level with the higher dose.ConclusionsThese data show that TNRX-257 has pharmacokinetics, bioactivity and a unique safety profile that support its clinical development for treating multiple cancer indications.Ethics ApprovalThis study was approved by Labcorp institution’s IACUC Board; study number 8486120