A phase Ib dose escalation study of the OX40 agonist MOXR0916 and the PD-L1 inhibitor atezolizumab in patients with advanced solid tumors.

101Background: OX40 is a co-stimulatory receptor that is transiently expressed by T cells upon antigen recognition. In murine models, OX40 engagement by an agonist anti-OX40 antibody can promote durable tumor regression associated with co-stimulation of effector T cells and reduction of regulatory T cells. This dual mechanism of action is predicted to complement the activity of PD-L1 blockade. MOXR0916 is a humanized effector-competent agonist IgG1 monoclonal antibody (mAb) that targets OX40 and atezolizumab is an engineered humanized IgG1 mAb that targets PD-L1. Methods: A Phase I, open-label, multicenter study was conducted to evaluate the safety and pharmacokinetics (PK) of MOXR0916 and atezolizumab in patients (pts) with locally advanced or metastatic solid tumors. A 3+3 dose-escalation was conducted with a 21-day window to evaluate dose-limiting toxicity (DLT). Escalating doses of MOXR0916 in combination with a fixed 1200 mg dose of atezolizumab were administered every 3 weeks (q3w). An expansion coh...