Funding for this research was provided by Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA (MSD). J Xu, Y Mao, N Xu, Y Bai, D Wang, X Chen, X Yin, Y Deng, J Yang, J Zhang, J Tang, Y Huang, J Li, S Luo, H Zheng, W Zhao and X Wu received institutional funding from Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA. M Xu, N Li and Y Mao are employees of MSD (China) Co., Ltd. A Gozman is an employee of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA and stockholders of Merck & Co., Inc., Rahway, NJ, USA. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.