aDuke Human Vaccine Institute, Department of Medicine

bDuke Human Vaccine Institute, Departments of Surgery, Immunology, and Molecular Genetics and Microbiology, Duke University School of Medicine, Durham, North Carolina, USA

Correspondence to Kevin O. Saunders, Duke Human Vaccine Institute, Departments of Surgery, Immunology, and Molecular Genetics and Microbiology, Duke University School of Medicine, Durham, NC 27710, USA. Tel: +1 919 684 1503; e-mail: [email protected]