1. Baxter Laboratory in Stem Cell Biology, Department of Microbiology and Immunology, Stanford University, Stanford, CA 94305, USA.
2. Department of Pathology, Stanford University, Stanford, CA 94305, USA.
3. Program in Immunology, Stanford University, Stanford, CA 94305, USA.
4. Department of Obstetrics and Gynecology, Division of Gynecologic Oncology, Stanford University, Stanford, CA 94305, USA.