The goal of this observational study is to investigate the development of vulvovaginal graft-versus-host- disease (GVHD), an under-reported and under-recognized manifestation of chronic GVHD. This study aims to characterize the vaginal microbiome in participants undergoing allogeneic hematopoietic cell transplantation (HCT). The main questions it aims to answer are: * Is the vaginal microbiome altered during allogeneic HCT? * What changes may help researchers understand the development of vulvovaginal GVHD? Participants will be asked to undergo an assessment of vulvovaginal symptoms through a vulvovaginal symptom questionnaire once pre-transplant, 6 months post-transplant, and twelve12 months post- transplant. Participants will also be asked to undergo a vaginal microbiome (collection of bacteria, fungi, and viruses that live on our bodies) evaluation through a vaginal exam performed by a gynecologist with collection of vaginal samples once pre-transplant and again six months post-treatment and twelve months post-transplant. If a participant develops symptoms of vulvovaginal GVHD at any point in time during the post-transplant follow up, the participant may partake in additional vaginal exams to diagnose GVHD at the time of symptom onset.