Dr. Mary S. Leffell is a Professor of Medicine and, along with Dr. Andrea A. Zachary, directs the Immunogenetics Laboratory of the Johns Hopkins University School of Medicine. Dr. Leffell has a Ph.D. in immunology from the University of North Carolina at Chapel Hill and is a Diplomate of both the American Board of Medical Laboratory Immunology (ABMLI) and the American Board of Histocompatibility and Immunogenetics(ABHI). She has 23 years experience in clinical immunology, histocompatibility and immunogenetics. Previously, she has directed the Immunology Service Laboratory at the Eastern Virginia Medical School and the Histocompatibility and Immunogenetics Laboratories at Norfolk Sentara Hospital and the Medical College of Georgia.

Dr. Leffell is a past president of the American Society for Histocompatibility(ASHI) and Immunogenetics and has served two terms on the Board of Directors of the United Network for Organ Sharing (UNOS). She has chaired the ASHI Accreditation Committee, the ASHI Accreditation Advisory Committee, and the South-Eastern Organ Procurement Foundation (SEOPF) histocompatibility committee. She has served on the National Marrow Donor Program (NMDP) histocompatibility committee, the Regulatory Affairs committee of the American Society for Stem Cell and Bone Marrow Transplantation, the examination committee of the ABHI and the membership committee of the American Society of Transplant Physicians. She is also a member of the International Transplantation Society, the American College of Allergy & Immunology, and the Association of Medical Laboratory Immunologists.

Dr. Leffell has served on the ABMLI and is a current member of the editorial board of Clinical & Diagnostic Immunology. She was the senior editor of the Handbook of Human Immunology and has been the section editor for Transplantation & Immunogenetics for the 5^th and 6^th editions of the Manual of Clinical Laboratory Immunology. In addition to her research articles, Dr. Leffell has authored several chapters and reviews of topics in clinical immunology and histocompatibility. She is a member of the steering committee and project director for the Native American, Alaska Native and Latino/Hispanic ASHI workshops.

Dr. Leffell is one of the founders and has served on the program committee and course faculty for the SEOPF Histocompatibility Specialist course since it was established in 1983. She has been an invited speaker at international, national and regional meetings and educational workshops.