Our Providers

We see patients at St. Louis Children's Hospital and at the St. Louis Children's Specialty Care Clinic.

Primary Physicians


Megan Cooper, MD, PhD
Director, Clinical Immunology
Director, Jeffrey Modell Diagnostic and Research Center for Primary Immunodeficiencies at St. Louis Children’s Hospital

Dr. Cooper received her medical degree and PhD at The Ohio State University in Columbus, Ohio. Her PhD work focused on understanding the biology of a subset of human immune cells known as “natural killer” or NK cells. After medical school, she completed her residency and fellowship at St. Louis Children’s Hospital and Washington University. Dr. Cooper’s laboratory investigates the genetic causes of primary immunodeficiencies. She is the Director of Clinical Immunology and the Jeffrey Modell Center at St. Louis Children’s Hospital. Dr. Cooper sees patients in Immunology and Rheumatology clinics. She is the Primary Investigator of our USIDNET enrolling site and several other immunodeficiency-related protocols.

Jeff Bednarski, MD, PhD
Dr. Bednarski received his medical degree and PhD from the University of Michigan Medical School. His clinical practice focuses on bone marrow transplantation for the treatment of malignant and immunological disorders in children and young adults. Dr. Bednarski is a part of the Primary Immune Deficiency Treatment Consortium and leads efforts at our institution to include our patients in these protocols. Dr. Bednarski also runs an institutional trial for a new transplant regimen for patients with immune deficiencies. His research laboratory focuses on basic mechanisms of B cell development.

Kay Horner, MD
Dr. Horner completed her medical degree and residency in internal medicine and pediatrics at St. Louis University, and her allergy/immunology fellowship at University of Texas Medical Branch in Galveston, Texas. She is board certified in pediatrics, internal medicine, and allergy and clinical immunology. In addition to general immunology, Dr. Horner has a special interest in DiGeorge Syndrome, and leads the Immunology evaluation of patients in a comprehensive DiGeorge syndrome clinic. Dr. Horner has been an integral part of the SCID task force for newborn screening in Illinois and Missouri.

Maleewan Kitcharoensakkul, MD
Dr. Kitcharoensakkul received her medical degree from Siriraj Hospital, Mahidol University, Thailand and completed her pediatric residency and fellowship in allergy, immunology, and pediatric rheumatology at St. Louis Children’s Hospital and Washington University. Dr. Kitcharoensakkul leads a monthly Clinical Immunology seminar that provides education to fellows, residents, and other trainees on primary immunodeficiencies. She is also involved in the SCID newborn screen task force, and represented our state at a meeting in Washington DC.

Pediatric Nurses

Katie Varrone, RN, MSN, CPNP-PC
Katie completed her Master of Science in Nursing at Saint Louis University and received her Pediatric Nurse Practitioner certification through the Pediatric Nursing Certification Board. She specializes in Pediatric Immunology through the Jeffrey Modell Center at St. Louis Children’s Hospital. Katie has a special interest in managing children with Primary Immune Deficiencies on immunoglobulin replacement therapy and is passionate about educating patients and their families regarding their care and treatment.

Beth Ervin, MSN, RN-CPN
Beth has worked in pediatrics for over 13 years. She received her Bachelor’s degree from Chamberlain College of Nursing in 2007 and her Masters of Nursing from Webster University in 2015. Beth is committed to working with patients and families affected by primary immune deficiencies. She enjoys educating patients and their families and making sure they have the guidance and resources they need through diagnosis and treatment.

Michelle Ritter, RN, BSN
Michelle has been a pediatric nurse for over 25 years and has experience in general medicine, hematology/oncology and emergency room nursing. More recently, Michelle has focused her career on research, and has expertise in human studies protocols and is interested in improving opportunities for our patients to participate in research. She obtained her Bachelors in Nursing from Webster University.