Doctoral Defense in Medical Sciences – Vaka Kristín Sigurjónsdóttir

Tuesday, 18 November 2025 – 13:00, Ceremonial Hall (Hátíðasalur), University of Iceland

Vaka Kristín Sigurjónsdóttir will defend her doctoral thesis in Medical Sciences at the Faculty of Medicine, University of Iceland.

The thesis is entitled:
Biomarkers in Pediatric Kidney Transplantation: Towards Personalized Immunosuppression and Improved Graft Survival
(Árangur nýraígræðslna hjá börnum: lífmerki og áhættumat til ákvörðunar ónæmisbælandi meðferðar)

Opponents:

Dr. Vasilis Kosmoliaptsis, Professor at the University of Cambridge and Transplant Surgeon at Addenbrooke’s Hospital, Cambridge

Dr. Jean-Luc Taupin, Professor at Paris Diderot University and Saint-Louis Hospital, Paris

Supervisor: Professor Runólfur Pálsson, Faculty of Medicine, University of Iceland
Co-supervisors: Professor Paul Grimm, Professor Abanti Chaudhuri, and Associate Professor Bing Melody Zhang, all at Stanford University

The ceremony will be chaired by Professor Þórarinn Guðjónsson and will take place in the Ceremonial Hall of the University of Iceland (Hátíðasalur) at 13:00.

Abstract
Kidney transplantation is the preferred treatment for children with end-stage kidney disease and has repeatedly been shown to improve both survival and quality of life compared with dialysis. Despite this, long-term outcomes remain below expectations. The aim of the study was to identify biomarkers that could help assess immune risk and guide individualized immunosuppression in pediatric kidney transplant recipients. The study was based on two pediatric patient cohorts: one from Stanford University (2004–2018) and the other from the Miami Transplant Institute (2022–2023).

The main focus was on immune response after transplantation:
1) variability in tacrolimus drug levels and its association with antibody formation and adherence; 2) the impact of newly formed donor-specific antibodies (C1q-positive) on graft loss; 3) HLA-DQαβ heterodimer mismatch; and 4) dosing strategies of rabbit antithymocyte globulin (rATG) for induction therapy.
Children with high tacrolimus variability or C1q-positive donor-specific antibodies were at increased risk of graft loss, while HLA-DQα05 mismatch doubled the likelihood of antibody formation. Low dose rATG was found to be safe and effective in children at low immunological risk.

This study introduces a biomarker-guided model for individualized immunosuppression in pediatric kidney transplantation. The model is built on early detection of immune risk through serial biomarkers, enabling intervention before clinical injury occurs. This approach shifts monitoring from reactive to preventive and allows immunosuppressive care to be tailored to the specific needs of each child. The ultimate goal is to improve long-term outcomes, prolong graft survival, and minimize complications associated with both over- and under-immunosuppression.

About the Doctoral Candidate
Vaka Kristín Sigurjónsdóttir was born in 1984. She graduated with a Cand. Med. degree in Medicine from the University of Iceland in 2012.

In 2013, she moved to the United States for postgraduate training, completing a residency in Pediatrics at Connecticut Children’s Medical Center and the University of Connecticut in 2016. She then completed a fellowship in Pediatric Nephrology at Lucile Packard Children’s Hospital and Stanford University in 2019.

Since 2021, Vaka has served as an Assistant Professor and Pediatric Nephrologist at the University of Miami, focusing on pediatric transplant medicine. She has also been a researcher at Stanford University since 2019, conducting studies in pediatric kidney disease and transplantation.

Vaka began her doctoral studies at the University of Iceland in 2019, and her PhD research has been carried out alongside her clinical and academic work abroad.