Evaluating Humoral Immune Responses Against HLA and Cytomegalovirus in Human Lung Transplantation

In the past 30 years, the global prevalence of chronic respiratory diseases has increased by 40%. Importantly, lung transplantation remains the only definitive treatment for patients with advanced lung disease. Despite the rapidly growing need for lung transplantation, lung transplant recipients have by far the worst survival rates among all solid organ transplant types, with a current median survival of only 6 years post transplantation. Chronic lung allograft dysfunction (CLAD) is the leading cause of limited long-term survival of lung transplant recipients, affecting approximately 50% of patients within 5 years post-transplantation. Previous studies have identified humoral alloimmune responses against mismatched donor HLA and cytomegalovirus (CMV) infection as primary independent risk factors for chronic deterioration of the transplanted allograft and the fatal diagnosis of CLAD. This dissertation is comprised of work that aims to address critical gaps in knowledge in the fields of transplant immunology and infectious disease. The first component focuses on CMV-specific humoral immunity in naturally infected healthy blood donors (Chapter 2) and in CMV seropositive lung transplant recipients (Chapter 3). The second area of study focuses on humoral alloimmune responses and current methods used to evaluate and characterize donor HLA-specific alloantibodies (Chapter 4), as well as factors contributing to HLA-DQ immunogenicity (Chapter 5). These projects utilized clinical data and longitudinally collected human plasma samples from the completed multicenter Clinical Trials in Organ Transplantation (CTOT)-20 and CTOT-22 consortium studies. The findings from Chapter 2 contribute to our knowledge of naturally acquired immunity against CMV, which informs strategies for antibody-based therapeutics to help treat CMV infection as well as CMV vaccine development. The results from Chapter 3 indicate that CMV-specific antibodies have the potential to be used as novel biomarkers for viremia risk, possibly in combination with other known risk factors for viremia including CMV-specific T cell responses. These tools may help inform antiviral treatment duration in clinical practice. Chapter 4 of this dissertation represents the first in-depth technical comparison across traditional and modified single antigen bead Luminex assays using IgG enriched sera for donor-HLA specific post-transplant monitoring. These findings may be useful for clinical workflows to help improve efficiency and cost by stratifying patient samples that may benefit from additional testing in modified assays. Finally, Chapter 5 of this dissertation examines the specificity and timing of donor HLA-specific antibodies (DSA), as well as other risk factors for DSA development. In this project, we detail novel strategies for calculating HLA-DQ mismatch by accounting for trans-encoded DQ heterodimer formation. The results from this study also reveal elevated risk for developing DSA among patients with high-risk epitope mismatches and suggest that different organs may require different HLA mismatch calculation strategies. Overall, the results from these projects advance our understanding of the human immune response to alloantigens and cytomegalovirus in lung transplantation and push the field forward to help improve patient outcomes.