The field of histocompatibility testing in support of solid-organ transplantation, like all medical science, is evolving at astonishing speed. The rapid pace of development is primarily driven by the increasing number of transplants being performed, and the quick translation of research techniques into clinically applicable assays and methods. The clinical immunogenetics/ human leukocyte antigen (HLA) laboratory at Puget Sound Blood Center is a well-respected and recognized leader in this field, and provides a fertile ground for studying the application of new methods and practices toward improved transplant patient care and clinical outcome. The Warner laboratory is working to enable clinicians to tailor their treatments to ensure the best possible outcome for patients undergoing transplantation.
Areas of Study
Natural Killer T Cells (NKT Cells)
NKT cells are unusual lymphocytes that share characteristics of innate (Natural Killer cells) and adaptive (T-cells) immunity. Upon activation, these cells rapidly secrete numerous cytokines that are capable of polarizing subsequent adaptive immune responses, and exert additional immunomodulatory capacity through direct cytotoxicity of other cells in the immune system, including dendritic cells. NKT cells have been implicated in autoimmune diseases, tumor development and progression, and transplantation tolerance.
NKT Cell Profiles in Renal Transplantation
The aim of this project is to examine the specific characteristics (profile) of NKT cells obtained from renal transplant recipients at different time points pre- and post-transplantation, and compare these profiles to transplant outcome. These profiles include absolute quantitation of NKT cells derived from peripheral blood samples, ex vivo expansion capacity, and cytokine production. Previous studies have reported a strong correlation with NKT cell-derived Th1/Th2 cytokine profiles to progression and disease status in multiple sclerosis patients, and NKT cells are necessary for tolerance induction in murine models of solid-organ transplantation. The working hypothesis is that NKT cell profiles may be used to predict graft outcome, assessed as either tolerance or rejection, and therefore allow tailoring of specific immunosuppression drug regimens. Regardless of the outcome, this study will provide novel data regarding NKT cell profiles in this specific population of patients. This project is being conducted in collaboration with Swedish Medical Center.
NKT Cell Profiles In Blood Product-Transfused Patients
As part of a recently funded SCCOR grant, Dr. Warner's lab will be examining NKT cell profiles (as above) in immunocompetent patients undergoing open-heart surgery. The patients will be split into three cohorts: those receiving standard, leukoreduced, or leukoreduced gamma-irradiated blood products. Because NKT cells appear to play a significant role in antigen presentation and immune regulation, the lab hypothesizes that the NKT cell profiles will differ between patients who become allosensitized as a result of transfusion and those who do not. In addition to allosensitization, the potential role of NKT cells in transfusion-associated immunomodulation will be examined.
Negative Costimulatory Molecules and NKT Cells
Positive costimulation has been demonstrated to play an important role in antigen-specific activation of NKT cells. However, while some studies have shown a role for NKT cells in amplifying immune responses, others have shown a role for NKT cells in negative regulation of immunity. These disparate results may be due to the presence of negative costimulation functions of NKT cells. Therefore, in collaboration with principal investigator Yvette Latchman, Dr. Warner's lab is examining the potential role of the PD-1 pathway in NKT function. If the various inhibitory effects of NKT cells in immunity can be linked to PD-1/PD-L1 interactions, it will provide important targets for therapeutic interventions in tumor immunity, autoimmunity, and transplantation medicine.
Unacceptable Antigen Assignment and Crossmatch Results
Recent advances in microparticle-based flow cytometry assays now allow for the detection and identification of antibodies against single-specificity HLA molecules. This is highly significant for patients who have been sensitized against numerous HLA specificities, because previous assays made it difficult to define every target of the antibody response. By identifying every antibody specificity in any given patient awaiting transplant, we can hypothetically predict crossmatch results with any donor, given the donor's HLA type. This will allow an enormous degree of flexibility and speed in the organ allocation process. We are conducting retrospective and prospective studies to determine the reliability of crossmatch prediction using this new method, with the goal of sharing our experience with other HLA labs throughout this country and the world. This work has the potential to profoundly change the way in which donor organs are allocated, and dramatically improve transplant patient care.
IgM Antibodies and Transplantation
Advances in assay methodology, related to those described above, now allow accurate determination of IgM antibodies directed against HLA molecules. The aim of this project is to define the frequency, specificity, and potential clinical relevance of IgM antibodies in solid-organ transplant recipients.
The Impact of Low-Titer Antibodies on Transplant Outcome
The newer assays for detecting antibodies against HLA are significantly more sensitive than the cell-based crossmatches used for determination of transplant donor/recipient compatibility. However, it is unclear whether antibodies undetectable by cell-based crossmatching are relevant to transplant outcome. Therefore, Dr. Warner's lab is performing a retrospective study in which patients who received renal transplants in 2001 will be tested for the presence of low-titer antibodies directed against mismatched donor HLA. His lab will then compare these results to graft and patient survival.
Dr. Warner's laboratory is also involved in studying the role of alloantibodies in Transfusion-Related Acute Lung Injury (TRALI), lung transplant rejection episodes, and the impact of minor histocompatibility antigens on solid-organ transplantation.