Christine Wardell’s bio
Christine Wardell is currently a Ph.D. candidate in Dr. Megan Levings’ lab at the BC Children’s Hospital Research Institute in Vancouver, BC. Her work focuses on detecting alloreactive T cells following transplantation and developing regulatory T cell therapies to prevent transplant rejection.
The trogocytosis assay: A blood-based assay to detect alloreactive immune cells
Christine Wardell, Caroline Lamarche, Vivian Fung, Paul Orban, Tom Blydt-Hansen & Megan Levings
Following receipt of a donor kidney, transplant recipients are maintained on immunosuppressive drugs to dampen their donor-reactive immune response, which would otherwise destroy the kidney. However, these drugs also suppress healthy immune responses against pathogens and cancer. Managing physicians continually adjust a patients’ immunosuppressant regimen to minimize infection risk while preserving graft health. These adjustments are made based on results from graft biopsies, which are invasive and infrequent, limiting physicians’ abilities to optimize immunosuppression. Our goal is to create a blood-based assay that detects immune cells that are reactive to donor human leukocyte antigens (HLAs), which are commonly mismatched in transplantation. Our assay is based on the immunological concept of “trogocytosis”, whereby immune cells that detect and bind strongly to target proteins, rip the target protein from the originating cell and re-incorporate it as a part of their own membrane. We hypothesize that donor HLA-reactive immune cells in transplant recipients trogocytose donor HLA, and that the frequency of trogocytosis+ cells negatively correlates with transplant health. The trogocytosis assay co-cultures recipient blood cells with K562s that express donor HLAs fused to a fluorescent protein; donor HLA-reactive immune cells trogocytose the fluorescent donor HLA, making them enumerable by flow cytometry. We have optimized the parameters of this assay based on an HLA-A2-reactive CD8+ T cell clone. HLA trogocytosis correlates well with conventional activation-induced markers (4-1BB, CD25 and CD69). Trogocytosis efficiency is dependent on K562:T cell ratio, plating density, and peaks at 24 hours of co-culture. The assay has an approximate sensitivity of detecting 1 donor-reactive T cell in 500 T cells. We are currently testing the trogocytosis assay on cryopreserved blood from HLA-A2- recipients of HLA-A2+ kidney transplants and correlating outcomes with biopsy results. The trogocytosis assay may serve as a reproducible and reliable way to assess transplant health using recipient blood.