Research
Our research team investigates the response to alloantigen and viruses with a focus on human immunology. The lab utilizes state of the art technologies to examine the underlying mechanisms of the immune response following transplantation including viral complications.
Our primary goal is to expand knowledge to develop diagnostics and therapeutics that improve outcomes following solid organ transplantation.
NK cell reactivity to allo- and viral antigens
We developed a novel live cell imaging assay to specifically examine how NK cells interact with target cells. NK cells form different types of synapses that result in distinct functional outcomes: cytotoxic, inhibitory, and regulatory. We examined how NKp46, a major NK cell activating receptor that is involved in the elimination of target cells, functions in NK immunological synapse formation and demonstrated that NKp46 signaling directly regulates the NK lytic immune synapse.
NK cells are critical in the early immune response to EBV but their role in controlling expansion of infected B cells is not understood. Our studies using computational cellular deconvolution approaches of public gene array data sets indicate that NK cells are increased in EBV+ PTLD tumor lesions, and in vitro studies demonstrate that NKG2A+ is expressed on NK cells which recognize and kill autologous EBV-infected B cells. Further, the non-classical MHC molecule, HLA-E, the ligand for NKG2A, is expressed on EBV+ B cell lymphoma lines and peptides from EBV latent cycle proteins can bind to HLA-E. NKG2A+ NK cells recognize and respond to EBV+ B cells and may function as a checkpoint molecule. Targeting the NKG2A/HLA-E interaction can potentiate the ability of NKG2A+ immune cells to mediate cytotoxicity against EBV+ B cell lymphomas.
Exosomes and microRNAs in immune responses
We have demonstrated that exosomes contain and transfer microRNAs (miRs) between cells that allow for local and distant intercellular communication. We have recently demonstrated that a miRNA, miR-181, when expressed by hepatic plasmacytoid dendritic cells p(DC), significantly prolongs allograft survival. Current studies focus on understanding the mechanism of how miR-181 pDC alters the immune system to promote allograft survival.
We are now determining if graft-derived exosomes initiate alloimmune responses. RNA-Seq will determine the miRNome of sorted graft and host exosomes from patient samples establishing the relationship between exosome cargo, donor HLA, immune responses, and allograft status after transplantation.
Pathogenesis of B Cell lymphomas
Previous work in our lab has shown that EBV infection of B lymphocytes reshapes the host cell microRNA (miRNA) landscape and coopts a variety of important cellular signaling pathways including PI3K/Akt/mTOR and ERK MAPK. Many of these changes are induced by the EBV protein, latent membrane protein 1 (LMP1) and play a significant role in B cell transformation, immune evasion and viral persistence. Ongoing studies are directed towards exploiting this knowledge to develop novel, rationally designed diagnostics and therapeutics for EBV+ B cell lymphomas. Current approaches include delivery of small molecule inhibitors and miRNA to B cell lymphomas that target the PI3K/Akt/mTOR pathway while preserving allograft survival using pre-clinical animal models of cancer and transplantation. Other ongoing studies examine the potential of LMP1 variants as biomarkers to determine individuals at risk of developing EBV+ B cell lymphomas and as determinants of oncogenesis. We continue to investigate mechanisms by which EBV modulates the host immune response to promote lymphomagenesis.
CyTOF identifies novel cell populations that define immune status
Liver allografts are well tolerated and indeed, some liver allograft recipients retain stable graft function in the absence of immunosuppression. A major gap in the field is identifying those patients who would retain healthy graft function without immunosuppression. To define an immune signature of recipients of liver allografts who are operationally tolerant, we utilized mass cytometry (CyTOF) to comprehensively characterize the immune system of recipients of liver allografts with stable graft function in the absence of immunosuppression, in comparison to age-matched recipients on conventional immunosuppression and healthy donors. Our study identified a T cell population that is significantly increased in operationally tolerant patients as compared to two other groups. This biomarker of operational tolerance may allow identification of transplant recipients who can be successfully removed from immunosuppression and those who require closer monitoring. Currently, CyTOF is being used to identify unique cellular, molecular, and functional changes in the early immune response that are associated with, and predictive of, graft outcomes in experimental models and recipients of solid organ allografts. The development of novel and robust surrogate endpoints of allograft status will be a major advance in the field and lead to more robust diagnostics and therapeutics.
Viral immunity
We have had a long-standing interest in immunity to Epstein Barr virus (EBV), particularly in the setting of transplantation. While EBV infection is ubiquitous, the outcome of infection varies widely, from asymptomatic to aggressive lymphoid and epithelial cancers. We seek to understand what determines whether infection with EBV results in a protective immune response, chronic viral DNAemia, or malignancy. This knowledge has significance with respect to our basic understanding of viral immunity, identification of individuals at risk of EBV-associated disease, and development of vaccines and immunotherapies for EBV. Current approaches to address this topic include utilizing CyTOF to reveal the high-dimensional EBV-specific phenotype and function of T cells and NK cells in individuals that control the virus versus those that do not. Complimentary studies utilize single cell approaches to define EBV- and CMV-specific T cell receptor usage and diversity in transplant recipients. Using whole genome sequencing of EBV we have identified variations in latent cycle immunodominant antigens that are associated with the development of EBV+ B cell lymphomas. We will utilize immunogenomics to determine whether these variations lead to altered host immunity and/or increased viral pathogenesis.
The immune response to solid organ and cellular allografts
Our laboratory has extensive experience with a variety of experimental rodent transplant models (skin, heart, liver and limb) as well as clinical samples to define mechanisms of graft rejection and immune regulation following solid organ transplantation. We have also used embryonic stem cells and induced pluripotent stem cells to generate neural progenitor cells and hepatocyte-like cells and have examined the immune response to stem cell derived allografts. These studies have identified key molecular pathways of allograft rejection involving T cells and NK cells. Ongoing studies are examining the role of specific myeloid subsets in alloactivation and the diversity and specificity of memory B cells and plasmablasts in transplant recipients.