No abstract

Induction of pro-inflammatory T cell immunity is augmented by innate dendritic cell (DC) maturation commonly initiated by Toll-like receptor (TLR) signaling. We demonstrate that ligation of TLR3, 4, and 9 induces murine DC production of complement components and local production of the anaphylatoxin C5a. In vitro, ex vivo, and in vivo analyses show that TLR-induced DC maturation as assessed by surface phenotype, expression profiling by gene array, and functional ability to stimulate T cell responses, requires autocrine C3a- and C5a-receptor (C3ar1/C5ar1) signaling. Studies employing bone marrow chimeric animals and Foxp3-GFP/ERT2-Cre/dTomato fate mapping mice show that TLR-initiated, DC autocrine C3ar1/C5ar1 signaling causes expansion of effector T cells and instability of regulatory T cells and contributes T cell-dependent transplant rejection. Together, our data position immune cell-derived complement production and autocrine/paracrine C3ar1/C5ar1 signaling as crucial intermediary processes that link TLR-stimulation to DC maturation and the subsequent development of effector T cell responses.

Introduction

Purpose of review To summarize the current knowledge regarding mechanisms linking the complement system to transplant injury, highlighting findings reported since 2013. Recent findings Building upon the documentation that complement activation is a pathogenic mediator of post-transplant ischemia-reperfusion (IR) injury, emerging evidence indicates blocking either the classical or lectin pathways attenuates IR injury in animal models. Immune cell-derived and locally activated complement, including intracellular C3 positively modulates allo-reactive T cell activation and expansion, while simultaneously inhibiting regulatory T cell induction and function, together promoting transplant rejection. While alloantibody-initiated complement activation directly injures target cells, complement-dependent signals activate endothelial cells to facilitate T cell dependent inflammation. Complement activation within allografts contributes to progressive chronic injury and fibrosis. Summary The complement cascade, traditionally considered relevant to transplantation only as an effector mechanism of antibody-initiated allograft injury, is now understood to damage the allograft through multiple mechanisms. Complement activation promotes post-transplant IR injury, formation and function of allo-antibody, differentiation and function of alloreactive T cells, and contributes to chronic progressive allograft failure. The recognition that complement impacts transplant injury at many levels provides a foundation for targeting complement as a therapy to prolong transplant survival and improve patient health.

As recent advancements in the chimeric antigen receptor-T cells have revolutionized the way blood cancers are handled, potential benefits from producing off-the-shelf, standardized immune cells entail the need for development of allogeneic immune cell therapy. However, host rejection driven by HLA disparity in adoptively transferred allogeneic T cells remains a key obstacle to the universal donor T cell therapy. To evade donor HLA-mediated immune rejection, we attempted to eliminate T cell’s HLA through the CRISPR/Cas9 gene editing system. First, we screened 60 gRNAs targeting B2M and multiple sets of gRNA each targeting α chains of HLA-II (DPA, DQA and DRA, respectively) using web-based design tools, and identified specific gRNA sequences highly efficient for target deletion without carrying off-target effects. Multiplex genome editing of primary human T cells achieved by the newly discovered gRNAs yielded HLA-I- or HLA-I/II-deficient T cells that were phenotypically unaltered and functionally intact. The overnight mixed lymphocyte reactions demonstrated the HLA-I-negative cells induced decreased production of IFN-γ and TNF-α in alloreactive T cells, and deficiency of HLA-I/II in T cells further dampened the inflammatory responses. Taken together, our approach will provide an efficacious pathway toward the universal donor cell generation by manipulating HLA expression in therapeutic T cells.