Donor-recipient human leukocyte antigen A mismatching is associated with hepatic artery thrombosis, sepsis, graft loss, and reduced survival after liver transplant.

Human leukocyte antigen (HLA) matching is not routinely performed for liver transplantation as there is no consistent evidence of benefit; however, the impact of HLA mismatching remains uncertain. We explored the effect of class I and II HLA mismatching on graft failure and mortality. A total of 1042 liver transplants performed at a single center between 1999 and 2016 with available HLA typing data were included. The median follow-up period was 9.38 years (interquartile range 4.9-14) and 350/1042 (33.6%) transplants resulted in graft loss and 280/1042 (26.9%) in death. Graft loss and mortality were not associated with the overall number of mismatches at HLA-A, HLA-B, HLA-C, HLA-DR, and HLA-DQ loci. However, graft failure and mortality were both increased in HLA mismatching on graft failure and mortality the presence of one (p = 0.004 and p = 0.01, respectively) and two (p = 0.01 and p = 0.04, respectively) HLA-A mismatches. Elevated hazard ratios for graft failure and death were observed with HLA-A mismatches in univariate and multivariate Cox proportional hazard models. Excess graft loss with HLA-A mismatch (138/940 [14.7%] mismatched compared with 6/102 [5.9%] matched transplants) occurred within the first year following transplantation (odds ratio 2.75; p = 0.02). Strikingly, transplants performed at a single all grafts lost due to hepatic artery thrombosis were in HLA-A-mismatched transplants (31/940 vs. 0/102), as were those lost due to sepsis (35/940 vs. 0/102). In conclusion, HLA-A mismatching was associated with increased graft loss and mortality. The poorer outcome for the HLA-mismatched group was due to hepatic artery thrombosis and sepsis, and these complications occurred exclusively with HLA-A-mismatched transplants. These data suggest that HLA-A mismatching is important for outcomes following liver transplant. Therefore, knowledge of HLA-A matching status may potentially allow for enhanced surveillance, clinical interventions in high-risk transplants or stratified HLA-A matching in high-risk recipients.

Author Correction: TMEM16F activation by Ca2+ triggers plasma membrane expansion and directs PD-1 trafficking.

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TMEM16F activation by Ca2+ triggers plasma membrane expansion and directs PD-1 trafficking.

TMEM16F is a Ca2+ -gated ion channel that is required for Ca2+ -activated phosphatidylserine exposure on the surface of many eukaryotic cells. TMEM16F is widely expressed and has roles in platelet activation during blood clotting, bone formation and T cell activation. By combining microscopy and patch clamp recording we demonstrate that activation of TMEM16F by Ca2+ ionophores in Jurkat T cells triggers large-scale surface membrane expansion in parallel with phospholipid scrambling. With continued ionophore application,TMEM16F-expressing cells then undergo extensive shedding of ectosomes. The T cell co-receptor PD-1 is selectively incorporated into ectosomes. This selectivity depends on its transmembrane sequence. Surprisingly, cells lacking TMEM16F not only fail to expand surface membrane in response to elevated cytoplasmic Ca2+, but instead undergo rapid massive endocytosis with PD-1 internalisation. These results establish a new role for TMEM16F as a regulator of Ca2+ activated membrane trafficking.

Immune modulation by genetic modification of dendritic cells with lentiviral vectors.

Our work over the past eight years has focused on the use of HIV-1 lentiviral vectors (lentivectors) for the genetic modification of dendritic cells (DCs) to control their functions in immune modulation. DCs are key professional antigen presenting cells which regulate the activity of most effector immune cells, including T, B and NK cells. Their genetic modification provides the means for the development of targeted therapies towards cancer and autoimmune disease. We have been modulating with lentivectors the activity of intracellular signalling pathways and co-stimulation during antigen presentation to T cells, to fine-tune the type and strength of the immune response. In the course of our research, we have found unexpected results such as the surprising immunosuppressive role of anti-viral signalling pathways, and the close link between negative co-stimulation in the immunological synapse and T cell receptor trafficking. Here we review our major findings and put them into context with other published work.

PD-L1 co-stimulation, ligand-induced TCR down-modulation and anti-tumor immunotherapy.

PD-1 engagement on the surface of effector T cells strongly suppresses their cytotoxic function, which constitutes a major obstacle for T cell-mediated anti-tumor activities. Surprisingly, PD-1 is strongly upregulated in T cells, engaging its ligand PD-L1 during antigen presentation. However, our recent published data may provide an explanation for this apparent contradiction.

PD-L1/PD-1 Co-Stimulation, a Brake for T cell Activation and a T cell Differentiation Signal.

For T cell activation, three signals have to be provided from the antigen presenting cell; Signal 1 (antigen recognition), signal 2 (co-stimulation) and signal 3 (cytokine priming). Blocking negative co-stimulation during antigen presentation to T cells is becoming a promising therapeutic strategy to enhance cancer immunotherapy. Here we will focus on interference with PD-1/PD-L1 negative co-stimulation during antigen presentation to T cells as a therapeutic approach. We will discuss the potential mechanisms and the therapeutic consequences by which interference/inhibition with this interaction results in anti-tumour immunity. Particularly, we will comment on whether blocking negative co-stimulation provides differentiation signals to T cells undergoing antigen presentation. A major dogma in immunology states that T cell differentiation signals are given by cytokines and chemokines (signal 3) rather than co-stimulation (signal 2). We will discuss whether this is the case when blocking PD-L1/PD-1 negative co-stimulation.

On the Mechanism of T cell receptor down-modulation and its physiological significance.

Effective, long-lasting immune responses largely depend upon T cell reponses. Antigen-specific T lymphocytes are activated and differentiate into effector T cells after antigen presentation by professional antigen presenting cells (APCs). However, T cell responses are tightly regulated to prevent T cell hyperactivation which may end up in autoimmune pathology. One of these regulatory mechanisms is ligand-induced TCR down-modulation, a process by which TCRs are removed from the T cell surface shortly after engagement with their cognate antigenic peptide associated to MHC molecules on the APC. TCR down-modulation is a complicated process. Here we briefly describe the three main models that attempt to clarify this mechanism in the context of T cell activation and function.

PD-L1 co-stimulation contributes to ligand-induced T cell receptor down-modulation on CD8+ T cells.

T cell receptor (TCR) down-modulation after antigen presentation is a fundamental process that regulates TCR signal transduction. Current understanding of this process is that intrinsic TCR/CD28 signal transduction leads to TCR down-modulation. Here, we show that the interaction between programmed cell death 1 ligand 1 (PD-L1) on dendritic cells (DCs) and programmed death 1 (PD-1) on CD8 T cells contributes to ligand-induced TCR down-modulation. We provide evidence that this occurs via Casitas B-lymphoma (Cbl)-b E3 ubiquitin ligase up-regulation in CD8 T cells. Interference with PD-L1/PD-1 signalling markedly inhibits TCR down-modulation leading to hyper-activated, proliferative CD8 T cells as assessed in vitro and in vivo in an arthritis model. PD-L1 silencing accelerates anti-tumour immune responses and strongly potentiates DC anti-tumour capacities, when combined with mitogen-activated kinase (MAPK) modulators that promote DC activation.