Distribution of intrahepatic T, NK and CD3(+)CD56(+)NKT cells alters after liver transplantation: Shift from innate to adaptive immunity?

The role of natural killer T cells in liver transplantation

Natural killer T cells (NKTs) are innate-like lymphocytes that are abundant in the liver and participate in liver immunity. NKT cells express both NK cell and T cell markers, modulate innate and adaptive immune responses. Type I and Type II NKT cells are classified according to the TCR usage, while they recognize lipid antigen in a non-classical major histocompatibility (MHC) molecule CD1d-restricted manner. Once activated, NKT cells can quickly produce cytokines and chemokines to negatively or positively regulate the immune responses, depending on the different NKT subsets. In liver transplantation (LTx), the immune reactions in a series of processes determine the recipients' long-term survival, including ischemia-reperfusion injury, alloresponse, and post-transplant infection. This review provides insight into the research on NKT cells subpopulations in LTx immunity during different processes, and discusses the shortcomings of the current research on NKT cells. Additionally, the CD56-expressing T cells are recognized as a NK-like T cell population, they were also discussed during these processes.

Natural Killer T Cell Diversity and Immunotherapy

Invariant natural killer T cells (iNKTs), a type of unconventional T cells, share features with NK cells and have an invariant T cell receptor (TCR), which recognizes lipid antigens loaded on CD1d molecules, a major histocompatibility complex class I (MHC-I)-like protein. This interaction produces the secretion of a wide array of cytokines by these cells, including interferon gamma (IFN-γ) and interleukin 4 (IL-4), allowing iNKTs to link innate with adaptive responses. Interestingly, molecules that bind CD1d have been identified that enable the modulation of these cells, highlighting their potential pro-inflammatory and immunosuppressive capacities, as required in different clinical settings. In this review, we summarize key features of iNKTs and current understandings of modulatory α-galactosylceramide (α-GalCer) variants, a model iNKT cell activator that can shift the outcome of adaptive immune responses. Furthermore, we discuss advances in the development of strategies that modulate these cells to target pathologies that are considerable healthcare burdens. Finally, we recapitulate findings supporting a role for iNKTs in infectious diseases and tumor immunotherapy.

Natural Killer T-like Cells: Immunobiology and Role in Disease

CD56+ T cells are generally recognized as a distinct population of T cells and are categorized as NKT-like cells. Although our understanding of NKT-like cells is far from satisfactory, it has been shown that aging and a number of disease situations have impacted these cells. To construct an overview of what is currently known, we reviewed the literature on human NKT-like cells. NKT-like cells are highly differentiated T cells with "CD1d-independent" antigen recognition and MHC-unrestricted cell killing. The genesis of NKT-like cells is unclear; however, it is proposed that the acquisition of innate characteristics by T cells could represent a remodeling process leading to successful aging. Additionally, it has been shown that NKT-like cells may play a significant role in several pathological conditions, making it necessary to comprehend whether these cells might function as prognostic markers. The quantification and characterization of these cells might serve as a cutting-edge indicator of individual immune health. Additionally, exploring the mechanisms that can control their killing activity in different contexts may therefore result in innovative therapeutic alternatives in a wide range of disease settings.

Differential location of NKT and MAIT cells within lymphoid tissue

Natural Killer T (NKT) cells and Mucosal-Associated Invariant T (MAIT) cells are innate-like T cells that express semi-invariant αβ T cell receptors (TCRs) through which they recognise CD1d and MR1 molecules, respectively, in complex with specific ligands. These cells play important roles in health and disease in many organs, but their precise intra-organ location is not well established. Here, using CD1d and MR1 tetramer staining techniques, we describe the precise location of NKT and MAIT cells in lymphoid and peripheral organs. Within the thymus, NKT cells were concentrated in the medullary side of the corticomedullary junction. In spleen and lymph nodes, NKT cells were mainly localised within T cell zones, although following in vivo activation with the potent NKT-cell ligand α-GalCer, they expanded throughout the spleen. MAIT cells were clearly detectable in Vα19 TCR transgenic mice and were rare but detectable in lymphoid tissue of non-transgenic mice. In contrast to NKT cells, MAIT cells were more closely associated with the B cell zone and red pulp of the spleen. Accordingly, we have provided an extensive analysis of the in situ localisation of NKT and MAIT cells and suggest differences between the intra-organ location of these two cell types.

Dysregulated Peripheral Invariant Natural Killer T Cells in Plaque Psoriasis Patients

Background: Psoriasis is a common immune-mediated skin disease that involves T-cell-mediated immunity. Invariant natural killer T (iNKT) cells are a unique lymphocyte subpopulation that share properties and express surface markers of both NK cells and T cells. Previous reports indicate that iNKT cells regulate the development of various inflammatory diseases. IL-17 is a key cytokine in the pathogenesis of psoriasis and a key therapeutic target. Secukinumab is a fully human IgG1κ antibody that targets IL-17A, thereby antagonizing the biological effects of IL-17.

Objective: To explore the expression of iNKT cells in psoriasis patients and the effect of secukinumab on them.

Methods: We examined the frequencies of iNKT cells, Tregs, naïve and memory CD4⁺and CD8⁺T cells in the PBMCs as well as their cytokine production in a cohort of 40 patients with moderate-to-severe plaque psoriasis and 40 gender- and age-matched healthy controls. We further collected peripheral blood of another 15 moderate-to-severe plaque psoriasis patients who were treated with secukinumab and evaluated the proportion of iNKT cells in the PBMCs at baseline and week 12.

Results: The frequencies of conventional CD4⁺ T cells, CD8⁺ T cells, and Tregs in the PBMCs were comparable between psoriasis patients and healthy controls, but the frequencies of Th17 cells, Tc1 cells and Tc17 cells were increased in psoriasis patients. The frequency of peripheral iNKT cells and CD69⁺iNKT cells was significantly decreased in psoriasis patients. Both iNKT2 cells and iNKT17 cells were increased in psoriasis patients, but the ratio of iNKT2 cells vs iNKT17 cells was significantly reduced in psoriasis patients. After receiving secukinumab, the proportion of iNKT cells in the PBMCs of patients was increased, while the proportion of iNKT17 cells was decreased.

Conclusion: Dysregulated iNKT cells may be involved in the pathogenesis of psoriasis and secukinumab may play a regulatory role on iNKT cells.

Mast cell-mediated mechanistic pathways in organ transplantation

Adaptive immunity has gained importance in transplant immunology for years, based on models in which T-cells orchestrate the immune responses during rejection. Most recently, researches revealed that innate immune cells, including mast cells (MCs) also play a pivotal role in allograft rejection. MC mediated immunoregulatory responses influence the innate and adaptive immune responses. Their capability to produce an array of both pro-inflammatory and anti-inflammatory mediators, expressing a wide range of costimulatory molecules in addition to acting as antigen-presenting cells (APCs), make them effective immune cells far beyond their classical role as primary orchestrator cells of allergy. Activated regulatory Tcells (Treg) cells contribute to MC recruitment into grafts by releasing interleukin (IL)-9. Tregs are capable of stabilizing MCs and suppressing IgE mediated degranulation through interaction of Treg expressing OX40 with MCs expressing OX40L. MCs in turn release transforming growth factor (TGF)-β and IL-10 which possess suppressive properties. Thus, these cells can suppress the proliferation of T-cells and support the generation of Tregs. MCs in addition to orchestrating immune responses in grafts by cell-to-cell interactions with variety of immune cells, cause histologic changes, mainly fibrosis by releasing mediators such as histamine, fibroblast growth factor-2 (FGF-2), TGF-β, chymase, and cathepsin G. The role of MCs in transplant rejection remains controversial. The accumulation of MCs in rejected grafts suggests that they play a role in preventing graft tolerance, and contribute to the progression of chronic rejection of allografts. However, high expression of MC-related gene products in tolerant grafts and their known interaction with Tregs on the other hand, support the notion that they are an integral component in achieving peripheral tolerance.

CD56+ T cells are increased in kidney transplant patients following cytomegalovirus infection

BACKGROUND

CD56+ T cells previously have been identified as potentially cytotoxic lymphocytes, and relative numbers are increased in some infectious diseases.

PATIENTS AND METHODS

Relative proportions of CD56+ T cells were measured by flow cytometry in groups of renal transplant patients differing in cytomegalovirus (CMV) status of donor (D) and recipient (R). These measurements were related to episodes of CMV viremia.

RESULTS

Patient groups in which recipients (R+) or donors (D+/R-) were CMV+ had significantly higher proportions of CD56+ T cells (5.11 ± 0.69% and 5.42 ± 1.01%, respectively) than the D-/R- group (1.9 ± 0.35%; P = 0.0018 and 0.017, respectively). In the high-risk D+/R- group, it was found that patients who had post-transplant CMV viremia had higher levels than those who remained CMV negative (9.09 ± 2.34% vs. 3.16 ± 1.22%; P = 0.01). CD56+ T cells from R+ and D+/R- groups had higher proportions of both CD4+ and CD8+ cells than the D-/R- group. When activation markers were examined, some CD56+ T cells from both CMV+ groups had a TEM phenotype, with significantly more expressing CD45RO and NKG2C, and less expressing CD28, CD62L, CD127, and CD161 compared to the D-/R- group. Some CD56+ T cells showed specificity for CMV antigens and similar proportions of CD8+ cells were positive for class I HLA-CMV tetramers containing immunodominant CMV peptides compared to the majority CD56- T cells.

CONCLUSION

The results show significant increases in proportions of CD56+ T cells in relation to CMV infection in renal transplant patients and suggest that these cells have a cytotoxic function against CMV-infected cells.

Alloimmune activation promotes anti-cancer cytotoxicity after rat liver transplantation

Liver transplantation for hepatocellular carcinoma (HCC) results in a specific condition where the immune response is potentially directed against both allogeneic and cancer antigens. We have investigated the level of anti-cancer immunity during allogeneic immune response. Dark Agouti-to-Lewis and Lewis-to-Lewis rat liver transplantations were performed and the recipients anti-cancer immunity was analysed at the time of alloimmune activation. The occurrence of rejection in the allogeneic recipients was confirmed by a shorter survival (p<0.01), increased liver function tests (p<0.01), the presence of signs of rejection on histology, and a donor-specific ex vivo mixed lymphocyte reaction. At the time of alloimmune activation, blood mononuclear cells of the allogeneic group demonstrated increased anti-cancer cytotoxicity (p<0.005), which was related to an increased natural killer (NK) cell frequency (p<0.05) and a higher monocyte/macrophage activation level (p<0.01). Similarly, liver NK cell anti-cancer cytotoxicity (p<0.005), and liver monocyte/macrophage activation levels (p<0.01) were also increased. The alloimmune-associated cytotoxicity was mediated through the NKG2D receptor, whose expression was increased in the rejected graft (p<0.05) and on NK cells and monocyte/macrophages. NKG2D ligands were expressed on rat HCC cells, and its inhibition prevented the alloimmune-associated cytotoxicity. Although waiting for in vivo validation, alloimmune-associated cytotoxicity after rat liver transplantation appears to be linked to increased frequencies and levels of activation of NK cells and monocyte/macrophages, and is at least in part mediated through the NKG2D receptor.