CD8+ T cell subsets TC1 and TC2 cause different histopathologic forms of murine cardiac allograft rejection

Research progress on CD8+ T cell immune regulation in allogenic transplantation

With advances in tissue typing, organ preservation techniques, and clinical surgery, organ transplantation has gained popularity as a treatment option for various end-stage diseases. Allogeneic transplantation has been widely adopted and extensively researched in clinical practice. Despite significant breakthroughs and progress in immunosuppression, this procedure is still associated with several adverse reactions and complications. Therefore, there is a continuing need to explore new immunological approaches to provide fresh insights and guidance for clinical transplantation. CD8+ T cells, traditionally known for their cytotoxic function and their ability to recognize transplanted organs as "non-self" entities, display cytotoxicity. However, recent studies have unveiled that CD8+ T cells have various subtypes and functions that extend beyond conventional cytotoxicity. These CD8+ T cell subtypes include Effector CD8+ T cells, Memory CD8+ T cells, and CD8Treg cells. This review examines the immune regulatory mechanisms of CD8+ T cells in allogeneic transplantation and discusses the potential applications of CD8+ T cells in treating tumors in transplant recipients who are receiving immunosuppressive therapy. These findings offer theoretical guidance for reducing post-transplant rejection reactions and improving adverse prognoses, offering new hope for improved clinical survival rate.

Anticancer nanocage platforms for combined immunotherapy designed to harness immune checkpoints and deliver anticancer drugs

The interaction of programmed cell death 1 ligand 1 (PD-L1) with its receptor, programmed cell death 1 (PD-1), inhibits T cell responses. Monoclonal antibodies that block this interaction have been shown effective as immunotherapy. However, only a subset of cancers exhibits a durable response to PD-1/PD-L1 blockade. Moreover, antibody-based immune checkpoint blockade is costly and is occasionally accompanied by systemic side effects. To overcome these limitations of antibody-based immune checkpoint blockade, an immune checkpoint-blocking ferritin nanocage displaying 24 PD-L1 binding peptides (PD-L1pep1) on its surface was designed and constructed. These ferritin nanocages displaying PD-L1pep1 (PpNF) specifically bind to PD-L1 expressed on cancer cells or to purified PD-L1 with a ~30 nM binding affinity. The addition of PpNF to co-cultures of T cells and cancer cells inhibited PD-1/PD-L1 interactions and restored T cell activities. In a mouse model of syngeneic colon cancer, PpNF specifically targeted tumors and showed antitumor activity. Moreover, PpNF nanocages encapsulating the chemotherapeutic drug doxorubicin had more potent antitumor activity than a monoclonal antibody against PD-L1. These results demonstrate that ferritin nanocages displaying surface PD-L1pep1 can be efficiently applied for immunotherapy, especially when encapsulating small chemotherapeutic drugs. These nanocages may have promise as an immunotherapeutic nanomedicine against various solid tumors.

Investigation of hub genes and immune status in heart transplant rejection using endomyocardial biopsies

T cell‒mediated rejection (TCMR) and antibody‐mediated rejection (ABMR) are severe post‐transplantation complications for heart transplantation (HTx), whose molecular and immunological pathogenesis remains unclear. In the present study, the mRNA microarray data set GSE124897 containing 645 stable, 52 TCMR and 144 ABMR endomyocardial biopsies was obtained to screen for differentially expressed genes (DEGs) between rejected and stable HTx samples and to investigate immune cell infiltration. Functional enrichment analyses indicated roles of the DEGs primarily in immune‐related mechanisms. Protein‐protein interaction networks were then constructed, and ICAM1, CD44, HLA‐A and HLA‐B were identified as hub genes using the maximal clique centrality method. Immune cell infiltration analysis revealed differences in adaptive and innate immune cell populations between TCMR, ABMR and stable HTx samples. Additionally, hub gene expression levels significantly correlated with the degree and composition of immune cell infiltration in HTx rejection samples. Furthermore, drug‐gene interactions were constructed, and 12 FDA‐approved drugs were predicted to target hub genes. Finally, an external GSE2596 data set was used to validate the expression of the hub genes, and ROC curves indicated all four hub genes had promising diagnostic value for HTx rejection. This study provides a comprehensive perspective of molecular and immunological regulatory mechanisms underlying HTx rejection.

Phage display-identified PD-L1-binding peptides reinvigorate T-cell activity and inhibit tumor progression

Blockade of programmed cell death ligand-1 (PD-L1) restores T-cell activity and enhances anti-tumor immunity. Screening a phage-displayed peptide library for peptides that selectively bind to PD-L1-overexpressing cells identified two peptides, CLQKTPKQC and CVRARTR (PD-L1Pep-1 and PD-L1Pep-2, respectively) that appeared to block PD-L1. PD-L1Pep-1 and PD-L1Pep-2 preferentially bound to high PD-L1-expressing cells over low PD-L1-expressing cells; binding was further enhanced by interferon-γ, an inducer of PD-L1 expression. Binding affinities of PD-L1Pep-1 and PD-L1Pep-2 were approximately 373 and 281 nM, respectively. Cellular binding of the PD-L1-binding peptides was reduced by silencing PD-L1 gene expression or competition with anti-PD-L1 antibody. PD-L1Pep-1 and PD-L1Pep-2 induced the internalization and downregulated cell surface levels of PD-L1. The PD-L1-binding peptides restored cytokine secretion and T-cell proliferation to cells inhibited by co-culture with tumor cells or culture on PD-L1-coated plates. Intravenously injected PD-L1Pep-1 and PD-L1Pep-2 efficiently homed to tumor tissues, inhibited tumor growth, and increased CD8+/FoxP3+ ratio in mice. The PD-L1-binding peptides in combination with doxorubicin or PD-L1-targeted liposomal doxorubicin inhibited tumor growth and increased CD8+/FoxP3+ ratio more efficiently than doxorubicin alone and untargeted liposomal doxorubicin, respectively. These results suggest that PD-L1Pep-1 and PD-L1Pep-2 block PD-L1 and reinvigorate T-cell activity, inhibiting tumor growth by enhancing anti-tumor immunity.

The Transcription Factor NFATc1 Supports the Rejection of Heterotopic Heart Allografts

The immune suppressants cyclosporin A (CsA) and tacrolimus (FK506) are used worldwide in transplantation medicine to suppress graft rejection. Both CsA and FK506 inhibit the phosphatase calcineurin (CN) whose activity controls the immune receptor-mediated activation of lymphocytes. Downstream targets of CN in lymphocytes are the nuclear factors of activated T cells (NFATs). We show here that the activity of NFATc1, the most prominent NFAT factor in activated lymphocytes supports the acute rejection of heterotopic heart allografts. While ablation of NFATc1 in T cells prevented graft rejection, ectopic expression of inducible NFATc1/αA isoform led to rejection of heart allografts in recipient mice. Acceptance of transplanted hearts in mice bearing NFATc1-deficient T cells was accompanied by a reduction in number and cytotoxicity of graft infiltrating cells. In CD8⁺ T cells, NFATc1 controls numerous intracellular signaling pathways that lead to the metabolic switch to aerobic glycolysis and the expression of numerous lymphokines, chemokines, and their receptors, including Cxcr3 that supports the rejection of allogeneic heart transplants. These findings favors NFATc1 as a molecular target for the development of new strategies to control the cytotoxicity of T cells upon organ transplantation.

T lymphocytes and macrophages in the intestinal tissues of dogs infected with Leishmania infantum

This study was about a semi-quantitative analysis of T lymphocytes (CD4+ and CD8+, FoxP3+ regulatory T cells), and macrophages in the gut wall of dogs naturally infected with Leishmania infantum. Thirteen dogs were divided into three groups: group 1 (G1, n=5), dogs with canine visceral leishmaniasis (CVL) and infected with L. infantum amastigotes in the intestine; group 2 (G2, n=5), dogs with CVL but without intestinal amastigotes; and group 3 (G3, n=3), uninfected dogs (control group). There was no significant difference (p ≥ 0.05) on CD4+ and Treg cell numbers among the groups, whereas the levels of CD8+ T cells and macrophages were significantly higher in dogs from G1 group than in G2 and G3 (p ≤ 0.05), especially in intestinal segments with high parasite burden. Parasite burden correlated positively with levels of CD8+ T cells and macrophages (p ≤ 0.05), but was inversely correlated to levels of CD4+ T lymphocytes and FoxP3+ Treg cells. In conclusion, in the intestine of dogs with CVL, the increase of CD8+ T cells and macrophages population associated with high parasite burdens, but no changes of CD4+ T cells and FoxP3+ Treg cells suggest a possible immunoregulation by the parasite not dependent on Treg cells.

Absence of Galectin-1 accelerates CD8⁺ T cell-mediated graft rejection

Galectin-1 (Gal-1) is a member of a family of endogenous β-galactose-binding proteins with a role in preventing autoimmune diseases and chronic inflammation. In this study, the involvement of Gal-1 in graft rejection was investigated by using Gal-1-deficient mice (Gal-1⁻/⁻). We demonstrate that in the absence of Gal-1, skin grafts are rejected earlier compared with those of WT mice, and that this is due to the role played by CD8⁺ T cells in graft rejection. The difference in graft survival observed between Gal-1⁻/⁻ and WT mice was explained by both an increase in the percentage of antigen-specific CD8+ T cells and by preferential secretion of IFN-γ and IL-17 by CD8⁺ T cells in Gal-1⁻/⁻ mice compared with WT mice. This study suggests that endogenous expression of Gal-1 contributes to graft survival. The results obtained from the use of mice deficient in Gal-1 also confirm a key role for CD8⁺ T cells in graft rejection.

Donor dendritic cell proliferation and migration in hepatic allografts by pretransplant intraportal infusion of recipient blood into donor rats

INTRODUCTION

We have reported that recipient blood transfusion pretransplant prolongs hepatic allograft survival in rats. This study further investigated the mechanisms of the phenomenon.

MATERIALS AND METHODS

Male LEW and ACI rats were used as liver transplant recipients and donors, respectively. Experimental animals were divided into control; treatment experimental; and intraportally transfused (1 mL recipient blood) at 7 days before transplantation.

RESULTS

Rat survival time was significantly longer among the experiment versus the control group. A large number of donor-source dendritic cells were detected among infiltrating cells in the liver and spleen in the experimental group.

CONCLUSION

We concluded that the prolonged survival of hepatic allograft in these rats was associated with donor dendritic cell proliferation and migration.

Host-based Th2 cell therapy for prolongation of cardiac allograft viability

Donor T cell transfusion, which is a long-standing approach to prevent allograft rejection, operates indirectly by alteration of host T cell immunity. We therefore hypothesized that adoptive transfer of immune regulatory host Th2 cells would represent a novel intervention to enhance cardiac allograft survival. Using a well-described rat cardiac transplant model, we first developed a method for ex vivo manufacture of rat host-type Th2 cells in rapamycin, with subsequent injection of such Th2.R cells prior to class I and class II disparate cardiac allografting. Second, we determined whether Th2.R cell transfer polarized host immunity towards a Th2 phenotype. And third, we evaluated whether Th2.R cell therapy prolonged allograft viability when used alone or in combination with a short-course of cyclosporine (CSA) therapy. We found that host-type Th2.R cell therapy prior to cardiac allografting: (1) reduced the frequency of activated T cells in secondary lymphoid organs; (2) shifted post-transplant cytokines towards a Th2 phenotype; and (3) prolonged allograft viability when used in combination with short-course CSA therapy. These results provide further support for the rationale to use “direct” host T cell therapy for prolongation of allograft viability as an alternative to “indirect” therapy mediated by donor T cell infusion.

Lymphatic injury and regeneration in cardiac allografts

BACKGROUND

Severed donor heart lymphatics are not anastomosed to recipient lymphatics in cardiac transplantation. We evaluated the effects of cellular infiltrates of T cells and macrophages on the morphology of lymphatics in heart grafts.

METHODS

Dark agouti hearts were transplanted to Lewis or control dark agouti rats on subtherapeutic doses of cyclosporin. Transplants were examined by immunohistology and quantitative immunofluorescence microscopy using lymphatic endothelial hyaluronan receptor-1 as a lymphatic marker and CD8 and CD68 as markers for cellular infiltration at selected intervals from 1 to 8 weeks posttransplantation.

RESULTS

Allograft inner myocardial lymphatic density decreased by more than 30-fold at 1 week and recovered to only 15% of the native level at 8 weeks posttransplantation. In contrast, allograft lymphatics in and near the epicardium showed no significant density decline but increased in size by more than 5-fold at 2 weeks, and sustained approximately 3-fold increase at 8 weeks posttransplantation. Lymphatic changes correlated temporally with the extent of T cell and macrophage infiltration in allografts, which peaked at 2 to 3 weeks posttransplantation. When grafts were retransplanted from allogeneic to isogeneic recipients at 3 weeks posttransplantation, inner lymphatic density returned close to native level within 2 weeks after retransplantation.

CONCLUSIONS

This is the first characterization of regional and morphologic effects of immunologic responses on heart lymphatics after transplantation. Elimination of alloimmune responses produces rapid restoration of inner lymphatic vessels, suggesting that lymphatics injured during rejection can recover when rejection is reversed during the posttransplantation course.

A novel role of CD4 Th17 cells in mediating cardiac allograft rejection and vasculopathy

T-bet plays a crucial role in Th1 development. We investigated the role of T-bet in the development of allograft rejection in an established MHC class II–mismatched (bm12 into B6) model of chronic allograft vasculopathy (CAV). Intriguingly, and in contrast to IFN-γ^−/− mice that are protected from CAV, T-bet^−/− recipients develop markedly accelerated allograft rejection accompanied by early severe vascular inflammation and vasculopathy, and infiltration by predominantly IL-17–producing CD4 T cells. Concurrently, T-bet^−/− mice exhibit a T helper type 1 (Th1)–deficient environment characterized by profound IFN-γ deficiency, a Th2 switch characterized by increased production of interleukin (IL) 4, IL-5, IL-10, and IL-13 cytokines, as well as increased production of the proinflammatory cytokines IL-6, IL-12p40, and IL-17. Neutralization of IL-17 inhibits accelerated allograft rejection and vasculopathy in T-bet^−/− mice. Interestingly, CD4 but not CD8 T cell deficiency in T-bet^−/− mice affords dramatic protection from vasculopathy and facilitates long-term graft acceptance. This is the first study establishing that in the absence of Th1-mediated alloimmune responses, CD4 Th17 cells mediate an aggressive proinflammatory response culminating in severe accelerated allograft rejection and vasculopathy. These results have important implications for the development of novel therapies to target this intractable problem in clinical solid organ transplantation.

IFN-gamma prevents early perforin-granzyme-mediated destruction of kidney allografts by inducing donor class I products in the kidney

Interferon-gamma (Ifng) protects organ allografts: mouse kidney allografts lacking Ifng receptors rapidly fail with massive ischemic necrosis around days 5 to 7, reflecting microcirculation failure. We hypothesized that Ifng protects the graft by preventing perforin-granzyme-mediated cytotoxic damage to the microcirculation by inducing class Ia and/or Ib products. We transplanted kidney allografts lacking Ifng receptors into various knockout hosts. The necrosis/congestion phenotype did not require host B cells or IL-4 and IL-13 receptors, but required the T-cell alloresponse: it did not occur if the hosts were syngeneic or T-cell deficient. However, host perforin-granzyme mechanisms were required: no necrosis developed if hosts lacked either perforin or granzymes A and B. The ability of Ifng to protect the allograft required donor class I products: allografts lacking class I products due to Tap1 or beta2 microglobulin deficiency developed a similar necrosis-congestion phenotype at day 7 despite Ifng receptors being present. Thus when host cytotoxic T cells infiltrate organ allografts, Ifng prevents their perforin-granzyme mechanism from compromising the microcirculation by a mechanism requiring donor class Ia or Ib products. We propose that donor class Ia or Ib products are needed to trigger inhibitory receptors on effector T cells.

Disparate Primary and Secondary Allospecific CD8+ T Cell Cytolytic Effector Function in the Presence or Absence of Host CD4+ T Cells

The role of CD4+ T cells in promoting CD8+ T cell effector activity in response to transplant Ags in vivo has not been reported. We used a hepatocellular allograft model known to initiate both CD4-dependent and CD4-independent rejection responses to investigate the contribution of CD4+ T cells to the development, function, and persistence of allospecific CD8+ T cell effectors in vivo. Complete MHC-mismatched hepatocellular allografts were transplanted into C57BL/6 (CD4-sufficient) or CD4 knockout (CD4-deficient) hosts. The development of in vivo allospecific cytotoxicity was determined by clearance of CFSE-labeled target cells. CD8+ T cell cytotoxic effector activity was enhanced in response to allogeneic hepatocellular grafts with a greater magnitude of allocytotoxicity and a prolonged persistence of CTL effector activity in CD4-sufficient hosts compared with CD4-deficient hosts. Cytolytic activity was mediated by CD8+ T cells in both recipient groups. In response to a second hepatocyte transplant, rejection kinetics were enhanced in both CD4-sufficient and CD4-deficient hepatocyte recipients. However, only CD4-sufficient hosts developed recall CTL responses with an augmented magnitude and persistence of allocytotoxicity in comparison with primary CTL responses. These studies show important functional differences between alloreactive CD8+ T cell cytolytic effectors that mature in vivo in the presence or absence of CD4+ T cells.

CD8+ T-cell content in diagnostic lymph nodes measured by flow cytometry is a predictor of survival in follicular lymphoma

PURPOSE

Follicular lymphoma is a heterogeneous disease with variable prognosis and clinical course. We hypothesized that the presence of nonmalignant T cells in the microenvironment of the tumor may affect the outcome.

EXPERIMENTAL DESIGN

Using flow cytometry, we evaluated the T-cell subsets in the lymph node microenvironment of follicular lymphoma. All patients in South Stockholm County with indolent follicular lymphoma and with flow cytometry done on a diagnostic lymph node between 1994 and 2004 were included (N = 139). Diagnosis and grade (1, 2, and 3a) were confirmed by re-review. Flow cytometry results were reanalyzed. Lymphocyte subsets, the Follicular Lymphoma International Prognostic Index, grade, and clinical characteristics were evaluated in univariable and multivariable Cox analysis with respect to overall survival (OS) and disease-specific survival (DSS).

RESULTS

Higher CD8+ T-cell levels correlated with longer OS and DSS, independently of the Follicular Lymphoma International Prognostic Index (OS, P = 0.017; DSS, P = 0.020) and independently of all other prognostic factors (OS, P = 0.001; DSS, P = 0.004). Median OS was not reached for patients in the upper quarter of CD8+ T-cell levels (>8.6%), 10.4 years for patients in the middle half (4.2-8.6%), and 6.0 years for patients in the lower quarter (<4.2%). Furthermore, patients who had not required treatment within 6 months from diagnosis had more CD8+ T cells (P = 0.011).

CONCLUSIONS

Higher levels of CD8+ T cells predict a better prognosis, and these data support an important role for nonmalignant immune cells in the biology of follicular lymphoma. Evaluating the CD8+ T cells by flow cytometry at diagnosis may provide prognostic information.

Recipient Blood Pre-Transplant Transfusion Prolongs Hepatic Allograft Survival in Rats

BACKGROUND

The pre-transplant administration of donor antigens to recipients is reported to prolong transplanted organ survival. We investigated the effect of pre-transplant intraportal administration of recipient blood on rat hepatic allograft survival.

MATERIALS AND METHODS

Male LEW (RT1l) and ACI (RT1a) rats were used as transplant recipients and donors, respectively. Before transplantation, donors were transfused with recipient blood. Experimental animals were divided into groups as follows: group I, no treatment; group II, pre-treatment with recipient blood via the penile vein 7 days before transplantation; group III, pre-treatment with recipient blood via the portal vein 5 days before transplantation; and group IV, pre-treatment with recipient blood via the portal vein 7 days before transplantation. Serum interferon (IFN)-gamma concentrations were measured post-operatively.

RESULTS

Animals in group I survived a mean of 10.1 +/- 0.7 days. The survival of groups II and III was 10.6 +/- 1.6 and 13.1 +/- 0.9 days, respectively. The survival rate in group IV was prolonged significantly to 33.7 +/- 2.6 days. Serum concentrations of IFN-gamma were increased significantly in group IV, as compared with group I. The ratio of OX76+CD4+ or OX76+CD8+ T cells to OX76-CD4+ or OX76-CD8+ T cells was greater in group IV, as compared group I. OX76+CD8+ T cells from hepatic allografts in group IV expressed IFN-gamma and interleukin (IL)-10, but not IL-2 mRNA. Apoptotic hepatic infiltrates were greater in group IV, as compared to group I.

CONCLUSION

The cytokine profile of donor CD8+ T cells from allografts treated by the intraportal administration of recipient blood is associated with apoptosis of graft-infiltrating cells and the prolonged survival of hepatic allografts in rats.

Stress and substance P but not the substance P-metabolite SP5-11 trigger murine abortion by augmenting TNF-alpha levels at the feto-maternal interface

In a well-established murine abortion model, stress is thought to trigger fetal rejection by inducing a proinflammatory immune response via substance P (SP), being tumour necrosis factor (TNF)-alpha-producing CD8+ T cells involved. Interestingly, the SP metabolite SP5-11 also binds to SP receptors and mediates SP-like effects on immune cells at sites of inflammation. No data were available regarding the effects of SP5-11 on pregnancy outcome in the CBA/J x DBA/2J abortion-prone combination. We investigated the influence of SP5-11 in contrast to stress or SP on the abortion rate and the cytokine production by lymphocytes as well as on the levels of CD8+ T cells. Stress and SP boosted the abortion rate and increased the percentage of type 1 [TNF-alpha, interferon-gamma, interleukin (IL)-12] and type 2 (IL-4 and IL-10) cytokine-producing lymphocytes in blood and decidua, predominantly CD8+ T cells. Interestingly, SP5-11 did not significantly affect the abortion rate or cytokine production in the decidua, while increasing the Th1 and Th2 cytokine production systemically. Our data suggest that stress and SP induce abortion by augmenting the local levels of TNF-alpha, which seems therefore to be a potent trigger of miscarriage. On the contrary, the SP metabolite SP5-11 only affects the systemic cytokine production without boosting the abortion rate in this experimental model.

Murine B16 Melanomas Expressing High Levels of the Chemokine Stromal-Derived Factor-1/CXCL12 Induce Tumor-Specific T Cell Chemorepulsion and Escape from Immune Control

The chemokine, stromal-derived factor-1/CXCL12, is expressed by normal and neoplastic tissues and is involved in tumor growth, metastasis, and modulation of tumor immunity. T cell-mediated tumor immunity depends on the migration and colocalization of CTL with tumor cells, a process regulated by chemokines and adhesion molecules. It has been demonstrated that T cells are repelled by high concentrations of the chemokine CXCL12 via a concentration-dependent and CXCR4 receptor-mediated mechanism, termed chemorepulsion or fugetaxis. We proposed that repulsion of tumor Ag-specific T cells from a tumor expressing high levels of CXCL12 allows the tumor to evade immune control. Murine B16/OVA melanoma cells (H2b) were engineered to constitutively express CXCL12. Immunization of C57BL/6 mice with B16/OVA cells lead to destruction of B16/OVA tumors expressing no or low levels of CXCL12 but not tumors expressing high levels of the chemokine. Early recruitment of adoptively transferred OVA-specific CTL into B16/OVA tumors expressing high levels of CXCL12 was significantly reduced in comparison to B16/OVA tumors, and this reduction was reversed when tumor-specific CTLs were pretreated with the specific CXCR4 antagonist, AMD3100. Memory OVA-specific CD8+ T cells demonstrated antitumor activity against B16/OVA tumors but not B16/OVA.CXCL12-high tumors. Expression of high levels of CXCL12 by B16/OVA cells significantly reduced CTL colocalization with and killing of target cells in vitro in a CXCR4-dependent manner. The repulsion of tumor Ag-specific T cells away from melanomas expressing CXCL12 confirms the chemorepellent activity of high concentrations of CXCL12 and may represent a novel mechanism by which certain tumors evade the immune system.

Aortic allograft vasculopathy is mediated by CD8(+) T cells in Cyclosporin A immunosuppressed mice

We investigated the role of CD4(+) T cells and CD8(+) T cells in mediating allograft vasculopathy in Cyclosporin A (CyA) immunosuppressed mice. We first established that a dose of 50 mg/kg/d CyA was required to prevent acute rejection in C57BL/6 mice. CyA given at 50 mg/kg/d did not prevent allograft vasculopathy in either cardiac or aortic transplants in these mice. Using CD4(-/-) and CD8(-/-) mice, we established that CyA immunosuppression at this dose was only effective at preventing allograft vasculopathy in mice lacking CD8(+) T cells. This implicates CD8(+) T cells in the development of AV in situations of clinical cardiac transplantation where CyA is still the mainstay of immunosuppressive therapy. We confirmed the important role for CD8(+) T cells in AV in the face of CyA immunosuppression by allopriming mice in the presence of CyA and transferring alloprimed T cells into RAG1(-/-) immunodeficient mice. The RAG1(-/-) mice were also treated with CyA. In this situation (CyA present during the allopriming and in the recipient), only primed CD8(+) T cells could mediate AV, primed CD4(+) T cells could not. Alloprimed CD8(+) T cells raised in the presence of CyA exhibited markedly reduced direct recognition responses (as measured by MLR) and effector responses (as measured by cytotoxic activity). In contrast indirect activation was retained. We interpret these data to suggest that in the face of CyA immunosuppression CD4(+) T cell effector function is ablated while CD8(+) T cell function remains partially intact. The in vitro data suggest that the indirect pathway remains intact in this population of CyA resistant CD8(+) T cells.

CD8 Lymphocytes are Sufficient for the Development of Chronic Rejection

BACKGROUND

The role of CD8 lymphocytes, in chronic rejection or cardiac allograft vasculopathy (CAV), is incompletely understood. The purposes of this study were to determine whether CD8 lymphocytes, in the absence of CD4 lymphocytes, are capable of causing the intimal lesions of CAV; and if so, to define the effector mechanism(s) of CD8 lymphocytes.

METHODS

We modified a previously characterized major histocompatibility complex class II mismatched murine model of CAV. Wild-type CD8 lymphocytes were transferred to nude mice followed by heterotopic heart transplantation. Recipient mice were then treated with a CD40 activating antibody, which is known to provide help for CD8 lymphocyte activation, in the absence of CD4 lymphocytes. Donor hearts were harvested on day 40 posttransplantation and analyzed for cellular infiltrates and intimal thickening. In separate experiments, isolated perforin -/-, Fas ligand (FasL) -/-, and interferon (IFN)-gamma -/- CD8 lymphocytes were transferred to nude mice followed by identical experimented protocol.

RESULTS

With adaptive transfer of wild-type CD8 lymphocytes, the donor hearts were infiltrated with activated CD8 lymphocytes and displayed significant intimal lesions. Adoptive transfer of perforin -/- and FasL -/- CD8 lymphocytes to nude mice resulted in similar patterns of CD8 lymphocyte infiltration and similar severity of intimal lesions. The donor hearts from IFN-gamma -/- CD8 lymphocyte reconstituted recipients displayed minimal intimal lesions, although CD8 lymphocytes were present in the allografts.

CONCLUSIONS

Unprimed CD8 lymphocytes in the absence of CD4 lymphocytes can cause intimal lesions of CAV. CD8 lymphocytes production of IFN-gamma, but not the perforin or the FasL-mediated cytotoxicity, is the critical step in the development of intimal lesions.

Immunosuppression, eotaxin and the diagnostic changes in eosinophils that precede early acute heart allograft rejection

Peripheral blood eosinophil counts (EOS) are undetectable in 40% blood samples sent for routine haematology at Papworth Hospital during the first 3 months after heart transplantation (HTx). Increases in EOS usually precede the development of allograft rejection by a median of 4 days. We compared the effects of cyclosporin (dose and total blood concentration), prednisolone (dose and both total and unbound plasma concentrations) and azathioprine, as well as plasma concentrations of the CCR-3 chemokines, eotaxin and RANTES, on changes in EOS in 47 consecutive HTx recipients, with a median follow-up of 90 (IQR 85-95) days. Multivariate analysis confirmed the independent association between both prednisolone dose (P<0.0001) and eotaxin (P<0.0001) and changes in EOS. The plasma eotaxin concentration was, in turn, most closely associated with the cyclosporin dose (P<0.001) and plasma prednisolone concentration (P=0.022). The blood cyclosporin concentration (P=0.028), EOS (P=0.012) and prednisolone dose (P=0.015) were all independently associated with the risk of treated acute rejection. When prednisolone pharmacokinetic parameters were substituted for the prednisolone dose in this multivariate model, only the pharmacokinetic parameter retained a significant association with the risk of rejection. Changes in EOS preceding cardiac allograft rejection are directly associated with plasma eotaxin concentrations and indirectly with prednisolone dosage. Cyclosporin may also indirectly influence these changes by inhibiting eotaxin production. EOS, prednisolone dose and blood cyclosporin concentrations were independently associated with the risk of acute rejection. The total and unbound fractions of prednisolone in plasma appear to be even more closely related to rejection but are difficult to measure. Monitoring EOS, as a surrogate measure of prednisolone immunosuppression, may be more cost-effective for controlling rejection than conventional cyclosporin monitoring in the first 6 weeks after HTx.

Requirement for Donor and Recipient CD40 Expression in Cardiac Allograft Rejection: Induction of Th1 Responses and Influence of Donor-Derived Dendritic Cells

Costimulation through the CD40-CD40 ligand (CD40L) pathway is critical to allograft rejection, in that anti-CD40L mAb therapy prolongs allograft survival. However, the majority of studies exploring CD40-CD40L interactions have targeted CD40L. Less is known about the requirement for donor- and/or host-derived CD40 during rejection. This study assessed the relative contributions of donor and recipient CD40 expression to the rejection process. As the effectiveness of costimulatory blockade may be mouse strain dependent, this study explored the requirement for donor and recipient CD40 expression in BALB/c and C57BL/6 mice. Wild-type (WT) and CD40(-/-) BALB/c recipients readily rejected WT and CD40(-/-) C57BL/6 allografts, and rejection was associated with a prominent Th1 response. In contrast, CD40(-/-) C57BL/6 recipients failed to reject WT or CD40(-/-) BALB/c allografts and did not mount Th1 or Th2 responses. However, injection of donor CD40(-/-) dendritic cells induced both Th1 and Th2 responses and allograft rejection in CD40(-/-) C57BL/6 recipients. Finally, WT C57BL/6 mice rejected CD40(-/-) allografts, but this rejection response was associated with muted Th1 responses. These findings demonstrate that 1) CD40 expression by the recipient or the graft may impact on the immune response following transplantation; 2) the requirement for CD40 is influenced by the mouse strain; and 3) the requirement for CD40 in rejection may be bypassed by donor DC. Further, as CD40 is not required for rejection in BALB/c recipients, but anti-CD40L mAb prolongs graft survival in these mice, these results suggest that anti-CD40L therapy functions at a level beyond disruption of CD40-CD40L interactions.

Development of a novel transgenic mouse for the study of interactions between CD4 and CD8 T cells during graft rejection

The goal of this study was the development of a system in which the cooperative interactions between CD4 and CD8 T cells specific for defined peptides from a single minor histocompatibility antigen could be studied. A transgenic mouse strain that expresses chicken ovalbumin (Act-mOVA) on the surface of all cells in the body was produced as a source of tissues containing such an antigen. Skin grafts from Act-mOVA donors were rapidly and completely rejected by wild-type recipients, but only when both CD4 and CD8 T cells were present. CD4 T cells by themselves caused an incomplete form of rejection characterized by rapid but partial contraction of Act-mOVA grafts. CD8 T cells alone caused complete rejection of Act-mOVA skin grafts but only after a long delay. Adoptively transferred ovalbumin-specific TCR-transgenic CD4 and CD8 T cells were stimulated by Act-mOVA graft antigens and CD8 T-cell accumulation in the grafts was enhanced by specific CD4 T cells. These findings, together with the fact that the ligand for ovalbumin peptide-specific CD8 T cells can be detected in Act-mOVA tissues with an MHC-restricted antibody, make this an ideal system for the study of cooperation between CD4 and CD8 T cells.

IL-12 is required for differentiation of pathogenic CD8+ T cell effectors that cause myocarditis

Cardiac antigen-specific CD8(+) T cells are involved in the autoimmune component of human myocarditis. Here, we studied the differentiation and migration of pathogenic CD8(+) T cell effector cells in a new mouse model of autoimmune myocarditis. A transgenic mouse line was derived that expresses cardiac myocyte restricted membrane-bound ovalbumin (CMy-mOva). The endogenous adaptive immune system of CMy-mOva mice displays tolerance to ovalbumin. Adoptive transfer of naive CD8(+) T cells from the ovalbumin-specific T cell receptor-transgenic (TCR-transgenic) OT-I strain induces myocarditis in CMy-mOva mice only after subsequent inoculation with ovalbumin-expressing vesicular stomatitis virus (VSV-Ova). OT-I effector T cells derived in vitro in the presence or absence of IL-12 were adoptively transferred into CMy-mOva mice, and the consequences were compared. Although IL-12 was not required for the generation of cytolytic and IFN-gamma-producing effector T cells, only effectors primed in the presence of IL-12 infiltrated CMy-mOva hearts in significant numbers, causing lethal myocarditis. Furthermore, analysis of OT-I effectors collected from a mediastinal draining lymph node indicated that only effectors primed in vitro in the presence of IL-12 proliferated in vivo. These data demonstrate the importance of IL-12 in the differentiation of pathogenic CD8(+) T cells that can cause myocarditis.

Contrasting alloreactive CD4+ and CD8+ T cells: there's more to it than MHC restriction

Surface expression of CD4 or CD8 is commonly used to identify T-cell subsets that recognize antigen presented by class II MHC or class I MHC, respectively. This holds true for T cells that respond to allogeneic MHC molecules that are directly recognized as foreign, as well as peptides from allogeneic MHC molecules that are indirectly presented by self MHC molecules. CD4 or CD8 expression was initially believed to define cytokine secreting helper T cells or cytotoxic cells, respectively. However, this association of phenotype and function is not absolute, in that CD4+ cells may possess lytic activity and CD8+ cells secrete cytokines, notably IFNgamma. Recently, additional fundamental differences in the immunobiology of these T-cell subsets have been identified. These include differences in costimulatory requirements, cytokine responsiveness, cytokine production, cell survival, and the maintenance of memory. This review will survey these differences, emphasizing alloreactive T-cell responses as well as relevant observations that have been made in other systems.

The role of CD8+ T cells during allograft rejection

Organ transplantation can be considered as replacement therapy for patients with end-stage organ failure. The percent of one-year allograft survival has increased due, among other factors, to a better understanding of the rejection process and new immunosuppressive drugs. Immunosuppressive therapy used in transplantation prevents activation and proliferation of alloreactive T lymphocytes, although not fully preventing chronic rejection. Recognition by recipient T cells of alloantigens expressed by donor tissues initiates immune destruction of allogeneic transplants. However, there is controversy concerning the relative contribution of CD4+ and CD8+ T cells to allograft rejection. Some animal models indicate that there is an absolute requirement for CD4+ T cells in allogeneic rejection, whereas in others CD4-depleted mice reject certain types of allografts. Moreover, there is evidence that CD8+ T cells are more resistant to immunotherapy and tolerance induction protocols. An intense focal infiltration of mainly CD8+CTLA4+ T lymphocytes during kidney rejection has been described in patients. This suggests that CD8+ T cells could escape from immunosuppression and participate in the rejection process. Our group is primarily interested in the immune mechanisms involved in allograft rejection. Thus, we believe that a better understanding of the role of CD8+ T cells in allograft rejection could indicate new targets for immunotherapy in transplantation. Therefore, the objective of the present review was to focus on the role of the CD8+ T cell population in the rejection of allogeneic tissue.

CD8 T cells are sufficient to mediate allorecognition and allograft rejection

Different T cell subsets may play different roles in allorecognition and allograft rejection. It has been suggested that CD8 T cells can only initiate rejection with help from CD4 T cells. Since CD8 T cells may have different requirements for allorecognition and for costimulation, it is important to clarify the role of CD8 cells in rejection. We examined the role of CD8 cells in allorecognition using a TCR transgenic mouse transplantation model. In our study, CD8 cells were able to recognize alloantigens and reject allografts in the absence of help from CD4 T cells. Furthermore our study provides a model to study the mechanisms of CD8-mediated allograft rejection. It may be important in the future, to consider that CD8 T cells may need to be targeted independently of CD4 T cells in strategies used to prevent rejection and induce tolerance.