Hugh Auchincloss

The Programmed Death-1 (PD-1) Pathway Regulates Autoimmune Diabetes in Nonobese Diabetic (NOD) Mice

Programmed death-1 (PD-1) receptor, an inhibitory costimulatory molecule found on activated T cells, has been demonstrated to play a role in the regulation of immune responses and peripheral tolerance. We investigated the role of this pathway in the development of autoimmune diabetes. PD-1 or PD-L1 but not PD-L2 blockade rapidly precipitated diabetes in prediabetic female nonobese diabetic (NOD) mice regardless of age (from 1 to 10-wk-old), although it was most pronounced in the older mice. By contrast, cytotoxic T lymphocyte–associated antigen 4 (CTLA-4) blockade induced disease only in neonates. Male NOD mice also developed diabetes after PD-1–PD-L1 pathway blockade, but NOR mice, congenic to NOD but resistant to the development of diabetes, did not. Insulitis scores were significantly higher and frequency of interferon γ–producing GAD-reactive splenocytes was increased after PD-1–PD-L1 pathway blockade compared with controls. Interestingly, PD-L1 but not PD-L2 was found to be expressed on inflamed islets of NOD mice. These data demonstrate a central role for PD-1–PD-L1 interaction in the regulation of induction and progression of autoimmune diabetes in the NOD mouse and provide the rationale to develop new therapies to target this costimulatory pathway in this disease.

Symptomatic cytomegalovirus disease in the cytomegalovirus antibody seropositive renal transplant recipient treated with OKT3

A prospective study to investigate risk factors for CMV disease was conducted in 94 renal transplant recipients. CMV disease was defined as either unexplained fever for >3 days with viremia or unexplained fever for >3 days with isolation of CMV from the urine or throat wash and at least one of the following: leukopenia, elevated serum alanine aminotransferase, or biopsy-proved invasive tissue infection of the lung or gastrointestinal tract. Fifty-three patients received immunosuppressive regimens consisting of prednisone and cyclosporine, with or without azathioprine. The remaining 41 patients were treated with these agents plus OKT3 (21 received OKT3 to treat rejection, 20 received OKT3 prophylactically). Thirty-seven patients were at minimal risk of CMV disease (donor and recipient seronegative for CMV); 12 patients were at risk of primary disease (donor seropositive, recipient seronegative), and 45 were at risk of reactivation disease (recipient seropositive at the time of transplantation). The incidences of CMV disease in the 3 groups were 0%, 58%, and 36%, respectively. Although the incidence of CMV disease in patients at risk of primary disease was not influenced by the immunosuppressive regimen, immunosuppression had a profound effect on the occurrence of CMV disease in CMV-seropositive transplant recipients. The incidence of CMV disease in those receiving OKT3 was 59%; but only 21% in those who did not receive OKT3. OKT3 increased the risk of CMV disease five-fold (odds ratio 5.2 (95% confidence limits 1.4–17.5)). In the CMV-seropositive patient, OKT3 was also the most important predictor of CMV disease by multivariate analysis (P<0.002). A pilot study of preemptive therapy with ganciclovir (2.5 mg/kg daily during OKT3 therapy) in 17 patients decreased the incidence of CMV disease without appreciable toxicity.

A prospective, randomized, clinical trial of intraoperative versus postoperative thymoglobulin in adult cadaveric renal transplant recipients

Background. Delayed graft function (DGF) is frequently observed in recipients of cadaveric renal transplants. Previous retrospective or nonrandomized studies have suggested that intraoperative administration of polyclonal antithymocyte preparations may reduce the incidence of DGF, possibly by decreasing ischemia-reperfusion injury. Methods. We performed a prospective randomized study of Thymoglobulin induction therapy in adult cadaveric renal transplant recipients. Between January 2001 and January 2002, 58 adult cadaveric renal transplant recipients were randomized to receive intraoperative or postoperative Thymoglobulin induction therapy. Three to six doses of Thymoglobulin (1 mg/kg/dose) were administered during the first week posttransplant. Baseline immunosuppression consisted of tacrolimus (54 of 58) or cyclosporine A (4 of 58), steroids, and mycophenolate mofetil. DGF was defined by the requirement for hemodialysis within the first week posttransplant. Results. There were no significant differences between the two groups in recipient demographics, donor age, cold ischemia time, or total number of doses of Thymoglobulin administered. Intraoperative Thymoglobulin administration was associated with significantly less DGF and a lower mean serum creatinine on postoperative days 10 and 14 (P <0.05). Posttransplant length of stay was also significantly shorter for the intraoperative Thymoglobulin patient group. The acute rejection rate was also lower in the intraoperative treatment group but this did not achieve statistical significance. There was no difference in the incidence of cytomegalovirus disease between the two groups. Conclusions. The results of this study indicate that intraoperative Thymoglobulin administration, in adult cadaveric renal transplant recipients, is associated with a significant decrease in DGF, better early allograft function in the first month posttransplant, and a decreased posttransplant hospital length of stay.

Curative and β cell regenerative effects of α1-antitrypsin treatment in autoimmune diabetic NOD mice

Invasive insulitis is a destructive T cell-dependent autoimmune process directed against insulin-producing β cells that is central to the pathogenesis of type 1 diabetes mellitus (T1DM) in humans and the clinically relevant nonobese diabetic (NOD) mouse model. Few therapies have succeeded in restoring long-term, drug-free euglycemia and immune tolerance to β cells in overtly diabetic NOD mice, and none have demonstrably enabled enlargement of the functional β cell mass. Recent studies have emphasized the impact of inflammatory cytokines on the commitment of antigen-activated T cells to various effector or regulatory T cell phenotypes and insulin resistance and defective insulin signaling. Hence, we tested the hypothesis that inflammatory mechanisms trigger insulitis, insulin resistance, faulty insulin signaling, and the loss of immune tolerance to islets. We demonstrate that treatment with α1-antitrypsin (AAT), an agent that dampens inflammation, does not directly inhibit T cell activation, ablates invasive insulitis, and restores euglycemia, immune tolerance to β cells, normal insulin signaling, and insulin responsiveness in NOD mice with recent-onset T1DM through favorable changes in the inflammation milieu. Indeed, the functional mass of β cells expands in AAT-treated diabetic NOD mice.

ANTIGEN PROCESSING AND PRESENTATION IN TRANSPLANTATION

For many years the direct stimulation of T cells in response to donor MHC antigens expressed on donor antigen-presenting cells has been the focus of transplantation immunology. Indirect recognition in response to peptides of donor antigens presented by self MHC molecules on recipient antigen-presenting cells has not generally been considered an important feature of graft rejection. Recent evidence suggests that indirect responses may be more important than previously considered and the new emphasis on indirect pathways in allograft rejection has raised new issues, many of which are unresolved.

The role of CD154-CD40 versus CD28-B7 costimulatory pathways in regulating allogeneic Th1 and Th2 responses in vivo

We used signal transducer and activator of transcription 4 (STAT4) and STAT6 gene knockout (-/-) mice as recipients of fully mismatched cardiac allografts to study the role of T-cell costimulatory pathways in regulating allogeneic T-helper 1 (Th1) versus Th2 responses in vivo. STAT4(-/-) mice have impaired Th1 responses, whereas STAT6(-/-) mice do not generate normal Th2 responses. Cardiac allografts from C57BL/6 mice were transplanted into normal wild-type (WT), STAT4(-/-), and STAT6(-/-) BALB/c recipients. STAT4(-/-) and STAT6(-/-) mice rejected their grafts with the same tempo as untreated WT recipients. CD28-B7 blockade by a single injection of CTLA4Ig induced long-term engraftment and donor-specific tolerance in all three groups of recipients. CD154 blockade by a single injection of MR1 was effective in prolonging allograft survival and inducing tolerance in STAT4(-/-) mice but was only marginally effective in STAT6(-/-) recipients and WT controls. In addition, a similar protocol of MR1 was ineffective in prolonging graft survival in CD28(-/-) BALB/c recipients, suggesting that the lack of efficacy seen in WT and STAT6(-/-) mice is not due to the presence of a functional CD28-B7 pathway. Furthermore, there was a similar differential effect of CD28-B7 versus CD154-CD40 blockade in inhibiting immune responses in animals immunized with ovalbumin and complete Freunds adjuvant. These novel data indicate that Th1 and Th2 cells are differentially regulated by CD28-B7 versus CD154-CD40 costimulation pathways in vivo and may have potential implications for the development of therapeutic strategies such as T-cell costimulatory blockade in humans.

Analysis of the Role of Negative T Cell Costimulatory Pathways in CD4 and CD8 T Cell-Mediated Alloimmune Responses In Vivo

Negative costimulatory signals mediated via cell surface molecules such as CTLA-4 and programmed death 1 (PD-1) play a critical role in down-modulating immune responses and maintaining peripheral tolerance. However, their role in alloimmune responses remains unclear. This study examined the role of these inhibitory pathways in regulating CD28-dependent and CD28-independent CD4 and CD8 alloreactive T cells in vivo. CTLA-4 blockade accelerated graft rejection in C57BL/6 wild-type recipients and in a proportion of CD4−/− but not CD8−/− recipients of BALB/c hearts. The same treatment led to prompt rejection in CD28−/− and a smaller proportion of CD4−/−CD28−/− mice with no effect in CD8−/−CD28−/− recipients. These results indicate that the CTLA-4:B7 pathway provides a negative signal to alloreactive CD8+ T cells, particularly in the presence of CD28 costimulation. In contrast, PD-1 blockade led to accelerated rejection of heart allografts only in CD28−/− and CD8−/−CD28−/− recipients. Interestingly, PD-1 ligand (PD-L1) blockade led to accelerated rejection in wild-type mice and in all recipients lacking CD28 costimulation. This effect was accompanied by expansion of IFN-γ-producing alloreactive T cells and enhanced generation of effector T cells in rejecting allograft recipients. Thus, the PD-1:PD-L1 pathway down-regulates alloreactive CD4 T cells, particularly in the absence of CD28 costimulation. The differential effects of PD-1 vs PD-L1 blockade support the possible existence of a new receptor other than PD-1 for negative signaling through PD-L1. Furthermore, PD-1:PD-L1 pathway can regulate alloimmune responses independent of an intact CD28/CTLA-4:B7 pathway. Harnessing physiological mechanisms that regulate alloimmunity should lead to development of novel strategies to induce durable and reproducible transplantation tolerance.

Cutting Edge: Recipient MHC Class II Expression Is Required to Achieve Long-Term Survival of Murine Cardiac Allografts After Costimulatory Blockade

To study the role of the direct and indirect pathways in achieving tolerance, we used genetically altered mouse strains in two ways: 1) MHC class II-deficient mice were used as donors of skin and cardiac grafts to eliminate the direct CD4+ T cell response, and 2) B6 II−4+ mice, which are MHC class II-deficient mice expressing an MHC class II transgene only on thymic epithelium, were used as recipients of normal grafts. These mice cannot mount an indirect response. Eliminating the indirect pathway actually made it more difficult to achieve prolonged allograft survival when we used costimulatory blockade than when both pathways were available. Costimulatory blockade was ineffective even when CD4+ T cells from normal animals were transferred into recipients that lacked MHC class II molecules. These results suggest that an active CD4+ response through the indirect pathway is necessary for costimulatory blockade to be effective in prolonging allograft survival.

Liver transplantation for primary hepatic cancer.

Although early survival following transplantation for primary hepatic cancer is excellent, previously reported high recurrence rates have generally discouraged liver replacement for this indication. Since the inception of the Boston Center for Liver Transplantation (BCLT) in 1983, 33 of 383 (8.6%) liver allograft recipients have undergone orthotopic transplantation as definitive treatment for otherwise unresectable cancer. Diagnoses included hepatocellular carcinoma (HCCA) in 24 patients (73%), and cholangiocarcinoma (CHCA) in 9 patients (27%). Actuarial survival rates for patients with hepatocellular carcinoma were 71%, 56%, and 42% at 1, 2, and 3 years, respectively. The actuarial survival rates for patients with cholangiocarcinoma were 89% at 6 months, and 56% at 1, 2, and 3 years. Of the nine patients with cholangiocarcinoma, 56% (5/9) developed recurrent disease. Although this recurrence rate is disheartening, because of the lack of other morbidity, long-term survival in these patients is comparable to patients with HCCA. In contrast, recurrent hepatocellular carcinoma developed in 25% of recipients (5/20) who survived longer than 3 months posttransplantation. Other causes of death in patients with hepatocellular carcinoma included perioperative complications, 16.6% (4/24); sepsis, 8.3% (2/24); coronary artery disease, 4.2% (1/24); and lymphoma, 4.2% (1/24). Favorable prognostic factors included: primary tumor less than 3 cm in size and absence of associated cirrhosis. These results emphasize that orthotopic liver transplantation can provide a long-term cure for approximately 50% of patients whose primary hepatic malignancy is unresectable by conventional procedures.

Acute humoral rejection in hepatitis C-infected renal transplant recipients receiving antiviral therapy.

The use of interferon‐alpha (IFN) in hepatitis C (HCV)‐infected renal recipients has been associated with acute rejection and graft loss. We reviewed our recent experience in HCV (+) renal recipients treated with antiviral therapy for biopsy proven chronic hepatitis C. Twelve HCV (+) recipients who recently received antiviral therapy were analyzed. Post‐treatment sera were tested for donor‐specific human leukocyte antigen (HLA) antibodies (DSA). Within 6 months of initiating antiviral therapy, two of 12 patients (17%) developed acute rejection, which was characterized as acute humoral rejection (de novo DSA in serum and C4d deposits in peritubular capillaries). Both progressed to graft failure. Nine of the remaining 10 patients tested did not have DSA. The use of IFN was associated with severe acute humoral rejection (C4d +, DSA +). The recognition of IFN‐associated acute humoral rejection in this series may explain the high rate of graft loss reported previously in renal recipients receiving IFN.