John H. Fechner

An Interaction between Kynurenine and the Aryl Hydrocarbon Receptor Can Generate Regulatory T Cells

The aryl hydrocarbon receptor (AHR) has been known to cause immunosuppression after binding dioxin. It has recently been discovered that the receptor may be central to T cell differentiation into FoxP3+ regulatory T cells (Tregs) versus Th17 cells. In this paper, we demonstrate that kynurenine, the first breakdown product in the IDO-dependent tryptophan degradation pathway, activates the AHR. We furthermore show that this activation leads to AHR-dependent Treg generation. We additionally investigate the dependence of TGF-β on the AHR for optimal Treg generation, which may be secondary to the upregulation of this receptor that is seen in T cells postexposure to TGF-β. These results shed light on the relationship of IDO to the generation of Tregs, in addition to highlighting the central importance of the AHR in T cell differentiation. All tissues and cells were derived from mice.

Campath-1H induction plus rapamycin monotherapy for renal transplantation: results of a pilot study.

Campath‐1H, an anti‐CD52 monoclonal antibody, was used as induction therapy (40 mg i.v. total dose) in 29 primary human renal transplants, and the patients were maintained on rapamycin monotherapy (levels 8–15 ng/mL) post‐transplant. Campath‐1H profoundly depletes lymphocytes long‐term and more transiently depletes B cells and monocytes. All patients are alive and well at 3–29 months of follow up. One graft was lost because of rejection. There have been no systemic infections and no malignancies. Eight of 29 patients have experienced rejection, which was successfully treated in seven of eight patients. Five of these patients had pathological evidence of a humoral component of their rejection. Seven of the 29 patients were converted to standard triple therapy on account of rejection. Rapamycin was generally well tolerated in that there were no significant wound‐healing problems; two lymphoceles required surgical drainage; and most patients were treated with a lipid‐lowering agent. Flow crossmatch testing post‐transplant revealed evidence of alloantibody in two patients tested with previous combined cellular and humoral rejection. Biopsies have shown no chronic allograft nephropathy to date. In view of the relatively high incidence of early humoral rejection, we plan to modify the immunosuppressive regimen in subsequent pilot studies. This clinical trial provides insight into the use of Campath‐1H induction in combination with rapamycin maintenance monotherapy.

Microchimerism linked to cytotoxic T lymphocyte functional unresponsiveness (clonal anergy) in a tolerant renal transplant recipient.

A patient was found to be functionally tolerant of a maternal kidney allograft as evidenced by good graft function 5 years after cessation of all immunosuppressive drug therapy. Despite normal in vitro proliferative and IL-2 responses, patient anti-donor 1° MLR cultures yielded little donor-specific CTL activity in either bulk or limiting dilution analysis (LDA) cultures. Using polymerase chain reaction, the patients PBL and skin were found to contain donor-derived Bw6+ cells. Removal of Bw6+ donor cells from the patient PBL with mAb and immunomagnetic beads before stimulation with donor PBL on day 0 failed to restore donor-specific CTL in either bulk 1° MLR or LDA cultures. Restimulation of 1° cultures with donor stimulator cells plus exogenous IL-2, however, completely restored anti-donor HLA class I-specific CTL, indicating class I-specific CTL precursors were not clonally deleted. Fresh patient PBL, as well as donor cell-enriched fractions, when added at the initiation of 3° MLR cultures, inhibited the generation of anti-donor CTL, whereas donor cell-depleted fractions did not. The inhibition was cell dose-dependent, was specific for the anti-donor response, and was radioresistant (1200 rad). Thus, the clinical tolerance observed in patients with microchimerism may be due to the presence of veto cells within the circulating donor cell pool.

FN18-CRM9 immunotoxin promotes tolerance in primate renal allografts

BACKGROUND Transplant tolerance, rather than immunity, may be favored in the setting of a lower mature lymphoid mass in the recipient induced by anti-T cell agents. A novel immunosuppressive agent, FN18-CRM9, known to specifically kill T cells with great potency, was evaluated in a transplant model. METHODS In order to ablate recipient T cells, the immunotoxin FN18-CRM9 was administered to rhesus monkey recipients of MHC-mismatched renal allografts. Donor lymphocytes were injected intrathymically into some animals. RESULTS All monkeys with T-cell depletion by immunotoxin had prolonged allograft survival, and tolerance confirmed by skin grafting has been confirmed in five of six long-surviving recipients. CONCLUSIONS In this clinically relevant model, profound but transient T-cell depletion by a single agent substantially promotes tolerance.

CD4+CD25+FOXP3+ regulatory T cells increase de novo in kidney transplant patients after immunodepletion with campath-1H

Campath‐1H (Alemtuzumab) is an effective immunodepletion agent used in renal transplantation. To evaluate its influence on T lymphocytes during repletion, we analyzed peripheral blood from Campath‐1H‐treated renal allograft recipients for the presence of FOXP3+ regulatory T (Treg) cells. Flow cytometry demonstrated that CD4+CD25+FOXP3+ lymphocytes increased significantly within the CD4+ T‐cell population, skewing Treg/Teff (T effector) ratios for up to several years. In contrast, Treg levels in patients treated with anti‐CD25 (Basiliximab) and maintained on CsA demonstrated a sustained decrease. The increase in Tregs in Campath‐1H treated patients developed independent of maintenance immunosuppression. Importantly, the increase in Tregs was not fully explained by their homeostatic proliferation, increased thymic output, or Treg sparing, suggesting de novo generation/expansion. Consistent with this, in vitro stimulation of PBMCs with Campath‐1H, with or without anti‐CD3, activation led to an increase in CD4+CD25+FOXP3+ cells that had suppressive capabilities. Together, these data suggest that Campath‐1H promotes an increase in peripheral Tregs and may act as an intrinsic generator of Tregs in vivo.

BAFF is increased in renal transplant patients following treatment with alemtuzumab

Alemtuzumab is a monoclonal antibody that depletes T and B cells and is used as induction therapy for renal transplant recipients. Without long‐term calcineurin inhibitor (CNI) therapy, alemtuzumab‐treated patients have a propensity to develop alloantibody and may undergo antibody‐mediated rejection (AMR). In pursuit of a mechanistic explanation, we analyzed peripheral B cells and serum of these patients for BAFF (Blys) and BAFF‐R, factors known to be integral for B‐cell activation, survival, and homeostasis. Serum BAFF levels of 22/24 alemtuzumab‐treated patients were above normal range, with average levels of 1967 pg/mL compared to 775 pg/mL in healthy controls (p = 0.006). BAFF remained elevated 2 years posttransplant in 78% of these patients. BAFF‐R on CD19+ B cells was significantly downregulated, suggesting ligand/receptor engagement. BAFF mRNA expression was increased 2–7‐fold in CD14+ cells of depleted patients, possibly linking monocytes to the BAFF dysregulation. Addition of recombinant BAFF to mixed lymphocyte cultures increased B‐cell activation to alloantigen, as measured by CD25 and CD69 coexpression on CD19+ cells. Of note, addition of sirolimus (SRL) augmented BAFF‐enhanced B‐cell activation whereas CNIs blocked it. These data suggest associations between BAFF/BAFF‐R and AMR in alemtuzumab‐treated patients.

T-lymphocyte Alloresponses of Campath-1h-treated Kidney Transplant Patients

Background. Kidney transplant patients given Campath-1H (Alemtuzumab) immunodepletion therapy and long-term rapamycin monotherapy have excellent graft survival and function at three years. As an initial step in understanding the characteristics of repopulated T lymphocytes in these patients, we performed several assays to assess alloreactivity. Methods. We measured T-cell responses using CFSE-labeled recipient lymphocytes in a direct one-way MLR, and also analyzed the kinetics of expression of IFN-γ. We examined the T-cell responses of Campath-treated transplant patients on monotherapy versus those treated with anti-CD25 (Basiliximab) induction therapy and maintenance immunosuppression consisting of cyclosporine A, mycophenolate mofetil, and steroids. Results. On average, proliferative responses to donor antigen were equal between Campath and control groups. However, the Campath group displayed a greater response to third party compared to donor antigen (CD3+ P=0.04, CD4+ P=0.07, CD8+ P<0.01), whereas the control group did not display a greater response to third party (CD3+ P=0.69, CD4+ P=0.72, CD8+ P=0.60). Interestingly, more Campath patients (4 of 15) than control patients (0 of 8) displayed donor specific unresponsiveness as gauged by IFN-γ expression and T-cell proliferation (P=0.15). Conclusions. These studies suggest that Campath-1H in conjunction with rapamycin monotherapy retains intact immune responses to third party alloantigen, yet may promote hyporesponsiveness to donor antigen.

Metastable Tolerance to Rhesus Monkey Renal Transplants Is Correlated with Allograft TGF-β1+CD4+ T Regulatory Cell Infiltrates

Approaches that prevent acute rejection of renal transplants in a rhesus monkey model were studied to determine a common mechanism of acceptance. After withdrawal of immunosuppression, all 14 monkeys retained normal allograft function for >6 mo. Of these, nine rejected their renal allograft during the study, and five maintained normal function throughout the study period. The appearance of TGF-β1+ interstitial mononuclear cells in the graft coincided with a nonrejection histology, whereas the absence/disappearance of these cells was observed with the onset of rejection. Analysis with a variety of TGF-β1-reactive Abs indicated that the tolerance-associated infiltrates expressed the large latent complex form of TGF-β1. Peripheral leukocytes from rejecting monkeys lacking TGF-β1+ allograft infiltrates responded strongly to donor Ags in delayed-type hypersensitivity trans-vivo assays. In contrast, allograft acceptors with TGF-β1+ infiltrates demonstrated a much weaker peripheral delayed-type hypersensitivity response to donor alloantigens (p < 0.01 vs rejectors), which could be restored by Abs that either neutralized active TGF-β1 or blocked its conversion from latent to active form. Anti-IL-10 Abs had no restorative effect. Accepted allografts had CD8+ and CD4+ interstitial T cell infiltrates, but only the CD4+ subset included cells costaining for TGF-β1. Our data support the hypothesis that the recruitment of CD4+ T regulatory cells to the allograft interstitium is a final common pathway for metastable renal transplant tolerance in a non-human primate model.

Monotherapy with the novel human anti-CD154 monoclonal antibody ABI793 in rhesus monkey renal transplantation model.

Background. This study assesses the safety and efficacy of the novel human anti-human CD154 monoclonal antibody ABI793 in rhesus monkeys. Methods. Outbred rhesus monkeys were used for renal transplantation from major histocompatibility complex-mismatched donors. Seven recipients were treated with ABI793, and six untreated recipients were used as controls. Graft function was monitored by urine output, serum creatinine, and renal biopsy. Phenotypic analysis of peripheral blood lymphocytes and mixed lymphocyte reaction were performed before transplantation and periodically after transplantation. Anti-donor major histocompatibility complex class I antibody levels were measured at the time of sacrifice. Results. Monkeys in the treated group demonstrated prolonged graft survival compared with controls. One monkey was sacrificed because of a urine leak on postoperative day 13. Three monkeys were sacrificed because of acute rejection (days 44, 149, and 158). Two monkeys were sacrificed because of chronic active rejection (days 154 and 221). One monkey was sacrificed on day 139 without rejection to observe the effects of ABI793 in the absence of rejection. There were no obvious clinical side effects of ABI793, but microscopic thromboembolic changes were observed in two monkeys. Lymphocyte subsets remained unaltered in all monkeys. Mixed lymphocyte reaction showed nonspecific suppression 6 weeks after transplantation. The monkeys with chronic active rejection showed relatively strong alloantibody responses. Conclusions. ABI793 induces prolonged renal allograft survival in rhesus monkeys. Nevertheless, thromboembolic complications may occur and chronic allograft nephropathy may develop after anti-CD154 treatment is discontinued.

Primate renal transplants using immunotoxin.

BACKGROUND T-lymphocyte depletion 7 days before transplantation with immunotoxin FN 18-CRM9 has resulted in tolerance to subsequent renal allografts. We tested the effect of giving immunotoxin on the day of the transplantation and evaluated its effect on rhesus monkey and allograft survival, on antibody production, and on T-cell recovery. METHODS Major histocompatibility complex mismatched renal allografts were performed in rhesus monkeys. Immunotoxin was given starting on the day of transplantation, with and without prednisone and mycophenolate mofetil for 3 days. T-cell subsets and alloantibody levels were measured by flow cytometry. The ability of treated monkeys to develop antibody to tetanus, diphtheria, and xenoantibody was measured. Histology of renal transplants was read in a blinded manner. RESULTS Immunotoxin started on the day of transplantation resulted in prolonged allograft survival in all treatment groups. Graft loss between days 50 and 135 was most often due to interstitial nephritis. Later graft loss was due to chronic rejection. Monkeys had intact antibody responses to alloantigen, tetanus, diphtheria, and xenoantibody. Their CD4 cells recovered gradually over 6 months. CONCLUSIONS Immunotoxin reliably prolongs renal allograft survival when started on the day of transplantation, but interstitial nephritis and chronic rejection limit the development of long-term tolerance. T-cell-dependent B-cell responses remain intact after treatment.