Leflunomide, malononitriloamides, and transplantation immunology

The Effects of FK778 in Combination With Tacrolimus and Steroids: A Phase II Multicenter Study in Renal Transplant Patients

BACKGROUND

In animal and in vitro models, FK778 inhibits acute rejection, modifies vasculopathy, and shows anti-viral activity. We report first efficacy and safety data of FK778 in human kidney transplant recipients at two concentration-controlled ranges.

METHODS

In a double-blind manner, 149 patients were randomized to a 12-week treatment with FK778 in combination with tacrolimus (Tac) and corticosteroids (S). Of the high-level group (H), 49 patients received 2 x 600 mg/day FK778 and continued on 150 mg/day, 54 patients of the low-level group (L) got 1 x 600 mg/day followed by 75 mg/day, and 46 patients received placebo (P). Subsequent FK778 doses were adjusted to trough levels of 100-200 microg/mL (H) and 10-100 microg/mL (L). The primary endpoint was the incidence of biopsy proven acute rejection (AR).

RESULTS

In 93% of the patients in group L, targeted plasma trough levels were reached by Day 3; in half of the patients in group H, the targeted levels were reached by Day 9. Graft survival at week 16 was 89.7%, 88.8%, and 91.3%, and the incidences of AR were 26.5%, 25.9%, and 39.1% for groups H, L, and P. For the subgroup of patients in which target levels were reached by week 2, incidences were 7.7%, 27.1%, and 39.1%, respectively. Anemia, the most frequently reported adverse event especially in group H, was reversible. Mean total cholesterol and LDL-cholesterol levels were reduced during FK778 treatment compared with group P.

CONCLUSION

FK778 is pharmacologically active, well-tolerated, and safe. To fully benefit from this promising new drug, FK778 dosing will be optimized in subsequent studies.

Leflunomide analogue FK778 is vasculoprotective independent of its immunosuppressive effect: potential applications for restenosis and chronic rejection

BACKGROUND

Leflunomide (LFM) inhibits experimentally both acute and chronic allograft rejection. The inhibition of dihydroorotate dehydrogenase (DHODH) in pyrimidine synthesis is suggested to be the major immunosuppressive mechanism. The mechanism of its vasculoprotective effect is not known, although it may be linked to inhibition of receptor tyrosine kinases (RTK). Here, we have investigated whether sufficient vasculoprotective effect could be obtained upon administration of FK778, a LFM analogue with shorter half-life, and compared the dose response with that of a known platelet-derived growth factor RTK inhibitor, imatinib, after endothelial injury in vivo.

METHODS AND RESULTS

Wistar rats were used for aorta denudations. The rats remained untreated or received either FK778 or imatinib (STI571) at decreasing oral doses from 10 mg/kg per day. Half of the animals in both treatment groups also received uridine to reverse DHODH activity. Morphometric analysis was done after 14 day follow-up. In the untreated group, moderate neointima formation was detected. FK778 almost completely inhibited intimal formation, with or without uridine addition (P<0.05). Imatinib also inhibited neointima formation (P<0.05), whereas exogenous uridine reversed its effect.

CONCLUSIONS

Our results demonstrate that FK778 inhibits neointima formation by way of a mechanism that is independent of DHODH inhibitory activity on vascular smooth muscle cell. Interestingly, the effect of imatinib was inhibited by uridine, suggesting that part of its action on vascular stenosis could be mediated through inhibition of pyrimidine synthesis.

Transplantation tolerance and autoimmunity after xenogeneic thymus transplantation

Successful grafting of vascularized xenografts (Xgs) depends on the ability to reliably induce both T cell-independent and -dependent immune tolerance. After temporary NK cell depletion, B cell suppression, and pretransplant infusion of donor Ags, athymic rats simultaneously transplanted with hamster heart and thymus Xgs developed immunocompetent rat-derived T cells that tolerated the hamster Xgs but provoked multiple-organ autoimmunity. The autoimmune syndrome was probably due to an insufficient development of tolerance for some rat organs; for example, it led to thyroiditis in the recipient rat thyroid, but not in simultaneously transplanted donor hamster thyroid. Moreover, grafting a mixed hamster/rat thymic epithelial cell graft could prevent the autoimmune syndrome. These experiments indicate that host-type thymic epithelial cells may be essential for the establishment of complete self-tolerance and that mixed host/donor thymus grafts may induce T cell xenotolerance while maintaining self-tolerance in the recipient.

Immunomodulatory effects of pretransplant donor blood transfusion on T-cell-independent xenoreactive immunity

BACKGROUND

Pretransplant blood transfusions have beneficial effects on both clinical and experimental allograft survival. In the present study, we examined whether pretransplant hamster blood transfusions (pHBT) alone or together with peritransfusion immunosuppressive strategies designed to target B cells and/or natural killer (NK) cells, could modulate T cell-independent (T-I) xenoreactivity in athymic nude rats.

METHODS

Hamster or mouse hearts were heterotopically xenotransplanted into untreated or treated athymic nude rats receiving either pHBT, anti-B cell or anti-NK cell therapy alone or their combinations. Xenoreactive antibodies (xAbs) and the percentage of NK cells were analyzed by FACScan analysis. NK cytotoxicity was measured by a standard 4 hr 51Cr release assay. Xenografts (Xgs) were examined by hematoxylin-eosin (H&E), by light microscopic method with Masson's trichrome and orcein staining, by immunofluorescent staining for immunoglobulin M and C3 deposition, and by immunohistochemical staining for infiltration of NK cells and macrophages (Mphis).

RESULTS

In 1 of 6 rats given pHBT alone 2 weeks before receiving hamster xenografts, Xg survival was prolonged to 55 days compared with 3.0+/-1.2 days in the other 5 animals and with 3.0+/-0.6 days in untreated animals. In the 55 days, surviving Xg infiltration of Mphis and NK cells was seen together with severe signs of chronic rejection, such as fibrosis and obliterative vasculopathy. The addition of the anti-B cell immunosuppressant MNA715 (malononitriloamide x920715, 20 mg/kg/day) from day -14 to day +14 or of 100 microL of rabbit anti-asialo GM1 serum ([anti-ASGM1] an NK cell depleting antibody) on day -14 resulted in a significant and species-specific prolongation of the survival of hamster Xgs, respectively 59.8+/-9.6 days and 58.2+/-14.7 days (P<0.001 vs. control group), but not of mouse heart Xgs that were rejected in a normal tempo. All prolonged hamster Xgs were infiltrated with Mphis and NK cells and developed severe lesions of chronic rejection, such as fibrosis and obliterative vasculopathy. In contrast, MNA715 or anti-ASGM1 alone had no effect on Xg survival (4.8+/-1.7 days and 2.7+/-0.6 days, respectively). Combined MNA715/anti-ASGM1 treatment only moderately promoted Xg survival (10+/-5.0 days; P<0.001). A simultaneous administration of pHBT, MNA715, and anti-ASGM1 induced indefinite and species-specific Xg survival in all recipients. In vivo and in vitro studies demonstrated that both T-I B cell and NK cell species-specific xenotolerance were achieved.

CONCLUSIONS

Pretransplant blood transfusion may have a species-specific immunomodulatory effect on T-I xenoreactivity. This effect is further enhanced by a temporary co-administration of MNA715 or by a single injection of anti-ASGM1. A combination of pHBT, MNA715, and anti-ASGM1 induces species-specific T-I xenotolerance.

Maintenance and reversibility of natural killer cell- and T cell-independent B lymphocyte xenotolerance in athymic nude rats

BACKGROUND

We previously described that a tolerogeneic regimen (TR) including (1) the infusion of a minced hamster heart suspension (MHH), (2) a single injection of an anti-natural killer (NK) cell serum (rabbit anti-asialo GM1 serum), and (3) a 4-week course of the B cell immunosuppressant leflunomide (20 mg/kg/ day) induced T cell-independent (T-I) B lymphocyte and NK cell tolerance for hamster xenoantigens in T-deficient athymic nude rats. In addition, the TR allowed for long-term hamster cardiac xenograft (Xg) survival when Xgs were transplanted 2 weeks (Day 0) after the initiation of the TR (started on Day - 14). The present study was undertaken to investigate some of the characteristics of this T-I xenotolerance in more detail.

METHODS

To investigate the duration of the effect of the TR on the T-I xenotolerance, hamster Xgs were transplanted at various times after initiation of the TR. To investigate whether the maintenance of the T-I xenotolerance depended on the presence of the graft, tolerated Xgs were removed on Day +28, and the subsequent evolution of the T-I xenotolerance as well as of second hamster Xg was followed. In addition, the reversibility of NK cell nonresponsiveness by recombinant interleukin-2 was investigated in vitro.

RESULTS

Xgs transplanted on day 0 or Day +7 showed long-term survival. However, all Xgs transplanted on Day +15, +30, and +60 were rapidly rejected. The latter rejection occurred in the absence of formation of anti-hamster immunoglobulin (Ig)M xenoreactive antibodies (xAbs) but correlated with the recovery of anti-hamster NK cell reactivity from day +14 on. Rejected Xgs showed infiltration of NK cells but absence of IgM xAbs or complement factor deposition. When tolerated first Xgs (transplanted on Day 0) were removed on Day +28, second hamster Xgs survived without treatment when transplanted 1 or 2 weeks later. However, second hamster Xgs transplanted 3 weeks after removal of the first Xgs were all rapidly rejected. Again, the latter rejection was characterized by the infiltration of the Xgs with NK cells and by the absence of anti-hamster IgM xAbs formation. Xenoreactive NK cell nonresponsiveness was not only shorter than xenoreactive B cell nonresponsiveness, but was also more fragile. This was evident from the fact that after addition of recombinant interleukin-2 in vitro, specific anti-hamster NK nonresponsiveness was easily broken.

CONCLUSIONS

NK cell and T-I B cell xenotolerance can be induced in T-deficient rats. Compared with B cell xenotolerance, the maintenance of NK cell xenotolerance is much shorter, more dependent on the presence of the graft, and easily reversible in vitro.

Induction of T-independent xenotolerance in a semi-discordant hamster-to-presensitized, nude rat model

BACKGROUND

We have previously demonstrated that in a concordant hamster-to-nude rat cardiac transplant model, T-independent specific B-lymphocyte and natural killer (NK)-cell tolerance could be induced, leading to long-term xenograft (Xg) survival. Here, we investigated whether the same could be achieved in a clinically more relevant semi-discordant model involving hamster hearts transplanted into pre-sensitized, nude rats.

METHODS

Sensitized, nude rats with high titers of anti-hamster immunoglobulin (Ig)M xenoantibodies (XAbs) were prepared by transplanting a first hamster heart without treatment. One week after rejection, a complete tolerizing regimen was given, including the following: a) an i.v. injection of hamster heart antigens; b) a 4-week administration of malononitriloamide; and c) a single injection of an anti-NK antiserum. Two weeks later, a second hamster heart was grafted. The isotype and level of XAb were examined by fluorescence-activated cell sorting. NK cytotoxicity was evaluated by a standard 4-hr 51Cr release assay. Hamster heart Xgs were examined by conventional histologic and immunohistochemical analysis.

RESULTS

Untreated, presensitized, nude rats developing high titers of IgM XAb underwent hyperacute rejection within 4 hr (n=4) after transplantation of the second hamster heart. Immunohistochemical analysis showed intensive staining for IgM and C3 along the vascular endothelia in the rejected Xgs. In contrast, presensitized, nude rats receiving the complete tolerizing regimen had a rapid decrease in anti-hamster IgM XAb. The second hamster hearts were not rejected and showed long-term survival even after withdrawal of malononitriloamide (n=6). Moreover, tolerant rats showed specific B-lymphocyte tolerance and a specific continuous absence of anti-hamster NK-cell reactivity.

CONCLUSION

T-independent B-lymphocyte and NK-cell xenotolerance can also be achieved in recipients with pre-existing IgM XAb.