Population pharmacokinetics and exposure-response relationships for basiliximab in kidney transplantation. The U.S. Simulect Renal Transplant Study Group

Current immunosuppressant regimens: considerations for critical care

While current immunosuppressive drug regimens have significantly increased the rate of successful transplantation outcomes, they convey potentially serious and overlapping adverse effects. Cyclosporine and tacrolimus are the cornerstones of current immunosuppression, achieving excellent one-year renal graft survival rates. Other promising new drugs include sirolimus, which has been demonstrated to reduce efficacy failure rates among renal transplant recipients, and everolimus, which is currently undergoing clinical trials. Agents targeting novel sites in the immune response or disrupting the ischemia-reperfusion cascades are currently under development. Among them, only FTY720 is undergoing large-scale human clinical trials. With its unique mechanism of action and synergistic interactions with cyclosporine and sirolimus, it may provide the foundation for a new era in immunosuppression.

Infliximab induces potent anti-inflammatory and local immunomodulatory activity but no systemic immune suppression in patients with Crohn's disease

BACKGROUND

Anti-TNFalpha therapy with infliximab is effective for Crohn's disease. Infliximab neutralizes the biological activities of TNFalpha, a cytokine involved in host-defence against certain infections.

AIM

To evaluate the effects of infliximab on the gut and peripheral immune system functions.

METHODS

Biopsies and blood samples from three clinical trials of infliximab in Crohn's disease were analysed. Pharmacokinetics, changes in leucocyte counts and T cell subsets, T cell function, and cytokine profiles of lamina propria mononuclear cells (LPMC) and peripheral blood mononuclear cells (PBMC) were analysed.

RESULTS

Infliximab has a serum half-life of 9.5 days and is still detectable in serum 8 weeks after infusion. Leucocyte counts showed consistent changes from baseline toward normal values after therapy. Monocytes and lymphocytes were modestly increased, while neutrophils were decreased 4 weeks after treatment. Lymphocyte subsets and T cell proliferative responses were not altered after therapy. The proportion of PBMCs capable of producing IFNgamma and TNFalpha did not change, while Th1 cytokine production by stimulated LPMC was decreased after infliximab therapy.

CONCLUSION

The clinical efficacy of infliximab is based on local anti-inflammatory and immunomodulatory effects in the bowel mucosa, without generalized suppression of systemic immune functions in Crohn's disease patients.

Differential influence of azathioprine and mycophenolate mofetil on the disposition of basiliximab in renal transplant patients

Pharmacokinetic sampling was performed in two multicenter trials in which basiliximab (anti-CD25 monoclonal antibody) was administered with triple immunosuppression consisting of cyclosporine microemulsion, corticosteroids, and either azathioprine or mycophenolate mofetil. Blood samples were collected over 12 wk post-transplant from 31 azathioprine-treated and 66 mycophenolate mofetil-treated patients. Empirical Bayes estimates of each patient's basiliximab disposition parameters were derived and the duration of CD25 saturation was estimated as the time over which serum concentrations exceeded 0.2 microg/mL as confirmed by flow cytometry measurements. Basiliximab clearance was 29+/-14 mL/h when coadministered with azathioprine and 18+/-8 mL/h with mycophenolate mofetil. Both were significantly lower compared with a clearance of 37+/-15 mL/h from a previous study of basiliximab with dual therapy (p<0.001). As a consequence of the lower clearance of basiliximab, the durations of CD25 saturation were prolonged in the presence of azathioprine (50+/-20 d; range, 13--84) and mycophenolate mofetil (59+/-17 d; range, 28--94) compared with dual therapy (36+/-14 d; range, 12--91). A total of 27 acute rejection episodes occurred during the first 6 months in the two studies. Durations of CD25 saturation were not different in these patients compared with those who remained rejection-free in each study. A single patient among 57 who were screened developed anti-idiotype antibodies to basiliximab. The average duration of CD25 saturation was prolonged by 39 and 64% in the presence of azathioprine and mycophenolate mofetil, respectively. This graded effect was also observed for basiliximab clearance and may be due in part to a differentially reduced humoral response to basiliximab. Nonetheless, the range of CD25 saturation durations and basiliximab clearances did not extend outside the range when basiliximab was used with dual therapy in the absence of these agents. Hence, no dosing adjustment is deemed necessary when basiliximab is used in triple immunosuppressive therapy including either azathioprine or mycophenolate mofetil.

Drug therapy for acute graft-versus-host disease prophylaxis

The mechanisms of many immunosuppressive drugs have been defined, allowing for a rational approach to the use of these agents in GVHD prophylaxis. In addition to standard drugs such as methotrexate, cyclosporine, tacrolimus, and glucocorticoids, new agents-mycophenolate mofetil, tresperimus, rapamycin, basiliximab, and daclizumab-are now part of the immunosuppressive armamentarium. Improved understanding of tolerance has resulted in new approaches to prevention of GVHD. Anti-CD40L, CTLA-4-Ig, tresperimus, and rapamycin are agents that are being explored in this area and have shown impressive results in animal models. Currently, the standard therapy for acute GVHD prophylaxis in matched sibling transplants remains cyclosporine and methotrexate. Lower dose methotrexate, particularly in combination with tacrolimus, has shown good results in single arm studies with low toxicity, but this has not been tested in a randomized study. For unrelated donor transplants there is less GVHD when tacrolimus, rather than cyclosporine, is combined with methotrexate; there seems little reason to use cyclosporine in this setting. GVHD is still the major barrier to more widespread use of unrelated donor transplants and improved regimens are needed. In vivo T-cell depletion using Campath-1 or ATG is being used in high-risk patients. Data on its efficacy are so far anecdotal. Due to the variation in grading of GVHD between centers, randomized studies are needed to quantify the relative merits of different regimens, and participation in such studies is encouraged.