By Peter Sottong
Joseph Murray, MD, performed the first successful human kidney transplant at Peter Brent Brigham Hospital in Boston when a kidney donated by the patient’s twin brother was transplanted. Its success was attributed to the lack of a rejection response on the part of the patient. In these early days of transplantation medicine, the primary concern was controlling the near–term rejection response to ensure the patient’s survival. Since then, better immunosuppressant drugs and drug combinations have permitted the transplant procedure to evolve to one of a more routine nature, in which the focus is long–term patient and graft survival.
The survival rate at 3 months (the period of highest risk of acute rejection) for most transplants is now more than 90%, as reported in the 2001 OPTN Annual Report for 1991–2000; however, the graft survival rate at 3 years can fall as low as 53% (pancreas transplant). In the latter case, the graft loss is the result of organ failure that occurs slowly, as the immune system becomes less responsive to immunosuppression therapy. In addition, adverse effects and long-term toxicity also contribute to this chronic rejection of the graft and death of the patient.
In fact, the most common cause of late-graft loss is premature death of the recipient in which the transplanted organ is still functional. Death of kidney transplant recipients with a functioning graft increased from 23.8% in 1970–1979 to 37.5% in 1990–1999, while organ rejections fell by half during the same period (65.7% in 1970–1979 to 30.3% for 1990–1999).1 Infections, stroke, cardiac disease, and cancers are among the causes of death in transplant patients with good graft function. These conditions are often the result of oversuppression.2
Organ toxicities such as renal failure due to the antirejection drugs administered to recipients of nonrenal transplants have been recently highlighted in the New England Journal of Medicine.3 These researchers established that 17% of the transplant recipients developed chronic kidney failure, and a third of those developed end-stage renal disease requiring dialysis or a kidney transplant. Certain transplants were associated with higher rates of kidney failure. By the fifth anniversary of the transplant, nearly 11% of heart patients, 15% of lung patients, 18% of liver patients, and 21.3% of intestine recipients had kidney failure.
For these reasons the current aim of transplant physicians is to optimize the level of immunosuppression to prevent rejection while avoiding other adverse effects of oversuppression.4 To do this, methods are being studied to develop low toxicity regimens and tailor the immunosuppressive protocols to individual patient needs.5,6,7,8 The Clinical Practice Guidelines Committee of the American Society of Transplantation has developed guidelines to help physicians optimize care for individual renal transplant patients, and other strategies that focus on tailoring dosage are being developed. They have concluded that, because the window is narrow in which some of the strong immunosuppressive agents are efficacious but not toxic, monitoring immunosuppression is crucial. In addition, it has been suggested that continual refinement of a transplant patient’s immunosuppressive regimen may be more desirable than a permanent one, because drug adjustments based on both long-term and short-term toxicity and efficacy concerns can be incorporated.9 This approach is facilitated by more individualized immunosuppressive protocols.
Organ recipients are widely diverse in their response to immunosuppressant drugs due to age; ethnic background; the presence of other medical conditions such as diabetes, osteoporosis, and cardiovascular disease; graft state (eg, pathology and age); and the status of an individual’s immune system.2,5,6 Drugs are administered primarily on the basis of body weight, and monitoring the therapeutic drug levels in the patient’s blood is routine for the major immunosuppressants. However, because the immunological condition of individuals is different, and because multidrug therapies are often employed, the usefulness of assessing a therapeutic drug level as a tool for drug-dosing decisions is limited. The FDA has recognized this limitation in guidelines issued last year.10 In this document, the FDA cautioned that because of the individual differences in sensitivities to the drugs, toxicities, type of transplant, time post-transplant, and other factors, individual cyclosporine values cannot be the sole indicator that changes in treatment regimens are needed.
In addition to the drug monitoring assays, blood chemistry tests such as serum creatinine and transaminase values, which are indicative of organ function, are also typically performed to monitor transplant organ health. Organ biopsies are also used as a method for understanding the progression of rejection. While these tests are helpful in determining impending rejections, the indication of abnormal results occurs late in the process. Until recently, these have been the only routine approaches available to physicians.
Drugs that mute the effect of the body’s immune system can produce side effects—ranging from weight gain to more severe complications such as diabetes and bone thinning—and create susceptibility to infection and cancer. Because of the danger of long-term adverse effects as a result of prolonged use of these drugs, there is an interest in attempting to wean patients off traditional drug regimes by using ever-decreasing doses. While this is still controversial, Thomas Starzl, MD,a noted organ transplant pioneer at the University of Pittsburgh, recently announced his agreement with this idea.11 Reversing his previous position on the use of antirejection drugs, he has now implemented a low-dose approach as a matter of routine at the medical center. This goal of inducing “immune tolerance” in which transplant patients can maintain good graft function with few or no drugs has been noted by others7,12,13. Toward this end, scientists and physicians at the Immune Tolerance Network, headquartered at the University of California, San Francisco, which is sponsored by a joint contract from the National Institutes of Health and the Juvenile Diabetes Foundation, solicit, develop, implement and assess strategies and assays for inducing, maintaining, and monitoring tolerance for kidney, liver, and islet cell transplants. Close surveillance on patients who are receiving reduced drug doses is essential.14
To understand the exact level of immunosuppression during tolerance or standard maintenance protocols, treating physicians need accurate insight into the individual patient’s immune status. Achieving this has been difficult because the therapeutic drug monitoring assays do not correlate with the dose of the drug administered due to individual pharmacokinetic differences and the monoclonal antibody methodology used for their detection15 and because the patient’s immunologic response to these drugs may not be accurately reflected by the drug level detected in the blood. A means of assessing the pharmacodynamic effect of these drugs or drug combinations on the immune system would be valuable in understanding their potential antagonistic or synergistic effect in any given patient because these immunosuppressive drugs have no biological end points for dose adjustment.4 Until now, there has been no such method available for the direct assessment of these pharmacodynamics in transplant recipients that takes into account the cumulative effect of complex interactive factors such as time post-transplant, type of organ, and interactions with other drugs.16
The survival rate at 3 months for most transplants is now 90%.
An article in Clinical Transplantation describes results of an in vitro clinical assay used in a multicenter study for measuring the global immune response in transplant patients undergoing immunosuppressant therapies that addresses this clinical need.16 ImmuKnow™, an immune cell function assay from Cylex Inc of Columbia, Md uses the plant lectin phytohemagglutinin (PHA) to stimulate lymphocytes, and measures increases in intracellular adenosine triphosphate (ATP) following activation.17 Whole blood samples are used to maintain the presence of the drug during overnight incubation, after which CD4 cells are selected using paramagnetic particles coated with a monoclonal antibody to the CD4 epitope. The major immunosuppression drugs are designed to inhibit T-cell activation.18 Therefore, by comparing stimulated T-cell responses to unstimulated ones, quantitative assessment of the ability of the immune system to respond to stimulation is achievable. The Cylex bioassay, which uses established T-cell reactivity ranges in the assessment of functional immunity for an individual solid organ recipient at any point in time, was cleared by the FDA in 2002.
The ImmuKnow Immune Cell Function Assay provides “biological end point” information useful in assessing the impact of immunosuppressive therapies on patients’ immune systems. With specific measurement data of the status of the immune system obtained for each organ transplant recipient, individualized therapies can be designed to better evaluate the net effect of therapeutic drug treatments and dosage reduction or increases and to better optimize treatment protocols.
For additional information contact Peter Sottong, Vice President, Cylex Inc (410) 964-0236.
References:
1. Howard RJ, PR Patton, AI Reed, et al. The changing causes of graft loss and death after kidney transplant. Transplantation 2002;73:1923-1928.
2. Ojo AO, Hansen JA, Wolfe, RA, et al. Long-term survival in renal transplant recipients with graft function. Kidney International. 2000;57(1):307-313.
3. Ojo, AO, Held PJ, Port, FK, et al. Chronic renal failure after transplantation of non-renal organ. New England Journal of Medicine. 2003;349 (10):931-940.
4. Bennett WM. Immunosuppression with mycophenolic acid: one size does not fit all. Journal American Society of Nephrology. 2003;14:2414-2416.
5. Danovitch GM. Choice of immunosuppressive drugs and individualization of immunosuppressive therapy for kidney transplant patients. Transplantation Proceedings. 1999;31 (suppl 8A): 2S-6S.
6. Halloran PF, A Melk and C Barth. Rethinking chronic allograft neuropathy: the concept of accelerated senescence. Journal American Society of Nephrology. 1999:10 (1): 167-181.
7. Raimondo ML and Burroughs AK. Single-agent immunosuppression after liver transplantation: what is possible? Drugs. 2002;62:1587-1597.
8. Vilatoba M, Contreras JL, and Eckhoff DE. New immunosuppressive strategies in liver transplantation: balancing the efficacy and toxicity. Current Opinion in Organ Transplantation. 2003;8:2:139-145.
9. Lo A and Alloway RR. Strategies to reduce toxicities and improve outcomes in renal transplant recipients. Pharmacotherapy. 2002;22(3): 316-318.
10. US Department of Health and Human Services, Food and Drug Administration, Center for Devices and Radiological Health, Chemistry and Toxicology Branch, Division of Clinical Laboratory Devices, Office of Device Evaluation, Class II Special Controls Guidance Document: Cyclosporine and Tacrolimus Assays: Draft Guidance for Industry and FDA. February 2002.
11. Waldholz M. Transplant pioneer rejects approach he helped create. Wall Street Journal, June 2, 2003.
12. Takatsuki MS, Uemoto Y, Inomata, et al. Weaning of immunosuppression in living donor liver transplant recipients. Transplantation. 2001;72:449-454.
13. Kasiske BL, H Chakhera, T Louis and J Z Ma. Immunosuppression withdrawal in renal transplantation. Transplant Proceedings. 2000:32:1506-1507.
14. Knoll GA, I MacDonald, A Khan, C van Walraven. Mycophenolate mofetil dose reduction and the risk of acute rejection after renal transplantation. Journal American Society of Nephrology. 2003;14:2381-2386.
15. Venkataramanan R, Shaw CM, Sarkozi L, et al. Clinical utility of monitoring tachnolimus blood concentrations in liver transplant patients. Journal of Clinical Pharmacology. 2001;41:542-551.
16. Kowalski RD, Post MC, Schneider, et al. Immune cell function testing: an adjunct to therapeutic drug monitoring in transplant patient management. Clinical Transplantation. 2003;17:77-88.
17. Wier, ML, Methods for measurement of lymphocyte function U.S Patent. 1998; # 5,773,232.
18. Lin J, Farmer JD Jr, Lane WS, et al. Calcineurin is a common target of cyclophilin – cyclosporin and FKBP – FK506 complexes. Cell. 1991;66:807-815.
