Total lymphoid irradiation in renal transplantation

Individuality: the barrier to optimal immunosuppression

Immunosuppressive therapy aims to protect transplanted organs from host responses. Individuals have unique repertoires of responses to foreign antigens and toxic reactions to immunosuppressants; the former determining the type or intensity of rejection reactions and the latter influencing the severity of iatrogenic effects. Because existing agents target molecules that are widely distributed in tissues, new strategies must selectively block lymphoid cells only, disrupt alloresponses but not innate immune responses, interact synergistically with other agents, facilitate the homeostatic process that naturally leads to graft acceptance and ideally only interrupt donor-specific responses. Approaches presently under investigation aim to alter cell trafficking, or selectively deviate the maturation of antigen-presenting cells or inhibit lymphocyte-activation cascades - events that are crucial to rejection responses.

Tolerogenic immunosuppression for organ transplantation

BACKGROUND

Insight into the mechanisms of organ engraftment and acquired tolerance has made it possible to facilitate these mechanisms, by tailoring the timing and dosage of immunosuppression in accordance with two therapeutic principles: recipient pretreatment, and minimum use of post-transplant immunosuppression. We aimed to apply these principles in recipients of renal and extrarenal organ transplants.

METHODS

82 patients awaiting kidney, liver, pancreas, or intestinal transplantation were pretreated with about 5 mg/kg of a broadly reacting rabbit antithymocyte globulin during several hours. Post-transplant immunosuppression was restricted to tacrolimus unless additional drugs were needed to treat breakthrough rejection. After 4 months, patients on tacrolimus monotherapy were considered for dose-spacing to every other day or longer intervals.

FINDINGS

We frequently saw evidence of immune activation in graft biopsy samples, but unless this was associated with graft dysfunction or serious immune destruction, treatment usually was not intensified. Immunosuppression-related morbidity was virtually eliminated. 78 (95%) of 82 patients survived at 1 year and at 13-18 months. Graft survival was 73 (89%) of 82 at 1 year and 72 (88%) of 82 at 13-18 months. Of the 72 recipients with surviving grafts, 43 are on spaced doses of tacrolimus monotherapy: every other day (n=6), three times per week (11), twice per week (15), or once per week (11).

INTERPRETATION

The striking ability to wean immunosuppression in these recipients indicates variable induction of tolerance. The simple therapeutic principles are neither drug-specific nor organ-specific. Systematic application of these principles should allow improvements in quality of life and long-term survival after organ transplantation.

Long-term follow-up after total lymphoid irradiation in pediatric heart transplant recipients

BACKGROUND

Total lymphoid irradiation (TLI) is used to treat recurrent allograft rejection. Short-term success and complication rates have been reported in pediatric and adult cardiac transplant populations. We report the long-term efficacy and safety of TLI in treating intractable rejection in pediatric patients.

METHODS

Eight pediatric patients were treated with TLI (7 for recurrent rejection, 1 for risk of medication non-compliance). Therapy consisted of a mid-plane dose of 8 Gy administered with a 6-MeV linear accelerator using an anterior-posterior opposed technique. We reviewed outcomes for a total of 40 patient-years of follow-up.

RESULTS

We encountered rejection (>Grade 2 by International Society for Heart and Lung Transplantation criteria) in 56.7% +/- 34.7% of biopsies performed within 90 days before TLI. Rejection rates dropped to 3.1% +/- 8.8% within the first 90 days (p < 0.005) after therapy and remained low at 5.6% +/- 1.3% (p < 0.05) during the first year after completion of TLI. Median time from TLI to the first subsequent rejection episode was 305 days (range, 77-1,920 days). Long-term follow-up (>3 years) of 5 patients demonstrated a continuing low incidence of rejection. Non-Hodgkin's lymphoma was diagnosed in 1 of 8 patients, graft coronary artery disease in 4 of 8 patients, and restrictive cardiomyopathy in 1 of 8 patients after TLI.

CONCLUSIONS

Total lymphoid irradiation is an effective treatment for recurrent rejection and has short- and long-term efficacy. Morbid events may include cancer, graft coronary artery disease, and restrictive cardiomyopathy.

Tolerance in baboon kidney transplantation with total lymphoid irradiation (TLI) and anti-CD3/CD4-idarubicin conjugates

BACKGROUND

We previously reported the induction of transplantation tolerance by a modified wide field method of pretransplant total lymphoid irradiation (TLI), cumulative dose 800 cGy, given as 80 or 100 cGy fractions twice/week, in approximately one-third of chacma baboons receiving liver or kidney allografts (1-4) and in vervet monkeys receiving baboon kidney xenografts (5). In this study, the effects of the administration of brief courses of anti-CD3 or CD4-Idarubicin conjugates on the frequency and predictability of tolerance induction by TLI were examined.

METHODS

TLI was administered pretransplant in doses of 800, 600, or 400 cGy. The conjugates were administered either after transplantation in doses of 0.25 mg/kg body weight, 3 times/week for 2 weeks, or as a single dose of 1.0 mg/kg body weight 24 hr before transplantation.

RESULTS

Operational tolerance, defined as normal graft function >1 year after transplantation, was obtained in one-half of six baboons receiving the single dose of 1 mg/kg of Idarubicin conjugate pretransplant after 800 cGy of TLI and also in one of four baboons treated with 400 cGy of TLI and a single dose of anti-CD3 conjugate before transplantation. By contrast, administration of the conjugated antibodies 3 times/week for 2 weeks after transplantation prevented tolerance induction in all animals, providing further evidence for the involvement of active mechanisms, capable of inhibition by immunosuppressive agents, in tolerance induction with TLI, and of relevance to our reported clinical experience with TLI (6).

CONCLUSIONS

These promising findings invite further studies with a larger number of animals and additional brief regimens of irradiation and antibody dosages and specificities.

Non-human to human organ transplantation: its biologic basis and a potential role for radiation therapy

There is an inadequate supply of human donor organs for transplantation. Xenotransplantation, the transplantation of organs from non-human animals to humans, is one of the potential solutions to this problem. The pig appears to be the preferred donor. For xenotransplantation to be successful, researchers must deal with three fundamental problems: (1) Hyperacute rejection of porcine organs, related to binding of xenoreactive natural antibodies of the recipient to antigens on the graft's endothelial cells, must be overcome. (2) Transmission of animal pathogens to humans must be prevented. Concern about zoonosis is not only directed to the transplant recipient but also concerns the risk that an infectious agent will be transferred from the recipient to the general population. (3) The xenografted organ must be physiologically compatible with the recipient. The physiological function of a pig organ in a human and its ability to sustain a human are problematic. Total lymphoid irradiation (TLI) and thoraco-abdominal irradiation (TAI) as immunosuppressive modalities have been investigated in rodent-to-rodent, large mammals and non-human primates-to-primates, and pig-to-primate models. In certain clinical situations, TLI and TAI may prove to be important components for the preparation of the xenotransplant recipient. Progress in genetic engineering and cloning may soon lead to clinical trials in xenotransplantation.

History of clinical transplantation

The emergence of transplantation has seen the development of increasingly potent immunosuppressive agents, progressively better methods of tissue and organ preservation, refinements in histocompatibility matching, and numerous innovations in surgical techniques. Such efforts in combination ultimately made it possible to successfully engraft all of the organs and bone marrow cells in humans. At a more fundamental level, however, the transplantation enterprise hinged on two seminal turning points. The first was the recognition by Billingham, Brent, and Medawar in 1953 that it was possible to induce chimerism-associated neonatal tolerance deliberately. This discovery escalated over the next 15 years to the first successful bone marrow transplantations in humans in 1968. The second turning point was the demonstration during the early 1960s that canine and human organ allografts could self-induce tolerance with the aid of immunosuppression. By the end of 1962, however, it had been incorrectly concluded that turning points one and two involved different immune mechanisms. The error was not corrected until well into the 1990s. In this historical account, the vast literature that sprang up during the intervening 30 years has been summarized. Although admirably documenting empiric progress in clinical transplantation, its failure to explain organ allograft acceptance predestined organ recipients to lifetime immunosuppression and precluded fundamental changes in the treatment policies. After it was discovered in 1992 that long-surviving organ transplant recipients had persistent microchimerism, it was possible to see the mechanistic commonality of organ and bone marrow transplantation. A clarifying central principle of immunology could then be synthesized with which to guide efforts to induce tolerance systematically to human tissues and perhaps ultimately to xenografts.

Local graft irradiation after failure of modern immunosuppression in acute cellular and vascular graft rejection

PURPOSE

With improved chemical immunosuppressive agents, approximately 90% of rejection episodes can be reversed. However, in situations of failed immunosuppression, graft loss becomes inevitable. Our objective is to assess the efficacy of local graft irradiation (LGI) as an effort of last resort in a contemporary group of patients in whom graft failure to irreversible cellular and vascular rejection is imminent.

METHODS AND MATERIALS

A total of 308 renal transplantations were performed at our institution from 1992 to 1995, and an overall 1-year graft survival rate of 90% has been seen as a result of improvement in chemical immunosuppression. However, 6 patients were referred for LGI when all other measures failed to reverse the rejection crisis. Parameters that were studied in these patients included graft function and postirradiation graft histology.

RESULTS

Irradiation was associated with reversal of the rejection crisis and resulted in documented histological long-term graft survival in 1 of the 6 patients (17%). Two of the six patients (33%) had reversal of the rejection episode based on postirradiation biopsy of the renal allograft. Three of the six patients showed some level of clinical improvement of graft function for varying periods of time. One patient maintained stable allograft function without deterioration and with continued independence from hemodialysis. One recipient died from sepsis despite histologic improvement after irradiation.

CONCLUSIONS

Our impression is that LGI is indicated when all other measures have failed to reverse an acute rejection episode in the transplanted renal allograft. The role of radiation in this setting should be studied further.

Total lymphoid irradiation for refractory acute rejection in heart-lung and lung allografts

Persistent or recurrent acute allograft rejection (AR) refractory to high-dose steroid therapy can adversely affect long-term outcomes of heart-lung (HLT), bilateral-lung (BLT), and single-lung (SLT) transplantations. The use of total lymphoid irradiation (TLI) for the management of refractory acute AR in six transplant recipients (two men, four women; mean age, 29.8 +/- 3.8 years) is detailed. There are two HLT (primary pulmonary hypertension [PPH], cystic fibrosis [CF]), 1 BLT (pulmonary hypertension postventricular septal defect repair), and 3 SLT (sarcoid, PPH, congenital heart disease with atrial septal defect) recipients. Refractory AR is defined as persistent rejection unresponsive to high-dose steroid therapy in all cases. The BLT and SLT recipients had at least two moderate and one mild AR events per patient. The HLT recipients had at least two moderate acute heart and one severe and one mild asynchronous acute lung rejection events per patient. A total of 800 cGy of total lymphoid irradiation (TLI) was administered over a 5-week period. Mild and transient leukopenia was the only observed side effect. The patient with PPH received TLI 313 days after HLT for recurrent AR at another institution and died of ARDS 4 weeks after completing TLI. The patient with CF received TLI 707 days after HLT and died 457 days after TLI of severe obliterative bronchiolitis (OB) with multiorgan failure. The patient with BLT received TLI 176 days after transplant and died 372 days after TLI of respiratory failure related to severe rejection. One patient with SLT received TLI 78 days after transplant and died 679 days after TLI of severe acute AR. The two remaining patients with SLTs have been free from acute AR for more than 4 years. The patient with sarcoidosis received TLI 37 days after SLT following a clinical rejection event and two severe acute AR events. He is alive with normal lung function 5 years later. The patient with PPH received TLI 108 days after SLT following three moderate acute AR events and is alive with stable OB 4 years later. These limited preliminary results suggest that TLI has merit for the treatment of intractable acute AR following HLT and lung transplantation.

Anti-CD4 monoclonal antibody treatment combined with total lymphoid irradiation and cyclosporin A in hamster-to-rat cardiac transplantation. Analysis of lymphocyte subsets and anti-donor xenoantibodies

Combined treatment with total lymphoid irradiation and cyclosporin A results in prolonged graft survival in concordant xenogeneic cardiac transplantation, but reproducible long-term graft acceptance has proved to be difficult. Anti-CD4 monoclonal antibody treatment has been successful in inhibiting heart graft rejection in allogeneic models. Used as monotherapy in a concordant xenogeneic model for pancreatic islet transplantation, prolonged graft survival has been reported; however, no beneficial effect on primarily vascularized heart grafts was noted. The object of this investigation was to combine these treatment strategies with respect to reproducible long-term hamster heart graft survival in rats, to monitor the effect on lymphocyte subpopulations, and to determine possible anti-donor antibody formation correlated to time of rejection. Graft survival after combined preoperative total lymphoid irradiation and postoperative cyclosporin A + anti-CD4 monoclonal antibody treatment was prolonged from 14 to > 100 days (compared to spontaneous graft survival of three to four days), with long-term graft function in four of 19 recipients. Total white blood counts in the postoperative course were characterized by an unproportional increase of Ig+ cells and an incomplete recovery of CD4+ cells. Flow-cytometric analysis of anti-donor antibodies showed low levels of preformed antibodies and increasing amounts of strain-, but not donor-specific antibodies, correlated to the time of rejection. Long-term survivors with functioning grafts at the time of sacrifice had an initially moderate antibody increase with subsequent decrease to baseline levels. Our results indicate that total lymphoid irradiation combined with cyclosporin A and anti-CD4 monoclonal antibodies can prolong graft survival significantly in concordant hamster-to-rat cardiac xenotransplantation.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of parabiosis for investigating the mechanism of transplantation tolerance in bone marrow chimeras induced by total lymphoid irradiation

The mechanism of transplantation tolerance in total lymphoid irradiation (TLI)-induced semiallogeneic bone marrow chimeras without clinical evidence of graft-versus-host disease (GVHD) was investigated using the technique of surgical parabiosis. When held in parabiosis with normal BALB/c mice, BALB/c---- (BALB/c x C57BL/6)F1 (BALB----F1) chimeras survived 7-9 days, significantly (P less than 0.001) shorter than the 12-19 day survival of normal F1 hybrids kept in parabiosis with normal BALB, and in contrast to indefinite (greater than 200 days) survival of syngeneic BALB parabiotic partners. When C57 skin grafts were placed on BALB mice held in parabiosis with BALB----F1 chimeras, C57 skin grafts survived 50-60 days, in contrast to 10-14 days in normal BALB recipients (P less than 0.001). Lethal GVHD, induced in sublethally irradiated F1 recipients by 10(7) BALB spleen cells, could not be delayed or prevented by cotransfer of 10(7) to 30 x 10(7) tolerant BALB spleen cells obtained from stable BALB----F1 chimeras. GVHD reactivity of BALB spleen cells isolated from BALB----F1 chimeras tolerant of C57 could not be recovered by depletion of Lyt2 cytotoxic suppressor cells. Taken together, in the absence of suppressive capacity by suppressor cells, these data support functional clonal deletion as the primary mechanism responsible for the maintenance of unresponsiveness to host alloantigens in TLI-induced semiallogeneic chimeras, since no protection against induction of GVHD could be documented in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

Total lymphoid irradiation and antigen-specific tolerance: future therapy for experimental myasthenia gravis?

Total lymphoid irradiation (TLI) is effective in the immunosuppressive treatment of human and experimental autoimmune disorders, including experimental autoimmune myasthenia gravis (EAMG). Under certain circumstances. TLI may facilitate the induction of specific tolerance to antigens present during or shortly after the TLI treatment. This study was designed to determine whether TLI could induce or enhance tolerance to acetylcholine receptor (AChR), the antigen in myasthenia gravis, or to other antigens. We presented the antigens in various potentially tolerogenic forms to rats that were first pre-treated with TLI, or controls treated with sham irradiation. Injection of deaggregated human gamma globulin (HGG), a classical tolerogen, was most effective; it produced antigen-specific tolerance, which was significantly enhanced by pre-treatment with TLI. Injection of HGG coupled to rat peritoneal cells induced a moderate degree of specific tolerance; in this case, pre-treatment with TLI added only nonspecific suppression. In contrast, AChR, either in solubilized form with no adjuvant, or coupled to syngeneic rat peritoneal cells, failed to induce tolerance, and actually primed the immune system, when given alone or in conjunction with TLI. Subsequent challenge with AChR resulted in an enhanced (secondary) anti-AChR antibody response. These results show that the nature of the antigen itself may predispose to tolerance or to immune stimulation. AChR appears to be highly immunogenic. However, if a tolerogenic fragment or form of AChR can be identified, its use in combination with TLI may result in specific tolerance. If such specific tolerance can be induced during an ongoing autoimmune reaction to AChR, it would be an effective treatment for myasthenia gravis.

Treatment with total lymphoid irradiation, cyclosporin A and a monoclonal anti-T-cell antibody in a hamster-to-rat heart transplantation model: graft survival and morphological analysis

Treatment with preoperative total lymphoid irradiation and post-transplant cyclosporin A has been shown to have a synergistic effect on graft survival in allo- and xenotransplantation. Specific monoclonal antibodies against T cells and T cell subpopulations could offer new ways of preventing graft rejection in xenotransplantation. Graft survival and histology were examined after total lymphoid irradiation plus cyclosporin A treatment versus cyclosporin A plus a monoclonal antibody in a concordant, heterotopic, hamster-to-rat heart transplantation model. Preoperative total lymphoid irradiation was given at a dose of 1.25 Gy, 12 times over a period of 3 weeks. Cyclosporin A at a dose of 12.5 mg/kg per day was administered perorally and OX-19, a pan T cell monoclonal antibody, was given as intraperitoneal injections at doses of 100 micrograms or 500 micrograms/kg per day from day 0 until graft rejection. While total lymphoid irradiation alone prolonged graft survival to 9.4 days, total lymphoid irradiation plus cyclosporin A extended graft survival to a mean of 22 days. Cyclosporin alone or combined with the monoclonal antibody could not increase graft survival significantly when compared to untreated animals, which rejected their grafts within 3.7 days. Vascular rejection was the characteristic morphological finding, even after some weeks of excellent graft function. In conclusion, total lymphoid irradiation and cyclosporin A had a synergistic effect on graft survival in this concordant xenotransplantation model, although recent impressive results from other groups could not be reproduced. Total lymphoid irradiation combined with cyclosporin A appears to delay a primary humoral graft rejection, while the mechanism of rejection, judged by histology, stays the same.

Irradiation for xenogeneic transplantation

Xenogeneic transplantation (XT) is the transplantation of organs or tissues from a member of one species to a member of another. Mammalian species frequently have circulating antibody which is directed against the foreign organ irrespective of known prior antigen exposure. This antibody may lead to hyperacute rejection. There is no reliable means to avert hyperacute rejection once it ensues so efforts must be directed towards eliminating the pre-existing antibody. In those species in which hyperacute rejection of xenografts does not occur, cell-mediated rejection, similar to allograft rejection, may occur. It is in the prevention of this latter form of rejection that radiation is most likely to be beneficial in XT. Both total lymphoid irradiation (TLI) and selective lymphoid irradiation (SLI) have been investigated for use in conjunction with XT. TLI has contributed to the prolongation of pancreatic islet-cell xenografts from hamsters to rats. TLI has also markedly prolonged the survival of cardiac transplants from hamsters to rats. A more modest prolongation of graft survival has been seen with the use of TLI in rabbit-to-rat exchanges. Therapy with TLI, cyclosporine, and splenectomy has markedly prolonged the survival of liver transplants from hamsters to rats, and preliminary data suggest that TLI may contribute to the prolongation of graft survival in the transplantation of hearts from monkeys to baboons. SLI appears to have prolonged graft survival, when used in conjunction with anti-lymphocyte globulin, in hamster-to-rat cardiac graft exchanges. The current state of knowledge of the use of irradiation in experimental XT is reviewed.

Low-dose-rate total lymphoid irradiation: a new method of rapid immunosuppression

Total Lymphoid Irradiation (TLI) has been successful in inducing immunosuppression in experimental and clinical applications. However, both the experimental and clinical utility of TLI are hampered by the prolonged treatment courses required (23 days in rats and 30-60 days in humans). Low-dose-rate TLI has the potential of reducing overall treatment time while achieving comparable immunosuppression. This study examines the immunosuppressive activity and treatment toxicity of conventional-dose-rate (23 days) vs low-dose-rate (2-7 days) TLI. Seven groups of Lewis rats were given TLI with 60Co. One group was treated at conventional-dose-rates (80-110 cGy/min) and received 3400 cGy in 17 fractions over 23 days. Six groups were treated at low-dose-rate (7 cGy/min) and received total doses of 800, 1200, 1800, 2400, 3000, and 3400 cGy over 2-7 days. Rats treated at conventional-dose-rates over 23 days and at low-dose-rate over 2-7 days tolerated radiation with minimal toxicity. The level of immunosuppression was tested using allogeneic (Brown-Norway) skin graft survival. Control animals retained allogeneic skin grafts for a mean of 14 days (range 8-21 days). Conventional-dose-rate treated animals (3400 cGy in 23 days) kept their grafts 60 days (range 50-66 days) (p less than .001). Low-dose-rate treated rats (800 to 3400 cGy total dose over 2-7 days) also had prolongation of allogeneic graft survival times following TLI with a dose-response curve established. The graft survival time for the 3400 cGy low-dose-rate group (66 days, range 52-78 days) was not significantly different from the 3400 cGy conventional-dose-rate group (p less than 0.10). When the total dose given was equivalent, low-dose-rate TLI demonstrated an advantage of reduced overall treatment time compared to conventional-dose-rate TLI (7 days vs. 23 days) with no increase in toxicity. This was accomplished without compromise of the immunosuppressant activity of TLI as demonstrated by comparable allogeneic skin graft survival times between the two 3400 cGy treatment groups. This clinical advantage would prove to be beneficial where immediate suppression of the immune system is desirable.

Treatment of experimental myasthenia gravis with total lymphoid irradiation

Total lymphoid irradiation (TLI) has been reported to be effective in the immunosuppressive treatment of certain human and experimental autoimmune disorders. We have investigated the effects of TLI in Lewis rats with experimental autoimmune myasthenia gravis (EAMG) produced by immunization with purified torpedo acetylcholine receptor (AChR). The radiation is given in 17 divided fractions of 200 rad each, and nonlymphoid tissues are protected by lead shielding. This technique suppresses the immune system, while minimizing side effects, and permits the repopulation of the immune system by the patient's own bone marrow cells. Our results show that TLI treatment completely prevented the primary antibody response to immunization with torpedo AChR, it rapidly abolished the ongoing antibody response in established EAMG, and it suppressed the secondary (anamnestic) response to a boost of AChR. No EAMG animals died during TLI treatment, compared with six control animals that died of EAMG. TLI produces powerful and prompt immunosuppression and may eventually prove useful in the treatment of refractory human myasthenia gravis.