Immunopathology of human T cell responses to skin, artery and endothelial cell grafts in the human peripheral blood lymphocyte/severe combined immunodeficient mouse

Blood vessels and their endothelial lining are major stimulators and targets of the rejection response. The immunological properties of human endothelial cells differ significantly from those of other species and new models are needed for proper study of human vessels in the transplant setting. We have employed the human peripheral blood lymphocyte/severe combined immunodeficiency (huPBL/SCID) mouse for this purpose. We describe here our results involving transplantation of human skin, human artery and cultured human endothelial cells. We also describe our more limited experience using porcine skin and artery transplantation to study human T cells responses to pig endothelium.

Sirolimus-based immunosuppression with reduce dose cyclosporine or tacrolimus after renal transplantation

Sirolimus (SRL), a fermentation product of Streptomyces hygroscopicus, complexes with the FKBP12 to inhibit cyclin dependent kinase(s), collectively termed the target of rapamycin (TOR), causing G(1)-S phase cell cycle arrest. Safety and efficacy have been documented in clinical renal transplantation, but concerns were raised due to important biologically relevant side effects. Hyperlipidemia was identified, beginning with early clinical experiences, and the unexpected findings that SRL may exacerbate CsA associated nephrotoxicity was observed during the pivotal phase III studies. This report details results of our experience using SRL (target trough concentration, 10-15 ng/mL) with low dose CsA (target trough concentration, 50-100 ng/mL), seeking to determine whether this approach might provide effective immunosuppression while reducing associated nephrotoxicity. Among 121 renal transplant recipients, 62 received the SRL based regimen and 59 received MMF with all patients receiving CsA and prednisone. Similar to earlier clinical experiences, hematopoeitic abnormalities and hyperlipidemia were observed among patients who received SRL, and those abnormalities were readily controlled. However, unlike observations from the phase III SRL studies, renal function was not adversely affected. These findings support the growing body of evidence indicating that SRL based immunosuppression in combination low dose calcineurin inhibitors and corticosteroids is safe, efficacious, and without associated renal toxicity.

Treatment of osteoporosis and osteopenia in long-term renal transplant patients with alendronate

Bone mineral density (BMD) and biochemical markers of bone-turnover were evaluated in a 2-year study in 58 long-term renal transplant recipients with good renal function. In the first year of study, data were collected and patients with osteoporosis and parameters of high bone turnover were classified as being at high risk for on-going bone loss (Group A; n = 29). Patients with lesser degrees of bone loss or without biochemical parameters of high bone turnover were followed longitudinally (Group B; n = 29). Group A patients were then placed on alendronate 10mg/day and both groups were followed for an additional year. Changes in regional BMD and bone-turnover markers between the first and second year within each group were analyzed using paired tests. BMD in Group A, which had declined at the lumbar spine (- 1.6 +/- 0.5%) and total femur (-1.5 +/- 0.4%) during the first year of the study, increased on alendronate therapy at both the lumbar spine (+3.4 +/- 0.6%, p = 0.001) and total femur (+1.6 +/- 0.6%, p <0.001). These patients also experienced a significant decline in levels of serum alkaline phosphatase, osteocalcin, urinary levels of deoxypyridinoline and pyridinoline. In contrast, neither BMD nor biochemical markers changed significantly over 2 years in Group B. The current results demonstrate that renal transplant patients with osteoporosis and biochemical parameters of high bone turnover are at continued risk for bone loss. Therapy with a bisphosphonate can reverse this bone loss and even increase bone mass in these patients. Whether patients with lesser degrees of bone loss and/or patients without parameters of high bone turnover can also benefit from bisphosphonate therapy deserves further study.

Multicenter evaluation of a polyurethaneurea vascular access graft as compared with the expanded polytetrafluoroethylene vascular access graft in hemodialysis applications

OBJECTIVES

The purpose of this study was to compare in a randomized, prospective, and controlled study, the performance of a multilayered, self-sealing polyurethane vascular access graft (PVAG) and expanded polytetrafluoroethylene (ePTFE) vascular access grafts in hemodialysis applications. Performance measures included graft survival, complications, time to early cannulation, and hemostasis times after cannulation.

STUDY DESIGN

A total of 142 patients were randomized equally to receive one of the two grafts after meeting all eligibility requirements. All patients were followed up prospectively to 12 months or to the end of secondary patency. Specifically, this study documented the performance of the PVAG and ePTFE grafts by determining the patencies and complications for both grafts.

RESULTS

Patient characteristics between the two groups were similar with respect to risk factors and demographic characteristics (P >.05). Life-table patencies from the date of first dialysis were primary patency: PVAG 55% versus ePTFE 47% (6 months) and PVAG 44% versus ePTFE 36% (12 months) and secondary patency: PVAG 87% versus ePTFE 90% (6 months) and PVAG 78% versus ePTFE 80% (12 months). None of these differences were significant (P >.05). Both primary and secondary patencies were also not significantly different when the date of implantation was the starting point. Adverse events and complications were similar for the two groups, except the PVAG group had a higher incidence of technical complications manifested by graft kinking when compared with the control cohort (P <.05). Additionally, there was no significant difference in complication rates between these two groups with regard to infection and bleeding. When the time to hemostasis after cannulation was compared at 5minutes or less, there were more PVAG cannulation sites that achieved hemostasis compared with ePTFE sites, and this difference was significant (P <.0001). When time to first dialysis access was compared between the two grafts, 53.9% of all PVAG grafts were cannulated before 9 days versus none with the ePTFE grafts (P <.001). However, long-term graft survival was not significantly different when PVAG patients were stratified into early (< 9 days) and the late access (9 >/= days) groups (P =.29).

CONCLUSIONS

The PVAG graft allows for early access without compromising long-term performance. Both PVAG and standard ePTFE grafts have similar long-term outcomes, despite early access with the PVAG vascular access grafts.

Parameters of high bone-turnover predict bone loss in renal transplant patients: a longitudinal study

BACKGROUND

Osteoporosis is a serious complication of kidney transplantation. Various factors have been postulated to contribute to posttransplant bone loss, among them treatment with corticosteroids, the use of cyclosporine and cyclosporine-like agents, and persistent hyperparathyroidism. In a previous cross-sectional study of long-term renal transplant recipients, we observed that osteoporosis or osteopenia was present in 88% of patients. Because biochemical markers of bone formation (serum osteocalcin) and bone resorption (urine pyridinoline, PYD, and deoxypyridinoline, DPD) were elevated in the majority of study subjects, we hypothesized that elevated rates of bone-turnover contribute to posttransplant bone loss in long-term renal transplant patients. This study was performed to examine this hypothesis.

METHODS

The study population was composed of 62 patients who were more than 1-year postrenal transplantation and who had preserved renal function. They were followed prospectively for 1 year. Biochemical markers of bone-turnover were measured at study entry, and patients were classified as having high bone-turnover based on elevated urinary levels of at least one marker of bone resorption (i.e., PYD or DPD) and/or serum osteocalcin (group 1). If none of these were present, they were classified as having normal bone-turnover (group 2). Bone mineral density (BMD) was measured by dual energy x-ray absorptiometry (DEXA) at time of entry into the study and again after 1 year of follow-up. The changes in BMD at the lumbar spine, hip, and wrist over the period of the study were compared between the high and normal bone-turnover groups.

RESULTS

Forty-three patients (69%) were classified as having high bone-turnover (Group 1), and 19 patients (31%) were classified as having normal bone-turnover (Group 2). There was a statistically significant difference in change in BMD between the two groups at the lumbar spine (-1.11+/-0.42%, high bone-turnover, vs. 0.64+/-0.54%, normal bone-turnover; P=0.02) and the hip (-0.69+/-0.38%, high bone-turnover, vs. 1.36+/-0.66%, normal bone-turnover; P=0.006). Whereas group 2 had stable bone mass, group 1 exhibited bone loss at these skeletal sites.

CONCLUSIONS

Our results indicate that bone loss is greater in renal transplant recipients with elevated biochemical markers of bone-turnover, suggesting that these markers may be useful in identifying patients at risk for continued bone loss. These data support the hypothesis that continued bone loss in long-term renal transplant recipients is associated with high bone-turnover. If accelerated bone resorption does play a role in posttransplant bone loss, this would provide a strong rationale for use of antiresorptive therapy for the prevention and treatment of this complication.

Human T cells infiltrate and injure pig coronary artery grafts with activated but not quiescent endothelium in immunodeficient mouse hosts

BACKGROUND

We have previously demonstrated that human artery grafts transplanted to immunodeficient mice are infiltrated and injured by unsensitized allogeneic human T cells. We extended our investigations to human anti-porcine xenoresponses in this model.

METHODS

Pig coronary artery segments were interposed into the infrarenal aorta of severe combined immunodeficiency/beige mice. After 7 days, certain recipients were reconstituted with human leukocytes and/or treated with proinflammatory cytokines. The grafts were harvested after 1-70 days and examined by histology, immunohistochemistry, and morphometry.

RESULTS

Pig artery grafts from untreated mice had no evidence of injury, leukocytic infiltrate, or endothelial cell activation up to 70 days postoperatively, despite deposition of murine complement. Host reconstitution with human peripheral blood mononuclear cells resulted in a discrete population of circulating T cells that did not infiltrate or injure the grafts up to 28 days after adoptive transfer. Administration of porcine interferon-gamma for up to 28 days sustained the expression of graft vascular cell adhesion molecule-1 and major histocompatibility complex antigens, but did not initiate recruitment of human leukocytes. In contrast, treatment with human tumor necrosis factor for 7 days induced the de novo expression of porcine E-selectin by graft endothelial cells and elicited human T cell infiltration and human peripheral blood mononuclear cell-dependent vascular injury.

CONCLUSIONS

The human peripheral blood mononuclear cell-severe combined immunodeficiency/beige mouse model identifies a significant difference between human T cell allogeneic and xenogeneic responses in vivo. Xenografts with quiescent endothelium are not infiltrated or injured by T cells under the same conditions in which allografts are rejected. Activation of pig coronary artery endothelial cells by human tumor necrosis factor, but not porcine interferon-gamma, elicits cellular xenoresponses.

RAD in de novo renal transplantation: comparison of three doses on the incidence and severity of acute rejection

BACKGROUND

The effects of three doses of RAD (40-O-[2-hydroxyethyl]-rapamycin), a novel macrolide with potent immunosuppressive and antiproliferative properties, on the incidence and severity of acute rejection episodes as well as its tolerability were evaluated in a dose-ranging study in de novo renal transplant recipients.

METHODS

In this double-blind, parallel group, multicenter study, recipients were randomized to receive 1 mg, 2 mg, or 4 mg/day of RAD in combination with Neoral (cyclosporine, USP MODIFIED) and corticosteroids. The incidence and severity of biopsy-proven acute rejection episodes, graft survival, patient survival, infection rates, laboratory measurements, and adverse events were compared across groups after 6 months of therapy.

RESULTS

Among the 103 recipients, patients receiving 1, 2, or 4 mg/day experienced a 32.4%, 14.7%, or 25.7% incidence of biopsy-proven acute rejection episodes within the first 6 months posttransplantation, respectively. Even though the study was not powered to demonstrate efficacy, the incidence of moderate and severe acute rejection episodes was found to be significantly lower among patients in the 2 mg and 4 mg/day groups than in the 1 mg/day group (P=0.002 and P=0.006, respectively). Overall graft and patient survival rates were excellent. RAD was generally well tolerated. Although blood lipid levels increased in all groups, changes were manageable with lipid-lowering agents and did not warrant discontinuation of study medication. The incidence of viral and fungal infections was low; however, it was higher among recipients treated with 4 mg/day.

CONCLUSIONS

In combination with Neoral and corticosteroids, RAD doses of 2 mg and 4 mg/day resulted in lower rates of acute rejection episodes and efficacy failure than the 1 mg/day dose and were significantly more effective in reducing the severity of rejection. Large-scale, controlled, follow-up studies are currently in progress to confirm these initial findings.

A prospective economic evaluation of basiliximab (Simulect) therapy following renal transplantation

BACKGROUND

Immunoprophylaxis with basiliximab (Simulect), an anti-interleukin-2-receptor (anti-IL-2R; CD25) chimeric monoclonal antibody, has been demonstrated to significantly reduce the incidence of acute cellular rejection in adult renal allograft recipients (32% vs. placebo, p < 0.01).

METHODS

An economic evaluation was conducted as part of a U.S. multi-center, randomized, double-blind, placebo-controlled clinical trial comparing basiliximab plus dual immunosuppressive therapy (cyclosporine modified [Neoral] and corticosteroids) to dual therapy alone. Healthcare resources utilized by the 346 subjects in the 'intent-to-treat' population were prospectively collected over the 1-yr study period. Direct medical costs were determined for all hospitalizations, outpatient provider visits, procedures (excluding the initial transplant procedure), laboratory and diagnostic tests, and immunosuppressants, including basiliximab when administered.

RESULTS

Total first-year medical costs were lower for the basiliximab group than for the placebo group ($28 927 vs. $32 300, difference = $3373). although this difference was not statistically significant. First-year hospital costs for treating acute rejection were also lower for the basiliximab group ($9328 vs. $10761, difference = $1433); however, this difference did not achieve statistical significance. Importantly, the efficacy analysis demonstrated a significant reduction in the incidence of acute rejection (38 vs. 55%, p < 0.01) in the basiliximab arm, and this was accomplished without increasing the overall cost of care. Fewer basiliximab-treated patients (8 vs. 15%,, p = 0.03) were hospitalized. This observation suggested less serious illness and reduced treatment costs among basiliximab-treated patients, because the overall incidence of infection was similar between the groups. The adverse event profile of patients receiving basiliximab was clinically and economically indistinguishable from that of those treated with placebo.

CONCLUSION

Induction immunosuppression with basiliximab, combined with cyclosporine modified and corticosteroids, was therapeutically beneficial and contained medical costs during the initial post-transplant year.

Temporal changes of cytokines and nitric oxide products in urine from renal transplant patients

BACKGROUND

Acute rejection and urinary tract infection (UTI) both increase nitric oxide synthase (NOS) activity in urine from renal transplant patients. Also, with rejection, a regulatory interplay between nitric oxide (NO) and cytokines has been suggested. Thus, measurement of the temporal changes of NOS products and cytokines in urine will provide a strategy for the diagnosis of acute rejection and for its differentiation from UTI.

METHODS

Soluble interleukins (ILs) and NOS-related products, cyclic GMP (cGMP), nitrate, and nitrite were measured in 192 urine samples consecutively collected from 13 patients within the first three months of transplantation. Sixty-seven additional urine specimens were collected randomly from 24 patients for follow-up analysis of the nitrate test.

RESULTS

Among patients who experienced rejection, the percentage (%) binding of IL-2 increased within the first five days (P = 0.0004) after transplantation and one to five days prior to the clinical diagnosis (dx) of rejection (P = 0.02). Tumor necrosis factor-alpha, IL-6, and IL-8 increased at the time of rejection dx (P < or = 0.01). With UTI, IL-2 (P = 0.01) decreased one to five days prior to dx, and IL-10 (P = 0.003) increased one to five days after dx. Although cGMP and nitrate are dependent variables, cGMP increased (P < or =0.0009) with both rejection and UTI, and nitrate increased (P = 0.0001) with rejection and decreased (P = 0.0001) with UTI. Prior to formal dx (1 to 5 days), urine nitrate clearly differentiated rejection (3004 to 7451 micromol/L) from UTI (90 to 885 micromol/L) and controls (1059 to 3235 micromol/L). The additional 67 urines demonstrated that the sensitivity of the nitrate test for rejection and UTI was 100%.

CONCLUSIONS

In renal transplant patients, specific temporal changes in urine cytokine levels do occur with acute rejection and UTI, but urine nitrate levels are the most precise at differentiating rejection from UTI.

In vivo formation of complex microvessels lined by human endothelial cells in an immunodeficient mouse

We have identified conditions for forming cultured human umbilical vein endothelial cells (HUVEC) into tubes within a three-dimensional gel that on implantation into immunoincompetent mice undergo remodeling into complex microvessels lined by human endothelium. HUVEC suspended in mixed collagen/fibronectin gels organize into cords with early lumena by 24 h and then apoptose. Twenty-hour constructs, s.c. implanted in immunodeficient mice, display HUVEC-lined thin-walled microvessels within the gel 31 days after implantation. Retroviral-mediated overexpression of a caspase-resistant Bcl-2 protein delays HUVEC apoptosis in vitro for over 7 days. Bcl-2-transduced HUVEC produce an increased density of HUVEC-lined perfused microvessels in vivo compared with untransduced or control-transduced HUVEC. Remarkably, Bcl-2- but not control-transduced HUVEC recruit an ingrowth of perivascular smooth-muscle alpha-actin-expressing mouse cells at 31 days, which organize by 60 days into HUVEC-lined multilayered structures resembling true microvessels. This system provides an in vivo model for dissecting mechanisms of microvascular remodeling by using genetically modified endothelium. Incorporation of such human endothelial-lined microvessels into engineered synthetic skin may improve graft viability, especially in recipients with impaired angiogenesis.

Human TNF can induce nonspecific inflammatory and human immune-mediated microvascular injury of pig skin xenografts in immunodeficient mouse hosts

TNF activates endothelial cells to express cell surface molecules that are necessary to recruit a local infiltrate of leukocytes. Because the actions of this proinflammatory cytokine are not species restricted, we investigated whether human TNF can up-regulate porcine endothelial adhesion molecules to elicit human T cell infiltration and damage of pig skin xenografts in a chimeric immunodeficient mouse model. We have previously demonstrated the vigorous rejection of human skin allografts and the absence of injury to porcine skin xenografts in human PBMC-SCID/beige mice. Intradermal administration of human TNF at high doses (600 or 2000 ng) caused nonspecific inflammatory damage of pig skin grafts, whereas low concentrations of TNF (60 or 200 ng) resulted in human PBMC-dependent injury of porcine endothelial cells. There was a strong correlation among pig skin xenograft damage, human T cell infiltration, and the TNF-induced up-regulation of swine MHC class I and class II molecules, VCAM-1, and, in particular, the de novo expression of porcine E-selectin. The microvascular damage and leukocytic infiltration elicited by TNF were enhanced by porcine IFN-gamma, suggesting that xenografts may be less prone to cytokine-mediated injury due to the species-restricted effects of recipient IFN-gamma. Our results indicate that maintenance of a quiescent endothelium, which does not express E-selectin or other activation-dependent adhesion molecules, is important in preventing human anti-porcine T cell xenoresponses in vivo and that TNF signaling molecules and TNF-responsive gene products are appropriate therapeutic targets to protect against human T cell-mediated rejection of pig xenografts.

Interferon-gamma elicits arteriosclerosis in the absence of leukocytes

Atherosclerosis and post-transplant graft arteriosclerosis are both characterized by expansion of the arterial intima as a result of the infiltration of mononuclear leukocytes, the proliferation of vascular smooth muscle cells (VSMCs) and the accumulation of extracellular matrix. They are also associated with the presence of the immunomodulatory cytokine interferon-gamma (IFN-gamma). Moreover, in mouse models of atheroma formation or allogeneic transplantation, the serological neutralization or genetic absence of IFN-gamma markedly reduces the extent of intimal expansion. However, other studies have found that exogenous IFN-gamma inhibits cultured VSMC proliferation and matrix synthesis, and reduces intimal expansion in response to mechanical injury. This discrepancy is generally explained by the idea that IFN-gamma either directly activates macrophages, or, by increasing antigen presentation, indirectly activates T cells within the lesions of atherosclerosis and graft arteriosclerosis. These activated leukocytes are thought to express the VSMC-activating cytokines and cell-surface molecules that cause the observed arteriosclerotic responses. Here we have inserted pig and human arteries into the aorta of immunodeficient mice, and we show that IFN-gamma can induce arteriosclerotic changes in the absence of detectable immunocytes by acting on VSMCs to potentiate growth-factor-induced mitogenesis.

A novel united network for organ sharing region kidney allocation plan improves transplant access for minority candidates

BACKGROUND

We report the consequences of a novel kidney allocation system on access of non-Caucasians (NC) to kidney transplantation. This new plan has provided a balance of allocation determinants between time waiting, HLA match, and geography (population density between donor and recipient center).

METHODS

Three sequential systems of regional allocation were analyzed: period I (September 1994 to September 1996), period II (September 1996 to November 1997), and period III (December 1997 to March 1 1999). Periods II and III are reflective of the new allocation plan.

RESULTS

During periods II and III, the NC rate of kidney transplantation increased closer to the NC proportion on the wait list, comparatively exceeding the national UNOS data. There was no statistical difference in regional mean wait time between Caucasian and NC. Improvements in access to transplantation for NCs between period I and periods II and III appear to be related to changes in geographic allocation weight from local unit to population density points, to the inclusion of the entire region in the plan, and to the deletion of intermediate degrees of B/DR mismatching in the revised plan. Despite the increased proportion of NCs on the wait list from period I to period III, the percentage difference between the proportion of NCs waiting on the list and the proportion NCs receiving a transplant fell from 7.8% to 4.9%.

CONCLUSIONS

These data demonstrate that this new allocation plan was associated with improved access of minority candidates to transplantation. The broadening of geographic allocation and the alteration of HLA points appear to permit a more favorable opportunity for renal transplantation to NC candidates. selection, compared to the UNOS formula. In this report, we analyze the consequences of the Region 1 allocation system on the access of non-Caucasian (NC) candidates to cadaver donor kidney transplantation.

Human allogeneic vascular rejection after arterial transplantation and peripheral lymphoid reconstitution in severe combined immunodeficient mice

BACKGROUND

Interspecies differences create important shortcomings in existing animal models used to describe in vivo events responsible for allograft rejection. Alloimmune destruction of human dermal microvessels, histologically consistent with rejection, has been demonstrated in human skin-grafted severe combined immunodeficient (SCID) mice receiving allogeneic human peripheral blood mononuclear cells (PBMC). We have now documented human alloimmune injury in a vascularized, SCID-human arterial transplantation model.

METHODS

Fresh human artery was used to replace the CB.17 SCID/beige mouse infrarenal aorta. Seven days later, 3x10(8) human PBMC were administered intraperitoneally, and lymphocyte engraftment was considered successful when circulating human CD3+ cells were later identified in peripheral blood.

RESULTS

Forty-six of 49 (94%) mice undergoing transplantation survived, including 14 controls with arterial grafts receiving no PBMC. Twenty-eight of 32 mice demonstrated circulating human CD3+ cells, 14 days after PBMC administration. Animals were killed at 14, 21, or 28 days after receiving allogeneic PBMC, and arteries were recovered for histology and immunohistology. All 14 control mice had patent transplanted grafts with normal vascular histology and no lymphoid infiltration. Damage to transplanted arteries among lymphocyte-engrafted mice was apparent by 14 and 21 days in some animals, whereas 16 of 22 exhibited moderate to severe intimal, medial, and/or adventitial lymphocytic infiltration with intimal expansion by day 28. The infiltrate consisted of HLA-A, -B, -C+, and -DR+, human CD3+ cells, approximately equally distributed as CD4+ and CD8+ subsets. Some infiltrating lymphocytes were cytolytic cells as demonstrated by perforin staining. The endothelium of transplanted human arteries exhibited endothelialitis, and the endothelial cells stained intensely with anti-HLA-A, -B, -C and anti-HLA-DR antibodies. The expanded intima was predominantly smooth muscle cells, staining positively for smooth muscle alpha-actin, HLA-A, -B, -C and HLA-DR. Medial necrosis was not observed.

CONCLUSION

The results provide evidence of alloimmune-mediated vascular rejection in this human arterial transplantation model.

A new allocation plan for renal transplantation

BACKGROUND

A novel plan of renal allograft allocation has been conducted by United Network for Organ Sharing Region 1 transplant centers since September 3, 1996, based upon HLA matching, time waiting, and population distance points. The objectives of this plan were to achieve a balance between increasing the opportunity of renal transplantation for those patients listed with long waiting times and promoting local organ donor availability.

METHODS

A single list of candidates was formulated for each cadaver donor, assigning a maximum of 8 points for time waiting, a maximum of 8 points for population distance from the donor hospital, and HLA points based upon the degree of B/DR mismatch. Additional points were awarded to a cross-match-negative patient with a panel-reactive antibody of >80%, and to pediatric patients.

RESULTS

The total number of kidneys transplanted to patients who had waited >3 years was 100 (46%), and to patients who had waited >2.5-3 years was 29 (13%). However, the total number of kidneys transplanted to patients with the maximum population distance points was only 72 (33%). Thus, although the plan achieved a favorable distribution of kidneys to patients with longer waiting times (nearly 60%), the other, equally important objective of promoting local donor availability was not initially accomplished. Moreover, minor HLA B/DR differences between the donor and the recipient (i.e., not phenotypically matched) were unexpectedly consequential in determining allocation. As a result of these observations, the following adjustments were made in the plan (as of December 3, 1997): a maximum of 10 points for population distance, a maximum of 8 points for time waiting (both by a linear correlation), and the retention of HLA points for 0 B/DR mismatch only. After these interval changes, the percentage of patients receiving a kidney with some population distance points increased from 85% to 96%. Conclusions. We have shown that a heterogeneous region of multiple transplant centers can devise (and modify) an innovative and balanced plan that provides an equitable system of allocation for an ever-increasing number of patients.