Mechanisms Of Graft Failure Research Articles

Aging Decreases the Ultimate Tensile Strength of Bone–Patellar Tendon–Bone Allografts

The purpose of this study was to determine whether aging imparts a clinically significant effect on the (1) mechanism of graft failure and (2) structural, material, and viscoelastic properties of patellar tendon allografts by evaluating these properties in younger donors (≤30 years of age) and older donors (>50 years of age). A total of 34 younger (≤30 years of age) and 34 older (>50 years of age) nonirradiated, whole bone-tendon-bone allografts were prepared for testing by isolating the central third of the patellar tendon using a double-bladed 10-mm width scalpel under a 10-N load to ensure uniformity of harvest. Bone blocks were potted in polymethylmethacrylate within custom molds. Tendon length and cross-sectional area were measured using an area micrometer. A mechanical loading system was used to precondition the grafts for 100 cycles with a load between 50 N and 250 N (1 Hz). A creep load (500 N) was then applied at a rate of 100 mm/min (10 minutes). Grafts were allowed to recover at 1 N (10 minutes), followed by pull-to-failure at a rate of 100% strain per second. Mechanisms of failure (midsubstance vs avulsion) were noted and the structural, material, and viscoelastic properties calculated and compared between groups. There were 33 (97%) midsubstance tears in the younger group and 28 (82%) in the older group (P= .034). Younger grafts showed greater ultimate load to failure (1,782 N [1,533, 2,032] vs 1,319 N [1,103, 1,533]) (P= .006) and ultimate tensile stress (37.4 MPa [32.4, 42.4] vs 27.5 MPa [22.9, 32.0]) (P= .006). There were no significant differences in displacement (P= .595), stiffness (P= .950), strain (P= .783), elastic modulus (P= .114), creep displacement (P= .881), and creep strain (P= .614). This invitro study suggests that aging weakens the bone-tendon junction and decreases the ultimate tensile strength of patellar tendon allografts. However, aging did not affect the displacement, strain, stiffness, elastic modulus, creep displacement, or creep strain of patellar tendon allografts. Surgeons should be aware that patellar tendon allografts from donors >50 years of age have a lower ultimate tensile stress than donors ≤30 years of age.

Outcomes of Boston Keratoprosthesis Implantation for Failed Keratoplasty After Keratolimbal Allograft

To evaluate factors that contribute to keratoplasty failure after keratolimbal allograft (KLAL) and report the outcomes of Boston keratoprosthesis type I (KPro) as salvage therapy. Retrospective noncomparative case series of 7 eyes in 7 consecutive patients with ocular surface disease and limbal stem cell deficiency treated with KPro after failed KLAL. Mechanisms of graft failure, KPro device retention rate, and preoperative and postoperative best-corrected visual acuities were studied. In the studied cohort, keratoplasty graft failure occurred at an average of 9.9 months (range, 1-17 months) after KLAL. Among the 7 eyes reviewed, 4 had tube shunts, 3 of which contributed directly to endothelial graft failure. One eye failed due to fungal keratitis, 1 eye failed due to immune-mediated endothelial rejection, and 2 eyes failed due to recurrent surface disease. During an average follow-up of 585 days (19.5 months) after KPro, best-corrected visual acuity improved from a median of counting fingers CF@2ft (range, hand motions to 20/400) to a median of 20/400 (range, CF@3ft to 20/25). There was 85.7% (6 of 7) retention of implanted devices at the last follow-up, with 1 eye requiring repeat KPro for corneal melt and implant extrusion after abrupt cessation of immunosuppression. Despite successful KLAL outcomes and systemic immunosuppression, patients who undergo ocular surface reconstruction with KLAL are still at risk for subsequent keratoplasty failure. Keratoprosthesis is a viable salvage therapy for visual rehabilitation in these patients. Adequate immunosuppression is important in postoperative management of these patients.

Developments towards tissue-engineered, small-diameter arterial substitutes

This article reviews the present state of small-diameter vascular substitution, the mechanisms of graft failure and the ongoing matters of graft design, with particular attention to small-caliber grafts. Tissue engineering of blood vessels with the mechanical properties of native vessels and with the antithrombotic properties required is really a great challenge. Recent advances, however, indicate that the goal of providing a tissue-engineered vascular graft that will remain patent in vivo for substantial periods of time, is achievable. This review describes the specific requirements of the successful replacement artery from a biomaterial- and tissue-engineering perspective, as well as various approaches in vascular tissue engineering including cells and cell sources, scaffolds and their improvements as well as bioreactors and signaling.

Inhibitory effects of NFκB decoy oligodeoxynucleotides on neointimal hyperplasia in a rabbit vein graft model

Autologous vein remains the commonly used conduit for bypass grafts; however, neointimal hyperplasia is known to be one of the major disease processes in vein graft failure. In this study, we focused on the important role of NFκB which controls the expression of numerous genes for various cytokines and adhesion molecules in the mechanism of graft failure. Thus, we investigated the inhibitory effect of NFκB decoy oligodeoxynucleotides (ODN) on vein graft failure in a rabbit hypercholesterolemic model. Jugular vein to carotid artery interposition grafts in rabbits were transfected intraoperatively with NFκB decoy ODN (40 μmol/l) by ex-vivo pressure-mediated transfection (300 mm Hg, 10 min). Treatment with NFκB decoy ODN significantly suppressed intimal hyperplasia 4 weeks after vein implantation as compared to scrambled decoy ODN, and increased medial thickness, leading to a significant reduction in intima-to-media ratio. Treatment with NFκB decoy ODN significantly inhibited the recruitment of macrophages and the proliferation of vascular smooth muscle cells (VSMC), while apoptosis in VSMC was significantly increased by NFκB decoy ODN. In addition, a study of vascular reactivity demonstrated that transfection of grafts with NFκB decoy ODN significantly improved endothelium-mediated vasorelaxation as compared to scrambled decoy ODN. Here, we demonstrated that inhibition of NFκB activation using decoy ODN inhibited the development of neointimal hyperplasia, followed by suppression of inflammatory changes and accumulation of VSMC in the neointima of rabbit vein grafts. The present study raises the possibility of a novel strategy for prevention of graft failure.

Fludarabin and rabbit antithymocyte globulin as conditioning for repeat transplantation after primary and secondary graft failure following unrelated hematopoietic stem cell transplantation

Introduction: Primary or secondary graft failure is a serious complication of allogeneic stem cell transplantation. The underlying mechanism may be rejection mediated by recipient immunocompetent cells or loss of donor hematopoiesis due to other, often unknown causes. We here report on the results of second transplantation in 8 patients reconditioned with fludarabin and ATG in which an immunological cause of graft failure was either proven or suspected. Patients and Methods: Six male and 2 female patients with hematologic malignancies, median age 45 (22-55) years, receiving unrelated stem cell transplants in our institution within the last 6 years, experienced primary (n = 5) or secondary (n = 3) graft failure. Match was 7/8 in one, 8/8 in three, 8/10 in three and 9/10 in one case. Primary conditioning was myeloablative in all patients and included rabbit ATG either Genzyme or Fresenius in all but one. Graft source was bone marrow in 7 and PBSC in one case, respectively. Mechanism of graft failure was evaluated by morphology, immunophenotyping, chimerism and kinetics and was judged rejection in three and probably immunologically mediated in 5 cases. At a median of 42 (35-71) days following the first transplant 7 patients received PBSC and one patient bone marrow as a second transplant, 4 from the same and 4 from a different unrelated donor. Matches of the new donors were 6/8, 7/8, 8/10 and 10/10. Two earlier patients were given fludarabin 100 and 120 mg/m2 combined with ATG Genzyme 5 mg/kg BW, the later ones fludarabin 150 mg/m2 together with ATG 7.5 mg/kg BW. Results: Seven out of 8 patients engrafted at a median of 14 days after second and 58 days after first transplant. One non-engraftment occurred in a polytransfused patient with refractory anemia and primary rejection, after reconditioning with fludarabin 100 mg/m2 and ATG 5 mg/kg BW and grafting with the same donor. At a median observation time of 555 (266-2020) days 4 patients are alive and well. Four patients died at a median of 135 (75-337) days: two from relapse, one from aGvHD °IV and one from fungal sepsis. Conclusion: In primary and secondary graft failure after allogeneic stem cell transplantation, for reconditioning a highly immunosuppressive regimen with limited toxicity is warranted. Fludarabin 150 mg/m2 and ATG Genzyme 7.5 mg/kg BW is a very efficient and well tolerated combination enabling engraftment even across a two HLA antigen barrier.

REDUCED ALLOGENICITY OF CRYOPRESERVED ALLOGRAFTS IN LIGHT OF DENDRITIC CELL PERFORMANCE

A219 Aims: Cryopreserved human heart valves and vessels are now widely used for its superiority to prosthetic materials in its antithrombogenesity and resistance to infection. However, mechanism of graft failure is still a matter of debate. Our objective is to investigate immunological reactions and roles of dendritic cells (DC) as a possible cause for chronic graft failure after allograft implantation, which are the most potent antigen-presenting cells in the immune system Methods: Syngeneic rat thoracic aortic graft (Lewis to Lewis) or allogeneic thoracic aortic graft (Lewis to Brown Norway) was implanted infrarenally, either fresh or after cryopreservation. The grafts were explanted 28 days after surgery. Immunohistochemical examinations using antibodies to CD83 and CD32 were performed, focusing on DC detection. As control, fresh and cryopreserved allografts after rapid thawing were also examined histologically. Results: Number of grafts were; fresh syngeneic (syn-F) 3, cryopreserved syngeneic (syn-CH) 6, fresh allogeneic (allo-F) 4, and cryopreserved allogeneic (allo-CH) 3. As for CD83, none of syn-F group were stained. Two (/6) of syn-CH were positive. All 4 grafts of allo-F group were positive, whereas only one graft was positive in allo-CH. These positive staining were found in adventitia of the aorta CD32 was also positive in wider area including the same spot positive for CD83. Conclusions: Though this is still a preliminary study, our data suggests that dendritic cells are responsible for immunological reaction especially in allogeneic transplantation. Also, vascular cryopreserved grafts have less allo-antigenicity, and thus result in reduced immunological response.

THE HEPATIC EXTRACELLULAR MATRIX DURING COLD ISCHEMIA/WARM REPERFUSION OF THE RAT LIVER: ROLE OF MATRIX METALLOPROTEINASES IN ITS ALTERATION.

A310 Background: Poor initial graft function remains a major clinical problem in human liver transplantation. Its incidence (15 to 25% of transplanted patients) appears to depend on the length of cold storage and has thus been ascribed to injury from harvesting, cold storage and warm reperfusion after blood vessel reconnection; i.e. cold ischemia/warm re-perfusion (CI-WR) injury. The underlying mechanism of CI-WR injury has been studied extensively over the last decade, but it remains poorly understood. Recently, it has been demonstrated that different time courses and mechanisms of cell death occur in rat livers after CI-WR, with early sinusoidal endothelial cell necrosis followed by delayed hepatocyte apoptosis. These processes did not appear to be of major importance in the mechanism of graft failure since both were similar under non-lethal and lethal conditions. By contrast, prolonged CI was associated with an alteration of the extracellular matrix (ECM), leading to extensive coagulative necrosis of hepatocytes as found in conditions ending in graft failure. Aims: Since it is known that warm ischemia/WR of livers induces an increased local synthesis of metalloproteinases (MMPs), proteases implicated in the degradation of the hepatic ECM, we looked if the same phenomenon was occurring during prolonged CI/WR of rat livers ensuing in ECM disappearance responsible for the graft malfunction. Methods: Rat livers were preserved for 0, 24 (viable livers) and 42 h (non-viable livers) in the UW solution (4°C), then reperfused for 0, 10, 20, 30, 40, 60, 90, and 120 minutes with a krebs buffer solution (37°C) containing 20% erythrocytes. The first 15 mLs of the liver rinsing solution were taken during early WR and frozen liver biopsies were obtained at the end of each period (n=4 in all groups). Total liver RNAs and proteins were extracted, then MMP and their natural inhibitor (TIMP) expression was analysed by Northern Blot quantitative analysis and MMP activity was nalyzed using a fluorescent substrate (MCA-MAT) or by zymography. Results: although most of these genes are not expressed in the normal rat liver, there was an induction of MMP-13 and 14 expression as well as of TIMP-1 and 2 expression in all livers, independently from CI or WR periods. There was also an increased MMP activity in all livers, as measured ding a in presence or absence of an inhibitor (BB94), whatever the experimental condition. An increased activity of MMPs (particularly gelatinases A and B) was found in the initial flush solution. Comments: These data are quite different from those observed following warm ischemia/WR, particularly when considering that, following CI, the ECM rapidly deteriorates with WR. However since this phenomenon occurs very early during WR, it might be due to the liberation of MMPs already present in sinusoidal endothelial cells and released by their necrosis during prolonged CI, as suggested by our data and others. Conclusion: Induction of hepatic MMP synthesis does not occurs following prolonged CI/WR of rat livers and thus has no major role in the alteration of the hepatic extracellular matrix observed under these conditions. This phenomenon might result from the local passive release of preformed MMPs from dead hepatic cells.

Sinusoidal endothelial cell and hepatocyte death following cold ischemia-warm reperfusion of the rat liver.

Cold ischemia-warm reperfusion (CI-WR) injury of the liver is characterized by marked alterations of sinusoidal endothelial cells (SECs), whereas hepatocytes appear to be relatively unscathed. However, the time course and mechanism of cell death remain controversial: early versus late phenomenon, necrosis versus apoptosis? We describe the occurrence and nature of cell death after different periods of CI with University of Wisconsin (UW) solution and after different periods of WR in the isolated perfused rat liver model. After 24- and 42-hour CI (viable and nonviable livers, respectively), similar patterns of liver cell death were seen: SEC necrosis appeared early after WR (10 minutes) and remained stable for up to 120 minutes. After 30 minutes of WR, apoptosis increased progressively with WR length. Based on morphological criteria, apoptotic cells were mainly hepatocytes within liver plates or extruded in the sinusoidal lumen. In addition, only after 42-hour CI were large clusters of necrotic hepatocytes found in areas of congested sinusoids. In these same livers, the hepatic microcirculation, evaluated by means of the multiple-indicator dilution technique, revealed extracellular matrix disappearance with no-flow areas. In conclusion, different time courses and mechanisms of cell death occur in rat livers after CI-WR, with early SEC necrosis followed by delayed hepatocyte apoptosis. These processes do not appear to be of major importance in the mechanism of graft failure because they are similar under both nonlethal and lethal conditions; this is not the case for the loss of the extracellular matrix found only under lethal conditions and associated with hepatocyte necrosis.

Chimerism analysis by lineage-specific fluorescent polymerase chain reaction in secondary graft failure after allogeneic stem cell transplantation.

Chimerism analysis is essential in understanding the etiology of graft failure occurring after allogeneic stem cell transplantation. The detection of marrow and/or blood host cells suggests graft rejection, relapse of the underlying disease, or a state of stable mixed chimerism. However, complete donor chimerism may be observed in some cases. Our objective was to characterize, by a sensitive process of chimerism analysis, six cases of graft failure occurring after transplant. Six cases of secondary graft failure, in which previous analysis had shown complete donor chimerism by standard polymerase chain reaction amplification of variable number of tandem repeats, were studied. In order to detect a minority population of recipient cells, we increased the sensitivity of the process by using fluorescent polymerase chain reaction and analyzing the origin of T, B, and natural killer lymphocytes at the time of graft failure. The complete donor origin of mononuclear cells and lymphocytic populations was confirmed with this method in five of six patients. In the remaining patient, diagnosis of graft failure was clarified by the detection of a previously undetected mixed chimerism, compatible with graft rejection. In the other five patients, graft rejection was thereby excluded and graft failure could be related to viral infection or to graft-versus-host disease. Our sensitive process of fluorescent lineage-specific chimerism analysis may help in distinguishing between graft rejection and other mechanisms of graft failure, which is essential for deciding appropriate therapy.

Detection of "functional" valves in reversed saphenous vein bypass grafts: identification with duplex ultrasonography.

Although venous valve lesions have been cited as a mechanism of graft failure, the fate of venous valves in reversed saphenous vein (RSV) bypass grafts is unclear. The basis for this uncertainty is the difficulty in postoperative identification and follow-up of valve sites and the infrequent pathologic submission of vein graft lesions. This report describes the features of "functional" valves (FV) visualized in RSV grafts by ultrasonic duplex scanning. Sixty-six RSV infrainguinal vein grafts were prospectively studied with duplex ultrasonography from January 1992 to December 1995. Grafts were studied at 1, 2, 3, 4, 6, 9, 12, 18, and 24 months, then annually. FV identification was based on a characteristic ultrasound Doppler waveform and color flow pattern and visualization of the leaflets by B-mode imaging. The waveform consists of end-systolic valve closure followed by variable degrees of reflux. Immediate postoperative reactive hyperemia precludes detection, because flow reversal in the graft is needed for identification. Since August 1994, 14 FV have been identified in 11 (17%) of 66 RSV grafts. The mean time to FV recognition after implantation was 10 months (range, 1 to 52 months), and the average follow-up was 15 months. One valve was completely competent. Seven (50%) of the FV were associated with the development of a < 50% diameter reducing stenosis by Doppler velocity criteria. None of the FV has required intervention. "Functional" vein valves in RSV grafts are common and can be identified by ultrasonic duplex imaging. Awareness of the characteristics of FV during routine duplex graft surveillance will undoubtedly increase detection. The variable time course to identification of FV and duration of "function" warrants continued follow-up to determine the relationship of these valves to the development of stenotic lesions and graft failure.

Cryopreserved saphenous vein allografts for below-knee lower extremity revascularization.

Cryopreserved saphenous vein allografts have been offered as an alternative conduit for bypass in ischemic limbs. The authors examined the efficacy of this conduit for arterial bypass to the distal popliteal and tibial arteries in patients in whom autogenous vein was not available. Previous experience with arterial and venous allografts has been unsatisfactory because of aneurysmal degeneration and poor patency. Endothelial loss and host rejection have been suggested as mechanisms of graft failure. Cryopreservation by modern techniques with rate controlled freezing, dimethyl sulfoxide (DMSO), and other cryopreservants, has addressed these issues and rekindled interest in vein allografts. Over a period of more than 5 years, 115 cryopreserved vein allografts were implanted in 87 limbs to the distal popliteal (14) or tibial (101) arteries. The indication for surgery was rest pain in 56 procedures (49%), gangrene in 36 (31%), claudication in 21 (18%), and replacement of aneurysmal allografts in 2. Follow-up was 1 to 61 months (mean 25 months). There was no significant difference in patency related to site of proximal or distal anastomosis, patency of runoff vessels, use of anticoagulation, age, sex, diabetes, hypertension, smoking, indication, source of graft, or use of multiple segments. Revision was required in six grafts for aneurysmal dilatation. Histologic examination of explanted sections of allografts showed no immune response, and immunosuppressive drugs were not used. Although limb salvage has been satisfactory, long-term patency rates for cryopreserved vein allografts are poor when compared with autogenous vein. The cost of cryopreserved allografts far exceeds that of prosthetic grafts, for which comparable and superior results have been reported. Use of cryopreserved vein allografts should be reserved for situations in which adequate lengths of autogenous vein do not exist and the risk of infection of prosthetic grafts is high.

Macrophage activation and leukocyte adhesion after liver transplantation.

Reperfusion injury involving oxygen radicals, leukocyte adhesion, and Kupffer cell activation has been suggested to contribute to the failure of transplanted livers. The aim of this study was to evaluate Kupffer cell activity, leukocyte adhesion, and the effect of the calcium channel blocker nisoldipine after rat liver transplantation by means of in vivo fluorescence microscopy to further investigate the mechanism of graft failure. Inclusion of 1.4 microM nisoldipine to the University of Wisconsin cold storage solution (UW) did not improve sinusoidal perfusion and vasoconstriction after transplantation compared with UW alone (82.7 +/- 1.0% vs. 79.2 +/- 1.7% perfused sinusoids; 7.3 +/- 0.1 vs. 8.0 +/- 0.2 microns diam of sinusoids; means +/- SE). Permanent as well as temporary adhesion of leukocytes rose from 9.4 +/- 0.8 and 10.2 +/- 0.5% in sham-operated controls to 19.1 +/- 2.2 and 19.2 +/- 0.5% after liver transplantation, respectively. Inclusion of the calcium channel blocker reduced permanent (9.1 +/- 0.8%; P < 0.05) and temporary adherent leukocytes (11.3 +/- 1.0%; P < 0.05). Phagocytosis of latex beads by Kupffer cells or other phagocytic cells as a function of activity rose after transplantation (e.g., periportal area: 509 +/- 44/mm2) compared with controls (316 +/- 22/mm2). This was significantly reduced by inclusion of nisoldipine to UW (322 +/- 32/mm2). The results of this study demonstrate activation of Kupffer cells and increase of leukocyte adhesion to the sinusoidal endothelial wall during reperfusion of transplanted livers. A calcium-dependent release of mediators by Kupffer cells that promote leukocyte adhesion is suggested as an underlying mechanism.

Evidence that free radicals are involved in graft failure following orthotopic liver transplantation in the rat--an electron paramagnetic resonance spin trapping study.

The purpose of these studies was to determine whether free radicals were formed as a consequence of reperfusion during orthotopic liver transplantation and whether their formation was related to graft failure. Grafts were stored for 18 hr in Euro-Collins solution or for 48 hr in University of Wisconsin solution (nonsurvival conditions) and reperfused with blood containing the spin trap alpha-phenyl N-tert-butylnitrone (PBN). Venous blood samples (4-5 ml) were collected, and serum was extracted with chloroform and methanol (2:1) and analyzed for radical adducts by electron paramagnetic resonance (EPR) spectroscopy. In samples from livers stored under nonsurvival conditions, EPR spectra were detected indicating the presence of PBN radical adducts. In contrast, radical adduct formation was 3- to 4-fold lower in similar experiments performed with untransplanted livers or with livers stored under survival conditions (1 hr in Ringer's solution or 24 hr in UW solution). Oxygen radicals are more likely involved in the production of radical adducts because formation was nearly completely prevented by superoxide dismutase plus catalase or Carolina rinse, which contains glutathione, desferrioxamine mesylate, and allopurinol. Radical adduct formation was much greater in a blood-free perfusion system where oxygen delivery was high, suggesting that blood elements are not necessary for radical adduct formation. An inverse correlation between survival of livers stored in UW solution and radical adduct signal was observed in this study. Thus, it is concluded that free radicals formed during reperfusion are involved in the mechanism of graft failure following liver transplantation in the rat.

Mechanisms of graft failure after human marrow transplantation: a review

Graft failure (GF) following bone marrow transplantation (BMT) in man is usually attributed to allograft rejection; however, other mechanisms of GF exist. Exposure of the developing allograft to viruses, myelotoxic drugs, and damage to the host-derived marrow stroma during graft-versus-host disease (GVHD) may all cause GF. Later, in the posttransplant course, recurrence of the original disease may ultimately destroy or replace the graft. Overall allogeneic rejection remains the most important cause of GF and most in vivo and in vitro evidence points to a T cell mechanism. The incidence of rejection after clinical BMT is very variable and highly dependent on HLA and non HLA histocompatibility differences between donor and recipient, the level of recipient sensitisation pre-BMT and the immunosuppressive protocols used pre-transplant and for the prevention of GVHD.

Mechanisms of graft failure

Mechanisms of graft failure

Effect of HLA compatibility on engraftment of bone marrow transplants in patients with leukemia or lymphoma.

We analyzed the relevance of HLA compatibility to sustained marrow engraftment in 269 patients with hematologic neoplasms who underwent bone marrow transplantations. Each patient received marrow from a family member who shared one HLA haplotype with the patient but differed to a variable degree for the HLA-A, B, and D antigens of the haplotype not shared. These 269 patients were compared with 930 patients who received marrow from siblings with identical HLA genotypes. All patients were treated with cyclophosphamide and total-body irradiation followed by the infusion of unmodified donor marrow cells. The rate of graft failure was 12.3 percent among the recipients of marrow from a donor with only one identical haplotype, as compared with 2.0 percent among recipients of marrow from a sibling with the same HLA genotype (both haplotypes inherited from the same parents) (P less than 0.0001). The incidence of graft failure correlated with the degree of donor HLA incompatibility. Graft failure occurred in 3 of 43 transplants (7 percent) from donors who were phenotypically HLA-matched with their recipient (haplotypes similar, but not inherited from the same parents), in 11 of 121 donors (9 percent) incompatible for one HLA locus, in 18 of 86 (21 percent) incompatible for two loci, and in 1 of 19 (5 percent) incompatible for three loci (P = 0.028). In a multivariate binary logistic regression analysis, independent risk factors associated with graft failure were donor incompatibility for HLA-B and D (relative risk = 2.1; 95 percent confidence interval, 1.7 to 2.5; P = 0.0004) and a positive crossmatch for anti-donor lymphocytotoxic antibody (relative risk = 2.3; 95 percent confidence interval, 1.8 to 2.8; P = 0.0038). Residual host lymphocytes were detected in 11 of 14 patients with graft failure, suggesting that the mechanism for graft failure could be host-mediated immune rejection. We conclude that donor HLA incompatibility and prior alloimmunization are significant risk factors for graft failure, and that a more effective immunosuppressive regimen than those currently used is needed for consistent achievement of sustained engraftment of marrow transplanted from donors who are not HLA-identical siblings.

Evidence for the involvement of host-derived OKT8-positive T cells in the rejection of T-depleted, HLA-identical bone marrow grafts.

The recent introduction of a variety of techniques for removing T cells from bone marrow grafts has reduced the incidence of graft-versus-host disease (GVHD)-associated morbidity and mortality. Whether this advance will be translated into improved patient survival is unclear at present, mainly because these procedures increase the risk of graft failure. Since 1983 we have transplanted 25 consecutive leukemia patients with HLA-identical sibling grafts purged of T cells by a single incubation with the monoclonal antibody Campath-1 and donor complement. This approach was successful in reducing T cell contamination of the graft and preventing acute and chronic GVHD. In this group of patients two suffered irreversible graft failure and one developed reversible graft failure. In a similarly sized group of patients previously transplanted with unpurged marrow according to the Seattle protocol, no episodes of graft failure occurred. Since other causes of graft failure, such as drug toxicity or viral infections, could be largely excluded, this suggested that the graft failures were specifically related to the purging process. In haploidentical bone marrow transplantation (BMT) O'Reilly has identified residual host-versus-graft activity (HVG) as a cause of graft failure. The causes and mechanisms of graft failure in T-depleted HLA-identical sibling transplants have not been extensively investigated to date. In the three graft failures observed by us, the loss of the graft was preceded by the appearance of a population of activated lymphocytes. We have determined the phenotype and origin of this population and investigated its interactions with donor hemopoietic tissue in vitro.

Recurrence of aplastic anemia following cyclophosphamide and syngeneic bone marrow transplantation: evidence for two mechanisms of graft failure

Two patients with aplastic anemia were treated with high-dose cyclophosphamide and marrow transplantation from their normal, genetically identical twin. Both patients rapidly recovered normal marrow function, but marrow failure recurred 13 and 18 months later. Because donor and host pairs were identical twins, these cases of graft failure could not have resulted from the usual cause of graft failure, ie, immunological reactivity of host cells against unshared minor histocompatibility antigens of the donor. These results imply that there are at least two mechanisms responsible for graft failure after marrow transplantation for severe aplastic anemia.

Recurrence of Aplastic Anemia Following Cyclophosphamide and Syngeneic Bone Marrow Transplantation: Evidence for Two Mechanisms of Graft Failure

Two patients with aplastic anemia were treated with high-dose cyclophosphamide and marrow transplantation from their normal, genetically identical twin. Both patients rapidly recovered normal marrow function, but marrow failure recurred 13 and 18 months later. Because donor and host pairs were identical twins, these cases of graft failure could not have resulted from the usual cause of graft failure, ie, immunological reactivity of host cells against unshared minor histocompatibility antigens of the donor. These results imply that there are at least two mechanisms responsible for graft failure after marrow transplantation for severe aplastic anemia.