Diagnosis and treatment of osteogenic sarcomas, techniques of reconstructions. Future prospects

PATIENTS AND METHODS: We have performed 34 massive bone-cartilage grafts with a follow-up of 2 to 7 years (1988-1993) including 5 complete joint grafts of the knee. Between 1988 and 1993, 8 massive diaphyso-metaphyseal bone grafts were performed. Joint reconstructions using massive bone-cartilage allografts are increasingly used in routine oncology surgery. Long-term rehabilitation and possibilities of immediate anatomic reconstruction of the articular surface, together with mid-term results suggest that the functional results are promising compared with major reconstruction prostheses. Indications for operations are being increasingly widened to younger subjects who have undergone partial or total joint exeresis for tumour. Sleeved prostheses were used for 12 reconstructions (1988-1993) for sarcoma of the knee. RESULTS The risk of sepsis are comparable for the different groups and are mainly related to the quality of the skin repair during chemotherapy. Fractures of the graft occur when the fixation is insufficient or when rehabilitation exercises were too aggressive. Non-consolidation was exceptional when the junction between the allograft and the receiver bone is not surrounded with autologous spongious autografts. Joint instability and arthrosis depend on the stability of the ligament reconstruction. To this day, no Charcot type joint disease has been demonstrated, periarticular innervation has maintained joint trophism. DISCUSSION: There are still some incompletely resolved problems concerning the revascularization of the graft, its integration into the skeleton, the outcome of the grafted cartilage and that of the ligament formations attached to the graft or used as allografts. These massive grafts must be studied over a longer period of time but the early results are encouraging. Sleeved grafts using bone-bank specimens could be an intermediary solution which appears to be indicated in cases where the tumoural resection was particularly large removing bone, cartilage, ligaments and muscles. With these sleeved prostheses, the muscles can be refixed onto the graft thus reducing the risk of shank fracture and loosening. The use of a tibial graft with the patellar tendon is helpful in reconstructing the extensor apparatus. However, if rehabilitation is not undertaken rapidly and followed regularly for several months, the graft favours the development of muscular adherances which can be a major limitation to joint mobility.     

Apoptosis as a mechanism of tissue injury in liver allograft rejection

Recent studies suggest that apoptosis is an important mechanism of cell death in the rejection of liver allografts and that infiltrating host lymphocytes mediate this process. The first section of this chapter addresses the cells and molecules that initiate the immune response following transplantation of a liver allograft. The recognition of donor alloantigens by infiltrating host lymphocytes stimulates a cascade of immune events which culminate in development of the effector cells that mediate tissue damage. Studies which demonstrate that apoptosis of hepatocytes and bile duct cells accompany allograft rejection are detailed in the second section of this chapter. The final section discusses the potential pathways which lead to apoptosis in liver allograft rejection. The contributions of the granule-exocytosis pathway, the Fas-mediated pathway, and cytokines to the induction of apoptosis in liver allografts are discussed. In addition, the concept that alloreactive graft infiltrating cells are deleted by apoptosis is presented. A further understanding of the mechanisms involved in apoptosis will lead to unique approaches toward the goal of achieving allograft tolerance.     

Prevalence of asthma and wheeze in primary school children in northern Jordan

While the existence of chimeric cells in host tissue following organ transplantation is well documented, its distribution, temporal evolution and relationship to allograft survival is less clear. To explore this phenomenon, Lewis recipients of ACI cardiac allografts representing a wide range of immunosuppressive protocols and graft survival times were examined for the presence of chimerism using a sensitive polymerase chain reaction assay. Four groups of animals were examined: untransplanted animals receiving donor specific transfusion (DST)/cyclosporine A (CsA); allograft recipients with no treatment; recipients treated with DST/CsA/supplementary immunosuppression with rejection at 21-183 days; and recipients sacrificed with functioning allografts, treated with DST/CsA/supplementary immunosuppression and surviving > 200 days. To elucidate variations in the tissue distribution of chimeric cells, bone marrow, skin, liver, spleen, and thymus were examined in each animal. Untransplanted animals receiving DST/CsA displayed no evidence of chimerism. In animals receiving a cardiac allograft but no treatment, there was extensive evidence of chimerism in four of five animals. Chimerism was also detected in seven of nine animals with intermediate graft survival at the time of rejection. In animals with long-term graft survival, only four of eight displayed chimerism. These results suggest that, without immunosuppression, early chimerism does not lead to prolonged graft survival and that, even when graft survival is moderately prolonged, these cells are not sufficient to prevent rejection. In conclusion, chimerism appears to be a common phenomenon following transplantation, is not a result of DST, and may not be necessary for maintenance of long-term graft survival.     

Cell survival following bone-anterior cruciate ligament-bone allograft transplantation: DNA fingerprints, segregation, and collagen morphological analysis of multiple markers in the canine model

Bone-anterior cruciate ligament-bone allograft transplantation has become recognized as a potential solution to reconstruction of the anterior cruciate ligament (ACL). The purpose of this study was to determine the time-dependent fibrocyte donor cell survival rate after cryopreserved bone-ACL-bone allograft transplantation. Additionally, bony incorporation of the pediculated bone plugs was examined. The ability to successfully transplant allogenous ACL fibrocytes and have them survive has not previously been documented. In this study, DNA fingerprints identified and documented the survival rate of the cellular DNA in transplanted ACL allografts for ACL re-construction in the knee joints of 10 skeletally mature dogs. At 4, 8, 26 and 52 weeks after ACL allograft transplantation, DNA probes, H & E, Giemsa, Goldner, PAS and polarized light staining was done to demonstrate the time-dependent changes in the allografts after transplantation. At 4 weeks host fibrocytes began to grow into the graft; however, histologically the cells could not be distinguished as to host or donor origin. After 4 weeks the DNA pattern reflected only the band pattern of the host. This reveals the early cellular infiltration activity of the host into the ACL allograft, also demonstrated in the light microscopy stainings. The survival rate of transplanted allogenous ACL fibrocytes had not been documented before this study. There is no evidence that ACL allograft cells survive in the intra-articular environment of the host's knee. Within 4 weeks ACL allografts became completely repopulated with host cells. The cells that migrate early into the ACL allografts are probably of synovial origin because they are present before revascularization and collagen reorganization occur. We conclude from this study that viable cells in transplanted ACL allografts did not survive longer than 4 weeks after intra-articular transplantation. Advances in molecular biology may offer new approaches to alter or stimulate fibrocyte population and function in the transplanted ACL allograft used for ACL reconstruction. New methods to maintain the viability of donor cells may be necessary to improve the biomechanical and histological properties of autografts or allografts for ACL reconstruction.     

Structural allograft in two-stage revisions for failed septic hip arthroplasty

We report 11 patients having revision of total hip arthroplasty using massive structural allografts for failure due to sepsis and associated bone loss. All patients had a two-stage reconstruction and the mean follow-up was 47.8 months (24 to 72). Positive cultures were obtained at the first stage in nine of the 11 patients, with Staphylococcus epidermidis being the most common organism. The other two patients had draining sinuses with negative cultures. There was no recurrence of infection in any patient. The mean increase in the modified Harris hip score was 45 and all the grafts appeared to have united to host bone. Two patients required additional procedures, but only one was related to the allograft. Complications included an incomplete sciatic nerve palsy and one case of graft resorption. Our results support the use of massive allografts in failed septic hip arthroplasty in which there is associated bone loss.     

The Ranawat Award. Histology of nine structural bone grafts used in total knee arthroplasty

The cross section radiographs and histology of nine bone grafts were examined to determine whether grafts are durable enough to support a total knee implant when the load is shared by host bone, graft bone, and a stemmed component. All cases had cemented total knee arthroplasties with stemmed components adjacent to bulk grafts. The cases included autografts and allografts, which had been in situ for an average of 41 months (range, 20-62 months). Seven of the grafts were retrieved postmortem from three patients (four knees), and two were retrieved at revision surgery from one patient. The allografts all were intact, but had not revascularized. The autografts were viable bone. New bone was being laid down on the dead graft bone at the periphery of the allografts. No change in the bone to cement interface, no graft collapse, no development of radiolucent lines, and no component loosening occurred in these cases. The promising clinical results of bone grafts in total knee arthroplasties were confirmed by the examination of these grafts at the cellular level. Using stemmed components in bone grafted knee reconstructions may have increased graft durability and protected the grafts from fatigue failure.     

Comparison of the growth and fate of fetal spinal iso- and allografts in the adult rat injured spinal cord

Most studies investigating early fetal CNS graft-host interactions and host immune responses have been performed using intracerebral transplantation paradigms. The purpose of this study was to establish the early developmental dynamics of fetal graft integration with the injured host spinal cord and to determine whether fetal allografts in this environment are subject to rejection. ACI rat fetal spinal cord (FSC) tissue was grafted into acute lesion cavities of adult WF rat spinal cords. Graft development and/or rejection was followed from 1 to 45 days posttransplantation with morphometric, histological, and immunocytochemical methods. We determined that all FSC grafts in acute resection lesions of the adult rat spinal cord undergo an early substantial cellular attrition, but following favorable attachment to healthy host tissue margins, they rebound and grow to fill the lesion cavity by approximately 45 days. We also determined that FSC allografts into nonimmunosuppressed adult recipients are consistently rejected, but only after an early period of growth and maturation. The onset of rejection is characterized by extensive cellular infiltration coincidental with graft and host MHC antigen expression. The implications of delayed graft development and graft-host integration are discussed relative to interconnectivity and long-term potential for graft-derived benefits. The observed rejection response was characteristic of first-order allograft rejection and underscores a lack of immunological privilege in the microenvironment of the injured spinal cord.     

Acetabular reconstruction with impacted morselized cancellous allografts in cemented hip arthroplasty: a histological and biomechanical study on the goat

Bone defects in total hip arthroplasty revision surgery can be restored with different types of bone graft. The use of impacted morselized allograft chips in combination with cement is the treatment of our choice. To establish the incorporation capacity of the grafts and mechanical stability of the implant, an animal model in the goat was developed. An acetabular defect was created and restored with morselized grafts and a cemented cup. Postoperative performance of the reconstruction was followed both histologically and biomechanically. Histology showed that consolidation of the graft with the host bone bed had occurred within 3 weeks. In the following period a front of vascular sprouts infiltrated the graft. Graft resorption, woven bone deposition, and subsequent remodeling resulted in a new trabecular structure. This structure contained only scarce remnants of the original dead graft material. At the graft-cement interface, graft resorption and new bone formation had resulted in areas of direct vital bone-cement contact. Locally, a soft tissue interface was present. After longer follow-up periods, progressive interface formation and loosening of the cups were found in most animals. Mechanical testing showed that the stability of the reconstruction increased during the first 12 postoperative weeks. Thereafter, the stability decreased, probably by soft-tissue interface formation at the graft cement interface. We conclude that cemented morselized allografts have a high capacity to incorporate. Initial cup stability is adequate to provoke graft incorporation with decreasing stability after the incorporation process has been completed.     

Newer knowledge of the immunology of bone and cartilage

By the use of modern techniques, the nature of the immunological response to bone and cartilage grafts is becoming clear. Fresh bone, whether cancellous or cortical, will elicit a cell-mediated immunological response; removal of the bone marrow has little effect in reducing immunogenicity. Antibodies against cellular components of the graft are detectable in the recipient only when host and donor have a disparity for the major histocompatibility (H) antigen. Treatment of bone grafts, for the bone bank, by freezing removes their immunogenicity with regard to antibody production but leaves them capable of stimulating the cellmediated immune response. Freeze drying, on the other hand, impairs immunogenicity for both types of responses. Cartilage, grafted alone, is probably non-antigenic as far as both immune responses are concerned and, although there have been a few reports of stimulation of CMI and antibody production by cartilage, these have not been confirmed. Cartilage cells do, however, possess antigens of the major H-antigen system. The cartilage graft is therefore antigenic but only feebly immunogenic, as the matrix proteoglycans protect the cells from the afferent arm of the immune response. Osteoarticular allografts, consisting of both bone and cartilage, sensitize the host due to their bone components. The effect of the immune response upon the bone allograft is to destroy the graft-derived first phase of osteogenesis which, in turn, leads to a poor or non-existent host phase of new bone formation in most allografts. The exact effector mechanism by means of which this destruction is brought about is not known. Bone grafts may be protected from the immune response by use of immunosuppressive measures. Cartilage enjoys a considerable measure of protection from immunological effectors by virtue of its matrix. If this breaks down then the cartilage can become permeable to antibodies. It is suggested that "lymphokines," produced by sensitized lymphocytes, may play some role in destroying the cartilage graft.     

The acute phase response and laboratory testing

A model of sensitization by intraperitoneal lymph node inoculation was developed to test the hypothesis that hyperacute rejection (HAR) could occur in sensitized recipients of vascularized pancreas allografts. Ten pairs of outbred mongrel dogs that were lymphocytotoxic cross-match assay negative were inoculated with homogenized lymph nodes on either three or four occasions at fortnightly intervals before renal transplantation. A renal allograft from the same donor was used to test the HAR response and to further enhance sensitization by rejection of a vascularized organ. Pancreas transplants were performed 2 weeks later, with biopsies of the graft and blood samples taken at 0, 10, 20, and 30 min and then at 30-min intervals until the grafts were no longer viable. All renal and pancreas grafts were rejected in a classical hyperacute pattern. Within 4 min of revascularization of the pancreas, central lobular hemorrhage and vascular congestion appeared, followed by general edema. Histology demonstrated parallel changes of edema, vascular congestion, necrosis, hemorrhage, and leukocytic infiltrate, which all preceded graft infarction. A sharp decline in both arterial and venous white blood cell count and platelets occurred within 10 min of revascularization with initial sequestration and subsequent release of platelets from the graft (P=0.02). In summary, HAR of the allografted pancreas can be observed by the surgeon within minutes of revascularization, with predictable macroscopic and microscopic changes. This study supports the use of routine lymphocytotoxic cross-match tests for all recipients of pancreas transplants and implies that particular care is warranted in regraft pancreas allograft recipients.     

Treatment of major defects of bone with bulk allografts and stemmed components during total knee arthroplasty

We reviewed the results an average of fifty months (range, twenty-four to 120 months) after the use of thirty-five allografts in thirty patients during primary or revision total knee replacement. Twenty-nine femoral-head allografts, five distal femoral allografts, and one proximal tibial allograft were used in conjunction with a long-stemmed implant to reconstruct large osseous defects. The patients were evaluated clinically, radiographically, and subjectively (with use of a questionnaire). Twenty-six (87 per cent) of the thirty patients had a good or excellent clinical result, and no revisions were necessary. As none of the patients had collapse of the graft, subsidence of the implant, or revision, we believe that the outcome of treatment with a femoral-head allograft, particularly in association with a component inserted with cement, is excellent. Four non-porous-coated components were placed without cement on structural allografts. Radiographically, three of those components subsided, but none of the three needed revision and two were associated with a good clinical result. Our current practice is to cement components in all arthroplasties involving grafting. Our findings suggest that the use of a stemmed component reduces the stress on the allograft, host bone, and fixation interface. In addition, such a component contributes to the longevity of a total knee replacement associated with a bone graft. Additional studies with long-term follow-up are necessary to confirm this outcome.     

The use of arterial allografts in aortic graft infections. A three year experience on eighteen patients

BACKGROUND: We describe our experience in the treatment of aortic graft infections by replacing them with arterial homografts as suggested by the good results recently described. METHODS: Between March 1994 and March 1997 eighteen patients with infections of the aortofemoral bifurcation segments have been treated. All patients underwent a complete explantation of the infected graft and an in situ revascularization with arterial homograft harvested in multiorgan removal. Eight segments were freshly preserved, 10 were cryopreserved. Four patients were operated as emergencies, of which 3 for aorto-enteric fistulas. All others presented a serious septic state. RESULTS: Three patients died in the early postoperative period: one of acute infarction and two of homograft related causes. In the follow-up there was only one death from acute infarction, a branch occlusion and two allograft enteric fistulas successfully treated by surgery. All surviving patients are submitted to periodical haemodynamic and tomographic control with an average follow-up of 22 months (range 3 months to 3 years) and there has been no allograft degeneration so far. CONCLUSIONS: The use of homologue arterial allografts has shown good results in the treatment of serious aortic graft infections resulting in adequate peripheral vascularization. There have been no significant degenerations to date, either in fresh or cryopreserved allografts.     

Use of full cortical allograft to repair a metatarsal fracture in a foal

A 4-month-old Quarter Horse colt was admitted for repair of an open, comminuted fracture of the proximal portions of the diaphyses of the left second, third, and fourth metatarsal bones. Initial repair included internal fixation and cancellous bone graft. However, the third metatarsal bone became infected and failed to heal. After removal of infected portions of the bone, a 5-cm, fullthickness cortical allograft was placed in the defect. Rigid internal fixation provided stability for the allograft and remaining fracture fragments so that the horse was able to bear weight on the second and fourth metatarsal bones. The allograft was ultimately resorbed; however, appositional bone growth permitted a massive, functional metatarsal bone to form that incorporated the second, third, and fourth metatarsal bones. The colt went on to compete successfully, long term, as a show horse.     

Articular cartilage transplantation

This report describes the biopsy findings in four of 30 patients treated with cadaver osteochondral shell allografts for osteoarthritis in the knee. This study demonstrates that graft cartilage cells can survive in excess of 25 months, and that host bone can completely replace graft bone by creeping substitution. An inflammatory reaction in synovium and bone marrow was found in only one of four cases. Graft failure was related to prolonged down time of donor cartilage in one case and mechanical factors related to osteoarthritis in the apposing femoral surface in other cases. The clinical success of these grafts is attributed to the prolonged viability of cartilage cells, the capacity of host bone to join graft cartilage without histologic reaction, and the host's immunologic tolerance, which obviates the need for immunosuppressive therapy.     

Ionic mechanisms mediating the differential effects of methohexital and thiopental on action potential duration in guinea pig and rabbit isolated ventricular myocytes

BACKGROUND: The stress response to injury concept has been proposed as a mechanism of chronic rejection. This hypothesis has been tested with a rat cardiac allograft model in recipients pretreated with donor bone marrow (BM) cells. Chronic rejection is manifested in this BM group by obliterative arteriopathy and the epicardium and endocardium contains lymphocytic infiltrates resembling Quilty lesions. Pretreatment with a liver allograft (the orthotopic liver transplant [OLTx] group) is associated with an absence of chronic rejection in the transplanted heart. METHODS AND RESULTS:. Stress responses in the allograft were assessed by determining heat shock protein (hsp) expression by immunohistology of graft tissues and immunoblot analysis of stromal tissue lysates with monoclonal antibodies (mAb) to mammalian hsp60, the inducible hsp72, the constitutively expressed hsc73, and the grp78 C-terminal sequence KSEKDEL (grp78seq). Immunostaining showed clusters of grp78seq-positive cells in the inflammatory infiltrates of obliterated blood vessels and Quilty lesions in the BM group of cardiac allografts. Such grp78seq-positive cells were not seen in the OLTx group of heart allografts nor in syngrafts. Neither group showed significantly different graft myocyte staining of grp78 or hsp72, whereas hsp60 and hsc73 showed higher expression in the BM group and, to a lesser extent, the OLTx group. The increased expression of hsc73 was seen especially in the obliterated arteries and in myocytes nearby cellular infiltrates. Immunoblot analysis of graft stromal tissue lysates showed additional bands with mAb to hsp60 and hsc73 for the OLTx and especially the BM group. No significant bands were seen for hsp72 and grp78. Lymphocytes isolated from chronically rejecting allografts reacted with irradiated autologous spleen cells in the presence of mycobacterial hsp65 and interleukin-2. Culturing of graft-infiltrating cells with mycobacterial hsp71 and interleukin-2 yielded lymphocyte clones without alloreactivity, but with strong proliferative responsiveness to self-antigen-presenting cells and, only in the presence of mycobacterial hsp71 or murine grp78. This T-cell reactivity seemed to require intact hsp molecules because treatment of hsp71 with proteolytic enzymes, polymyxin, or ATP abrogated this induction of the stimulatory effect of self-antigen-presenting cells. These T cells are similar to the hsp-dependent, autoreactive lymphocytes cloned from acutely rejecting rat allografts. CONCLUSIONS: These findings support the concept that the pathogenesis of chronic rejection involves a stress response and the participation of graft-infiltrating autoreactive T cells that operate under hsp-dependent mechanisms.     

Rejection of cardiac allografts by T cells expressing a restricted repertoire of T-cell receptor V beta genes

We have recently shown that T cells infiltrating cardiac allografts early in graft rejection use a limited T-cell receptor (TCR) V beta repertoire. In this study we tested whether this limited repertoire of V beta genes is important for graft rejection. A cell line, AL2-L3, was established from LEW lymphocytes infiltrating ACI heart allografts 2 days after transplantation. This cell line is composed of CD4+ T cells that primarily recognize the class II RTI.B major histocompatibility complex (MHC) molecule expressed by the donor graft. This cell line precipitated acute rejection of donor hearts with a median survival time (MST) of 10.5 days following adoptive transfer to sublethally irradiated LEW recipients. This rate of graft rejection was significantly (P < 0.0007) accelerated when compared with a MST of 60 days for allografts in irradiated control recipients. The AL2-L3-mediated acceleration of graft rejection was donor specific as WF third-party heart allografts were rejected with a delayed tempo (MST = 28.5 days). The V beta repertoire of this cell line was primarily restricted to the expression of V beta 4, 15 and 19 genes. The nucleotide sequence analysis of the beta-chain cDNAs from this cell line demonstrated that the restricted use of the V gene repertoire was not shared with the N, D and J regions. A wide variety of CDR3 loops and J beta genes were used in association with selected V beta genes. These data provide evidence for the role a restricted repertoire of V beta genes plays in cardiac allograft rejection in this model. The restricted usage of the V beta repertoire in an early T-cell response to allografts may provide the opportunity to therapeutically disrupt the rejection reaction by targeting selected T-cell populations for elimination at the time of organ transplantation.     

Early cardiac allograft rejection is independent of regional myocardial blood flow

Noninvasive telemetric monitoring of canine heterotopic cardiac allograft unipolar peak-to-peak amplitude (UPPA) has permitted prospective surveillance for rejection; moreover, this technique is able to reliably detect rejection before the development of histologic evidence of myocyte necrosis. This study was performed to determine whether early cardiac allograft rejection and the accompanying decline in allograft UPPA were associated with alterations in regional myocardial blood flow (RMBF). Seven heterotopic, intrathoracic canine cardiac transplantations were performed using triple-drug immunosuppression. Native hearts and allografts were instrumented with right ventricular and left ventricular epicardial screw-in electrodes connected to subcutaneous telemeters. Daily measurement of native and graft UPPA was performed; using radioactive microspheres, native and graft RMBF were determined during the control period and when UPPA had declined by 15%, 30%, and 45%. Graft histologic status was determined by endomyocardial biopsy at the time of RMBF determination. Mean duration of the study was 19.7 +/- 3.9 days. Rejection was documented in all animals. The UPPA was stable in native hearts; UPPA declined in the allografts after the onset of rejection. A biphasic change in allograft blood flow was seen. Initially RMBF increased as UPPA declined; a 30% to 45% reduction in UPPA was associated with a 41% increase in RMBF (p = 0.028 versus allograft control). Subsequently, a significant decline in blood flow was observed for reductions in UPPA greater than 45% (0.68 +/- 0.44 versus 1.07 +/- 0.47 mL.g-1 x min-1 for a 30% to 45% decline in UPPA; p = 0.007).(ABSTRACT TRUNCATED AT 250 WORDS)     

Patterns of allosensitization in allograft recipients: long-term cardiac allograft acceptance is associated with active alloantibody production in conjunction with active inhibition of alloreactive delayed-type hypersensitivity

BACKGROUND: The immunologic characteristics of experimental allograft acceptance remain ill-defined. This study evaluates humoral and cell-mediated immunity in transiently immunosuppressed mice that have accepted cardiac allografts. METHODS: DBA/2-->C57BL/6 heterotopic cardiac allograft recipients were immunosuppressed with either GK1.5 monoclonal antibody or gallium nitrate and monitored for donor-reactive delayed-type hypersensitivity (DTH) assessed by ear challenge and for alloantibody production detected by flow cytometry. RESULTS: Cardiac allograft function continued for >90 days in approximately 50% of GK1.5-treated and 97% of gallium nitrate-treated transplant recipients. All nonsuppressed recipients lost graft function within 7 to 10 days. Among mice that accepted allografts, donor-reactive IgG was produced by about 50% of GK1.5 monoclonal antibody-treated mice and 80% of gallium nitrate-treated mice. None of the these mice exhibited donor-reactive DTH responses, and all could down-regulate third-party DTH responses in a donor alloantigen-dependent manner. This down-regulation is not found in nonsuppressed allograft recipients or in naive mice. Importantly, transfer into SCID mice of splenocytes from mice that accepted allografts, but not naive splenocytes, provided them with a similar ability to accept cardiac allografts, even if the grafts co-expressed third-party alloantigens. CONCLUSIONS: IgG alloantibody production by murine cardiac allograft recipients is not a precise indicator of allosensitization leading to either cardiac allograft rejection or acceptance. However, expression of alloreactive DTH is a reliable indicator of allosensitization leading to acute rejection, and the absence of DTH in association with active DTH down-regulatory mechanisms is a reliable indicator of allograft acceptance in this experimental model. Thus, DTH analysis may hold more promise than alloantibody detection for clinical assessment of posttransplant immune status.