Mapping transmembrane residues of proteinase activated receptor 2 (PAR2) that influence ligand-modulated calcium signaling.

Proteinase-activated receptor 2 (PAR2) is a G protein-coupled receptor involved in metabolism, inflammation, and cancers. It is activated by proteolysis, which exposes a nascent N-terminal sequence that becomes a tethered agonist. Short synthetic peptides corresponding to this sequence also activate PAR2, while small organic molecules show promising PAR2 antagonism. Developing PAR2 ligands into pharmaceuticals is hindered by a lack of knowledge of how synthetic ligands interact with and differentially modulate PAR2. Guided by PAR2 homology modeling and ligand docking based on bovine rhodopsin, followed by cross-checking with newer PAR2 models based on ORL-1 and PAR1, site-directed mutagenesis of PAR2 was used to investigate the pharmacology of three agonists (two synthetic agonists and trypsin-exposed tethered ligand) and one antagonist for modulation of PAR2 signaling. Effects of 28 PAR2 mutations were examined for PAR2-mediated calcium mobilization and key mutants were selected for measuring ligand binding. Nineteen of twenty-eight PAR2 mutations reduced the potency of at least one ligand by >10-fold. Key residues mapped predominantly to a cluster in the transmembrane (TM) domains of PAR2, differentially influence intracellular Ca2+ induced by synthetic agonists versus a native agonist, and highlight subtly different TM residues involved in receptor activation. This is the first evidence highlighting the importance of the PAR2 TM regions for receptor activation by synthetic PAR2 agonists and antagonists. The trypsin-cleaved N-terminus that activates PAR2 was unaffected by residues that affected synthetic peptides, challenging the widespread practice of substituting peptides for proteases to characterize PAR2 physiology.

Safe Conversion From Tacrolimus to Belatacept in High Immunologic Risk Kidney Transplant Recipients With Allograft Dysfunction.

There is no literature on the use of belatacept for sensitized patients or regrafts in kidney transplantation. We present our initial experience in high immunologic risk kidney transplant recipients who were converted from tacrolimus to belatacept for presumed acute calcineurin inhibitor (CNI) toxicity and/or interstitial fibrosis/tubular atrophy. Six (mean age = 40 years) patients were switched from tacrolimus to belatacept at a median of 4 months posttransplant. Renal function improved significantly from a peak mean estimated glomerular filtration rate (eGFR) of 23.8 ± 12.9 mL/min/1.73 m(2) prior to the switch to an eGFR of 42 ± 12.5 mL/min/1.73 m(2) (p = 0.03) at a mean follow-up of 16.5 months postconversion. No new rejection episodes were diagnosed despite a prior history of rejection in 2/6 (33%) patients. Surveillance biopsies performed in 5/6 patients did not show subclinical rejection. No development of donor-specific antibodies (DSA) was noted. In this preliminary investigation, we report improved kidney function without a concurrent increase in risk of rejection and DSA in six sensitized patients converted from tacrolimus to belatacept. Improvement in renal function was noted even in patients with chronic allograft fibrosis without evidence of acute CNI toxicity. Further studies with protocol biopsies are needed to ensure safety and wider applicability of this approach.

Pathway-selective antagonism of proteinase activated receptor 2.

BACKGROUND AND PURPOSE: Proteinase activated receptor 2 (PAR2) is a GPCR associated with inflammation, metabolism and disease. Clues to understanding how to block PAR2 signalling associated with disease without inhibiting PAR2 activation in normal physiology could be provided by studies of biased signalling. EXPERIMENTAL APPROACH: PAR2 ligand GB88 was profiled for PAR2 agonist and antagonist properties by several functional assays associated with intracellular G-protein-coupled signalling in vitro in three cell types and with PAR2-induced rat paw oedema in vivo. KEY RESULTS: In HT29 cells, GB88 was a PAR2 antagonist in terms of Ca(2+) mobilization and PKC phosphorylation, but a PAR2 agonist in attenuating forskolin-induced cAMP accumulation, increasing ERK1/2 phosphorylation, RhoA activation, myosin phosphatase phosphorylation and actin filament rearrangement. In CHO-hPAR2 cells, GB88 inhibited Ca(2+) release, but activated G(i/o) and increased ERK1/2 phosphorylation. In human kidney tubule cells, GB88 inhibited cytokine secretion (IL6, IL8, GM-CSF, TNF-α) mediated by PAR2. A rat paw oedema induced by PAR2 agonists was also inhibited by orally administered GB88 and compared with effects of locally administered inhibitors of G-protein coupled pathways. CONCLUSIONS AND IMPLICATIONS: GB88 is a biased antagonist of PAR2 that selectively inhibits PAR2/G(q/11)/Ca(2+)/PKC signalling, leading to anti-inflammatory activity in vivo, while being an agonist in activating three other PAR2-activated pathways (cAMP, ERK, Rho) in human cells. These findings highlight opportunities to design drugs to block specific PAR2-linked signalling pathways in disease, without blocking beneficial PAR2 signalling in normal physiology, and to dissect PAR2-associated mechanisms of disease in vivo.

Modulating human proteinase activated receptor 2 with a novel antagonist (GB88) and agonist (GB110).

BACKGROUND AND PURPOSE: Many cells express proteinase activated receptor 2 (PAR2) on their plasma membrane. PAR2 is activated by proteolytic enzymes, such as trypsin and tryptase that cleave the receptor N-terminus, inititating signalling to intracellular G proteins. Studies on PAR2 have relied heavily upon activating effects of proteases and peptide agonists that lack stability and bioavailability in vivo. EXPERIMENTAL APPROACH: A novel small molecule agonist GB110 and an antagonist GB88 were characterized in vitro against trypsin, peptide agonists, PAR2 antibody, PAR1 agonists and flow cytometry,in seven cell lines using intracellular Ca(2+) mobilization and examined in vivo against PAR2- and PAR1-induced rat paw oedema. KEY RESULTS: GB110 is a potent non-peptidic agonist activating PAR2-mediated Ca(2+) release in HT29 cells (EC(50) ∼200 nM) and six other human cell lines, inducing PAR2 internalization. GB88 is a unique PAR2 antagonist, inhibiting PAR2 activated Ca(2+) release (IC(50) ∼2 µM) induced by native (trypsin) or synthetic peptide and non-peptide agonists. GB88 was a competitive and surmountable antagonist of agonist 2f-LIGRLO-NH(2), a competitive but insurmountable antagonist of agonist GB110, and a non-competitive insurmountable antagonist of trypsin. GB88 was orally active and anti-inflammatory in vivo, inhibiting acute rat paw oedema elicited by agonist GB110 and proteolytic or peptide agonists of PAR2 but not by corresponding agonists of PAR1 or PAR4. CONCLUSIONS AND IMPLICATIONS: The novel PAR2 agonist and antagonist modulate intracellular Ca(2+) and rat paw oedema, providing novel molecular tools for examining PAR2-mediated diseases.

MicroRNA profiles in allograft tissues and paired urines associate with chronic allograft dysfunction with IF/TA.

Despite the advances in immunosuppression, renal allograft attrition over time remains unabated due to chronic allograft dysfunction (CAD) with interstitial fibrosis (IF) and tubular atrophy (TA). We aimed to evaluate microRNA (miRNA) signatures in CAD with IF/TA and appraise correlation with paired urine samples and potential utility in prospective evaluation of graft function. MiRNA signatures were established between CAD with IF/TA versus normal allografts by microarray. Validation of the microarray results and prospective evaluation of urine samples was performed using real-time quantitative-PCR (RT-qPCR). Fifty-six miRNAs were identified in samples with CAD-IF/TA. Five miRNAs were selected for further validation based on array fold change, p-value and in silico predicted mRNA targets. We confirmed the differential expression of these five miRNAs by RT-qPCR using an independent set of samples. Differential expression was detected for miR-142-3p, miR-204, miR-107 and miR-211 (p < 0.001) and miR-32 (p < 0.05). Furthermore, differential expression of miR-142-3p (p < 0.01), miR-204 (p < 0.01) and miR-211 (p < 0.05) was also observed between patient groups in urine samples. A characteristic miRNA signature for IF/TA that correlates with paired urine samples was identified. These results support the potential use of miRNAs as noninvasive markers of IF/TA and for monitoring graft function.

Multimodality therapy and liver transplantation in patients with cirrhosis and hepatocellular carcinoma: 6 years, single-center experience.

The treatment of patients with cirrhosis and hepatocellular carcinoma (HCC) has improved dramatically over the past 10 years. We conducted a 6-year prospective study, using multimodality ablation therapy (MMT) combined with liver transplantation (LTx) for patients with cirrhosis and unresectable HCC. Subjects were classified as: group 1 (n = 35), intention to treat with MMT + LTx; group 2 (n = 16), contemporaneous LTx with "incidental" HCC on explants; group 3 (n = 94), MMT alone; and group 4 (n = 19), palliative care alone. MMT included trans-arterial chemo-embolization (54.4%), trans-arterial chemo-infusion (28.6%), and radio frequency ablation (17%). Group 1, with a mean wait time of 11.6 months pre-MELD era and 5.4 months post-MELD era, had a mean of 2.4 +/- 1.2 MMTs and achieved 1- 3-, and 5-year patient survivals of 100, 100, and 76%, respectively, which was not different from group 2 (incidental HCC), namely 93, 93, and 93%, respectively; or to a contemporaneous non-HCC LTx group: namely 84.3, 78.7, and 73.9%, respectively. Despite careful pretransplant HCC staging, 22.8% (8 of 35) group 1 subjects were understaged. Those subjects in group 1 with true T1-2 stage HCC achieved 100% cancer-free survival at 5 years. Only three cases of HCC recurrence occurred in our series, all of whom were understaged. Our data suggest that pretransplant MMT followed by timely LTx provides excellent disease-free survival at 5 years for patients with true T1-2 stage HCC and cirrhosis. Pretransplant HCC understaging contributes to posttransplant HCC recurrence after LTx.

Salvage procedure for unexpected portal vein thrombosis in living donor liver transplantation.

Portal vein thrombosis (PVT) is considered a relative contraindication to living donor liver transplantation (LDLTx) due to technical difficulty and ethical considerations. So far, there have been a few reported cases of LDLTx with PVT, most of which were treated by thrombectomy with or without a venous conduit. We report a case of LDLTx in an unexpected recipient with grade 4 diffuse PVT, which was successfully managed using a variceal left gastric vein and a deceased donor iliac vein conduit to create a "de novo portal vein" for splanchnic inflow to the right lobe. The patient experienced an uneventful postoperative course with normal blood flow in the de novo portal vein at 1-year follow up. This report demonstrated that a variceal collateral vein can be used as appropriate alternative inflow for the right lobe in LDLTx cases in which an unexpected PVT is encountered.

Hepatic angiosarcoma and liver transplantation: case report and literature review.

Hepatic angiosarcoma is a rare malignant vascular tumor that accounts for up to 2% of all primary liver tumors. Accurate diagnosis of this tumor is difficult, especially if the patient has no history of exposure to specific carcinogens including thorotrast, arsenicals, and vinyl chloride monomer. Diagnosis of diffuse angiosarcoma by means of liver biopsy has been reported as treacherous and nondiagnostic. Herein, we present a case of a 61-year-old Caucasian male with history of cryptogenic cirrhosis, normal alpha-fetoprotein, and pretransplant abnormal liver MRI who underwent nondiagnostic liver biopsies followed by liver transplantation. High grade diffuse angiosarcoma was diagnosed in the explanted liver. The patient developed bone metastases at 8 months and is alive 1 year posttransplantation. Diffuse liver tissue infiltration seen pretransplant on CT scan or MRI, suggesting the possibility of diffuse liver lesions (HCC, angiosarcoma, etc) must be fully investigated with all techniques available including multiple open liver biopsies to avoid the sacrifice of a liver allograft in these patients.

Non-resective ablation therapy for hepatocellular carcinoma: effectiveness measured by intention-to-treat and dropout from liver transplant waiting list.

BACKGROUND: Orthotopic liver transplantation (OLT) for patients with small hepatocellular carcinoma (HCC) is widely accepted, and the usefulness of local ablation techniques as a bridge for liver transplantation is still under investigation. METHODS: From December 1997 to February 2003, patients with cirrhosis and T0-T1-T2-T3 stage HCC received multi-modality ablative therapy (MMT) for the treatment of their HCC and were evaluated for OLT; listed, and transplanted when an allograft became available. MMT included radiofrequency ablation (RFA), and/or Trans-Arterial Chemo-Embolization (TACE), and alcohol (EtOH) ablation, followed by Trans-Arterial Chemo-Infusion (TACI), with repeated treatments based on follow up hepatic magnetic resonance imaging (MRI) during the waiting period for OLT. RESULTS: A total of 135 HCC patients were seen at our center within this time frame. The intention-to-treat group included 33 (24.4%) patients with T0, T1, T2, T3 HCC and cirrhosis. There were 31 men and two women. The mean age was 53.6 +/- 7.2 yr. All patients received MMT with a mean of 2.90 +/- 1.5 procedures per patient. Tumor-node-metastasis (TNM) stages at time of listing were: T0 in one patient, T1 in nine patients, T2 in 17 patients, and T3 in six patients. Twenty-eight (85%) patients have received OLT. Five (12.19%) patients were listed and removed (dropout) from the transplant waiting list after waiting 5, 5, 5, 8, and 14 months respectively. The waiting time of the HCC listed group was 9.1 +/- 14.8 months with a mean follow up of 32 months. OLT patient survival and cancer-free survival are 92.9% and 95.24%, respectively; the overall survival of intention-to-treat group was 79% at 32 months follow up. Predictors of dropout included an alpha-fetoprotein (AFP, >400 ng/mL) and T3 HCC stage. CONCLUSION: Aggressive ablation therapy with a short transplant waiting time optimizes the use of OLT for curative intent in selective cirrhotic HCC patients.

Massive hepatic artery atherosclerosis of an otherwise suitable donor liver: a case report.

Most of the few reports about hepatic artery disease found in the literature describe hepatic artery aneurysms or hepatic artery calcifications. Atherosclerosis of the hepatic artery is not commonly evaluated during deceased donor liver procurement. Herein we present a case of a stable 47-year-old Caucasian female donor whose liver function tests were within normal limits and a liver biopsy showed less than 5% steatosis. The liver when received at our center appeared grossly unremarkable. Back-table evaluation showed a complete occlusion of the trunk of the proper hepatic artery. The pathology report revealed hepatic occlusion due to arterial atherosclerosis. Transplantation was canceled, and the liver was used for isolated hepatocyte perfusion, revealing < 25% hepatocyte viability. Hepatic artery atherosclerosis and patency need to be evaluated at the time of procurement to prevent recipient morbidity due to anesthetic induction, or initiation of a recipient abdominal incision prior to declining the liver graft for this rare finding.

Non-resective ablation and liver transplantation in patients with cirrhosis and hepatocellular carcinoma (HCC): safety and efficacy.

We investigated the efficacy of nonresective ablation techniques and the tumor-free survival of cirrhotic patients undergoing liver transplantation for hepatocellular carcinoma (HCC). In group 1, 11 HCC patients were treated with these techniques and transplanted. On the waiting list, patients were treated to complete ablation, judged by gadolinium-enhanced MRI and alpha-fetoprotein (AFP) levels. Group 1 was compared with a concurrent group of 10 liver transplant patients (group 2) with incidental HCC (stages T1 three patients, T2 seven patients). The group 1 patients received 36 procedures (4 alcohol ablations, 14 trans -hepatic artery chemo-embolizations, 15 trans -hepatic chemo-infusions, and 3 radio frequency ablations) for treatment of 13 liver masses. Tumor-node-metastasis (TNM) stage was reduced in eight patients (72.7%), unchanged in two patients and increased in one patient before transplantation. The mean waiting time for transplantation was 12.9 7.6 months. Both groups had a tumor-free survival of 100%, at 30 12 months post transplant. On pathology, 54.5% of explanted livers had residual viable HCC after tumor treatment, and 36.4% (4/11) explants had synchronous lesions. Non-resective ablation therapy is safe and effective in reducing the HCC progression in cirrhotic patients awaiting liver transplantation. The cancer-free survival rate in this treatment group is equal to that for incidental T1-T2 HCCs.

Humoral responses to pig-to-baboon cardiac transplantation: implications for the pathogenesis and treatment of acute vascular rejection and for accommodation.

Organs transplanted between phylogenetically-disparate species, such as from the pig into the primate, are subject to hyperacute and acute vascular rejection. Hyperacute rejection of a porcine organ by a primate is thought to be initiated by the binding of xenoreactive natural antibodies to Galalpha1-3Gal expressed on the endothelial lining of blood vessels in the xenograft. The factor(s) which initiates acute vascular rejection is uncertain; however, there is some evidence implicating xenoreactive antibodies. The nature of the humoral response which might contribute to acute vascular rejection of a porcine organ was investigated in baboons which received a porcine cardiac xenograft plus immunosuppression with methylprednisolone, azathioprine, and cyclosporine. Following rejection and surgical removal of the xenografts, the serum concentration of xenoreactive antibodies increased in untreated animals but in immunosuppressed animals was similar to the concentration in preimmune serum. The antibodies in the sensitized recipients were specific for Galalpha1-3Gal (70-95%) and other determinants (5-30%). However, cross-blocking studies showed that, following xenotransplantation, the immunosuppressed baboons had no detectable IgM or IgG directed against "new" endothelial antigens. These results indicate that antibodies made by immunosuppressed individuals in response to xenotransplantation are much like xenoreactive natural antibodies and suggest that acute vascular rejection might in some cases be addressed by therapeutic strategies aimed at those antibodies.

The humoral immune response in humans following cross-perfusion of porcine organs.

A major question in xenotransplantation is the nature of the humoral response that would occur following the transplantation of a xenogeneic organ into an immunosuppressed recipient as such a response could mediate delayed types of injury to the graft. To begin to address this issue we characterized the changes in the properties of xenoreactive antibodies occurring in patients exposed to porcine organs under conditions simulating transplantation. In two patients whose blood had been cross-perfused through porcine livers as a treatment for hepatic failure, the titer of xenoreactive IgM increased by four-fold and the titer of xenoreactive IgG increased by sixty-fold within ten days after perfusion procedures. The xenoreactive IgM and IgG antibodies were specific for Gal alpha 1-3Gal based on binding to porcine endothelial cells and bovine thyroglobulin, which express this determinant, and on the decrease in binding following treatment of porcine endothelial cells or bovine thyroglobulin with alpha-galactosidase. The sequential addition to endothelial cells of amounts of serum known to saturate antibody-binding sites obtained before and ten days after perfusion of porcine organs revealed no increase in binding of IgM above the level observed with serum obtained before perfusion, suggesting that new determinants were not identified. Moreover, the functional avidity of binding to porcine endothelial cells of IgM in serum obtained before and ten days after perfusion of porcine organs was unchanged. Even at later times, the presence of newly elicited antibodies against porcine aortic endothelial cell targets was not detected. Thus, exposure to porcine antigens in a vascularized organ results in increases in the levels of xenoreactive IgM and IgG antibodies--however, these antibodies exhibit properties similar to natural antibodies.

Variation in the level of xenoantigen expression in porcine organs.

Hyperacute rejection of vascularized porcine to primate xenografts is initiated by the binding of xenoreactive natural antibodies to donor endothelium. We tested the hypothesis that the level of xenoantigen expression varies in the population of potential porcine donors and may determine the amount of binding of xenoreactive natural antibodies to a porcine organ perfused by xenogeneic blood. Two hundred ninety pigs were studied using an inhibition ELISA that quantitated the xenoantigen level on porcine platelets. Based on this assay, the levels of xenoantigen expression in the population adhered to a normal distribution. Kidneys from pigs found to express high antigen levels and kidneys from pigs found to express low antigen levels were perfused with baboon blood using an extracorporeal circuit. In multiple experiments, a significant difference was observed in the amount of xenoreactive natural antibody adsorbed by high antigen versus low antigen organs. Normalizing for the weight of the perfused organs and for levels of natural antibody in individual baboons, high antigen organs adsorbed 3.6 +/- 1.3 U of xenoreactive natural antibody/g and low antigen organs adsorbed -0.8 +/- 1.0 U of xenoreactive natural antibody/g (P < 0.002). Immunopathology of tissues from the perfused organs demonstrated more deposition of IgM and C4 in high than in low xenoantigen organs. The quantitative relationship between binding of xenoreactive natural antibodies to platelets and to whole organs suggests that platelets are a valid representation of endothelial cell antigen expression in vivo. Despite the probable importance of Gal alpha(1-3)Gal as an epitope recognized by xenoreactive natural antibodies, differences in the binding to platelets or to organs of the GS-I-B4 lectin that recognizes that sugar had no correlation with the differences in binding of IgM to these tissues. Variation in expression of xenoantigen may be exploited to selectively breed donors for xenotransplantation that are less susceptible to attack by xenoreactive natural antibodies.

Human complement regulatory proteins protect swine-to-primate cardiac xenografts from humoral injury.

The susceptibility of xenografts to hyperacute rejection is postulated to reflect in part failure of complement regulatory proteins (CRPs) to control activation of heterologous complement on graft endothelium. To test this concept, transgenic swine expressing the human CRP decay accelerating factor and CD59 were developed using a novel expression system involving transfer of the proteins from erythrocytes to endothelial cells. Hearts from transgenic swine transplanted into baboons had markedly less vascular injury and functioned for prolonged periods compared to hearts from nontransgenic swine. These results indicate that expression of human CRPs in xenogeneic organs may contribute to successful xenografting and suggest that intercellular protein transfer might be a useful approach for expression of heterologous proteins in endothelial cells.

Cardiac xenografts between primate species provide evidence for the importance of the alpha-galactosyl determinant in hyperacute rejection.

Transplants performed between phylogenetically disparate species are subject to hyperacute rejection initiated by binding of xenoreactive natural Abs to endothelium in the donor organ. Binding of these Abs activates complement, leading to tissue injury and destruction of the graft. Human xenoreactive natural Abs recognize Gal alpha 1-3Gal beta 1-4GlcNAc (galactose alpha 1-3galactose beta 1-4-N-acetylglucosame); however, the relative importance of this Ag in graft rejection has not been proved. The present study was conducted to test the potential importance of alpha-galactosyl (alpha-Gal) determinants in the pathogenesis of hyperacute rejection. To this end, hearts (n = 3) from New World monkeys (Saimiri scureus, squirrel monkey), which can synthesize Gal alpha 1-3Gal, were transplanted heterotopically into Old World monkeys (Papio species, baboon), which do not synthesize Gal alpha 1-3Gal determinants and which have circulating anti-alpha Gal Abs. The xenografts were rejected in 51 to 56 min (mean +/- SD = 53.3 +/- 2.5), results similar to those observed in porcine grafts transplanted into baboons. Histologic analysis of the hearts revealed thrombosis and intraparenchymal hemorrhage and immune deposits consisting of IgM, Clq, C3, C4, C5b, and the membrane attack complex, but not properdin or factor B of the recipient deposited on graft endothelium. Sera obtained from baboons after perfusion of squirrel monkey kidneys revealed depletion of alpha-Gal-specific Abs and anti-pig endothelial cell Abs. These findings provide strong evidence that the Abs that accumulate in New World monkey organs during perfusion with baboon blood are the same Abs that would accumulate in a porcine organ transplanted into a primate and suggest that hyperacute rejection is not necessarily a reflection of phylogenetic distance but that the expression of terminal alpha-Gal residues provides an adequate target to initiate that process.

Graft-versus-host reaction-induced immune modulation. I. Donor-recipient genetic disparity and the differential expression of Lyt-2, L3T4, and Ly-6 during acute reactions in the host thymus.

To investigate the effects of graft-vs-host reactions (GvHR) on cells in a central lymphoid compartment, GvHR were induced across class I/II or class II only major histocompatibility complex differences utilizing the parent into nonirradiated F1 hybrid (P----F1) model. Thymocytes were subsequently examined during the acute stage of GvHR for the expression of Lyt-2, L3T4, and Ly-6 cell surface molecules. Class I/II "suppressive" GvHR resulted in a dramatic decrease (greater than 85%) in total thymocyte numbers by 2 wk after parental cell injection. Although a dramatic decrease in the percentages of Lyt-2 (85%----30%) and L3T4 (95%----50%) expression was observed, the percentage of thymocytes expressing Ly-6 was markedly increased compared to uninjected controls (5%----greater than 80%). This increased percentage was not due solely to a selective loss of Ly-6 negative cells from the thymus, since the actual number of Ly-6 positive cells was greater in GvHR mice than in controls. Class II GvHR during the same time interval resulted in a less dramatic decrease (20 to 60%) in total thymocyte numbers. In addition, the effect on the percentages of Lyt-2 (85%----approximately 70%) and L3T4 (95%----approximately 85) expression was subtle and transient. However, intrathymic Ly-6 expression was again clearly enhanced (5%----20 to 30%). Class I/II "proliferative" or "stimulatory" GvHR differ from "suppressive" reactions in that they are characterized by stimulatory pathologic symptoms and the appearance of autoimmune abnormalities. Such GvHR were found to result in minimal alteration of total thymocyte numbers. Similarly, the percentage expression of Lyt-2 and L3T4 was marginally affected. However, the percentage of Ly-6 expression was increased from 5%----20 to 30% and thus these intrathymic lymphocyte profiles more closely resemble those of class II as compared to class I/II "suppressive" GvHR. The present findings therefore demonstrate that major histocompatibility complex differences alone do not necessarily determine the effects of GvHR on recipient thymocytes and that Ly-6 is a useful marker for the early detection of GvHR-associated immunologic events.