Search

The Banff Working Group on Liver Allograft Pathology reviewed and discussed literature evidence regarding antibody-mediated liver allograft rejection at the 11th (Paris, France, June 5-10, 2011), 12th (Comandatuba, Brazil, August 19-23, 2013), and 13th (Vancouver, British Columbia, Canada, October 5-10, 2015) meetings of the Banff Conference on Allograft Pathology. Discussion continued online. The primary goal was to introduce guidelines and consensus criteria for the diagnosis of liver allograft antibody-mediated rejection and provide a comprehensive update of all Banff Schema recommendations. Included are new recommendations for complement component 4d tissue staining and interpretation, staging liver allograft fibrosis, and findings related to immunosuppression minimization. In an effort to create a single reference document, previous unchanged criteria are also included.

Background T-cell receptor Vδ2 γδ T cells (Vδ2 cells) participate in host defense, whereas Vδ1 γδ T cells (Vδ1 cells) may regulate immune responses. Vδ1 cells appear to play a role in fetomaternal tolerance and our aim was to examine their role in liver transplant tolerance. Methods To determine whether Vδ1 cells increase within accepted grafts after semiallogeneic pediatric liver transplantation, the Vδ1/Vδ2 ratio was assessed at the transcriptional level and the complementarity-determining region 3 loop of the δ chain of Vδ1 cells was sequenced in biopsies from immunosuppression-free (n=6) or almost free (n=3) liver transplant recipients, referred to as group tolerance (Gr-Tol; n=9). The results were compared with biopsies from grafts of recipients on maintenance immunosuppression due to concern of rejection (Gr-IS; n=11). Chronically rejected grafts (Gr-CR; n=6) and normal livers (Gr-NL; n=8) were also examined. Results The Vδ1/Vδ2 ratio was the highest in Gr-Tol (0.07±0.06) compared with Gr-IS (0.03±0.02; P=0.04), Gr-CR (0.01±0.02; P=0.008), and Gr-NL (0.02±0.04; P=0.01). There was an identical complementarity-determining region 3 sequence (100% homologous) among all recipients in Gr-Tol, which was dominant in six of nine recipients. This sequence was not seen in Gr-IS or Gr-CR, although it was observed in five of six normal livers. Conclusions A unique Vδ1-bearing T-cell clone accumulates within accepted human liver grafts. It might be useful as a biomarker of tolerance and the identification of its ligand might aid in the development of a novel strategy for tolerance induction.

Background. Some experimental transplant-tolerance models have shown that the presence of regulatory T cells within grafts is important for the development of tolerance (Tol). , Methods. To determine if the presence of regulatory T cells correlates with graft acceptance in living-donor liver-transplantation tolerance, the expression of Foxp3 mRNA and the presence of CD4 + , CDB + , and Foxp3 + cells were quantified in biopsies from tolerant recipients by real-time polymerase chain reaction and by immunohistochemistry and immunofluorescent staining (Gr-Tol). The results were compared with biopsies from the recipients on maintenance immunosuppression (Gr-IS), grafts removed because of chronic rejection (Gr-CR), or normal liver (Gr-NL). Results. The expression ofFoxp3 mRNA in Gr-Tol was higher than that in Gr-IS (P=0.07) and Gr-NL (P

Outcome for highly immunogenic lung transplantation remains unsatisfactory despite the development of potent immunosuppressants. The poor outcome may be the result of a lack of minimally invasive methods to detect early rejection. There is emerging clinical evidence that, paradoxically, expression of forkhead box P3 (FOXP3, a specific marker for the regulatory T cells) is upregulated within rejecting grafts.Orthotopic lung transplantation was performed using miniature swine without immunosuppression. Rejection was monitored by chest radiography and open lung biopsy. Expressions levels of FOXP3, perforin, Fas-L and IP-10 mRNA were quantified in the peripheral blood. In addition, rescue immunosuppressive therapy (steroid plus tacrolimus) was administered on post-operative day (POD) 4 or 6.Early rejection was detected by open lung biopsy, but misdiagnosed by chest radiography on POD 4. Expression of FOXP3 in the peripheral blood reached its highest value as early as POD 4, followed by a decline. Such an increase of FOXP3 was not observed in recipients given high-dose tacrolimus. Neither perforin, Fas-L or IP-10 in the peripheral blood exhibited significant fluctuations in the early phase of rejection. Rescue immunosuppressive therapy from POD 4, when peak FOXP3 was seen, prolonged graft survival (27.2 days, versus 9.1 days without immunosuppression, p0.001), in contrast to POD 6, when rejection was suspected by chest radiography (11.5 days, p = not statistically significant [NS]).In a miniature swine lung transplantation model, the FOXP3 mRNA level in the peripheral blood was upregulated at an early phase of rejection. The clinical implication of this finding remains to be elucidated.

Operational tolerance (graft acceptance in an immunosuppression (IS)-free environment) after living-donor liver transplantation (LDLT) could occur by our elective protocol in some patients. There is, nevertheless, no reliable parameter to monitor patients who may discontinue IS without a risk of rejection. To identify such parameters, we systemically phenotyped peripheral blood mononuclear cells from operationally tolerant patients. An increase was observed in the frequency of CD4+CD25high+ cells, B cells and Vdelta1/Vdelta2 gammadeltaT-cells ratio in operationally tolerant patients (Gr-tol; n = 12), compared with those from age-matched volunteers (Gr-vol; n = 24) or patients on IS (Gr-IS; n = 19). The frequency of NK cells was decreased in Gr-tol, compared with those in Gr-IS or Gr-vol. The frequency of NKT cells was decreased after LDLT, compared with that in Gr-vol. Although the contribution of those subsets to the tolerant state remains elusive, the results may provide important clues for reliable indicators of tolerance after LDLT.

Background. Regulatory cells prevent graft loss to acute rejection and induce tolerance, possibly by promoting Th2 deviation. Th2 cytokines stimulate B cells, which cause alloantibody-mediated chronic rejection. We searched to determine whether regulatory cell-mediated tolerance protects or not against chronic rejection. Methods. Heart transplantation (Htx) was performed using RA (RT1 P ) and PVG (RT1 c ) rats as donor and recipients. Donor-specific blood transfusion (DSBT) was given on preTx day 12. Secondary grafts were implanted at day 100. Splenocytes were transferred from tolerant rats (and controls) into lightly irradiated (450 rad) naive PVG, which received RA Htx. Primary Htx were investigated for the development of vascular occlusion (VO), the production of Th1/Th2 intragraft cytokines, and for the nature of graft infiltrate as well as for endothelial deposition of immunoglobulin (Ig)G isotypes and complement (C3) binding. Results were compared with rejecting controls (no DSBT) and syngeneic Htx. Results. RA Htx were rejected within 10 days (8, 9, 10x4). PreTx DSBT prolonged primary Htx survival indefinitely (>140 days) with acceptance of secondary donor-specific (but not third-party) grafts (P

Background/aims: Steroids are traditionally used in liver transplantation as a part of a triple or quadruple immunosuppressive regimen. Steroids act non-specifically and cause multiple side-effects. Most liver transplantation centers reduce the dosage of steroids and eventually withdraw them after various time intervals. A few steroid-free trials have been recently conducted after liver transplantation but long-term data are not yet available. In addition, in these trials steroids were usually given during surgery. We report the long-term (median = 40 months) follow-up data of a prospective pilot study designed to determine whether liver transplantation could be performed with no steroids at all (neither during nor after surgery). Methods: Twenty-one consecutive liver transplantations in 20 adult patients between August 1998 and July 1999 were prospectively included in an ab initio steroid-free immunosuppressive protocol. Mean age was 54 yr (40–67 yr). Tacrolimus (through levels, 8–10 ng/mL) and azathioprine (1–2 mg/kg) were started after liver transplantation. Patients were not given steroids during or after liver transplantation except in the event of rejection or in case of tacrolimus or azathioprine toxicity requiring significant dose reduction and/or withdrawal. Results: There has been no case of primary graft dysfunction or non-function. Eleven of 21 liver transplantations (52%) received no steroids throughout the whole study. Rejection developed in five of 21 liver transplantations (23.5%). These rejections responded to standard i.v. steroids (plus ATG in one patient), followed by an oral steroid taper stopped 3 months after rejection. Steroids were transiently given in six liver transplantations for non-immune reasons: two with tacrolimus-induced neurotoxicity, three cases where azathioprine was discontinued, and one for an allergic reaction; four of these six patients are off steroids at last follow-up. The 3-yr graft and patient survival is 95 and 100%, respectively. Conclusions: Steroids are not necessary in more than 50% of liver transplantations. Steroids were transiently needed to treat acute rejection in 23.5% liver transplantations and for toxicity of calcineurin inhibitors or azathioprine or other reason in 28%. Of the patients who received steroids, the majority (70%) was eventually taken off steroids. This prospective single-center pilot study shows that liver transplantation without steroids is feasible and yields no penalty in terms of acute and chronic rejection, immune graft loss, graft function, patient and graft survival.

We developed a rodent model in which donor-specific blood transfusion (DSBT) promotes hyporesponsiveness and graft acceptance. In this model, signs of immune activation are present early posttransplant, with preserved proliferative responses against the donor and a dense cellular infiltrate in tolerant grafts. Intriguingly, an early accumulation of IFN-gamma is seen in grafts destined to become tolerized, supporting recent evidence that Th1 cytokines play a role in tolerance induction. Specific regulatory cells capable of propagating tolerance into naive recipients are operating. These mechanisms of immune activation and the generation of regulatory cells are influenced by immunosuppression (steroids and calcineurin inhibitors). In this model, in a second phase, a Th2 immune deviation occurs and is associated with the development of chronic rejection (vascular obliteration, endothelial IgG deposition, and complement binding). It remains unclear whether chronic rejection in this model is caused by Th2 type regulatory cells or whether chronic rejection is the consequence of an insufficient number of regulatory cells. In the clinic, the current strategy of profoundly inhibiting immune activation (in particular Th1 cytokines/responses) by using high dose calcineurin inhibitors and steroids may prove antagonistic with the development of tolerance, particularly when immunomodulatory strategies (such as DSBT) are applied. Development of chronic rejection in a regulation-based tolerance model suggests that deletion-based tolerogenic strategies may offer a more robust protection against chronic rejection.

Background. Intestinal transplantation (Itx) remains the most difficult form of transplantation. This is due to the high immunogenicity of the bowel that currently obligates Itx patients to heavy immunosuppression, which causes infection, posttransplant lymphoproliferative disease (PTLD), and drug toxicity. Wider application of Itx depends on the development of tolerogenic strategies to promote engraftment while reducing the need for immunosuppression. We applied a strategy to clinical Itx that combines intraportal donor-specific blood transfusion with a deliberately low immunosuppression protocol (no high-dose steroids; lower tacrolimus level). Methods. A 55-year-old patient received a combined liver/Itx. Donor-specific whole blood was taken from the donor during procurement and transfused in the recipient portal vein after graft reperfusion. For induction immunosuppression, no intravenous bolus of steroids was given; only two doses of anti-interleukin 2 receptor antibody were administered. The patient received posttransplantation maintenance immunosuppression with lower tacrolimus levels than average (15 ng/ml first month; 5-10 ng/ml thereafter), low-dose azathioprine (1 mg/kg first to third months; 0.5 mg/kg thereafter), and low-dose steroids (Medrol 8 mg twice daily first and second months; 4 mg twice thereafter). The patient was monitored for rejection, graft-versus-host disease, infection, and PTLD. Protocol biopsy specimens were taken from the distal ileum (2 per week). Results. Clinical, endoscopic, and histologic signs of rejection did not develop. Chimerism was identified at day 28. Graft-versus-host disease was absent clinically. Chimerism was self-limiting and disappeared without modifying baseline immunosuppression and without observing a change in graft function. The patient remained free of systemic opportunistic infections, PTLD, and drug toxicity. Total parenteral nutrition was stopped at 7 weeks after transplantation. The patient remains free of total parenteral nutrition and free of rejection at 14 months after transplantation. Conclusions. We describe an Itx patient who remained rejection free despite receiving significantly lower immunosuppression than average. We hypothesize that intraoperative immunomodulation via intraportal donor-specific blood transfusion in the absence of nonspecific overimmunosuppression promoted Itx acceptance.

Background. CD4 + CD25 ++ CD45RA + cells (naive regulatory T cells [naive-Tregs]) have been identified as a functionally premature form of CD4 + CD25 +++ CD45RA - cells (conventional-Tregs). However, their contribution to transplant tolerance remains to be elucidated. Method. We examined the frequency and the function of conventional and naive-Tregs in the peripheral blood derived from operationally tolerant patients after pediatric living-donor liver transplant (Gr-tol). The data were compared with those of patients who were unable to be weaned off immunosuppression due to rejection (group-intolerance [Gr-intol]), patients in the process of weaning immunosuppression (Gr-weaning) and healthy volunteers (group-healthy volunteers [Gr-vol]). Results. In Gr-tol, the frequency of conventional-Tregs was significantly higher than that in Gr-vol and tended to be higher than that in Gr-intol. The frequency of naive-Tregs was significantly decreased in Gr-intol versus those in Gr-tol, -weaning, and -vol. In mixed lymphocyte reactions, donor-specific hyporesponsiveness of CD4 + cells was observed only in Gr-tol but not in the other groups. Depletion of conventional or naive-Tregs from CD4 + cells demonstrated that the suppressive properties of donor antigen-reactive conventional and naive-Tregs were upregulated compared with those of third-party antigen-reactive conventional and naive-Tregs in Gr-tol only. Conclusions. This is the first report providing detailed evidence that donor-specific naive-Tregs were generated and their suppressive properties were upregulated in the peripheral blood of tolerant patients, whereas their frequency was downregulated in intolerant patients. Therefore, we speculate that not only conventional-Tregs play a role in Tx tolerance but also the role of naive-Tregs is critical.

Objective Kidney transplantation in rats is an important research model. Various methods have been reported, but there is no “standard operation.” We investigated a 1-stage versus a 2-stage native nephrectomy and the type of ureteral anastomosis seeking to establish a standard, reproducible and successful method. Materials and Methods We used PVG (RT1c-RT1Ac: B/Dc) male rats, weighing approximately 200 to 250 g, that underwent transplantation after right recipient nephrectomy. Left recipient nephrectomy was performed either 10 days later or simultaneously. The ureteric anastomosis was fashioned 2 ways: using a ureteral stent or by bladder insertion. Results Urinary complications (obstruction or reflux) were observed in 77.8% when a ureteral stent was used for the ureteric anastomosis versus 28.6% when using the bladder insertion technique (P = .0211). Transplanted rats with nephrectomy of both native kidneys at the time of grafting showed a perioperative mortality of 70%, whereas those hosts with a 2-stage nephrectomy displayed a mortality rate of 22% (P = .0025). Conclusions The bladder insertion technique reduced the incidence of urological complications in rats. In addition, unilateral native nephrectomy at the time of operation with delayed contralateral nephrectomy was better tolerated than simultaneous bilateral nephrectomy. These 2 surgical variants allowed us to perform kidney transplantation with a high degree of success.

Background. After intestinal transplantation (ITx), rejection is vigorous and tolerance is difficult to achieve. A possible reason for this phenomenon is that ITx and ischemia reperfusion injury are accompanied by translocation of lipopolysaccharide (LPS), a "danger" signal capable of activating adaptive alloimmunity against Tx antigens. Methods. To study that, we used our previously described rat model where donor-specific blood transfusion (DSBT) induces tolerance to fully mismatched heart allografts. Results. In this model, control grafts are rejected within 9 days, whereas 100% of DSBT pretreated grafts survive long term. In contrast with heart Tx, an identical DSBT protocol failed to induce tolerance in 57% of recipients after ITx (P

Background Operational tolerance is defined as long-term acceptance of a transplanted organ after complete cessation of immunosuppression (IS), but may not always protect against antigen-dependent changes in graft morphology. Method IS free patients after living-donor liver transplantation (LDLT) underwent protocol biopsy (tolerance group [Gr-Tol]) and were evaluated for rejection and fibrosis. The degree of fibrosis was compared with those in the patients on maintenance IS group (Gr-IS) and the base line normal liver group (Gr-BS). When bridging fibrosis or progression of fibrosis was observed, IS was reintroduced or increased in Gr-Tol or in the patients in the weaning process. Results Neither acute nor chronic rejection was observed. The degree of fibrosis, however, was significantly greater in Gr-Tol than those in Gr-IS and Gr-BS. In Gr-Tol, the number of graft infiltrating FOXP3 cells was significantly increased, the interval between LDLT and biopsy plus the donor age was significantly longer, and recipient age at LDLT was significantly younger, compared with those in Gr-IS. However, none of these three parameters correlated with the degree of fibrosis. In 7 of 11 patients in whom IS was reintroduced or increased, the improvement of fibrosis was observed by the subsequent biopsy. Conclusion Grafts of operationally tolerant patients after LDLT did not exhibit acute or chronic rejection, but they exhibited fibrosis. It remains elusive whether fibrosis observed in tolerant grafts is antigen dependent. The finding that after [corrected] the reintroduction or the increase of IS fibrosis was improved supported the possibility that fibrosis in operationally tolerant patients was antigen dependent.

Background. Idiopathic thrombocytopenic purpura (ITP) is a rare complication after liver transplantation. 1,2 We describe three cases of ITP in pediatric patients after a living-related liver transplantation (LRLT). Methods. Of 266 patients who underwent an LRLT between June 1990 and June 1996, severe thrombocytopenia developed in three pediatric patients after transplantation, and ITP was also diagnosed. The original disease was biliary atresia in all cases, and the patients were given a partial liver graft from a living-related mother and subsequently treated with tacrolimus and low-dose steroids as an immunosuppressive regimen. Results. The duration until the onset of ITP after transplantation in the three cases was 1 day, 3 months, and 13 months, respectively. The platelet-associated IgG levels increased in all cases. A preceding viral infection was suspected in two of the three cases. All patients were treated with intravenous gamma globulin with a transient recovery of thrombocytopenia in two cases and a sustained recovery in another. Conclusions. Transplant clinicians need to be aware of the possibility of ITP complication because a sudden onset of severe thrombocytopenia can occur even in patients who are apparently doing well after undergoing an LRLT.

ET-Kyoto solution (ET-K) is an extracellular-type organ preservation solution containing the cytoprotective disaccharide, trehalose. A previous study reported the supplement of dibutyryl cyclic adenosine monophosphate (db-cAMP) in conventional ET-K to attenuate lung ischemia-reperfusion injury. In this study, the efficacy of this modified ET-K for liver preservation was investigated by comparison with University of Wisconsin solution (UW). ET-K was supplemented with db-cAMP (2 mmol/L). Lewis rats were randomly assigned to two groups, and liver grafts were flushed and stored at 4°C for 24 h with ET-K or UW before syngeneic liver transplantation. The graft function and histological changes at 4 h posttransplant as well as 7-day survival were evaluated. Recipient rat survival rate was significantly higher in the ET-K group than in the UW group. Preservation in ET-K resulted in a significant reduction in serum parenchymal transaminase level and promotion of bile production in comparison with UW. The serum hyaluronic acid level, an indicator of sinusoidal endothelial cell injury, was significantly lower after ET-K preservation than that in UW. Histologically, at 4 h after transplantation, the liver grafts preserved in UW solution demonstrated a greater degree of injury than those in ET-K, which appeared to be apoptosis, rather than necrosis. The continuity of the sinusoidal lining was better preserved in ET-K than in UW. In conclusion, ET-K supplemented with db-cAMP is superior to UW in rat liver preservation. This modified ET-K might therefore be a novel candidate for the procurement and preservation of multiple organs.

In the setting of our pediatric living-donor liver transplantation (LDLT), 87 patients (15.0% of all the patients: significantly higher proportion, compared with those of other transplant centers) achieved complete withdrawal of immunosuppression, which is referred to as "operational tolerance". Immunosuppressants were completely discontinued for 54 patients as scheduled, and for 33 because of EBV infection or other complications. Immunological analyses of the peripheral blood derived from operationally tolerant patients demonstrated that non-deletional tolerance takes place in which potentially reactive T cells to donor-antigens remain physically in the immune repertoire, but specifically suppressed by certain mechanisms. Not only CD4(+)CD25(high+) T cells were increased in the proportion in the tolerant patients' peripheral lymphocytes and suppressed MLR specifically to the donor antigen, but also FOXP3 expressing cells were present within the tolerant liver. Thus, among several mechanisms accounting for non-deletional tolerance, Tregs are likely to involve at least in part in our tolerant patients. Vdelta1gammadeltaT cells, a subset of gammadeltaT cells, which otherwise reside mainly in the intestine, emerge into the peripheral blood during successful pregnancy but not abortive pregnancy. Since Vdelta1gammadeltaT cells produce massive IL-10, it is proposed that Vdelta1gammadeltaT cells induce fetomaternal tolerance by promoting Th2 immune deviation. Consistent with pregnancy, IL-10 producing Vdelta1gammadeltaT cells emerge into the blood of our tolerant patients. This may reflect a common feature between fetomaternal tolerance and transplant tolerance. We began protocol biopsy in post-LDLT patients who exhibit normal liver function from January 2003. Operationally tolerant patients, albeit showing normal liver function, exhibited decrease in size and increase in number of the bile duct and the fibrosis to a greater extent, compared with patients on maintenance immunosuppression. This warrants serial protocol biopsy before and after complete cessation of immunosuppression even in the presence of normal liver function.

Recent evidence suggests that CD4+CD25+ regulatory T cells (Tregs) affect immune responses, including those to alloantigens in organ transplants. We have followed a group of liver allograft recipients with good liver graft function who have been weaned off immunosuppression (IS). The purpose of this study was to determine whether Tregs contributed functionally to the mechanisms of graft acceptance. Material and methods The functional assay used peripheral blood obtained from LTx recipients free of immunosuppression. The Whole population of CD4+ T cells and the CD4+ T cells depleted of CD4+CD25 high cells were tested for proliferation against donor versus third party stimulators. Moreover to determine the antigen-specificity of the Tregs, serially diluted numbering of CD4+CD25+ T cells were co-cultured with CD4+CD25− T cells. The proliferation responses were examined toward donor versus third party stimulators. Result CD4+ T cells from all LTx recipients off immunosuppression showed hyporesponsiveness to the donor but not to third party stimulators. However, even after depletion of the CD4+CD25 high population, the cells continued to be hyporesponsive toward the donor. In four out of five cases, the suppression exhibited by CD4+CD25+ T cells was more specific for the donor. Discussion These findings suggest that donor alloantigen specific regulation by Tregs is one of multiple mechanisms that may contribute to the maintenance of liver graft survival in the absence of immunosuppression.

BACKGROUND We previously documented an early (day-2) interferon (IFN)-gamma accumulation in cardiac allografts of rats made tolerant by donor-specific blood transfusion (DSBT) but not in rejecting controls. This contrasted with the IFN-gamma peak seen later (day 5) in rejecting but not in tolerant rats. METHODS To further examine the role of early intragraft IFN-gamma in DSBT-induced tolerance, we studied whether IFN-gamma up-regulation correlates with the magnitude of the DSBT effect and how IFN-gamma is influenced by interventions abrogating tolerance. RESULTS The protective effect of DSBT depended upon the timing of administration: day-12 DSBT induced indefinite graft survival; day-6 DSBT gave a moderate, and day-0 DSBT, no graft prolongation. IFN-gamma up-regulation correlated with the DSBT effect: it was maximal after day-12 DSBT, intermediate after day-6 DSBT, and absent after day-0 DSBT. Tolerant splenocytes transferred tolerance into naive rats in a donor-specific manner, indicating that alloantigen-specific regulatory cells operate. Thymectomy prevented regulatory cells development, caused further amplification of intragraft IFN-gamma, and led to rejection, although graft survival was still prolonged. CONCLUSIONS Day 2 intragraft IFN-gamma correlates with the DSBT protective effect. Thymectomy abrogates DSBT-induced tolerance, prevents regulatory cell development, and paradoxically causes further accumulation of intragraft IFN-gamma. These data indicate that DSBT has a stimulatory and a (thymus-dependent) inhibitory effect on early intragraft IFN-gamma. Intragraft IFN-gamma is beneficial, providing it occurs early and remains moderate. The role of intragraft IFN-gamma in tolerance and rejection depends upon the timing and the degree of production and perhaps the type of IFN-gamma producing cells (regulatory or effector).

Donor-specific blood transfusion (DSBT) promotes graft acceptance in certain experimental and clinical situations. However, the exact nature of the operating mechanisms, and in particular the role of Th1/Th2 cytokines, remains controversial. We recently described a fully mismatched rat combination [RA rat (RT1p) to PVG rat (RT1c)] in which a single pre-transplant (Tx) DSBT induces donor-specific tolerance following heart transplantation (Htx). In order to delineate better the role of Th1 and Th2 cytokines in the development of tolerance versus rejection, we studied the intragraft mRNA for Th1 and Th2 cytokines at different time points post-Tx in rejecting and DSBT-tolerized heart grafts. We performed reverse transcriptase-polymerase chain reaction (RT-PCR) to examine intragraft Th1/Th2 cytokines profile. In contrast to findings from previous data, we detected an early (post-Tx day 2) Th1 cytokine upregulation. Th1 downregulation/Th2 immune deviation was observed only at a later period (post-Tx day 30). Consistent with this Th1 early upregulation, a dense mononuclear cellular infiltrate was seen in tolerized grafts, which was equivalent to that seen in rejecting grafts. Despite in vivo unresponsiveness, peripheral lymphocyte derived from tolerant animals proliferated against donor-matched antigens to the same degree as against those of a third party until post-Tx day 30. Altogether, these observations (dense graft cellular infiltrate, early post-Tx Th1 cytokine production, early preserved cellular proliferative responses), suggest that the development of tolerance is preceded by an active Th1 cytokine-mediated immune response. The mechanisms by which an early Th1 response promotes tolerance need to be further studied.