Effect of ultraviolet-B-irradiated donor-specific blood transfusions and peritransplant immunosuppression with cyclosporine on rat cardiac allograft survival

We have previously demonstrated that pretreatment of ACI recipients with ultraviolet-irradiated donor-specific blood transfusion (UV-DST) leads to permanent cardiac allograft survival without further host immunosuppression (ACI rats are weak responders to Lewis lymphocytes in mixed-lymphocyte reaction). This study examines the effect of UV-DST and the timing of transfusions on ACI cardiac allograft survival in Lewis recipients with and without the addition of peritransplant cyclosporine (CsA) (20 mg/kg i.m.) given on days 0, +1, and +2 in relation to the time of transplantation. The mean survival time (MST) of ACI cardiac allografts in Lewis recipients was significantly increased to 33.6 +/- 5.7 days (P less than 0.001) by CsA treatment alone as compared to 6.5 +/- 0.5 days survival in control. When DST was given on day -3 combined with CsA, graft survival was increased to 42.0 +/- 9.3 days (P less than 0.01), as compared to 5.8 +/- 1.3 days when DST alone was used. When DST was irradiated with ultraviolet B (UV-DST) and administered on day -3 combined with peritransplant CsA, the MST was increased to 68.83 +/- 16.1 days as compared to an MST of 10.0 +/- 1.0 days in controls treated with UV-DST alone. When UV-DST was given on day -7 and combined with peritransplant CsA immunosuppression, the results were similar. However, when UV-DST was peritransplant CsA course, 4 of 6 recipients maintained their ACI heart allografts indefinitely (greater than 300 days) in contrast to the effect of UV-DST alone (MST of 13.5 days). Third-party (W/F) UV-irradiated blood transfusions were ineffective in prolonging ACI cardiac allografts in Lewis rats, regardless of whether the transfusions were given alone or in combination with peritransplant immunosuppression with CsA. In conclusion, these results demonstrate that UV-DST combined with a brief peritransplant immunosuppression with CsA induces prolonged heart allograft survival in a histoincompatible, strong responder host, and that such effect is donor specific. The use of UV-DST combined with peritransplant CsA immunosuppression offers a promising approach to achieving organ transplant unresponsiveness, and decreased sensitization to the donor blood elements, which eventually may have important clinical implications.     

Induction of donor-specific unresponsiveness to rat cardiac allograft by donor leukocytes and cyclosporine

Many recent reports have emphasized the importance of donor antigens in the induction of allograft tolerance. This study examines the effect of pretransplant infusion of 10(8) donor leukocytes (DL) combined with peritransplant cyclosporine (CsA) on W/F cardiac allograft survival in Lewis rats. Peritransplant recipient treatment consisted of CsA 20 mg/kg given i.m. on days 0, +1, and +2 relative to heart transplantation. Lewis recipients, 5-8 per group, were pretreated with 10(8) DL with or without peritransplant CsA. A single DL transfusion on day -3 or day -7 prior to transplantation significantly prolonged the mean survival time (MST) of W/F hearts from 7.0 +/- 0.9 days in controls to 12.2 +/- 4.5 days and 12.4 +/- 1.0 days (P less than 0.01), respectively. Two DL infusions on days -7 and -3 or on days -14 and -7 prolonged the MST to 10.6 +/- 1.3 days (P less than 0.02) and 16.4 +/- 2.8 days (P less than 0.001), respectively. The administration of peritransplant CsA alone significantly prolonged W/F heart allograft survival to 43.1 +/- 2.7 days. When pretransplant DL transfusion on day -3 was combined with CsA treatment, 4/8 animals maintained their grafts indefinitely (greater than 100 days). Similarly, DL infusion on day -7 with peritransplant CsA led to indefinite graft survival in 3/5 animals. Administration of DL on days -7 and -3 combined with CsA resulted in indefinite graft survival (greater than 100 days) in 4/6 animals. Transfusion of DL on day -3 alone or in combination with peritransplant CsA, had no effect on a third-party (ACI) heart allograft survival prolongation compared with appropriate controls. To define the underlying mechanisms responsible for donor-specific unresponsiveness in this model, pooled sera and unseparated spleen cells were passively transferred from recipients of long-term cardiac allografts to syngeneic rats receiving donor-type (W/F) or third-party (ACI) cardiac allografts. Transfer of serum (1 ml on days 0, and 1, 0.5 ml on days +2, +3, and +4) from ungrafted recipients of DL on days -14 and -7 led to significant donor graft survival of 9.8 +/- 0.4 days (P less than 0.02) in unmodified hosts. Similarly, passive transfer of serum obtained at 20 and 100 days after transplantation significantly prolonged the MST of donor-type hearts in syngeneic untreated hosts to 11.3 +/- 0.8 and 10.0 +/- 1.1 days, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)     

Intestinal allograft survival in the rat following pretreatment with donor-specific UV-B-irradiated leukocytes and peritransplant immunosuppression with cyclosporine

Previous studies from our laboratory showed that pretreatment with ultraviolet-B-irradiated donor leukocytes (UV-B DL) combined with brief peritransplant cyclosporine (CyA) resulted in indefinite survival of Wistar/Furth rat cardiac allografts in Lewis recipients. This study was designed to examine the effect of pretransplant UV-B DL with or without peritransplant CyA on orthotopic intestinal allografts in the same rat strain combination. The results showed that while low-dose CyA treatment alone (10 mg/kg i.m. on days 0, +1, and +2) had no effect on intestinal allograft rejection, 20 mg/kg (on days 0, +1, and +2) CyA significantly (P0.001) prolonged graft survival, with 33% of the hosts surviving indenfinitely. The highest dose of CyA (30 mg on days 0, +1, and +2) abrogated rejection, but most transplant recipients succumbed to infection and functional ileus due to a toxic side effect of CyA. Pretreatment with UV-B DL on days -14 and-7 alone did not prolong intestinal allograft survival. Combination of a subtherapeutic CyA dose (20 or 10 mg/kg) given on days 0, +1, and +2 with pretransplant UV-B DL on days-14 and -7 did not alter the survival of intestinal allografts compared to treatment with CyA alone. This suggests that pretreatment with UV-B DL with or without peritransplant administration of CyA has no effect on intestinal allograft survival, in contrast to the effect of such combined treatment on cardiac allograft survival, where indefinite graft survival is observed. This difference in the effect of pretransplant UV-B DL on intestinal and cardiac allograft survival is most likely due to organ-specific immunogenicity, particularly to the relative density of class I and II histocompatibility antigens present in heart or intestine.     

Peritransplant streptavidin recipient treatment prolongs rat cardiac allograft survival

BACKGROUND: Because streptavidin shows high localization in inflamed tissues, it might also interfere with the proliferation of cells involved in allograft rejection. METHODS AND RESULTS: Treatment of na?ve ACI recipients with 20 mg/kg streptavidin i.p. alone significantly prolonged Lewis cardiac allografts from a mean survival time of 9.8+/-0.7 days in controls to 19.8+/-6.5 days, with one recipient accepting the graft permanently (>250 days). Peritransplant streptavidin treatment combined with 0.5 ml of antilymphocyte serum (ALS) transient immunosuppression led to permanent graft survival (>250 days) in 6 of 10 recipients. Second-set skin grafts performed 60 days after the primary cardiac allograft were prolonged to 45 days, whereas the third party Wistar-Furth (WF) skin grafts were rejected in 15 days without the rejection of the primary Lewis cardiac allografts. Pathology of transplanted cardiac allografts at 100 days showed no mononuclear cell infiltration or chronic allograft vasculopathy. Streptavidin given for 5 days at 20 mg/kg caused a moderate initial weight loss but had no effect on hematologic, biochemical, and histologic parameters in the treated recipients. CONCLUSION: This study demonstrates that peritransplant recipient treatment with streptavidin combined with peritransplant ALS induces prolonged cardiac and second-set skin allograft survival. We conclude that recipient peritransplant streptavidin treatment may provide a new strategy for the induction of transplant tolerance.     

Intrathymic injection of donor alloantigens induces donor-specific vascularized allograft tolerance without immunosuppression.

The induction of donor-specific tolerance could prevent the side effects of immunosuppression while improving allograft survival. Male adult Buffalo (RT1b) rats underwent an intrathymic (IT), portal venous (PV), intrasplenic (IS), or subcutaneous (SQ) injection of 25 x 10(6) major histocompatibility complex (MHC) mismatched Lewis (RT1(1)), UV-B-irradiated Lewis (RT1(1)), ACI (RT1a), or syngeneic Buffalo (RT1b) splenocytes. At the completion of the donor alloantigen injection, 1 mL rabbit anti-rat lymphocyte serum (ALS) was administered intraperitoneally to the Buffalo recipients, and 21 days later a heterotopic Lewis or ACI heart was transplanted. Intrathymic injection of donor alloantigen induced a donor-specific tolerance that allowed the cardiac allograft to survive indefinitely (mean survival time [MST] > 140.7 days) in 84% of the recipients without further immunosuppression, whereas groups receiving antigen injections at other sites (PV, IS, and SQ) plus ALS rejected cardiac allografts in normal fashion (MST approximately 8.0 days). Buffalo recipient rats with long-term surviving Lewis cardiac allografts after Lewis IT injection and ALS subsequently rejected a heterotopic third-party ACI cardiac allograft in normal fashion (MST approximately 7 days), whereas a second Lewis cardiac allograft was not rejected (MST > 116 days). Microchimerism is unlikely because Lewis allograft survival was also prolonged (MST > 38.7 days) in rats receiving UV-B-irradiated splenocytes IT, which cannot proliferate. Survival of Lewis renal allografts was also prolonged, but not indefinitely, in Buffalo recipients possessing a long-term surviving Lewis cardiac allograft (MST approximately 17.6 days versus 7 days for control). This model emphasizes the potential role of exposure of immature thymocytes to foreign donor alloantigens during maturation in the thymic environment for the development of unresponsiveness to an MHC-mismatched donor-specific vascularized allograft.     

Infectious tolerance mediated by CD8+ T-suppresor cells after UV-B-irradiated donor-specific transfusion and rat heart transplantation

AIMS: CD8+CD28- human T-suppressor cells (Ts), which can be generated in vitro, act directly on APC rendering them tolerogenic to unprimed and primed CD4+ T cells. The aim of this study was to investigate the possibility that CD8+ T cells mediate the induction of tolerance in a heart transplantation model in rodents. MATERIALS AND METHODS: Blood from Lewis rats was UV-B-irradiated and transfused into ACI recipients on days -21, -14, and -7 before heart allograft transplantation on day 0. CD4(+) and CD8(+) T cells were positively selected from ACI rats, which had tolerated Lewis heart allografts for more than 100 days and were adoptively transferred to naive ACI rats pretreated (day -1) with gamma irradiation. These ACI rats underwent transplantation with Lewis hearts 24 hours after adoptive transfer of putative T-suppressor cells. RESULTS: Adoptive transfer of CD8(+) T cells from tolerant ACI to naive ACI rats significantly prolonged Lewis heart mean allograft survival time (MST +/- SD) to 69 +/- 13 days as compared with 15 +/- 1 and 14 +/- 1 days in animals adoptively transferred with CD4+ T cells or untreated controls, respectively (P < .001). Similarly, adoptive transfer of CD8(+) T cells from secondary ACI recipients to naive syngeneic animals also significantly prolonged survival of heart allografts to MST +/- SD of 72 +/- 4 for CD8(+) and 15 +/- 4 days for CD4(+) T cells (P < .001). CONCLUSIONS: These data demonstrate that allogeneic tolerance induced in ACI recipients by treatment with UV-B-irradiated blood from Lewis donors is mediated by CD8+ T-suppressor cells.     

Mechanisms of immunologic unresponsiveness induced by ultraviolet-irradiated donor-specific blood transfusions and peritransplant cyclosporine

Recipient pretreatment with UV-B irradiated donor-specific blood transfusions (UV-DST) combined with peritransplant cyclosporine on days 0, +1, and +2 leads to permanent cardiac allograft survival in the ACI-to-Lewis rat strain combination. This study investigates the mechanisms of immunologic unresponsiveness induced by UV-DST and CsA by examining several in vitro and in vivo parameters in long-term cardiac allograft recipients. The results of the in vitro studies demonstrate that thoracic duct lymphocytes (TDL) of treated and allografted Lewis rats respond less in a mixed lymphocyte reaction to donor splenic lymphocytes (SpL) by 69%, 75%, and 73% (P less than 0.001) at 30, 50, and 100 days after transplantation, respectively, compared with controls, while the response to a third-party (W/F) SpL is unimpaired. In coculture experiments, the TDL from treated recipients specifically suppressed the response of unmodified Lewis TDL to ACI SpL by 59% and 40% (P less than 0.01) at 30 and 50 days after transplantation, respectively, while responses to W/F SpL were suppressed by only 3-6%. The sera obtained from ungrafted rats transfused with UV-DST suppressed the MLR between unmodified Lewis TDL and ACI SpL by 31% (P less than 0.05) while the sera from UV-DST and CsA-treated and allografted rats specifically suppressed the MLR by 75%, 80% (P less than 0.001) and 37% (P less than 0.01) at 10, 30, and 50 days after transplantation, respectively. In vivo adoptive transfer of 10(4) donor-type dendritic cells (DC) into recipients of beating cardiac allografts at 40 or 60 days after transplantation led to rapid and acute allograft rejection, while the adoptive transfer of 10(8) unseparated SpL obtained at 50 days after transplantation from treated Lewis recipients to syngeneic naive hosts led to a modest but significant prolongation of ACI test cardiac allografts. The transfer of serum from treated and allografted recipients at 10, 30, and 50 days after transplantation led to specific and significant prolongation of test grafts in syngeneic naive hosts. These findings suggest that the mechanisms underlying the in vivo immunologic unresponsiveness induced by pretreatment with UV-DST and peritransplant CsA include inactivation without elimination of class II-antigen presenting cells (APC), generation of specific serum suppressor factor(s) and/or antiidiotypic antibody, and induction of donor-specific suppressor cells.     

Interstitial class II-positive cell depletion by donor pretreatment with gamma irradiation. Evidence of differential immunogenicity between vascularized cardiac allografts and islets

We used an allograft pretreatment regimen involving lethal total-body gamma irradiation of donor rats eight days prior to transplantation to compare directly the immunogenicty of immediately-vascularized heart allografts with isolated, neovascularized pancreatic islet allografts. TBI pretreatment of heart donors (IHT) caused a modest prolongation in cardiac allograft survival compared with controls in a low-responding fully-allogeneic strain combination, Lewis-to-ACI. The addition of 10(5) donor-type dendritic cells (DCs) at the time of transplantation reversed the prolongation of IHT in this strain combination. Donor pretreatment with TBI did not lead to prolonged cardiac allograft survival in either a high-responding combination, ACI-to-Lewis, or in an MHC class II-compatible strain combination, F344-to-Lewis. In contrast, islets from irradiated donors (IIT) showed markedly prolonged survival in both low-responding (Lewis-to-ACI) and high-responding (W/F-to-Lewis) strain combinations. The addition of 10(5) donor-type DCs to the islets at the time of transplantation caused the rejection of only two of six IIT in the Lewis-to-ACI combination. Combined pretreatment regimens involving TBI-pretreated cardiac allografts--such as recipient immunosuppression with peritransplant cyclosporine (10 mg/kg on days 0, 1, and 2) or the combination of TBI (1000 cGy on day -3) and cyclophosphamide (300 mg/kg on day -5) in a pretreatment regimen--did not lead to synergistic graft prolongation in the low-responding Lewis-to-ACI combination. Immunohistologic studies showed that eight days after TBI rat hearts and islet were both greater than 90% depleted of class II (0X6+) interstitial dendritic cells while class I (0X18+) expression was unchanged. IIT are able to increase class II expression when donors are treated with recombinant gamma interferon (4000 U/day on days -3, -2, and -1). MLR data showed that ACI recipients of Lewis IIT reacted normally to donor (Lewis) and third-party (W/F) stimulator cells greater than 100 days after transplantation. The apparent greater immunogenicity of heart allografts as compared with islets in this model could be due to (1) a quantitative difference between the number of residual class II-positive cells in hearts and islets or a greater nnon-MHC antigenic load in the heart grafts given its larger size, or (2) a quanlitative difference between hearts and islets due to the presence of a vascular endothelium in the immediately vascularized heart that can present alloantigen and provide a major stimulus to rejection.     

Humoral immunity in allograft rejection. The role of cytotoxic alloantibody in hyperacute rejection and enhancement of rat cardiac allografts

The role of humoral immunity in graft rejection in the rat model remains controversial. Passive transfer of cytotoxic alloantibody (CAA) has resulted either in hyperacute rejection or in graft enhancement. This study examines the effect of transfer of CAA on cardiac allograft survival in three rat strain combinations that are fully mismatched at the major histocompatibility (MHC) loci. Strain-specific immune responsiveness in donor-recipient pairs varied from low (Lewis-to-ACI) to high (ACI-to-Lewis) as measured by mixed lymphocyte reactions. CAA was obtained from rats sensitized by three successive skin grafts at weekly intervals. Group 1 (high responder recipients), which consisted of Lewis rats presensitized to ACI and had a lymphocytotoxicity titer of 1:512 to 1:2048, rejected ACI cardiac allografts in 10.8 +/- 7.2 hr compared with 6.5 +/- 0.5 days in naive controls (p less than 0.001). Injection of 1 ml of high-titer CAA into naive Lewis rats immediately after ACI cardiac grafting led to hyperacute rejection of ACI hears in 2.1 +/- 0.8 hr while 1 ml of CAA followed by 2 ml of guinea pig complement (GPC) resulted in even faster rejection (mean survival time (MST) of 23.8 +/- 4.7 min). Injection of 2 ml GPC alone or in combination with 1 ml naive Lewis serum had no effect on graft survival. Multiple pretransplant injections of 1 ml of CAA on days -3, -2,-1, and 0 relative to transplantation resulted in significant prolongation of allograft survival (MST of 10.3 +/- 0.3 days; P less than 0.01). In group 2 (intermediate responder recipients), where Lewis rats were presensitized to WF strain and where cytotoxicity titer was 1:16 to 1:256, the recipients rejected WF hearts in 23.8 +/- 5.8 hr compared with 6.8 +/- 0.8 days in unsensitized control recipients (P less than 0.001). Injection of 1 ml of Lewis anti-WF CAA resulted in prolonged graft survival of 9.7 +/- 3.5 days, while injection of 1 ml of CAA followed by 2 ml of GPC caused hyperacute rejection in 104 +/- 61.7 min. Pretransplant injections of CAA on days -3, -2, -1, and 0 resulted in enhancement, with an MST of 16.3 +/- 1.3 days (P less than 0.001). In group 3 (low responder recipients), ACI presensitized to Lewis developed a cytotoxicity titer of 1:2 to 1:32 and rejected Lewis hearts in 5.3 +/- 0.4 days compared with 10.6 +/- 1.0 days in naive recipients.(ABSTRACT TRUNCATED AT 400 WORDS)     

Characteristics and function of suppressor T lymphocytes in immunologically unresponsive rats following pretreatment with UV-B-irradiated donor leukocytes and peritransplant cyclosporine

Lewis rats pretreated with UV-B-irradiated donor leukocytes (UV-DL) and peritransplant cyclosporine (CsA...CsA, 20 mg/kg on days 0, +1, and +2) accepted W/F heart allografts permanently. This study of donor-specific immunologic unresponsiveness and its cellular mechanisms shows that the induction phase of unresponsiveness is partially mediated by W3/25+ T cells, while its maintenance is dependent on the presence of 0 x 8+ T cells. In vivo adoptive transfer of either splenocytes, T lymphocytes (T cells), or W3/25+ T cells from ungrafted, UV-DL-transfused rats into unmodified syngeneic Lewis rats that received test grafts 24 hr later led to significant prolongation of donor-specific graft survival. Adoptive transfer of 0 x 8+ cells did not influence donor-type (W/F) test graft rejection. Adoptive transfer of SpL, T cells and 0 x 8+ cells from UV-DL and CsA-treated recipients of W/F heart allografts at 20 or 180 days after transplantation led to significant donor-specific graft prolongation in naive syngeneic hosts, while adoptive transfer of W3/25+ cells, in this group, did not affect test graft survival. However, the adoptive transfer of SpL or of T cell subsets did not influence third-party (ACI) graft survival. In-vitro mixed lymphocyte reaction between thoracic duct lymphocytes obtained at various intervals following grafting from UV-DL and CsA treated Lewis recipients of W/F heart allografts and donor-type SpL resulted in significantly reduced reactivity by 78%, 75%, 69% (P less than 0.001) and 43% (P less than 0.02) compared with controls when responder TDL were obtained at 20, 50, 100, and 180 days after transplantation, respectively. In coculture studies, the MLR response to donor SpL was specifically suppressed by 60%, 57%, 46%, and 50% (P less than 0.01) at 20, 50, 100, and 180 days after transplantation, respectively, compared with controls. These data indicate that the induction of specific unresponsiveness to heart allografts in this model is mediated, in part, initially by the appearance in the host of specific W3/25+ cells either induced or recalled by UV-DL transfusion, and that a stable state of immunologic unresponsiveness is subsequently dependent on the presence of 0 x 8+ suppressor cells.     

IgG alloantibody responses to donor-specific blood transfusion in different rat strain combinations as a predictor of renal allograft survival.

Donor-specific blood transfusion prolongs the survival of fully allogeneic ACI (RT1a) renal allografts in PVG (RT1c) recipients from 7-10 days to greater than 100 days. We have observed significant differences in the alloantibody (Ab1) responses to ACI renal allografts in control and DSBT-treated PVG recipients: DSBT is associated with decreased IgG and IgM alloantibody circulating in serum, deposited in the allograft, and produced in culture by splenocytes. In the present studies the effects of DSBT on alloantibody production and renal allograft survival were extended to examine other recipient strains: F344 (RT1lv1), BN (RT1n), W/F (RT1u) and LEW (RT1l). Animals of each recipient strain were injected i.v. with 0.5 ml of ACI blood alone or followed by a renal allograft. Studies on the kinetics of IgM and IgG alloantibody responses were performed by flow cytometry on lymphocytes from donor ACI, PVG, and PVG.R1 (RT1.Aa class I MHC antigen on PVG background) rats. In F344 and PVG rats, DSBT from ACI rats elicited a transient IgM response that peaked at day 7 and was not followed by a switch to IgG. In control PBS transfused F344 recipients, an ACI renal allograft stimulated both IgM and IgG alloantibody production. DSBT pretreatment significantly decreased circulating IgG alloantibody following ACI renal transplantation and prolonged graft survival in F344 recipients. In DSBT-treated F344 recipients that rejected ACI renal allografts acutely, small amounts of IgG (5-12 mode channel shift) were detected in sera harvested 7 days after transplantation, whereas almost no IgG was detected in the sera from DSBT treated F344 rats that accepted their renal allografts indefinitely. In contrast, DSBT alone from ACI to BN, W/F, or LEW strains elicited a transient IgM response that peaked at day 7 and was followed by a strong IgG response that peaked on days 10-14 and remained high through day 21. DSBT failed to prolong ACI renal allograft survival in any of these strains (survival less than 11 days in control and DSBT rats). The alloantibody response to DSBT in all five recipient strains examined was directed primarily to RT1.Aa class I MHC antigens, as determined by binding studies on lymphocytes from ACI, PVG and PVG.R1 rats and alloantibody blocking studies using biotinylated rat monoclonal antibodies to distinct epitopes of the RT1.Aa antigen. The relative magnitude of blocking of R2/10P and R2/15S binding by sera from BN, W/F, and LEW rats was: control allograft recipients greater than DSBT pretreated allograft recipients greater than DSBT alone.(ABSTRACT TRUNCATED AT 400 WORDS)     

The effect of soluble complement receptor type 1 on hyperacute allograft rejection.

A major obstacle to successful organ transplantation in sensitized recipients is antibody-mediated hyperacute rejection. We hypothesized that human recombinant soluble complement receptor type 1 (sCR1), which inhibits activation of the complement cascade at multiple stages, would delay this process. Using a well-established model of hyperacute rejection, 21 Lewis rats each received three successive ACI rat skin grafts which resulted in high serum titers of ACI-specific antibodies. These hypersensitized Lewis rats then received heterotopic ACI cardiac allografts. Immediately prior to allograft reperfusion, sCR1 at 3 mg/kg (n = 11) or an equivalent volume of phosphate-buffered saline (PBS) (n = 10) was administered intravenously. Five minutes following allograft reperfusion, hemolytic complement activity was reduced by 63 +/- 2% (SEM) in the sCR1 group vs 25 +/- 3% in the PBS group (P less than 0.0001, Wilcoxon rank sum test (WRST)). Graft survival in the sCR1 group was prolonged to 32.0 +/- 4.47 hr vs 3.25 +/- 0.81 hr in the PBS group (P less than 0.0001, WRST). Serial histologic examination of allografts showed that sCR1 therapy prevented the early development of luminal platelet thrombi in the allograft coronary vessels. This study demonstrates that a single 3 mg/kg dose of sCR1 significantly prolongs ACI cardiac allograft survival in the hypersensitized Lewis rat recipient. Complement inactivation, mediated by sCR1, may prove useful for transplantation in sensitized recipients.     

Intravenous and portal venous administration of modified donor antigen prolongs rat parathyroid allograft survival

The effect of pretransplant (day -6) systemic intravenous or portal venous immunization with modified donor antigen combined with cyclophosphamide treatment (75 mg/kg on day -4) on rat parathyroid allograft survival was evaluated. Systemic intravenous preimmunization of Buffalo recipients with 10(8) untreated Lewis donor spleen cells plus cyclophosphamide resulted in 100% accelerated rejection of Lewis parathyroid allografts (mean survival time, 7.3 +/- 0.9 days vs 10.8 +/- 1.1 days for controls). Portal venous administration of untreated cells plus cyclophosphamide reduced accelerated rejection to 40% but could not prolong graft survival (10.8 +/- 2.7 days). Intravenous or portal venous preimmunization with heat-inactivated cells (45 degrees C for 60 minutes) plus cyclophosphamide also did not prolong graft survival, with accelerated rejection occurring in 20% and 40% of recipients, respectively. In contrast, preimmunization by either route with ultraviolet B-irradiated cells (UVB; 12,000 joule/m2) plus cyclophosphamide significantly prolonged graft survival (intravenous = 22.2 +/- 6.0 days and portal venous = 21.4 +/- 7.2 days; p less than 0.005), with no accelerated rejection. Preimmunization with UVB cells combined with cyclophosphamide was synergistic, because neither treatment alone prolonged allograft survival (UVB cell preimmunization only = 10.8 +/- 1.3 days; cyclophosphamide only = 12.6 +/- 2.6 days). The effect of UVB preimmunization was donor specific because third-party Wistar-Furth UVB cells had no effect on Lewis graft survival (12.5 +/- 2.9 days). We conclude that pretreatment with UVB-modified donor antigen plus cyclophosphamide induces allospecific immune hyporesponsiveness and prolongs parathyroid allograft survival.     

Production of antiidiotypic antibodies in the rat: in vitro characterization of specificity and correlation with in vivo specific suppression of cardiac allograft immune reaction across major histocompatibility complex

We studied the effect of antiantidonor major histocompatibility complex antibodies (antiidiotypic antibodies) in vivo on ACI cardiac allograft survival in Lewis rats and correlated the results with in vitro mixed lymphocyte culture. Lewis anti-ACI hyperimmune sera (Ab1) were obtained from animals that have rejected successive ACI skin grafts. Purified immunoglobulin (Ig) G and IgM fractions were obtained from the sera. These putative "idiotypic antibodies" (IgG fractions) were used to immunize groups of five naive Lewis rats. Purified Ig (0.5 mg) was mixed with 0.5 ml incomplete Freund's adjuvant and injected intraperitoneally -15, -7, and -3 days before and at the time of ACI cardiac allografting. The median allograft survival time was 11.2 +/- 0.7 days in animals treated with Ab1 compared with 6.4 +/- 0.5 days in untreated control rats (p less than 0.001). Use of IgM with adjuvant did not prolong graft survival. Purified IgG obtained from sera collected before transplantation was tested for antiidiotypic antibodies with the complement-mediated cytotoxicity assay. For this, serial dilutions of the hyperimmune serum were tested for cytotoxicity against ACI lymphocyte in the presence of Ig from sera collected after immunization with Ab1. Blocking was demonstrated by sera and IgG obtained from Lewis rats that received anti-ACI IgG (Ab1) with adjuvant. The blocking activity of purified IgG (Ab2) was strain specific because it did not block the reaction of Lewis hyperimmune sera against third-party Wistar-Furth rats. Thoracic duct lymphocytes from immunized recipients showed no blastogenic responses when tested in in mixed lymphocyte culture for reactivities against splenocytes from ACI rats. The finding that Lewis rats treated with Ig from sera containing anti-ACI antibodies exhibit impaired anti-ACI T- and B-cell reactivity and prolong allograft survival suggests that pretreatment of recipients with idiotypic antibodies leads to development of antiidiotypic antibodies that modulate alloreactivity suppressing allograft rejection.     

Use of allochimeric proteins to mitigate graft-versus-host and host-versus-graft immune responses to rat small bowel allografts

BACKGROUND: We aimed to identify the polymorphic epitopes that mitigate graft-versus-host disease (GvHD) and host-versus-graft response (HvGR) toward rat small bowel allografts in rats. METHODS: We tailored class I major histocompatibility complex (MHC) allochimeric antigens encoding 10 al-helical (alpha(1h)l58-80-RT1.Aa) or 4 (alpha(1h)l/u62-69-RT1.Aa) polymorphic amino acids. In the GvHD model, ACI (RT1a) donors were pretreated (day -14) with an intrathymic injection of alpha(1h)l58-80-RT1.Aa, alpha(1h)l/u62-69-RT1.Aa, or RT1.Al protein, with or without simultaneous intravenous injection of anti-T-cell receptor R73 monoclonal antibodies. Wistar-Furth (WF; RT1u) donors were tested with a similar protocol. In the HvGR model, ACI recipients were treated with a protocol designed to induce transplantation tolerance toward WF heart allografts: a portal vein injection of alpha(1h)l/u62-69-RT1.Aa protein and cyclosporine (4 mg/kg, intramuscular; days 0-6). RESULTS: GvHD was prevented in all (ACI x LEW) F1 recipients (RT1a/l) by pretreating ACI donors with R73 monoclonal antibody and recipient RT1.Al or alpha(1h)l58-80-RT1.Aa protein. Similarly, pretreatment of WF donors with RT1.Aa protein also prevented GvHD in (ACI x WF) F1 recipients. However, in a combined GvHD/HvGR model, ACI recipient perioperative treatment designed to prevent HvGR only modestly prolonged WF small bowel allograft survival (27.7+/-5.3 days compared to 17.4+/-4.6 days in the cyclosporine-alone group). In contrast, application of the two protocols significantly prolonged WF allograft survival (55.6+/-34.6 days), with two of seven recipients surviving more than 100 days. CONCLUSION: Simultaneous inhibition of GvHD and HvGR significantly prolongs small bowel allograft survival.     

The use of direct ultraviolet irradiation and cyclosporine in facilitating indefinite pancreatic islet allograft acceptance

We have previously shown that direct ultraviolet (UV) irradiation of islets can reduce their immunogenicity without alteration of their endocrine function and effect prolonged survival of islet allografts in the Lewis-to-ACI strain combination without the use of immunosuppression. This study extends that work to investigate the survival of UV-irradiated Wistar-Furth islets in streptozotocin-diabetic Lewis rats, in which case the recipient is a relatively "high responder" to W/F alloantigens. Lewis recipients of 24-hr cultured W/F islets uniformly rejected islet allografts within one week of transplantation while the additional immunosuppression with cyclosporine (CsA) at 15 or 30 mg/kg on days 0, +1, and +2 was ineffective in prolonging islet allograft survival. Wistar-Furth islets, which were UV-irradiated at 850-900 J/m2 and cultured for 24 hr prior to transplantation, did not survive any longer than those in control animals receiving untreated islets (MST 5.5 +/- 1 day). When UV irradiation of islets was combined with recipient peritransplant treatment with CsA at 15 mg/kg on days 0, +1, and +2 islet allograft survival was markedly prolonged (MST of 18 +/- 4.1 days). Treatment of diabetic recipients of UV irradiated islets with an increased dose of CsA (30 mg/kg) during the same peri-transplant period (0, +1, +2 days) resulted in 100% islet allograft survival beyond 120 days. This data demonstrate the effectiveness and synergism between the use of the pretransplant UV irradiation of islet allograft and the peritransplant immunosuppression of the recipient with CsA in inducing prolonged islet allograft survival in "high responder" recipients, in which the singular use of either modality may be ineffective.     

Sensitized B lymphocytes contribute to acute allograft rejection

The contribution of sensitized B lymphocytes to second-set allograft rejection has been relatively ignored despite their regular appearance in rejecting allografts. This study presents evidence that adoptively transferred sensitized B lymphocytes accelerate the rate of acute allograft rejection in a sublethally irradiated rat cardiac allograft model. Donors of reconstituting B lymphocytes were sensitized with three consecutive ACI skin grafts. Transplantation of a heart from an ACI strain donor into a Lewis strain recipient (complete RT1 mismatch) results in rejection in 6.8 +/- 0.3 days. When the allograft donor and recipient are irradiated with 650 cGy prior to transplantation, rejection occurs at 31.5 +/- 3.0 days. Irradiated recipients reconstituted with 10(6) syngeneic sensitized splenic B cells reject their grafts in 20.1 +/- 2.0 days, while reconstitution with 10(6) unsensitized syngeneic B cells has no effect on the rate of rejection (P = 0.0007). These data strongly suggest that sensitized B lymphocytes have a marked accelerating effect on the tempo of allograft rejection.     

The mechanism of the induction of immunologic unresponsiveness to rat cardiac allografts by recipient pretreatment with donor lymphocyte subsets

In continuation of our studies using UV-B-irradiated DST and donor leukocyte (DL) recipient pretreatment to induce specific unresponsiveness to organ allografts, we have examined the relative contributions of splenic lymphocyte populations and T lymphocyte subsets in the induction of immunologic unresponsiveness. Our data show that enriched populations of MHC class II-positive B lymphocytes and the W3/25+ T cell subset obtained from splenic leukocytes using immunoadsorbent columns in conjunction with mAbs led to indefinite graft survival (greater than 100 days) in the Lewis-to-ACI rat cardiac allograft model. In contrast, pretreatment with T lymphocytes or the Ox8+ T subset was relatively ineffective in prolonging cardiac allograft survival. In addition, third-party (W/F) W3/25+ T cell recipient pretreatment did not influence the survival of Lewis cardiac allografts in ACI recipients, thus confirming the specificity of pretreatment with the T cell subset in graft prolongation. Furthermore, we have examined the underlying mechanisms of donor-specific unresponsiveness induced by donor spleen cells, B lymphocytes, and W3/25+ T cells using adoptive transfer assays. Serial adoptive transfer studies demonstrated the presence of 0x8+ suppressor T cells in the spleens of unresponsive recipients bearing well-functioning cardiac allografts and of serum "suppressor factors" that have the capacity for specifically prolonging donor-type test graft survival in naive syngeneic rats. Our findings suggest that the induction of specific unresponsiveness in this model is dependent on a sequential collaboration between the appearance of donor-specific serum factor(s) (humoral phase) and donor-specific suppressor T cells (cellular phase). These results may be potentially useful in planning future strategies for the induction of unresponsiveness to clinical organ allografts by immunologic manipulation of the host with MHC class II-positive B cell and CD4+ T cell clones.     

Intrathymic immunomodulation in sensitized rat recipients of cardiac allografts: requirements for allorecognition pathways.

BACKGROUND: Intrathymic injection of alloantigen in the form of donor cells, soluble major histocompatibility complex (MHC) molecules, or MHC allopeptides induces donor-specific tolerance in a variety of acute allograft rejection models. We have previously shown that a single intrathymic injection of donor spleen cells into pre-sensitized rats abrogates accelerated (circa 24-hour) rejection and prolongs the survival of cardiac allografts to about 7 days. The present study was designed to investigate the mechanisms by which intrathymic administration of donor cells modifies the course of accelerated rejection. METHODS: Lewis RT1(1) (LEW) rats sensitized by transplantation with Wistar-Furth RT1(u) (WF) skin grafts received WF cardiac allografts 7 days later-a classic model of accelerated rejection. At the time of skin challenge, however, certain animals received intrathymic cell suspensions (either allogeneic or syngeneic) or donor-derived class I and/or class II MHC peptides. RESULTS: Control animals (sensitized by skin grafts but receiving no other treatment) rejected cardiac allografts within 24 hours. Intrathymic injection of WF splenocytes at the time of skin transplantation abrogated rejection at 24 hours and prolonged cardiac allograft survival to 6.6+/-0.6 days (p<0.001), whereas intrathymic administration of syngeneic (LEW) or allogeneic third party Brown Norway RT1(n) cells was ineffective in this regard. Intrathymic injection of gamma-irradiated donor cells marginally extended cardiac allograft survival to 3.0+/-0.9 days (p< 0.001), but the grafts were still rejected in an accelerated fashion. Intrathymic injection of donor-derived class I and/or class II MHC allopeptides at the same time period also failed to prolong cardiac allograft survival beyond 3 days. In the group receiving unmodified donor cells, elevated immunoglobulin M (IgM) and immunoglobulin G (IgG) allo-antibodies were found at the time of cardiac transplantation; this pattern was not observed with any other treatment. CONCLUSION: The superiority of non-modified donor spleen cells over gamma-irradiated donor cells or donor specific allopeptides in modifying the course of accelerated cardiac rejection suggests that direct allorecognition is the dominant pathway initiating rejection in sensitized transplant recipients. Marked alterations in the antidonor IgM and IgG responses are associated with successful abrogation of accelerated rejection by thymic immunomodulatory mechanisms.     

Prolongation of rat hepatic allografts by donor splenocyte infusion and peritransplant cyclosporine treatment

This study examined the effect of pretransplant infusion of donor splenocytes and peritransplant Cyclosporine (CsA) treatment on Wistar orthotopic liver allograft survival in recipient SD rats. Treatment with either donor splenocytes or CsA significantly prolonged the survival of recipients. When pretransplant infusion of donor splenocytes combined with peritransplant use of CsA, 4/7 animals survived indefinitely (greater than 150 days). T cell subsets classification in the peripheral blood of long survivors by means of McAbs (MRC W/OX) and flow cytometer were significantly different from those in controls. The percentage of W3/25+ cells was lower and that of OX-8+ cells was higher with a decreased ratio of W3/25+/OX-8+. These results suggested the important role of suppressor T-lymphocytes in the induction of specific immunologic unresponsiveness to rat hepatic allografts.