Efficacy of Perioperative Portal Venous Inoculation with Donor Lymphocytes on Skin Graft Survivals in the Rat

Although the administration of donor lymphocytes via portal vein (PV) on the day of transplantation significantly prolongs rat renal allograft survivals and the unresponsive state is mediated by an antigen-specific suppressor factor in the serum, significant variations exist among rodent models in terms of immunogenecity and mechanism of antigen presentation. The present studies sought to assess the effect of perioperative PV inoculation with donor lymphocytes on skin allograft survivals. Donor lymphocytes were prepared from Brown-Norway (BN, RT-1^a) or third-party DA (RT-1^a) rat spleens and lymph nodes and injected via PV or intravenously to Lewis (LEW, RT-1¹) hosts on the day of skin grafting. Untreated LEW hosts rejected BN skin grafts at 9.0 ± 1.4 days (n= 10). Intravenous administration of 1 ± 10⁸ BN cells into LEW hosts on day 0 did not prolong the skin graft survivals (MST= 8.6 ± 1.2 days, n= 7, NS), whereas PV inoculation of 1 × 10⁸ BN cells prolonged skin graft survival to 13.4 ± 3.9 (n= 8, P <. 01). PV administration of 1 × 10⁸ DA cells to LEW hosts did not prolong the survival of BN skin grafts (MST= 8.6 ± 1.5 days, n= 6). PV inoculation with BN cells inhibited the generation of anti-BN delayed-type hypersensitivity (DTH) response in the hosts, whereas untreated control hosts or hosts inoculated with third-party DA cells could not inhibit the anti-BN DTH response. When serum harvested from PV-treated LEW hosts on day 7 was added to MLC, it suppressed the reaction toward donor BN cells by 61%, but not toward third-party DA stimulators (4.8% suppression, NS). Moreover, adoptive transfer of the serum from PV-treated LEW rats into the virgin secondary LEW hosts significantly prolonged the graft survivals of BN kidney from 7.8 to 16.3 ±1.1 days (n= 6, P ≤. 01), but not third-party DA renal graft (MST= 7.7 ± 0.5, n= 8, NS) or BN skin graft (MST= 9.8 ± 1.2 days, n= 5, NS). These studies suggest that the suppressor mechanism demonstrated in the PV-treated renal transplant model might be similarly active in the hosts who received skin grafts simultaneously with the PV inoculation of donor cells.     

Evidence that indefinite survival of small bowel allografts achieved by a brief course of cyclosporine or FK506 is not due to systemic hyporesponsiveness.

The immunological status of Lewis (LEW) recipients of indefinitely surviving (greater than 400 days) orthotopic Brown-Norway (BN) small bowel allografts was investigated 1 to 1 1/2 years after cessation of immunosuppressive therapy with either cyclosporine or FK506 and compared with recipients of syngeneic grafts. A normal proliferative response (as measured by a mixed lymphocyte culture) of recipient peripheral lymph node lymphocytes in response to the donor-specific (BN) and the third-party (ACI) antigen, was observed in all experimental groups. Cytolytic T cell generation (as measured by a standard 51Cr-release cytotoxicity assay) in response to the donor-specific (BN) and the third-party (ACI) antigen was observed also in all groups. A FACS analysis of allograft-recipient splenocytes showed no evidence for systemic lymphoid chimerism. BN or ACI skin grafts transplanted onto recipients of allogeneic and syngeneic small bowel grafts were rejected completely in 12-17 days, while the intestinal grafts remained functional. Immunohistologic evaluation of the allografts, using anti-BN class I and anti-Lewis class II monoclonal antibodies showed anti-BN staining on the epithelial and endothelial structures, whereas the mononuclear cells in the lamina propria stained positively with the anti-LEW monoclonal antibody. However, lymphoid depletion and scarring of Peyer's patches and mesenteric lymph nodes as well as focal obliterative mesenteric arteriopathy, indicative of an indolent chronic rejection, were observed. These data demonstrate that recipients of indefinitely surviving small bowel allografts remain immune competent and do not retain the intestinal graft on the basis of specific hyporesponsiveness to the donor antigens.     

Long-term prolongation of cardiac allografts by subtherapeutic levels of cyclosporine in rats conditioned with pretransplant blood transfusions and cyclosporine

This study was aimed at ascertaining whether long-term graft survival was achievable with short term cyclosporine (CsA) therapy or with subtherapeutic doses of CsA in rats conditioned with blood transfusions (BT) combined with CsA. Previous studies had shown that donor-specific transfusions combined with a short course of CsA interacted synergistically, resulting in considerable prolongations of ACI and BUF grafts in LEW hosts receiving no postoperative treatment. The donor-specific depression of alloreactivity was confirmed in the present study by showing a depression of mixed-lymphocyte reaction (MLR) reactivity as well as of humoral antidonor responses in BT-CsA conditioned rats. The effects of postoperative CsA were then studied in recipients conditioned with BT-CsA or BT alone. ACI and BUF cardiac graft survival in LEW hosts conditioned with BT and treated with a five-day postoperative course of CsA (20 mg/kg/day) were indistinguishable from graft survival in untransfused hosts (ACI: 35.6 +/- 15.5 vs. 38.8 +/- 7.4; BUF: 58.4 +/- 39.8 vs. 48.0 +/- 21.7) indicating no interaction between BT and CsA under these conditions. In contrast, the effect of a post-operative five-day course of CsA (10 mg/kg/day) was extended by conditioning the recipients with donor-specific BT and CsA (ACI:41.7 +/- 7.0 vs. 27.4 +/- 11.6; P less than 0.05). More remarkably, a thirty-day course of subtherapeutic doses of CsA (2.5 mg/kg/day) resulted in long-term prolongation (greater than 100 days) of ACI grafts in a large proportion of hosts conditioned with donor-specific BT and CsA, while the majority of controls conditioned with nonspecific BT and CsA or CsA alone rejected their grafts within three weeks (P less than 0.01). The possible mechanisms of this phenomenon are discussed.     

Genetics of the blood transfusion effect on heart allografts in rats

Working with the recently available recombinant haplotypes of the rat major histocompatibility complex (MHC)--RT1, we investigated the effect of various types of blood transfusion (BT) on allograft prolongation, including blood identical for the whole RT1 haplotype with that of the donor or for only a part of it. One or two milliliters of donor blood significantly prolonged graft survival in the (LEW X BN)F1----LEW or the LEW X 1W----LEW X 1A combination. The optimal regimen consisted of two BTs given 15 and 7 days prior to grafting; BTs given at day -30 were ineffective. A BT given on the day of the operation was effective, but sequential BTs after grafting did not further increase graft survival. In the (LEW X BN)F1----LEW combination, blood from congenic LEW X 1N rats significantly prolonged graft survival, but third-party BTs were ineffective or had only a borderline effect when transfused (1 ml, 8 times) within the three months before transplantation. This showed the major role of the RT1 system as well as the specificity of the model. Although the survival of LEW X 1A heart grafts transplanted into LEW X 1W recipients could not be significantly prolonged by donor blood, with the reverse--and "weaker"--combination (LEW X 1W----LEW X 1A), 2 ml of donor blood led, in all cases, to greater than 100 days graft survival. In this last combination, third-party BT (LEW X 1N) was again totally ineffective. Blood from RT1-recombinant rats was used to test the role of the respective RT1.A, B, and C regions, in the enhancing effect. BTs from LEW X 1AR2 or LEW X 1WR2 recombinants--sharing, respectively, RT1.C and RT1.A with the graft donor--were only moderately effective, as compared with BTs from the graft donor. On the other hand, LEW X 1WR1 BTs--sharing the RT1.A and RT1.B regions with the graft donor--had a much more powerful effect on heart survival. The results strongly suggest that the RT1.B region (coding for Ia-like antigens) must be shared by the graft and blood donor in order to mediate a significant graft prolongation.     

Cyclosporin A spares selectively lymphocytes with donor-specific suppressor characteristics

The effect of cyclosporin A (Cy A) on the host responses to heart allografts have been examined in rats following administration of the drug for 7 days after grafting. All grafts functioned greater than 100 days without rejection episodes in animals of major histocompatibility differences. Thymic or splenic lymphocytes (1 X 10(8) from LEW recipients of (LEW X BN)F1 hearts were transferred at varying periods into untreated LEW rats transplanted with (LEW X BN)F1 test hearts 24 hr later. Test grafts survived 12 to 16 days significantly (P less than 0.001) longer than in untreated animals (MST +/- SD = 7 +/- 0.3 days). Cells from normal LEW animals, Cy A-treated but ungrafted, and grafted but not treated animals, all failed to prolong test graft survival. Specificity of the effect was tested in vivo, using hearts from donor and third-party rats, and in vitro, using the mixed lymphocyte response (MLR). In vivo, thymocytes from treated LEW recipients of (LEW X WF)F1 grafts failed to prolong (LEW X BN)F1 test grafts; conversely, transferred thymocytes from LEW recipients of LEW X BN)F1 grafts failed to prolong (LEW X WF)F1 grafts. The MLR of lymphocytes from Cy A-treated rats was significantly decreased against donor lymphocytes but not against third-party lymphocytes. Additionally, both cellular and humoral immunity mounted by Cy A-treated recipients was depressed throughout the entire follow-up period. Prolonged heart graft survival after 7 days of Cy A treatment suggests emergence of cells with specific suppressor activity, which in turn may cause profound abrogation of host effector responses against vascularized organ allografts.     

The effect of cyclosporin administered during a third-party blood transfusion protocol on humoral immune responses.

Antigen pre-treatment in animals undoubtedly prolongs graft survival. In man, however, routine pre-transplantation blood transfusions have recently become controversial, principally because of the adverse effect of transfusion-induced sensitisation on graft survival rates. We have monitored the effect of cyclosporin administered during a planned programme of third-party blood transfusions on the development of both cytotoxic and anti-idiotypic antibodies. A total of 24 patients were recruited to the study; ten received cyclosporin with blood transfusions (BT) (group 1), 14 received BT alone (group 2). Anti-HLA antibodies developed in 3 of 9 patients in group 1 and 8 of 12 patients in group 2 (P less than 0.05). Anti-idiotypic antibody activity was detectable in 9 of 9 patients in group 1 and 7 of 12 patients in group 2 (P less than 0.006). The mechanism by which cyclosporin can prevent an anti-HLA antibody response and promote an anti-idiotypic response is unclear.     

Down-regulation of the immune response to histocompatibility antigens and prevention of sensitization by skin allografts by orally administered alloantigen.

The effects of oral administration of major histocompatibility antigens on the alloimmune response have not been investigated. Lymphocytes from inbred LEW (RT1u) rats that were pre-fed allogeneic WF (RT1l) splenocytes exhibited significant antigen specific reduction of the mixed lymphocyte response in vitro and delayed-type hypersensitivity response in vivo, when compared with unfed controls. In an accelerated allograft rejection model, LEW rats were presensitized with BN (RT1n) skin allografts 7 days before challenging them with (LEW x BN)F1 or BN vascularized cardiac allografts. While sensitized control animals hyperacutely reject their cardiac allografts within 2 days, animals prefed with BN splenocytes maintained cardiac allograft survival to 7 days, a time similar to that observed in unsensitized control recipients. This phenomenon was antigen-specific, as third-party WF grafts were rejected within 2 days. Immunohistologic examination of cardiac allografts harvested on day 2 from the fed animals had markedly reduced deposition of IgG, IgM, C3, and fibrin. In addition, there were significantly fewer cellular infiltrates of total white blood cells, neutrophils, macrophages, T cells, IL-2 receptor-positive T cells, and mononuclear cells with positive staining for the activation cytokines IL-2 and IFN-g. On day 6 posttransplant, the grafts from fed animals showed immunohistologic changes typical of acute cellular rejection usually seen in unsensitized rejecting controls. Feeding allogeneic splenocytes prevents sensitization by skin grafts and transforms accelerated rejection of vascularized cardiac allografts to an acute form typical of unsensitized recipients. Oral administration of alloantigen provides a novel approach to down-regulate the specific systemic alloimmune response against histocompatibility antigens.     

Blood-transfusion-induced suppression of cytotoxic T lymphocyte responses in mice

B6AF1 (H-2KbkDbd) mice were transfused weekly with 0.1 ml of whole blood from DBA/2 (H-2d) mice. One week after each transfusion, spleen and serum samples were collected. Blood transfusions did not induce blood donor alloantigen-specific cytotoxic T lymphocytes (CTL) in spleens of B6AF1 mice. When spleen cells from transfused mice were sensitized to alloantigens in mixed lymphocyte culture in vitro, it was observed that 1-3 transfusions induced suppression of blood donor-specific CTL activity. No suppression of CTL activity was found after 4 transfusions. The cell-mixing experiments demonstrated that the suppression of CTL activity following initial 2 blood transfusions was due to the presence of suppressor cells. The presence of antibodies in sera of transfused B6AF1 mice capable of inhibiting CTL was investigated using the CTL-inhibition test. In these experiments, cytotoxic T lymphoblasts generated in MLC in vitro by culturing normal B6AF1 spleen cells with x-irradiated DBA/2 cells were treated with serum before testing them for cytotoxicity. The antibodies capable of inhibiting CTL responses were demonstrable in sera from transfused mice. Three and four BT sera caused significant inhibition of CTL responses. The CTL-inhibitory antibodies were specific for effector cells of the B6AF1 mice and for target cells of the blood donor DBA/2 mice. These results suggest that the inhibition of CTL responses is caused by antibodies directed against the recognition sites on effector T lymphocytes. The data from this study, therefore, demonstrate that BT cause suppression of the recipient's CTL responses against alloantigens present on the blood donor, and that this suppression is mediated by suppressor cells after the initial 1 to 2 transfusions and by antibodies directed against the CTL antigen-specific receptors after subsequent transfusions.     

Detection of serum-blocking factors by inhibition of allorosette formation in rats with long-surviving renal allografts following short-term postoperative ALS treatment.

Thirty-nine (LEW x BN)F1 kidneys were transplanted to LEW rats. Twenty-four untreated recipients survived for a mean time of 16.1 +/- 1.7 days (group 1). Fifteen recipients received 4 ml of antilymphocytic serum per rat (group 3). In the last group 10 recipients survived for more than 4 months. The spleen cells of these permanently surviving 10 rats were obtained by splenectomy and used in a graft-versus-host assay, and this assay showed that the reactivity of these cells was normal. Following splenectomy the animals were given an (LEW x BN)F1 skin allograft, followed 18 days by a second. After another 18 days (LEW x Buf)F1 "third party" skin allografts were transplanted to the same animals. Animals of group 2 rejected their first grafts with a mean survival time of 12.2 +/- 1.2 days, whereas the second grafts were rejected normally as were the third party grafts. Attempts were made to detect lymphocytotoxic antibodies and haemagglutinins before and after the transplantation of skin grafts and none could be found up to day 53. The sera of group 2 inhibited allorosette formation by 38%. This serum-blocking factor was donor specific. It is probable that the survival of the kidney transplants following antilymphocytic serum treatment was brought about by the development of blocking antibodies.     

Specific unresponsiveness to fully allogeneic kidney allografts in rats induced by procarbazine hydrochloride and antilymphocyte serum

A short course of procarbazine hydrochloride (PCH; 50 mg/kg) and antilymphocyte serum (ALS; 5 ml/kg), administered to Lewis (LEW;RT1(1] rats in the first week following transplantation of Brown Norway (BN;RT1n) kidneys, substantially prolonged allograft survival and induced long-term survival in 62% of the grafts. The two agents acted synergistically, in that neither of them administered alone had much effect. Graft recipients did not produce detectable cytotoxic antibodies and antigen-reactive cells injected i.v. were not diverted to the liver, thus showing that neither antibodies nor immune complexes are likely to mediate the unresponsiveness. Spleen cells from graft-bearing recipients failed to cause graft-versus-host responses (GVHR) in both (LEW X BN)F1 and (LEW X DA)F1 hybrids, but they specifically suppressed the GVHR given by normal syngeneic cells to donor strain (BN) antigens. This suppression was specific because the response against third-party antigens (DA; RT1a) was unaffected. Adoptive transfer of spleen and thymus cells from PCH-ALS-treated LEW rats bearing healthy BN kidneys caused a profound prolongation of BN graft survival in sublethally irradiated LEW recipients. This transfer was specific and mediated by W3/13+ (T) lymphocytes. It is concluded that a limited regimen of PCH and ALS given in the first postoperative week incites the generation of specific suppressor T lymphocytes and that this form of immunosuppression, even without preoperative donor antigen, is an effective way of prolonging kidney allograft survival.     

Role of antibody in rat renal allograft rejection. II. Failure to enhance renal allografts by sensitization to donor class I antigens presented by donor strain erythrocytes

BN rats were immunized with one or three doses of 1 X 10(8) highly purified LEW erythrocytes (LEW-E) yielding IgM antibody (IgM-BN rats) and IgG antibody (IgG-BN rats) to LEW class I antigens, respectively. LEW kidneys transplanted into IgM-BN rats elicited cytotoxic T cell responses and lymphocytotoxic antibody responses comparable to those elicited by LEW renal grafts in unmodified BN rats. However, LEW kidneys were rejected by IgM-BN hosts in a slightly delayed fashion compared with controls (mean rejection times (MRTs), 9.4 versus 7.1 days); delayed rejection was associated with the absence of anti-LEW IgG hemagglutinins from the recipients' blood and the absence of vasculonecrotic lesions from rejected renal grafts. LEW kidneys inserted into IgG-BN rats were rejected in a slightly accelerated fashion compared with controls (MRT, 6.6 days). Lymphocytotoxins developed in IgG-BN recipients of LEW kidneys in a fashion similar to that of controls, but cytotoxic T cell responses were delayed up to the 6th day after transplantation. These observations confirm our previous finding that cytotoxic T cells do not play a decisive role in acute rejection in this model. The association observed between delayed or accelerated rejection of LEW kidneys by BN rats sensitized with LEW-E and the absence or presence of anti-donor IgG hemagglutinins in the blood of these recipients after transplantation suggests an important role for IgG anti-donor class I antibodies in the rejection of LEW renal allografts by BN rats.     

Control of humoral and cellular immunity-mediated accelerated heart allograft rejection in sensitized rats by low dose FK 506 and splenectomy

ACI heart grafts are rejected, at an accelerated pace, in Lewis (LEW) rats sensitized by donor-type blood admixed with immunoadjuvant (adjuvant complete Freund, ACF) 7 days earlier. In an in vitro study, the anti-ACI cytotoxic antibody titers in the serum increased from 1:4 in nonsensitized rats to 1:128 in sensitized rats; the spontaneous blastogenesis in spleen cells was higher in sensitized rats than in nonsensitized rats; spleen cells from sensitized rats showed a strong proliferative response against donor strain stimulator cells compared with the control; the cytotoxic T cell activity of spleen cells from sensitized rats was higher than that of spleen cells from nonsensitized rats. Treatment with low dose FK 506 in combination with splenectomy (Spx) synergistically prolonged the heart allograft survival in this sensitized rat model. In conclusion: (1) Both humoral and cellular responses against the donor antigen appear in the serum and in the spleen of rats sensitized by donor-type blood admixed with immunoadjuvant ACF. (2) A low dose of FK506 together with Spx appears to control this sensitization through different mechanisms, resulting in a prolongation of heart allograft survival.     

The role of T suppressor cells in the maintenance of spontaneously accepted orthotopic rat liver allografts.

Orthotopic liver allografts from BN donors to LEW recipients are spontaneously accepted, and the recipients develop donor-specific immunological unresponsiveness. This unresponsiveness may be mediated by suppressor T cells. Immunomagnetically purified splenic T cells from LEW rats bearing BN liver grafts were shown to adoptively transfer suppression of skin, heart, and kidney graft rejection in a donor-specific manner, prolonging the survival of BN but not third-party DA grafts. However, the suppressor T cells were sessile, being resident in the spleen but not present in thoracic duct lymph. The presence of a nonrecirculating suppressor T cell in rats spontaneously accepting liver transplants is strongly suggestive of an important function in the maintenance of donor-specific unresponsiveness, although the contribution of other possible mechanisms of unresponsiveness has not been investigated.     

The role of class I major histocompatibility complex antigens in prolonging the survival of hepatic allografts in the rat

In an attempt to study the role of class I major histocompatibility complex antigens in inducing immunological unresponsiveness, the survival rates of hepatic allografts were compared in rats pretreated with blood taken from various rat strains. A single intravenous injection of 1 ml fresh heparinized whole blood seven days before transplantation significantly prolonged the survival of subsequent donor-specific hepatic allografts in the fully allogeneic ACI(RT1a)-to-LEW(RT1l) rat combination. However, pretreatment with blood taken from the third-party strain BN(RT1n) did not produce suppression of rejection, attesting to the specificity of the pretransplant transfusion effect. Interestingly, pretransplant transfusion of PVG.r1 blood, sharing only the RT1.A MHC region with ACI, significantly prolonged the survival of ACI-to-LEW hepatic allografts. In addition, no lymphocytotoxic antibodies could be detected at 30 or 100 days after transplantation in animals with long-surviving hepatic allografts pretreated with either PVG.r1 or ACI whole blood. On the other hand, pretreatment with PVG(RT1c) blood increased the survival of ACI-to-LEW hepatic allografts only moderately compared with controls. This finding may be consistent with a partial effect of some third-party blood transfusion. The experimental data suggest that the class I MHC antigens can be immunosuppressive in rat hepatic allografts. Adoptive transfer of 5 x 10(7) splenocytes taken from long-term-surviving hepatic allografts pretreated with donor ACI whole blood or PVG.r1 blood into irradiated (750 rads) LEW rats prolonged the survival of donor-type skin grafts, whereas third-party strain (BN) grafts were rejected. This finding suggests the presence of donor-specific suppressor cells.     

Reduction of sensitization induced by blood transfusion in the rat by monoclonal antibodies.

Primary and secondary alloantibody responses were monitored in (AOxPVG)F1 hybrid rats after three transfusions of DA blood; the initial transfusion was either untreated or pretreated with monoclonal antibody directed to class I antigens or other cell surface markers. Mean antibody activity in recipient sera against class I DA antigens was significantly decreased by pretreatment with the monoclonal antibodies. The most marked suppression was associated with pretreatment by antibodies to the four major nonoverlapping epitopes of the RT1Aa antigen. Subsequent transfusions of DA blood failed to stimulate a secondary response. Crossreactivity of the alloantibody reactivity with BDIX antigens was diminished by pretreating the transfusions with rat anti-RT1A antibodies and, to a lesser extent, with a mouse monoclonal antibody (OX-18) to a common class I determinant. Monoclonal antibody pretreatment had no effect on the humoral response to class II DA antigens. These studies indicate that blood transfusions pretreated with monoclonal antibodies induce a less-potent cytotoxic humoral immune response and that reactivity is most effectively suppressed by completely masking the class I antigen. This technique may prove of clinical value in preventing the sensitization caused by blood transfusions in potential transplant recipients.     

Alloantibody and transferable suppressor activity induced by cyclosporine and blood transfusions in the rat

The effect of cyclosporine on the alloantibody response to blood transfusion was investigated in inbred strains of rats by IHA and CELISA; recipient animals differed from the donors at the class I (RT1A) or both class I and class II (RT1B) antigens of the major histocompatibility complex. Alloantibody titers stimulated in high responder PVGu/c animals by blood transfusions were attenuated by cyclosporine; this effect was not demonstrated in low responder PVGc rats, as alloantibody titers decreased after further blood transfusions whether or not cyclosporine was given. Cyclosporine not only reduced the initial IgM response but suppressed the subsequent production of IgG. Splenocytes from rats receiving cyclosporine and blood transfusions from donors that differed from the recipients at the class I antigen were effective in suppressing the subsequent antibody response to blood transfusion. When blood transfusions from donors which differed from the recipients at both class I and class II antigenic loci were given after splenocyte transfer, a greater degree of immunosuppression was detected than if the transfusion donor differed only at the class I locus. These data suggest that the sensitization produced by blood transfusions and the persistence or decline of the alloantibody response depend upon the responder status of the recipient. Blood transfusions given with cyclosporine are capable of inducing suppressor activity that is transferable in spleen homogenates. Subsequent alloantibody responses are influenced by the class I and class II disparities of the donor and recipient animals. If these results can be extrapolated to clinical practice, cyclosporine should be given with pretransplant blood transfusions to prevent sensitization, and the transfusion donor should differ from the recipient at both class I and class II antigenic loci.     

Suppression of antibody response to transfusions in rats by preconditioning with antibody-coated cells

In a Lewis-BN rat model, the antibody response to transfused blood cells from strongly histoincompatible donors was suppressed by preincubation of blood with specific antidonor antiserum or broadly reactive heterologous antilymphocyte serum (ALS). Suppression was achieved even when excess antiserum was removed by washing prior to injection. The suppressive effect was dose-dependent. Broadly reactive ALS was even more effective than specific antidonor antiserum in inhibiting the primary antibody response. Lewis animals pretreated three times with ALS-coated BN blood showed no secondary antibody response against subsequent BN-blood booster injections. Our experiments may be relevant for the prevention of undesired sensitization to donor-specific transfusions prior to related donor kidney transplantation.     

Soluble antigen and cyclosporine-induced specific unresponsiveness in rats. Frequency of alloantigen-specific T cytotoxic cells in normal, sensitized, and unresponsive rats

The cellular mechanisms of unresponsiveness induced with a combined KCl-extracted donor antigen (HAg) and CsA regimen were dissected by limiting-dilution (LD) assay. While untreated Wistar-Furth (WFu, RT1u) rats reject Buffalo (BUF, RT1b) heart allografts within a mean survival time of 6.6 +/- 0.5 days, recipients treated with 3 cycles of CsA alone (-1,0,1; 7,8,9; 15,16,17) maintained BUF heart allografts up to an MST of 22.5 +/- 8.9 days. When CsA was combined with BUF HAg (-1), BUF heart survival was further prolonged up to an MST of 34.2 +/- 6.6 days, while third-party BN HAg was ineffective (MST of 21.5 +/- 2.1 days). On day 10 postgrafting, the frequency of T cytotoxic cells (fTc) within the splenic pan-T-cell population was 1:1437 +/- 301 in CsA and 1:1087 +/- 438 in CsA/HAg treated recipients. In contrast, on day 30 postgrafting, both CsA and CsA/HAg treated WFu rats bearing functional BUF hearts showed within their splenic pan-T-cell populations a profound decrease in fTc to 1:2966 +/- 824 with CsA alone and to 1:4946 +/- 938 with CsA/HAg treatment. In contrast, both untreated WFu rats who rejected BUF heart allografts and CsA-treated WFu recipients who had rejected their BUF heart allografts on day 20 displayed an increased fTc to 696 +/- 243 and to 1:1169, respectively, when examined at day 30 postgrafting. Additionally, both the W3/25+ and OX8+ T cell subsets specifically suppressed the proliferative response of normal WFu T cells against BUF and, to a lesser degree, third-party BN irradiated stimulators. Thus, CsA-treated animals develop a potent specific-suppressor mechanism that is augmented by pretreatment with donor soluble antigen. This suppressor activity may decrease the frequency of alloantigen-specific Tc cells and thereby prolong the survival of BUF heart allografts.     

The difficulty of eliminating donor leukocyte microchimerism in rat recipients bearing established organ allografts

BACKGROUND: Unequivocal eradication of donor leukocyte microchimerism from recipients of long-surviving organ transplants has never been reported. Here we describe a drastic attempt to accomplish this objective. METHODS: In control experiments, a rank order of microchimerism and of associated donor specific nonreactivity was produced in Brown-Norway (BN) rats by transplantation of Lewis (LEW) liver, bone marrow cell (BMC) and heart allografts under a brief course of tacrolimus. The degree of microchimerism at 60 and 110 days was estimated with semiquanitative immunocytochemical and PCR techniques. Tolerance at 110 days was assessed in the different control groups by challenge transplantation of na?ve LEW hearts. In parallel experimental groups, an attempt was made to eliminate microchimerism from the BN recipients. The animals were submitted at 60 days to 9.5-Gy total body irradiation (TBI), reconstituted immediately with na?ve BN BMC, and tested for donor specific nonreactivity by LEW heart transplantation at 110 days. RESULTS: After the TBI-reconstitution at 60 days, microchimerism was undetectable in BMC recipients at 110 days, significantly reduced in heart recipients, and least affected in liver recipients. Except in liver recipients, abrogation of LEW-specific nonreactivity was demonstrated by rejection of the priming grafts, or by rejection of the challenge heart grafts, and by in vitro immune assay. CONCLUSIONS: It is difficult to eliminate microchimerism in organ recipients once the donor cells have settled into tissue niches.     

Indirect T-cell allorecognition and the mechanisms of immunosuppression by allogeneic blood transfusions

LEW rats given twice weekly intravenous transfusions of DA blood for 10 weeks showed a strong antibody response to intact DA class I antigens at day 7 that declined to undetectable levels by week 6. The response remained undetectable for the remainder of the course, in spite of the repeated transfusions of DA blood. At week 6 during the blood transfusion course, the LEW rats were immunised with a DA class I peptide known to be recognised by LEW CD4 + T cells in a LEW APC-dependent manner. This resulted in the prompt reappearance of a strong antibody response to intact DA class I antigen. However, in vitro T-cell proliferation responses to peptide 1 appeared to be partially suppressed by the blood transfusions. Immunisation of LEW rats with this peptide 4 weeks before commencement of the course of DA blood transfusions prevented the decline in antibody levels normally seen during the blood transfusion course. These data indicate that the multiple blood transfusions are able to induce, in non-sensitised recipients, a reversible suppression of the indirect T-helper response specific for allogeneic peptides in the blood transfusion. Although our protocol of twice weekly transfusions does not correspond to the clinical pattern of blood transfusions, our results raise the possibility that antigenic cross-reactivity at the level of small polymorphic MHC peptides between blood and organ donors might represent the immunological basis for the beneficial effects of random blood transfusions. Received: 4 December 1996 Received after revision: 16 April 1997 Accepted: 16 April 1997