Selective modulation of T-cell immunity by intrathymic cellular transplantation

Undifferentiated Murine Embryonic Stem Cells Cannot Induce Portal Tolerance but May Possess Immune Privilege Secondary to Reduced Major Histocompatibility Complex Antigen Expression

Induction of donor-specific tolerance using embryonic stem (ES) cells followed by transplantation of ES cell-derived tissues from the same allogeneic strain could theoretically engender successful transplantation without immunosuppression. We sought to induce tolerance using bona fide murine ES cells in immunocompetent mice. ES cells were evaluated for the expression of markers restricted to undifferentiated cells [stage-specific embryonic antigen-1 (SSEA-1) and OCT-4] and the ability to form teratomas in immunodeficient mice. BALB/cByJ mice underwent intraportal inoculation with YC5-EYFP ES cells (129 strain; R1-derived) or saline followed by transplantation with 129X1/SvJ, CBA/J, or BALB/cByJ nonvascularized, neonatal cardiac grafts. Mice were sacrificed at graft failure and underwent histologic evaluation of transplanted grafts and lymphoid organs. ES cells and early differentiated progeny underwent real time (RT)-PCR and fluorescence-activated cell sorting (FACS) analysis to detect major histocompatibility complex (MHC) gene transcription and antigen expression. ES cells expressed markers restricted to undifferentiated cells while maintaining the ability to form teratomas in immunodeficient mice. No prolongation of allograft survival or evidence of lymphoid chimerism was observed in immunocompetent recipient mice despite hepatic teratoma formation. MHC class I, class II, and nonclassical antigens were undetectable on ES cells and early differentiated progeny despite the presence of mRNA transcripts. Class I expression was strongly upregulated upon exposure to gamma-interferon. Intraportal inoculation with murine ES cells does not produce lymphoid chimerism or induce donor-specific unresponsiveness to neonatal cardiac grafts in unmanipulated immunocompetent hosts. However, specific differentiated cell types such as ES cellderived dendritic cells, or alternate routes of ES cell administration, may be effective. ES cells appear to have immune privilege, allowing them to form teratomas in immunocompetent mice.

Intrathymic inoculation of donor antigen: an ineffective strategy for prolonging xenograft survival

The aim of this study was to determine whether intrathymic inoculation of the recipient with donor antigen and short-term depletion of peripheral lymphocytes would lead to donor-specific unresponsiveness to rat pancreatic islet xenografts. The results were compared directly with an allograft model to determine whether there were substantial differences in the mechanisms of graft prolongation between allografts and xenografts using an identical conditioning regimen. Streptozotocin-induced diabetic C57B6 mice were injected with up to 0.3 ml of rat anti-mouse lymphocyte serum (ALS) 1 day before intrathymic injection of donor splenocytes. DA rat islet xenografts or Balb/c mouse islet allografts were transplanted 3 days later. ALS depleted CD3+ and CD4+ peripheral blood T lymphocytes to less than 5% of values in control mice by 24 h. Median islet xenograft survival (MGS) was 9 days in untreated mice, 28 days in mice receiving 0.2 ml of ALS and 32 days in mice receiving 0.3 ml of ALS alone. Intrathymic injection of 5 x 10(6) DA splenocytes plus 0.2 ml of ALS did not improve islet xenograft survival beyond 28 days. Increasing the intrathymic inoculum to 10(7) DA splenocytes with or without a higher dose of ALS (0.3 ml) did not increase MGS beyond 26 days, although 2 out of 18 animals survived beyond 100 days. These long-term surviving mice rejected a second DA rat islet graft in less than 22 days, indicating that tolerance was not achieved. To confirm the efficacy of this treatment regimen in allotransplantation, diabetic C57B6 mice received 10(7) Balb/c splenocytes intrathymically and 0.3 ml of ALS. A Balb/c islet allograft was performed 3 days later. Allograft survival was similar to that of rat islet xenografts with 40%, (4 out of 10) of grafts surviving beyond 100 days. In contrast to the xenograft recipients, a second Balb/c islet allograft survived indefinitely, indicating that tolerance was achieved. Histology of the long-surviving allografts showed intact islets with a sparse cellular infiltrate, whereas the long-surviving xenografts (> 100 days) showed a large cellular infiltrate and significant islet destruction. To investigate further the role of the thymus, adult thymectomized C57B6 mice were treated with 0.3 ml of ALS and received a DA rat islet xenograft. The median graft survival was 52 days and no graft survived beyond 80 days, suggesting that peripheral xenoreactive T cells remained after ALS treatment and greater T-cell depletion was necessary to obtain permanent engraftment. These results show that peripheral xenoreactive T cells which remain after profound T-cell depletion are capable of rejecting an islet xenograft despite intrathymic inoculation of donor antigen. The T-cell-mediated xenograft response appears to be stronger and more difficult to suppress than the allograft response using this strategy.

T-cell receptor expression in C57BL/6 mice that reject or are rendered tolerant to bm1 cardiac grafts

To study the molecular immunologic features of allograft rejection and tolerance induction by intrathymic pretreatment we developed a murine model of cardiac transplantation. In this model the transplant recipient was the C57BL/6 mouse with its major histocompatibility phenotype H-2b. Donors of cells for intrathymic pretreatment and of hearts for grafting were mice of the bm1 mutation. The bm1 mutation involves substitution of three amino acids in one of the alpha helixes of the class I H-2Kb molecule. Because of the discrete molecular configuration of the transplant antigen we hypothesized that there would be limited heterogeneity of receptor expression on C57BL/6 T cells responding to bm1 cardiac grafts and that intrathymic pretreatment would alter the T-cell repertoire of graft recipients by causing elimination of T cells responsible for graft rejection. Mice were given 0.3 ml of antilymphocyte serum intraperitoneally and had intrathymic injection of 25 x 10(6) bm1 splenocytes 12 to 21 days before transplantation with a bm1 cardiac graft. Flow cytometric analysis of lymph node and spleen cells was used to study the V beta T-cell repertoire of graft recipients. Cells were stained with monoclonal antibodies to CD3 and 13 V beta regions (n = 5, each group) of T cells in naive, sensitized, and tolerant animals. Untreated C57BL/6 mice (n = 9) rejected bm1 cardiac grafts a mean of 20.4 days after transplantation. Twelve mice pretreated with antilymphocyte serum and intrathymic bm1 cells had permanent graft survival (> 100 days, p < 0.0001). Animals treated with antilymphocyte serum alone (n = 5) or pretreated animals undergoing third-party BALB/c grafts (n = 4) rejected grafts in the normal time frame. There was significant alteration of percentage receptor expression of V beta 5.1, 7, 12, 13, and 17a in sensitized and tolerant mice. Of interest, V beta 7 expression was increased in the sensitized mice (3.8% to 8.3%,p = 0.005) and was virtually eliminated in tolerant mice (p = 0.005). In conclusion, these data suggest that V beta 7 is a critical receptor in the C57BL/6 response to subcutaneous bm1 cardiac grafts. Pretreatment of graft recipients with one dose of antilymphocyte serum and intrathymic bm1 cells appears to produce permanent tolerance to bm1 grafts with elimination of T cells expressing receptor chain V beta 7.

Suppressor cells and intrathymic inoculation of donor alloantigens in cardiac transplantation

BACKGROUND

Donor-specific tolerance to a rat heterotopic cardiac allograft has been achieved by the pretransplantation intrathymic injection of donor splenocytes and a single intraperitoneal injection of antilymphocyte serum (ALS). Permanent tolerance is achieved without subsequent immunosuppression therapy. This study investigated the mechanisms responsible for maintenance of the tolerant state.

METHODS

Tolerance was produced in Lewis rats by the administration of 1 mL of ALS intraperitoneally and 5 x 10(7) Lewis Brown Norway (LBN) splenocytes intrathymically 21 days before heterotopic transplantation using an LBN donor.

RESULTS

In tolerant Lewis rats bearing LBN allografts for more than 100 days, rejection could not be produced by the intravenous injection of naive Lewis spleen cells (5 x 10(7) cells x 1 day, n = 5; 5 x 10(7) cells x 3 days, n = 5) or cells from Lewis rats sensitized to LBN tissues (5 x 10(7) cells x 3 days, n = 5). Naive Lewis recipients were pretreated with ALS and 6 days later with intravenous spleen cells (25 x 10(7), n = 5) or lymphoid cells (10 to 15 x 10(7), n = 5) from a tolerant animal bearing a viable LBN graft. When transplantation with an LBN donor was done the next day, significant prolongation of LBN allograft survival (mean survival time 32.8 days, p < 0.01; and 22.2 days, p < 0.01; respectively) was seen. Wistar-Furth allograft survival was not prolonged by treatment with ALS and intravenous spleen (n = 5) or lymph node (n = 5) cells from rats tolerant to LBN tissues (mean survival time 8.6 and 9.2 days, control 9 days; p = not significant). The administration of ALS alone (n = 5) did not prolong LBN graft survival (mean survival time 11.8 days).

CONCLUSION

These data suggest that transferable suppressor cells specific for the donor strain are at least in part responsible for the maintenance of long-term allograft survival after intrathymic pretreatment with allogeneic cells.