A strategy for organ allografts without using immunosuppressants or irradiation

In the Acute Phase of Trypanosoma cruzi Infection, Liver Lymphoid and Myeloid Cells Display an Ambiguous Phenotype Combining Pro- and Anti-Inflammatory Markers

Multiple cell populations, cellular biochemical pathways, and the autonomic nervous system contribute to maintaining the immunological tolerance in the liver. This tolerance is coherent because the organ is exposed to high levels of bacterial pathogen-associated molecular pattern (PAMP) molecules from the intestinal microbiota, such as lipopolysaccharide endotoxin (LPS). In the case of Trypanosoma cruzi infection, although there is a dramatic acute immune response in the liver, we observed intrahepatic cell populations combining pro- and anti-inflammatory markers. There was loss of fully mature Kupffer cells and an increase in other myeloid cells, which are likely to include monocytes. Among dendritic cells (DCs), the cDC1 population expanded relative to the others, and these cells lost both some macrophage markers (F4/80) and immunosuppressive cytokines (IL-10, TGF-β1). In parallel, a massive T cell response occured with loss of naïve cells and increase in several post-activation subsets. However, these activated T cells expressed both markers programmed cell death protein (PD-1) and cytokines consistent with immunosuppressive function (IL-10, TGF-β1). NK and NK-T cells broadly followed the pattern of T cell activation, while TCR-γδ cells appeared to be bystanders. While no data were obtained concerning IL-2, several cell populations also synthesized IFN-γ and TNF-α, which has been linked to host defense but also to tissue injury. It therefore appears that T. cruzi exerts control over liver immunity, causing T cell activation via cDC1 but subverting multiple populations of T cells into immunosuppressive pathways. In this way, T. cruzi engages a mechanism of hepatic T cell tolerance that is familiar from liver allograft tolerance, in which activation and proliferation are followed by T cell inactivation.

Development of a Safeguard System Using an Episomal Mammalian Artificial Chromosome for Gene and Cell Therapy

The development of a safeguard system to remove tumorigenic cells would allow safer clinical applications of stem cells for the treatment of patients with an intractable disease including genetic disorders. Such safeguard systems should not disrupt the host genome and should have long-term stability. Here, we attempted to develop a tumor-suppressing mammalian artificial chromosome containing a safeguard system that uses the immune rejection system against allogeneic tissue from the host. For proof-of-concept of the safeguard system, B16F10 mouse melanoma cells expressing the introduced H2-K(d) major histocompatibility complex (MHC class I)-allogenic haplotype were transplanted into recipient C57BL/6J mice expressing MHC H2-K(b). Subcutaneous implantation of B16F10 cells into C57BL/6J mice resulted in high tumorigenicity. The volume of tumors derived from B16F10 cells expressing allogenic MHC H2-K(d) was decreased significantly (P < 0.01). Suppression of MHC H2-K(d)-expressing tumors in C57BL/6J mice was enhanced by immunization with MHC H2-K(d)-expressing splenocytes (P < 0.01). These results suggest that the safeguard system is capable of suppressing tumor formation by the transplanted cells.

[Proteasomes on thyroid tissue allotransplantation under induction of donor specific tolerance in rats]

The proteasomes in the liver of August rats (RT1C) were investigated 30 days after the allotransplantation of Wistar rat (RT1u) thyroid tissue under renal capsule with/without induction of donor specific tolerance by donor splenocyte intraportal administration. The level of the total proteasome pool, immune proteasomes containing the LMP2 and/or LMP7 subunits, proteasome 19S- and 11S-regulators was defined. The intact and sham-operated August rats were used as control groups. The level of all immune proteasome forms and 11S regulator increased while the level of the total proteasome pool and 19S regulator decreased in the liver of experimental animals compared to the control groups that indicated changes of liver functional state after transplantation. The 19S/11S ratio increased in the liver of non-tolerated rats compared to tolerated animals. In the liver of tolerated rats with survived transplants, the quantity of mononuclear cells, expressing the immune subunit LMP2, greatly increased in comparison with control and non-tolerated animals. Study of the survived transplants showed the increase of the ratio of LMP2/LMP7 immune subunits and 19S/11S regulators in them compared to the tissue replacing the rejected transplants. In the control intact thyroid tissue, the immune proteasomes were almost not revealed, while 19S/11S ratio was maximal. Thus, the development of the immune reaction or its suppression is accompanied by change of the balance between different proteasome forms. The immune subunit LMP7 and 11S regulator are connected with the response against donor tissue. On the contrary, the immune subunit LMP2 and 19S regulator are likely to be important for the immune tolerance development and survived tissue functioning. The low content of the immune proteasomes in the follicle cells was found by immunofluorescence assay. The formation of antigens for major histocompatibility complex class I molecules was impaired by low immune proteasome content that led to immunological tolerance to hormone-producing follicle cells.

Chimeric acceleration by donor CD4+CD25+T-reg depleted fraction in splenocyte transplantation

BACKGROUND

We have established a splenocytic chimera model that can induce donor-specific tolerance and reconstitute the recipient immune system by donor splenocytes.

AIM

To accelerate such reconstitution, we investigated the role of donor-derived CD4(+)CD25(+) regulatory T-cells (T-reg).

METHODS

We established C3H/B6D2F1 mixed bone marrow chimeras in lethally irradiated C3H mice. We transplanted skin grafts from C57BL/6 mice 30 d later. After an additional 30 d, we transplanted the following types of splenocytes from B6C3F1 mice: total splenocytes (group A), CD4(+)CD25(+) T-reg depleted splenocytes (group B), CD8(+)-depleted splenocytes (group C), and CD4(+)-depleted splenocytes (group D). We assessed class I major histocompatibility complex, percentage of chimeric cells in peripheral blood, and survival of skin grafts in each group.

RESULTS

Group A and B mice switched to splenocytic chimeras, permitting the long-term survival of skin grafts. The proportions of H-2K(b+)H-2K(k-) cells in group B were significantly lower than those in group A on day 14 (0.47% ± 0.68% versus 9.49% ± 8.30%; P = .01) and day 21 (0.16% ± 0.25% versus 3.35% ± 2.78%; P = .01). The initial increase in the proportion of H-2K(b+)H-2K(k+) double-positive cells in group B was faster than that in group A (from 0.33% ± 0.10% versus. 0.39% ± 0.14% before splenocyte injection to 39.03% ± 30.50% versus 10.73% ± 11.54% on day 7; P = .02). The initial increase in the proportion of CD8(+) T-cells was faster in group B than in group A (from 2.72% ± 0.52% versus 2.49% ± 1.07% before splenocyte injection to 29.61% ± 26.72% versus 4.92% ± 1.56% on day 7; P = .04).

CONCLUSIONS

The depletion of CD4(+)CD25(+) T-reg fraction in donor splenocytes can accelerate switching to splenocytic chimera.

Partially MHC-matched donor CD8+ T cells are indispensable for switching to splenocytic chimerism

BACKGROUND

We have shown that partially major histocompatibility complex (MHC)-matched splenocytes can replace bone marrow (BM) and maintain skin grafts by establishing splenocytic chimeras. Our aim was to identify the population of splenocytes that are indispensible for switching from BM to splenocytic chimerism.

METHODS

C3H/B6D2F1 mixed BM chimeras were established in lethally irradiated C3H mice. Skin grafts from C57BL/6 mice were transplanted 30 d later. After an additional 30 d, splenocytes from B6C3F1 mice were transplanted to establish splenocytic BM chimeras using total splenocytes (group A), CD90(+)-depleted splenocytes (group B), CD4(+)-depleted splenocytes (group C), or CD8(+)-depleted splenocytes (group D).

RESULTS

In group A, the BM switched to splenocyte-derived BM chimeras. Total B6C3F1 splenocytes created stable splenocyte BM chimeras that permitted long-term retention of skin grafts, without rejection. In groups B and D, the splenocytes failed to replace the recipient BM, and there was no decrease in the number of recipient-derived BM cells compared with group A from d 14 to 28 after splenocyte injection, as was the case for CD8(+) T cells. In group C mice, the recipient BM was slowly and incompletely replaced.

CONCLUSIONS

Partially MHC-matched donor CD8(+) T cells are indispensable for generating splenocyte chimeras in BM and maintaining allogeneic skin grafts.

Increased CD4+CD25+Foxp3+ regulatory T cells in tolerance induced by portal venous injection

BACKGROUND

A portal vein injection (PVI) of allogeneic donor antigen is known to prolong the survival of a subsequently transplanted allograft; however, the underlying mechanism remains to be clarified.

METHODS

Irradiated C57BL/6 (B6) splenocytes were injected into BALB/c mice via the portal vein. Seven days after injection, the proportions of CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cells were determined in the blood, liver, and spleen. CD4(+) and CD8(+) T cells were isolated from BALB/c mice that received PVI of B6 splenocytes (PVI mice), adoptively transferred into recipient BALB/c mice 1 day before B6 or third-party C3H heart transplantation, and graft survival was compared. B6 or C3H heart allografts were implanted into anti-CD25 monoclonal antibody (mAb)-treated PVI and untreated PVI mice, and graft survivals were compared. The percentages of CD4(+)CD25(+)Foxp3(+) Treg, cytokine profiles, and ratios of apoptosis were determined in anti-CD25 mAb-treated PVI and untreated PVI mice.

RESULTS

PVI of allogeneic cells induced antigen-specific tolerance and increased the percentage of CD4(+)CD25(+)Foxp3(+) Treg. Adoptive transfer of CD4(+) T cells, but not CD8(+) T cells, from PVI mice prolonged B6 heart allograft survival. Depletion of CD4(+)CD25(+) T cells prevented the induction of tolerance and decreased the percentage of CD4(+)CD25(+)Foxp3(+) Treg in the CD3(+) T-cell pool, and thus was associated with decreased production of interleukin (IL)-4 and apoptosis of T cells.

CONCLUSION

Increased CD4(+)CD25(+)Foxp3(+) Treg play an important role in portal vein tolerance induction, at least partly via increasing the production of IL-4 and decreasing apoptosis of T cells.

Portal venous donor-specific transfusion in conjunction with sirolimus prolongs renal allograft survival in nonhuman primates

Pretransplant exposure to donor antigen is known to modulate recipient alloimmunity, and frequently results in sensitization. However, donor-specific transfusion (DST) can have a protolerant effect that is dependent on route, dose and coadministered immunosuppression. Rodent studies have shown in some strain combinations that portal venous (PV) DST alone can induce tolerance, and uncontrolled clinical use of PVDST has been reported. In order to determine if pretransplant PVDST has a clinically relevant salutary effect, we studied it and the influence of concomitant immunosuppression in rhesus monkeys undergoing renal allotransplantation. Animals received PVDST with unfractionated bone marrow and/or tacrolimus or sirolimus 1 week prior to transplantation. Graft survival was assessed without any posttransplant immunosuppression. PVDST alone or in combination with tacrolimus was ineffective. However, PVDST in combination with sirolimus significantly prolonged renal allograft survival to a mean of 24 days. Preoperative sirolimus alone had no effect, and peripheral DST with sirolimus prolonged graft survival in 2/4 animals, but resulted in accelerated rejection in 2/4 animals. These data demonstrate that PVDST in combination with sirolimus delays rejection in a modest but measurable way in a rigorous model. It may thus be a preferable method for donor antigen administration.

Pretransplant infusion of mesenchymal stem cells prolongs the survival of a semiallogeneic heart transplant through the generation of regulatory T cells

In this study, we investigated whether mesenchymal stem cells (MSC) had immunomodulatory properties in solid organ allotransplantation, using a semiallogeneic heart transplant mouse model, and studied the mechanism(s) underlying MSC tolerogenic effects. Either single (portal vein, day -7) or double (portal vein, day -7 and tail vein, day -1) pretransplant infusions of donor-derived B6C3 MSC in B6 recipients induced a profound T cell hyporesponsiveness and prolonged B6C3 cardiac allograft survival. The protolerogenic effect was abrogated when donor-derived MSC were injected together with B6C3 hematopoietic stem cells (HSC), suggesting that HSC negatively impact MSC immunomodulatory properties. Both the induction (pretransplant) and the maintenance phase (>100 days posttransplant) of donor-derived MSC-induced tolerance were associated with CD4(+)CD25(+)Foxp3(+) Treg expansion and impaired anti-donor Th1 activity. MSC-induced regulatory T cells (Treg) were donor-specific since adoptive transfer of splenocytes from tolerant mice prevented the rejection of fully MHC-mismatched donor-specific secondary allografts but not of third-party grafts. In addition, infusion of recipient-derived B6 MSC tolerized a semiallogeneic B6C3 cardiac allograft, but not a fully MHC-mismatched BALB/c graft, and expanded Treg. A double i.v. pretransplant infusion of recipient-derived MSC had the same tolerogenic effect as the combined intraportal/i.v. MSC infusions, which makes the tolerogenic protocol applicable in a clinical setting. In contrast, single MSC infusions given either peritransplant or 1 day after transplant were less effective. Altogether these findings indicate that MSC immunomodulatory properties require HSC removal, partial sharing of MHC Ags between the donor and the recipient and pretransplant infusion, and are associated with expansion of donor-specific Treg.

Donor bone marrow cells play a role in the prevention of accelerated graft rejection induced by semi-allogeneic spleen cells in transplantation

Spleen or spleen plus bone marrow cells from (BALB/cxC57Bl/6)F1 donors were transferred into BALB/c recipients 21 days before skin or cardiac transplantation. Prolonged graft survival was observed on recipients treated with the mixture of donor-derived cells as compared to those treated with spleen cells alone. We evaluated the expression of CD45RB and CD44 by splenic CD4+ and CD8+ T cells 7 and 21 days after donor cell transfer. The populations of CD8+CD45RBlow and CD8+CD44high cells were significantly decreased in mice pre-treated with donor spleen and bone marrow cells as compared to animals treated with spleen cells only, although these cells expanded in both groups when compared to an earlier time-point. No differences were observed regarding CD4+ T cell population when recipients of donor-derived cells were compared. An enhanced production of IL-10 was observed seven days after transplantation in the supernatants of spleen cell cultures of mice treated with spleen and bone marrow cells. Taken together these data suggest that donor-derived bone marrow cells modulate the sensitization of the recipient by semi-allogeneic spleen cells in part by delaying the generation of activated/memory CD8+ T cells leading to enhanced graft survival.

Cell death recognition model for the immune system

It is essential for the immune system to recognize markers or understand rules required for discriminating antigens that should be actively responded to from those be tolerated. Although the classic self-nonself theory over the past five decades has been challenged by "danger" model and "infectious nonself" model, etc., no theories could fit for all. Cell death is important not only for its role in homeostasis, but also for its decisive effects on the immune responses. Different ways of cell death, apoptosis or necrosis, transmit fundamentally opposite driving forces for the immune system, inducing tolerance or initiating adaptive immune responses. The progress in understanding phagocytosis and process of apoptotic and necrotic cells leads the author to propose "cell death" recognition model for the immune system. Four principles are important in this model. First, only antigens shedding from apoptotic or necrotic cells rather than those from healthy cells, can be presented to naïve T cells. Second, either apoptotic cells or necrotic cells, but not healthy cells, can attract phagocytes, namely dendritic cells (DC) or macrophages that are also antigen presenting cells (APC), to scavenge dead cells. Third, macrophages or DC residing in non-lymphoid tissues phagocytose dying/dead cells, migrate to lymphoid tissues and present antigens to naïve T cells there. Fourth, tolerance or adaptive responses are not dependent on whether the antigens are self or nonself, but on the ways of cell death during antigen presentation. Importantly, tolerance and adaptive immunity are all dominant responses and the impact of cell death on immune responses is a dynamic balance between them. "Cell death" recognition model could more easily explain various immune phenomena, including infection, self tolerance and autoimmunity, tumor immunity as well as transplant rejection. Investigation into the roles and mechanisms of cell death mediated immune responses and finding out key modulators will prompt better understanding the ways of immune recognition and provide novel strategies for the management of autoimmunity, tumors, infections as well as transplantation.

Extensive Studies on Perfusion Method Plus Intra-Bone Marrow-Bone Marrow Transplantation Using Cynomolgus Monkeys

The collection of bone marrow cells (BMCs) using a perfusion method has been advantageous not only because of the low contamination of BMCs with T cells from the peripheral blood but also the enrichment of stromal cells, which support hemopoiesis. Before the application of this new method to humans, its safety needed to be confirmed using cynomolgus monkeys. We therefore performed the perfusion method on more than 100 cynomolgus monkeys using the long bones (such as the humerus and femur) and also the iliac bones (for human application); in the more than 150 trials to date, there have been no accidental deaths. Furthermore, the technical safety of a new method for the intra-bone marrow (IBM) injection of BMCs (termed IBM-bone marrow transplantation) has also been confirmed using 30 monkeys. Disclosure of potential conflicts of interest is found at the end of this article.

Synergistic effects of injection of bone marrow cells into both portal vein and bone marrow on tolerance induction in transplantation of allogeneic pancreatic islets

We have established a new method for allogeneic pancreatic islet (PI) transplantation: relatively low doses of irradiation followed by simultaneous transplantation of PIs and bone marrow cells (BMCs) via the portal vein (PV). In the present study, we have compared this method with intra-bone marrow (IBM)-bone marrow transplantation (BMT), and with a combination of both methods. Streptozotocin (STZ)-induced diabetic-recipient rats, Fischer 344 (F344, RT1A(l), RT1B(l)), were irradiated 1 day before transplantation. PIs of Brown Norway rats (BN, RT1A(n), RT1B(n)) were transplanted into the liver of the diabetic F344 rats via the PV. BMCs from BN rats were injected into the recipients' bone marrow (IBM), PV or intravenously (IV) or by a simultaneous combination of PV plus IBM (PV+IBM). We compared graft survival among the groups of '9 Gy+IBM'(10/10 accepted), '9 Gy+PV'(7/10 accepted), '9 Gy+IV'(0/7 accepted), '9 Gy+PV+IBM'(8/8 accepted), '8.5 Gy+IBM'(4/9 accepted), '8.5 Gy+PV'(0/7 accepted), '8.5 Gy+IV'(0/7 accepted), '8.5 Gy+PV+IBM'(9/12 accepted), '8 Gy+IBM'(2/10 accepted) and '8 Gy+PV+IBM'(2/8 accepted). As we reported previously, PV-BMT is more effective in inducing the acceptance of allogeneic PIs than IV-BMT. However, IBM-BMT requires less pretreatment than PV-BMT. (PV+IBM)-BMT was found to be the most effective in inducing the acceptance of allogeneic PIs. These results suggest that allogeneic PI-transplantation in conjunction with (PV+IBM)-BMT could become a viable strategy.

CD8 T cell of donor splenocyte mixed with bone marrow cells is more effective than CD4 T cell for induction of donor-specific tolerance in sublethally irradiated mice

BACKGROUND

We previously demonstrated that even a low dose of bone marrow cells (BMCs) established donor-specific tolerance if mixed with splenocytes (SPLCs). In this study, T-cell subsets CD4 (CD4SP) and CD8 (CD8SP) of donor SPLCs were investigated for their contribution to the enhancement of BMC engraftment leading to donor-specific tolerance in sublethally irradiated mice.

METHODS

Sublethally irradiated C57BL/6 recipient mice were intravenously injected BMCs mixing with CD4SP or CD8SP harvested from BALB/c donor mice. The degree of chimerism in the peripheral blood lymphocytes (PBLs) and in the SPLCs was analyzed using FACS, mixed lymphocyte reaction, and skin graft transplantation 3 months after injection.

RESULTS

Recipients injected with 3 x 10(6) donor BMCs admixed with 10 x 10(6) donor CD8SP established chimerism. However, recipients injected with the same dose of BMCs admixed with 5 x 10(6) CD4SP, 10 x 10(6) CD4SP, and 5 x 10(6) CD8SP did not established chimerism. CD8SP contained 44% of Ly6A/E (Stem Cell Antigen-1 (Sca-1))-positive cells based on FACS analysis, whereas only 6% of CD4SP were positive for Ly6A/E. MLR supernates of donor SPLCs chimeric mice using admixture with CD8SP dominated by Th2 cytokines. In contrast, mixting with MLR supernates from failed chimera showed dominant Th1 cytokines.

CONCLUSIONS

CD8SP seems to make a major contribution to enhance BMC engraftment and induce donor-specific tolerance. Ly6A/E (Sca-1)-positive cells need to be further investigated for their contribution to the establishment of chimerism.

Impact of portal venous pancreas graft drainage on kidney graft outcome in simultaneous pancreas-kidney recipients reported to UNOS

Clinical data on the potential immunologic impact of portal (PD) vs. systemic (SD) venous pancreas graft drainage on outcome remains controversial. We reviewed the UNOS database to study the effect of PD vs. SD on the incidence of kidney graft rejection and survival in first cadaveric simultaneous pancreas-kidney (SPK) recipients transplanted 1994-2001. We studied three groups: all SPK (n=6629, 13% PD) (group I), SPK on tacrolimus (n=3563, 17% PD) (group II), and SPK on tacrolimus performed at centers with significant PD experience (n=948, 46% PD) (group III). The cumulative kidney graft rejection incidence for PD vs. SD was only significantly different in group I (for PD vs. SD, respectively: at 6 months, 31% vs. 36% [p=0.015]; at 1 year, 37% vs. 43% [p=0.006]). Kidney graft survival was similar in all groups for PD vs. SD. Multivariate analysis of group III showed only transplantation during the earlier era (1994-96), but not SD, to be an independent risk factor for kidney graft rejection. Portal venous pancreas graft drainage does not affect kidney graft rejection and survival in SPK recipients on tacrolimus. Our data suggests that the efficacy of current immunosuppressive protocols and increasing center experience are clinically much more relevant than any potential immunologic advantage of portal venous drainage in SPK recipients.

Tolerance: is it achievable in pediatric solid organ transplantation?

Significant advances have been made in the understanding of allograft rejection. There is growing awareness that allograft acceptance, or tolerance, is also an active process rather than a passive absence of rejection. Mechanistic awareness of this process has spawned many preclinical strategies for the prevention of allograft rejection without the need for chronic immunosuppression. These therapies are currently entering clinical trials. This article reviews the prevailing therapies that hold promise for future clinical application. In particular, their application in children is discussed, as are biologic aspects of childhood immunity that may play a role in the success or failure of these strategies.

Absence of a relationship between the increased survival of skin grafts provoked by additional spleen transplantation and the detection of donor chimeric cells in rats

The goal of this study was to examine the relationship between the effects of spleen transplantation on the acceptance of a skin allograft from the same donor and the detection of donor chimerism in recipient tissues. Male Sprague-Dawley rats and female Wistar rats were used as donors and recipients, respectively. Four experimental groups were established: group C: only skin grafting was performed; group S: recipients were splenectomized before skin grafting; group 1: skin grafts were performed immediately after splenectomy of recipients and spleen transplantation, and group 2: splenectomy of the recipients and spleen grafting were performed 48 h before skin grafting. All animals were sacrificed 14 weeks after surgery. The rate of acceptance of skin grafts was significantly higher in animals that received both skin and spleen transplantations than in group C (p = 0.03) or in group S (p = 0.04). Detection of donor chimeric cells was significantly more frequent in rats after spleen transplantation than in group C (p = 0.03). However, the detection of chimeric cells was not related to the acceptance of skin grafts. To conclude, the beneficial effect of spleen auxiliary transplantation on allograft survival was not related to the detection of long-term chimerism in the recipient's tissues.

A liver tolerates a portal antigen by generating CD11c+ cells, which select Fas ligand+ Th2 cells via apoptosis

Administration of an antigen (Ag) per oral route leads to apoptosis of Ag-specific CD4(+) T cells and to development of Th2 cells expressing Fas ligand (FasL) in the liver. We determined whether presentation of an ingested Ag in the liver alone was enough to select these FasL(+)Th2 cells and explored how this selection was achieved in the liver. Ovalbumin (OVA) administered orally was colocalized with class II(+) cells in the periportal and parenchymal area of the liver. On coculture with naive OVA-specific CD4(+) T cells, hepatic CD11c(+) cells from mice fed OVA generated Ag-specific Th2 cells. This was achieved by apoptosis of CD4(+) T cells, decrease of interleukin 12 (IL-12) secretion, and increase of IL-18 secretion by the CD11c(+) cells. Addition of IL-12 to this coculture prevented apoptosis of the CD4(+) T cells, which was associated with up-modulation of IL-2 receptor beta chain expression. Administration of IL-12 to mice fed OVA prevented apoptosis of OVA-specific CD4(+) T cells in the liver. Moreover, adoptive transfer of hepatic CD11c(+) cells from mice fed OVA together with OVA-specific CD4(+) T cells led to development of Th2 cells as well as apoptosis of the transferred CD4(+) T cells in the lymph nodes of the recipient mice on immunization with OVA. In conclusion, presentation of an ingested Ag by hepatic CD11c(+) cells selects Th2 cells resistant to apoptosis in the liver, which is mediated in part by down-regulation of IL-12 secretion by the former cells.

Treatment of autoimmune diseases in mice by a new method for allogeneic bone marrow transplantation

Remarkable advances have been made in bone marrow transplantation (BMT), which has become a powerful strategy for the treatment of leukemia, aplastic anemia, congenital immunodeficiency, and also autoimmune disease. Using various animal models, allogeneic (allo) BMT has been found to be useful in the treatment of various autoimmune diseases. In MRL/lpr mice, which are radiosensitive (<8.5 Gy) and are an animal model for autoimmune diseases, conventional BMT resulted in only transient effects; the manifestations of the autoimmune diseases recurred 3 months after BMT. Using MRL/lpr mice, we have very recently established a new strategy for allo BMT. We injected bone marrow cells (BMC) directly into the bone marrow cavity (intrabone marrow [IBM] injection) of recipients that had received fractionated irradiation. This 'IBM-BMT' was found to be effective in treating autoimmune diseases in radiation-sensitive and chimeric-resistant MRL/lpr mice. In addition, this strategy was found to be applicable for the transplantation of organs. We believe that these strategies for BMT and organ transplantation herald a new era in transplantation.

Successful multilineage engraftment of human cord blood cells in pigs after in utero transplantation

BACKGROUND

Successful engraftment of human hematopoietic stem and progenitor cells (HSPCs) in a large animal may serve not only as a model to study human hematopoiesis but also as a bioreactor to expand human HSPCs in vivo. The aim of this study was to accomplish xenotransplantation of human HSPCs into pig.

METHODS

Total mononuclear or CD34-positive HSPCs obtained from human cord blood were xenotransplanted percutaneously under an ultrasonographic guidance into preimmune pig fetuses. Peripheral blood and bone marrow (BM) cells of recipient pigs were collected and analyzed for the presence of human cells by a polymerase chain reaction to detect human specific Alu sequence on DNA extracted from those cells. Fluorescence-activated cell sorting (FACS) analysis was also performed to detect human hematopoietic cells.

RESULTS

Transplantation of human cord blood cells into pig fetuses aged less than 52 days postcoitus resulted in a good engraftment rate. In one case, engraftment was detected up to 315 days posttransplantation by polymerase chain reaction. Human hematopoietic cells were detectable also by FACS in peripheral blood and BM. Furthermore, human CD34+ HSPCs were also observed in the BM of recipients. Those CD34+ cells in BM were sorted by FACS and subjected to further analyses. First, in vitro colony formation assay resulted in formations of multilineage colonies. Second, when they were transplanted into an immunodeficient mouse they were engrafted in the mouse.

CONCLUSIONS

These data indicate an engraftment of human HSPCs in pig BM. In utero transplantation of human HSPCs into a preimmune pig fetus is useful to establish a pig reproducing human hematopoiesis.

Mixed bone marrow or mixed stem cell transplantation for prevention or treatment of lupus-like diseases in mice

Scientific analyses fortified by interpretations of immunodeficiency diseases as 'experiments of nature' have revealed the specific immune systems to be comprised of T cells subserving cell-mediated immunities plus B cells and plasma cells which produce and secrete antibodies. These two separate cellular systems regularly interact with each other to produce a coordinated defense which permits mammals to live within a sea of microorganisms that threaten the integrity and the survival of individuals. We have shown that bone marrow transplantation (BMT) can be used as a form of cellular engineering to construct or reconstruct the immune systems and cure otherwise fatal severe combined immunodeficiency. When severe aplastic anemia complicated the first BMT which was performed to cure a fatal severe combined immunodeficiency, a second BMT cured for the first time a complicating severe aplastic anemia. Subsequently, BMT has been used effectively to treat some 75 otherwise fatal diseases such as resistant leukemias, lymphomas, inborn errors of metabolism, and genetic anomalies of the hematopoietic development such as sickle cell anemia, thalassemia, congenital neutropenias, and many other diseases. More recently, we have employed BMT in mice both to cure and cause autoimmunities, and, together, these experiments showed that autoimmunities actually reside in the hematopoietic stem cells. We have also found that mixed BMT or mixed hematopoietic stem cell transplantation (HSCT) can be used to prevent and cure the most complex autoimmunities such as those occurring in BXSB mice and in (NZW x BXSB)F1 W/BF1 mice. Untreated, the former develop fulminating lethal glomerulonephritis plus numerous humoral autoimmunities. Mice of the (W/B)F1 strain develop autoimmune thrombocytopenic purpura, coronary vascular disease with myocardial infarction, glomerulonephritis, and numerous autoantibodies. All of these abnormalities are prevented or cured by mixed syngeneic (autoimmune) plus allogeneic (normal healthy) BMT or mixed peripheral blood HSCT. Thus, the most complex autoimmune diseases can be prevented or cured in experimental animals by mixed syngeneic plus allogeneic BMT or HSCT which produce stable mixed chimerism as a form of cellular engineering.

New strategies for BMT and organ transplantation

Bone marrow transplantation (BMT) is now one of the most powerful strategies for the treatment of hematologic disorders (leukemia, aplastic anemia, etc), congenital immunodeficiencies, metabolic disorders, and also autoimmune diseases. Using various autoimmune-prone mice, we have previously shown that conventional allogeneic (allo) BMT can be used to treat a range of autoimmune diseases. We have very recently established new strategies for BMT and organ grafts. For BMT, to minimize the contamination of BMCs with T cells from the peripheral blood, we developed, using cynomolgus monkeys, a "Perfusion Method" to replace the conventional aspiration method for collecting bone marrow cells (BMCs). We injected the BMCs collected this way directly into the bone marrow cavity of recipients that had received fractionated irradiation (intra-bone marrow [IBM] injection). This "IBM-BMT" was found to be effective in treating autoimmune diseases in radiation-sensitive and chimeric-resistant MRL/lpr mice. in addition, this strategy was found to be applicable for the transplantation of organs, such as the skin and pancreas islets in mice and rats. We believe that these strategies for BMT and organ transplantation herald a new era in transplantation.

Pancreatic islet transplantation using the nonhuman primate (rhesus) model predicts that the portal vein is superior to the celiac artery as the islet infusion site

We've established a nonhuman primate islet allotransplant model to address questions such as whether transplanting islets into the gut's arterial system would more safely and as effectively support long-term islet allograft survival compared with the traditional portal vein approach. We reasoned that islets make up <2% of pancreatic cell mass but consume an estimated 20% of arterial blood flow, suggesting an advantage for the arterial site. Access to the arterial system is also easier and safer than the portal system. Pancreatectomized rhesus macaques were transplanted with allogeneic islets infused into either the portal vein (n = 6) or the celiac artery (n = 4). To prevent rejection, primates were given daclizumab, tacrolimus, and rapamycin. In five of six portal vein experiments, animals achieved normoglycemia without exogenous insulin. In contrast, none of the animals given intra-arterial islets showed even transient insulin independence (P = 0.048). Two of the latter animals received a second islet transplant, this time to the portal system, and both achieved insulin independence. Thus, intraportal islet transplantation under conventional immunosuppression is feasible in primates and can result in long-term insulin independence when adequate immunosuppression is maintained. Arterial islet injection, however, does not appear to be a viable islet transplantation technique.

Allogeneic chimerism established with a mixture of low dose bone marrow cells and splenocytes in sublethally irradiated mice

BACKGROUND

Allogeneic chimerism has been established in graft-accepting recipients and the donor cells in the host may act in a major way to facilitate the induction of tolerance. In this study, we examined the effects of allogeneic chimerism after injecting donor bone marrow cells (BMCs) mixed with splenocytes (SPLCs) to the sublethally conditioned recipients.

METHODS

In BALB/c(H-2(d)) to B6(H-2(b)) combination, B6 recipients were irradiated at 7.5 Gy and were injected a mixture of donor BMCs and SPLCs intravenously. On day 90 after injection, the degree of chimerism in peripheral blood lymphocytes (PBL) and in the splenocytes was checked by flow cytometry.

RESULTS

In groups which were injected varying BMCs, when > 45 x 10(6) BMCs were injected into B6, a large percentage of donor cells were detected in PBL and in the spleen. In contrast, when < 30 x 10(6) BMCs were injected into B6, only a small percentage of donor cells were detected. In the groups which were injected 3 x 10(6) BMCs with varying SPLCs, when > 10 x 10(6) SPLCs were added, a large percentage of donor cells were detected in PBL and SPLCs, but a small percentage of donor cells were detected with the addition of < 3 x 10(6) SPLCs. A high percentage of chimeric mice showed donor specific tolerance in vitro, mixed lymphocyte responses, and in vivo, skin grafting. In contrast, only a small percentage of chimeric mice showed no donor specific tolerance by skin grafting.

CONCLUSION

These findings suggested that even a low dose of BMCs can establish a state of allogeneic chimerism and donor specific tolerance if combined with SPLCs.

Efficacy of donor splenocytes mixed with bone marrow cells for induction of tolerance in sublethally irradiated mice

BACKGROUND

High dose of bone marrow cells (BMCs) has been reported to be essential to establish donor-specific tolerance. In clinical settings, a large quantity of BMCs is very difficult to be obtained. Our previous report demonstrated that even a low dose of BMCs could establish donor-specific tolerance if mixed with splenocytes (SPLCs). In the present study, various components of SPLCs were purified or removed and were investigated their contribution for enhancement of bone marrow engraftment leading to donor-specific tolerance in sublethally irradiated mice.

METHODS

Sublethally irradiated C57BL/6 recipient mice were intravenously injected 3 x 10(6) BMCs mixed with various components and various numbers of SPLCs harvested from BALB/c donor mice. One week after injection, skin grafting was performed. The degree of chimerism in peripheral blood lymphocytes (PBLs) and in SPLCs was analyzed by FACS 3 months after transplantation.

RESULTS

Recipients receiving 3 X 106 BMCs mixed with 10 x 10(6) T cell-enriched SPLCs established chimerism. Recipients receiving BMCs mixed with macrophage-depleted SPLCs also showed chimeirism and donor-specific tolerance. B cell-enriched SPLCs did not help small dose of BMCs to establish chimerism. Irradiated SPLCs were not effective to induce tolerance even with additional infusion to recipients.

CONCLUSIONS

Active effects of splenic T cells were more important to help engraftment of small dose of BMCs than B cells, but the interaction between T and B cells might play some roles to enhance BMC engraftment. Splenic macrophages or dendritic cells might have some adverse effects against tolerance induction. Fatal graft-versus-host disease (GVHD) might be avoided by depleting adherent cells from SPLCs, so macrophages or dendritic cells were also considered as key components to induce donor-specific tolerance and prevent GVHD in this model.

Administration of an antigen at a high dose generates regulatory CD4+ T cells expressing CD95 ligand and secreting IL-4 in the liver

Ags administered orally at a high dose are absorbed in immunogenic forms and perfuse the liver, which raises a question regarding the relevance of hepatic lymphocyte activation to the systemic hyporesponsiveness against the ingested Ag. Oral administration of 100 mg of OVA to the mice led to massive cell death of OVA-specific (KJ1-26+)CD4+ T cells by Fas-Fas ligand (FasL)-mediated apoptosis in the liver, which was associated with the emergence of hepatic KJ1-26+CD4+ T cells expressing FasL. Hepatic CD4+ T cells in OVA-fed mice secreted large amounts of IL-4, IL-10, and TGF-beta(1) upon restimulation in vitro and inhibited T cell proliferation. Adoptive transfer of these hepatic CD4+ T cells to naive mice and subsequent antigenic challenge led to suppression of T cell proliferation as well as IgG Ab responses to OVA; this effect was mostly abrogated by a blocking Ab to FasL. i.p. administration of an Ag at a high dose also generated hepatic CD4+FasL+ T cells with similar cytokine profile as T cells activated by oral administration of Ags at a high dose. Finally, we did not see an increase in FasL+ cells in the hepatic CD4+Vbeta8+ T cell subset of MRL/lpr/lpr mice given staphylococcal enterotoxin B, indicating the requirement for Fas-mediated signals. These hepatic CD4+FasL+ regulatory cells may explain the tolerogenic property of the liver and play roles in systemic hyporesponsiveness induced by an Ag administered at a high dose.

Treatment of streptozotocin-induced diabetes mellitus by transplantation of islet cells plus bone marrow cells via portal vein in rats

BACKGROUND

We have established a new method for the transplantation of allogeneic pancreatic islets (PIs) using sublethal irradiation (9 Gy) plus simultaneous transplantation of PIs and bone marrow cells (BMCs) via the portal vein (PV) followed by intravenous (i.v.) injection of donor BMCs (9 Gy + PV + i.v.).

METHODS

Approximately 600 PIs of Brown Norway (BN: RT1An, RT1Bn) rats were transplanted into the liver of streptozotocin-induced diabetic Fischer 344 (F344: RT1Al, RT1Bl) rats via the PV. BMCs (3x108) of BN rats were injected via the PV or i.v. into the recipients simultaneously. In some groups, additional i.v. injections of BMCs from BN rats were given 5 days after the PI transplantation.

RESULTS

All the recipients (10 of 10) in the 9 Gy + PV + i.v. group showed normoglycemia for more than 1 year, whereas PIs were rejected within 30 days after transplantation in the group of 9 Gy + i.v. + i.v.

CONCLUSIONS

These results suggest that simultaneous transplantation of PIs and BMCs via the PV is effective in inducing persistent tolerance.

New approaches to immunosuppression in liver transplantation

With the continued improvements in outcome following liver transplantation, the drawbacks associated with conventional immunosuppression regimens become increasingly apparent. Although up to 70% of patients develop a histological infiltrate of the graft (acute rejection), many of these will resolve spontaneously, and chronic rejection is rare. If a robust form of allograft acceptance or tolerance can be established, then immunosuppression can be withdrawn along with all the accompanying risks. The liver is already known to be associated with downregulated immune responses; the mechanism for this is unclear, but may be related to a number of mechanisms known to be involved in peripheral tolerance. There are many strategies being studied for achieving allograft tolerance, including the use of modern immunosuppressants, antibodies that target key molecules in the immune response, and recruitment of leukocytes to allografts. In the interim, it is necessary to look for safe protocols that allow trials of tolerance strategies without putting patients at increased risk.

A new method for tolerance induction: busulfan administration followed by intravenous injection of neuraminidase-treated donor bone marrow

The portal venous (p.v.) administration of foreign cells induces donor-specific tolerance. Recently, we have demonstrated that the p.v. administration of donor cells elicits donor-specific tolerance across major histocompatibility complex barriers. In the present study, utilizing the intrahepatic tolerance-inducing system, we have established a new method for organ transplantation using both busulfan ([Bu] to provide a sufficient "space" for the donor hematopoietic cells to expand in the recipient) and neuraminidase ([Neu] to enhance the trapping of i.v.-injected cells in the liver). Radiolabeled bone marrow cells (BMCs) were found to exclusively accumulate in the livers of the recipients as a result of the Neu treatment. Furthermore, hematopoietic progenitors (forming hematopoietic foci) in the accumulated BMCs were retained in the recipient livers for at least 18 days. C57BL/6 (B6) mice that had been transplanted with skins of BALB/c mice immediately after the injection of BALB/c BMCs showed a 90% skin graft survival rate over 400 days as a result of using the combination of injecting 50 mg/kg Bu into the B6 mice and treatment of the BALB/c BMCs with 0.25 U/ml Neu (50 Bu + 0.25 Neu). However, the survival rate significantly decreased when either the Bu or Neu treatment was omitted. In tolerant recipients, microchimerism was observed in the various hematolymphoid organs. T cells collected from the tolerant recipients suppressed proliferative responses to the donor-alloantigens but enhanced the production of Th2 and Th3 cytokines. These findings suggest that the enhanced retention of donor BMCs in the recipient livers as a result of the Bu and Neu treatments efficiently induces tolerance induction. Therefore, this "single-day protocol" would be of great advantage for human organ transplantation.

Thymic microchimerism correlates with the outcome of tolerance-inducing protocols for solid organ transplantation

This study found that pretransplant infusion of donor peripheral blood leukocytes, either total leukocytes (peripheral blood leukocytes) or peripheral blood mononuclear cells (PBMC), under appropriate immunomodulating conditions was more effective than donor bone marrow (BM) in prolonging the survival of rats that received kidney grafts. A higher percentage of MHCII(+) cells was found in donor PBMC than in BM cells, and depletion of MHCII(+) cells from donor PBMC abolished their tolerogenic potential. By the analysis of microchimerism in rats infused with donor cells and killed at different time points thereafter, the better tolerogenic potential of leukocyte infusion related to a higher capability of these cells to engraft the recipient thymus. PCR analysis on OX6-immunopurified cells revealed the presence of donor MHCII(+) cells in the thymus of these animals. The role of intrathymic microchimerism was reinforced by findings that thymectomy at the time of transplant prevented tolerance induction by donor leukocytes. Donor DNA was found in the thymus of most long-term graft animals that survived, but in none of those that rejected their grafts. The presence of intrathymic microchimerism correlated with graft survival, and microchimerism in other tissues was irrelevant. PCR analysis of DNA from thymic cell subpopulations revealed the presence of donor MHCII(+) cells in the thymus of long-term surviving animals. Thus, in rats, donor leukocyte infusion is better than donor BM for inducing graft tolerance, defined by long-term graft survival, donor-specific T cell hyporesponsiveness, and reduced interferon gamma production. This effect appears to occur through migration of donor MHCII(+) cells in the host thymus.

New method for thyroid transplantation across major histocompatibility complex barriers using allogeneic bone marrow transplantation

BACKGROUND

It has been shown that allogeneic bone marrow transplantation (BMT) after lethal irradiation elicits donor-specific tolerance for organ or tissue transplantation across major histocompatibility complex (MHC) barriers. Recently, we have demonstrated that the portal venous (p.v.) administration of donor bone marrow cells (BMCs) elicits donor-specific tolerance across MHC barriers by only two administrations of an immunosuppressant (CsA or FK-506). In our study, using the central and intrahepatic tolerance-inducing system, we have established a new method for thyroid transplantation with BMT that would be more applicable to humans.

METHODS

In addition to sublethal (6-5 Gy) irradiation, recipient B6 (H-2b) mice received injections i.p. with the myeloablative drug busulfan (BU) on day -2 to provide a sufficient "space" for the donor hematopoietic cells to expand in the recipients. To induce the intrahepatic tolerance, donor BALB/c (H-2d) BMCs were treated with neuraminidase (Neu), which enhances the trapping of i.v. injected BMCs in the liver. After the injection of Neu-treated BMCs, the thyroid organs from the BALB/c mice were engrafted under the renal capsules.

RESULTS

A 90% graft survival rate was obtained over 100 days by a combination of BU administration, 6 Gy irradiation, and i.v. injection of Neu-treated BMCs [BU+6 Gy+(Neu) i.v.], and a 70% graft survival rate was obtained by [BU+5 Gy+(Neu) i.v.]. However, the graft survival rate significantly decreased when either the BU or Neu treatment was omitted. T cells collected from the tolerant recipients suppressed the proliferative responses to donor alloantigens.

CONCLUSIONS

Using both BU and Neu treatments, we have succeeded in inducing long-term tolerance and preventing the rejection of thyroid allografts by the single-day protocol.

Successful allogeneic bone marrow transplantation. Crucial roles of stromal cells in prevention of graft rejection

We have previously found that a major histocompatibility complex (MHC) restriction exists between pluripotent hemopoietic stem cells (P-HSCs) and stromal cells. Based on this finding, we have recently found using chimerism-resistant mouse combinations that successful allogeneic (allo) BMT can be executed by recruiting donor bone marrow stromal cells. The strategies include donor bone grafts under the skin, injection of whole bone marrow cells (BMCs) including stromal cells via the portal vein (PV), and injection of whole BMCs directly into the bone marrow cavity (intra-bone marrow [IBM] injection). In this paper, we show how stromal cells play crucial roles in overcoming chimerism-resistant allo BMT.

Transplantation tolerance induced by mixed chimerism

Although short- and long-term results after organ transplantation have improved considerably in recent years, morbidity and mortality rates in graft recipients remain high. The induction of lifelong donor-specific tolerance would dramatically improve outcome after organ transplantation. Although many tolerance protocols have been successful in rodent studies, most of these approaches have failed when attempted in large animals or humans. Robust tolerance, in contrast, has been demonstrated with mixed chimerism regimens not only in rodents but also in large animal models, including non-human primates. Furthermore, mixed chimerism protocols have been developed that would be feasible in cadaveric, and thus in thoracic, transplantation. The induction of mixed hematopoietic chimerism is therefore an attractive experimental approach for development of clinical tolerance protocols. One of the obstacles to widespread clinical application of this concept is the remaining toxicity of the host conditioning. Recent advances, however, have led to substantially milder protocols that could become clinically acceptable in the foreseeable future. This article provides a short overview of the basic mechanisms by which immunologic tolerance may be induced, describes the concept of mixed chimerism as a promising approach for clinical tolerance induction, and reviews recent progress in developing clinically feasible mixed chimerism protocols.

Crucial role of donor-derived stromal cells in successful treatment for intractable autoimmune diseases in mrl/lpr mice by bmt via portal vein

We have recently established a new bone marrow transplantation (BMT) method for the treatment of intractable autoimmune diseases in MRL/lpr mice; the method consists of fractionated irradiation (5.5 Gy x 2), followed by BMT of whole bone marrow cells (BMCs) from allogeneic C57BL/6 mice via the portal vein (abbreviated as 5.5 Gy x 2 + PV). In the present study, we investigate the mechanisms underlying the early engraftment of donor-derived cells in MRL/lpr mice by this method. In the mice treated with this method, the number of donor-derived cells possessing the mature lineage (Lin) markers rapidly increased in the BM, spleen, and liver; almost 100% were donor-derived cells by 14 days after the treatment. The number of donor-derived hemopoietic progenitor cells (defined as c-kit(+)/Lin(-) cells) increased in the BMCs, hepatic mononuclear cells, and especially spleen cells by 14 days after the treatment. Simultaneously, hemopoietic foci adjoining donor-derived stromal cells were observed in the liver when injected via the PV, but not via the peripheral vein (i.v.). When adherent cell-depleted BMCs were injected via the PV, recipients showed a marked reduction in the survival rate. However, when mice were transplanted with adherent cell-depleted BMCs with cultured stromal cells, all the recipients survived. These findings suggest that not only donor hematopoietic stem cells (HSCs) but also donor stromal cells administered via the PV were trapped in the liver, resulting in the early engraftment of donor HSCs in cooperation with donor-derived stromal cells. This new strategy to facilitate the early recovery of hemopoiesis would therefore be of great advantage in human application.

Successful allogeneic bone marrow transplantation (BMT) by injection of bone marrow cells via portal vein: stromal cells as BMT-facilitating cells

We examined the importance of the coadministration of bone marrow (BM) stromal cells with BM cells via the portal vein. A significant increase in the number of day-14 colony-forming unit-spleen (CFU-S) was observed in the recipient mice injected with hemopoietic stem cells (HSCs) along with donor BM stromal cells obtained after three to four weeks of culture. Histological examination revealed that hematopoietic colonies composed of both donor hemopoietic cells and stromal cells coexist in the liver of these mice. However, when donor HSCs plus BM stromal cells were administered i.v., neither the stimulatory effects on CFU-S formation nor the hemopoietic colonies in the recipient liver were observed. These findings suggest that the interaction of HSCs with stromal cells in the liver is the first crucial step for successful engraftment of allogeneic HSCs. It is likely that donor stromal cells and HSCs trapped in the liver migrate into the recipient BM and spleen, where they form CFU-BM and CFU-S, respectively.

A novel strategy for organ allografts using sublethal (7 Gy) irradiation followed by injection of donor bone marrow cells via portal vein

A new strategy for organ allografts that does not require recourse to immunosuppressants is established in mice. The strategy includes sublethal (7 Gy) irradiation followed by the injection of donor bone marrow cells (BMCs) via the portal vein (P.V.) and organ allografts 1 day after irradiation. Irradiation doses (< or =7 Gy) are found to allow the recipients to survive without the need to reconstitute the BMCs, as the recipient hematolymphoid cells can gradually recover. One hundred percent of recipients irradiated with 7 Gy followed by either P.V. or i.v. injection of donor BMCs accept organ allografts (the skin, pancreas, and adrenal glands) for more than 1 year. However, organ allograft survival rates decrease when irradiation doses are reduced; the skin graft survival rate of mice treated with 6.5 Gy and P.V. injection of BMCs is 79%, whereas that of mice treated with 6.5 Gy and i.v. injection is 50%, indicating that the P.V. injection of BMCs induces persistent tolerance more effectively than the i.v. injection. H-2 typing reveals that almost all the hematolymphoid cells (>98%) in the peripheral blood and hematolymphoid organs are donor-derived even 1 year after the treatment (7 Gy and P.V.). The T cells are tolerant to both donor-type and host-type MHC determinants. The major mechanism underlying the persistent tolerance induced by this strategy seems to be because of clonal deletion. This simple and safe strategy would be of great advantage for human organ transplantation.

Treatment of autoimmune diseases by hematopoietic stem cell transplantation

Remarkable advances have been made in bone marrow transplantation (BMT), which now has become a powerful strategy for the treatment of leukemia, aplastic anemia, congenital immunodeficiency disorders, and autoimmune diseases. Using various animal models, allogeneic BMT has been found to be useful in the treatment of autoimmune diseases. In MRL/lpr mice, which are radiosensitive (<8.5 Gy) and are an animal model for autoimmune disorders, conventional BMT resulted in only transient effects; the manifestations of the autoimmune diseases recurred 3 months after BMT. However, the combination of BMT plus bone grafts (to recruit donor stromal cells) was capable of preventing the recurrence of autoimmune diseases in MRL/lpr mice. This strategy was found to be ineffective in the treatment of MRL/lpr mice that had developed autoimmune diseases, because these mice were more sensitive to the effects of radiation after the onset of lupus nephritis due to uremic enterocolitis. We have recently discovered a safer strategy for treatment of autoimmune diseases, which includes fractionated irradiation (5.5 Gy x 2) (day -1) followed by portal venous injection (day 0) plus intravenous injection (day 5) of donor unfractionated bone marrow cells. We successfully treated autoimmune diseases in MRL/lpr mice using this strategy; 100% of MRL/lpr mice treated in this fashion survive >1 year after treatment. We identified the mechanisms underlying the components of this approach and have found that stromal cells play a crucial role in successful BMT. In this review, the conditions essential for successful allogeneic BMT are discussed.

Intra-bone marrow injection of allogeneic bone marrow cells: a powerful new strategy for treatment of intractable autoimmune diseases in MRL/lpr mice

Intractable autoimmune diseases in chimeric resistant MRL/lpr mice were treated by a new bone marrow transplantation (BMT) method consisting of fractionated irradiation, 5.5 Gy x 2, followed by intra-bone marrow (IBM) injection of whole bone marrow cells (BMCs) from allogeneic normal C57BL/6 (B6) mice (5.5 Gy x 2 + IBM). In MRL/lpr mice treated with this method, the number of donor-derived cells in the bone marrow, spleen, and liver rapidly increased (almost 100% donor-derived cells by 14 days after the treatment), and the number of donor-derived hemopoietic progenitor cells concomitantly increased. Furthermore, donor-derived stromal cells were clearly detected in the cultured bone pieces from MRL/lpr mice treated with 5.5 Gy x 2 + IBM. All the recipients thus treated survived more than 1 year (> 60 weeks after birth) and remained free from autoimmune diseases. Autoantibodies decreased to almost normal levels, and abnormal T cells (Thy1.2(+)/B220(+)/CD4(-)/CD8(-)) disappeared. Hematolymphoid cells were reconstituted with donor-derived cells, and newly developed T cells were tolerant to both donor (B6)-type and host (MRL/lpr)-type major histocompatibility complex determinants. Successful cooperation was achieved among T cells, B cells, and antigen-presenting cells when evaluated by in vitro antisheep red blood cell responses. These findings clearly indicate that this new strategy (IBM-BMT) creates the appropriate hemopoietic environment for the early recovery of hemopoiesis and donor cell engraftment, resulting in the complete amelioration of intractable autoimmune diseases in chimeric resistant MRL/lpr mice without recourse to immunosuppressants. This strategy would therefore be suitable for human therapy.

Implantation of xenografts into parkinsonian rat brain after portal venous administration of xenogeneic donor spleen cells

Object. The purpose of the present study was to examine the effect of pretransplantation portal venous immunization with ultraviolet B (UVB)—treated donor spleen cells on neural xenograft transplantation.

Methods. Cells from a murine catecholaminergic cell line derived from the B6/D2 F1 mouse, CATH.a, were used as a xenograft. Thirty hemiparkinsonian rats were divided into three different treatment groups. Group 1 received saline in the dopamine-denervated striatum; Group 2 received xenograft cells; and Group 3 received portal venous administration of UVB-irradiated B6/D2 F1 splenocytes 7 days before receiving xenograft cells. Xenograft function was determined by reviewing apomorphine-induced rotation at 2-week intervals, and xenograft survival was examined at 4 and 12 weeks after transplantation by immunohistochemical staining for murine tyrosine hydroxylase (THase). Rotational behavior was improved in both xenograft-transplanted groups (Groups 2 and 3); however, the animals in Group 3 displayed a significantly reduced rotational behavior compared with Group 2. In Group 2, many inflammatory cells and a few THase-positive cells were found at the graft sites 4 weeks after transplantation. In Group 3, however, a large number of THase-positive cells were found with few inflammatory cells. The THase-positive cells disappeared in the Group 2 rats at 12 weeks, but remained in Group 3 animals. In Group 3 rats proliferation of spleen cells in a mixed lymphocyte reaction was suppressed in a donor-specific fashion.

Conclusions. This work demonstrates improved neural xenograft survival and function by pretransplantation portal venous immunization with UVB-irradiated xenogeneic donor splenocytes. On the basis of these findings, the authors suggest the possibility of creating donor-specific immunological tolerance in the brain by administration of xenogeneic donor lymphocytes via the portal vein.

Immunity or tolerance: opposite outcomes of microchimerism from skin grafts

Solid organ transplants contain small numbers of leukocytes that can migrate into the host and establish long-lasting microchimerism. Although such microchimerism is often associated with graft acceptance and tolerance, it has been difficult to demonstrate a true causal link. Using skin from mutant mice deficient for leukocyte subsets, we found that donor T-cell chimerism is a 'double-edged sword' that can result in very different outcomes depending on the host's immunological maturity and the antigenic disparities involved. In immunologically mature hosts, chimerism resulted in immunity and stronger graft rejection. In immature hosts, it resulted in tolerance to the chimeric T cells, but not to graft antigens not expressed by the chimeric cells. Clinical efforts aimed at augmenting chimerism to induce tolerance must take into account the maturation state of host T cells, the type of chimerism produced by each organ and the antigenic disparities involved, lest the result be increased rejection rather than tolerance.

Long-term (>1 year) analyses of chimerism and tolerance in mixed allogeneic chimeric mice using normal mouse combinations

We examined the induction of tolerance using pancreas allografts over the long term (>1 year) in mice for the human application of mixed allogeneic bone marrow transplantation (BMT). T cell-depleted BM cells (BMCs) of C57BL/6 (B6) and C3H/He (C3H) mice were transplanted at various ratios into lethally irradiated B6 mice. The percentages of C3H cells in the chimeric mice gradually decreased, finally declining to only a small percentage, except when the ratio of donor to recipient BMCs was 100:1. However, despite the marked decreases in C3H-type cells, all the pancreas allografts of C3H mice were accepted when more than 1% C3H cells were detected in the peripheral blood. To examine the relationships between percentages of transplanted donor cells and acceptance of pancreas allografts, various percentages of donor and recipient BMCs (5% to 30%) were transplanted. It was found that more than 10% donor cells were necessary for the pancreas allografts to be accepted. In vitro assays for mixed lymphocyte reaction and generation of cytotoxic T-lymphocytes revealed that spleen cells in chimeric mice accepting pancreas allografts are tolerant to both host-type and donor-type major histocompatibility complex (MHC) determinants, but show a vigorous responsiveness to third-party MHC determinants. Since donor-type hemopoietic stem cells (HSCs) were detected in the BM and the liver of the chimeric mice, donor-derived HSCs and donor-derived hematolymphoid cells are responsible for the induction of tolerance. It should be noted that the percentage of donor-type HSCs is higher in the liver (6.2%) than in the BM (0.9%).

New strategies for allogeneic bone marrow transplantation and organ allografts

In humans, the success rate of bone marrow transplantation (BMT) across major histocompatibility complex (MHC) barriers is not high due to: (1) graft-versus-host reaction (GvHR); (2) graft rejection, and (3) incomplete T cell recovery. In mice, GvHR can be prevented if T cell- depleted bone marrow cells (BMCs; <2% T cells) are used. Graft rejection can be prevented by either bone grafts (to recruit donor-derived stromal cells) or the injection of donor BMCs via the portal vein (p.v; to induce donor-specific tolerance). T cell functions are recovered by BMT plus bone grafts if the thymic functions of recipients are not completely lost. After the complete loss of thymic functions (due to aging), BMT plus embryonal thymus grafts should be carried out.Recently, we have found that persistent donor-specific tolerance can be induced if allogeneic hemopoietic stem cells are injected via the p.v. Based on these findings, we have established new strategies for organ allografts. Without irradiation, donor BMCs should be injected from the p.v. injection on day 0 plus i.v. injection on day 5, and an immunosuppressant (CsA or FK506) should be used on days 2 and 5. Without using immunosuppressants, sublethal irradiation (7 Gy) followed by skin allografts plus allogeneic BMC injection via the p.v. should be carried out. This leads to a 100% acceptance of skin and pancreas allografts for more than 300 days. The recipient mice show mixed allogeneic chimerism, and spleen cells from the recipients show tolerance to both donor-type and host-type MHC determinants in the assays for mixed lymphocyte reaction and generation of cytotoxic T lymphocytes. We have confirmed that these strategies are applicable to other animals such as pigs and rats. We therefore believe that they will become viable and valuable strategies for human organ allografts.

Co-transplantation of donor-derived hepatocytes induces long-term tolerance to cardiac allografts in a rat model

BACKGROUND

Liver allografts transplanted between MHC-disparate mice, rats, and swine are spontaneously accepted in most strain combinations without requirement for immunosuppression. The underlying mechanism has, however, remained elusive. Here, we demonstrate that co-transplantation of donor-derived hepatocytes protect Lewis (RT1.A1) cardiac allografts from acute and chronic rejection in DA (RT1.Aa) recipients indefinitely.

METHODS

Livers of donor Lewis rats were harvested and the hepatocytes separated from hepatic leukocytes by collagenase digestion and gradient separation. DA recipient animals were transplanted Lewis cardiac allografts and simultaneously intraportally infused either Lewis-derived hepatocytes or hepatic leukocytes. Recipient animals were either not further treated or received a single dose of 15 mg/kg cyclosporine.

RESULTS

Donor hepatocytes alone significantly protected syngeneic cardiac allografts from rejection, whereas hepatic leukocytes failed to influence graft survival. In combination with cyclosporine, recipient cardiac allografts were indefinitely protected from rejection. Graft-infiltrating cells in tolerant animals presented as clusters of CD4+ T cells and stained mostly positive for interleukin-4, whereas graft-infiltrating cells in rejected allografts were predominantly positive for interferon-gamma. Adoptive transfer of splenocytes derived from tolerant animals protected Lewis cardiac allografts from rejection in DA recipients without immunosuppression. In contrast, hepatic leukocytes protected only 50% of the allografts from rejection.

CONCLUSION

We propose that donor hepatocytes induce permanent engraftment of syngeneic allografts by establishing a Th2 type alloresponse that is transferable to new graft recipients. The results of this study demonstrate that liver parenchymal cells significantly mediate spontaneously liver-induced tolerance.

Prolonged allograft survival through conditional and specific ablation of alloreactive T cells expressing a suicide gene

BACKGROUND

Control of antidonor activated T cells involved in allograft rejection while preserving immunocompetence is a challenging goal in transplantation. Engineered T cells expressing a viral thymidine kinase (TK) suicide gene metabolize the nontoxic prodrug ganciclovir (GCV) into a metabolite toxic only to dividing cells. We evaluated this suicide gene strategy for inducing transplantation tolerance in mice.

METHODS

Transgenic mice expressing TK in mature T cells were analyzed for (i) specific T-cell depletion under GCV treatment upon various stimulations; (ii) outcome of allogeneic nonvascularized skin or heart allografts under a short 14-day GCV treatment initiated at the time of transplantation; and (iii) the capacities of T cells from such allotransplanted mice to proliferate in mixed lymphocyte reactions and to induce graft-versus-host disease in irradiated recipients with the genetic background of the donor allograft.

RESULTS

Upon in vitro or in vivo GCV treatment, only activated dividing TK T cells but not B cells were efficiently depleted. Acute rejection of allogeneic grafts was prevented and a significant prolongation of graft survival was obtained, although associated with signs of chronic rejection. Prolonged skin graft survival correlated with decreased in vitro and in vivo T-cell reactivities against donor alloantigens, whereas overall immunocompetence was preserved.

CONCLUSIONS

Efficient and specific depletion of alloreactive TK T cells can be achieved by administrating GCV. These results open new perspectives for the control of allogeneic graft rejection using suicide gene therapy.

Xenotransplantation: is the risk of viral infection as great as we thought?

Two major hurdles remain before xenotransplantation can enter the clinic. The first is the more technical issue of being able to overcome the human immune response that leads to rejection of transplanted organs/cells from other species. The second, reviewed here, concerns the potential risk of inadvertent transfer of animal viruses present in the xenotransplant that are able to infect the human recipient. The threat from viruses is a particularly contentious topic because it poses a risk not only to those individuals who receive xenotransplants, but also to healthy individuals who come into contact, either directly or indirectly, with the xenotransplant recipient. In this review, we describe some of the virus types, in addition to the much discussed porcine endogenous retroviruses that might cross the species barrier, and assess the risk of such viruses causing disease in human hosts.