The Mandible Ameliorates Facial Allograft Rejection and Is Associated with the Development of Regulatory T Cells and Mixed Chimerism

Vascularized composite allografts contain various tissue components and possess relative antigenicity, eliciting different degrees of alloimmune responses. To investigate the strategies for achieving facial allograft tolerance, we established a mouse hemiface transplant model, including the skin, muscle, mandible, mucosa, and vessels. However, the immunomodulatory effects of the mandible on facial allografts remain unclear. To understand the effects of the mandible on facial allograft survival, we compared the diversities of different facial allograft-elicited alloimmunity between a facial osteomyocutaneous allograft (OMC), including skin, muscle, oral mucosa, and vessels, and especially the mandible, and a myocutaneous allograft (MC) including the skin, muscle, oral mucosa, and vessels, but not the mandible. The different facial allografts of a BALB/c donor were transplanted into a heterotopic neck defect on fully major histocompatibility complex-mismatched C57BL/6 mice. The allogeneic OMC (Allo-OMC) group exhibited significant prolongation of facial allograft survival compared to the allogeneic MC group, both in the presence and absence of FK506 immunosuppressive drugs. With the use of FK506 monotherapy (2 mg/kg) for 21 days, the allo-OMC group, including the mandible, showed prolongation of facial allograft survival of up to 65 days, whereas the myocutaneous allograft, without the mandible, only survived for 34 days. The Allo-OMC group also displayed decreased lymphocyte infiltration into the facial allograft. Both groups showed similar percentages of B cells, T cells, natural killer cells, macrophages, and dendritic cells in the blood, spleen, and lymph nodes. However, a decrease in pro-inflammatory T helper 1 cells and an increase in anti-inflammatory regulatory T cells were observed in the blood and lymph nodes of the Allo-OMC group. Significantly increased percentages of donor immune cells were also observed in three lymphoid organs of the Allo-OMC group, suggesting mixed chimerism induction. These results indicated that the mandible has the potential to induce anti-inflammatory effects and mixed chimerism for prolonging facial allograft survival. The immunomodulatory understanding of the mandible could contribute to reducing the use of immunosuppressive regimens in clinical face allotransplantation including the mandible.

Use of Thymidine Kinase Recombinant Adenovirus and Ganciclovir Mediated Mouse Liver Preconditioning for Hepatocyte Xenotransplantation

Hepatocyte transplantation is the best approach to maintain and propagate differentiated hepatocytes from different species. Host liver has to be adapted for transplanted hepatocytes productive engraftment and proliferation being required a chronic liver injury to eliminate host hepatocytes and provide a proliferative advantage to the transplanted hepatocytes. Most valuable mouse models for xenograft hepatocyte transplantation are based on genetically modified animals to cause a chronic liver damage and to limit host hepatocyte regeneration potential. We present a methodology that generates a chronic liver damage and can be applied to any host mouse strain and animal species based on the inoculation of a recombinant adenovirus to express herpes simplex thymidine kinase in host hepatocytes sensitizing them to ganciclovir treatment. This causes a prolonged liver damage that allows hepatocyte transplantation and generation of regenerative nodules in recipient mouse liver integrated by transplanted cells and host sinusoidal. Obtained chimeric animals maintain functional chimeric nodules for several weeks, ready to be used in any study.

Reduced-intensity conditioning and HLA-matched haemopoietic stem-cell transplantation in patients with chronic granulomatous disease: a prospective multicentre study

BACKGROUND

In chronic granulomatous disease allogeneic haemopoietic stem-cell transplantation (HSCT) in adolescents and young adults and patients with high-risk disease is complicated by graft-failure, graft-versus-host disease (GVHD), and transplant-related mortality. We examined the effect of a reduced-intensity conditioning regimen designed to enhance myeloid engraftment and reduce organ toxicity in these patients.

METHODS

This prospective study was done at 16 centres in ten countries worldwide. Patients aged 0-40 years with chronic granulomatous disease were assessed and enrolled at the discretion of individual centres. Reduced-intensity conditioning consisted of high-dose fludarabine (30 mg/m(2) [infants <9 kg 1·2 mg/kg]; one dose per day on days -8 to -3), serotherapy (anti-thymocyte globulin [10 mg/kg, one dose per day on days -4 to -1; or thymoglobuline 2·5 mg/kg, one dose per day on days -5 to -3]; or low-dose alemtuzumab [<1 mg/kg on days -8 to -6]), and low-dose (50-72% of myeloablative dose) or targeted busulfan administration (recommended cumulative area under the curve: 45-65 mg/L × h). Busulfan was administered mainly intravenously and exceptionally orally from days -5 to -3. Intravenous busulfan was dosed according to weight-based recommendations and was administered in most centres (ten) twice daily over 4 h. Unmanipulated bone marrow or peripheral blood stem cells from HLA-matched related-donors or HLA-9/10 or HLA-10/10 matched unrelated-donors were infused. The primary endpoints were overall survival and event-free survival (EFS), probabilities of overall survival and EFS at 2 years, incidence of acute and chronic GVHD, achievement of at least 90% myeloid donor chimerism, and incidence of graft failure after at least 6 months of follow-up.

FINDINGS

56 patients (median age 12·7 years; IQR 6·8-17·3) with chronic granulomatous disease were enrolled from June 15, 2003, to Dec 15, 2012. 42 patients (75%) had high-risk features (ie, intractable infections and autoinflammation), 25 (45%) were adolescents and young adults (age 14-39 years). 21 HLA-matched related-donor and 35 HLA-matched unrelated-donor transplants were done. Median time to engraftment was 19 days (IQR 16-22) for neutrophils and 21 days (IQR 16-25) for platelets. At median follow-up of 21 months (IQR 13-35) overall survival was 93% (52 of 56) and EFS was 89% (50 of 56). The 2-year probability of overall survival was 96% (95% CI 86·46-99·09) and of EFS was 91% (79·78-96·17). Graft-failure occurred in 5% (three of 56) of patients. The cumulative incidence of acute GVHD of grade III-IV was 4% (two of 56) and of chronic graft-versus-host disease was 7% (four of 56). Stable (≥90%) myeloid donor chimerism was documented in 52 (93%) surviving patients.

INTERPRETATION

This reduced-intensity conditioning regimen is safe and efficacious in high-risk patients with chronic granulomatous disease.

FUNDING

None.

Involvement of bone marrow stem cells in periodontal wound healing

OBJECTS

To test the hypothesis whether bone marrow stem cells (BMSCs) could migrate into the periodontium as the precursor available for the repair of tissue injury.

METHODS

A chimeric mouse model was established by transplanting BMSCs derived from red fluorescent protein mouse into irradiated BALB/c mice. Subsequently, a periodontal defect was created beside the maxillary first molar and filled with ceramic bovine bone. Finally, the chimeric mice were divided into three groups and were observed 3, 14 and 28 days later respectively. The involvement of BMSCs in periodontal defects was analysed using an in vivo imaging system and immunohistochemical staining of CD45, CD105 and CD31. Cell surface marker expression in injured tissue was also compared with that in normal tissue.

RESULTS

Increasing numbers of BMSCs migrated into the periodontal defect with time. The distribution was initially limited to ceramic bovine bone and then around blood vessels and near alveolar bone. Furthermore, expression of CD105 and CD31 was much higher in injured periodontal tissue than that in healthy periodontium, although CD45 was not expressed in either of these tissues.

CONCLUSION

BMSCs, but not haemopoietic stem cells, were involved in periodontal defect; they entered the periodontium probably via blood vessels.

Testicular and ovarian gonocytes from 20-day incubated chicken embryos contribute to germline lineage after transfer into bloodstream of recipient embryos

The present study was conducted to elucidate whether testicular and ovarian gonocytes obtained from 20-day incubated chicken embryos (stage 45) have the ability to migrate to the germinal ridges and contribute to germline lineage after transfer into the bloodstream of recipient embryos. Testicular and ovarian gonocytes were first identified as relatively large cells in a population of gonadal cells. The proportions of testicular and ovarian gonocytes in the total gonadal cells were 0.94 and 0.75% respectively, recognised as chicken vasa homologue-positive cells. Then, the dissociated gonadal cells obtained from 20-day incubated embryos containing testicular or ovarian gonocytes, with or without transfection, were transferred into recipient embryos. Expression of the introduced GFP gene was observed in the gonads of 6.5-day cultured recipient embryos (stage 30) in males and females, suggesting that the transferred testicular and ovarian gonocytes have the ability to migrate to the germinal ridges and enter the gonads. Furthermore, the presence of the donor-derived DNA was detected in the gonads of 20-day cultured recipient embryos in males and females, and also in the sperm samples obtained from the hatched male putative chimaeric chickens, suggesting that the transferred testicular and ovarian gonocytes were incorporated into the germline of chimaeric embryos and chickens. It is concluded that testicular and ovarian gonocytes obtained from 20-day incubated embryos have the ability to migrate to the germinal ridges after transfer into the bloodstream of recipient embryos, enter the gonads and contribute to the germline lineage of chimaeric embryos and chickens.

Quantitative assessment of mixed chimerism in allogeneic stem cell transplant patients: a comparison of molecular genetic and cytogenetic approaches

After allogeneic stem cell transplantation, dual donor and recipient populations may be present. Donor/recipient ratio changes over time may predict clinical outcome: accurate measurement of these changes are needed. Chimerism may be measured by XY-fluorescence in situ hybridization for donor/recipient sex mismatch, or polymerase chain reaction amplification of short tandem repeat loci with donor/recipient sex match. Patients were monitored by each method. Additionally, mononuclear cells from 2 sex-mismatched individuals were mixed and analyzed using both methods. Each gave concordant estimates of patient chimerism and discriminated cell population ratios in mixed blood. We conclude that cytogenetic and molecular methods give accurate donor chimerism estimates.

Elimination of insulitis and augmentation of islet beta cell regeneration via induction of chimerism in overtly diabetic NOD mice

Type 1 diabetes in both humans and nonobese diabetic (NOD) mice results from autoreactive T cell destruction of insulin-producing beta cells. Cure of type 1 diabetes may require both reversal of autoimmunity and regeneration of beta cells. Induction of chimerism via allogeneic hematopoietic cell transplantation has been shown to reestablish tolerance in both prediabetic and diabetic NOD mice. However, it is unclear whether this therapy augments beta cell regeneration. Furthermore, this procedure usually requires total body irradiation conditioning of recipients. The toxicity of total body irradiation conditioning and potential for graft-versus-host disease (GVHD) limit the application of allogeneic hematopoietic cell transplantation for treating type 1 diabetes. Here we report that injection of donor bone marrow and CD4+ T cell-depleted spleen cells induced chimerism without causing GVHD in overtly diabetic NOD mice conditioned with anti-CD3/CD8 and that induction of chimerism in new-onset diabetic NOD mice led to elimination of insulitis, regeneration of host beta cells, and reversal of hyperglycemia. Therefore, this radiation-free GVHD preventive approach for induction of chimerism may represent a viable means for reversing type 1 diabetes.

Microchimerism and Stem Cell Transplantation in Multiple Sclerosis

Scientific advances have demonstrated that autoreactive cells are a component of the healthy immune repertoire. If we define autoimmunity as an active induction of autoreaction, the solution should be an active induction of self-tolerance, and may indicate the direction to explore the future therapies. Microchimerism (MC) refers to the presence of a limited number of nonhost cells in the body of an individual. These cells can enter via blood transfusion and organ transplantation or naturally through pregnancy. Chimeric cells engraft in the host body, develop, proliferate, and are accepted by the immune system as self. These include stem cells that enter the maternal body during fetal stages. These stem cells are also postulated to be helpful reservoirs in protecting the host body. MC has been considered a risk factor in autoimmune disease induction. However, today we know it is a natural phenomenon. MC can be considered a natural model of successful transplantation, the earliest engrafting cells being fetal mesenchymal stem cells (MSCs). MSCs have two notable features. They have an immunosuppressive quality when encountering the adoptive immune system and they display repair-inducing potential within damaged tissues. For the fetus, MC appears to be an effective factor in maternal tolerance induction toward the fetal graft and for the mother; these novel fetal cells might be useful in disease conditions occurring after pregnancy. Hematopoietic stem cell transplantation has become an accepted treatment option for both malignant and nonmalignant diseases and this unique procedure is now being investigated as a potential therapy for multiple sclerosis (MS). Due to the dichotomous properties of MSC, suppressing aggressive immune dysfunction while promoting damaged tissue repair, they may be appropriate therapy for MS.

Pre-/post-otic rhombomeric interactions control the emergence of a fetal-like respiratory rhythm in the mouse embryo

How regional patterning of the neural tube in vertebrate embryos may influence the emergence and the function of neural networks remains elusive. We have begun to address this issue in the embryonic mouse hindbrain by studying rhythmogenic properties of different neural tube segments. We have isolated pre- and post-otic hindbrain segments and spinal segments of the mouse neural tube, when they form at embryonic day (E) 9, and grafted them into the same positions in stage-matched chick hosts. Three days after grafting, in vitro recordings of the activity in the cranial nerves exiting the grafts indicate that a high frequency (HF) rhythm (order: 10 bursts/min) is generated in post-otic segments while more anterior pre-otic and more posterior spinal territories generate a low frequency (LF) rhythm (order: 1 burst/min). Comparison with homo-specific grafting of corresponding chick segments points to conservation in mouse and chick of the link between the patterning of activities and the axial origin of the hindbrain segment. This HF rhythm is reminiscent of the respiratory rhythm known to appear at E15 in mice. We also report on pre-/post-otic interactions. The pre-otic rhombomere 5 prevents the emergence of the HF rhythm at E12. Although the nature of the interaction with r5 remains obscure, we propose that ontogeny of fetal-like respiratory circuits relies on: (i) a selective developmental program enforcing HF rhythm generation, already set at E9 in post-otic segments, and (ii) trans-segmental interactions with pre-otic territories that may control the time when this rhythm appears.

Smad5 is dispensable for adult murine hematopoiesis

Smad5 is known to transduce intracellular signals from bone morphogenetic proteins (BMPs), which belong to the transforming growth factor-β (TGF-β) superfamily and are involved in the regulation of hematopoiesis. Recent findings suggest that BMP4 stimulates proliferation of human primitive hematopoietic progenitors in vitro, while early progenitors from mice deficient in Smad5 display increased self-renewal capacity in murine embryonic hematopoiesis. Here, we evaluate the role of Smad5 in the regulation of hematopoietic stem cell (HSC) fate decisions in adult mice by using an inducible MxCre-mediated conditional knockout model. Surprisingly, analysis of induced animals revealed unperturbed cell numbers and lineage distribution in peripheral blood (PB), bone marrow (BM), and the spleen. Furthermore, phenotypic characterization of the stem cell compartment revealed normal numbers of primitive lin–Sca-1+c-Kit+ (LSK) cells in Smad5–/– BM. When transplanted in a competitive fashion into lethally irradiated primary and secondary recipients, Smad5-deficient BM cells competed normally with wild-type (wt) cells, were able to provide long-term reconstitution for the hosts, and displayed normal lineage distribution. Taken together, Smad5-deficient HSCs from adult mice show unaltered differentiation, proliferation, and repopulating capacity. Therefore, in contrast to its role in embryonic hematopoiesis, Smad5 is dispensable for hematopoiesis in the adult mouse.

Human embryonic stem cell-derived hematopoietic cells are capable of engrafting primary as well as secondary fetal sheep recipients

The human/sheep xenograft model has proven valuable in assessing the in vivo hematopoietic activity of stem cells from a variety of fetal and postnatal human sources. CD34+/lineage- or CD34+/CD38- cells isolated from human embryonic stem cells (hESCs) differentiated on S17 feeder layer were transplanted by intraperitoneal injections into fetal sheep. Chimerism in primary transplants was established with polymerase chain reaction (PCR) and flow cytometry of bone marrow and peripheral blood samples. Whole bone marrow cells harvested from a primary recipient were transplanted into a secondary recipient. Chimerism was established as described before. This animal was stimulated with human GM-CSF, and an increase in human hematopoietic activity was noted by flow cytometry. Bone marrow aspirations cultured in methylcellulose generated colonies identified by PCR to be of human origin. We therefore conclude that hESCs are capable of generating hematopoietic cells that engraft primary recipients. These cells also fulfill the criteria for long-term engrafting hematopoietic stem cells as demonstrated by engraftment and differentiation in the secondary recipient.

Selection based on CD133 and high aldehyde dehydrogenase activity isolates long-term reconstituting human hematopoietic stem cells

The development of novel cell-based therapies requires understanding of distinct human hematopoietic stem and progenitor cell populations. We recently isolated reconstituting hematopoietic stem cells (HSCs) by lineage depletion and purification based on high aldehyde dehydrogenase activity (ALDH(hi)Lin- cells). Here, we further dissected the ALDH(hi)-Lin- population by selection for CD133, a surface molecule expressed on progenitors from hematopoietic, endothelial, and neural lineages. ALDH(hi)CD133+Lin- cells were primarily CD34+, but also included CD34-CD38-CD133+ cells, a phenotype previously associated with repopulating function. Both ALDH(hi)CD133-Lin- and ALDH(hi)CD133+Lin- cells demonstrated distinct clonogenic progenitor function in vitro, whereas only the ALDH(hi)CD133+Lin- population seeded the murine bone marrow 48 hours after transplantation. Significant human cell repopulation was observed only in NOD/SCID and NOD/SCID beta2M-null mice that received transplants of ALDH(hi)CD133+Lin- cells. Limiting dilution analysis demonstrated a 10-fold increase in the frequency of NOD/SCID repopulating cells compared with CD133+Lin- cells, suggesting that high ALDH activity further purified cells with repopulating function. Transplanted ALDH(hi)CD133+Lin- cells also maintained primitive hematopoietic phenotypes (CD34+CD38-) and demonstrated enhanced repopulating function in recipients of serial, secondary transplants. Cell selection based on ALDH activity and CD133 expression provides a novel purification of HSCs with long-term repopulating function and may be considered an alternative to CD34 cell selection for stem cell therapies.

Vasculogenesis and angiogenesis in the mouse embryo studied using quail/mouse chimeras

Using quail/chick chimeras, we have previously shown that different embryonic territories are vascularized through two distinct mecanisms, angiogenesis and vasculogenesis. Angiogenesis occurs in tissues of somatopleural origin, vasculogenesis occurs in territories of splanchnopleural origin. The aim of this work was to establish if these modes of vascularization were conserved in the mammalian embryo. Since in vivo manipulations with mammalian embryos are difficult to perform, we used a quail/mouse chimera approach. Mouse limb buds of somatopleural origin, and visceral organ rudiments of splanchnopleural origin, were grafted into the coelomic cavity of 2.5 day-old quail embryos. After four to seven days, the hosts were killed and the origin of the endothelial cells in the mouse tissues was determined by double staining with the quail endothelial and hematopoietic cell-specific marker, QH1 and mouse-specific VEGFR2 and VEGFR3 probes. Our findings show that the great majority of vessels which developed in the mouse limbs was QH1+, indicating that these tissues were vascularized by angiogenesis. Conversely, visceral organs were vascularized through the vasculogenesis process by mouse endothelial cells which differentiated in situ. These results demonstrate for the first time that in the mouse embryo, as previously shown in avian species, the tissues from somatopleural origin are vascularized by angiogenesis, while rudiments of a splanchnopleural origin are vascularized by vasculogenesis, both at vascular and lymphatic levels.

Mouse-chick neural chimeras

Embryonic chimera production was used to study the developmental processes of the mouse nervous system. The difficulty of performing in situ transplantation experiments of neural primordium of mouse embryo was overcome by isotopic and isochronic grafting of mouse neural tube fragments into chick embryo. Mouse neural tube cells differentiated perfectly in ovo and neural crest cells associated with the grafted neural tube were able to migrate and reach the normal arrest sites of host neural crests. Cranial neural crest cells penetrated into chick facial areas and entered into the development of dental bud structures, participating in vibrissa formation. Depending on graft level, in ovo implanted mouse neural crest cells formed different components of the peripheral nervous system. At trunk level, they located in spinal ganglia and orthosympathetic chains and gave rise to Schwann cells lining the nerves. When implanted into the lumbosacral region, they penetrated into the enteric nervous system. At the precise 18-24 somite level, they colonized host adrenal gland. Mouse neural tube was involved in the mechanisms required to maintain myogenesis in host somites. Furthermore in ovo grafts of mouse cells from genetically modified embryos, in which many mutations induce early death, are particularly useful to investigate cellular events involved in the development of the nervous system and to identify molecular events of embryogenesis.

Long-term persistence of a nonintegrated lentiviral vector in mouse hematopoietic stem cells

OBJECTIVE

Lentiviral transduction is an established method for efficiently modifying the gene expression program of primary cells, but the ability of the introduced construct to persist as an episome has not been well studied.

MATERIAL AND METHODS

Here we investigated this issue in lethally irradiated female mice injected with 300 or 3000 doubly sorted male lin(neg), Sca-1(high), c-kit(high), Thy-1.1(low) mouse bone marrow cells that had been exposed in vitro to self-inactivating lentivirus vector encoding a green fluorescence protein (GFP) cDNA. Seven to sixteen months later, bone marrow cells from primary mice were injected into secondary female recipients and another 8 months later into tertiary female recipients. Integration study was performed on individual spleen colonies by Southern blot analysis. Inverse polymerase chain reaction (PCR) and sequence of amplified vector-derived DNA was used to verify Southern blot results.

RESULTS

Spleen colony-forming cell study revealed that a small fraction of the spleen colonies contained integrated provirus as shown by Southern blot analysis. Unexpectedly, many spleen colonies were found to contain a nonintegrated episomal form of the provirus, which was confirmed by an inverse PCR analysis. In some of the spleen colonies containing only the episomal form, GFP-expressing cells were also detected. Lentiviral sequences were present in hematopoietic tissues of primary mice but not in other tissues.

CONCLUSIONS

These results demonstrate that lentiviral vectors produce episomal circles in hematopoietic stem cells that can be transferred through many cell generations and expressed in their progeny.

The use of CD 34(+) mobilized peripheral blood as a donor cell source does not improve chimerism after in utero hematopoietic stem cell transplantation in non-human primates

In utero hematopoietic stem cell transplantation is a therapeutic procedure that could potentially cure many developmental diseases affecting the immune and hematopoietic systems. In most clinical and experimental settings of fetal hematopoietic transplantation the level of donor cell engraftment has been low, suggesting that even in the fetus there are significant barriers to donor cell engraftment. In postnatal hematopoietic transplantation donor cells obtained from mobilized peripheral blood engraft more rapidly than cells derived from marrow. We tested the hypothesis that use of donor hematopoietic/stem cells obtained from mobilized peripheral blood would improve engraftment and the level of chimerism after in utero transplantation in non-human primates. Despite the potential competitive advantage from the use of CD 34(+) from mobilized peripheral blood, the level of chimerism was not appreciably different from a group of animals receiving marrow-derived CD 34(+) donor cells. Based on these results, it is unlikely that this single change in cell source will influence the clinical outcome of fetal hematopoietic transplantation.

Heterogeneity of engrafted bone-lining cells after systemic and local transplantation

The outcome of various osteoprogenitor-cell transplantation protocols was assessed using Col1a1-GFP reporter transgenic mice. The model requires the recipient mice to undergo lethal total body irradiation (TBI) followed by rescue with whole bone marrow. When the mice are rescued with total bone marrow from a Col1a1-GFP transgenic mouse, green fluorescence protein (GFP)-positive donor cells can be observed on most endosteal and trabecular bone surfaces. Although the cells express an osteoblast-restricted GFP, they fail to progress to osteocytes, do not form a mineralized matrix, and do not generate bone nodules in vitro. However when calvarial progenitor cells derived from the same transgenic mice are injected into the bone marrow space, osteogenesis by the donor cells is observed. Using different GFP colors that distinguish the donor and recipient osteoblasts, commingling of the 2 cells types is observed along the mineralizing osteoblast surface as well as within the osteocyte population of the endosteal bone. Despite the ability of the injected progenitor cells to produce bone within the injected bone, they lack the ability to form mineralized bone nodules when explanted to primary osteoblast culture. These reagents and imaging protocols will be useful in evaluating other cells having a better progenitor potential than calvarial-derived stromal cells.

No evidence of plasticity in hair follicles of recipients after allogeneic hematopoietic stem cell transplantation

Here we show in a prospective quantitative study of 115 patients after allogeneic hematopoietic stem cell transplantation that hair follicles remain exclusively of recipient type despite full whole blood donor-type chimerism. Our data indicate that unmanipulated hematopoietic donor stem cells do not contribute directly to reconstitution even in an organ at highest need for repair.

Stable multilineage chimerism across full MHC barriers without graft-versus-host disease following in utero bone marrow transplantation in pigs

Stable engraftment of hematopoietic progenitors and multilineage chimerism following in utero bone marrow transplantation could be a promising modality for treatment of prenatally diagnosed blood dyscrasias. For treatment of these diseases, stable chimerism in the myeloid and erythroid lineages is important because it is anticipated that donor-derived cells will compensate for defects in these host lineages. In the present study, a preparation of bone marrow that includes fresh, unmanipulated marrow mixed with T-cell-depleted marrow to achieve 1.5% T-cell content, was injected into the intrahepatic portion of the umbilical vein of porcine fetuses at mid-gestation. Donor hematopoietic progenitor cell engraftment was assessed in fetal liver and recipient bone marrow postnatally by donor-specific polymerase chain reaction of colony-forming units. Chimerism was assessed in lymphoid tissues and peripheral blood by flow cytometry. Graft-versus-host disease (GVHD) was assessed by histological analysis of biopsies of skin, bone marrow, liver, and intestine. In this report, we demonstrate that stable multilineage chimerism across a full major histocompatibility complex disparity can be achieved without GVHD through in utero bone marrow transplantation.

The MRL mouse heart healing response shows donor dominance in allogeneic fetal liver chimeric mice

We previously demonstrated that after a severe cryoinjury to the right ventricle of the heart, adult MRL mice display structural and functional recovery with myocardial tissue replacement resembling that seen in amphibians. The control non-regenerating adult C57BL/6 (B6) mouse shows a predominant scar response. In the present study, radiation chimeras reconstituted with fetal liver cells from either healer MRL or nonhealer B6 mice were generated to test for a transfer of phenotype. Allogeneic MRL fetal liver cells were injected into x-irradiated (9 Gy) B6 mice and B6 fetal liver cells were injected into x-irradiated MRL mice. In these allogeneic chimeras, the healing response to cardiac cryoinjury was predominantly of the donor phenotype. Thus, MRL fetal liver cells transferred the healing phenotype to the B6 nonhealer with the appearance of Y-chromosome positive, donor-derived cardiomyocytes in the injury site and MRL-like healing with little scar. Similarly, B6 fetal liver cells transferred the nonhealing phenotype to the MRL with little cardiomyocyte growth and an acellular B6-like scar. These results are in contrast to the ear hole closure response which was of the recipient phenotype. We conclude that, in the case of the heart, fetal liver-derived stem cells regulate regenerative healing.

The transplantation of neural stem cells and predictive factors in hematopoietic recovery in irradiated mice

A number of surprising observations have shown that stem cells, in suitable conditions, have the ability to produce a whole spectrum of cell types, regardless, whether these tissues are derived from the same germ layer or not. This phenomenon is called stem cell plasticity, which means that tissue-specific stem cells are mutually interchangeable. In our experiments, as a model, we used neural stem cells (NSCs) harvested from fetal (E14-15) neocortex and beta-galactosidase positive. In the first experiment we found that on days 12 and 30 after sub-lethal irradiation (LD 8.5 Gy) and (beta-galactosidase(+)) NSCs transplantation all mice survived, just as the group with bone marrow transplantation. Moreover, the bone marrow of mice transplanted NSCs contained the number of CFU-GM colonies with beta-galactosidase(+) cells which was as much as 50% higher. These differences were statistically significant, p<0.001. In the second experiment, we studied kinetics of (beta-galactosidase(+)) NSCs after their transplantation to sub-lethally irradiated mice. Histochemistry of tissues was performed on days 12 and 30 post-transplantation, and beta-galactosidase(+) cells were detected with the help of histochemical examination of removed tissues (lung, liver, spleen, thymus, and skeletal muscle). In tissues removed on day 12 post-transplantation, we found a significantly higher number of beta-galactosidase(+) cells in the spleen and thymus on day 30. While we presumed the presence beta-galactosidase(+) cells in the spleen, as spleen and reticuloendothelial system represent an important retaining system for different cell types, the presence of beta-galactosidase(+) cells in the thymus was rather surprising but very interesting. This indicates a certain mutual and close interconnection of transplanted stem cells and immune system in an adult organism. In the third experiment, we verified the mutual interchange of Sca-1 surface antigen in the bone marrow cells and NSCs before transplantation. Analysis of this antigen showed 24.8% Sca-1 positive cells among the bone marrow cells, while NSCs were Sca-1 negative. Our experiments show that NSCs share hemopoietic identity and may significantly influence the recovery of damaged hematopoiesis but do not have typical superficial markers as HSCs. This result is important for the determination of predictive factors for hemopoiesis recovery, for stem cell plasticity and for their use in the cell therapy.

Reconstitution of hematopoiesis following intrauterine transplantation of stem cells

In utero hematopoietic stem cell transplantation is an entirely nonmyeloablative approach to achieve mixed hematopoietic chimerism and associated donor-specific tolerance. This chapter provides the rationale and methodologic detail for the administration of stem cells to the "preimmune" mouse fetus by a variety of routes. The development of murine model systems for in utero transplantation has accelerated progress in the field of in utero hematopoietic stem cell transplantation. Creative use of these models should also have experimental application to the fields of fetal gene therapy, stem cell biology, and developmental biology.

A role for bone marrow–derived cells in the vasculature of noninjured CNS

The contribution of hematopoietic cells to the formation of blood vessels is currently the focus of intense scrutiny. Bone marrow–derived endothelial progenitor cells are thought to generate endothelial cells in many tissues, including myocardium, muscle, and certain tumors. In the central nervous system (CNS), however, the possible role of bone marrow–derived angiocompetent cells remains unclear. Here we have investigated the long-term involvement of bone marrow–derived cells in the maintenance of endothelial structures in the brain, spinal cord, and retina. Using hematopoietic chimeras stably expressing green fluorescent protein (GFP) in bone marrow–derived tissues, we found large numbers of hematopoietic cells closely associated with vessels in the CNS. None of these cells, however, showed an endothelial phenotype. They were positive for monocytic and microglial surface markers and demonstrated active phagocytosis of neighboring endothelial elements. Bone marrow–derived, vasculature-associated cells in the noninjured adult CNS are distinct from endothelial cells, but play an active role in vascular structures.

Green fluorescent protein labeling of primordial germ cells using a nontransgenic method and its application for germ cell transplantation in salmonidae

Transplanting primordial germ cells (PGCs) has a number of potential applications in fish bioengineering. Previously, we established a system to visualize live PGCs in the rainbow trout by introducing the green fluorescent protein (Gfp) gene driven by rainbow trout vasa gene regulatory regions. However, for PGC transplantation to be practically useful in aquaculture, visualization of PGCs using a nontransgenic technique is required. In this study, we demonstrate a method for labeling PGCs from various fish species by introducing chimeric RNAs composed of the Gfp coding region and vasa gene 3'-untranslated regions (UTRs); these sequences play a critical role in stabilizing mRNA in zebrafish PGCs. The GFP chimeric RNAs, including vasa 3'-UTR RNAs from rainbow trout, Nibe croaker, and zebrafish, were microinjected into the cytoplasm of fertilized eggs of several Salmonidae species. All the resulting embryos showed specific labeling in PGCs after the somatogenesis stage, which continued to be visible for at least 50 days. To apply this technique to PGC transplantation, PGCs labeled with chimeric RNA were microinjected into the peritoneal cavity of newly hatched salmonid embryos. The GFP labeling was sufficiently long-lived for the initial stage of donor PGC behavior to be followed in the recipient embryos. Importantly, donor PGCs from brown trout and masu salmon were incorporated into xenogeneic genital ridges in recipient rainbow trout. This nontransgenic method for labeling fish PGCs should be extremely useful for applications of PGC transplantation where the resulting progeny are to be released into the environment, such as PGC cryopreservation for fish stocks and surrogate brood stock technology.

Analysis of the vascular potential of hematopoietic stem cells

The hematopoietic stem cells residing in the bone marrow have tremendous proliferative and self-renewing capacity, and until recently these cells were thought to produce only progeny of the blood lineages. We have recently demonstrated that these cells are capable of producing endothelial cells of blood vessels. This chapter will outline the methodology for producing chimeric mice through labeled bone marrow transplantation and induction of these donor cells in order to track their plasticity, or their ability to produce non-hematopoietic tissues, specifically blood vessels.

Neural crest derivatives in ocular and periocular structures

In vertebrates, the eye is an ectodermal compound structure associating neurectodermal and placodal anlagen. In addition, it benefits early on from a mesenchymal ectoderm-derived component, the neural crest. In this respect, the construction of chimeras between quail and chick has been a turning point, instrumental in appraising the contribution of the cephalic neural crest to the development of ocular and periocular structures. Given the variety of crest derivatives underscored in the developing eye, this study illustrates the fascinating ability of this unique structure to finely adapt its differentiation to microenvironmental cues. This analysis of neural crest cell contribution to ocular development emphasizes their paramount role to design the anterior segment of the eye, supply refracting media and contribute to the homeostasy of the anterior optic chamber.

Use of flow cytometry and combined DNA surface staining for analysis of hematopoietic development in the Xenopus embryo

Xenopus embryos provide a model for studying the earliest stages in the development of the vertebrate hematopoietic system. This chapter provides detailed procedures describing the production of hematopoietic chimeras in Xenopus embryos and the analysis of these chimeras using flow cytometry. Protocols for analysis include the determination of deoxyribonucleic acid content of hematopoietic cells, staining of cells with antibodies against cell surface antigens and the combined analysis of deoxyribonucleic content and cell surface phenotype. Examples of data that can be expected are included.

Identification of a novel population of human cord blood cells with hematopoietic and chondrocytic potential

With the exception of mature erythrocytes, cells within the human hematopoietic system are characterized by the cell surface expression of the pan-leukocyte receptor CD45. Here, we identify a novel subset among mononuclear cord blood cells depleted of lineage commitment markers (Lin-) that are devoid of CD45 expression. Surprisingly, functional examination of Lin-CD45- cells also lacking cell surface CD34 revealed they were capable of multipotential hematopoietic progenitor capacity. Co-culture with mouse embryonic limb bud cells demonstrated that Lin-CD45-CD34- cells were capable of contributing to cartilage nodules and differentiating into human chondrocytes. BMP-4, a mesodermal factor known to promote chondrogenesis, significantly augmented Lin-CD45-CD34- differentiation into chondrocytes. Moreover, unlike CD34+ human hematopoietic stem cells, Lin-CD45-CD34- cells were unable to proliferate or survive in liquid cultures, whereas single Lin-CD45-CD34- cells were able to chimerize the inner cell mass (ICM) of murine blastocysts and proliferate in this embryonic environment. Our study identifies a novel population of Lin-CD45-CD34- cells capable of commitment into both hematopoietic and chondrocytic lineages, suggesting that human cord blood may provide a more ubiquitous source of tissue with broader developmental potential than previously appreciated.

Immunohistochemical analysis of nervous system regeneration in chimeric individuals of Dorvillea bermudensis (Polychaeta, Dorvilleidae)

In regeneration experiments, 0.5% of the two- or five-segmented fragments of the polychaete Dorvillea bermudensis were found unexpectedly transplanted: two fragments of each that were lying close together during the initial period, fused and regenerated a chimeric individual. Of the three theoretical possibilities (i.e. fusion of (i). two posterior ends; (ii). one anterior and one posterior end; (iii). or two anterior ends) only the last two were realized. The similarly oriented fragments regenerated a normal animal while anterior-anterior fused ones produced two heads or a double head. Whether the ventral cords of the fragments are located vis-à-vis or adjacent, influences the course of regeneration as well. Immunohistochemical methods (anti-acetylated alpha-tubulin) in conjunction with confocal laser scanning microscopy were used to investigate the wiring pattern of the nervous systems of the grafts. In all cases, at least two supraesophageal ganglia were formed and palps, antennae and nuchal organs were innervated by the correct nerves but, in special cases, were innervated vice versa from the other brain. From these results it can be concluded that fusion of a regenerating connective with another connective results in formation of a new brain, irrespective of whether it belongs to the same nerve cord or not.

Chimaerism and erythroid marker expression after microinjection of human acute myeloid leukaemia cells into murine blastocysts

It has been suggested that the embryonic microenvironment can control the survival and the transformed phenotype of tumour cells. Here, we addressed the hypothesis that the murine embryonic microenvironment can induce the differentiation of human tumour cells. To examine such interactions, we injected human leukaemic cells into preimplantation murine blastocysts at embryonic day 3.5 of gestation (E3.5). Microinjection of human KG-1 myeloid leukaemia cells and primary human acute myeloid leukaemia (AML) cells led to the generation of chimaeric embryos and adults. We observed that in E12.5 murine embryos, KG-1 cells were preferentially detected in yolk sac and peripheral blood, while primary AML cells mainly seeded the aorta gonad mesonephros region of chimaeric embryos. Analysis of the donor contribution in 15 different adult tissues showed that progeny of primary AML cells seeded to various haematopoietic and nonhaematopoietic tissues. Chimaeric embryos and adults showed no apparent tumour formation. Furthermore, analysis of chimaeric E12.5 embryos revealed that the progeny of human KG-1 cells activated erythroid-specific human globin and glycophorin A expression. In summary, our data indicate that human AML cells activate markers of erythroid differentiation after injection into early murine embryos.

Pluripotency of cryopreserved blastomeres of the goldfish

To examine the pluripotency of cryopreserved blastomeres, we transplanted them into blastula. Donor blastomeres were prepared from blastula of goldfish (Carassius auratus) and cryopreserved in liquid nitrogen for two months. Fifty-five percent and 44% of blastomeres survived after thawing. Cryopreserved blastomeres were transplanted to the blastula of triploid crucian carp (C. a. longsdorfii), which reproduces gynogenetically in nature. At four days after the operation, resultant chimeric embryos transplanted with cryopreserved blastomeres showed a survival rate (41.6%) lower than that of embryos transplanted with unfrozen blastomeres (57.1%). Transplanted blastomeres were histologically identified in various organs derived from all three germ layers. A primordial germ cell differentiated from a cryopreserved blastomere was detected in one of the 32 chimeric fish examined. These results suggest blastomeres that survive after cryopreservation retain their pluripotency and are able to differentiate into both somatic and germ cell lines.

Human pulmonary chimerism after hematopoietic stem cell transplantation

Many of the body's tissues once thought to be only locally regenerative may, in fact, be actively replaced by circulating stem cells after hematopoietic stem cell transplantation. Localization of donor-derived cells ("chimerism") has recently been shown to occur in the lungs of mice after either hematopoietic stem cell transplantation or infusion of cultured marrow. To determine whether tissues of the human lung might be similarly derived from extrapulmonary sources, we examined lung specimens from a retrospective cohort of female allogeneic hematopoietic stem cell transplant recipients who received stem cells from male donors. Tissue samples from three such patients who had undergone diagnostic lung biopsy or autopsy were examined. Slides were stained by immunohistochemistry for cytokeratin (epithelium) and platelet endothelial cell adhesion molecule, CD31 (PECAM) (endothelium) and were imaged and then examined by fluorescent in situ hybridization analysis to identify male cells. The resulting overlapping in situ hybridization and immunohistochemistry images were examined for the presence and, if present, cell type of donor cells in the lung. We found significant rates of epithelial (2.5-8.0%) and endothelial (37.5-42.3%) chimerism. These results suggest that significant chimerism of the human lung may follow hematopoietic stem cell transplantation and that adult human stem cells could potentially play a therapeutic role in treatment of the damaged lung.

Extensive chimerism in liver transplants: vascular endothelium, bile duct epithelium, and hepatocytes

The transplanted liver has been shown to be particularly capable of inducing tolerance. An explanation may be the presence of chimerism. Cells of donor origin have been found in recipient tissues after transplantation of any solid organ. Evidence for the presence of cells of recipient origin within the transplanted liver is very limited. We investigated whether nonlymphoid cells of recipient origin can be found within human liver allografts. Five male patients who received a liver transplant from a female donor and 11 patients who received an HLA-I mismatched liver transplant were studied. We confirmed our observations with two different techniques in combination with double-staining techniques. To identify male cells in female liver transplants, we used in situ hybridization for sex chromosomes. To identify specific HLA class I antigens of recipient origin, we used immunohistochemistry with HLA class I-specific antibodies. Double staining was performed to discriminate different cell lineages and inflammatory cells. Endothelial cells of recipient origin were found in 14 of 16 donor livers. Bile duct epithelial cells of recipient origin were found in 5 of 16 cases. Hepatocytes of recipient origin were seen in only 1 of the 5 studied sex-mismatched donor livers. Our study provides evidence that cells of recipient origin can replace biliary epithelial cells, endothelial cells, and hepatocytes within the human liver allograft. This is consistent with the concept that circulating pluripotent progenitor cells exist, capable of differentiating into endothelial cells, epithelial cells, and hepatocytes.

Mechanisms of tolerance induction through the transplantation of donor hematopoietic stem cells: central versus peripheral tolerance

The transplantation of donor hematopoietic stem cells has been used successfully in numerous experimental settings to induce donor-specific tolerance. After appropriate host conditioning, hematopoietic stem-cell transplantation leads to a lasting state of donor macrochimerism that is associated with a robust form of tolerance. One of the key factors in the success of this approach is its reliance on intrathymic clonal deletion to ensure lifelong tolerization of newly developing T cells. Evidence for ongoing central deletion comes from studies following superantigen-reactive T cells and from experiments using mice transgenic for an alloreactive T-cell receptor. In protocols inducing tolerance through macrochimerism, the preexisting mature T-cell repertoire is controlled by either globally destroying all T cells before the hematopoietic cell transplantation or, in more recent models, by tolerizing it through co-stimulation blockade. The peripheral mechanisms induced by hematopoietic stem-cell transplantation and co-stimulation blockade include both extrathymic clonal deletion and the nondeletional mechanisms anergy, suppression, or both. In addition to these immunologic hurdles, a physiologic engraftment barrier has to be surmounted for the successful induction of mixed chimerism. This can be achieved by cytoreductive host treatment or by the infusion of high numbers of donor hematopoietic cells. A detailed delineation of the mechanisms responsible for tolerance induction after hematopoietic stem-cell transplantation is expected to help in the translation of these experimental protocols to clinical organ transplantation.

How should chimerism be decoded?

To date, the significance of chimerism has not been fully understood. In particular, microchimerism can be associated with allograft acceptance or rejection. Several factors may influence the immunologic consequences of chimerism. In this review, the major factors influencing these consequences are briefly described. Subsequently, the different methods available for detecting and tracking donor-derived cells are listed. These techniques have been mainly developed concomitantly with nonmyeloablative hematopoietic allografts to monitor immunosuppression. Finally, the authors suggest how these methods may help to improve the understanding of microchimerism in solid organ transplantation.

[The status of chymeric cells in human to pig spleen transplantation model]

OBJECTIVE

To establish a human to pig xenotransplantation GVHD model to simulate the human anti pig grafts immunoreaction in vivo.

METHODS

The Chinese Neijiang pigs were immunosuppressed by CTX followed by the transplant of human spleen slices into pig's peritoneal cavity. We tested the routine items of the pigs' peripheral blood regularly, monitored the chimeric level by FCM, and examined the cytotoxicities of both human anti pig and pig anti human by CML.

RESULT

The pigs all survived during the experimental period. The PBWBC decreased by 85% after 4 days of giving CTX. The chimeric peaks appeared on day 2 and day 14 after transplant. The cytotoxicity of human anti pig was always less than that of pig anti human, although it increased significantly after 2 weeks of transplant.

CONCLUSION

There might be a dynamic changeable balance of HVG, microchimerism, and GVH due to the reaction between the chimeric human cells and the pig cells in the human to pig spleen xenotransplantation model.

Flt3-L augments the engraftment of donor-derived bone marrow cells when combined with sublethal irradiation and costimulatory (CD28/B7 and CD40/CD40L) blockade

T-cell costimulatory blockade as a constituent for recipient conditioning prior to bone marrow transplantation has led to the development of less toxic protocols for the establishment of donor cell chimerism. We therefore hypothesized that the addition of the hematopoietic growth factor, Flt3-ligand (Flt3-L), to the perioperative inhibition of the CD28/B7 and CD40/CD40 ligand costimulatory pathways would enhance the engraftment of allogeneic bone marrow. Recipient BALB/c ByJ (H-2(d), Mls(c), Vbeta6+/Vbeta8+ TCR) received a single sublethal dose of total body irradiation (300 rad) 6 h prior to transplantation IV with unfractionated donor CBA/J (H-2(k), Mls(d), Vbeta6-/Vbeta8+ TCR) bone marrow cells. CTLA4-Ig and/or MRI were administered at 500 microg IP on days 0, 2, 4, and 6 posttransplantation. Flt3-L was administered at 10 microg IP on days 0-6. Donor cell chimerism was determined on days 30-90 by flow cytometric analysis. Donor-specific tolerance was assessed by skin grafting. In vitro TCR cross-linking assays and flow cytometry were utilized to explore the deletion of donor-reactive T cells. Recipients receiving CTLA4-Ig and MRI engrafted allogeneic bone marrow cells in the peripheral blood (3/6; 50%) with chimerism being detected at 2-31%. Addition of Flt3-L to this preconditioning regimen enhanced the incidence of engraftment of donor bone marrow cells (10/13; 3-70%). Long-term survival of donor but not third-party-specific skin grafts demonstrated that donor-specific tolerance had been achieved in the chimeric recipients. Deletion of the donor-reactive T cells within the chimeric recipients was also observed. The addition of hematopoietic growth factors and cytokines to the nonmyeloablative regimen of sublethal irradiation and T-cell costimulatory blockade provides a novel strategy for the establishment of donor cell chimerism and for the induction of stable and robust donor-specific tolerance. The deletion of donor-reactive T cells using this protocol suggests the reliability and feasibility of this protocol for clinical transplantation.

Host cell-derived cardiomyocytes in sex-mismatch cardiac allografts

BACKGROUND

Mesenchymal precursor cells are able to respond to tissue signals and differentiate into a phenotype characteristic of mature cells of that tissue. We sought to investigate whether adult human cardiomyocytes can be derived from recipient precursor cells in sex-mismatched cardiac allografts.

METHODS

We studied four male patients who received hearts from female donors, and four female patients who received an allograft from a male donor. Four sex-matched transplant patients, two of each sex served as controls. Combined fluorescence in situ hybridization with probes specific for X- and Y-chromosomes and immunohistochemistry with alpha-actin was used to identify cardiac muscle cells 4 and 12 months after transplantation. Slides were examined with a fluorescence microscope to detect the presence of male cells with one X and one Y signal in the nucleus, and female cells containing two X signals.

RESULTS

Mature cardiomyocytes from the host (1-2%) were found in five endomyocardial biopsy specimens at 4 months, and in three specimens at 12 months. In addition, recipient cells negative for cytoplasmic alpha-actin were also identified (1-21% per slide). The number of infiltrating recipient cells was not associated with the degree of rejection of the sample or with the number of prior rejection episodes. Echocardiographic evaluation showed no improvement in cardiac performance in hearts from patients with more than 10% chimeric recipient cells.

CONCLUSIONS

Our data confirm the existence of mature cardiomyocytes derived from host cells, likely mesenchymal precursors, in the adult cardiac allograft in vivo.

Requirements for developing mixed-chimerism in nonmyeloablative total-lymphoid irradiated mice: role of IL-4 and immunoredirection

BACKGROUND

Adult mice treated with total-lymphoid irradiation (TLI) followed by hematopoietic cell transfer develop stable mixed-chimerism. The purpose of the study is to examine the requirements for the development of mixed-chimerism and characterize the immune responses associated with mixed-chimerism.

METHODS

T-cell number and function were examined in spleens of TLI-treated mice at various times after the completion of TLI by fluorescence-activated cell sorter (FACS) analysis and enzyme-linked immunosorbent assay (ELISA). TLI-treated BALB/c mice were injected with CAF(1) spleen cells between 2 and 28 days after completing TLI, with or without concurrent anti-IL-4. The extent of mixed-chimerism was determined using multiparameter FACS analysis. Enzyme-linked immunosorbent spot (ELISPOT) assays were used to measure anti-donor CD4+ and CD8+ immune responses.

RESULTS

TLI treatment results in transient lymphopenia, sparing CD4 cells relative to CD8 cells, followed by gradual, partial recovery over 28 days. Day 2 post-TLI T cells produce more interleukin (IL)-4, but less IL-2, interferon (IFN)-gamma and IL-10, while day 28 post-TLI T cells produce more IFN-gamma relative to IL-4. More than 70% of mice develop mixed-chimerism when injected with CAF(1) cells at 2 days post-TLI, while none become chimeric if injected at 28 days post-TLI. Mixed-chimeric mice contain more anti-donor Th2 CD4 cells and less anti-donor TC1 CD8 cells compared with nonchimeric mice and nonirradiated controls. Treatment with anti-IL-4 inhibits the development of mixed-chimerism ( <0.05), and these nonchimeric mice contain donor-reactive TC1 CD8 cells.

CONCLUSIONS

IL-4 plays a role in the development of mixed-chimerism, perhaps by inhibition of anti-donor TC1 CD8 cells or enhancement of anti-donor Th2 CD4 cells.

The role of passenger leukocyte genotype in rejection and acceptance of rat liver allografts

BACKGROUND

Although graft-resident passenger leukocytes are known to mediate acute rejection by triggering direct allorecognition, they may also act in an immunomodulatory fashion and play an important role in tolerance induction. Our purpose in the current study was to utilize rat bone marrow chimeras to evaluate the role of the genotype of passenger leukocytes in both acute rejection and tolerance of liver allografts.

METHODS

The fate of livers bearing donor-type, recipient-type, and third-party passenger leukocytes was evaluated in the MHC class I and II mismatched rejector combination ACI-->LEW and the acceptor combination PVG-->DA.

RESULTS

We report that although treatment of ACI liver donors with lethal irradiation does not lead to prolongation of graft survival in the ACI-->LEW strain combination, ACI livers bearing recipient-type (LEW) or third-party passenger leukocytes (BN) are rejected at a significantly slower rate. We confirm that lethal irradiation of PVG donor animals leads to abrogation of tolerance induction with acute rejection of their livers by DA recipients. However, the majority of PVG livers carrying donor-type (PVG), recipient-type (DA), or third-party (LEW) passenger leukocytes are accepted for >100 days. These DA recipients develop immune tolerance to the donor parenchyma (PVG).

CONCLUSIONS

Our findings demonstrate that long-term acceptance of liver allografts and tolerance induction is not dependent on the presence of donor-type passenger leukocytes and can be achieved with organs carrying donor-type, recipient-type, or third-party passenger leukocytes. The importance of the MHC framework on the surface of passenger leukocytes as a critical regulator of the immune response after transplantation of chimeric organs is substantiated by the delayed tempo of rejection of ACI livers bearing recipient-type or third-party passenger leukocytes in the ACI-->LEW strain combination.

The role of the graft in establishing tolerance

At the present time, clinical solid organ transplantation continues to rely on the use of non-specific immunosuppressive protocols in order to prevent graft rejection. However, these regimens bring with them complications related both to the global immunosuppression that they cause, and to toxicity related to individual drugs. The pursuit of protocols that will allow graft-specific tolerance thus remains a major goal of research both in animal models and in clinical practice. There is evidence that the graft itself may play an active part in establishing and maintaining donor-specific hyporesponsiveness and ultimately tolerance; the aim of this review is to analyze this role in more detail.

Activation of human endothelial cells by mobilized porcine leukocytes in vitro: implications for mixed chimerism in xenotransplantation

BACKGROUND

The induction of immunologic tolerance to pig antigens in primates may facilitate the development of successful clinical xenotransplantation protocols. The infusion of mobilized porcine peripheral blood leukocytes (PBPC, consisting of approximately 2% peripheral blood progenitor cells) into preconditioned baboons, intended to induce mixed hematopoietic cell chimerism, however, results in a severe thrombotic microangiopathy (TM) that includes vascular injury, microvascular thrombosis, and pronounced thrombocytopenia. Because the mechanisms responsible for TM are unclear, we have explored the effects of PBPC on human umbilical vein endothelial cell (HUVEC) activation.

METHODS

Confluent HUVEC monolayers were established in 96-well cell culture clusters. PBPC were mobilized from miniature swine with porcine interleukin 3 (pIL-3), porcine stem cell factor (pSCF), and human granulocyte-colony stimulating factor (hG-CSF) and were collected by leukapheresis. PBPC were added to HUVEC (0-1x10(7) PBPC/well) for 3- to 24-hr periods and, with cell-based ELISA techniques, surface levels of E-selectin, vascular cell adhesion molecule 1 (VCAM-1), and intercellular adhesion molecule 1 (ICAM-1) were measured. In some cases, peripheral blood leukocytes (PBL) were collected from pigs that did not receive pIL-3, pSCF, or hG-CSF and were added to HUVEC. PBPC were also sorted into subsets of CD2- cells, CD2+ cells, and cellular debris, each of which were added separately to HUVEC. Transwell permeable membrane inserts were placed over HUVEC to prevent direct cell-cell contact with PBPC in some instances.

RESULTS

PBPC from different pigs (n=6) induced an increase in the expression of E-selectin, VCAM-1, and ICAM-1 to levels 5, 4, and 2 times greater than baseline, respectively. ICAM-1 expression reached maximum levels after the addition of 6x10(5) PBPC/well. Expression of E-selectin and VCAM-1 increased further with the addition of greater numbers of PBPC, reaching maximum levels after the addition of 1x10(7) PBPC/well. PBPC-induced up-regulation of E-selectin, VCAM-1, and ICAM-1 had a maximum effect after approximately 6 hr, 12 hr, and 6 to 9 hr, respectively (n=3). The effects of fresh and frozen PBPC on HUVEC were similar (n=2). Compared to PBPC, PBL induced higher levels of E-selectin, VCAM-1, and ICAM-1 on HUVEC (n=2). The addition of CD2- cells to HUVEC induced an increase in E-selectin and VCAM-1 to levels 4 times greater than baseline, whereas the addition of CD2+ cells or debris did not elicit a substantial effect (n=2). Transwell permeable membranes prevented PBPC-induced up-regulation of E-selectin, VCAM-1, and ICAM-1 on HUVEC (n=2), suggesting that the mechanism of activation requires direct cell-cell contact.

CONCLUSIONS

Porcine PBPC activate HUVEC, as suggested by an increase in surface E-selectin, VCAM-1, and ICAM-1 levels, and have a maximum effect after 9 hr. Freezing of PBPC does not affect PBPC-induced activation of HUVEC. PBL induce greater activation of HUVEC than do PBPC. CD2- cells are primarily responsible for PBPC-induced activation of HUVEC and direct cell-cell contact is required. Removal of CD2- cells before the administration of PBPC or the use of agents that interrupt PBPC-endothelial cell interactions may prevent or treat TM in baboons.

CD8(+), alphabeta-TCR(+), and gammadelta-TCR(+) cells in the recipient hematopoietic environment mediate resistance to engraftment of allogeneic donor bone marrow

Historically, conditioning for engraftment of hematopoietic stem cells has been nonspecific. In the present study, we characterized which cells in the recipient hematopoietic microenvironment prevent allogeneic marrow engraftment. Mice defective in production of alphabeta-TCR(+), gammadelta-TCR(+), alphabeta- plus gammadelta-TCR(+), CD8(+), or CD4(+) cells were transplanted with MHC-disparate allogeneic bone marrow. Conditioning with 500 cGy total body irradiation (TBI) plus a single dose of cyclophosphamide (CyP) on day +2 establishes chimerism in normal recipients. When mice were conditioned with 300 cGy TBI plus a single dose of CyP on day +2, all engrafted, except wild-type controls and those defective in production of CD4(+) T cells. Mice lacking both alphabeta- and gammadelta-TCR(+) cells engrafted without conditioning, suggesting that both alphabeta- and gammadelta-TCR T cells in the host play critical and nonredundant roles in preventing engraftment of allogeneic bone marrow. CD8 knockout (KO) mice engrafted without TBI, but only if they received CyP on day +2 relative to the marrow infusion, showing that a CD8(-) cell was targeted by the CyP conditioning. The CD8(+) cell effector function is mechanistically different from that for conventional T cells, and independent of CD4(+) T helper cells because CD4 KO mice require substantially higher levels of conditioning than the other KO phenotypes. These results suggest that a number of cell populations with different mechanisms of action mediate resistance to engraftment of allogeneic marrow. Targeting of specific recipient cellular populations may permit conditioning approaches to allow mixed chimerism with minimal morbidity and could potentially avoid the requirement for myelotoxic agents altogether.