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Human Embryonic Stem Cells Possess Immune-Privileged Properties

^a Robarts Research Institute, Krembil Centre for Stem Cell Biology and Regenerative Medicine and FOCIS Centre for Clinical Immunology and Immunotherapeutics, London, Ontario, Canada;
^b Geron Corporation, Menlo Park, California;
^c The University of Western Ontario, Department of Microbiology and Immunology and Medicine, London, Ontario, Canada.

Key Words. Human embryonic stem cells • Immune response • Transplantation • Tolerance • T-cell proliferation

Correspondence: Mickie Bhatia, M.D., Robarts Research Institute, Krembil Centre for Stem Cell Biology and Regenerative Medicine, 100 Perth Drive, London, Ontario, Canada, N6A5K8. Telephone: 519-663-5777 ext. 34166; Fax: 519-663-2982; e-mail: mbhatia{at}robarts.ca

	ABSTRACT

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Human embryonic stem cells (hESCs) are envisioned to be a major source for cell-based therapies. Efforts to overcome rejection of hESCs include nuclear transfer and collection of hESC banks representing the broadest diversity of major histocompatability complex (MHC) polymorphorisms. Surprisingly, immune responses to hESCs have yet to be experimentally evaluated. Here, injection of hESCs into immune-competent mice was unable to induce an immune response. Undifferentiated and differentiated hESCs failed to stimulate proliferation of alloreactive primary human T cells and inhibited third-party allogeneic dendritic cell-mediated T-cell proliferation via cellular mechanisms independent of secreted factors. Upon secondary rechallenge, T cells cocultured with hESCs were still responsive to allogeneic stimulators but failed to proliferate upon re-exposure to hESCs. Our study demonstrates that hESCs possess unique immune-privileged characteristics and provides an unprecedented opportunity to further investigate the mechanisms of immune response to transplantation of hESCs that may avoid immune-mediated rejection.

	INTRODUCTION

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For nearly 50 years, transplantation medicine has focused on innovative strategies to prevent rejection of donor alloanti-gens [1,2]. In addition to whole organ transplants, the emergence of cellular transplantation in the evolving field of regenerative medicine must now also be cognizant of potential rejection and the potential requirement of immune tolerance induction in the recipient [2]. The isolation of human embryonic stem cells (hESCs) provides an unlimited source of cells capable of producing a wide spectrum of cell types for replacement of degenerating tissue [3]. Efforts to overcome rejection of hESCs include nuclear transfer to create compatible cells and development of hESC banks representing the broadest diversity of human major histocompatabil-ity complex (MHC) polymorphorisms [2]. Despite the continued exploration into approaches to avoid rejection of transplanted cells, immune responses to hESCs have yet to be evaluated.

Survival of transplanted cells correlates with the number of differences in major histocompatibility (MHC) antigens between donor and recipient that triggers T-cell responses and rejection of cells with disparate MHC profiles [1]. One exception to this rule is maternal tolerance to the fetal conceptus expressing paternal antigens [4,5]. In spite of our growing understanding of the immune system, the mechanism of immune privilege exhibited by fetal tissue remains unknown [4, 6–9]. Accordingly, it is reasonable to assume that immune responses to human embryonic cells may reveal unanticipated results, and therefore must be examined experimentally.

	RESULTS

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Representative analysis of alkaline phosphatase and stage-specific embryonic antigen-4 (SSEA-4) by immuno-staining or SSEA-4, SSEA-1, TRA-1-60, and TRA-1-81 by flow cytometry for both H1 and H9 hESCs is shown in Figures 1A and B, demonstrating the quality and undifferentiated phenotype of hESCs used in this study. The expression of MHC antigens on human tissues determines the outcome of alloantigen-specific T-cell responses in vitro and in vivo [1]. Although most mammalian cells express MHC class I antigens, expression of MHC class II molecules is more restricted [10]. Human fetal cord blood mononuclear cells (FB-MNCs) were shown to express MHC class I (A, B, C molecules), similar to hESC lines H1, H7, and H9 (Fig. 1C). Human FB-MNCs expressed low levels of MHC-II (DP, DQ, DR molecules), whereas none of the hESC lines examined (H1, H7, and H9) expressed MHC-II molecules on the cell surface (Fig. 1D).

View larger version (53K): [in this window] [in a new window]   Figure 1. Class I and II major histocompatability complex (MHC) expression on human embryonic stem cells (hESCs). (A): Alkaline phosphatase and stage-specific embryonic antigen-4 (SSEA-4) by immunostaining and (B) SSEA-4, SSEA-1, TRA-1-60, and TRA-1-81 by flow cytometry for both H1 and H9 hESCs were performed to confirm quality and undifferentiated phenotype of cells used in this study. Flow cytometry analysis was determined for primary human fetal cord blood mononuclear cells (FB-MNCs) and hESC lines H1, H7, and H9. Cord-blood mononuclear cells (CBMCs) and hESC cultured in standard conditions [20] were stained with antibodies against (C) MHC-I A, B, C (mean fluorescent intensity for hESCs ranging from 37 to 42), and (D) MHC-II DP, DQ, DR molecules. Representative histograms are shown for FB-MNC (n = 4) and hESC lines (n = 8). (E): Detection of stably transduced green fluorescent protein (GFP) expressing hESC cultures by fluorescence microscopy. Panels from left to right: hESC cultures, hESCs dissociated into single-cell suspensions, cross-sections of mice 24 and 48 hours after intramuscular injection. Injected hESCs could be visualized at the specific site introduced (n = 4). (F): Leukocyte infiltration was examined 48 hours after intramuscular injection of 2–5 x106 of human MBA-1 cells, FB-MNCs, or hESCs into immune-compromised Prk-/-severe combined immunodeficient (SCID) mice. Histopatho-logical analysis of muscle sections revealed that injection of either MBA-1 or FB-MNCs was able to induce a granulocytic infiltration response in these immune-compromised recipients, whereas injection of 2 x106 hESCs had no effect. (G): Leukocyte infiltration was examined 48 hours after intramuscular injection of PBS containing endotoxin (vehicle) or 2–5 x106 hESC-H1 or H9 cells resuspended in vehicle in wild-type immune-competent CD-1 mice. As expected, injection of vehicle alone induced a positive inflammatory immune response, as revealed by infiltrating leukocytes observed by histopathological analysis, whereas no infiltrate was detected upon injection of vehicle together with hESCs, suggesting that hESCs inhibited this reaction in vivo. Unlike hESCs, MBA-1 cells injected with vehicle did not inhibit the positive inflammatory response. Volume of injection ranged from 5 to 8 µl.

Using these procedures, human MBA-1 cells or FB-MNCs that were introduced into immune-compromised Prk-/-mice resulted in the infiltration of murine granulocytes as determined by histological analysis (Fig. 1F, left and middle panels). In contrast, no granulocytic infiltration was detectable in mice injected with hESCs (Fig. 1F, right panel), suggesting that in an in vivo immune-compromised environment, similar to patients receiving immune-suppressive treatment, hESCs do not induce an inflammatory response.

To further evaluate the in vivo immune response to hESCs, we introduced hESCs by intramuscular injection into immune-competent CD-1 mice. In contrast to immune-compromised Prk-/- recipients (Fig. 1F), injection of endo-toxin-containing PBS (vehicle) induced both lymphocyte and granulocyte infiltration at the site of injection (Fig. 1G, left panel). However, injection of vehicle together with hESCs abrogated leukocyte infiltration (Fig. 1G, right panel), in contrast to co-injection of MBA-1 cells with vehicle (Fig. 1G, center panel). These observations indicate that hESCs fail to elicit and inhibit proinflammatory responses in immunocompetent mice, suggesting that hESCs may not be immunogenic in a xenotransplant setting.

Since the inability of hESCs to evoke an immune response in mice (Fig. 1F, G) may be xenospecific, the immune responses to hESCs, were examined using primary human immune cells. First, we analyzed the expression of costimulatory molecules by undifferentiated and differentiated hESCs since these molecules are known to augment T-cell proliferation. Similar to previous studies, undifferentiated hESCs express high levels of alkaline phosphatase (Fig. 2A) and cell surface SSEA-4 (Fig. 2B). In contrast, differentiated hESCs, comprising embryoid bodies cultured in the absence of fibroblast growth factor (FGF) and the presence of serum, undergo rapid reduction in alkaline phosphatase expression by day 3, and complete loss by day 20 of differentiation (Fig. 2A), in addition to the lack of SSEA-4 expression (Fig. 2B).

View larger version (38K): [in this window] [in a new window]   Figure 2. Undifferentiated or differentiated human embryonic stem cells (hESCs) do not induce proliferation of allogeneic T cells. (A): Human hESC cultures and day-3 and day-20 embryoid bodies cultured in 20% fetal calf serum (FCS), in the absence of fibroblast growth factor (FGF) treatment were stained for alkaline phosphatase (Alk-Phos; blue) known to be expressed on primitive hESCs. (B): Flow cytometric analysis on B-lymphoblastoid cell line LG2, undifferentiated hESCs (H1 and H9), and cells derived from day-20 embryoid bodies representing differentiated hESCs for cell surface stage-specific embryonic antigen-4 (SSEA-4), and T-cell costimu-latory molecules CD40, B7.1, and B7.2. (C): Human hESCs (H9 and H1) were irradiated and used as stimulator cells for peripheral blood mononuclear cells (PBMCs) at 1:1 cell-to-cell ratio in a mixed lymphocyte response (MLR). Proliferation was determined in counts per minute (cpm) after [3H]-thymidine incorporation. Results shown are representative for six independent experiments, using individual PBMC donors and shown as an average stimulation index. (D): Peripheral blood lymphocytes (PBLs), enriched for T cells, were incubated with irradiated allogeneic dendritic cells (DCs) or hESC lines H1, H7, and H9, as indicated. T-cell proliferation was measured by [3H]-thymidine incorporation. Allogeneic DCs, expressing class I and class II molecules (data not shown), induced a significant proliferation of the T cells. Data represent the mean of stimulation index + standard error of the mean (SEM) of at least duplicate wells from four donors. Treated H1 and H9 hESCs and fibroblasts were exposed to gamma-interferon (IFN-)treatment for 7 days at 10 ng/ml. Major histocompatability complex (MHC)-I expression (measured as mean fluorescence intensity [MFI]) increased from 50 to 322 in response to IFN-(inset), with no change in MHC-II (inset) after 50–100 units of IFN-treatment for 72 hours prior to fluorescence-activated cell sorter FACS analysis. (E): Undifferentiated and differentiated (embryoid body cells) hESCs were irradiated and used as stimulator cells for PBMC at 1:2, 1:10, and 1:15 cell-to-cell ratio in an MLR reaction. Results shown are representative for six independent experiments, using individual PBMC donors and shown as an average stimulation index. indicates statistical differences, p < .01. Abbreviations: hEB, human embryoid body.

Based on the inability of hESCs to induce allogeneic T-cell responses, we examined whether this effect was passive or due to active inhibition of allogeneic T-cell response. As expected, a proliferative response was detected when PBLs were cocultured with allogeneic sources of professional antigen-presenting dendritic cells (DCs). Addition of hESCs to these cocultures inhibited T-cell proliferation in response to allogeneic DCs (Fig. 3A). This inhibitory activity was observed for all hESC lines examined. In contrast, addition of human fibroblasts to the cocultures did not inhibit allo-geneic T-cell proliferation. Serial reduction of the number of hESCs cocultured with the responding PBLs and allogeneic DCs resulted in a gradual loss of the inhibitory effect, suggesting that inhibition by hESCs was dependent on the number of inhibitory hESCs (Fig. 3B).

View larger version (25K): [in this window] [in a new window]   Figure 3. Human embryonic stem cells (hESCs) abrogate T-cell proliferation in mixed lymphocyte response (MLR) via mechanisms independent of secreted factors. (A): 1 x105 of irradiated hESCs (H1, H7, or H9) or human fibroblasts were added to wells containing 1 x105 T cells, together with allogeneic irradiated dendritic cells (DCs). At a T:DC ratio of 10:1, significant T-cell proliferation was observed by [3H]-thymidine incorporation. When DC and T cells were incubated in the presence of the hESCs, T-cell proliferation was significantly reduced. Human fibroblasts did not have an inhibiting effect on allogeneic T-cell proliferation (not shown). Data represent the mean of CPM + SEM. (B): 1 x105Tcells were incubated for 5 days with different numbers of fibroblasts, or hESCs (H1 or H9) in the presence of 1 x104 allogeneic DCs. Allogeneic DC-induced T-cell proliferation was significantly inhibited at a 1:1 ratio of T cells and hESCs. Data represent CPM + SEM. (C): Supernatants from cultures of undifferentiated hESCs or differentiated hESCs (day-20 human embryroid bodies) were added at 1:2, 1:10, and 1:100 dilutions to allogeneic-induced T-cell proliferation reactions. Addition of supernatants had no effect on normal allogeneic-induced T-cell proliferation, whereas (D) addition of either fixed or unfixed hESCs was able to inhibit T-cell proliferation. indicates statistical differences, p < .01. Abbreviations: CPM, counts per minute; PBL, peripheral blood lymphocyte; SEM, standard error of the mean.

The ability of third-party hESCs to inhibit alloantigen-induced T-cell proliferation suggests that hESCs may be tolerogenic. To address this issue, T cells from primary MLR (1° MLR) reactions were harvested and rechallenged in secondary MLR (2° MLR) reactions (Fig. 4A, B, respectively). Similar to previous experiments and autologous-control MLR reactions, fixed or nonfixed hESCs did not induce T-cell proliferation, as compared with allogeneic-responding T cells (Fig. 4A). As determined by 7-AAD dye exclusion and tryphantrypan blue staining, greater than 95% of T cells harvested from all 1° MLR reactions were viable (data not shown), indicating that the absence of T-cell proliferation was not due to cell death induced by cocultured hESCs. Upon secondary rechallenge, active responder T cells derived from primary allo-MLRs continued to proliferate in the presence of alloantigen, or phorbol 12-myristate 13-acetate (PMA) + ionomycin that induces T-cell proliferation via receptor-independent mechanisms (Fig. 4B). However, primary T-cell alloresponders failed to proliferate when exposed to hESCs in 2° MLRs, indicating that hESCs fail to induce T-cell alloresponse. Similar effects were observed using T-cell responders from auto-1° MLRs. More important, the T cells that failed to respond to fixed or nonfixed hESCs in 1° MLRs, were still able to proliferate in response to secondary allogeneic stimulation or PMA + ionomycin treatment. In contrast, re-exposure of these 1° MLR responders to hESCs had no effect on T-cell proliferation. Taken together, we suggest that T cells exposed to hESCs are not induced to become tolerant but are inhibited to proliferate when they are in direct contact with hESCs.

View larger version (18K): [in this window] [in a new window]   Figure 4. No evidence of T-cell tolerance in secondary rechallenge of Tcells previously exposed to human embryonic stem cells (hESCs). (A): Primary mixed lymphocyte reactions (1° MLRs) were performed, and T-cell proliferation was measured and shown as thymidine incorporation. (B): T cells isolated from 1° MLRs, termed 1° MLR responders, were rechallenged in secondary MLRs (2° MLRs) using allogeneic peripheral blood lymphocytes (PBLs), phorbol 12-myristate 13-acetate (PMA) + ionomycin, media (control), and hESCs as stimulators. Abbreviation: CPM, counts per minute.

	DISCUSSION

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Immunosuppressive drugs allow the majority of transplant recipients to accept allogeneic donated tissue and prevent acute graft rejection. However, immunosuppression has complications, including the increased susceptibility to infections [17]. Our study indicates that hESCs possess mechanisms that counteract immune responses, thereby providing protection to hESC-derived allografts while allowing locally inhibited T cells to respond to other foreign antigens. However, this same beneficial property also reveals the risk of seeding transplanted hosts with hESCs capable of neoplastic growth.

The immunologically privileged state of the human embryo has been attributed to a unique relationship between the maternal host and fetal tissue that is dependent on the physiology and structure of the placenta [4, 6–9]. Based on our current observations using hESCs as a model, the lack of maternal immuno-genic response to the human embryo may be independent of complex in vivo interactions mediated by the placental barrier [5] but instead is due to unique properties of embryonic human cells that inhibit local immune responses to the fetus.

The combination of regenerative medicine strategies using stem cells [18] and evidence for the lack of immune response to undifferentiated and differentiated hESCs suggests that a scientific branch of immunology is evolving [19]. Further study into "stem cell immunobiology" will reveal the exact mechanisms that account for the unique immunological properties of human stem cells and will likely have an impact on both our basic understanding of immune response and future approaches of cell replacement therapy.

	METHODS

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Flow Cytometry Analysis
Cell-surface markers were analyzed by immunostaining and flow cytometry. The following antibodies against these molecules and their respective isotype controls were used: HLA-A, B, C; HLA-DP, DQ, DR (BD-Pharmingen, San Diego, CA). 5 x10⁵ cells were incubated with antibody for 30 minutes on ice, washed with phosphate-buffered saline (PBS) + 2% fetal bovine serum (FBS), and 1 µM Na-Azide. Following addition of propidium iodide (1–2 µg/1 x10⁵ cells), flow cytometric analysis was performed on a fluorescence-activated cell sorter (FACS), FACScan or FACalibur flow cytometer (Becton, Dickinson, San Jose, CA) using the CELLQuest program (Becton, Dickinson). The hESC lines analyzed in these studies were H1 (passages 36–45), H7 (passages 37–43), and H9 (passages 31–40). Human ESCs and differentiated human embryoid bodies were cultured as previously described [20].

Mixed Lymphocyte Reactions and T-Cell Inhibition Assays
PBMCs and FB-MNCs were isolated from heparinized samples from healthy volunteers on Ficoll-Hypaque gradient (Amersham Pharmacia Biotech AB, Uppsala, Sweden). Cells were washed and resuspended in complete-culture RPMI 1640 medium containing 2 mM L-glutamine, penicillin (100 U/ml), streptomycin (100 µg/ml), and 10% FBS. Then 100 µl of responder cells at 1 x10⁶ cells/ml and different numbers of irradiated (5000 rads) stimulator cells were placed in 96-well U-bottom plates and incubated at 37°C for 5–6 days. Plates were pulsed with 1 µCi/well of [3H]-thymi-dine for 18 hours before harvesting. Cells were harvested onto glass fiber filters, and [3H]-thymidine incorporation was quantified using a beta counter (1450 Microbeta Trilux, Wallac, Turku, Finland). To measure allogeneic T-cell proliferation, nonadherent mononuclear cells, containing mostly primary T cells, were isolated from buffy coats from normal healthy volunteers. Following Ficoll-Hypaque density gradient centrifugation and a subsequent 2-hour incubation period at 37°C, the nonadherent T cells were collected and frozen in 60% AIM-V, 30% FBS, and 10% dimethylsulfox-ide (DMSO) for later use. The remaining adherent cells were cultured for 7 days in AIM-V containing 10 ng/ml human recombinant GM-CSF (R&D Systems Inc., Minneapolis, MN) and 10 ng/ml IL-4 (R&D Systems). Nonadherent DCs were collected on the 7th day. Human ESC lines were cultured as described previously. A human fibroblast line was used as a control. Following irradiation, the stimulators—DCs (3000 Rad), BJ (3000 Rad), or hES-cellC lines (1000 Rad)—were plated in 96-well round-bottom plates in AIM-V medium at concentrations ranging from 1 x10⁵ to 1 x10², as indicated in the figures. T cells were added at a concentration of 1 x10⁵ T cells/well, and the plates were incubated in AIM-V for 5 days. Some 16–20 hours before the harvest, the wells were pulsed with [3H]-thymidine. The [3H]-thymidine cellular incorporation for these experiments was measured using a Packard plate harvester and counter. For assays related to inhibition of allogeneic DC-stimulated T-cell proliferation, T cells and stimulators were isolated and treated as described under allogeneic T-cell proliferation. Following a 0- or 2-hour incubation of 1 x10⁵ T cells with varying numbers of irradiated human fibroblasts and hESCs (1 x10⁵ to 3.3 x10³), 1 x10⁴/well-irradiated allogeneic DCs were added to the cultures. Fixation of hESCs was performed by incubation with 4% paraformaledehyde for 10 minutes, followed by three subsequent washes in PBS. The cells were pulsed for the last 16–20 hours, and [3H]-thymidine incorporation was measured after 5 days incubation. Secondary MLRs were performed in a similar fashion, with the exception of using purified T cells harvested from primary MLR reactions.

Histopathological Analysis after In Vivo Injection
Leg muscles of Prk-/- severe combined immunodeficient (SCID) and wild-type CD-1 recipients from Jackson Laboratories (Bar Harbor, ME) were cut in half through the central point of injection marked with tracking dye. These animal studies were performed in accordance and approval from our local Animal Care and Veterinary Services (ACVS) at the University of Western Ontario. Tissue was fixed in 10% buffered formalin overnight and then incubated with 0.1 M PBS containing 15% and 30% sucrose at 4°C, each for 8 hours. The two halves were embedded side by side with HISTO PREP compound (Fisher Scientific, Hampton, NH). Thirty serial sections (5 µm) were made by cryostat sectioning for each specimen. Every second section was kept for hematoxylin and eosin (H&E) staining. The presence of leukocytes was identified by their characteristic morphology in H&E-stained sections at 1,000xmagnification. All of the specimens were coded so that the measurements were done blindly and confirmed by random reanalysis of approximately one-second of the specimens by the same examiner (R > 0.97).

	ACKNOWLEDGMENTS

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This work was supported in part by a grant from the Multiple Organ Transplant Initiative, Geron Corporation, London Health Sciences Centre, and a Canadian Research Chair in Stem Cell Biology and Regenerative Medicine to M.B. and in Transplantation and Immunology to J.M. We would like to thank Christina Bhatia, Krysta Levac, and Francis Karanu for insights leading to completion of this study. The authors confirm that there are no conflicts of interest related to commercial affiliations regarding this work.

	REFERENCES

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1. Janeway CA Jr. The role of self-recognition in receptor repertoire development. Members of the Janeway Laboratory. Immunol Res 1999;19:107–118.[Medline]

2. Bradley JA, Bolton EM, Pedersen RA. Stem cell medicine encounters the immune system. Nat Rev Immunol 2002;2:859–871.[CrossRef][Medline]

3. Thomson JA, Itskovitz-Eldor J, Shapiro SS et al. Embryonic stem cell lines derived from human blastocysts. Science 1998;282:1145–1147.[Abstract/Free Full Text]

4. Jiang SP, Vacchio MS, Bennett WA et al. Multiple mechanisms of peripheral T cell tolerance to the fetal "allo-graft." J Immunol 1998;160:3086–3090.[Abstract/Free Full Text]

5. Mellor AL, Munn DH. Immunology at the maternal-fetal interface: lessons for T cell tolerance and suppression. Annu Rev Immunol 2000;18:367–391.[CrossRef][Medline]

6. Gaunt G, Ramin K. Immunological tolerance of the human fetus. Am J Perinatol 2001;18:299–312.[CrossRef][Medline]

7. Bennett WA, Lagoo-Deenadayalan S, Whitworth NS et al. First-trimester human chorionic villi express both immunoregulatory and inflammatory cytokines: a role for interleukin-10 in regulating the cytokine network of pregnancy. Am J Reprod Immunol 1999;41:70–78.

8. Carosella ED, Dausset J, Rouas-Freiss N. Immunotol-erant functions of HLA-G. Cell Mol Life Sci 1999; 55:327–333.[CrossRef][Medline]

9. Munn DH, Zhou M, Attwood JT et al. Prevention of allo-geneic fetal rejection by tryptophan catabolism. Science 1998;281:1191–1193.[Abstract/Free Full Text]

10. Viret C, Janeway CA Jr. MHC and T cell development. Rev Immunogenet 1999;1:91–104.[Medline]

11. Tschopp J, Martinon F, Burns K. NALPs: a novel protein family involved in inflammation. Nat Rev Mol Cell Biol 2003;4:95–104.[CrossRef][Medline]

12. Trinchieri G. Interleukin-12 and the regulation of innate resistance and adaptive immunity. Nat Rev Immunol 2003;3:133–146.[CrossRef][Medline]

13. Sirard C, Laneuville P, Dick JE et al. Expression of bcr-abl abrogates factor-dependent growth of human hema-topoietic M07E cells by an autocrine mechanism. Blood 1994;83:1575–1585.[Abstract/Free Full Text]

14. Lebkowski JS, Gold J, Xu C et al. Human embryonic stem cells: culture, differentiation, and genetic modification for regenerative medicine applications. Cancer J 2001;7:S83–93.

15. Fruh K, Yang Y, Ponzio NM. Antigen presentation by MHC class I and its regulation by interferon gamma. Curr Opin Immunol 1999;11:76–81.[CrossRef][Medline]

16. Drukker M, Katz G, Urbach A et al. Characterization of the expression of MHC proteins in human embryonic stem cells. Proc Natl Acad Sci U S A 2002;11:11.[CrossRef]

17. Fishman JA. Overview: fungal infections in the transplant patient. Transpl Infect Dis 2002;4:3–11.

18. Fandrich F, Lin X, Chai GX et al. Preimplantation-stage stem cells induce long-term allogeneic graft acceptance without supplementary host conditioning. Nat Med 2002;8:171–178.[CrossRef][Medline]

19. Fandrich F, Dresske B, Bader M et al. Embryonic stem cells share immune-privileged features relevant for tolerance induction. J Mol Med 2002;80:343–350.[CrossRef][Medline]

20. Xu C, Inokuma MS, Denham J et al. Feeder-free growth of undifferentiated human embryonic stem cells. Nat Biotechnol 2001;19:971–974.[CrossRef][Medline]

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