Transduction of dendritic cell progenitors with a retroviral vector encoding viral interleukin-10 and enhanced green fluorescent protein allows purification of potentially tolerogenic antigen-presenting cells

BACKGROUND

Dendritic cells (DC) are important antigen-presenting cells that play critical roles in the initiation and modulation of immune responses. Genetic engineering of DC to express immunosuppressive molecules is a novel approach to the inhibition of allograft rejection. Retroviral delivery of viral interleukin (vIL)-10 to replicating myeloid DC progenitors (DCp) impairs their T-cell stimulatory capacity and promotes the induction of antigen-specific T-cell hyporesponsiveness. However, transduction efficiency with retroviral vectors is comparatively low. Enhanced green fluorescent protein (EGFP) is important both as a marker of gene transduction and for the selection of transduced cells. Our aims were to construct a retroviral vector encoding both vIL-10 and EGFP, to positively select transduced DC, and to assess the impact of these highly purified, vIL-10-secreting antigen-presenting cells on allogeneic T-cell responses.

METHODS

DCp propagated from bone marrow of C57BL10 (H2b) mice in granulocyte-macrophage colony-stimulating factor (GM-CSF)+IL-4 were transduced with a retroviral vector encoding both vIL-10 and EGFP by centrifugal enhancement. Gene transfer efficiency was determined by flow cytometry. Transduced cells were flow sorted, and vIL-10 secretion was quantified by ELISA. DC function was assessed by the ability of the cells to induce naive allogeneic (C3H; H2k) T-cell proliferation and cytotoxic T lymphocyte generation.

RESULTS

Retrovirally transduced DC expressed both vIL-10 and EGFP gene products. Approximately 20% of unsorted cells expressed EGFP, as determined by flow cytometry. vIL-10 was produced at a mean rate of 31 ng/40 hr/10(6) cells. After sorting, the incidence of EGFP+ DC was increased dramatically to at least 95%, and the production of vIL-10 was increased approximately three- to fourfold, to a mean of 107 ng/40 hr/10(6) cells. These highly purified, vIL-10-secreting DC exhibited markedly diminished capacity to induce allogeneic T-cell proliferative and cytotoxic responses.

CONCLUSIONS

DCp retrovirally transduced to express both vIL-10 and EGFP can be rapidly identified and sorted to high levels of purity. The availability of highly enriched preparations of vIL-10-transduced DC facilitates studies of their immunoregulatory function and may enhance their therapeutic potential in transplantation or autoimmune disease.

Differential effects of exogenous interleukin-10 on cardiac allograft survival: inhibition of rejection by recipient pretreatment reflects impaired host accessory cell function

BACKGROUND

There have been conflicting reports of the influence of exogenous mammalian interleukin (IL)-10 on immune reactivity. These findings may reflect the pleiotropic effects of IL-10 on the functions of antigen-presenting cells and immune effector cells. The purpose of this study was to extend observations of the influence of the cytokine on organ allograft survival and to investigate its effects on the function of accessory and immune effector cells in a mouse cardiac transplant model.

METHODS

C3H (H2k) recipients of heterotopic vascularized B10 (H-2b) heart allografts were treated with recombinant (r) mouse IL-10 over a wide range of doses (0.2-200 microg/day), either before the transplant (days -3, -2, -1), peri-operatively (days -1, 0, 1), or after the transplant (days 0-6). Anti-donor cytotoxic T lymphocyte activity of host spleen and graft-infiltrating cells, and circulating complement-dependent cytotoxic antibody titers were determined by isotope release assays. Mixed leukocyte reactions were used to determine the influence of IL-10 on the function of antigen-presenting cells and allogeneic responder T cells.

RESULTS

Recipient pre-transplant administration of IL-10 (days -3, -2, -1) prolonged graft survival at all doses tested. Donor pretreatment with IL-10 (25 microg/day; days -3, -2, -1) was also effective, but less. A pre-transplant or perioperative course of IL-10, however, did not significantly affect the immunosuppressive action of tacrolimus given on days 0-6. If given only after the transplant, IL-10 either had no effect on graft survival or (at high dosage) accelerated rejection and prevented the immunosuppressive effect of cyclosporine. Pretransplant treatment of graft recipients with IL-10 reduced splenic anti-donor cytotoxic T lymphocyte activity and the incidence of graft-infiltrating CD8+ cells. There was no significant effect on circulating alloantibody titers. MLR assays revealed that preincubation of responder cells, but not stimulator spleen cells with IL-10, inhibited T cell proliferation, whereas addition of IL-10 after the start of culture modestly enhanced proliferation. Preincubation of purified T responders with IL-10 showed no inhibitory effect.

CONCLUSION

The modest and opposing effects of exogenous IL-10 on organ allograft survival are dependent on timing and dosage. Recipient pretreatment prolongs graft survival. This finding, together with the MLR results, suggest that IL-10 inhibits the function of host immune accessory cells and that the direct pathway of alloantigen presentation may be less susceptible to inhibition by IL-10.

Cyclosporine A inhibits the expression of costimulatory molecules on in vitro-generated dendritic cells: association with reduced nuclear translocation of nuclear factor kappa B

BACKGROUND

The maturation of dendritic cells (DC) is influenced by various factors, in particular cytokine-mediated signaling events. These include modulation of the activation of nuclear factor kappa B (NF-kappaB), which controls the transcription of genes encoding major histocompatibility complex (MHC) antigens, and costimulatory/accessory molecules for T-cell activation. Here, we investigated the influence of cyclosporine A (CsA) on the in vitro maturation of DC, and on the nuclear translocation and DNA binding of NF-kappaB.

METHODS

DC progenitors were propagated from mouse bone marrow in granulocyte-macrophage colony-stimulating factor (GM-CSF) or in GM-CSF plus either transforming growth factor (TGF)-beta or interleukin (IL)-4, in the presence or absence of CsA (1 microg/ml). After 5 days of culture, cell surface expression of MHC class I/II, CD40, CD80, and CD86 was analyzed by flow cytometry, and nuclear NF-kappaB proteins by electrophoretic mobility shift, antibody supershift, and Western blot assays. The antigen-presenting function of DC was determined in one-way mixed leukocyte reactions.

RESULTS

Exposure of replicating DC progenitors propagated in GM-CSF or GM-CSF+TGF-beta to CsA reduced costimulatory molecule expression, without affecting MHC antigen expression. Nuclear extracts from the CsA-treated DC revealed a decrease in nuclear translocation of NF-kappaB (p50). Mixed leukocyte reaction data were consistent with the flow cytometry and gel shift assay results, and showed reduced allostimulatory ability of the CsA-treated cells compared with untreated controls. Addition of IL-4 from the start of DC cultures conferred resistance to CsA-induced inhibition of NF-kappaB nuclear translocation and DC maturation.

CONCLUSIONS

CsA differentially inhibits the expression of key cell surface costimulatory molecules by in vitro-generated DC. This effect can be overcome, at least in part, by IL-4 and augmented by TGF-beta. The inhibition is linked to a decrease in nuclear translocation/DNA binding of NF-kappaB. Thus, CsA can alter the antigen-presenting function of DC for T-cell activation.

Increased apoptosis of immunoreactive host cells and augmented donor leukocyte chimerism, not sustained inhibition of B7 molecule expression are associated with prolonged cardiac allograft survival in mice preconditioned with immature donor dendritic cells plus anti-CD40L mAb

BACKGROUND

We previously reported the association among donor leukocyte chimerism, apoptosis of presumedly IL-2-deficient graft-infiltrating host cells, and the spontaneous donor-specific tolerance induced by liver but not heart allografts in mice. Survival of the rejection-prone heart allografts in the same strain combination is modestly prolonged by the pretransplant infusion of immature, costimulatory molecule-(CM) deficient donor dendritic cells (DC), an effect that is markedly potentiated by concomitant CM blockade with anti-CD40L (CD154) monoclonal antibody (mAb). We investigated whether the long survival of the heart allografts in the pretreated mice was associated with donor leukocyte chimerism and apoptosis of graft-infiltrating cells, if these end points were similar to those in the spontaneously tolerant liver transplant model, and whether the pretreatment effect was dependent on sustained inhibition of CM expression of the infused immature donor DC. In addition, apoptosis was assessed in the host spleen and lymph nodes, a critical determination not reported in previous studies of either spontaneous or "treatment-aided" organ tolerance models.

METHODS

Seven days before transplantation of hearts from B10 (H-2b) donors, 2x10(6) donor-derived immature DC were infused i.v. into C3H (H-2k) recipient mice with or without a concomitant i.p. injection of anti-CD40L mAb. Donor cells were detected posttransplantation by immunohistochemical staining for major histocompatibility complex class II (I-Ab) in the cells of recipient lymphoid tissue. CM expression was determined by two-color labeling. Host responses to donor alloantigen were quantified by mixed leukocyte reaction, and cytotoxic T lymphocyte (CTL) assays. Apoptotic death in graft-infiltrating cells and in areas of T-dependent lymphoid tissue was visualized by terminal deoxynucleotidyltransferase-catalyzed dUTP-digoxigenin nick-end labeling and quantitative spectrofluorometry. Interleukin-2 production and localization were estimated by immunohistochemistry.

RESULTS

Compared with control heart transplantation or heart transplantation after only DC administration, concomitant pretreatment with immature donor DC and anti-CD40L mAb caused sustained elevation of donor (I-Ab+) cells (microchimerism) in the spleen including T cell areas. More than 80% of the I-Ab+ cells in combined treatment animals also were CD86+, reflecting failure of the mAb to inhibit CD40/ CD80/CD86 up-regulation on immature DC in vitro after their interaction with host T cells. Donor-specific CTL activity in graft-infiltrating cells and spleen cell populations of these animals was present on day 8, but decreased strikingly to normal control levels by day 14. The decrease was associated with enhanced apoptosis of graft-infiltrating cells and of cells in the spleen where interleukin-2 production was inhibited. The highest levels of splenic microchimerism were found in mice with long surviving grafts (>100 days). In contrast, CTL activity was persistently elevated in control heart graft recipients with comparatively low levels of apoptotic activity and high levels of interleukin-2.

CONCLUSION

The donor-specific acceptance of rejection-prone heart allografts by recipients pretreated with immature donor DC and anti-CD40L mAb is not dependent on sustained inhibition of donor DC CM (CD86) expression. Instead, the pretreatment facilitates a tolerogenic cascade similar to that in spontaneously tolerant liver recipients that involves: (1) chimerism-driven immune activation, succeeded by deletion of host immune responder cells by apoptosis in the spleen and allograft that is linked to interleukin-2 deficiency in both locations and (2) persistence of comparatively large numbers of donor-derived leukocytes. These tolerogenic mechanisms are thought to be generic, explaining the tolerance induced by allografts spontaneously, or with the aid of various kinds of immunosuppression.

Hepatic dendritic cells: immunobiology and role in liver transplantation

Traditional investigations of hepatic dendritic cells (DC) have focused on immunohistochemical studies of these cells within normal and pathological liver tissue. The recent availability of reagents for the improved characterization of DC, together with cytokine-based methods for the expansion of liver DC both in vivo and in vitro have begun to provide new insight into the immunobiology of these important antigen-presenting cells. Hepatic DC probably play a key role in the host response to blood-borne pathogens, and in the pathogenesis of infectious and autoimmune liver diseases. They appear to be important in determining the balance between liver transplant tolerance and rejection. Their possible role in oral and portal venous tolerance remains to be defined. In this article, we focus on emerging aspects of hepatic DC immunobiology, with particular reference to liver transplantation.

Genetic engineering of dendritic cells to express immunosuppressive molecules (viral IL-10, TGF-beta, and CTLA4Ig)

There is growing evidence that, in addition to their role as initiators of immune responses, dendritic cells (DC) can exhibit tolerogenic properties. Immature DC deficient in cell surface costimulatory/accessory molecules can prolong organ and pancreatic islet allograft survival, whereas in vitro manipulation of DC by exposure to a variety of factors (e.g., viral interleukin-10; CTLA4Ig) can confer tolerogenic properties on these cells. Genetic engineering of DC to express immunosuppressive molecules is, in theory, an attractive approach to the therapy of allograft rejection and possibly, autoimmune disorders.

Dendritic cells as regulators of immune reactivity: implications for transplantation

Dendritic cells are now regarded not only as the initiators but also as regulators of immune responses. They are potentially powerful tools for the therapeutic manipulation of immune reactivity in cancer, infectious disease, and allograft rejection. We provide a brief overview of the properties of dendritic cells, with emphasis on recently acquired information, then focus attention on their capacity to modulate immune reactivity, and its relevance to transplantation.

Adenoviral delivery of CTLA4Ig into myeloid dendritic cells promotes their in vitro tolerogenicity and survival in allogeneic recipients

Dendritic cells (DC) are highly specialized antigen-presenting cells (APC) that initiate and modulate immune responses. They are essential for naive T cell activation, but may also play roles both in central and peripheral tolerance. Blockade of costimulatory pathways that provide the crucial second signal for lymphocyte activation is one strategy to augment the potential tolerogenicity of DC. Here, in vitro propagated DC were transduced using an adenoviral (Ad) vector to express the gene encoding cytotoxic T lymphocyte antigen 4-immunoglobulin (CTLA4lg), which blocks interaction of CD80 and CD86 on DC with CD28 on T cells. Supernatants of AdCTLA4lg-transduced DC strikingly inhibited mixed leukocyte reactions (MLR) induced by non-transduced DC. Whereas transduction of marker genes (LacZ or enhanced green fluorescence protein (EGFP)) did not alter their potent allostimulatory activity, DC transduced with CTLA4lg exhibited striking reductions in cell surface staining for CD86, but not MHC class II, and were poor stimulators of T cell proliferation and cytotoxic T lymphocyte (CTL) responses. In addition, they induced alloantigen-specific T cell hyporesponsiveness. They were detected, following local injection, in significantly increased numbers in the lymphoid tissue of unmodified allogeneic recipients. This is the first report of the functional properties of DC genetically engineered to express CTLA4lg.

Trafficking of APC from liver allografts of Flt3L-treated donors: augmentation of potent allostimulatory cells in recipient lymphoid tissue is associated with a switch from tolerance to rejection

Livers transplanted across major histocompatibility complex (MHC) barriers in mice are normally accepted without recipient immune suppression, and induce a state of functional tolerance. However, markedly increasing functional dendritic cells (DC) in the 'passenger leucocyte' population by donor pretreatment with the hematopoietic growth factor Flt3-ligand (Flt3L; 10 microg/day for 10 days) results in acute allograft rejection. In this study, molecular, immunohistochemical and flow cytometric analysis of donor cell traffick into recipient lymphoid tissue 24 h after liver transplantation (C57BL/10 [H2b]-->C3H [H2k]) was performed. In addition, the capacity of donor-derived cells in these tissues to stimulate host T cell proliferation was examined. Reverse transcriptase polymerase chain reaction analysis revealed increases in donor genomic DNA in both thymi and spleens of mice given livers from Flt3L-treated donors compared to controls. Donor MHC class II+ (IAb+) cells in spleens were strikingly elevated (10-fold) in the former group. Two-colour flow cytometry revealed a similar increase in donor-derived H-2Kb+/I-Ab+ cells, and in the incidence of donor leucocytes expressing CD40, CD80, and CD86. CD11c+ DC comprised approximately 40% of the I-Ab+ cells in spleens of mice given livers from Flt3L-treated donors. These changes were associated with the presence, in spleens, of potent allostimulatory activity for naive recipient strain T cells, that was not observed in normal liver recipients. Elicitation of allograft rejection, associated with enhanced trafficking of stimulatory donor antigen-presenting cells (APC), in particular DC, suggests that normal liver graft survival and tolerance induction may be linked to failure/counter-regulation of APC-driven stimulation of effective anti-donor T cell responses.

Prevention and restoration of second-set liver allograft rejection in presensitized mice: the role of "passenger" leukocytes, donor major histocompatibility complex antigens, and host cytotoxic effector mechanisms

BACKGROUND

The aim was to determine whether sublethal donor total body irradiation (TBI) might be as effective as lethal TBI in preventing mouse second-set liver allograft rejection, and to evaluate the role of passenger leukocytes, donor major histocompatibility complex (MHC) antigens, and host effector mechanisms in the response to livers from sublethally irradiated donors.

METHODS

B10 (H2b) donors received various doses of TBI at different times before their livers were transplanted orthotopically into normal or donor skin-presensitized C3H (H2k) recipients. The influence of irradiation on graft non-parenchymal cells (NPC) was determined by monoclonal antibody staining, and flow cytometric analysis. Hematopoietic cells within the grafts were reconstituted by intravenous infusion of syngeneic or third-party bone marrow cells. Allograft survival was determined in recipients that received no treatment, or that were given spleen cells from either normal B10 donors, or MHC class I - or class II-deficient mice syngeneic with the donors. Cytotoxic activity of graft-infiltrating cells and host spleen cells, and complement-dependent cytotoxic alloantibody titers were determined by isotype release assays.

RESULTS

The protective effect of donor TBI was observed both at lethal (9.5 Gy) and sublethal doses (5 and 3 Gy; graft median survival time: >100 days). Extended delay in liver transplantation, allowing hematopoietic recovery and graft reconstitution eliminated the effect. Liver NPC were reduced about 80% within 24 hr of 3 Gy TBI, with a selective reduction in the incidence of B cells. The NPC-depleted livers underwent accelerated rejection when donor (but not third-party) spleen cells (5 x 10(7) were administered systemically to the recipient immediately after graft revascularization. Spleen cells from MHC class I-deficient (but not MHC class II-deficient) mice failed to fully restore accelerated rejection of TBI liver grafts. Freshly isolated graft NPC, or spleen cells from TBI liver recipients, harvested 4 days after transplantation, exhibited lower, donor-specific cytotoxic activity than cells from mice given normal livers. Recipients of TBI livers also showed much lower serum complement-dependent cytotoxic alloantibody titers.

CONCLUSIONS

By substantially depleting "passenger leukocytes," sublethal donor TBI undermines anti-donor cell-mediated and humoral immune reactivity and inhibits second-set liver allograft rejection in presensitized recipients. The interval between irradiation and transplantation is important in conferring resistance to rejection. Expression of MHC class I on donor leukocyte infusions is important for overcoming resistance to second-set rejection induced by donor irradiation.

Evidence for a Role of IL-17 in Organ Allograft Rejection: IL-17 Promotes the Functional Differentiation of Dendritic Cell Progenitors

IL-17 is a T cell-derived cytokine that stimulates stromal cells and macrophages to secrete proinflammatory cytokines. We hypothesized that IL-17 might play a role in alloimmune responses, and that interference with its activity might suppress allograft rejection. IL-17R:Fc or control IgG was added at the start of mouse MLR or was administered i.p. (100–500 μg/day) for different durations post-transplant to murine recipients of MHC-mismatched cardiac allografts. IL-17R:Fc (50–200 μg/ml) markedly inhibited T cell proliferation in vitro and significantly prolonged nonvascularized cardiac allograft median survival time from 13 to 20 days (100 μg/day; days 0 and 1) or to 19 days (100–300 μg/day; days 0–4). Survival of vascularized grafts was also extended significantly from 10.5 to 19 days by IL-17R:Fc (500 μg/day; days 0–6). To address a possible mechanism by which IL-17 may promote alloreactivity, we examined the influence of IL-17 on the differentiation and function of bone marrow-derived cells propagated in granulocyte-macrophage CSF with or without IL-4 to promote dendritic cell (DC) growth. A minor proportion of CD11c+ DC expressed the IL-17R. IL-17 promoted the maturation of DC progenitors, as evidenced by increased cell surface expression of CD11c, costimulatory molecules (CD40, CD80, CD86), and MHC class II Ag, and allostimulatory capacity. IL-17 had a lesser effect on the phenotype and function of more fully differentiated myeloid DC. These findings suggest a role for IL-17 in allogeneic T cell proliferation that may be mediated in part via a maturation-inducing effect on DC. IL-17 appears to be a novel target for therapeutic intervention in allograft rejection.

Evidence for a role of IL-17 in organ allograft rejection: IL-17 promotes the functional differentiation of dendritic cell progenitors

IL-17 is a T cell-derived cytokine that stimulates stromal cells and macrophages to secrete proinflammatory cytokines. We hypothesized that IL-17 might play a role in alloimmune responses, and that interference with its activity might suppress allograft rejection. IL-17R:Fc or control IgG was added at the start of mouse MLR or was administered i.p. (100-500 microg/day) for different durations post-transplant to murine recipients of MHC-mismatched cardiac allografts. IL-17R:Fc (50-200 microg/ml) markedly inhibited T cell proliferation in vitro and significantly prolonged nonvascularized cardiac allograft median survival time from 13 to 20 days (100 microg/day; days 0 and 1) or to 19 days (100-300 microg/day; days 0-4). Survival of vascularized grafts was also extended significantly from 10.5 to 19 days by IL-17R:Fc (500 microg/day; days 0-6). To address a possible mechanism by which IL-17 may promote alloreactivity, we examined the influence of IL-17 on the differentiation and function of bone marrow-derived cells propagated in granulocyte-macrophage CSF with or without IL-4 to promote dendritic cell (DC) growth. A minor proportion of CD11c+ DC expressed the IL-17R. IL-17 promoted the maturation of DC progenitors, as evidenced by increased cell surface expression of CD11c, costimulatory molecules (CD40, CD80, CD86), and MHC class II Ag, and allostimulatory capacity. IL-17 had a lesser effect on the phenotype and function of more fully differentiated myeloid DC. These findings suggest a role for IL-17 in allogeneic T cell proliferation that may be mediated in part via a maturation-inducing effect on DC. IL-17 appears to be a novel target for therapeutic intervention in allograft rejection.