Dendritic cells genetically engineered to express Fas ligand induce donor-specific hyporesponsiveness and prolong allograft survival

Alternatives to immunosuppressive drugs in human islet transplantation

Although intensive insulin therapy has resulted in improved metabolic control and decreases in the incidence of complications, the occurrence of severe hypoglycemia remains an issue, as does the continued potential for complications. Islet transplantation, a promising treatment for type I diabetes, has been shown to improve blood sugar levels and decrease or even abrogate the incidence of hypoglycemia. The lack of tissue availability and the toxic effects of immunosuppressants, however, limit the application of islet transplantation as a cure for diabetes. This article discusses possible alternatives to immunosuppressive drugs in human islet transplantations.

Retroviral delivery of transforming growth factor-beta1 to myeloid dendritic cells: inhibition of T-cell priming ability and influence on allograft survival

BACKGROUND

Transforming growth factor (TGF)-beta inhibits the maturation and function of antigen-presenting cells. Our purpose was to evaluate the impact of retroviral delivery of human TGF-beta1 to murine myeloid dendritic cell (DC) progenitors on (i) their in vitro properties, (ii) their in vivo function, and (iii) their influence on organ allograft survival.

METHODS

C57BL10 (B10; H2b) bone marrow cells were lineage depleted and stimulated with granulocyte-macrophage colony-stimulating factor for 6 days. Replicating DC progenitors were transduced on days 2, 3, and 4 of culture by ecotropic retrovirus encoding human TGF-beta1 using centrifugal enhancement. Secretion of TGF-beta1 and other cytokines was quantified by enzyme immunoassay. Allogeneic C3H/HeJ (C3H; H2k) T-cell proliferative responses and generation of cytotoxic T lymphocytes in mixed leukocyte reaction were determined by [3H]thymidine incorporation and 51Cr release assays, respectively. DC migration was analyzed by immunohistochemistry, and their impact on survival of intra-abdominal heart transplants was determined.

RESULTS

Maximal TGF-beta1 transduction efficiency was 60%. The TGF-beta-transduced DC showed pronounced impairment (>80%) of T-cell allostimulatory activity in vitro. After their IV injection, B10 TGF-beta-transduced DC (IAb+) were detected in T-cell areas of spleens of allogeneic C3H recipients. Splenic T-cell responses to donor alloantigens of mice that received TGF-beta-transduced DC were severely impaired. This was accompanied by marked inhibition of interleukin-2 and interferon-gamma production in response to restimulation with donor alloantigen. Survival of B10 cardiac allografts in C3H mice given B10 TGF-beta-transduced DC (2x106 IV, 7 days before transplantation), was extended modestly but significantly.

CONCLUSION

Retroviral transduction of myeloid DC progenitors to overexpress TGF-beta is associated with marked impairment of their T-cell allostimulatory activity but with only modest prolongation of organ allograft survival.

Fas-ligand--iron fist or Achilles' heel?

Experimental and physiological expression of the pro-apoptotic molecule Fas-ligand can induce inflammation under certain conditions. Discussed here are the experimental situations, possible mechanisms, and pathways that mediate this response.

Killing of naive T cells by CD95L-transfected dendritic cells (DC): in vivo study using killer DC-DC hybrids and CD4(+) T cells from DO11.10 mice

Dendritic cells (DC) play the dual task of initiating cellular immunity against potentially harmful foreign antigens (Ag), while maintaining immunological tolerance to self-Ag and environmental Ag. As an approach to induce Ag-specific suppression, we and others introduced CD95 ligand (L) cDNA into DC. The resulting "killer" DC delivered apoptotic signals, instead of activation signals, to primed CD4(+) T cells in vitro and induced Ag-specific immunosuppression in vivo. To study the impact of killer DC on naive T cells, the fate of Ag-reactive T cells and the extent of their depletion after killer DC treatment, we performed in vitro and in vivo reconstitution experiments using: (a) killer DC-DC hybrids created between CD95L-transduced XS106 DC clone (A/J origin) and splenic DC from BALB/c mice, (b) CD4(+) T cells isolated from DO11.10 transgenic mice (BALB/c background), and (c) OVA(323-339) peptide as relevant Ag. Ovalbumin (OVA)-pulsed killer DC-DC hybrids inhibited DO11.10 T cell activation triggered by conventional DC, instead of inducing their activation. Rapid apoptosis of T cells was observed after co-culture with OVA-pulsed killer DC-DC hybrids, but not with non-pulsed killer DC-DC hybrids or OVA-pulsed control DC-DC hybrids. For in vivo reconstitution, (BALB/cxA/J)F1 mice received subcutaneous administration of killer DC-DC hybrids, followed by intravenous inoculation of DO11.10 T cells. Killer DC-DC hybrids migrated preferentially to draining lymph nodes albeit with relatively low efficiency (0.5-1% recovery) and they induced significant, but incomplete (30-40%) killing of DO11.10 T cells in this location. These results document the abilities of CD95L-transduced DC to trigger apoptosis of naive T cells in an Ag-specific manner, to overrule T cell activation signals delivered by conventional DC, and to reduce local frequencies of Ag-reactive T cells in vivo. Our data also uncover two major limitations (relatively low homing efficiency and incomplete elimination of Ag-reactive T cells) that remain to be overcome for clinical application of CD95L-transduced DC strategy.

Zinc chloride-mediated reduction of apoptosis as an adjunct immunosuppressive modality in cardiac transplantation

BACKGROUND

Zinc (Zn) blocks caspase-3 activation in cardiac allografts and therefore may synergistically decrease apoptosis along with cyclosporine (CsA), which inhibits mitochondrial release of cytochrome c. Simultaneous treatment of rat recipients of heterotopic heart transplants with zinc chloride (ZnCl(2)) thus may allow lower doses of CsA for immunosuppression.

METHODS

PVG (RT1(c)) rat hearts were transplanted heterotopically into the abdomen of ACI (RT1(a)) rats. Group 1 (n = 15) rats received no treatment. Group 2 rats (n = 8) received 2 mg/kg/day CsA (sub-therapeutic dose) by oral gavage. Group 3 rats (n = 9) received 2 mg/kg/day oral CsA in addition to 1 mg/kg/day sub-cutaneous ZnCl(2) delivered by osmotic pump. All rats were imaged using Annexin V-bound (99m)Technetium ((99m)Tc-Annexin V) on post-operative Day 4 and subsequently killed. Annexin V avidly binds apoptotic cells in vivo. Region of interest per whole body (WB) data were calculated using the images. The allograft survival study was conducted with n = 11, 6, and 5 in control, CsA, and CsA+Zn groups, respectively. Finally, percentages of allografts that reached tolerance were measured in both CsA-only and CsA+Zn groups (n = 8 each).

RESULTS

Zinc chloride had an additive effect with CsA on apoptotic blockade and graft survival. The regions of interest per WB uptake of (99m)Tc-Annexin V were 2.43% +/- 0.37%, 2.08% +/- 0.52%, and 1.49% +/- 0.29%*, and acute survivals were 6.4 +/- 1.7, 7.2 +/- 2.1, and 11.2 +/- 2.5* days for control, CsA, and CsA+Zn groups, respectively (*p < 0.001 vs controls). In addition, 87.5% of allografts became tolerant and survived for 90 days in the CsA+Zn group compared with only 37.5% in the CsA-only group (p = 0.049).

CONCLUSION

Zinc-mediated reduction of apoptosis served as an effective adjunct immunosuppressive therapy to CsA in a rat model of cardiac transplantation.

Identification and immunocytochemical analysis of DCNP1, a dendritic cell-associated nuclear protein

Dendritic cells (DCs) are potent antigen-presenting cells (APCs). Among so-called professional APCs, only DCs can activate naive T cells to initiate immune response. To better understand molecular mechanisms underlying unique functions of DCs, we searched for genes specifically expressed in human DCs, using PCR-based cDNA subtraction in conjunction with differential screening. cDNAs generated from CD34(+) stem cell-derived CD1a(+) DC were subtracted with cDNA from monocytes and used for generation of a cDNA library. The cDNA library was differentially screened to select genes expressed in DCs more abundantly than in monocytes. We identified a gene encoding a protein composed of 244 amino acids, which we designated as DCNP1 (dendritic cell nuclear protein 1). In Northern blot analysis, DCNP1 mRNA was highly expressed in mature DCs and at a lower level in immature DCs. In contrast, monocytes and B cells do not express the gene. In multiple human tissue Northern blot analysis, expression of DCNP1 was detected in brain and skeletal muscle. To examine subcellular localization of DCNP1, we performed immunofluorescence analysis using an anti-DCNP1 polyclonal antibody and found the molecule to be localized mainly in the perinucleus. In an immunohistochemical analysis, we compared the expression of DCNP1 with CD68, a marker for DCs and macrophages, in spleen, lymph node, liver, and brain. While DCNP1-positive cells showed a similar tissue distribution to CD68-positive cells, the number of DCNP1-positive cells was much smaller than that of CD68-positive cells. Our findings are consistent with the proposal that DCNP1 is specifically expressed in DCs.

Dendritic cells and second signal blockade: a step toward allograft tolerance?

The ultimate goal of clinical organ transplantation is to induce immunological tolerance to the allograft. Dendritic cells, the main antigen-presenting cells, are a complex system including numerous subsets, capable of inducing T-cell activation, and thus initiating an immune response, but also of inducing tolerance. In organ transplantation, the problem is even more complex because of the coexistence of dendritic cells from the donor, responsible for direct recognition of foreign antigens by T cells, and dendritic cells from the recipient, responsible for indirect antigen presentation to host T cells. Among the various methods of immunomanipulation aiming at inducing tolerance, blockade of the second signal pathway by monoclonal antibodies (anti-CD28, anti-B7, anti CD40, anti-CD40L, CTLA4-Ig) has yielded promising but incomplete results. Viral transfection of recipient immature dendritic cells encoding for immunosuppressive or apoptotic molecules, such as interleukin 10, transforming growth factor-beta, CTLA4-Ig, or Fas ligand, is also able to induce hyporesponsiveness. Another very promising method consists of associating donor cells (bone marrow cells, CD34+ cells, dendritic cells) and polyclonal or monoclonal antibodies (anti-CD4, anti-CD40L, CTLA4-Ig) to induce microchimerism and partial tolerance. Reflecting on these data would seem to be an interesting direction for future prospects.

Dendritic cells transduced with viral interleukin 10 or Fas ligand: no evidence for induction of allotolerance in vivo

Dendritic cells (DC) are the most potent presenters of alloantigens and therefore are responsible for the induction of allograft rejection. Genetic modifications of DC allowing the expression of a tolerogenic molecule may render them immunosuppressive. We transduced bone marrow-derived DC with recombinant MFG retrovirus encoding either viral interleukin (vIL)-10 or Fas ligand (FasL) to induce transplantation tolerance. Up to 10 ng/ml of bioactive vIL-10 was produced by DC after transfer of the corresponding gene. Although the inhibitory properties of vIL-10-transduced DC were revealed in vitro in a mixed lymphocyte culture, no clear down-regulation of the allogeneic response was observed in vivo after single or multiple injections of those DC overexpressing vIL-10. When we transduced wild-type bone marrow-derived DC with recombinant MFG retrovirus encoding murine FasL, cells quickly died, probably because of suicidal or fratricidal Fas-dependent death. Indeed, only DC from Fas-deficient lpr mice survived to FasL gene transfer. Those FasL-transduced lpr DC exhibited a strong cytotoxic activity against Fas-positive targets in vitro. DC overexpressing FasL did not behave as immunosuppressive DC in vivo. The subcutaneous injection of FasL+ lpr DC in MHC class II-disparate mice hyperactivated the allospecific proliferation of T cells in the draining lymph nodes compared with mice treated with control-transduced DC. These results argue against the development of FasL+ DC or vIL-10-secreting DC as immunosuppressive tools in vivo. The alternative pathways of T-cell activation triggered by these genetically modified DC need to be investigated.

Manipulation of dendritic cells for tolerance induction in transplantation and autoimmune disease

Dendritic cells (DC) constitute a complex system of uniquely well-equipped antigen-presenting cells that initiate and regulate immune responses. Extensive recent studies have improved our understanding of DC development, differentiation, activation, and function. DC exist as distinct subsets that differ in their lineage affiliation, surface molecule expression, and biological function. These factors seem to determine the T-cell polarizing signals and type of T cell response-T helper 1, T helper 2, or T regulatory- induced by DC (1). Evidence has accumulated that DC play an important role in both central and peripheral tolerance via various mechanisms, including induction of T-cell anergy, immune deviation, T regulatory cell activity, and promotion of activated T-cell apoptosis. Although many of the details of the molecular basis of DC tolerogenicity have yet to be elucidated, emerging information suggests that costimulatory molecule deficiency, expression of death-inducing ligands (in particular Fas [CD95] ligand), microenvironmental factors (in particular anti-inflammatory/immunosuppressive cytokines), and inhibition of gene transcription regulatory proteins (e.g., nuclear factor-kappaB) can impart tolerogenic potential to DC (2). Manipulation of DC by control of their maturation and differentiation, or genetic engineering of these cells to express immunosuppressive molecules, offers potential for therapy of allograft rejection and autoimmune disease. In this brief overview, we outline principles and methods for generation of "tolerogenic" DC and outcomes that have been reported in experimental models. Space constraints limit literature citations.

Dendritic cells: immune regulators in health and disease

Dendritic cells (DCs) are bone marrow-derived cells of both lymphoid and myeloid stem cell origin that populate all lymphoid organs including the thymus, spleen, and lymph nodes, as well as nearly all nonlymphoid tissues and organs. Although DCs are a moderately diverse set of cells, they all have potent antigen-presenting capacity for stimulating naive, memory, and effector T cells. DCs are members of the innate immune system in that they can respond to dangers in the host environment by immediately generating protective cytokines. Most important, immature DCs respond to danger signals in the microenvironment by maturing, i.e., differentiating, and acquiring the capacity to direct the development of primary immune responses appropriate to the type of danger perceived. The powerful adjuvant activity that DCs possess in stimulating specific CD4 and CD8 T cell responses has made them targets in vaccine development strategies for the prevention and treatment of infections, allograft reactions, allergic and autoimmune diseases, and cancer. This review addresses the origins and migration of DCs to their sites of activity, their basic biology as antigen-presenting cells, their roles in important human diseases and, finally, selected strategies being pursued to harness their potent antigen-stimulating activity.

Immunosuppressive properties of CD95L-transduced "killer" hybrids created by fusing donor- and recipient-derived dendritic cells

Allogeneic immune responses, which are initiated by dendritic cells (DCs) of both donor and host origins, remain a major obstacle in organ transplantation. Presentation of intact major histocompatibility complex (MHC) molecules by allogeneic DCs and allogeneic peptides by syngeneic DCs leads to complex allogeneic immune responses. This study reports a novel strategy designed to suppress both pathways. A stable DC line XS106 (A/J mouse origin) was transfected with CD95L cDNA and fused with splenic DCs purified from allogeneic BALB/c mice. The resulting "killer" DC-DC hybrids: (1) expressed CD95L and MHC class I and class II molecules of both A/J and BALB/c origins, while maintaining otherwise characteristic surface phenotypes of mature DCs; (2) inhibited MHC class I- and class II-restricted mixed leukocyte reactions between the parental strains by triggering apoptosis of alloreactive T cells; and (3) abolished delayed-type hypersensitivity responses of A/J (and BALB/c) mice to BALB/c-associated (and A/J-associated) alloantigens when injected intravenously into A/J (and BALB/c) mice. The onset of graft-versus-host disease in (BALB/c x A/J) F1 hosts receiving A/J-derived hematopoietic cell transplantation was suppressed significantly (P <.001) by killer DC-DC hybrid treatment. These results form both technical and conceptual frameworks for clinical applications of CD95L-transduced killer hybrids created between donor DCs and recipient DCs in the prevention of allogeneic immune responses following organ transplantation.

Potential of tolerogenic dendritic cells for transplantation

Dendritic cells (DC) are professional antigen (Ag)-presenting cells considered traditionally as the passenger leukocytes that, after migration from transplanted tissues, stimulate allospecific naive T cell responses and trigger acute rejection. However, there is recent evidence that, besides their role in central T lymphocyte deletion in the thymus, DC perform a crucial function to induce/maintain peripheral T cell tolerance. This paper outlines conceptual models that try to explain how DC may induce/maintain tolerance. It also considers how such ideas have been implemented recently in an effort to generate tolerogenic DC to induce donor Ag-specific tolerance/ immunosuppression and prolonged allograft survival. These approaches include genetic engineering of donor- or recipient-derived DC to express molecules capable of promoting tolerance to alloAg.

Activation through CD40 ligation induces functional Fas ligand expression by Langerhans cells

Langerhans cells (LC) are professional antigen-presenting cells of dendritic cell (DC) lineage and are critical for the induction of primary immune responses in skin. Following antigenic stimulation, LC migrate to regional lymph nodes and induce antigen-specific activation of T cells. After primary expansion, the majority of T cells undergo Fas/Fas ligand (FasL)-mediated apoptotic cell death, thereby suppressing their excessive expansion. Although recent investigations have indicated an immunoregulatory function for DC, whether LC could be involved in Fas/FasL-mediated suppression of activated T cells is still unclear. In this study, we found that LC express FasL after activation triggered through CD40 molecules on their surface, but not by stimulation with LPS or IFN-gamma. The functional significance of FasL expression by LC was demonstrated using two different assays for apoptosis induced in Jurkat cells. The apoptosis in Jurkat cells was completely blocked by anti-FasL blocking antibody, suggesting a Fas/FasL-mediated mechanism. These results indicate a new feedback mechanism to down-regulate T cell activation by LC through the interaction of the TNF receptor/ligand superfamily, CD40/CD40L and Fas/FasL.

The role of peripheral T-cell deletion in transplantation tolerance

The apoptotic deletion of thymocytes that express self-reactive antigen receptors is the basis of central (thymic) self-tolerance. However, it is clear that some autoreactive T cells escape deletion in the thymus and exist as mature lymphocytes in the periphery. Therefore, peripheral mechanisms of tolerance are also crucial, and failure of these peripheral mechanisms leads to autoimmunity. Clonal deletion, clonal anergy and immunoregulation and/or suppression have been suggested as mechanisms by which 'inappropriate' T-lymphocyte responses may be controlled in the periphery. Peripheral clonal deletion, which involves the apoptotic elimination of lymphocytes, is critical for T-cell homeostasis during normal immune responses, and is recognized as an important process by which self-tolerance is maintained. Transplantation of foreign tissue into an adult host represents a special case of 'inappropriate' T-cell reactivity that is subject to the same central and peripheral tolerance mechanisms that control reactivity against self. In this case, the unusually high frequency of naive T cells able to recognize and respond against non-self-allogeneic major histocompatibility complex (MHC) antigens leads to an exceptionally large pool of pathogenic effector lymphocytes that must be controlled if graft rejection is to be avoided. A great deal of effort has been directed toward understanding the role of clonal anergy and/or active immunoregulation in the induction of peripheral transplantation tolerance but, until recently, relatively little progress had been made towards defining the potential contribution of clonal deletion. Here, we outline recent data that define a clear requirement for deletion in the induction of peripheral transplantation tolerance across MHC barriers, and discuss the potential implications of these results in the context of current treatment modalities used in the clinical transplantation setting.

Human myeloid dendritic cells transduced with an adenoviral interleukin-10 gene construct inhibit human skin graft rejection in humanized NOD-scid chimeric mice

Human myeloid DC were generated from peripheral blood mononuclear cells by monocyte adhesion and subsequent culture with rhGM-CSF and rhIL-4. We transduced immature (day 5 of culture) myeloid DC with an E1-deleted replication-deficient adenoviral vector encoding the cytokine IL-10 (AdV IL-10) and a control adenovirus MX-17 (AdV MX 17). Human DC transduced with AdV IL-10 showed inhibition of the mixed leukocyte culture, reduced cell surface expression of co-stimulatory molecules (CD80/CD86) and were unable to produce the potent allo-stimulatory cytokine, interleukin-12. In order to test the in vivo properties of these cells a humanized immunodeficient mouse skin transplantation model was developed. Immunodeficient NOD-scid mice were engrafted with human skin, reconstituted via intraperitoneal injection with allogeneic mononuclear cells (MNC) mixed with 1 x 10(6) DC that were autologous to the skin donor and that had been transduced with either AdV IL-10 or AdV MX-17. Skin grafts were removed at day 7 and 14 after reconstitution and studied histologically for evidence of rejection. In animals that received DC modified with AdV IL-10 there was reduced skin graft rejection as characterized by reduced mononuclear cell infiltration and less dermo-epidermal junction destruction compared with those animals that received DC modified with the control virus alone. Injection of equivalent numbers of donor-derived fibroblasts transduced with AdV IL-10 were ineffective at modifying rejection of skin grafts. Immunosuppressive cytokine gene therapy targeting human DC is a novel means of inhibition of the alloimmune response.

Designer dendritic cells for tolerance induction: guided not misguided missiles

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that play crucial roles as initiators and modulators of adaptive immune responses. Although DC-based vaccines have been utilized successfully to generate cytolytic T-cell activity against tumor antigens (Ags), evidence has accumulated that DCs also have potent capabilities to tolerize T cells in an Ag-specific manner. DCs cultured in the laboratory can suppress auto- or alloimmunity. Current and prospective strategies to promote this inherent tolerogenic potential of DCs might prove to be important for the therapy of transplant rejection and autoimmune diseases.

Bone marrow-derived dendritic cells from experimental allergic encephalomyelitis induce immune tolerance to EAE in Lewis rats

We have previously shown that dendritic cells (DC), upon being pulsed in vitro with encephalitogenic myelin basic protein peptide 68-86 (MBP 68-86) and injected subcutaneously (s.c.) back to healthy Lewis rats, transfer immune tolerance to experimental allergic encephalomyelitis (EAE) induced by immunization with MBP 68-86 and Freund's complete adjuvant (FCA). We here assumed that DC become pulsed in EAE rats, and that expansion in vitro of such 'in vivo pulsed EAE-DC' might also have the capacity to induce immune tolerance to EAE, thereby eliminating the need for in vitro pulsing of DC with autoantigens which are still unknown in many autoimmune diseases in the human. In the present study, EAE-DC were generated from bone marrow of Lewis rats, with EAE induced with MBP 68-86 + FCA, and expanded in vitro by culture with GM-CSF and IL-4. In comparison with DC from normal rats, EAE-DC exhibited higher viability in the absence of growth factors, and presented specific antigen to naïve T cells in vitro. The DC derived from both EAE and healthy rats stimulated strong proliferation in an antigen-independent manner, lasting for 4 weeks after DC were s.c. injected into healthy rats. During this time, injection of EAE-DC did not induce clinical EAE. However, when these rats were immunized with MBP 68-86 + FCA, subsequent EAE was dramatically suppressed, and was associated with increased IFN-gamma expression, nitric oxide production, gradually reduced proliferation and cell apoptosis, compared with PBS-injected control EAE rats. LPS-treated DC did not induce tolerance, suggesting that the tolerance is mediated by an immature stage of DC. These observations support the hypothesis that EAE-DC can transfer immune tolerance to EAE, thereby omitting the step of characterizing specific autoantigen. Omitting the step of loading DC with antigen not only eliminates the extremely complex procedure of defining pathogenically-relevant autoantigens, but also avoids the risk of inducing immunogenicity of DC in the treatment of autoimmune diseases.

Down-regulation of human alloimmune responses by genetically engineered expression of CD95 ligand on stimulatory and target cells

Transgenic expression of apoptosis-inducing molecules could be a strategy to protect cells and tissues from destruction by apoptosis-susceptible effector T cells. Some evidence for the potency of this approach has been obtained in mouse and rat transplantation models. However, limited data are available on the capacity of apoptosis-inducing molecules to modulate human alloimmune responses. In this study we analyzed the in vitro consequences of an interaction of human T cells with allogeneic 293 cells and 293 transfectants stably expressing high levels of the apoptosis-inducing CD95 ligand (CD95L). Both, CD95L(-) and CD95L(+) 293 cells were able to activate allogeneic T cells as demonstrated by comparable CD25 expression at day 2 of culture. The analysis of viable T cells at day 7, however, revealed anti-293 cytotoxic activity only in cultures that had been stimulated with CD95L(-) 293 cells. Alloactivated effector T cells lysed CD95L(-) and CD95L(+) 293 targets with similar efficiency when tested in a 4-h 51Cr-release assay. Prolongation of the effector phase to 20 h resulted in a further increase in the destruction of CD95L(-) target cells, whereas lysis of CD95L(+) targets remained low. These data suggest that genetically engineered expression of CD95L on cells or tissues could be an approach to control human T cell reactivity towards allografts. During the induction of an alloimmune response depletion of cytotoxic precursor cells may be obtained by overexpressing CD95L on stimulatory cells; CD95L expression on graft tissue might limit T cell-mediated destruction of the transplant during the effector phase of the response.

Dendritic cells genetically engineered to express IL-4 inhibit murine collagen-induced arthritis

Dendritic cells (DCs) are specialized antigen-presenting cells that migrate from the periphery to lymphoid tissues, where they activate and regulate T cells. Genetic modification of DCs to express immunoregulatory molecules would provide a new immunotherapeutic strategy for autoimmune and other diseases. We have engineered bone marrow-derived DCs that express IL-4 and tested the ability of these cells to control murine collagen-induced arthritis (CIA), a model for rheumatoid arthritis in which Th1 cells play a critical role. IL-4-transduced DCs inhibited Th1 responses to collagen type II in vitro. A single injection of IL-4-transduced DCs reduced the incidence and severity of CIA and suppressed established Th1 responses and associated humoral responses, despite only transient persistence of injected DCs in the spleen. In contrast, control DCs and IL-4-transduced T cells or fibroblastic cells failed to alter the course of the disease. The functional effects correlated well with the differential efficiency of DC migration from various sites of injection to lymphoid organs, especially the spleen. The ability of splenic T cells to produce IL-4 in response to anti-CD3 was enhanced after the administration of IL-4-transduced DCS: These results support the feasibility of using genetically modified DCs for the treatment of autoimmune disease.

Differential effects of myeloid dendritic cells retrovirally transduced to express mammalian or viral interleukin-10 on cytotoxic T lymphocyte and natural killer cell functions and resistance to tumor growth

BACKGROUND

Genetic engineering of dendritic cells (DC) to express immunosuppressive molecule(s) offers potential for therapy of allograft rejection and autoimmune disease. Viral (v) interleukin (IL)-10, encoded by the Epstein-Barr virus, is highly homologous to mammalian (m) IL-10, but lacks certain of its T-cell stimulatory activities. Our aim was to evaluate and compare the influence of vIL-10 and mIL-10 gene transfer on the T-cell and natural killer (NK) cell stimulatory activity of DC, and their impact on the growth of transplantable tumors.

METHODS

Myeloid DC progenitors, propagated from the bone marrow of C57BL/6J (H2b) mice in granulocyte-macrophage colony-stimulating factor + IL-4, were transduced using retroviral supematant from the BOSC ecotropic packaging cell line. The function of the IL-b gene-modified DC was assessed by examining their ability to induce naive allogeneic T-cell proliferation and cytotoxic T lymphocyte (CTL) generation. MCA205 (H2b) sarcoma cells mixed with either vIL-10-, mIL-10-, or Zeo (control gene)-transduced DC were inoculated intradermally into C57BL/6J (syngeneic) or BALB/cJ (H2d) (allogeneic) recipients, which were monitored for tumor growth. The role of specific host effector cell populations in tumor resistance was determined by antibody depletion.

RESULTS

Compared with control gene-modified DC, both vIL-10- and mIL-10-transduced DC, which secreted the transgene product, showed reduced surface expression of MHC class II and costimulatory molecules, and impaired ability to induce T-cell proliferation. vIL-10-transduced DC were also inhibited with respect to CTL induction but did not affect the generation of NK cells. By contrast, mIL-10-transduced DC augmented CTL generation and NK cell activity. In the tumor transplant model, vIL-10-transduced DC enhanced tumor growth both in syngeneic and allogeneic hosts, whereas mIL-10-transduced cells inhibited tumor development. Depletion of CD4+ or CD8+ T cells or NK cells in mice given mIL-10-transduced DC reversed this therapeutic effect.

CONCLUSION

mIL-10 gene-modified myeloid DC promote CTL and NK cell-mediated responses and inhibit tumor growth. By contrast, vIL-10-engineered DC, which elicit diminished CTL responses and do not promote NK cell activity, seem to have therapeutic potential for inhibition of T cell-mediated immunity.

Effective treatment of established murine collagen-induced arthritis by systemic administration of dendritic cells genetically modified to express IL-4

Dendritic cells (DC) are APCs that are able to stimulate or inhibit immune responses, depending on levels of expression of MHC class I and II costimulatory molecules and cytokines. Our previous studies have suggested that the observed contralateral effect, where injection of a vector carrying certain immunomodulatory genes into one joint resulted in inhibition of arthritis in untreated joints, is mediated by in vivo modification of DC. Therefore, we have examined the ability of genetically modified DC to suppress established murine collagen-induced arthritis (CIA) after i.v. delivery. IL-4 has been shown to partially reduce the severity of CIA after repeated injection of recombinant protein or by injection of an adenoviral vector expressing IL-4. Here we demonstrate that i.v. injection of immature DC, infected with an adenoviral vector expressing IL-4, into mice with established CIA resulted in almost complete suppression of disease, with no recurrence for up to 4 wk posttreatment. Injection i.v. of fluorescently labeled DC demonstrated that the cells rapidly migrated to the liver and spleen after 6 h and to the lymph nodes by 24 h. In culture, spleen cells from DC/IL-4-treated mice produced less IFN-gamma after stimulation by collagen than did control groups. In addition, DC/IL-4 administration decreased the level of specific Abs against type II collagen, in particular the IgG2 Th1 isotype 14 days posttreatment. These results demonstrate the ability to treat effectively established murine arthritis by systemic administration of DC expressing IL-4.

Vaccination with autologous dendritic cells: from experimental autoimmune encephalomyelitis to multiple sclerosis

Autoimmune diseases such as multiple sclerosis (MS) are characterized by the loss of tolerance to self-determinants, activation of autoreactive lymphocytes and subsequent damage to single or multiple organs. The mechanisms by which autoimmune responses are triggered, and how activation of autoreactive lymphocytes is initiated and maintained, are not fully understood. Therapeutic approaches in autoimmune diseases have so far concentrated on antigens and T cells. Given the exceptional capacity of dendritic cells (DCs) to induce immunity in vivo, recent reports of the first successful clinical trials based on vaccination of tumor patients with autologous blood DCs pulsed in vitro with tumor antigen come as no surprise. The recent identification of tolerogenic subsets of DCs and their generation in culture may allow a novel approach to induce tolerance in autoimmune diseases. By selective in vitro manipulation of DCs and their subsequent reinfusion, DC-mediated tolerance has been achieved in animal models of human autoimmune diseases, including experimental autoimmune encephalomyelitis in Lewis rats and SJL/J mice and spontaneous diabetes in NOD mice. In vitro observations of human blood DCs are promising for DC-based treatment of MS and other diseases with an autoimmune component. Data from animal models and human materials suggest that DC-based immunotherapy could be beneficial at least as a complement to conventional therapy. Molecular-biological approaches to tolerogenic DCs could provide a rationale for designing immunotherapeutic strategies in autoimmune diseases.

Role of dendritic cells in the immune response against allografts

Graft-derived 'passenger' dendritic cells have been classically considered as the instigators of acute organ rejection. However, recent advances have revealed that dendritic cells are also involved in the induction/maintenance of peripheral tolerance. This paper briefly reviews the most recent knowledge of the role of donor and recipient dendritic cells during the immune response against allografts, and of the clinical potential of 'tolerogenic' dendritic cells.

Dendritic cells and prospects for transplantation tolerance

The past year has witnessed the resolution of some long-standing enigmas surrounding the immunobiology of dendritic cells, illuminating their opposing roles in peripheral tolerance and allograft rejection. Nevertheless these advances have posed many new questions, the answers to which may subtly influence our approach to the treatment of rejection while bringing ever closer the prospect of donor-specific transplanation tolerance.

Evidence for persistent expression of OX2 as a necessary component of prolonged renal allograft survival following portal vein immunization

Following portal vein (pv) pretransplant immunization of C3H mice, there is an early (within 2 days) increase in expression of the molecule OX2 seen on host dendritic cells (DC), along with increased survival of C57BL/6 renal allografts transplanted within 24 h of pv immunization. In addition, there is a marked polarization in cytokine production from lymphocytes harvested from the transplanted animals, with preferential production of IL-4, IL-10, and TGFbeta on donor-specific restimulation in vitro, and decreased production of IL-2, IFN-gamma, and TNFalpha compared with non-pv-immunized control transplanted mice. Both the increased renal allograft survival and the altered cytokine production are abolished by infusion of anti-mouse OX2 monoclonal antibody (3B6), even when antibody infusion is begun as late as 10 days following transplantation. Quantitative PCR analysis independently shows that OX2 expression is increased in the spleen and liver of transplanted mice as late as 21 days following pv immunization. In vitro studies with an OX2:Fc immunoadhesion had suggested that immunosuppression induced by this soluble form of the OX2 molecule was dependent primarily upon an early (OX2-dependent) signal. This discrepancy between in vivo and in vitro data possibly reflects a role for OX2 in the in vivo recruitment of other (immunregulatory) cells. Consistent with this hypothesis, regardless of the time (posttransplantation) of in vivo infusion of anti-OX2 antibody, within 2 days we observed a decline in the functional activity of a previously characterized immunoregulatory gammadeltaTCR(+) cell population, which can be monitored by its ability to regulate cytokine production in vitro.

Regulation of gene expression of murine MD-1 regulates subsequent T cell activation and cytokine production

The immunoadhesin (OX2:Fc) comprising the extracellular domain of murine OX2 linked to IgG2aFc, inhibits production of IL-2 and IFN-gamma by activated T cells and increases allograft and xenograft survival in vivo. Increased expression of OX2 on dendritic cells (DC) in vivo following preimmunization via the portal vein is also associated with elevated expression of MD-1. We have used antisense oligodeoxynucleotides (ODNs) to MD-1 to investigate the effect of inhibition of expression of MD-1 by DC on their function as allostimulatory cells. We also investigated by FACS analysis the cell surface expression of OX2, CD80, and CD86 on DC incubated with ODN-1 blocking MD-1 expression. Blocking MD-1 gene expression inhibits surface expression of CD80 and CD86, but not of OX2. DC incubated with ODN-1 to MD-1 did not stimulate IL-2 or IFN-gamma production, but generated cells able to suppress, in a second culture of fresh DC plus allogeneic T cells, production of IL-2 and IFN-gamma. This inhibition was blocked by anti-OX2 mAb. Infusion of DC preincubated with ODN-1 prolonged renal allograft survival, an effect also reversed by anti-OX2 mAb. By FACS, incubation of DC with anti-MD-1 Ab to promote capping eliminated cell surface expression of MD-1 and CD14 without altering DEC205, DC26, CD80, CD86, or OX2 expression. Thus OX2 and MD-1 are independent surface molecules on DC that may reciprocally regulate T cell stimulation. MD-1 is linked to CD14, a "danger receptor complex," and activation of this complex can regulate cell surface expression of CD80/CD86, which signal T cells.

Synergy in induction of increased renal allograft survival after portal vein infusion of dendritic cells transduced to express TGFbeta and IL-10, along with administration of CHO cells expressing the regulatory molecule OX-2

Dendritic cells (DC), generated from C57BL/6 mouse bone marrow cells cultured with GM-CSF and IL-4 for 9 days, were engineered to express constitutively the cytokines TGFbeta, IL-10, and IL-12, using adenovirus vectors constructed using an E1-deleted replication-deficient recombinant adenovirus carrying the appropriate cDNA for the relevant cytokines (Ad-TGFbeta, Ad-IL-12, or Ad-IL-10). C3H mice receiving nontransduced DC or pretransplant infusion of DC-Ad-LacZ showed increased survival of C57BL/6 renal grafts relative to that of control nonimmunized mice. Transfusion of Ad-IL-12-transduced DC abolished this increased survival, leading to a graft survival equivalent to that of controls with no DC. Optimal graft survival was seen in the group receiving a mixture of DC transduced with constructs for both IL-10 and TGFbeta. There was a correlation between increased graft survival and both inhibition of the induction of CTL and enhancement of a polarization to produce type-2 cytokines (IL-4, IL-10, and TGFbeta) on antigen-specific restimulation in vitro. These effects were more pronounced following concomitant infusion of CHO cells transfected with a full-length cDNA for murine OX-2.