Skin Graft Rejection Research Articles

PHYSIOLOGY AND ENDOCRINOLOGY SYMPOSIUM: Maternal immunological adjustments to pregnancy and parturition in ruminants and possible implications for postpartum uterine health: Is there a prepartum–postpartum nexus?1

Establishment of microbial infections in the reproductive tract can have negative consequences for reproductive function of the postpartum female. Most periparturient cows experience bacterial contamination of the uterus after parturition, but only a fraction of these develop subclinical or clinical disease. It is not well understood why one female resolves uterine infections after parturition while another develops disease. Perhaps those that develop metritis or endometritis are exposed to a greater bacterial load at parturition than those that successfully restore the uterus to a healthy condition. A second possibility is that females that develop bacterial disease have compromised immune function, either systemically or in the reproductive tract and associated lymph nodes. Here, the possibility is raised that maternal immunological adjustments to the presence of the allogeneic conceptus may predispose some females to metritis or endometritis. Several regulatory processes ensure that adaptive immune responses against paternal antigens on the conceptus are downregulated during pregnancy. Among these are immunosuppressive effects of progesterone, local accumulation of immune cells that can inhibit inflammation and T cell responses, including M2 macrophages and γδ T cells, and differentiation of regulatory T cells to inhibit alloreactive lymphocytes. Some immunological adjustments to the conceptus also make the uterus more susceptible to bacterial infection. For example, progesterone not only depresses skin graft rejection but also reduces uterine capacity to eliminate bacterial infections. Macrophages of M2 phenotype can inhibit inflammation and facilitate persistence of some microbial infections. At parturition, immune defenses in the uterus may be further weakened by loss of the luminal epithelium of the endometrium, which is part of the innate immune system, as well as by disappearance of intraepithelial γδ T cells that produce the antibacterial proteins granulysin and perforin. It is currently not known whether molecules and cells that inhibit immune responses during pregnancy persist after parturition but, if so, they could contribute to compromised immune function in the uterus. It is hypothesized that individual variation in immune adjustments to pregnancy and parturition and the reversal of these changes in the postpartum period are important determinants of susceptibility of the uterus to infection.

Human Bone Marrow- and Adipose Tissue-derived Mesenchymal Stromal Cells are Immunosuppressive In vitro and in a Humanized Allograft Rejection Model

BackgroundRecent studies with bone marrow (BM)-derived Mesenchymal Stromal Cells (MSC) in transplant recipients demonstrate that treatment with MSC is safe and clinically feasible. While BM is currently the preferred source of MSC, adipose tissue is emerging as an alternative. To develop efficient therapies, there is a need for preclinical efficacy studies in transplantation. We used a unique humanized transplantation model to study the in vivo immunosuppressive effect of human BM-MSC and adipose tissue-derived MSC (ASC).MethodsGene expression of BM-MSC and ASC and their capacity to inhibit activated PBMC proliferation was evaluated. The in vivo immunosuppressive effect of BM-MSC and ASC was studied in a humanized mouse model. SCID mice were transplanted with human skin grafts and injected with human allogeneic PBMC with or without administration of BM-MSC or ASC. The effect of MSC on skin graft rejection was studied by immunohistochemistry and PCR.ResultsBM-MSC and ASC expressed TGFβ, CXCL-10 and IDO. IDO expression and acitivity increased significantly in BM-MSC and ASC upon IFN-γ stimulation. IFN-γ stimulated BM-MSC and ASC inhibited the proliferation of activated PBMC in a significant and dose dependent manner. In our humanized mouse model, alloreactivity was marked by pronounced CD45+ T-cell infiltrates consisting of CD4+ and CD8+ T cells and increased IFN-γ expression in the skin grafts which were all significantly inhibited by both BM-MSC and ASC.ConclusionBM-MSC and ASC are immunosuppressive in vitro and suppress alloreactivity in a preclinical humanized transplantation model.

A Combination of Local Inflammation and Central Memory T Cells Potentiates Immunotherapy in the Skin

Adoptive T cell therapy uses the specificity of the adaptive immune system to target cancer and virally infected cells. Yet the mechanism and means by which to enhance T cell function are incompletely described, especially in the skin. In this study, we use a murine model of immunotherapy to optimize cell-mediated immunity in the skin. We show that in vitro-derived central but not effector memory-like T cells bring about rapid regression of skin-expressing cognate Ag as a transgene in keratinocytes. Local inflammation induced by the TLR7 receptor agonist imiquimod subtly yet reproducibly decreases time to skin graft rejection elicited by central but not effector memory T cells in an immunodeficient mouse model. Local CCL4, a chemokine liberated by TLR7 agonism, similarly enhances central memory T cell function. In this model, IL-2 facilitates the development in vivo of effector function from central memory but not effector memory T cells. In a model of T cell tolerogenesis, we further show that adoptively transferred central but not effector memory T cells can give rise to successful cutaneous immunity, which is dependent on a local inflammatory cue in the target tissue at the time of adoptive T cell transfer. Thus, adoptive T cell therapy efficacy can be enhanced if CD8(+) T cells with a central memory T cell phenotype are transferred, and IL-2 is present with contemporaneous local inflammation.

MHC Disparate Resting B Cells Are Tolerogenic in the Absence of Alloantigen-Expressing Dendritic Cells

Resting B cell (rB) populations have been shown to tolerize to soluble proteins and to minor-H but not to MHC alloantigens. We speculated that the reason for failing to tolerize to MHC alloantigen is that the few remaining dendritic cells (DCs) contaminating purified rB cell populations efficiently activate MHC allospecific T cells which are present at a higher frequency than T cells specific for minor-H alloantigen and soluble proteins. We established that MHC disparate rB cells are indeed tolerogenic when devoid of DC populations, as parental strain mice showed delayed skin graft rejection when infused with rB cells from mice in which MHC class I alloantigen was specifically targeted to T and B cells (CD2- transgenic mice). In contrast, treatment of parental strain mice with allogeneic rB cells purified from MHC- transgenic mice, in which is ubiquitously expressed, including DCs, induced accelerated graft rejection. We also showed that adding only 5,000 expressing DCs to CD2- rB cells abrogated the tolerogenic effect. Surprisingly, allogeneic rB cells prolonged graft survival in -primed mice. Thus, MHC disparate rB cells are tolerogenic and their failure to delay graft rejection can be explained by contaminating allogeneic DCs.

Functional Adaptive Immune Responses in Hematopoietic Chimeric Mice After Umbilical Cord Blood Cell Transplantation.

Abstract 2995 Introduction:An increasing number of clinical trials have demonstrated the usefulness of cord blood as a source of hematopoietic stem cells for reconstitution of the hematopoietic system. Nevertheless, due to a lack of convenient animal models, information about the immunological competence of umbilical cord blood cell (UCBC)-derived lymphocytes has been relatively limited. Recently, we have established a murine model of UCBC transplantation, which reconstitutes the hematopoietic system of immunodeficient mice, and studied the correct immunological functions of UCBC-derived lymphocytes generated in an allogeneic environment. Materials and Methods:UCBC prepared from C57BL/6 (H-2b) mice were transferred into lethally irradiated BALB/c (H-2d) mice lacking T- and B-lymphocytes (RAG2 knockout). In order to evaluate the adaptive immune response in the recipient mice, rejection of skin grafts from third-party C3H/He (H-2k) mice and antibody responses to immunization with a T-dependent antigen, 2,4,6-trinitrophenyl-keyhole limpet hemocyanin (TNP-KLH), were assessed. Additionally, the responsiveness of generated T cells was verified by mixed lymphocyte reaction (MLR) assay, cytotoxic T-lymphocyte (CTL) assay and phytohemagglutinin (PHA) blast formation assay. Results:In this UCBC transplantation model, the overall survival of the recipient mice was dose-dependent, and all surviving recipient mice were hematopoietic chimeras possessing all lineages. These allogeneic chimeras specifically rejected skin grafts from third-party C3H/He mice (rejection time; 9–16 days) while showing tolerance to skin grafts from both donor-type and recipient type, although with a significant delay in comparison to normal BALB/c mice (8–12 days) and C57BL/6 mice (9–11 days). Although accurate antibody responses of the allogeneic chimeras against TNP-KLH immunization were not anticipated, substantial amounts of TNP-specific IgG were detected in their sera. Interestingly, the level of TNP-specific IgM was significantly higher than that of normal BALB/c mice after TNP-KLH immunization, indicating retarded immunoglobulin class-switching in the allogeneic chimeras. The mechanism responsible for the antibody production by allogeneic chimeras still remains unclear. CTL and MLR assay revealed cell-mediated third-party-specific activity of killer and helper T cells, consistent with the tendency for the skin graft rejection and antibody production capability of the allogeneic chimeras to be inferior to those of normal mice. T cells of the allogeneic chimeras also proliferated non-specifically in response to PHA stimulation. The T-cell proliferation indices of the allogeneic chimeras when those of normal mice were taken as 100 were 21 in the MLR assay and 48 in the PHA blast formation assay, suggesting relative inferiority of the recognition and response system of T cells generated in an allogeneic environment. In any event, it may be important to note that T-dependent antigen-specific antibody production and alloantigen-specific rejection were substantial in the allogeneic chimeras. Conclusions:Overall, the present findings suggest that UCBC-derived lymphocytes generated in HLA-mismatched recipients are immunologically functional and competent. Regarding the relative inferiority of immune responses in the allogeneic chimeras, we predict the causes originate from narrowing of the T- and B-cell receptor repertoire by the allogeneic environment, and this possibility is now being examined. Disclosures:No relevant conflicts of interest to declare.

Regulatory T Cell Therapy Combined with Donor-Specific T Cell Deletion Promotes Long-Term Survival in Mouse Model of Allogeneic Islet Transplantation: Preconditioning Requirements and Mechanisms of Action

Regulatory T cell (Treg) prevention of transplant rejection requires drastic change of the balance of donor antigen-reactive Tregs to conventional T (Tconv) cells at the time of transplantation. To accomplish this, we preconditioned recipient mice using donor-specific transfusion (DST) followed by cyclophosphamide (Cy) treatment to reduce donor-reactive T cells before Treg infusion. This DST+Cy approach deleted 70-80% of donor-reactive T cells, but failed to prolong islet allograft survival. Infusion of 5 × 106 Tregs with direct donor reactivity led to long-term survival of BALB/c islets in 70% of the DST+Cy conditioned C57BL/6 recipients. Equal numbers of polyclonal Tregs significantly prolonged graft survival, but 90% of the recipients rejected their grafts by 100 days. However, increasing the numbers of polyclonal Tregs to 25 × 106 was able to confer long-term graft protection in 90% of the recipients. Mice receiving Treg therapy showed marked reduction of CD8+ T cells, but not CD4+ T cells, and concomitant increase of Tregs in the grafts during the first 14 days after transplantation. Mice with long-term protected grafts harbored donor-reactive T cells in the periphery and but had minimal T cells without detectable therapeutic Tregs within the grafts. Majority of the leukocytes present in the protected grafts were F4/80+CD11c-macrophages. However, the original islet grafts remained to be protected while the recipients were challenged with and rejected skin grafts from the same donor strain. Therapeutic Tregs altered the balance as well as the size of lymphocytic infiltrates early after transplantation likely through altering local inflammatory milieu, and conferred long-term graft protection locally in the grafts via infectious tolerance. Together, these results demonstrate a clinically viable approach to harness the tolerogenic property of Tregs for inducing long-term allograft survival and suggest Treg-mediated protection and biomarkers for Treg-induced tolerance reside locally in the grafts.

Epicutaneous immunization with protein antigen TNP-Ig alleviates TNBS-induced colitis in mice

BackgroundUlcerative colitis (UC) is a chronic inflammatory autoimmune disease with limited treatment modalities. The animal model of colitis induced by treatment with trinitrobenzene sulfonic acid (TNBS-colitis) is commonly used to test new therapies of this disease. In our previous work we found that epicutaneous (EC) immunization with protein antigen induced a state of profound immunosuppression that inhibited inflammatory response in contact sensitivity, in experimental autoimmune encephalomyelitis (EAE) and in allogeneic skin graft rejection. MethodsTNBS-induced colitis was used as an experimental model. ResultsIn our current work, we showed that EC immunization with TNP-conjugated mouse immunoglobulin (TNP-Ig) prior to induction of TNBS-colitis alleviates disease severity what was determined by the body weight, the length and the weight of the colon, the histological activity index (HAI) and myeloperoxidase activity (MPO). Observed amelioration of the disease in TNP-Ig patched mice was accompanied with decreased production of IFN-γ and IL-17A by splenocytes. Additionally, spleen cells isolated from mice EC immunized with TNP-Ig prior to colitis induction showed increased production of IL-10 suggesting that this cytokine might be involved in inhibiting inflammatory response in the colon. ConclusionThis work shows that EC immunization with protein antigen prior to TNBS-colitis induction ameliorates disease and observed suppression of inflammatory response in the colon might be mediated by IL-10.

Analysis of Human Biologics With a Mouse Skin Transplant Model in Humanized Mice

Preclinical testing of human therapeutic monoclonal antibodies has been limited in murine models due to species differences in pharmacokinetics and biologic responses. To overcome these constraints we developed a murine skin transplant model in humanized mice and used it to test human monoclonal antibody therapy. Neonatal NOD/SCID/IL2Rγc(null) mice (NSG) were reconstituted with human CD34(+) hematopoietic stem cells (hNSG). When adult, these mice rejected MHC mismatched murine C57BL/6J skin grafts. Rejection required adequate reconstitution with human cells. There was diffuse infiltration of the epidermis and dermis with hCD8 and hCD4 cells in rejected grafts by immunohistochemistry. Studies with B6/MHC class I and II knockout mice donors indicated that neither is required for rejection. Graft rejection was associated with the development of effector and central memory T cells and an increase in serum immunoglobulins. We also tested the effects of teplizumab (anti-CD3 mAb) and found it could delay skin graft rejection, whereas ipilimumab (anti-CTLA-4 [cytotoxic T-lymphocyte antigen-4] mAb) treatment accelerated rejection. These findings demonstrate that hNSG mice reliably and predictably reject a xenogenic mouse skin graft by a human T cell mediated mechanism. The model can be utilized to investigate the ability of human immunotherapies to enhance or suppress functional human immune responses.

Distinct in vivo CD8 and CD4 T cell responses against normal and malignant tissues.

Normal tissue and tumour grafts expressing the same alloantigens often elicit distinct immune responses whereby only normal tissue is rejected. To investigate the mechanisms that underlie these distinct outcomes, we compared the responses of adoptively transferred HY-specific conventional (CD8 and CD4) or regulatory T (Treg) cells in mice bearing HY-expressing tumour, syngeneic male skin graft or both. For local T cell priming, T cell re-circulation, graft localization and retention, skin grafts were more efficient than tumours. Skin grafts were also capable of differentiating CD4 T cells into functional Th1 cells. Donor T cell responses were inversely correlated with tumour progression. When skin graft and tumour transplants were performed sequentially, contemporary graft and tumour burden enhanced CD8 but reduced CD4 T cell responses causing accelerated skin-graft rejection without influencing tumour growth. Although both skin grafts and tumours were able to expand HY-specific Treg cells in draining lymph node (dLN), the proportion of tumour-infiltrating Treg cells was significantly higher than that within skin grafts, correlating with accelerated tumour growth. Moreover, there was a higher level of HY antigen presentation by host APC in tumour-dLN than in graft-dLN. Finally, tumour tissues expressed a significant higher level of IDO, TGFβ, IL10 and Arginase I than skin grafts, indicating that malignant but not normal tissue represents a stronger immunosuppressive environment. These comparisons provide important insight into the in vivo mechanisms that conspire to compromise tumour-specific adaptive immunity and identify new targets for cancer immunotherapy.

Allospecific CD4+ Effector Memory T Cells Do Not Induce Graft-versus-Host Disease in Mice

We studied whether allospecific CD4(+) effector memory T cells (T(EM)) could induce graft-versus-host disease (GVHD) using a novel GVHD model induced solely by CD4(+) T cell receptor transgenic TEa cells. Allospecific T(EM) generated in a lymphopenic host bore a typical memory phenotype. Moreover, these cells were able to elicit a faster and more effective proliferative response on challenge with alloantigen in vitro and to mediate "second-set" skin graft rejection in vivo. However, these allospecific T(EM) were unable to induce GVHD. Allospecific T(EM) recipients became tolerant to alloantigen as a result of clonal deletion. Even though allospecific T(EM) were able to respond to alloantigen initially, the expansion of these cells and inflammatory cytokine production during GVHD were dramatically decreased. The inability of allospecific T(EM) to sustain the alloresponse may be a result of enhanced activation-induced cell death. These observations provide insight into how allospecific CD4(+) T(EM) respond to alloantigen during GVHD and underscore the fundamental differences in alloresponses mediated by allospecific T(EM) in graft rejection and GVHD settings.

Regulatory T Cells in γ Irradiation-Induced Immune Suppression

Sublethal total body γ irradiation (TBI) of mammals causes generalized immunosuppression, in part by induction of lymphocyte apoptosis. Here, we provide evidence that a part of this immune suppression may be attributable to dysfunction of immune regulation. We investigated the effects of sublethal TBI on T cell memory responses to gain insight into the potential for loss of vaccine immunity following such exposure. We show that in mice primed to an MHC class I alloantigen, the accelerated graft rejection T memory response is specifically lost several weeks following TBI, whereas identically treated naïve mice at the same time point had completely recovered normal rejection kinetics. Depletion in vivo with anti-CD4 or anti-CD25 showed that the mechanism involved cells consistent with a regulatory T cell (T reg) phenotype. The loss of the T memory response following TBI was associated with a relative increase of CD4+CD25+ Foxp3+ expressing T regs, as compared to the CD8+ T effector cells requisite for skin graft rejection. The radiation-induced T memory suppression was shown to be antigen-specific in that a third party ipsilateral graft rejected with normal kinetics. Remarkably, following the eventual rejection of the first MHC class I disparate skin graft, the suppressive environment was maintained, with markedly prolonged survival of a second identical allograft. These findings have potential importance as regards the immunologic status of T memory responses in victims of ionizing radiation exposure and apoptosis-inducing therapies.

γδ T Cells Augment Rejection of Skin Grafts by Enhancing Cross-Priming of CD8 T Cells to Skin-Derived Antigen

γδ T cells possess innate like properties and are proposed to bridge the gap between innate and adaptive immunity. In this study we explored the role of γδ T cells in cutaneous immunity utilizing a skin transplantation model. Following engraftment of skin expressing cell associated model antigen (ovalbumin) in epithelial keratinocytes, skin resident γδ T cells enhanced graft rejection. While effector function of CD8 T cells was intact in the absence of γδ T cells, cross priming of CD8 T cell to graft derived antigen was impaired in the absence of γδ T cells. The reduced graft rejection and graft priming of γδ T cell deficient mice was evident in both acutely inflamed and well-healed grafting models. Furthermore, expression of the CD40 activation marker on migrating dendritic cells was lower in TCRδ-/- mice compared to wildtype mice, regardless of the presence or absence of inflammation associated with grafting. These results indicate that γδ T cells enhance graft priming and consequently the likelihood of a successful immune outcome in the context of skin graft rejection suggesting that γδ T cells may be an important component of immunity to epithelial cancers or infection.

Establishment of nonmyeloablative bone marrow chimerism by double negative Treg cells through inducing T cell clonal deletion and suppressing NK cell function (126.1)

Abstract In bone marrow transplantation, T cells and NK cells play important role for graft rejection. In addition, graft-versus-host-disease and establishment of stable chimeric states without complete marrow ablation remain as major obstacles post bone marrow transplantation. In this study, we aimed to establish mixed chimerism in a non-irradiation condition. Our data indicate that adoptive transfer of donor-derived TCRαβ+CD3+CD4-CD8-NK1.1-(double negative, DN) Treg cells prior to C57BL/6 to BALB/c bone marrow transplantation, in combination with cyclophosphamide but not cyclosporine, FK506, or rapamycin, established stable mixed chimerism that led to acceptance of C57BL/6 skin allografts and rejection of 3rd party C3H skin grafts. Adoptive transfer of CD4+ and CD8+ T cells, but not DN-Treg cells, induced graft-versus-host diseases in this regimen. The recipient T cell alloreacitve responsiveness was reduced in the DN-Treg cell-treated group and T cell receptor Vβ2, Vβ7 and Vβ8 clonal deletions were observed in both CD4+ and CD8+ T cells. Furthermore, DN-Treg cell treatment suppressed NK cell-mediated donor bone marrow rejection in perforin-dependent manner. Taken together, our results suggest that adoptive transfer of DN-Treg cells can control both adoptive and innate immunity and promote a stable mixed chimerism and donor-specific tolerance in the non-irradiation regimen.

Prior pancreatic islet transplantation mitigated the subsequent skin graft rejection against HY disparity in C57BL/6 with pre-existing immunological memory (126.15)

Abstract Several successful immunomodulatory strategies in specific pathogen-free rodents have failed in outbred larger animals by pre-existing memories. In our previous report, we showed that the islet transplantation across the minor histocompatibility of HY (male antigen) could induce immunological tolerance to male antigen in female C57BL/6 mice. In this study, we tested whether islet-transplantation-induced immunological tolerance could be achieved against the barrier of pre-existing immunological memory. Splenocytes isolated from male C57BL/6 were injected into syngeneic female mouse intraperitoneally. The induction of memory was confirmed by accelerated male skin rejection from 27 days (naïve control mouse) to 19 days. The islets isolated from male C57BL/6 mice were transplanted into renal subcapsule of the sensitized mice. 37.5% of sensitized recipients rejected male islets, whereas 100% of naïve recipients accepted the grafts. Remaining 62.5% of sensitized recipients that accepted male islets did not accept subsequent male skin graft. Although male skin graft failed to be accepted in the male islet-accepted recipients, the intensity of inflammatory response was significantly lower than that shown in presensitized mice without male islet graft. In conclusion, the islet-transplantation-induced immunological tolerance could not circumvent the barrier of immunological memory, however, it could mitigate the intensity of inflammatory rejection process.

Multiphoton intravital microscopy visualization of skin graft rejection in real time (126.14)

Abstract The current paradigm explaining organ graft rejection postulates that rejection is initiated by graft resident dendritic cells that reach the draining lymph nodes via lymphatics and activate naive alloreactive T cells. These newly activated T cells then migrate into the graft. However up to half the T cells recognizing allogeneic MHC in adult animals are already be of memory phenotype, and thus capable of direct entry into a graft site without prior activation in LNs. This is not the result of previous exposure to allo-Ag, but stems from the fact that the allo-MHC-specific and Ag-specific T cell receptor repertoires overlap each other. These pre-existing allo-reactive T cells represent a major barrier to organ transplantation. To understand the contributions of memory cells to skin graft rejection, we are using intravital multiphoton microscopy to track cellular interactions between memory cells, DCs and lymphatic and vascular endothelium during graft rejection and acceptance. Preliminary studies suggest that DCs from grafts are unable to exit the surgical site, most likely as a result of surgical disruption of lymphatic drainage from the transplanted skin. Further work will investigate trafficking of graft-reactive CD4 effector and Treg cells into the graft site.

Dickkopf-3, an immune modulator in peripheral CD8 T-cell tolerance

In healthy individuals, T cells react against incoming pathogens, but remain tolerant to self-antigens, thereby preventing autoimmune reactions. CD4 regulatory T cells are major contributors in induction and maintenance of peripheral tolerance, but a regulatory role has been also reported for several subsets of CD8 T cells. To determine the molecular basis of peripheral CD8 T-cell tolerance, we exploited a double transgenic mouse model in which CD8 T cells are neonatally tolerized following interaction with a parenchymal self-antigen. These tolerant CD8 T cells have regulatory capacity and can suppress T cells in an antigen-specific manner during adulthood. Dickkopf-3 (DKK3) was found to be expressed in the tolerant CD8 T cells and to be essential for the observed CD8 T-cell tolerance. In vitro, genetic deletion of DKK3 or blocking with antibodies restored CD8 T-cell proliferation and IL-2 production in response to the tolerizing self-antigen. Moreover, exogenous DKK3 reduced CD8 T-cell reactivity. In vivo, abrogation of DKK3 function reversed tolerance, leading to eradication of tumors expressing the target antigen and to rejection of autologous skin grafts. Thus, our findings define DKK3 as a immune modulator with a crucial role for CD8 T-cell tolerance.

Antigen‐specific regulatory T cells can induce tolerance to immunogenic grafts without the need for chronic immunosuppression

Regulatory CD4+CD25+Foxp3+ T cells (Tregs) play an important role in the induction of allospecific tolerance. However tolerance in solid organ transplantation by mere transfer of Tregs has been difficult. Besides this the stability of the differentiation phenotype of Tregs has recently been questioned.We therefore aimed in generating large numbers of stable allospecific Tregs from naïve T cells by retroviral transduction with Foxp3. These were tested in an immunogenic skin transplantation model (C57BL/6→BALB/c).We established a system of transduction of mouse T cells with ecotropic retroviruses expressing Foxp3 and Thy1.1 as a surface marker to follow up transduced T cells. Alloantigen‐specific Tregs were generated by stimulating naïve recipient CD4+ T cells with irradiated donor splenocytes. CD25+ and/or CD69+ allospecific recipient CD4+ T cells were isolated and transduced with Foxp3. Alloantigen‐specific Foxp3 T cells (iTregs) showed high expression for the Treg markers Foxp3, CTLA4 and GITR. They could suppress a MLR in an alloantigen‐specific manner. Furthermore, they could be expanded up to 18 fold in vitro while maintaining their Treg phenotype and expression of lymph node homing markers like CCR7 and CD62L. iTregs prevented skin graft rejection without the need for chronic immunosuppression and recipients showed systemic allospecific allotolerance. Alloantigen‐specific Tregs were far more potent than polyspecific Tregs. Mechanisms of tolerance were graft specific homing, expansion and long‐term persistence of Tregs within the graft (>100 days, 90% of intragraft Tregs were alloantigen‐specific). In fact, tolerance could be transferred with re‐transplantation of the tolerant graft onto secondary recipients. Third party grafts were readily rejected demonstrating specificity of tolerance. Due to the Foxp3 transduction, iTregs did not lose their Treg phenotype.The results prove that large numbers of stable alloantigen‐specific Tregs can be generated from a polyclonal repertoire of naïve T cells. This is the first time that allotolerance was achieved in a non‐lymphopenic transplant model using skin grafts in an immunogenic strain combination. Therefore, antigen‐specific Tregs might have a huge therapeutic potential after solid organ transplantation.

Sensitized Recipients Exhibit Accelerated but not Hyperacute Rejection of Vascularized Composite Tissue Allografts

Currently, the donor-recipient matching process for vascularized composite tissue allotransplantation (VCTA) closely follows the standard practices for solid organ transplantation. Sensitization is considered a contraindication to VCTA. However, the role of sensitization in VCTA rejection is largely unstudied. Major histocompatibility-mismatched ACI (RT1) donors and Wistar Furth (WF) (RT1) recipients were used to determine whether sensitization would lead to hyperacute rejection in VCTA as in other organs, such as kidneys. WF rats were presensitized to ACI antigens by skin transplantation and received heterotopic osteomyocutaneous VCTA flaps. Kidney transplants served as controls. Production of anti-donor antibody was detected in WF recipients after rejection of the ACI skin grafts. Sensitized WF rats rejected VCTA grafts from ACI rats significantly faster (P<0.05) than unsensitized recipients, but not hyperacutely. Rejection in the sensitized recipients was not prevented by immunosuppression with FK506 and mycophenolate mofetil. In contrast, kidney allografts from ACI rats were hyperacutely rejected within 30 min by sensitized recipients. To confirm the role of antibody-mediated rejection in the sensitized recipients, serum from presensitized rats was adoptively transferred into naïve WF rats. Hyperacute rejection occurred only in transplanted kidneys but not VCTA. Histologic examination of tissues from acceleratedly rejected VCTA showed dense lymphocytic infiltrates, and no antibody deposition. VCTA are rejected in an accelerated fashion but not hyperacutely in the presence of allosensitization and preformed anti-donor antibody. The rejection of VCTA in sensitized recipients is mainly cell mediated and differs mechanistically from that for renal transplants.

Arginine depletion as a mechanism for the immune privilege of corneal allografts.

The cornea is an immune privileged tissue. Since arginase has been found to modulate T-cell function by depleting arginine, we investigated the expression of arginase in the cornea and its possible role in immune privilege using a murine transplant model. We found that both the endothelium and epithelium of murine corneas express functional arginase I, capable of down-regulating T-cell proliferation in an in vitro culture system. The administration of the specific arginase inhibitor N-hydroxy-nor-l-Arg to recipient mice resulted in an accelerated rejection of allogeneic C57BL/6 (B6) corneal grafts. In contrast, in vivo blockade of arginase activity had no effect in altering the course of rejection of primary skin grafts that express little, if any, arginase. In addition, the inhibition of arginase did not alter systemic T-cell proliferation. These data show that arginase is functional in the cornea and contributes to the immune privilege of the eye, and that modulation of arginase contributes to graft survival.

New Approaches to Immunotherapy for HPV Associated Cancers

Cervical cancer is the second most common cancer of women worldwide and is the first cancer shown to be entirely induced by a virus, the human papillomavirus (HPV, major oncogenic genotypes HPV-16 and -18). Two recently developed prophylactic cervical cancer vaccines, using virus-like particles (VLP) technology, have the potential to prevent a large proportion of cervical cancer associated with HPV infection and to ensure long-term protection. However, prophylactic HPV vaccines do not have therapeutic effects against pre-existing HPV infections and do not prevent their progression to HPV-associated malignancy. In animal models, therapeutic vaccines for persisting HPV infection can eliminate transplantable tumors expressing HPV antigens, but are of limited efficacy in inducing rejection of skin grafts expressing the same antigens. In humans, clinical trials have reported successful immunotherapy of HPV lesions, providing hope and further interest. This review discusses possible new approaches to immunotherapy for HPV associated cancer, based on recent advances in our knowledge of the immunobiology of HPV infection, of epithelial immunology and of immunoregulation, with a brief overview on previous and current HPV vaccine clinical trials.