Direct Antigen Presentation by a Xenograft Induces Immunity Independently of Secondary Lymphoid Organs

Ovine model of burn wounds grafted with ovine cadaver skin

Shortage in autograft to cover burn wounds involves a frequent use of cadaver skin (CS) as a temporary cover to prevent infection, dehydration and preparation of wounds for subsequent autografting. We aimed to establish an ovine model of burn wound healing using ovine CS (OCS). Quality and efficacy of fresh and frozen OCS overlaid on to excised 3rd degree flame burn wounds in sheep were evaluated in comparison to autograft. Histologically, autografted wounds maintained normal skin structure at different time points. Wounds overlaid with fresh OCS graft showed signs of rejection starting from day 7. At day 14, the epidermis was mostly rejected. The rejection was completed by day 20 with signs of immunoreaction and presence of many immune cells. Frozen OCS was rejected in the same pattern. Immediately prior to grafting, the thickness was comparable between freshly prepared and frozen OCS for 10 or 40 days. Significant reduction in viability was detected in OCS frozen for 40 days. Both fresh or frozen ovine OCS were rejected within 10 days that mimics CS rejection time in humans (∼8.4 days), suggesting that ovine model of burn wound grafted with OCS can successfully be used in burn wound research mimicking clinical scenario.

Tumor-associated immune factors are associated with recurrence and metastasis in non-small cell lung cancer

Dynamic interaction between tumor cells and the microenvironment is critical for tumorigenesis, and cancer immunosurveillance plays an important role in the tumor evolution. In some tumors (such as esophageal cancer, pancreatic cancer and colorectal cancer), studies have shown that the number of tumor-infiltrating lymphocytes (TILs) has a significant relationship with the prognosis, but there is little research on the prognosis of TILs and non-small cell lung cancer (NSCLC) has been performed. Therefore, it is necessary to discover the relationship between the TILs and cytokines with NSCLC prognosis and metastasis in patients. Tumor samples were carefully examined for tissue preservation and complete follow-up. A total of 107 tumor samples from NSCLC patients with radical surgical resection were enrolled for the analysis. All samples were subjected to immunohistochemistry for detection of CD3, CD4, CD8, CD28, forkhead box protein P3 (Foxp3), cytotoxic T lymphocyte-associated protein-4, cyclooxygenase2 (COX-2), transforming growth factor β 1, interleukin-2 (IL-2), interleukin-6, interleukin-10, interleukin-12 receptor and hypoxia inducible factor 1a (HIF-1a). The number, function and location of the targets were analyzed to determine their correlation with disease-free survival (DFS) and overall survival (OS). Immunhistochemical results from 107 samples indicated that the FoxP3+ regulatory TIL (HR=1.336, P=0.031), IL-2 (HR=0.595, P=0.007) and HIF-1a (HR=1.510, P=0.002) levels in tumor cells closely correlated with DFS in a COX analysis model. FoxP3+ regulatory TILs (HR=1.566, P=0.002) significantly correlated with OS and tumor node metastasis staging. The patients were divided into two groups due to the coexpression pattern of the IL-2, FoxP3+ and HIF-1a. The high-risk group had an overall worse survival than those at low risk. We confirmed that Foxp3 expression in lymphocyte and IL-2 expression in tumor cells were associated with recurrence or transfer. Furthermore, we also observed that HIF-1a expression significantly correlated with DFS and OS.

The Role of Tumor-Infiltrating Lymphocytes in Development, Progression, and Prognosis of Non-Small Cell Lung Cancer

A malignant tumor is not merely an accumulation of neoplastic cells, but constitutes a microenvironment containing endothelial cells, fibroblasts, structural components, and infiltrating immune cells that impact tumor development, invasion, metastasis, and outcome. Hence, the evolution of cancers reflects intricate cellular and molecular interactions between tumor cells and constituents of the tumor microenvironment. Recent studies have shed new light on this complex interaction between tumor and host immune cells and the resulting immune response. The composition of the immune microenvironment differs across patients as well as in cancers of the same type, including various populations of T cells, B cells, dendritic cells, natural killer cells, myeloid-derived suppressor cells, neutrophils, and macrophages. The type, density, location, and organization of immune cells within solid tumors define the immune contexture, which has proved to be a major determinant of tumor characteristics and patient outcome. Lung cancer consists mostly of non-small cell lung cancer (85%); it is our most deadly malignant disease, with the 5-year survival rate being merely 15%. This review focuses on the immune contexture; the tumor-suppressing roles of tumor-infiltrating lymphocytes; and the relevance of this immune contexture for cancer diagnostics, prognostication, and treatment allocation, with an emphasis on non-small cell lung cancer.

NCR(+)ILC3 concentrate in human lung cancer and associate with intratumoral lymphoid structures

Tertiary lymphoid structures (TLSs) are a common finding in non-small cell lung cancer (NSCLC) and are predictors of favourable clinical outcome. Here we show that NCR(+) innate lymphoid cell (ILC)-3 are present in the lymphoid infiltrate of human NSCLC and are mainly localized at the edge of tumour-associated TLSs. This intra-tumoral lymphocyte subset is endowed with lymphoid tissue-inducing properties and, on activation, produces IL-22, TNF-α, IL-8 and IL-2, and activates endothelial cells. Tumour NCR(+)ILC3 may interact with both lung tumour cells and tumour-associated fibroblasts, resulting in the release of cytokines primarily on engagement of the NKp44-activating receptor. In patients, NCR(+)ILC3 are present in significantly higher amounts in stage I/II NSCLC than in more advanced tumour stages and their presence correlate with the density of intratumoral TLSs. Our results indicate that NCR(+)ILC3 accumulate in human NSCLC tissue and might contribute to the formation of protective tumour-associated TLSs.

Tertiary lymphoid structures are associated with higher tumor grade in primary operable breast cancer patients

Background

Tertiary lymphoid structures (TLS) are highly organized immune cell aggregates that develop at sites of inflammation or infection in non-lymphoid organs. Despite the described role of inflammation in tumor progression, it is still unclear whether the process of lymphoid neogenesis and biological function of ectopic lymphoid tissue in tumors are beneficial or detrimental to tumor growth. In this study we analysed if TLS are found in human breast carcinomas and its association with clinicopathological parameters.

Methods

In a patient group (n = 290) who underwent primary surgery between 2011 and 2012 we assessed the interrelationship between the presence of TLS in breast tumors and clinicopathological factors. Prognostic factors were entered into a binary logistic regression model for identifying independent predictors for intratumoral TLS formation.

Results

There was a positive association between the grade of immune cell infiltration within the tumor and important prognostic parameters such as hormone receptor status, tumor grade and lymph node involvement. The majority of patients with high grade infiltration of immune cells had TLS positive tumors. In addition to the degree of immune cell infiltration, the presence of TLS was associated with organized immune cell aggregates, hormone receptor status and tumor grade. Tumors with histological grade 3 were the strongest predictor for the presence of TLS in a multivariate regression model. The model also predicted that the odds for having intratumoral TLS formation were ten times higher for patients with high grade of inflammation than low grade.

Conclusions

Human breast carcinomas frequently contain TLS and the presence of these structures is associated with aggressive forms of tumors. Locally generated immune response with potentially antitumor immunity may control tumorigenesis and metastasis. Thus, defining the role of TLS formation in breast carcinomas may lead to alternative therapeutic approaches targeting the immune system.

Alternative immunomodulatory strategies for xenotransplantation: CD80/CD86-CTLA4 pathway-modified immature dendritic cells promote xenograft survival

Background

Xenotransplantation is a promising approach to circumventing the current organ shortage. However, T-cell-dependent anti-xenoresponses are a major challenge to successful xenografts. Given the advantages of the use of CTLA4-Ig in the survival of allografts, the purpose of the study was to investigate the therapeutic potential of CTLA4-IgG4 modified immature dendritic cells (imDCs) in the prevention of islets xenograft rejection.

Methods

CTLA4-IgG4 was constructed by the fusion of the extracellular regions of porcine CTLA4 to human the hIgG4 Fc region. The imDCs were induced and cultured from porcine peripheral blood mononuclear cells (PBMC). The CTLA4-IgG4 modified imDCs were delivered via the portal vein to the liver of diabetic mice (insulin-dependent diabetes mellitus) before islet xenografting, and mCTLA4-Ig was administered intravenously after xenotransplantation.

Results

The xenograft survival of mice receiving unmodified imDCs was approximately 30 days. However, following administration of CTLA4-IgG4 modified imDCs before grafting and mCTLA4-Ig after grafting, xenografts survived for more than 100 days. Flow cytometric analysis showed that the CD4⁺CD25⁺Foxp3⁺ Treg population was increased in spleens. The efficacy of donor CTLA4-IgG4 modified imDCs correlated partially with the amplification of Tregs.

Conclusions

These results confirm that selective inhibition of the direct and indirect pathways of T-cell activation by donor CTLA4-IgG4 modified imDCs and receptor CTLA4-Ig is a highly effective strategy to promote survival of xenografts.

Tumor microenvironment is multifaceted

Cancer initiation, progression, and invasion occur in a complex and dynamic microenvironment which depends on the hosts and sites where tumors develop. Tumors arising in mucosal tissues may progress in an inflammatory context linked to local viral and/or bacterial infections. At the opposite, tumors developing in immunoprivileged sites are protected from microorganisms and grow in an immunosuppressive environment. In the present review, we summarize and present our recent data on the influence of infectious context and immune cell infiltration organization in human Non-Small Cell Lung Cancers (NSCLC) progression. We show that stimulation of tumor cells by TLR for viral ssRNA, such as TLR7/8, or bacteria, such as TLR4, promotes cell survival and induces chemoresistance. On the opposite, stimulation by TLR3, receptor for double-stranded viral RNA, decreases tumor cell viability and induces chemosensitivity in some lung tumor cell lines. Since fresh lung tumor cells exhibit a gene expression profile characteristic of TLR-stimulated lung tumor cell lines, we suspect that viral and bacterial influence may not only act on the host immune system but also directly on tumor growth and sensitivity to chemotherapy. The stroma of NSCLC contains tertiary lymphoid structures (or Tumor-induced Bronchus-Associated Lymphoid Tissues (Ti-BALT)) with mature DC, follicular DC, and T and B cells. Two subsets of immature DC, Langerhans cells (LC) and interstitial DC (intDC), were detected in the tumor nests and the stroma, respectively. Here, we show that the densities of the three DC subsets, mature DC, LC, and intDC, are highly predictive of disease-specific survival in a series of 74 early-stage NSCLC patients. We hypothesize that the mature DC may derive from local activation and migration of the immature DC--and especially LC which contact the tumor cells--to the tertiary lymphoid structures, after sampling and processing of the tumor antigens. In view of the prominent role of DC in the immune response, we suggest that the microenvironment of early-stage NSCLC may allow the in situ activation of the adaptive response. Finally, we find that the eyes or brain of mice with growing B cell lymphoma are infiltrated with T cells and that the cytokines produced ex vivo by the tumoral tissues have an impaired Th1 cytokine profile. Our work illustrates that the host and external tumor microenvironments are multifaceted and strongly influence tumor progression and anti-tumor immune responses.

The immune microenvironments of lung and intraocular tumors

An increasing body of evidence underlines the prominent role of the immune microenvironment in cancer growth, invasion and metastasis. The local immune responses are specialized in the different organs. We will discuss the composition of the immune microenvironments and their role on tumor development in two cancers developing in opposite contexts: in the lung, which is at the interface of the outside world and in the eye, which is, an immunoprivileged site protected from it. We demonstrate that the immune system plays a major role in control of tumors, despite of these highly different tissue microenvironments.

Viability and Efficacy of Coverage of Cryopreserved Human Skin Allografts in Mice

Human skin allografts are considered one of the best temporary biological coverages for severe burn patients. Human skin allografts can be either viable or nonviable depending on their preservation modalities. However, there is a debate about the use of viable versus nonviable skin for severe burn patients because there is no established correlation between viability and efficacy of coverage. The authors tried to correlate the viability of cryopreserved human skin allografts as assessed by the MTT assay, with efficacy of coverage, intensity of rejection at day 8, and delay of wound healing in a xenograft model using human fresh skin (FS) and cryopreserved skin (CPS) on murine recipients (n = 49). Cryopreserved grafts were less rejectable than fresh grafts, with statistically significant different delays ( P = .0008). Mice that had received grafts healed with delays; the delays, whether associated with fresh grafts or cryopreserved grafts, were not statistically significant. On day 8 after the graft, the overall damage score for the tissue’s histological architectural integrity was higher for FS. Furthermore, flow cytometry analysis showed a significant increase in the number of CD4 and CD8 T-cells ( P = .001) in the spleens of FS-grafted mice. These results confirm that the use of viable CPS does not change the potential for healing.

Human leukemic cells loaded with alpha-galactosylceramide (alpha-GalCer) activate murine NKT cells in situ

Invariant NKT cells (NKT) cells become activated after stimulation with antigen-presenting cells (APCs) loaded with the NKT cell ligand, alpha-galactosylceramide (alpha-GalCer). In this study, we investigated whether human APCs loaded with alpha-GalCer have the ability to activate NKT cells in mice. We found that human dendritic cells (DCs) loaded with alpha-GalCer (hDC/Gal) and injected into C57BL/6 mice stimulated the secretion of IFN-gamma by activated murine NKT cells. Furthermore, the number of transferred hDC/Gal correlated with the number of recovered IFN-gamma-producing spleen cells, indicating that the capacity of APCs to load alpha-GalCer can be measured by IFN-gamma release in an ELISPOT assay. Finally, alpha-GalCer-loaded human leukemic cell lines and primary leukemic cells injected into C57BL/6 mice also had the capacity to stimulate murine NKT cells in vivo. These results indicate that in vivo murine NKT cell responses can be used to quantitate the alpha-GalCer-loading capacity of human APCs. This method could be utilized to develop future immunotherapies in which NKT cells are targeted for activation.

Immune infiltration in human cancer: prognostic significance and disease control

The interplay between tumors and their immunologic microenvironment is complex and difficult to decipher, but its understanding is of seminal importance for the development of novel prognostic markers and therapeutic strategies. This chapter discusses tumor-immune interactions in several human cancers that illustrate various aspects of this complexity and proposes an integrated scheme of the impact of local immune reactions on clinical outcome. Thus, the fact that a strong infiltration of memory T cells with a Th1 and cytotoxic pattern is the strongest predictor for recurrence and metastasis is exemplified in colorectal cancer in which intratumoral chemokines shape an efficient immune reaction. Based on these data, we propose an immune score that predicts recurrence in early stage (UICC-TNM stage I-II) cancers. Studies on non-small lung cancers have confirmed findings of colorectal cancers and have addressed the question of the sites where antitumor immune reactions may take place. Tertiary lymphoid structures (TLS) adjacent to the tumor nest are sites of intense activity with mature dendritic cells in contact with T cells and germinal-like centers with proliferating B cells. The large number of these TLS being correlated with disease specific and overall survival tempts to postulate that they are privileged sites to mount an efficient antitumor reaction. Inflammation is a major component of human tumors and chronic inflammation is generally of bad prognosis. Head and neck cancers are highly inflammatory and two ways to modulate inflammation in these diseases are presented here: soluble IL-15 receptor α (IL-15 Rα) increases the pro-inflammatory effect of IL-15 and aggravates inflammation resulting in poor prognosis when found at high levels in the plasma of patients. By contrast, infiltration of regulatory T cells is paradoxically beneficial for local control of head and neck tumors, probably by "cooling down" the inflammatory process. The modulation of other aspects of innate immunity may also result in paradoxical effects such as the signaling through Toll like receptors 7 and 8 expressed on lung tumor cells which induce an aggressive tumoral phenotype. Finally, the analysis of primary intraocular lymphoma, which develops in the eye, exemplifies the induction of an antitumor immune reaction in an "immune sanctuary," presenting all the complexities of the tumor-immune interplay in "open" tissues such as the colon or the lung.

Immune infiltration in human tumors: a prognostic factor that should not be ignored

The natural history of a tumor includes phases of 'in situ' growth, invasion, extravasation and metastasis. During these phases, tumor cells interact with their microenvironment and are influenced by signals coming from stromal, endothelial, inflammatory and immune cells. Indeed, tumors are often infiltrated by various numbers of lymphocytes, macrophages or mast cells. It is generally believed that the latter produce factors that maintain chronic inflammation and promote tumor growth, whereas lymphocytes may control cancer outcome, as evidenced in mouse models. In this study, we analyze data from large cohorts of human tumors, clearly establishing that infiltration of the primary tumor by memory T cells, particularly of the Th1 and cytotoxic types, is the strongest prognostic factor in terms of freedom from disease and overall survival at all stages of clinical disease. We review data suggesting that tertiary lymphoid structures adjacent to tumors and composed of mature dendritic cells (T and B cells organized as germinal centers) may be the site of an antitumor reaction. We propose an immune scoring based on the type, density and location of lymphocyte infiltrates as a novel prognostic factor for use in addition to tumor node metastasis staging to predict disease-free survival and to aid in decisions regarding adjuvant therapies in early stage human cancers.

Cutting edge: Acute lung allograft rejection is independent of secondary lymphoid organs

It is the prevailing view that adaptive immune responses are initiated in secondary lymphoid organs. Studies using alymphoplastic mice have shown that secondary lymphoid organs are essential to initiate allograft rejection of skin, heart, and small bowel. The high immunogenicity of lungs is well recognized and allograft rejection remains a major contributing factor to poor outcomes after lung transplantation. We show in this study that alloreactive T cells are initially primed within lung allografts and not in secondary lymphoid organs following transplantation. In contrast to other organs, lungs are acutely rejected in the absence of secondary lymphoid organs. Two-photon microscopy revealed that recipient T cells cluster predominantly around lung-resident, donor-derived CD11c(+) cells early after engraftment. These findings demonstrate for the first time that alloimmune responses following lung transplantation are initiated in the graft itself and therefore identify a novel, potentially clinically relevant mechanism of lung allograft rejection.

Long-term survival for patients with non-small-cell lung cancer with intratumoral lymphoid structures

PURPOSE

It has been established that the immune system plays an important role in tumor rejection. There is also compelling evidence that immune responses can develop independently of secondary lymphoid organs in tertiary lymphoid structures. We studied the presence and the correlation of tertiary lymphoid structures with clinical outcome in non-small-cell lung cancer (NSCLC), as the prognostic value of these structures in patients with cancer had not yet been established.

PATIENTS AND METHODS

This retrospective study was performed by immunohistochemistry on paraffin-embedded tissue specimens from 74 patients with early-stage NSCLC.

RESULTS

Tertiary lymphoid structures were detected in some tumors but not in nontumoral lungs. Thus we called these structures tumor-induced bronchus-associated lymphoid tissue (Ti-BALT). As in lymph nodes, Ti-BALTs were composed of mature dendritic cell (DC)/T-cell clusters adjacent to B-cell follicles and had features of an ongoing immune response. Because the quantitative counting of Ti-BALT was difficult to achieve, we used mature DCs that homed exclusively in Ti-BALT as a specific marker of these structures. Univariate analysis showed that the density of mature DCs was highly associated with a favorable clinical outcome (overall, disease-specific, and disease-free survival), suggesting that Ti-BALT may participate in antitumoral immunity. The density of tumor-infiltrating lymphocytes, in particular, CD4(+) and T-bet(+) Th1 T cells, was profoundly decreased in tumors weakly infiltrated by mature DCs.

CONCLUSION

The density of mature DCs was found to be a better predictor of clinical outcome than the other parameters tested. The number of tumor-infiltrating mature DCs may identify patients with early-stage NSCLC who have a high risk of relapse.

Both Infiltrating Regulatory T Cells and Insufficient Antigen Presentation Are Involved in Long-Term Cardiac Xenograft Survival

We have previously shown that pretransplant donor lymphocyte infusion (DLI) together with transient depletion of CD4(+) T cells could induce permanent rat-to-mouse heart graft survival, whereas depleting CD4(+) T cells alone failed to do so. In this study, we investigated the mechanism leading to long-term xenograft survival. We found that peripheral CD4(+) T cells from DLI/anti-CD4-treated mice could mount rat heart graft rejection after adoptive transfer into B6 CD4(-/-) mice. Infusing donor-Ag-loaded mature dendritic cells (DCs) could break long-term cardiac xenograft survival in DLI/anti-CD4-treated mice. Interestingly, when the number and phenotype of graft-infiltrating cells were compared between anti-CD4- and DLI/anti-CD4-treated groups, we observed a significant increase in both the number and suppressive activity of alphabeta-TCR(+)CD3(+)CD4(-)CD8(-) double negative regulatory T cells and decrease in the numbers of CD4(+) and CD8(+) T cells in the xenografts of DLI/anti-CD4-treated mice. Moreover, there was a significant reduction in MHC class II-high DCs within the xenografts of DLI/anti-CD4-treated recipients. DCs isolated from the xenografts of anti-CD4- but not DLI/anti-CD4-treated recipients could stimulate CD4(+) T cell proliferation. Our data indicate that functional anti-donor T cells are present in the secondary lymphoid organs of the mice that permanently accepted cardiac xenografts. Their failure to reject xenografts is associated with an increase in double negative regulatory T cells as well as a reduction in Ag stimulation by DCs found within grafts. These findings suggest that local regulatory mechanisms need to be taken into account to control anti-xenograft T cell responses.

Murine [corrected] myeloid dendritic cell-dependent toll-like receptor immunity is preserved with aging

The immune response is the result of the interplay between innate and adaptive immunity, yet the impact of aging on this interaction is unclear. Addressing this fundamental question will be critical for the development of effective vaccines for the rapidly rising older subpopulation that manifests increased prevalence of malignancies and infections. Therefore, we undertook the current study to investigate whether aging impairs toll-like receptor (TLR) function in myeloid dendritic cells and whether this leads to reduced T-cell priming. Our results demonstrate that innate TLR immune priming function of myeloid bone marrow derived and splenic dendritic cells (DC) is preserved with aging using both allogeneic and infectious murine experimental systems. In contrast, aging impairs in vitro and in vivo intrinsic T-cell function. Therefore, our results demonstrate that myeloid DCs manifest preserved TLR-mediated immune responses with aging. However, aging critically impairs intrinsic adaptive T-cell function.

Donor lymphoid organs are a major site of alloreactive T-cell priming following intestinal transplantation

We hypothesized that lymphoid organs within intestinal allografts contribute to their immunogenicity. Consistent with this hypothesis recipient T cells rapidly migrated to the lymph nodes and Peyer's patches of syngeneic and allogeneic intestinal grafts such that at 24 h approximately 50% of the lymphocytes isolated from donor lymphoid organs were of recipient origin. However, only in the lymphoid organs of allografts did recipient T cells display an activated phenotype, proliferate and produce IFNgamma. Rejection of allogeneic intestines lacking lymphoid organs was dramatically impaired in splenectomized, lymph node-deficient recipients compared to lymph node bearing, wild-type allogeneic intestines. This demonstrates the important role of donor lymphoid organs in the rejection process. Furthermore, recipient T cells proliferated more extensively and produced more IFNgamma in donor lymphoid organs than in recipient lymphoid organs, indicating that donor lymphoid organs play a dominant role in initiating the recipient anti-donor immune response following intestinal transplantation.

The role of hyaluronan degradation products as innate alloimmune agonists

Dendritic cells (DCs) play a key role in initiating alloimmunity yet the substances that activate them during the host response to transplantation remain elusive. In this study we examined the potential roles of endogenous innate immune agonists in activating dendritic cell-dependent alloimmunity. Using a murine in vitro culture system, we show that 135 KDa fragments of the extracellular matrix glycosaminoglycan hyaluronan induce dendritic cell maturation and initiate alloimmunity. Priming of alloimmunity by hyaluronan-activated DCs was dependent on signaling via TIR-associated protein, a Toll-like receptor (TLR) adaptor downstream of TLRs 2 and 4. However, this effect was independent of alternate TLR adaptors, MyD88 or Trif. Using an in vivo murine transplant model, we show that hyaluronan accumulated during skin transplant rejection. Examination of human lung transplant recipients demonstrated that increased levels of intragraft hyaluronan were associated with bronchiolitis obliterans syndrome. In conclusion, our study suggests that fragments of hyaluronan can act as innate immune agonists that activate alloimmunity.

Absence of Innate MyD88 Signaling Promotes Inducible Allograft Acceptance

Prior experimental strategies to induce transplantation tolerance have focused largely on modifying adaptive immunity. However, less is known concerning the role of innate immune signaling in the induction of transplantation tolerance. Using a highly immunogenic murine skin transplant model that resists transplantation tolerance induction when innate immunity is preserved, we show that absence of MyD88, a key innate Toll like receptor signal adaptor, abrogates this resistance and facilitates inducible allograft acceptance. In our model, absence of MyD88 impairs inflammatory dendritic cell responses that reduce T cell activation. This effect increases T cell susceptibility to suppression mediated by CD4+ CD25+ regulatory T cells. Therefore, this study provides evidence that absence of MyD88 promotes inducible allograft acceptance and implies that inhibiting innate immunity may be a potential, clinically relevant strategy to facilitate transplantation tolerance.