Mechanisms Of Immune Tolerance Research Articles

PReS13-SPK-1587: New biologic targets for the future and basic science behind them

The treatment of paediatric rheumatic diseases has made great progress in the last decade. The introduction of the biologicals meant (after the introduction of MTX) the second therapeutic revolution. This together with many improvements in related areas has greatly improved the quality of life of patients with rheumatic diseases. At present however, despite the introduction of more biological agents directed at immune targets the progression has stalled. The next challenge will be to: 1) Better understand the immune pathogenesis underlying the heterogeneity of the disease. 2) Identify patients at risk at the onset of disease and stratify them according to risk factors. 3) Personalize treatment based on their risk profiling. 4) Develop strategies that are aimed not only at suppressing disease but also at maintaining disease remission after withdrawing immune suprresion. Over the last years much progress has been made in all these area's. In this presentation we will discuss this progress, focusing on a better understanding of the mechanisms of immune tolerance, leading to new targets for intervention.

CD8α+ Jagged2high CD11bhigh Regulatory Dendritic Cells Prevent Acute Gvhd

Acute graft-versus-host disease (aGVHD) is still an important complication after allogeneic hematopoietic stem cell transplantation. Dendritic cells (DCs) are crucial for initiating cell-mediated adaptive immune responses or maintaining immune tolerance, which play key role on inducting of GVHD. We have reported a subset of dendritic cells (DCs), CD8α+ Jagged2high CD11bhigh regulatory dendritic cells (DCregs), which also express MHC molecules and low lever of costimulatory molecules, induce the production of regulatory T cells and inhibit the proliferation function of lymphocyte. In this study, we examined the role of the CD8α+ Jagged2high CD11bhighregulatory dendritic cells (DCregs) in murine major histocompatibility complex (MHC)-incompatible model of aGVHD in alloHSCT.BALB /c (H-2d) mice bone marrow cells (BMCs) were isolated and were induced to DCs generation by 4 cytokines, SCF (100ng/mL), IL-4 (20ng/mL), Flt3 ligand (25ng/mL), and GM-CSF (5ng/mL) for 3 days. The new DCs were selected by flow cytometry, and were co-cultured with Bone marrow mesenchymal stem cells (BMSCs) for 10 days. Characteristics of such regulatory dendritic cells and immune tolerance features were detected before and after co-culture by FCM analysis, ELISA kit, and mixed lymphocyte reaction. Male 8-week-old C57BL / 6 (H-2b) mice were used as donor, and female 8-week-old BALB / c (H-2d) were used as recipient. The recipient mice received SSD100, 30×30 radiation field, 700cGy total body irradiation (TBI) pretreatment, and grouped as follows: 1.normal control group, 2.TBI control group, 3. transplantat control group, 4. aGVHD group: 1 × 107 BMC and 1 × 107 spleen cells (SPC) were injected through caudal vein 5. DCregs groups: 1 × 107 BMC, 1 × 107 spleen cells (SPC) and 1 × 106DCregs were injected through caudal vein. Evaluate the severity of GVHD according to clinical manifestations (weekly the GVHD ratings), the survival time and histopathological examination.The results showed that novel DCs were transformed into CD8α+Jagged2highCD11bhigh Dcregs. The expression of CD86, CD80, CD40, and MHC-II were evidently decreased, while that of CD205, Jagged1 and Jagged2 were significantly increased on DCregs (P <0.05). Meanwhile, the percentage of treated DCs cells were increased in the G2 and S phase. Compared with DC control group, IL-6 and IL-12 expression were decreased significantly (P <0.05), IL-10 and TGF-beta expression was significantly elevated (P <0.05). CD8α+Jagged2highCD11bhighDcregs have stronger inhibitory effect of lymphocyte proliferation (P <0.05).The mice of transplant control group were observed to +60d and no GVHD clinical manifestation was observed. The clinical manifestations of aGVHD group is fatigue, piloerection, arched, progressive weight loss, hair removal, repeated skin ulcers, perianal redness and secretions, and all died within +40 d , while the median survival time was 27 days. The median survival of the DCregs group was +33 d, and two group of +30 d survival rates were 20% and 100%, respectively. aGVHD score (P<0.05) and histopathological changes at +33 d of DCregs group were better than the aGHVD group.CD8α+CD11b+jagged2highregulatory dendritic cells can reduce the symptom of GVHD, delay the death of aGVHD model, but the effect duration was short, and might need maintained by infusion repeatedly. The immune tolerance mechanisms of this novel DCregs might be relate to up-regulated Jagged1 and Jagged2 expression and T cell Notch signaling pathway activation. NOTESThe project was sponsored by grants from National Natural Science Foundation (No. 81270648 and 30972790), National Public Health Grand Research Foundation (No.201202017), and Guangdong Natural Science Foundation (No. S2012010009560). Disclosures:No relevant conflicts of interest to declare.

Overall picture of an emerging neonatal infectious disease induced by a superantigenic exotoxin mainly produced by methicillin‐resistant Staphylococcus aureus

Since 1992, many neonates in neonatal intensive care units in Japan have been developing fever and systemic exanthema. Immunological analyses of neonates with these symptoms has revealed that the bacterial superantigen, toxic shock syndrome toxin-1 (TSST-1) is the cause. The name neonatal TSS-like exanthematous disease (NTED) has been applied to this condition. The most striking clinical finding has been that none of the term neonates have developed shock or died of NTED. The timing of NTED epidemics has coincided with the spread of emerging TSST-1-producing methicillin-resistant Staphylococcus aureus clones in Japan. The low frequency of pregnant women with positive anti-TSST-1 antibody titers could be one reason for the spread of NTED in Japan. Neonates have immune tolerance against TSST-1 and may actively suppress the immune response to NTED with interleukin-10. According to the T cell responses in infants or young children with diseases induced by TSST-1, the pathophysiology of TSST-1-related diseases may be age-dependent. The precise mechanism of anergy and deletion of specific T cells stimulated with TSST-1 should be investigated in neonates infected with NTED. Both NTED and TSS might provide good models for analyzing the mechanism(s) of neonatal immune tolerance and the age-dependence of human immunity. This disease has not only become representative of diseases caused by superantigens, but has also yielded a considerable amount of evidence about human immune reactions against superantigens.

Immune Tolerance of Amniotic Fluid Stem Cell–Induced Rat Kidney Graft and Influences on Oxidative Stress

ObjectiveThis study aimed to use amniotic fluid stem cells of donors to induce immune tolerance of heterogenous rat kidney graft for investigating the formation mechanism of immune tolerance. MethodsWith Wistar rats as donors and Sprague-Dawley (SD) rats as receptors, the heterogenous kidney graft animal model was established, and amniotic fluid stem cells of Wistar rats were isolated and cultured. Moreover, 40 SD rats were randomly divided into 4 groups. Creatinine (Cr), blood urea nitrogen (BUN), interleukin (IL) 2, interferon (IFN) γ, and oxidative stress levels in serum were detected, flow cytometry was used to detect changes of CD4 and CD8 cells, and quantitative changes of urinary protein and pathologic changes of transplanted kidney were observed. ResultsBUN, Cr, IL-2, IFN-γ, and oxidative stress levels and urinary protein quantity in rat serum of the test group were significantly lower than those of the control group, creatinine clearance rate was significantly higher than that of the control group, and renal pathologic injury extent was significantly milder than that of the control group. ConclusionsAmniotic fluid stem cells can induce immune tolerance of rat kidney graft and inhibit oxidative stress level, improve kidney function, and alleviate kidney injury.

Loss of immune escape mutations during persistent HCV infection in pregnancy enhances replication of vertically transmitted viruses

Globally, about 1% of pregnant women are persistently infected with the hepatitis C virus (HCV)1. Vertical transmission occurs in 3–5% of cases2 and accounts for most new childhood HCV infections1,3. HCV-specific CD8+ cytotoxic T-lymphocytes (CTLs) play a vital role in the clearance of acute infections4–6, but in the 60–80% of infections that persist these cells become functionally exhausted or select mutant viruses that escape T-cell recognition7–9. Increased HCV replication during pregnancy10,11 suggests that maternofetal immune tolerance mechanisms12 may further impair HCV-specific CTLs, limiting their selection pressure on persistent viruses. To assess this possibility, we characterized the circulating viral quasispecies during and after consecutive pregnancies. This revealed a loss of some escape mutations in class I epitopes in pregnancy associated with emergence of more fit viruses13. CTL selection pressure was reimposed after childbirth, when escape mutations in these epitopes again predominated in the quasispecies and viral load dropped sharply14. Importantly, viruses transmitted perinatally were those with enhanced fitness due to reversion of escape mutations. Our findings indicate that immunoregulatory changes of pregnancy reduce CTL selection pressure on HCV class I epitopes, thereby facilitating vertical transmission of viruses with optimized replicative fitness.

Immune evasion in acute myeloid leukemia: current concepts and future directions.

Immune responses generated against malignant cells have the potential to inhibit tumor growth, or even eliminate transformed cells before a tumor forms. However, immune tolerance mechanisms that normally protect healthy tissues from autoimmune damage pose a formidable barrier to the development of effective anti-tumor immunity. Because malignant cells are derived from self-tissues, the majority of defined tumor antigens are either shared or aberrantly expressed self-proteins. Eliciting productive T cell responses against such proteins is challenging, as most high-affinity, self-reactive T cells are purged during thymic selection. Some T cells capable of tumor antigen recognition escape thymic deletion, but are functionally inhibited by peripheral tolerance mechanisms which limit their ability to attack a developing malignancy. Alternatively, some tumors express antigens derived from mutated self-proteins, viral proteins or self proteins expressed only during embryonic development. These antigens are recognized by the immune system as foreign and could be recognized by a relatively large number of peripheral T cells. Even in this scenario, tumors evade otherwise effective T cell responses by employing potent immunosuppressive mechanisms within their local environment. In the setting for solid malignancies, such as melanoma, a growing number of putative immune evasion mechanisms have been characterized. However, acute myeloid leukemia (AML) is a systemic disease, and the pathways it exploits to subvert the host immune response may be quite different than those of a solid tumor. Much remains unknown regarding the immune escape mechanisms promoted by AML, and whether efforts to thwart tolerance may influence the progression of this disease. Here, we review current concepts of immune evasion in AML, and speculate how potentially effective immunotherapeutic strategies might be developed to reverse immune tolerance in leukemia patients in the future.

Protein Kinase Cδ Deficiency Causes Mendelian Systemic Lupus Erythematosus With B Cell‐Defective Apoptosis and Hyperproliferation

Systemic lupus erythematosus (SLE) is a prototype autoimmune disease that is assumed to occur via a complex interplay of environmental and genetic factors. Rare causes of monogenic SLE have been described, providing unique insights into fundamental mechanisms of immune tolerance. The aim of this study was to identify the cause of an autosomal-recessive form of SLE. We studied 3 siblings with juvenile-onset SLE from 1 consanguineous kindred and used next-generation sequencing to identify mutations in the disease-associated gene. We performed extensive biochemical, immunologic, and functional assays to assess the impact of the identified mutations on B cell biology. We identified a homozygous missense mutation in PRKCD, encoding protein kinase δ (PKCδ), in all 3 affected siblings. Mutation of PRKCD resulted in reduced expression and activity of the encoded protein PKCδ (involved in the deletion of autoreactive B cells), leading to resistance to B cell receptor- and calcium-dependent apoptosis and increased B cell proliferation. Thus, as for mice deficient in PKCδ, which exhibit an SLE phenotype and B cell expansion, we observed an increased number of immature B cells in the affected family members and a developmental shift toward naive B cells with an immature phenotype. Our findings indicate that PKCδ is crucial in regulating B cell tolerance and preventing self-reactivity in humans, and that PKCδ deficiency represents a novel genetic defect of apoptosis leading to SLE.

Mechanism of immune tolerance induced by donor derived immature dendritic cells in rat high-risk corneal transplantation.

To study the role of immature dendritic cells (imDCs) on immune tolerance in rat penetrating keratoplasty (PKP) in high-risk eyes and to investigate the mechanism of immune hyporesponsiveness induced by donor-derived imDCs. Seventy-five SD rats (recipient) and 39 Wistar rats (donor) were randomly divided into 3 groups: control, imDC and mature dendritic cell (mDC) group respectively. Using a model of orthotopic corneal transplantation in which allografts were placed in neovascularized high-risk eyes of recipient rat. Corneal neovascularization was induced by alkaline burn in the central cornea of recipient rat. Recipients in imDC group or mDC group were injected donor bone marrow-derived imDCs or mDCs of 1×10(6) respectively 1 week before corneal transplantation via tail vein. Control rat received the same volume of PBS. In each group, 16 recipients were kept for determination of survival time and other 9 recipients were executed on day 3, 7 and 14 after transplantation. Cornea was harvested for hematoxylin-eosin staining and acute rejection evaluation, Western blot was used to detect the expression level of Foxp3. The mean survival time of imDC group was significantly longer than that of control and mDC groups (all P<0.05). The expression level of Foxp3 on CD4(+)CD25(+)T cells of imDC group (2.24±0.18) was significantly higher than that in the control (1.68±0.09) and mDC groups (1.46±0.13) (all P<0.05). Donor-derived imDC is an effective treatment in inducing immune hyporesponsiveness in rat PKP. The mechanism of immune tolerance induced by imDC might be inhibit T lymphocytes responsiveness by regulatory T cells.

Tryptamine and dimethyltryptamine inhibit indoleamine 2,3 dioxygenase and increase the tumor‐reactive effect of peripheral blood mononuclear cells

Indoleamine 2,3-dioxygenase (IDO) is an interferon-γ (IFN-γ)-induced tryptophan-degrading enzyme, producing kynurenine (KYN) that participates in the mechanism of tumor immune tolerance. Thus, IDO inhibition has been considered a strategy for anticancer therapy. The aim of this study was to identify whether the metabolites originated from the competitive routes of tryptophan metabolism, such as the serotonergic or N, N-dimethyltryptamine (DMT) pathways, have inhibitory effects on recombinant human IDO (rhIDO) activity. Serotonin and melatonin had no effect; on the other hand, tryptamine (TRY) and DMT modulated the activity of rhIDO as classical non-competitive inhibitors, with Ki values of 156 and 506 μM, respectively. This inhibitory effect was also observed on constitutively expressed or IFN-γ-induced IDO in the A172 human glioma cell line. TRY and DMT increased the cytotoxic activity of peripheral blood mononuclear cells (PBMCs) in co-culture assays. We conclude that the IDO inhibition by TRY and DMT contributed to a more effective tumor-reactive response by the PBMCs.

Modulation of IL-2Rα with daclizumab for treatment of multiple sclerosis

Multiple sclerosis (MS) is a debilitating neurological disorder involving autoimmune destruction of myelin. Although the pathogenic mechanisms underlying MS are not fully understood, T cells are thought to have a key role in orchestrating the aberrant CNS-directed adaptive immune response in the early and relapsing-remitting phase of disease. New therapeutic interventions with improved efficacy over existing drugs and good tolerability are needed. A promising therapy under investigation is daclizumab--a humanized monoclonal antibody directed against the IL-2 receptor α chain (CD25). Clinical trials have shown that daclizumab strongly inhibits disease activity and slows disease progression in MS. Novel and intriguing mechanisms of action of daclizumab have been identified that might explain its clinical efficacy--namely, expansion and enhancement of the immune regulatory function of CD56bright natural killer cells, reduction of early T-cell activation through blockade of IL-2 cross-presentation by dendritic cells, and reduction of lymphoid tissue inducer cells--thereby enhancing endogenous mechanisms of immune tolerance. This Review discusses the efficacy and safety of daclizumab in patients with MS and provides a detailed insight into the multifunctional mechanisms of action of this drug.

Human intestinal dendritic cells as controllers of mucosal immunity

Dendritic cells are the most potent, professional antigen-presenting cells in the body; following antigen presentation they control the type (proinflammatory/regulatory) of immune response that will take place, as well as its location. Given their high plasticity and maturation ability in response to local danger signals derived from innate immunity, dendritic cells are key actors in the connection between innate immunity and adaptive immunity responses. In the gut dendritic cells control immune tolerance mechanisms against food and/or commensal flora antigens, and are also capable of initiating an active immune response in the presence of invading pathogens. Dendritic cells are thus highly efficient in controlling the delicate balance between tolerance and immunity in an environment so rich in antigens as the gut, and any factor involving these cells may impact their function, ultimately leading to the development of bowel conditions such as celiac disease or inflammatory bowel disease. In this review we shall summarize our understanding of human intestinal dendritic cells, their ability to express and induce migration markers, the various environmental factors modulating their properties, their subsets in the gut, and the problems entailed by their study, including identification strategies, differences between humans and murine models, and phenotypical variations along the gastrointestinal tract.

Study on the anti‐atherosclerotic mechanisms of immune tolerance induced by heat shock protein 60

Backgroud and purposeTo study the anti‐atherosclerotic mechanisms of immune tolerance induced by Heat shock protein 60 (HSP60)Methods40 male SD rats were randomly divided into healthy control group, atherosclerosis group (AS group), H1 group (oral HSP60 before modeling AS) and H2 group (oral HSP60 after modeling AS). The content of CD36, SR‐A, NF‐κB, HSP60 and regulatory T cells (Treg) in the aorta, lymph nodes and peripheral blood were detection by immunohistochemistry, flow cytometry, Western blot, PCR and ELISA. The intimal and vessel diameter ratios were calculated by the image analysis system.ResultsThe levels of Treg cells in blood and lymphoid tissue increased. The pathological lesions of H1 group lighter than that of H2 group. The gene and protein expression of HSP60, SR‐A, CD36, NF‐κB in aorta of AS group were higher than that in the control group.The level of expression in the H1 group was lower than that in the H2 group. (P &lt;0.05).ConclusionThe immune tolerance induced by oral HSP60 could inhibit the arteries immune and inflammatory response, reduce the intimal injury and HSP60 antigen exposure and the degree of autoimmune response. Thereby it could also inhibit smooth muscle hyperplasia and maintain the stability of the fibrous plaques. Moreover, the earlier the oral HSP60, the better anti‐atherosclerosis effect.

Intravenous transfer of apoptotic cell-treated dendritic cells leads to immune tolerance by blocking Th17 cell activity

Apoptotic cell-induced tolerogenic dendritic cells (DCs) play an important role in induction of peripheral tolerance in vivo; however, the mechanisms of immune tolerance induced by these DCs are poorly understood. Here we show that treatment of apoptotic cells modulates expression of inflammation- and tolerance-associated molecules including Gr-1, B220, CD205 and galectin-1 on bone marrow-derived DCs. In addition, apoptotic cell-treated DCs suppress secretion of cytokines produced by Th17 cells. Our data also demonstrate that i.v. transfer of apoptotic cell-treated DCs blocks EAE development and down-regulates production of inflammatory cytokines such as IL-17A and IL-17F in CD4+ T cells. These results suggest that apoptotic cell-treated DCs may inhibit activity of Th17 cells via down-regulation of inflammatory cytokine production, thereby affecting EAE development in vivo. Our results reveal a potential mechanism of immune tolerance mediated by apoptotic cell-treated DCs and the possible use of apoptotic cell-treated DCs to treat autoimmune diseases such as MS/EAE.

Advances in basic and clinical immunology in 2012

Basic and clinical immunology articles published in the Journal in 2012 were mostly related to the expanding area of primary immunodeficiencies (PIDs). Novel forms of PID were identified by using whole-exome sequencing or after careful examination of flow cytometric data, as in the reports of lymphocyte-specific protein tyrosine kinase, CD27, and CD21 deficiencies. Absent IgG and IgA memory B cells were described in patients with hyper-IgE syndrome, which is consistent with defective antibody response and suggests a potential benefit of immunoglobulin replacement. Impaired production of antibodies to polysaccharide antigens by the human B-cell subset analog to murine B-1 cells was reported in a child with selective polysaccharide antibody deficiency. Increased production of inflammatory cytokines by monocyte-derived cells on Toll-like receptor activation was reported in patients with X-linked agammaglobulinemia, underscoring the important role of Bruton tyrosine kinase in modulation of inflammation. The mechanisms explaining susceptibility to yeast infections and development of chronic mucocutaneous candidiasis were extensively studied. Universal newborn screening for T-cell deficiencies is being implemented in several states, resulting in the diagnosis of a higher number of immunodeficient newborns than previously estimated. The use of laboratory testing to distinguish PIDs from HIV infection was clarified. In the management of PIDs, refinement of indication and strategies to hematopoietic stem cell transplantation resulted in improved outcomes. The use of anti-IL-6 mAbs showed promise as an alternative treatment in patients with Schnitzler syndrome.

Dendritic cells and the promise of antigen-specific therapy in rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic inflammatory disease resulting from an autoimmune response to self-antigens, leading to inflammation of synovial tissue of joints and subsequent cartilage and bone erosion. Current disease-modifying anti-rheumatic drugs and biologic inhibitors of TNF, IL-6, T cells and B cells block inflammation nonspecifically, which may lead to adverse effects, including infection. They do not generally induce long-term drug-free remission or restoration of immune tolerance to self-antigens, and lifelong treatment is usual. The development of antigen-specific strategies in RA has so far been limited by insufficient knowledge of autoantigens, of the autoimmune pathogenesis of RA and of the mechanisms of immune tolerance in man. Effective tolerance-inducing antigen-specific immunotherapeutic strategies hold promise of greater specificity, of lower toxicity and of a longer-term solution for controlling or even preventing RA. This paper reviews current understanding of autoantigens and their relationship to immunopathogenesis of RA, and emerging therapeutics that aim to leverage normal tolerance mechanisms for implementation of antigen-specific therapy in RA.

Mechanisms of immune tolerance to allergens in children

Because the prevalence of allergic diseases has significantly increased in recent years, understanding the causes and mechanisms of these disorders is of high importance, and intense investigations are ongoing. Current knowledge pinpoints immune tolerance mechanisms as indispensable for healthy immune response to allergens in daily life. It is evident that development and maintenance of allergens-pecific T cell tolerance is of vital importance for a healthy immune response to allergens. Such tolerance can be gained spontaneously by dose-dependent exposures to allergens in nature or by allergen-specific immunotherapy. Allergen-specific immunotherapy induces regulatory T cells with the capacity to secrete interleukin-10 and transforming growth factor-β, limits activation of effector cells of allergic inflammation (such as mast cells and basophils), and switches antibody isotype from IgE to the noninflammatory type IgG4. Although allergen-specific immunotherapy is the only method of tolerance induction in allergic individuals, several factors, such as long duration of treatment, compliance problems, and life-threatening side effects, have limited widespread applicability of this immunomodulatory treatment. To overcome these limitations, current research focuses on the introduction of allergens in more efficient and safer ways. Defining the endotypes and phenotypes of allergic diseases might provide the ability to select ideal patients, and novel biomarkers might ensure new custom-tailored therapy modalities.

Inflammation in aspergillosis: the good, the bad, and the therapeutic

Aspergillosis includes a spectrum of diseases caused by different Aspergillus spp. New insights into the cellular and molecular mechanisms of resistance and immune tolerance to the fungus in infection and allergy have been obtained in experimental settings. The fact that virulence factors, traditionally viewed as fungal attributes, are contingent upon microbial adaptation to various environmental stresses encountered in the human host implies that the host and fungus are jointly responsible for pathogenicity. Ultimately, despite the occurrence of severe aspergillosis in immunocompromised patients, clinical evidence indicates that aspergillosis also occurs in the setting of a heightened inflammatory response, in which immunity occurs at the expense of host damage and pathogen eradication. Thus, targeting pathogenicity rather than microbial growth, tolerance rather than resistance mechanisms of defense may pave the way to targeted anti-inflammatory strategies in difficult-to-treat patients. The challenge now is to translate promising results from experimental models to the clinic.

Gonadal steroids and humoral immunity

Humoral immune responses are sexually dimorphic. Female individuals generally exhibit more-robust antibody responses to vaccines and, in the clinical setting as well as in experimental models, are more likely than male individuals to produce autoreactive antibodies of pathogenic potential. A number of differences between the sexes might account for these observations, including differences in the dosage of specific X-chromosome and Y-chromosomal genes, increased exposure of female individuals to antigenic stimulation in childbearing, and differences in circulating concentrations of gonadal steroid hormones. The role of gonadal steroids in modulating such humoral immune responses has been studied for nearly a century, but advances in our knowledge of B-lymphocyte development and function, the mechanisms of immune tolerance, and the molecular basis of gonadal steroid hormone action are now yielding new understanding of the influence of gonadal steroid hormones on the humoral immune system. This Review examines how oestrogens and androgens modulate B-lymphocyte development and function, focusing on the areas of B-cell production in the bone marrow, the maintenance of immune tolerance for self antigens, and the processes of immunoglobulin heavy chain gene somatic hypermutation and class switch recombination during maturation of cells involved in humoral immune responses.

A Case-Matched Analysis Comparing Lenalidomide After Autologous or After Allogeneic Stem Cell Transplantation Demonstrates a Survival Advantage in Allografted Myeloma Patients

AbstractAbstract 1960 Introduction.Lenalidomide (Len) is a highly effective drug against multiple myeloma (MM). It acts through several mechanisms, such as a direct cytotoxic effect, anti-angiogenesis, microenvironment modifications, and immunomodulation. The latter property is particularly interesting in the setting of allogeneic stem cell transplantation (AlloSCT), since Len may interact favourably with the graft-versus-myeloma (GVM) effect. On the other side, the possibility of an over activation of the donor immune system raises some concerns about the safety of this treatment. In order to verify if Len is more effective when given after AlloSCT, we conducted among 7 Italian transplant centers a case-matched analysis comparing Len after autologous SCT (AutoSCT) vs. Len after AlloSCT. The hypothesis is that Len is more active when administered after AlloSCT. A secondary end-point of the study was the safety profile. Methods and results.In this retrospective study, the main matching criterion was represented by the number of treatment lines received before Len. In an attempt to uniform the treatment regimens, an intra-center matching was carried out. We collected data from 40 patients in each group. Baseline characteristics between Auto and Allo patients (pts) were similar, except for age at diagnosis (55 years, range 39–70, in Auto pts; 47 years, range 29 – 62, in Allo pts). The median number of previous lines of treatment was 3 (range 1–6) for both groups. Thirty-one (77%) Auto and 36 (90%) Allo pts received bortezomib. Similarly, 35 (87%) Auto and 21 (52%) Allo pts were previously treated with thalidomide. Twenty-one out of 40 (52%) Allo pts received SCT as a second or subsequent line of therapy. Before Len treatment, 14 (35%) Allo pts had acute graft-versus-host disease (aGVHD) (G1, 3 pts; G2, 8 pts; G3, 2 pts; G4, 1 pts), and 15 (37%) pts had chronic GVHD (cGVHD) (limited, 6 pts; extensive 9 pts). Median time between diagnosis and Len start was 65 months (range 14–162) in Auto, and 72 months(range 19–246) in Allo pts. Median time from transplant to Len start was 50 months (range 7–159) in Auto, and 21 months (range 6–134) in Allo pts. In all cases Len dosage was 25 mg, and it was combined with high or intermediate dose dexamethasone.Best responses for Auto and Allo patients were as follows: 5 vs. 3 CR, 6 vs. 8 VGPR, 12 vs. 13 PR, 9 vs. 8 SD, 8 vs. 8 PD. Time from Len start to the best response was 4 months for both groups. With a median follow-up from Len start of 22 months (range 2–60+), 3-years progression-free survival (PFS) was 13% in the Auto, and 43% in the Allo group (p=0.03). Median PFS was 9 months in Auto, and 16 months in Allo pts. Median OS was 22 months in the Auto group, and was not reached in the Allo group (p=0.05). Hematological toxicities were similar among the 2 groups. Neutropenia was observed in 16 (40%) patients in both the Auto and Allo group, thrombocytopenia in 10 (25%) Auto and 8 (20%) Allo pts, and anemia in 5 (12%) Auto and 2 (5%) Allo pts. Non-hematological toxicities were mild in both groups. In the Allo group one patients developed aGVHD after donor lymphocyte infusion, and 3 pts had a worsening of a pre-existing extensive cGVHD. Conclusions.The comparison between Auto and Allo pts has shown a benefit in terms of PFS and OS in the Allo group. This observation supports the hypothesis that Len may be synergic with the GVM effect. Interestingly, despite the same response rate between the 2 groups, clinical responses in Allo pts were more durable, reinforcing the hypothesis of the immunological control. On the other side, since Len has a potent immunomodulatory effect, this can raise concerns about its use after AlloSCT. The Dutch HOVON 76 trial has shown that the early administration of Len 10 mg after AlloSCT induces aGVHD in a substantial proportion of patients, causing unacceptable toxicity and the premature discontinuation of the study. However, in our retrospective study the median time between AlloSCT and Len administration was 21 months, and we did not observed any increase of GVHD. This suggests that the mechanisms of immune tolerance can mitigate the activation induced by Len, allowing a safe administration. Moreover, since in all cases dexamethasone was given with Len, its immunosuppressive effects may have harnessed the Len-induced immune activation, contributing to the treatment tolerability. In conclusion our case-matched study suggests that Len is more active when given after AlloSCT, still retaining a favorable toxicity profile. Disclosures:No relevant conflicts of interest to declare.

Human Blood Dendritic Cells Induce Tregs Through the PGE2-Independent Expression of an Active Form of IDO2 Enzyme

Abstract 1047Indoleamine 2,3-dioxygenase (IDO) enzymes (IDO1 and IDO2) critically regulate the rate-limiting step of tryptophan degradation along kynurenine pathway in several cellular subsets, including dendritic cells (DCs). In particular, it is known that IDO1 expression in DCs is induced by inflammatory mediators, especially PGE2, and enhances DCs tolerogenic capacity, such as the induction of T regulatory cells (Tregs). In absence of exogenous stimuli, IDO1 is driven to proteasomal degradation by SOCS3. Conversely, few and contrasting results are available about IDO2 expression and function in human DCs.We, then, besides IDO1, investigated the expression of IDO2 in human DC subsets, obtained from blood samples of healthy volunteers. Circulating myeloid and plasmacytoid DCs were purified and analyzed for the expression of both IDO enzymes.Our data demonstrate that myeloid DCs express higher levels of both IDO1 and IDO2 mRNA in comparison to plasmacytoid DCs. Moreover, PGE2 modulates IDO1 and IDO2 mRNA expression only in myeloid DCs and has no effect in plasmacytoid DCs.At protein level, IDO1 is expressed only in myeloid DCs and is modulated by PGE2, whereas IDO2 is expressed in both myeloid and plasmacytoid DCs and is not modulated by PGE2. Interestingly, when gene transcription or protein translation are inhibited, IDO2 protein expression persists independently from PGE2, while IDO1 expression requires PGE2 presence and needs continuous transcription and translation. Such discrepancy might be derived by a different binding of IDO1 and IDO2 to SOCS3, which in absence of pro-inflammatory stimuli is known to bind IDO1 and to drive it to proteasomal degradation. Indeed, SOCS3 immunoprecipitation and proteasomal inhibition experiments show that SOCS3 does not bind IDO2 which is not, therefore, driven to proteasomal degradation and is stably expressed.At the functional level, both myeloid and plasmacytoid DCs generate Tregs through an IDO-dependent mechanism, since the addition of IDO inhibitors 1-MT-D and 1-MT-L abrogate Tregs generation. More specifically, the silencing of IDO2 through its specific siRNA downregulates kynurenine production and Tregs generation, thus demonstrating that IDO2 is functionally active in DCs.In conclusion, our data demonstrate that, besides IDO1, human DCs also express IDO2, which contributes to tolerance by degrading tryptophan into kynurenine and by inducing Tregs. However, unlike IDO1, IDO2 expression is independent from inflammatory mediators, such as PGE2, and does not require continuous synthesis. These findings indicate IDO pathway as a critical check-point in the fine-tuning of DC-mediated tolerance induction. In particular, while IDO2 expression may confer a homeostatic tolerogenic capacity to DCs upon steady-state conditions, inflammation results in the induction of additional mechanisms of immune tolerance, such as the up-regulation of IDO1. Disclosures:Metz:New Link Genetics Corporation: Employment.