Synergy between rapamycin and FLT3 ligand enhances plasmacytoid dendritic cell-dependent induction of CD4+CD25+FoxP3+ Treg

A programmable releasing versatile hydrogel platform boosts systemic immune responses via sculpting tumor immunogenicity and reversing tolerogenic dendritic cells

Immunogenicity improvement is a valuable strategy for tumor immunotherapy. However, immunosuppressive factors bestow tolerogenic phenotype on tumor-infiltrating DCs, which exhibit weak antigen presentation and strong anti-inflammatory cytokines secretion abilities, limiting the effectiveness of tumor immunotherapy even if the tumor has adequate immunogenicity. Herein, we designed a programmable releasing versatile hydrogel platform (PIVOT) to sculpt tumor immunogenicity, increase intratumoral DCs and cDC1s abundance, and reverse the tolerogenic phenotype of DCs, thus promoting their maturation for boosting innate and adaptive immune responses. Responsive to tumoral reactive oxygen species (ROS), the hydrogel splits and promotes the activation of DCs and macrophages. Then, oxaliplatin is first released from PIVOT to sculpt tumor immunogenicity by inducing immunogenic cell death (ICD) and causing tumoral DNA fragments exposure simultaneously. Subsequently, the impaired DNA fragments bind to high mobility group protein 1 (HMGB1) forming the DNA-HMGB1 complex. Moreover, exogenous FMS-like tyrosine kinase 3 ligand (Flt-3L) recruits masses of DCs, especially cDC1s, which will endocytose the complex benefiting from TIM-3 blockade (αTIM3) that can reverse tolerogenic DCs. Finally, the endocytosis activates the cGAS-STING pathway of cDC1s, which promotes the secretion of type I IFN that triggers innate immune responses, and CXCL9 which recruits CD8+ effector T cells to initiate the following adaptive immune response against tumor progress. PIVOT achieves nearly 90 % tumor growth inhibition and induces systemic antitumor immune responses. In conclusion, this study focuses on ICD-mediated tumor immunogenicity sculpture and nucleic acid endocytosis-involved tolerogenic DCs reversal, providing a novel paradigm for enhancing DCs-based antitumor immune responses.

TLR9-independent CD8+ T cell responses in hepatic AAV gene transfer through IL-1R1-MyD88 signaling

Upon viral infection of the liver, CD8+ T cell responses may be triggered despite the immune suppressive properties that manifest in this organ. We sought to identify pathways that activate responses to a neoantigen expressed in hepatocytes, using adeno-associated viral (AAV) gene transfer. It was previously established that cooperation between plasmacytoid dendritic cells (pDCs), which sense AAV genomes by Toll-like receptor 9 (TLR9), and conventional DCs promotes cross-priming of capsid-specific CD8+ T cells. Surprisingly, we find local initiation of a CD8+ T cell response against antigen expressed in ∼20% of murine hepatocytes, independent of TLR9 or type I interferons and instead relying on IL-1 receptor 1-MyD88 signaling. Both IL-1α and IL-1β contribute to this response, which can be blunted by IL-1 blockade. Upon AAV administration, IL-1-producing pDCs infiltrate the liver and co-cluster with XCR1+ DCs, CD8+ T cells, and Kupffer cells. Analogous events were observed following coagulation factor VIII gene transfer in hemophilia A mice. Therefore, pDCs have alternative means of promoting anti-viral T cell responses and participate in intrahepatic immune cell networks similar to those that form in lymphoid organs. Combined TLR9 and IL-1 blockade may broadly prevent CD8+ T responses against AAV capsid and transgene product.

Suppression of anti-drug antibody formation against coagulation factor VIII by oral delivery of anti-CD3 monoclonal antibody in hemophilia A mice

Active tolerance to ingested dietary antigens forms the basis for oral immunotherapy to food allergens or autoimmune self-antigens. Alternatively, oral administration of anti-CD3 monoclonal antibody can be effective in modulating systemic immune responses without T cell depletion. Here we assessed the efficacy of full length and the F(ab')2 fragment of oral anti-CD3 to prevent anti-drug antibody (ADA) formation to clotting factor VIII (FVIII) protein replacement therapy in hemophilia A mice. A short course of low dose oral anti-CD3 F(ab')2 reduced the production of neutralizing ADAs, and suppression was significantly enhanced when oral anti-CD3 was timed concurrently with FVIII administration. Tolerance was accompanied by the early induction of FoxP3+LAP-, FoxP3+LAP+, and FoxP3-LAP+ populations of CD4+ T cells in the spleen and mesenteric lymph nodes. FoxP3+LAP+ Tregs expressing CD69, CTLA-4, and PD1 persisted in spleens of treated mice, but did not produce IL-10. Finally, we attempted to combine the anti-CD3 approach with oral intake of FVIII antigen (using our previously established method of using lettuce plant cells transgenic for FVIII antigen fused to cholera toxin B (CTB) subunit, which suppresses ADAs in part through induction of IL-10 producing FoxP3-LAP+ Treg). However, combining these two approaches failed to improve suppression of ADAs. We conclude that oral anti-CD3 treatment is a promising approach to prevention of ADA formation in systemic protein replacement therapy, albeit via mechanisms distinct from and not synergistic with oral intake of bioencapsulated antigen.

IL-15 blockade and rapamycin rescue multifactorial loss of factor VIII from AAV-transduced hepatocytes in hemophilia A mice

Hepatic adeno-associated viral (AAV) gene transfer has the potential to cure the X-linked bleeding disorder hemophilia A. However, declining therapeutic coagulation factor VIII (FVIII) expression has plagued clinical trials. To assess the mechanistic underpinnings of this loss of FVIII expression, we developed a hemophilia A mouse model that shares key features observed in clinical trials. Following liver-directed AAV8 gene transfer in the presence of rapamycin, initial FVIII protein expression declines over time in the absence of antibody formation. Surprisingly, loss of FVIII protein production occurs despite persistence of transgene and mRNA, suggesting a translational shutdown rather than a loss of transduced hepatocytes. Some of the animals develop ER stress, which may be linked to hepatic inflammatory cytokine expression. FVIII protein expression is preserved by interleukin-15/interleukin-15 receptor blockade, which suppresses CD8+ T and natural killer cell responses. Interestingly, mice with initial FVIII levels >100% of normal had diminishing expression while still under immune suppression. Taken together, our findings of interanimal variability of the response, and the ability of the immune system to shut down transgene expression without utilizing cytolytic or antibody-mediated mechanisms, illustrate the challenges associated with FVIII gene transfer. Our protocols based upon cytokine blockade should help to maintain efficient FVIII expression.

Single-cell RNA sequencing distinguishes dendritic cell subsets in the rat, allowing advanced characterization of the effects of FMS-like tyrosine kinase 3 ligand

Tissue-resident dendritic cells (DCs) are essential for immunological homeostasis and hold promise for a variety of therapeutic interventions. The rare nature of tissue-resident DCs and their suboptimal description in the lab rat model has limited their characterization. To address this limitation, FMS-like tyrosine kinase 3 ligand (FLT3L) has been utilized to expand these population in vitro and in vivo for investigative or therapeutic purposes. However, conflicting reports have suggested that FLT3L can either promote immune tolerance or enhance immunogenicity, necessitating clarification of the effects of FLT3L on DC phenotype and functionality. We first paired single-cell RNA sequencing with multicolour spectral flow cytometry to provide an updated strategy for the identification of tissue-resident classical and plasmacytoid DCs in the rat model. We then administered FLT3L to Lewis rats in vivo to investigate its effect on tissue-resident DC enumeration and phenotype in the liver, spleen, and mesenteric lymph nodes. We found that FLT3L expands classical DCs (cDCs) 1 and 2 in a dose-dependent manner and that cDC1 and cDC2 in secondary lymphoid organs had altered MHC I, MHC II, CD40, CD80, CD86, and PD-L1 cell-surface expression levels following FLT3L administration. These changes were accompanied by an increase in gene expression levels of toll-like receptors 2, 4, 7, and 9 as well as inflammatory cytokines IL-6 and TNF-α. In conclusion, FLT3L administration in vivo increases cDC enumeration in the liver, spleen, and mesenteric lymph nodes accompanied by a tissue-restricted alteration in expression of antigen presentation machinery and inflammatory mediators.

Unbalanced IDO1/IDO2 Endothelial Expression and Skewed Keynurenine Pathway in the Pathogenesis of COVID-19 and Post-COVID-19 Pneumonia

Despite intense investigation, the pathogenesis of COVID-19 and the newly defined long COVID-19 syndrome are not fully understood. Increasing evidence has been provided of metabolic alterations characterizing this group of disorders, with particular relevance of an activated tryptophan/kynurenine pathway as described in this review. Recent histological studies have documented that, in COVID-19 patients, indoleamine 2,3-dioxygenase (IDO) enzymes are differentially expressed in the pulmonary blood vessels, i.e., IDO1 prevails in early/mild pneumonia and in lung tissues from patients suffering from long COVID-19, whereas IDO2 is predominant in severe/fatal cases. We hypothesize that IDO1 is necessary for a correct control of the vascular tone of pulmonary vessels, and its deficiency in COVID-19 might be related to the syndrome’s evolution toward vascular dysfunction. The complexity of this scenario is discussed in light of possible therapeutic manipulations of the tryptophan/kynurenine pathway in COVID-19 and post-acute COVID-19 syndromes.

Immune responses to alglucosidase in infantile Pompe disease: recommendations from an Italian pediatric expert panel

Background

Classic infantile onset of Pompe disease (c-IOPD) leads to hypotonia and hypertrophic cardiomyopathy within the first days to weeks of life and, without treatment, patients die of cardiorespiratory failure in their first 1–2 years of life. Enzymatic replacement therapy (ERT) with alglucosidase alfa is the only available treatment, but adverse immune reactions can reduce ERT’s effectiveness and safety. It is therefore very important to identify strategies to prevent and manage these complications. Several articles have been written on this disease over the last 10 years, but no univocal indications have been established.

Methods

Our study presents a review of the current literature on management of immune responses to ERT in c-IOPD as considered by an Italian study group of pediatric metabolists and immunologists in light of our shared patient experience.

Results

We summarize the protocols for the management of adverse reactions to ERT, analyzing their advantages and disadvantages, and provide expert recommendations for their optimal management, to the best of current knowledge. However, further studies are needed to improve actual management protocols, which still have several limitations.

Durability of transgene expression after rAAV gene therapy

Recombinant adeno-associated virus (rAAV) gene therapy has the potential to transform the lives of patients with certain genetic disorders by increasing or restoring function to affected tissues. Following the initial establishment of transgene expression, it is unknown how long the therapeutic effect will last, although animal and emerging human data show that expression can be maintained for more than 10 years. The durability of therapeutic response is key to long-term treatment success, especially since immune responses to rAAV vectors may prevent re-dosing with the same therapy. This review explores the non-immunological and immunological processes that may limit or improve durability and the strategies that can be used to increase the duration of the therapeutic effect.

Regulatory T cells in ischemic stroke

Recent evidence shows that when ischemic stroke (IS) occurs, the BBB would be destructed, thereby promoting the immune cells to migrate into the brain, suggesting that the immune responses can play a vital role in the pathology of IS. As an essential subpopulation of immunosuppressive T cells, regulatory T (Treg) cells are involved in maintaining immune homeostasis and suppressing immune responses in the pathophysiological conditions of IS. During the past decades, the regulatory role of Treg cells has attracted the interest of numerous researchers. However, whether they are beneficial or detrimental to the outcomes of IS remains controversial. Moreover, Treg cells exert distinctive effects in the different stages of IS. Therefore, it is urgent to elucidate how Treg cells modulate the immune responses induced by IS. In this review, we describe how Treg cells fluctuate and play a role in the regulation of immune responses after IS in both experimental animals and humans, and summarize their biological functions and mechanisms in both CNS and periphery. We also discuss how Treg cells participate in poststroke inflammation and immunodepression and the potential of Treg cells as a novel therapeutic approach.

Everolimus-Induced Immune Effects after Heart Transplantation: A Possible Tool for Clinicians to Monitor Patients at Risk for Transplant Rejection

BACKGROUND

Patients treated with an inhibitor of the mechanistic target of rapamycin (mTORI) in a calcineurin inhibitor (CNI)-free immunosuppressive regimen after heart transplantation (HTx) show a higher risk for transplant rejection. We developed an immunological monitoring tool that may improve the identification of mTORI-treated patients at risk for rejection.

METHODS

Circulating dendritic cells (DCs) and regulatory T cells (Tregs) were analysed in 19 mTORI- and 20 CNI-treated HTx patients by flow cytometry. Principal component and cluster analysis were used to identify patients at risk for transplant rejection.

RESULTS

The percentages of total Tregs (p = 0.02) and CD39+ Tregs (p = 0.05) were higher in mTORI-treated patients than in CNI-treated patients. The principal component analysis revealed that BDCA1+, BDCA2+ and BDCA4+ DCs as well as total Tregs could distinguish between non-rejecting and rejecting mTORI-treated patients. Most mTORI-treated rejectors showed higher levels of BDCA2+ and BDCA4+ plasmacytoid DCs and lower levels of BDCA1+ myeloid DCs and Tregs than mTORI non-rejectors.

CONCLUSION

An mTORI-based immunosuppressive regimen induced a sufficient, tolerance-promoting reaction in Tregs, but an insufficient, adverse effect in DCs. On the basis of patient-specific immunological profiles, we established a flow cytometry-based monitoring tool that may be helpful in identifying patients at risk for rejection.

CXCR4 blockade reduces the severity of murine heart allograft rejection by plasmacytoid dendritic cell-mediated immune regulation

Allograft-specific regulatory T cells (T_reg cells) are crucial for long-term graft acceptance after transplantation. Although adoptive T_reg cell transfer has been proposed, major challenges include graft-specificity and stability. Thus, there is an unmet need for the direct induction of graft-specific T_reg cells. We hypothesized a synergism of the immunotolerogenic effects of rapamycin (mTOR inhibition) and plerixafor (CXCR4 antagonist) for T_reg cell induction. Thus, we performed fully-mismatched heart transplantations and found combination treatment to result in prolonged allograft survival. Moreover, fibrosis and myocyte lesions were reduced. Although less CD3⁺ T cell infiltrated, higher T_reg cell numbers were observed. Noteworthy, this was accompanied by a plerixafor-dependent plasmacytoid dendritic cells-(pDCs)-mobilization. Furthermore, in vivo pDC-depletion abrogated the plerixafor-mediated T_reg cell number increase and reduced allograft survival. Our pharmacological approach allowed to increase T_reg cell numbers due to pDC-mediated immune regulation. Therefore pDCs can be an attractive immunotherapeutic target in addition to plerixafor treatment.

Efficacy of AAV8-hUGT1A1 with Rapamycin in neonatal, suckling, and juvenile rats to model treatment in pediatric CNs patients

A clinical trial using adeno-associated virus serotype 8 (AAV8)-human uridine diphosphate glucuronosyltransferase 1A1 (hUGT1A1) to treat inherited severe unconjugated hyperbilirubinemia (Crigler-Najjar syndrome) is ongoing, but preclinical data suggest that long-term efficacy in children is impaired due to loss of transgene expression upon hepatocyte proliferation in a growing liver. This study aims to determine at what age long-term efficacy can be obtained in the relevant animal model and whether immune modulation allows re-treatment using the same AAV vector. Neonatal, suckling, and juvenile Ugt1a1-deficient rats received a clinically relevant dose of AAV8-hUGT1A1, and serum bilirubin levels and anti-AAV8 neutralizing antibodies (NAbs) in serum were monitored. The possibility of preventing the immune response toward the vector was investigated using a rapamycin-based regimen with daily intraperitoneal (i.p.) injections starting 2 days before and ending 21 days after vector administration. In rats treated at postnatal day 1 (P1) or P14, the correction was (partially) lost after 12 weeks, whereas the correction was stable in rats injected at P28. Combining initial vector administration with the immune-suppressive regimen prevented induction of NAbs in female rats, allowing at least partially effective re-administration. Induction of NAbs upon re-injection could not be prevented, suggesting that this strategy will be ineffective in patients with low levels of preexisting anti-AAV NAbs.

Current progress and limitations of AAV mediated delivery of protein therapeutic genes and the importance of developing quantitative pharmacokinetic/pharmacodynamic (PK/PD) models

While protein therapeutics are one of the most successful class of drug molecules, they are expensive and not suited for treating chronic disorders that require long-term dosing. Adeno-associated virus (AAV) mediated in vivo gene therapy represents a viable alternative, which can deliver the genes of protein therapeutics to produce long-term expression of proteins in target tissues. Ongoing clinical trials and recent regulatory approvals demonstrate great interest in these therapeutics, however, there is a lack of understanding regarding their cellular disposition, whole-body disposition, dose-exposure relationship, exposure-response relationship, and how product quality and immunogenicity affects these important properties. In addition, there is a lack of quantitative studies to support the development of pharmacokinetic-pharmacodynamic models, which can support the discovery, development, and clinical translation of this delivery system. In this review, we have provided a state-of-the-art overview of current progress and limitations related to AAV mediated delivery of protein therapeutic genes, along with our perspective on the steps that need to be taken to improve clinical translation of this therapeutic modality.

Dietary Intervention Impacts Immune Cell Functions and Dynamics by Inducing Metabolic Rewiring

Accumulating evidence has shown that nutrient metabolism is closely associated with the differentiation and functions of various immune cells. Cellular metabolism, including aerobic glycolysis, fatty acid oxidation, and oxidative phosphorylation, plays a key role in germinal center (GC) reaction, B-cell trafficking, and T-cell-fate decision. Furthermore, a quiescent metabolic status consolidates T-cell-dependent immunological memory. Therefore, dietary interventions such as calorie restriction, time-restricted feeding, and fasting potentially manipulate immune cell functions. For instance, intermittent fasting prevents the development of experimental autoimmune encephalomyelitis. Meanwhile, the fasting response diminishes the lymphocyte pool in gut-associated lymphoid tissue to minimize energy expenditure, leading to the attenuation of Immunoglobulin A (IgA) response. The nutritional status also influences the dynamics of several immune cell subsets. Here, we describe the current understanding of the significance of immunometabolism in the differentiation and functionality of lymphocytes and macrophages. The underlying molecular mechanisms also are discussed. These experimental observations could offer new therapeutic strategies for immunological disorders like autoimmunity.

Emerging roles of autophagy in hepatic tumorigenesis and therapeutic strategies in glycogen storage disease type Ia: A review

Glycogen storage disease type Ia (GSD-Ia) is an inherited metabolic disease caused by a deficiency in glucose-6-phosphatase-α (G6Pase-α or G6PC) which plays a critical role in blood glucose homeostasis by catalyzing the hydrolysis of glucose-6-phosphate (G6P) to glucose and phosphate in the terminal step of glycogenolysis and gluconeogenesis. Patients with GSD-Ia manifest life-threatening fasting hypoglycemia along with the excessive accumulation of hepatic glycogen and triglycerides which results in hepatomegaly and a risk of long-term complications such as hepatocellular adenoma and carcinoma (HCA/HCC). The etiology of HCA/HCC development in GSD-Ia, however, is unknown. Recent studies have shown that the livers in model animals of GSD-Ia display impairment of autophagy, a cellular recycling process which is critical for energy metabolism and cellular homeostasis. However, molecular mechanisms of autophagy impairment and its involvement in pathogenesis in GSD-Ia are still under investigation. Here, we summarize the latest advances for signaling pathways implicated in hepatic autophagy impairment and the roles of autophagy in hepatic tumorigenesis in GSD-Ia. In addition, recent evidence has illustrated that autophagy plays an important role in hepatic metabolism and liver-directed gene therapy mediated by recombinant adeno-associated virus (rAAV). Therefore, we highlight the possible role of hepatic autophagy in metabolic control and rAAV-mediated gene therapy for GSD-Ia. In this review, we also provide potential therapeutic strategies for GSD-Ia on the basis of molecular mechanisms underlying hepatic autophagy impairment in GSD-Ia.

Role of orally induced regulatory T cells in immunotherapy and tolerance

Oral antigen administration to induce regulatory T cells (Treg) takes advantage of regulatory mechanisms that the gastrointestinal tract utilizes to promote unresponsiveness against food antigens or commensal microorganisms. Recently, antigen-based oral immunotherapies (OITs) have shown efficacy as treatment for food allergy and autoimmune diseases. Similarly, OITs appear to prevent anti-drug antibody responses in replacement therapy for genetic diseases. Intestinal epithelial cells and microbiota possibly condition dendritic cells (DC) toward a tolerogenic phenotype that induces Treg via expression of several mediators, e.g. IL-10, transforming growth factor-β, retinoic acid. Several factors, such as metabolites derived from microbiota or diet, impact the stability and expansion of these induced Treg, which include, but are not limited to, FoxP3⁺ Treg, LAP⁺ Treg, and/or Tr1 cells. Here, we review various orally induced Treg, their plasticity and cooperation between the Treg subsets, as well as underlying mechanisms controlling their induction and role in oral tolerance.

Plasmacytoid dendritic cells and asthma: a review of current knowledge

INTRODUCTION

While medications are available to treat asthma symptoms and control inflammation, no treatments can cure asthma, and efforts to develop primary prevention strategies or improved exacerbation management are limited by incomplete knowledge of the mechanisms responsible for asthma development and progression. Plasmacytoid dendritic cells (pDC) are involved in anti-viral host defense and immune regulation, and increasing evidence suggests a role for pDC in asthma pathogenesis.

AREAS COVERED

We undertook a literature search using PubMed for articles including the phrase 'plasmacytoid dendritic cells and asthma' published from 2015 to 2020. We reviewed the remarkable progress made over the past 5 years in understanding the role of pDC in asthma pathogenesis and how pDC regulate anti-viral immune function. This review highlights key recent findings in asthma pathogenesis and virus-triggered asthma exacerbations; pDC biology and functionality; how pDC regulate the immune response; and pDC function in asthma.

EXPERT OPTION

A deeper understanding of pDC function provides an important foundation for future pDC-targeted therapies that might prevent and treat asthma.

Treg Enhancing Therapies to Treat Autoimmune Diseases

Regulatory T cells (Tregs) are a small yet critical subset of CD4+ T cells, which have the role of maintaining immune homeostasis by, for example, regulating self-tolerance, tumor immunity, anti-microbial resistance, allergy and transplantation rejection. The suppressive mechanisms by which Tregs function are varied and pleiotropic. The ability of Tregs to maintain self-tolerance means they are critical for the control and prevention of autoimmune diseases. Irregularities in Treg function and number can result in loss of tolerance and autoimmune disease. Restoring immune homeostasis and tolerance through the promotion, activation or delivery of Tregs has emerged as a focus for therapies aimed at curing or controlling autoimmune diseases. Such therapies have focused on the Treg cell subset by using drugs to suppress T effector cells and promote Tregs. Other approaches have trialed inducing tolerance by administering the autoantigen via direct administration, by transient expression using a DNA vector, or by antigen-specific nanoparticles. More recently, cell-based therapies have been developed as an approach to directly or indirectly enhance Treg cell specificity, function and number. This can be achieved indirectly by transfer of tolerogenic dendritic cells, which have the potential to expand antigen-specific Treg cells. Treg cells can be directly administered to treat autoimmune disease by way of polyclonal Tregs or Tregs transduced with a receptor with high affinity for the target autoantigen, such as a high affinity T cell receptor (TCR) or a chimeric antigen receptor (CAR). This review will discuss the strategies being developed to redirect autoimmune responses to a state of immune tolerance, with the aim of the prevention or amelioration of autoimmune disease.

B Cell Depletion Eliminates FVIII Memory B Cells and Enhances AAV8-coF8 Immune Tolerance Induction When Combined With Rapamycin

Hemophilia A is an inherited coagulation disorder resulting in the loss of functional clotting factor VIII (FVIII). Presently, the most effective treatment is prophylactic protein replacement therapy. However, this requires frequent life-long intravenous infusions of plasma derived or recombinant clotting factors and is not a cure. A major complication is the development of inhibitory antibodies that nullify the replacement factor. Immune tolerance induction (ITI) therapy to reverse inhibitors can last from months to years, requires daily or every other day infusions of supraphysiological levels of FVIII and is effective in only up to 70% of hemophilia A patients. Preclinical and recent clinical studies have shown that gene replacement therapy with AAV vectors can effectively cure hemophilia A patients. However, it is unclear how hemophilia patients with high risk inhibitor F8 mutations or with established inhibitors will respond to gene therapy, as these patients have been excluded from ongoing clinical trials. AAV8-coF8 gene transfer in naïve BALB/c-F8e16^−/Y mice (BALB/c-HA) results in anti-FVIII IgG1 inhibitors following gene transfer, which can be prevented by transient immune modulation with anti-mCD20 (18B12) and oral rapamycin. We investigated if we could improve ITI in inhibitor positive mice by combining anti-mCD20 and rapamycin with AAV8-coF8 gene therapy. Our hypothesis was that continuous expression of FVIII protein from gene transfer compared to transient FVIII from weekly protein therapy, would enhance regulatory T cell induction and promote deletion of FVIII reactive B cells, following reconstitution. Mice that received anti-CD20 had a sharp decline in inhibitors, which corresponded to FVIII memory B (B_mem) cell deletion. Importantly, only mice receiving both anti-mCD20 and rapamycin failed to increase inhibitors following rechallenge with intravenous FVIII protein therapy. Our data show that B and T cell immune modulation complements AAV8-coF8 gene therapy in naïve and inhibitor positive hemophilia A mice and suggest that such protocols should be considered for AAV gene therapy in high risk or inhibitor positive hemophilia patients.

Role of Small Intestine and Gut Microbiome in Plant-Based Oral Tolerance for Hemophilia

Fusion proteins, which consist of factor VIII or factor IX and the transmucosal carrier cholera toxin subunit B, expressed in chloroplasts and bioencapsulated within plant cells, initiate tolerogenic immune responses in the intestine when administered orally. This approach induces regulatory T cells (Treg), which suppress inhibitory antibody formation directed at hemophilia proteins induced by intravenous replacement therapy in hemophilia A and B mice. Further analyses of Treg CD4+ lymphocyte sub-populations in hemophilia B mice reveal a marked increase in the frequency of CD4+CD25-FoxP3-LAP+ T cells (but not of CD4+CD25+FoxP3+ T cells) in the lamina propria of the small but not large intestine. The adoptive transfer of very small numbers of CD4+CD25-LAP+ Treg isolated from the spleen of tolerized mice was superior in suppression of antibodies directed against FIX when compared to CD4+CD25+ T cells. Thus, tolerance induction by oral delivery of antigens bioencapsulated in plant cells occurs via the unique immune system of the small intestine, and suppression of antibody formation is primarily carried out by induced latency-associated peptide (LAP) expressing Treg that likely migrate to the spleen. Tolerogenic antigen presentation in the small intestine requires partial enzymatic degradation of plant cell wall by commensal bacteria in order to release the antigen. Microbiome analysis of hemophilia B mice showed marked differences between small and large intestine. Remarkably, bacterial species known to produce a broad spectrum of enzymes involved in degradation of plant cell wall components were found in the small intestine, in particular in the duodenum. These were highly distinct from populations of cell wall degrading bacteria found in the large intestine. Therefore, FIX antigen presentation and Treg induction by the immune system of the small intestine relies on activity of a distinct microbiome that can potentially be augmented to further enhance this approach.

Human Immune Responses to Adeno-Associated Virus (AAV) Vectors

Recombinant adeno-associated virus (rAAV) vectors are one of the most promising in vivo gene delivery tools. Several features make rAAV vectors an ideal platform for gene transfer. However, the high homology with the parental wild-type virus, which often infects humans, poses limitations in terms of immune responses associated with this vector platform. Both humoral and cell-mediated immunity to wild-type AAV have been documented in healthy donors, and, at least in the case of anti-AAV antibodies, have been shown to have a potentially high impact on the outcome of gene transfer. While several factors can contribute to the overall immunogenicity of rAAV vectors, vector design and the total vector dose appear to be responsible of immune-mediated toxicities. While preclinical models have been less than ideal in predicting the outcome of gene transfer in humans, the current preclinical body of evidence clearly demonstrates that rAAV vectors can trigger both innate and adaptive immune responses. Data gathered from clinical trials offers key learnings on the immunogenicity of AAV vectors, highlighting challenges as well as the potential strategies that could help unlock the full therapeutic potential of in vivo gene transfer.

Escape or Fight: Inhibitors in Hemophilia A

Replacement therapy with coagulation factor VIII (FVIII) represents the current clinical treatment for patients affected by hemophilia A (HA). This treatment while effective is, however, hampered by the formation of antibodies which inhibit the activity of infused FVIII in up to 30% of treated patients. Immune tolerance induction (ITI) protocols, which envisage frequent infusions of high doses of FVIII to confront this side effect, dramatically increase the already high costs associated to a patient's therapy and are not always effective in all treated patients. Therefore, there are clear unmet needs that must be addressed in order to improve the outcome of these treatments for HA patients. Taking advantage of preclinical mouse models of hemophilia, several strategies have been proposed in recent years to prevent inhibitor formation and eradicate the pre-existing immunity to FVIII inhibitor positive patients. Herein, we will review some of the most promising strategies developed to avoid and eradicate inhibitors, including the use of immunomodulatory drugs or molecules, oral or transplacental delivery as well as cell and gene therapy approaches. The goal is to improve and potentiate the current ITI protocols and eventually make them obsolete.

AAV Vector Immunogenicity in Humans: A Long Journey to Successful Gene Transfer

Gene therapy with adeno-associated virus (AAV) vectors has demonstrated safety and long-term efficacy in a number of trials across target organs, including eye, liver, skeletal muscle, and the central nervous system. Since the initial evidence that AAV vectors can elicit capsid T cell responses in humans, which can affect the duration of transgene expression, much progress has been made in understanding and modulating AAV vector immunogenicity. It is now well established that exposure to wild-type AAV results in priming of the immune system against the virus, with development of both humoral and T cell immunity. Aside from the neutralizing effect of antibodies, the impact of pre-existing immunity to AAV on gene transfer is still poorly understood. Herein, we review data emerging from clinical trials across a broad range of gene therapy applications. Common features of immune responses to AAV can be found, suggesting, for example, that vector immunogenicity is dose-dependent, and that innate immunity plays an important role in the outcome of gene transfer. A range of host-specific factors are also likely to be important, and a comprehensive understanding of the mechanisms driving AAV vector immunogenicity in humans will be key to unlocking the full potential of in vivo gene therapy.

Immune Responses to Viral Gene Therapy Vectors

Several viral vector-based gene therapy drugs have now received marketing approval. A much larger number of additional viral vectors are in various stages of clinical trials for the treatment of genetic and acquired diseases, with many more in pre-clinical testing. Efficiency of gene transfer and ability to provide long-term therapy make these vector systems very attractive. In fact, viral vector gene therapy has been able to treat or even cure diseases for which there had been no or only suboptimal treatments. However, innate and adaptive immune responses to these vectors and their transgene products constitute substantial hurdles to clinical development and wider use in patients. This review provides an overview of the type of immune responses that have been documented in animal models and in humans who received gene transfer with one of three widely tested vector systems, namely adenoviral, lentiviral, or adeno-associated viral vectors. Particular emphasis is given to mechanisms leading to immune responses, efforts to reduce vector immunogenicity, and potential solutions to the problems. At the same time, we point out gaps in our knowledge that should to be filled and problems that need to be addressed going forward.

Low-Dose Sirolimus Immunoregulation Therapy in Patients with Active Rheumatoid Arthritis: A 24-Week Follow-Up of the Randomized, Open-Label, Parallel-Controlled Trial

Background

We have reported previously the insufficient absolute number or functional defects of regulatory T cells (Tregs) in patients with rheumatoid arthritis (RA), challenging conventional unspecific immunosuppressive therapy. Sirolimus, a mTOR inhibitor, is reported to allow growth of functional Tregs; here, we investigated the efficacy of low-dose sirolimus combined with conventional immunosuppressants (sirolimus immunoregulation therapy) for RA treatment with lower side effects and better tolerance.

Methods

In this nonblinded and parallel-group trial, we randomly assigned 62 patients to receive conventional glucocorticoids and immunosuppressants with or without sirolimus at a dosage of 0.5 mg on alternate days for 24 weeks in a 2 : 1 ratio. The demographic features, clinical manifestations, and laboratory indicators including peripheral blood lymphocyte subgroups and CD4⁺T subsets were compared before and after the treatment.

Results

Finally, 37 patients in the sirolimus group and 18 in the conventional treated group completed the 6-month study. By 24 weeks, the patients with sirolimus experienced significant reduction in disease activity indicators including DAS28, ESR, and the number of tender joints and swollen joints (p < 0.001). Notably, they had a higher level of Tregs as compared with those with conventional therapy alone (p < 0.05), indicating that sirolimus could partly restore the reduced Tregs. Concomitantly, their usage of immunosuppressants for controlling disease activity was decreased as compared with the conventional group with no difference in blood routine, and liver and renal functions both before and after the treatment of sirolimus and between the two groups (p > 0.05).

Conclusions

Low-dose sirolimus immunoregulatory therapy selectively upregulated Tregs and partly replaced the usage of immunosuppressants to control disease activity without overtreatment and evaluable side effect. Further study is required using a large sample of RA patients treated with sirolimus for a longer period. This trial is registered at the Chinese Clinical Trial Registry (http://www.chictr.org.cn/showproj.aspx?proj=17245).

Plant cell-made protein antigens for induction of Oral tolerance

The gut associated lymphoid tissue has effective mechanisms in place to maintain tolerance to food antigens. These can be exploited to induce antigen-specific tolerance for the prevention and treatment of autoimmune diseases and severe allergies and to prevent serious immune responses in protein replacement therapies for genetic diseases. An oral tolerance approach for the prevention of peanut allergy in infants proved highly efficacious and advances in treatment of peanut allergy have brought forth an oral immunotherapy drug that is currently awaiting FDA approval. Several other protein antigens made in plant cells are in clinical development. Plant cell-made proteins are protected in the stomach from acids and enzymes after their oral delivery because of bioencapsulation within plant cell wall, but are released to the immune system upon digestion by gut microbes. Utilization of fusion protein technologies facilitates their delivery to the immune system, oral tolerance induction at low antigen doses, resulting in efficient induction of FoxP3⁺ and latency-associated peptide (LAP)⁺ regulatory T cells that express immune suppressive cytokines such as IL-10. LAP and IL-10 expression represent potential biomarkers for plant-based oral tolerance. Efficacy studies in hemophilia dogs support clinical development of oral delivery of bioencapsulated antigens to prevent anti-drug antibody formation. Production of clinical grade materials in cGMP facilities, stability of antigens in lyophilized plant cells for several years when stored at ambient temperature, efficacy of oral delivery of human doses in large animal models and lack of toxicity augur well for clinical advancement of this novel drug delivery concept.

Anti-drug Antibody Responses Impair Prophylaxis Mediated by AAV-Delivered HIV-1 Broadly Neutralizing Antibodies

Adeno-associated virus (AAV) delivery of potent and broadly neutralizing antibodies (bNAbs is a promising approach for the prevention of HIV-1 infection. The immunoglobulin G (IgG)1 subtype is usually selected for this application, because it efficiently mediates antibody effector functions and has a somewhat longer half-life. However, the use of IgG1-Fc has been associated with the generation of anti-drug antibodies (ADAs) that correlate with loss of antibody expression. In contrast, we have shown that expression of the antibody-like molecule eCD4-Ig bearing a rhesus IgG2-Fc domain showed reduced immunogenicity and completely protected rhesus macaques from simian-HIV (SHIV)-AD8 challenges. To directly compare the performance of the IgG1-Fc and the IgG2-Fc domains in a prophylactic setting, we compared AAV1 expression of rhesus IgG1 and IgG2 forms of four anti-HIV bNAbs: 3BNC117, NIH45-46, 10-1074, and PGT121. Interestingly, IgG2-isotyped bNAbs elicited significantly lower ADA than their IgG1 counterparts. We also observed significant protection from two SHIV-AD8 challenges in macaques expressing IgG2-isotyped bNAbs, but not from those expressing IgG1. Our data suggest that monoclonal antibodies isotyped with IgG2-Fc domains are less immunogenic than their IgG1 counterparts, and they highlight ADAs as a key barrier to the use of AAV1-expressed bNAbs.

Reprogrammed CD4+ T Cells That Express FoxP3+ Control Inhibitory Antibody Formation in Hemophilia A Mice

Coagulation Factor VIII (FVIII) replacement therapy in hemophilia A patients is complicated by the development of inhibitory antibodies, which often render the treatment ineffective. Previous studies demonstrated a strong correlation between induction of regulatory T cells (Treg) and tolerance to the therapeutic protein. We, therefore, set out to evaluate whether the adoptive transfer of FVIII-specific CD4⁺ Treg cells prevents inhibitor response to FVIII protein therapy. To this end, we first retrovirally transduced FoxP3⁺ into FVIII-specific CD4⁺ cells, which resulted in cells that stably express FoxP3, are phenotypically similar to peripherally induced Tregs and are antigen specific suppressors, as judged by in vitro assays. Upon transfer of the FVIII-specific CD4⁺ FoxP3⁺ cells into hemophilia A mice, development of inhibitory antibodies in response to administering FVIII protein was completely suppressed. Suppression was extended for 2 months, even after transferred cells were no longer detectable in the secondary lymphoid organs of recipient animals. Upon co-transfer of FoxP3⁺-transduced cells with the B cell depleting anti-CD20 into mice with pre-existing inhibitory antibodies to FVIII, the escalation of inhibitory antibody titers in response to subsequent FVIII protein therapy was dramatically reduced. We conclude that reprogramed FoxP3 expressing cells are capable of inducing the in vivo conversion of endogenous FVIII peripheral Tregs, which results in sustained suppression of FVIII inhibitors caused by replacement therapy in recipient hemophilia A animals.

[Rapamycin alleviates inflammation by up-regulating TGF-β/Smad signaling in a mouse model of autoimmune encephalomyelitis]

OBJECTIVE

To evaluate the efficacy of rapmycin for treatment of experimental autoimmune encephalomyelitis (EAE) in mice and explore the underlying mechanism.

METHODS

An EAE model was established in C57BL/6 mice. After immunization, the mice were divided into model group and rapamycin groups treated daily with low-dose (0.3 mg/kg) or high-dose (1 mg/kg) rapamycin. The clinical scores of the mice were observed using Knoz score, the infiltration of IL-17 cells in the central nervous system (CNS) was determined using immunohistochemistry; the differentiation of peripheral Treg cells was analyzed using flow cytometry, and the changes in the levels of cytokines were detected with ELISA; the changes in the expressions of p-Smad2 and p- smad3 were investigated using Western blotting.

RESULTS

High-dose rapamycin significantly improved the neurological deficits scores of EAE mice. In high-dose rapamycin group, the scores in the onset stage, peak stage and remission stage were 0.14±0.38, 0.43±1.13 and 0.14±0.37, respectively, as compared with 1.14±0.69, 2.14±1.06 and 2.2±0.75 in the model group. The infiltration of inflammatory IL-17 cells was significantly lower in high-dose rapamycin group than in the model group (43±1.83 vs 153.5±7.02). High-dose rapamycin obviously inhibited the production of IL-12, IFN-γ, IL-17 and IL-23 and induced the anti-inflammatory cytokines IL-10 and TGF-β. The percentage of Treg in CD4+ T cells was significantly higher in high- dose rapamycin group than in the model group (10.17 ± 0.68 vs 3.52 ± 0.32). In the in vitro experiment, combined treatments of the lymphocytes isolated from the mice with rapamycin and TGF-β induced a significant increase in the number of Treg cells (13.66±1.89) compared with the treatment with rapamycin (6.23±0.80) or TGF-β (4.87±0.85) alone. Rapamycin also obviously up-regulated the expression of p-Smad2 and p-Smad3 in the lymphocytes.

CONCLUSIONS

Rapamycin can promote the differentiation of Treg cells by up-regulating the expression of p-Smad2 and p-smad3 to improve neurological deficits in mice with EAE.

Regulation of Dendritic Cell Immune Function and Metabolism by Cellular Nutrient Sensor Mammalian Target of Rapamycin (mTOR)

Dendritic cell (DC) activation is characterized by an acute increase in glucose metabolic flux that is required to fuel the high anabolic rates associated with DC activation. Inhibition of glycolysis significantly attenuates most aspects of DC immune effector function including antigen presentation, inflammatory cytokine production, and T cell stimulatory capacity. The cellular nutrient sensor mammalian/mechanistic Target of Rapamycin (mTOR) is an important upstream regulator of glycolytic metabolism and plays a central role in coordinating DC metabolic changes and immune responses. Because mTOR signaling can be activated by a variety of immunological stimuli, including signaling through the Toll-like Receptor (TLR) family of receptors, mTOR is involved in orchestrating many aspects of the DC metabolic response to microbial stimuli. It has become increasingly clear that mTOR's role in promoting or attenuating inflammatory processes in DCs is highly context-dependent and varies according to specific cellular subsets and the immunological conditions being studied. This review will address key aspects of the complex role of mTOR in regulating DC metabolism and effector function.

Update on clinical gene therapy for hemophilia

In contrast to other diverse therapies for the X-linked bleeding disorder hemophilia that are currently in clinical development, gene therapy holds the promise of a lasting cure with a single drug administration. Near-to-complete correction of hemophilia A (factor VIII deficiency) and hemophilia B (factor IX deficiency) have now been achieved in patients by hepatic in vivo gene transfer. Adeno-associated viral vectors with different viral capsids that have been engineered to express high-level, and in some cases hyperactive, coagulation factors were employed. Patient data support that sustained endogenous production of clotting factor as a result of gene therapy eliminates the need for infusion of coagulation factors (or alternative drugs that promote coagulation), and may therefore ultimately also reduce treatment costs. However, mild liver toxicities have been observed in some patients receiving high vector doses. In some but not all instances, the toxicities correlated with a T-cell response directed against the viral capsid, prompting use of immune suppression. In addition, not all patients can be treated because of preexisting immunity to viral capsids. Nonetheless, studies in animal models of hemophilia suggest that the approach can also be used for immune tolerance induction to prevent or eliminate inhibitory antibodies against coagulation factors. These can form in traditional protein replacement therapy and represent a major complication of treatment. The current review provides a summary and update on advances in clinical gene therapies for hemophilia and its continued development.

Flt3L Treatment of Bone Marrow Donors Increases Graft Plasmacytoid Dendritic Cell Content and Improves Allogeneic Transplantation Outcomes

A higher number of donor plasmacytoid dendritic cells (pDCs) is associated with increased survival and reduced graft-versus-host disease (GVHD) in human recipients of unrelated donor bone marrow (BM) grafts, but not granulocyte colony-stimulating factor (G-CSF)-mobilized peripheral blood grafts. We show that in murine models, donor BM pDCs are associated with increased survival and decreased GVHD compared with G-CSF-mobilized pDCs. To increase the content of pDCs in BM grafts, we studied the effect of FMS-like tyrosine kinase 3 ligand (Flt3L) treatment of murine BM donors on transplantation outcomes. Flt3L treatment (300 μg/kg/day) resulted in a schedule-dependent increase in the content of pDCs in the BM. Mice treated on days -4 and -1 had a >5-fold increase in pDC content without significant changes in numbers of HSCs, T cells, B cells, and natural killer cells in the BM graft. In an MHC-mismatched murine transplant model, recipients of Flt3L-treated T cell-depleted (TCD) BM (TCD F-BM) and cytokine-untreated T cells had increased survival and decreased GVHD scores with fewer Th1 and Th17 polarized T cells post-transplantation compared with recipients of equivalent numbers of untreated donor TCD BM and T cells. Gene array analyses of pDCs from Flt3L-treated human and murine donors showed up-regulation of adaptive immune pathways and immunoregulatory checkpoints compared with pDCs from untreated BM donors. Transplantation of TCD F-BM plus T cells resulted in no loss of the graft-versus-leukemia (GVL) effect compared with grafts from untreated donors in 2 murine GVL models. Thus, Flt3L treatment of BM donors is a novel method for increasing the pDC content in allografts, improving survival, and decreasing GVHD without diminishing the GVL effect.

Rapamycin Nano-Micelle Ophthalmic Solution Reduces Corneal Allograft Rejection by Potentiating Myeloid-Derived Suppressor Cells' Function

Allograft rejection is the major cause of corneal allograft failure. Rapamycin (RAPA) has been reported as an effective and novel immunosuppressive agent for patients undergoing corneal transplantation. However, its high water insolubility and low bioavailability have strongly constrained its clinical application. In this study, we successfully developed a RAPA nano-micelle ophthalmic solution and found that corneal allograft survival in recipients treated with RAPA nano-micelle ophthalmic solution was significantly prolonged for more than 2 months, with less inflammatory infiltration, decreased production of pro-inflammatory factors, and elevated recruitment of myeloid-derived suppressor cells (MDSCs). MDSCs from mice treated with RAPA nano-micelle ophthalmic solution could significantly inhibit the proliferation of CD4⁺T cells through increased expressions of inducible nitric oxidase (iNOS) and arginase-1 (Arg-1). The activity blockade of Arg-1 and iNOS pharmacologically reversed their immunosuppressive ability. Moreover, the effects of RAPA were antagonized by the administration of anti-Gr-1 antibody or by inhibiting the activity of iNOS pharmacologically. In addition, RAPA nano-micelle also effectively alleviated allograft rejection in high-risk rabbit penetrating keratoplasty (PKP) models with corneal vascularization. Collectively, our results demonstrate that RAPA nano-micelle ophthalmic solution could improve the immunosuppressive activity of MDSCs through elevated expression of Arg-1 and iNOS, which highlights the possible therapeutic applications of RAPA against corneal allograft rejection.

Promises and limitations of immune cell-based therapies in neurological disorders

The healthy immune system has natural checkpoints that temper pernicious inflammation. Cells mediating these checkpoints include regulatory T cells, regulatory B cells, regulatory dendritic cells, microglia, macrophages and monocytes. Here, we highlight discoveries on the beneficial functions of regulatory immune cells and their mechanisms of action and evaluate their potential use as novel cell-based therapies for brain disorders. Regulatory immune cell therapies have the potential not only to mitigate the exacerbation of brain injury by inflammation but also to promote an active post-injury brain repair programme. By harnessing the reparative properties of these cells, we can reduce over-reliance on medications that mask clinical symptoms but fail to impede or reverse the progression of brain disorders. Although these discoveries encourage further testing and genetic engineering of regulatory immune cells for the clinical management of neurological disorders, a number of challenges must be surmounted to improve their safety and efficacy in humans.

Tolerance induction in hemophilia: innovation and accomplishments

PURPOSE OF REVIEW

Hemophilia is an X-linked blood coagulation genetic disorder, which can cause significant disability. Replacement therapy for coagulation factor VIII (hemophilia A) or factor IX (hemophilia B) may result in the development of high-affinity alloantibodies ('inhibitors') to the replacement therapy, thus making it ineffective. Therefore, there is interest in directing immunological responses towards tolerance to infused factors.

RECENT FINDINGS

In this review, we will discuss latest advancements in the development of potentially less immunogenic replacement clotting factors, optimization of current tolerance induction protocols (ITI), preclinical and clinical data of pharmacological immune modulation, hepatic gene therapy, and the rapidly advancing field of cell therapies. We will also evaluate publications reporting data from preclinical studies on oral tolerance induction using chloroplast-transgenic (transplastomic) plants.

SUMMARY

Until now, no clinical prophylactic immune modulatory protocol exists to prevent inhibitor formation to infused clotting factors. Recent innovative technologies provide hope for improved eradication and perhaps even prevention of inhibitors.

Fms-Like Tyrosine Kinase 3-Ligand Contributes to the Development and Function of the Subpopulation of CD8α+ Plasmacytoid Precursor Dendritic Cells in CD8+ /TCR- Facilitating Cells

Facilitating cells (FC) are a CD8⁺ TCR^- bone marrow subpopulation that enhance engraftment of purified hematopoietic stem cells (HSC) and induce antigen-specific CD4⁺ CD25⁺ FoxP3⁺ regulatory T cell (Treg) in vivo. The major subpopulation in FC resembles plasmacytoid precursor dendritic cells (p-preDC) both phenotypically and functionally. Here, we report that the number of FC was significantly reduced in Fms-like tyrosine kinase 3-ligand-knockout (Flt3-L-KO) mice. Specifically, there was a selective decrease in the B220⁺ CD11c⁺ CD11b^- p-preDC FC subpopulation. The p-preDC FC subpopulation in FC total is restored after Flt3-L administration to Flt3-L-KO mice. FC from Flt3-L-KO donors exhibit impaired facilitation of allogeneic HSC engraftment in ablatively conditioned mice (B6 → NOD) as well as in mice conditioned with reduced intensity conditioning (B6 → BALB/c). In addition, the number of CD4⁺ CD25⁺ Foxp3⁺ Treg from Flt3-L-KO mice is significantly decreased. This was associated with the expression of chemokine receptor CXCR3⁺ or CCR5⁺ on Treg. Treg from the spleen of Flt3-L-KO mice showed impaired facilitation of engraftment of allogeneic HSC compared to wild-type Treg. Flt3-L treatment significantly expanded Treg, and restored their facilitating function. These results suggest that Flt3-L is an important growth factor in the development and homeostasis of p-preDC FC and in the role of FC inducing generation of Treg. Flt3-L provides potent immunoregulatory properties that may be clinically useful to improve tolerance induction and enhance the function of allogeneic cell therapies. Stem Cells 2018;36:1567-1577.

Effect of TGF-β1 on blood CD4+CD25high regulatory T cell proliferation and Foxp3 expression during non-small cell lung cancer blood metastasis

Metastatic circulating tumor cells in non-small cell lung cancer (NSCLC) metastasis have been reported to be associated with an immune response. The present study aimed to provide a theoretical basis for the immunomodulatory processes during NSCLC blood metastasis. NSCLC blood and normal peripheral blood mononuclear cells (PBMCs) were collected. The quantity of cluster of differentiation (CD)4⁺CD25^high regulatory T (Treg) cells and the intracellular forkhead box protein 3 (Foxp3) expression in CD4⁺CD25^high Treg cells were determined by flow cytometry. Furthermore, the effect of transforming growth factor β1 (TGF-β1) on NSCLC blood CD4⁺CD25⁺ Treg cell proliferation was explored by activating blood mononuclear cells with an anti-CD3 monoclonal antibody, interleukin-2 and different doses of TGF-β1. Reverse transcription-quantitative polymerase chain reaction assays were used to detect the mRNA expression of Foxp3. Carboxyfluorescein succinimidyl ester staining was used to analyze the proliferation dynamics of lymphocyte subsets. Results indicate that the proportion of CD4⁺ T cells in the blood of patients with NSCLC was significantly higher compared with normal peripheral blood (P<0.01). Foxp3 expression in NSCLC blood Treg cells was significantly decreased compared with normal peripheral blood (P<0.01). NSCLC blood mononuclear cells treated with TGF-β1 at 1, 5 and 25 ng/ml significantly induced Foxp3 expression in CD4⁺CD25⁺ Treg cells compared with the control group (P<0.05). The proportion of CD4⁺CD25⁺ Treg and CD8⁺ T cells were elevated in generation 6, 7, 8 after 6 days of TGF-β1 treatment compared with untreated cells. The proportion of CD4⁺CD25⁺ Treg and CD8⁺ T cells were elevated in generation 8, 9 and with TGF-β1 treatment after 8 days compared with untreated cells. These results indicate that CD4⁺CD25⁺ Treg cells proliferate at a greater rate compared with CD8⁺ T cells after 4, 6 or 8 days of treatment. The proportion of CD4⁺CD25^high Treg cells in NSCLC blood was significantly higher (P<0.05) compared with normal peripheral blood. The number of Foxp3⁺ T cells was significantly lower (P<0.05) compared with normal peripheral blood. The data presented in this study suggest that NSCLC blood CD4⁺CD25^high Treg cells are functionally immature and that TGF-β1 may promote maturation.

Gene Therapy With Regulatory T Cells: A Beneficial Alliance

Gene therapy aims to replace a defective or a deficient protein at therapeutic or curative levels. Improved vector designs have enhanced safety, efficacy, and delivery, with potential for lasting treatment. However, innate and adaptive immune responses to the viral vector and transgene product remain obstacles to the establishment of therapeutic efficacy. It is widely accepted that endogenous regulatory T cells (Tregs) are critical for tolerance induction to the transgene product and in some cases the viral vector. There are two basic strategies to harness the suppressive ability of Tregs: in vivo induction of adaptive Tregs specific to the introduced gene product and concurrent administration of autologous, ex vivo expanded Tregs. The latter may be polyclonal or engineered to direct specificity to the therapeutic antigen. Recent clinical trials have advanced adoptive immunotherapy with Tregs for the treatment of autoimmune disease and in patients receiving cell transplants. Here, we highlight the potential benefit of combining gene therapy with Treg adoptive transfer to achieve a sustained transgene expression. Furthermore, techniques to engineer antigen-specific Treg cell populations, either through reprogramming conventional CD4⁺ T cells or transferring T cell receptors with known specificity into polyclonal Tregs, are promising in preclinical studies. Thus, based upon these observations and the successful use of chimeric (IgG-based) antigen receptors (CARs) in antigen-specific effector T cells, different types of CAR-Tregs could be added to the repertoire of inhibitory modalities to suppress immune responses to therapeutic cargos of gene therapy vectors. The diverse approaches to harness the ability of Tregs to suppress unwanted immune responses to gene therapy and their perspectives are reviewed in this article.

Innovative Approaches for Immune Tolerance to Factor VIII in the Treatment of Hemophilia A

Hemophilia A (coagulation factor VIII deficiency) is a debilitating genetic disorder that is primarily treated with intravenous replacement therapy. Despite a variety of factor VIII protein formulations available, the risk of developing anti-dug antibodies (“inhibitors”) remains. Overall, 20–30% of patients with severe disease develop inhibitors. Current clinical immune tolerance induction protocols to eliminate inhibitors are not effective in all patients, and there are no prophylactic protocols to prevent the immune response. New experimental therapies, such as gene and cell therapies, show promising results in pre-clinical studies in animal models of hemophilia. Examples include hepatic gene transfer with viral vectors, genetically engineered regulatory T cells (Treg), in vivo Treg induction using immune modulatory drugs, and maternal antigen transfer. Furthermore, an oral tolerance protocol is being developed based on transgenic lettuce plants, which suppressed inhibitor formation in hemophilic mice and dogs. Hopefully, some of these innovative approaches will reduce the risk of and/or more effectively eliminate inhibitor formation in future treatment of hemophilia A.

Gene Therapy-Induced Antigen-Specific Tregs Inhibit Neuro-inflammation and Reverse Disease in a Mouse Model of Multiple Sclerosis

The devastating neurodegenerative disease multiple sclerosis (MS) could substantially benefit from an adeno-associated virus (AAV) immunotherapy designed to restore a robust and durable antigen-specific tolerance. However, developing a sufficiently potent and lasting immune-regulatory therapy that can intervene in ongoing disease is a major challenge and has thus been elusive. We addressed this problem by developing a highly effective and robust tolerance-inducing in vivo gene therapy. Using a pre-clinical animal model, we designed a liver-targeting gene transfer vector that expresses full-length myelin oligodendrocyte glycoprotein (MOG) in hepatocytes. We show that by harnessing the tolerogenic nature of the liver, this powerful gene immunotherapy restores immune tolerance by inducing functional MOG-specific regulatory T cells (Tregs) in vivo, independent of major histocompatibility complex (MHC) restrictions. We demonstrate that mice treated prophylactically are protected from developing disease and neurological deficits. More importantly, we demonstrate that when given to mice with preexisting disease, ranging from mild neurological deficits to severe paralysis, the gene immunotherapy abrogated CNS inflammation and significantly reversed clinical symptoms of disease. This specialized approach for inducing antigen-specific immune tolerance has significant therapeutic potential for treating MS and other autoimmune disorders.

Autophagy determines efficiency of liver-directed gene therapy with adeno-associated viral vectors

Use of adeno-associated viral (AAV) vectors for liver-directed gene therapy has shown considerable success, particularly in patients with severe hemophilia B. However, the high vector doses required to reach therapeutic levels of transgene expression caused liver inflammation in some patients that selectively destroyed transduced hepatocytes. We hypothesized that such detrimental immune responses can be avoided by enhancing the efficacy of AAV vectors in hepatocytes. Because autophagy is a key liver response to environmental stresses, we characterized the impact of hepatic autophagy on AAV infection. We found that AAV induced mammalian target of rapamycin (mTOR)-dependent autophagy in human hepatocytes. This cell response was critically required for efficient transduction because under conditions of impaired autophagy (pharmacological inhibition, small interfering RNA knockdown of autophagic proteins, or suppression by food intake), recombinant AAV-mediated transgene expression was markedly reduced, both in vitro and in vivo. Taking advantage of this dependence, we employed pharmacological inducers of autophagy to increase the level of autophagy. This resulted in greatly improved transduction efficiency of AAV vectors in human and mouse hepatocytes independent of the transgene, driving promoter, or AAV serotype and was subsequently confirmed in vivo. Specifically, short-term treatment with a single dose of torin 1 significantly increased vector-mediated hepatic expression of erythropoietin in C57BL/6 mice. Similarly, coadministration of rapamycin with AAV vectors resulted in markedly enhanced expression of human acid-α-glucosidase in nonhuman primates.

CONCLUSION

We identified autophagy as a pivotal cell response determining the efficiency of AAVs intracellular processing in hepatocytes and thus the outcome of liver-directed gene therapy using AAV vectors and showed in a proof-of-principle study how this virus-host interaction can be employed to enhance efficacy of this vector system. (Hepatology 2017;66:252-265).

Preoperative application of combination of portal venous injection of donor spleen cells and intraperitoneal injection of rapamycin prolongs the survival of cardiac allografts in mice

OBJECTIVE

To investigate the effects of preoperative portal venous injection of donor spleen cells (PVIDSC) and intraperitoneal injection of rapamycin in the acute rejection of cardiac allograft in mice and the underlying mechanisms.

METHODS

Homogenous female B6 mice and BALB/c mice were used as recipients and donors of heart transplantation. These mice were randomly divided into different groups and received PVIDSC alone, rapamycin alone, or PVIDSC and rapamycin combined therapy. In addition, the underlying mechanism was studied by measuring a number of cytokines.

RESULTS

Preoperative combination of PVIDSC and intraperitoneal injection of rapamycin significantly prolonged the survival of heterotopic cardiac allograft in mice, but had no effects on the survival time of cardiac allografts in mice pre-sensitized by skin grafting. Preoperative combination of PVIDSC and intraperitoneal injection of rapamycin increased the expression of IL-10 and Foxp3 and reduced the expression of INF-. Short-term preoperative administration of rapamycin promotes the expression of CD4⁺CD25⁺Foxp3⁺ regulator T cells. However, preoperative using alone of rapamycin, or combination of PVIDSC and rapamycin had no effects on the inhibition of proliferation of memory T cells.

CONCLUSIONS

Preoperative application of combination of PVIDSC and rapamycin significantly prolonged the survival time of cardiac allografts in mice but not in mice pre-sensitized by skin grafting. This may be explained by the fact that combination of PVIDSC and rapamycin inhibited the cellular immune response and induced the expression of IL-10 from Tr1 cells and CD4⁺CD25⁺FoxP3⁺ regulatory T cells.

Complexity of immune responses to AAV transgene products - Example of factor IX

After two decades of research, in vivo gene transfer with adeno-associated viral (AAV) vectors has now resulted in successful treatments and even cures for several human diseases. However, the potential for immune responses against the therapeutic gene products remains one of the concerns as this approach is broadened to more patients, diverse diseases, and target organs. Immune responses following gene transfer of coagulation factor IX (FIX) for the treatment of the bleeding disorder hemophilia B has been extensively investigated in multiple animal models. Findings from these studies have not only influenced clinical trial design but have broader implications for other diseases. The impact of vector design and dose, as well as target organ/route of administration on humoral and cellular immune responses are reviewed. Furthermore, the potential for tolerance induction by hepatic gene transfer or combination with immune modulation is discussed.

Plasmacytoid and conventional dendritic cells cooperate in crosspriming AAV capsid-specific CD8+ T cells

Adeno-associated virus (AAV) is a replication-deficient parvovirus that is extensively used as a gene therapy vector. CD8⁺ T-cell responses against the AAV capsid protein can, however, affect therapeutic efficacy. Little is known about the in vivo mechanism that leads to the crosspriming of CD8⁺ T cells against the input viral capsid antigen. In this study, we report that the Toll-like receptor 9 (TLR9)-MyD88 pattern-recognition receptor pathway is uniquely capable of initiating this response. By contrast, the absence of TLR2, STING, or the addition of TLR4 agonist has no effect. Surprisingly, both conventional dendritic cells (cDCs) and plasmacytoid DCs (pDCs) are required for the crosspriming of capsid-specific CD8⁺ T cells, whereas other antigen-presenting cells are not involved. TLR9 signaling is specifically essential in pDCs but not in cDCs, indicating that sensing of the viral genome by pDCs activates cDCs in trans to cross-present capsid antigen during CD8⁺ T-cell activation. Cross-presentation and crosspriming depend not only on TLR9, but also on interferon type I signaling, and both mechanisms can be inhibited by administering specific molecules to prevent induction of capsid-specific CD8⁺ T cells. Thus, these outcomes directly point to therapeutic interventions and demonstrate that innate immune blockade can eliminate unwanted immune responses in gene therapy.

Innovating immune tolerance induction for haemophilia

INTRODUCTION

Haemophilia A is an X-linked bleeding disorder characterized by a deficiency of coagulation protein factor VIII (FVIII). A challenging complication of therapeutic FVIII infusions is the formation of neutralizing alloantibodies against the FVIII protein defined as inhibitors. The development of FVIII inhibitors drastically alters the quality of life of the patients and is associated with tremendous increases in morbidity as well as treatment costs.

AIM

Current clinical immune tolerance induction protocols to reverse inhibitors are lengthy, costly and not effective in all patients. Prophylactic protocols to prevent inhibitor formation have not yet been developed in the clinical setting. However, there has been ample progress towards this goal in recent years in preclinical studies using animal models of haemophilia.

METHODS

Here, we review the mechanisms that lead to inhibitor formation against FVIII and two promising new strategies for antigen-specific tolerance induction.

RESULTS

CD4+ T cells play an important role in the FVIII-specific B cell response. Immune tolerance can be induced based on transplacental delivery of FVIII domains fused to Fc or on oral delivery of leaf cells from chloroplast transgenic crop plants.

CONCLUSIONS

Recent literature suggests that prophylactic tolerance induction protocols for FVIII may be feasible in haemophilia A patients.

Dynamics of antigen presentation to transgene product-specific CD4+ T cells and of Treg induction upon hepatic AAV gene transfer

The tolerogenic hepatic microenvironment impedes clearance of viral infections but is an advantage in viral vector gene transfer, which often results in immune tolerance induction to transgene products. Although the underlying tolerance mechanism has been extensively studied, our understanding of antigen presentation to transgene product-specific CD4⁺ T cells remains limited. To address this, we administered hepatotropic adeno-associated virus (AAV8) vector expressing cytoplasmic ovalbumin (OVA) into wt mice followed by adoptive transfer of transgenic OVA-specific T cells. We find that that the liver-draining lymph nodes (celiac and portal) are the major sites of MHC II presentation of the virally encoded antigen, as judged by in vivo proliferation of DO11.10 CD4⁺ T cells (requiring professional antigen-presenting cells, e.g., macrophages) and CD4⁺CD25⁺FoxP3⁺ Treg induction. Antigen presentation in the liver itself contributes to activation of CD4⁺ T cells egressing from the liver. Hepatic-induced Treg rapidly disseminate through the systemic circulation. By contrast, a secreted OVA transgene product is presented in multiple organs, and OVA-specific Treg emerge in both the thymus and periphery. In summary, liver draining lymph nodes play an integral role in hepatic antigen presentation and peripheral Treg induction, which results in systemic regulation of the response to viral gene products.