Retroviral vectors induce epigenetic chromatin modifications and IL-10 production in transduced B cells via activation of toll-like receptor 2

Targeting the Toll-like receptor pathway as a therapeutic strategy for neonatal infection

Toll-like receptors (TLRs) are crucial transmembrane receptors that form part of the innate immune response. They play a role in the recognition of various microorganisms and their elimination from the host. TLRs have been proposed as vital immunomodulators in the regulation of multiple neonatal stressors that extend beyond infection such as oxidative stress and pain. The immune system is immature at birth and takes some time to become fully established. As such, babies are especially vulnerable to sepsis at this early stage of life. Findings suggest a gestational age-dependent increase in TLR expression. TLRs engage with accessory and adaptor proteins to facilitate recognition of pathogens and their activation of the receptor. TLRs are generally upregulated during infection and promote the transcription and release of proinflammatory cytokines. Several studies report that TLRs are epigenetically modulated by chromatin changes and promoter methylation upon bacterial infection that have long-term influences on immune responses. TLR activation is reported to modulate cardiorespiratory responses during infection and may play a key role in driving homeostatic instability observed during sepsis. Although complex, TLR signaling and downstream pathways are potential therapeutic targets in the treatment of neonatal diseases. By reviewing the expression and function of key Toll-like receptors, we aim to provide an important framework to understand the functional role of these receptors in response to stress and infection in premature infants.

Regulatory T cells and TLR9 activation shape antibody formation to a secreted transgene product in AAV muscle gene transfer

Adeno-associated viral (AAV) gene delivery to skeletal muscle is being explored for systemic delivery of therapeutic proteins. To better understand the signals that govern antibody formation against secreted transgene products in this approach, we administered an intramuscular dose of AAV1 vector expressing human coagulation factor IX (hFIX), which does not cause antibody formation against hFIX in C57BL/6 mice. Interestingly, co-administration of a TLR9 agonist (CpG-deoxyoligonucleotide, ODN) but not of lipopolysaccharide, caused a transient anti-hFIX response. ODN activated monocyte-derived dendritic cells and enhanced T follicular helper cell responses. While depletion of regulatory T cells (Tregs) also caused an antibody response, TLR9 activation combined with Treg depletion instead resulted in prolonged CD8⁺ T cell infiltration of transduced muscle. Thus, Tregs modulate the response to the TLR9 agonist. Further, Treg re-population eventually resolved humoral and cellular immune responses. Therefore, specific modes of TLR9 activation and Tregs orchestrate antibody formation in muscle gene transfer.

In vivo induction of regulatory T cells for immune tolerance in hemophilia

Current therapy for the X-linked coagulation disorder hemophilia is based on intravenous infusion of the specifically deficient coagulation factor. However, 20-30% of hemophilia A patients (factor VIII, FVIII, deficiency) generate inhibitory antibodies against FVIII. While formation of inhibitors directed against factor IX, FIX, resulting from hemophilia B treatment is comparatively rare, a serious complication that is often associated with additional immunotoxicities, e.g. anaphylaxis, occurs. Current immune tolerance protocols to eradiate inhibitors are lengthy, expensive, not effective in all patients, and there are no prophylactic tolerance regimens to prevent inhibitor formation. The outcomes of recent experiments in animal models of hemophilia demonstrate that regulatory CD4(+) T cells (Treg) are of paramount importance in controlling B cell responses to FVIII and FIX. This article reviews several novel strategies designed to in vivo induce coagulation factor-specific Treg cells and discusses the subsets of Treg that may promote immune tolerance in hemophilia. Among others, drug- and gene transfer-based protocols, lymphocyte transplant, and oral tolerance are reviewed.

Immune tolerance induction to factor IX through B cell gene transfer: TLR9 signaling delineates between tolerogenic and immunogenic B cells

A subset of patients with severe hemophilia B, the X-linked bleeding disorder resulting from absence of coagulation factor IX (FIX), develop pathogenic antibody responses during replacement therapy. These inhibitors block standard therapy and are often associated with anaphylactic reactions to FIX. Established clinical immune tolerance induction protocols often fail for FIX inhibitors. In a murine model of this immune complication, retrovirally transduced primary B cells expressing FIX antigen fused with immunoglobulin-G heavy chain prevented antibody formation to FIX and was also highly effective in desensitizing animals with preexisting response. In contrast, transplant of B cells that received the identical expression cassette via nucleofection of plasmid vector substantially heightened antibody formation against FIX, a response that could be blocked by toll-like receptor 9 (TLR9) inhibition. While innate responses to TLR4 activation or to retrovirus were minimal in B cells, plasmid DNA activated TLR9, resulting in CpG-dependent NF-κB activation/IL-6 expression and adaptor protein 3 dependent, CpG-independent induction of IFN-I. Neither response was seen in TLR9-deficient B cells. Therefore, TLR9 signaling in B cells, in particular in response to plasmid vector, is highly immunogenic and has to be avoided in design of tolerance protocols.

Development of Gene Transfer for Induction of Antigen-specific Tolerance

Gene replacement therapies, like organ and cell transplantation are likely to introduce neo-antigens that elicit rejection via humoral and/or effector T cell immune responses. Nonetheless, thanks to an ever growing body of pre-clinical studies it is now well accepted that gene transfer protocols can be specifically designed and optimized for induction of antigen-specific immune tolerance. One approach is to specifically express a gene in a tissue with a tolerogenic microenvironment such as the liver or thymus. Another strategy is to transfer a particular gene into hematopoietic stem cells or immunological precursor cells thus educating the immune system to recognize the therapeutic protein as "self". In addition, expression of the therapeutic protein in pro-tolerogenic antigen presenting cells such as immature dendritic cells and B cells has proven to be promising. All three approaches have successfully prevented unwanted immune responses in pre-clinical studies aimed at the treatment of inherited protein deficiencies, e.g. lysosomal storage disorders and hemophilia, and of type I diabetes and multiple sclerosis. In this review we focus on current gene transfer protocols that induce tolerance, including gene delivery vehicles and target tissues, and discuss successes and obstacles in different disease models.

Kinase control of latent HIV-1 infection: PIM-1 kinase as a major contributor to HIV-1 reactivation

Despite the clinical relevance of latent HIV-1 infection as a block to HIV-1 eradication, the molecular biology of HIV-1 latency remains incompletely understood. We recently demonstrated the presence of a gatekeeper kinase function that controls latent HIV-1 infection. Using kinase array analysis, we here expand on this finding and demonstrate that the kinase activity profile of latently HIV-1-infected T cells is altered relative to that of uninfected T cells. A ranking of altered kinases generated from these kinome profile data predicted PIM-1 kinase as a key switch involved in HIV-1 latency control. Using genetic and pharmacologic perturbation strategies, we demonstrate that PIM-1 activity is indeed required for HIV-1 reactivation in T cell lines and primary CD4 T cells. The presented results thus confirm that kinases are key contributors to HIV-1 latency control. In addition, through mutational studies we link the inhibitory effect of PIM-1 inhibitor IV (PIMi IV) on HIV-1 reactivation to an AP-1 motif in the CD28-responsive element of the HIV-1 long terminal repeat (LTR). The results expand our conceptual understanding of the dynamic interactions of the host cell and the latent HIV-1 integration event and position kinome profiling as a research tool to reveal novel molecular mechanisms that can eventually be targeted to therapeutically trigger HIV-1 reactivation.

Aberrant histone modification in peripheral blood B cells from patients with systemic sclerosis

OBJECTIVES

To investigate alterations in histone modifications in B cells and their role in the pathogenesis of systemic sclerosis (SSc).

METHODS

Global histone H3/H4 acetylation and H3K4/H3K9 methylation in B cells of SSc were tested by EpiQuik™ assay kits. Related histone modifier enzymes were measured by RT-PCR and Western blot.

RESULTS

Global histone H4 hyperacetylation and global histone H3K9 hypomethylation were observed in SSc B cells compared with controls. Expression of JHDM2A was significantly increased but HDAC2, HDAC7, and, SUV39H2 were significantly down-regulated in SSc B cells relative to controls. Global histone H4 acetylation and the expression of HDAC2 were negatively correlated. Global histone H3K9 methylation and the expression of SUV39H2 protein were positively correlated. Global H4 acetylation was positively correlated with disease activity and expression of HDAC2 protein was negatively correlated with skin thickness.

CONCLUSIONS

Histone modifications were altered in B cells in SSc correlating with skin thickness and disease activity.

Hypothalamic neuronal toll-like receptor 2 protects against age-induced obesity

Toll-like receptors (TLRs) are traditionally associated with immune-mediated host defense. Here, we ascribe a novel extra-immune, hypothalamic-associated function to TLR2, a TLR-family member known to recognize lipid components, in the protection against obesity. We found that TLR2-deficient mice exhibited mature-onset obesity and susceptibility to high-fat diet (HFD)-induced weight gain, via modulation of food intake. Age-related obesity was still evident in chimeric mice, carrying comparable TLR2⁺ immune cells, suggesting a non-hematopoietic-related involvement of this receptor. TLR2 was up-regulated with age or HFD in pro-opiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus, a brain area participating in central-metabolic regulation, possibly modulating the hypothalamic-anorexigenic peptide, α-melanocyte-stimulating hormone (α-MSH). Direct activation of TLR2 in a hypothalamic-neuronal cell-line via its known ligands, further supports its capacity to mediate non-immune related metabolic regulation. Thus, our findings identify TLR2 expressed by hypothalamic neurons as a potential novel regulator of age-related weight gain and energy expenditure.

Increased synapse formation obtained by T cell epitopes containing a CxxC motif in flanking residues convert CD4+ T cells into cytolytic effectors

The nature of MHC class II-binding epitopes not only determines the specificity of T cell responses, but may also alter effector cell functions. Cytolytic CD4+ T cells have been observed primarily in anti-viral responses, but very little is known about the conditions under which they can be elicited. Their potential as regulators of immune responses, however, deserves investigations. We describe here that inclusion of a thiol-disulfide oxidoreductase motif within flanking residues of class II-restricted epitopes results, both in vitro and in vivo, in elicitation of antigen-specific cytolytic CD4+ T cells through increased synapse formation. We show that both naïve and polarized CD4+ T cells, including Th17 cells, can be converted by cognate recognition of such modified epitopes. Cytolytic CD4+ T cells induce apoptosis on APCs by Fas-FasL interaction. These findings potentially open the way towards a novel form of antigen-specific immunosuppression.

Genetic modification of lymphocytes by retrovirus-based vectors

The genetic modification of lymphocytes is an important topic in the emerging field of gene therapy. Many clinical trials targeting immunodeficiency syndromes or cancer have shown therapeutic benefit; further applications address inflammatory and infectious disorders. Retroviral vector development requires a detailed understanding of the interactions with the host. Most researchers have used simple gammaretroviral vectors to modify lymphocytes, either directly or via hematopoietic stem and progenitor cells. Lentiviral, spumaviral (foamyviral) and alpharetroviral vectors were designed to reduce the necessity for cell stimulation and to utilize potentially safer integration properties. Novel surface modifications (pseudotyping) and transgenes, built using synthetic components, expand the retroviral toolbox, altogether promising increased specificity and potency. Product consistency will be an important criterion for routine clinical use.

Transduced B cells: B is for 'beneficial'!

B cells have been used as tolerogenic APCs for nearly two decades. However, the ability to transduce B cells for use in gene therapy has been hampered by the low efficiency of transduction of resting B cells. This has been partially overcome by mitogenic activation of these cells, a factor that is not without risks as activated B cells may become pathogenic. In this issue of the European Journal of Immunology, this challenge is met by achieving high-efficiency transduction of resting murine B cells with a lentiviral vector. Furthermore, the application of this protocol to generate MOG-expressing B cells and successfully prevent EAE, as described in this issue, is an important step forward in B-cell therapy.

B-Cell Gene Therapy for Tolerance Induction: Host but Not Donor B-Cell Derived IL-10 is Necessary for Tolerance

Genetically modified B cells are excellent tolerogenic antigen-presenting cells (APCs) in multiple models of autoimmunity. However, the mechanisms of action are still not completely understood. In our models, we generate antigen-specific tolerogenic B cells by transducing naïve or primed B cells with an antigen–immunoglobulin G (peptide–IgG) construct. In order to be transduced, B cells require activation with mitogens such as LPS. We and others have found that LPS stimulation of B cells upregulates the production of IL-10, a key cytokine for maintaining immune tolerance. In the current study, we defined the role of B-cell produced IL-10 in tolerance induction by using IL-10 deficient B cells as donor APCs. We found that peptide–IgG transduced IL-10 KO B cells have the same effects as wt B cells in tolerance induction in an experimental autoimmune encephalomyelitis model. Moreover, we demonstrated that the tolerogenic effect of peptide–IgG B cells was completely abrogated in anti-IL-10 receptor antibody treated recipients. Taken together, our results suggest that tolerance induced by peptide–IgG B-cell gene therapy requires IL-10 from the host but not donor B cells. These data shed important insights into the mechanisms of tolerance induction mediated by B-cell gene therapy.