Abnormal T cell-dependent B-cell responses in SCID mice receiving allogeneic bone marrow in utero. Severe combined immune deficiency

Experimental and clinical progress of in utero hematopoietic cell transplantation therapy for congenital disorders

In utero hematopoietic cell transplantation (IUHCT) is considered a potentially efficient therapeutic approach with relatively few side effects, compared to adult hematopoietic cell transplantation, for various hematological genetic disorders. The principle of IUHCT has been extensively studied in rodent models and in some large animals with close evolutionary similarities to human beings. However, IUHCT has only been used to rebuild human T cell immunity in certain patients with inherent immunodeficiencies. This review will first summarize the animal models utilized for IUHCT investigations and describe the associated outcomes. Recent advances and potential barriers for successful IUHCT are discussed, followed by possible strategies to overcome these barriers experimentally. Lastly, we will outline the progress made towards utilizing IUHCT to treat inherent disorders for patients, list out associated limitations and propose feasible means to promote the efficacy of IUHCT clinically.

Stem Cell Transplantation in the Fetus

BACKGROUND

In utero transplantation (IUT) of hematopoietic stem cells has the potential to treat a large number of hematologic and metabolic diseases amenable to partial replacement of the hematopoietic system.

METHODS

A review of the literature was conducted that focused on the clinical and experimental experience with IUT and, in this context, the development of the hematopoietic and immune systems.

RESULTS

Successful application of IUT has been limited to the treatment of various types of immunodeficiencies that affect lymphocyte development and function. Other congenital defects such as the thalassemias have not resulted in clinically significant engraftment. Recent efforts at understanding and overcoming the barriers to engraftment in the fetus have focused on providing a selective advantage to donor stem cells and fostering immune tolerance toward the donor cells. The critical cellular components of the graft that promote engraftment and tolerance induction are being evaluated in animal models. Improvements in engraftment have resulted from the inclusion of T cells and/or dendritic cells in the graft, as well as a strategy of combined prenatal and postnatal transplantation.

CONCLUSIONS

The advantages, necessity, and benefits of early treatment will continue to encourage development of IUT as a means to treat hematopoietic and other types of birth defects.

In utero stem cell transplantation and gene therapy: rationale, history, and recent advances toward clinical application

Recent advances in high-throughput molecular testing have made it possible to diagnose most genetic disorders relatively early in gestation with minimal risk to the fetus. These advances should soon allow widespread prenatal screening for the majority of human genetic diseases, opening the door to the possibility of treatment/correction prior to birth. In addition to the obvious psychological and financial benefits of curing a disease in utero, and thereby enabling the birth of a healthy infant, there are multiple biological advantages unique to fetal development, which provide compelling rationale for performing potentially curative treatments, such as stem cell transplantation or gene therapy, prior to birth. Herein, we briefly review the fields of in utero transplantation (IUTx) and in utero gene therapy and discuss the biological hurdles that have thus far restricted success of IUTx to patients with immunodeficiencies. We then highlight several recent experimental breakthroughs in immunology, hematopoietic/marrow ontogeny, and in utero cell delivery, which have collectively provided means of overcoming these barriers, thus setting the stage for clinical application of these highly promising therapies in the near future.

In utero stem cell transplantation and gene therapy: Recent progress and the potential for clinical application

Advances in prenatal diagnosis have led to the prenatal management and treatment of a variety of congenital diseases. Although surgical treatment has been successfully applied to specific anatomic defects that place the fetus at a risk of death or life-long disability, the indications for fetal surgical intervention have remained relatively limited. By contrast, prenatal stem cell and gene therapy await clinical application, but they have tremendous potential to treat a broad range of genetic disorders. If there are biological advantages unique to fetal development that favor fetal stem cell or gene therapy over postnatal treatment, prenatal therapy may become the preferred approach to the treatment of any disease that can be prenatally diagnosed and cured by stem cell or gene therapy. Here, we review the field including recent progress toward clinical application and imminent clinical trials for cellular and gene therapy.

TRAF6 is a critical regulator of LMP1 functions in vivo

EBV-encoded latent membrane protein 1 (LMP1) is critical for EBV-driven B-cell transformation and most EBV-associated malignancies and is also implicated in exacerbation of autoimmunity. LMP1 functionally mimics the TNFR superfamily member CD40, but LMP1-induced signals and downstream B-cell functions are amplified and sustained compared with those mediated by CD40. CD40 and LMP1 both depend upon TNFR-associated factor (TRAF) adaptor molecules to mediate signaling but use them differently. LMP1 is dependent upon TRAFs 3 and 5 to deliver B-cell activation signals, while CD40 predominantly uses TRAFs 2 and 6 for this purpose. Both LMP1 and CD40 functions in B cells require TRAF6, which physically associates with both receptors but via different binding sites. In B-cell CD40 signaling, TRAF6 is required for a particular subset of CD40-dependent immune functions in vivo. Inasmuch as CD40 and LMP1 use other TRAFs differentially, we predicted that TRAF6 is critical for a specific subset of LMP1 functions in vivo and that this subset will be overlapping but distinct from the TRAF6-requiring functions of CD40. This study tests this prediction using a B-cell-specific TRAF6-deficient mouse model. We found that B-cell TRAF6 is important for LMP1-mediated antibody and autoantibody production in mice, as well as germinal center formation, but not the secondary lymphoid organ enlargement that results from LMP1 transgenic expression. Results highlight differential TRAF6 requirements for specific B-cell functions by LMP1 versus CD40. These differences may make important contributions to the contrasts between normally regulated CD40 versus pathogenic LMP1-mediated signals.

TRAF binding is required for a distinct subset of in vivo B cell functions of the oncoprotein LMP1

EBV-encoded latent membrane protein 1 (LMP1) is important for EBV contributions to B cell transformation and many EBV-associated malignancies, as well as EBV-mediated exacerbation of autoimmunity. LMP1 functionally mimics TNF receptor (TNFR) superfamily member CD40, but LMP1 signals and downstream effects are amplified and sustained compared with CD40. CD40 and LMP1 both use TNFR-associated factor (TRAF) adaptor proteins, but in distinct ways. LMP1 functions require TRAFs 3, 5, and 6, which interact with LMP1. However, TRAFs can also contribute to signaling in the absence of direct interactions with cell surface receptors, so we investigated whether their roles in LMP1 in vivo functions require direct association. We show in this study that the LMP1 TRAF binding site was required for LMP1-mediated autoantibody production, the germinal center response to immunization, and optimal production of several isotypes of Ig, but not LMP1-dependent enlargement of secondary lymphoid organs in transgenic mice. Thus, LMP1 in vivo effects can be mediated via both TRAF binding-dependent and -independent pathways. Together with our previous findings, these results indicate that TRAF-dependent receptor functions may not always require TRAF-receptor binding. These data suggest that TRAF-mediated signaling pathways, such as those of LMP1, may be more diverse than previously appreciated. This finding has significant implications for receptor and TRAF-targeted therapies.

The case for intrauterine stem cell transplantation

The clinical burden imposed by the collective group of monogenic disorders demands novel therapies that are effective at achieving phenotypic cure early in the disease process before the development of permanent organ damage. This is important for lethal diseases and also for non-perinatally lethal conditions that are characterised by severe disability with little prospect of postnatal cure. Where postnatal treatments are limited to palliative options, intrauterine stem-cell therapies may offer the potential to arrest pathogenesis in the early undamaged fetus. Intrauterine stem-cell transplantation has been attempted for a variety of diseases, but has only been successful in immune deficiency states in the presence of a competitive advantage for donor cells. This disappointing clinical record requires preclinical investigations into strategies that improve donor cell engraftment, including optimising the donor cell source and manipulating the microenvironment to facilitate homing. This chapter aims to outline the current challenges of intrauterine stem-cell therapy.

In utero hematopoietic cell transplantation for the treatment of congenital anomalies

In utero hematopoietic cell transplantation (IUHCTx) is a promising strategy for the treatment of common hematopoietic disorders and for inducing immune tolerance in the fetus. Although the efficacy of IUHCTx has been demonstrated in multiple small and large animal models, the clinical application of this technique in humans has had limited success. Recent studies in mice have demonstrated that the maternal immune system plays a critical role in limiting engraftment in the fetus. This article reviews the therapeutic rationale of IUHCTx, potential barriers to its applications, and recent experimental strategies to improve its clinical success.

Anti-inflammatory effects of the neurotransmitter agonist Honokiol in a mouse model of allergic asthma

Chronic airway inflammation is a hallmark of asthma, an immune-based disease with great societal impact. Honokiol (HNK), a phenolic neurotransmitter receptor (γ-aminobutyric acid type A) agonist purified from magnolia, has anti-inflammatory properties, including stabilization of inflammation in experimentally induced arthritis. The present study tested the prediction that HNK could inhibit the chronic inflammatory component of allergic asthma. C57BL/6 mice sensitized to and challenged with OVA had increased airway hyperresponsiveness to methacholine challenge and eosinophilia compared with naive controls. HNK-treated mice showed a reduction in airway hyperresponsiveness as well as a significant decrease in lung eosinophilia. Histopathology studies revealed a marked drop in lung inflammation, goblet cell hyperplasia, and collagen deposition with HNK treatment. Ag recall responses from HNK-treated mice showed decreased proinflammatory cytokines in response to OVA, including TNF-α-, IL-6-, Th1-, and Th17-type cytokines, despite an increase in Th2-type cytokines. Regulatory cytokines IL-10 and TGF-β were also increased. Assessment of lung homogenates revealed a similar pattern of cytokines, with a noted increase in the number of FoxP3(+) cells in the lung. HNK was able to alter B and T lymphocyte cytokine secretion in a γ-aminobutyric acid type A-dependent manner. These results indicate that symptoms and pathology of asthma can be alleviated even in the presence of increased Th2 cytokines and that neurotransmitter agonists such as HNK have promise as a novel class of anti-inflammatory agents in the treatment of chronic asthma.

Latent membrane protein 1, the EBV-encoded oncogenic mimic of CD40, accelerates autoimmunity in B6.Sle1 mice

EBV infection is associated with development of the autoimmune disease systemic lupus erythematosus (SLE), and EBV can reactivate during SLE flares. Latent membrane protein 1 (LMP1) is an EBV-encoded oncogenic mimic of CD40 that can be re-expressed in PBMCs during SLE flares, as >90% of humans are latently EBV-infected. Whether LMP1 signaling exacerbates SLE is unknown. The phenotype of mice expressing a chimeric molecule with the mouse CD40 extracellular domain and the LMP1 intracellular signaling regions (mCD40-LMP1 transgenic [tg]) includes enhanced autoreactivity, yet these mice do not develop fatal autoimmune disease. We hypothesized that LMP1-mediated activation signals cooperate with and/or amplify events that predispose individuals to development of autoimmunity. To determine which aspects of autoimmunity may be exacerbated by LMP1, we bred mCD40-LMP1tg mice to two lupus-prone strains, B6.Sle1 and B6.Sle3, and analyzed autoimmunity parameters. LMP1(+)Sle1(+/+) mice developed enlarged lymphoid organs containing increased frequencies of germinal center, B cells, CD86(+) B cells, and activated and memory T cells compared with non-tg littermates. Anti-histone Abs were elevated in serum of LMP1(+)Sle1(+/+) mice, and they had signs of kidney pathology. LMP1(+)Sle1(+/+) B cells produced increased IL-6 and upregulated CD86 to a higher degree following CD40 stimulation in vitro, suggesting that the in vivo autoimmune exacerbation is B cell intrinsic. In contrast, the LMP1 transgene has no additional effects on autoimmunity on the B6.Sle3 background. These data indicate that LMP1-induced effects can cooperate with distinct subsets of host genes that predispose to autoimmunity and can thus be an exacerbating factor in autoimmune disease via multiple mechanisms.

Stem cell and genetic therapies for the fetus

Advances in prenatal diagnosis have led to the prenatal management of a variety of congenital diseases. Although prenatal stem cell and gene therapy await clinical application, they offer tremendous potential for the treatment of many genetic disorders. Normal developmental events in the fetus offer unique biologic advantages for the engraftment of hematopoietic stem cells and efficient gene transfer that are not present after birth. Although barriers to hematopoietic stem cell engraftment exist, progress has been made and preclinical studies are now underway for strategies based on prenatal tolerance induction to facilitate postnatal cellular transplantation. Similarly, in-utero gene therapy shows experimental promise for a host of diseases and proof-in-principle has been demonstrated in murine models, but ethical and safety issues still need to be addressed. Here we review the current status and future potential of prenatal cellular and genetic therapy.

Allogeneic hematopoietic stem cell transplantation recipients have defects of both switched and igm memory B cells

Allogeneic hematopoietic stem cell transplant (HSCT) recipients were assessed to elucidate memory B cell defects underlying their increased susceptibility to infections, particularly by encapsulated bacteria. Circulating IgM memory B cells (CD19+, CD27+, IgM+) and switched memory B cells (CD19+, CD27+, IgM(-)) were enumerated in allogeneic HSCT recipients (n = 37) and healthy controls (n = 35). T lymphocyte subpopulations and serum levels of immunoglobulins, including IgG subclasses, and antibodies to pneumococcal polysaccharides were also assayed. Allogeneic HSCT recipients were deficient in both switched memory and IgM memory B cells compared to healthy controls (both P < .0001), irrespective of time post-HSCT. Switched memory B cell deficiency correlated with CD4+ T cell deficiency, and both correlated with serum levels of IgG1 (P < .0001), possibly reflecting impaired B cell isotype switching in germinal centres. "Steady-state" serum levels of antibodies to pneumococcal polysaccharides did not correlate with circulating memory B cells. Graft-versus-host disease (GVHD) was associated with lower IgM memory B cell counts and lower serum levels of IgG2, IgG4, IgA, and pneumococcal antibodies. The increased susceptibility of allogeneic HSCT patients to infection may reflect a combination of memory B cell defects, which are most common in patients with a history of GVHD.

Prenatal stem cell transplantation and gene therapy

At the present time, the most likely and eminent application of stem cell therapy to the fetus is in utero hematopoietic stem cell transplantation (IUHCT), and this stem cell type will be discussed as a paradigm for all prenatal stem cell therapy. The authors feel that the most likely initial application of IUHCT will use adult HSC derived from bone marrow (BM) or peripheral blood (PB), and will focus this article on this specific approach. The article also reviews the experimental data that support the capacity of IUHCT to induce donor-specific tolerance.

Keratinocyte growth factor and androgen blockade work in concert to protect against conditioning regimen-induced thymic epithelial damage and enhance T-cell reconstitution after murine bone marrow transplantation

Myeloablative conditioning results in thymic epithelial cell (TEC) injury, slow T-cell reconstitution, and a high risk of opportunistic infections. Keratinocyte growth factor (KGF) stimulates TEC proliferation and, when given preconditioning, reduces TEC injury. Thymocytes and TECs express androgen receptors, and exposure to androgen inhibits thymopoiesis. In this study, we have investigated whether TEC stimulation via preconditioning treatment with KGF and leuprolide acetate (Lupron), 2 clinically approved agents, given only before conditioning would circumvent the profound TEC and associated T-cell deficiency seen in allogeneic bone marrow transplant (BMT) recipients. Only combined treatment with KGF plus leuprolide acetate normalized TEC subset numbers and thymic architecture. Thymopoiesis and thymic output were supranormal, leading to the accelerated peripheral reconstitution of naive CD4 and CD8 T cells with a broad Vbeta repertoire and decreased homeostatic T-cell proliferation. Combined therapy facilitated T:B cooperativity and enabled a B-cell humoral response to a CD4 T cell-dependent neoantigen challenge soon after BMT. In vivo antigen-specific CD8 T-cell responses and clearance of a live pathogen was superior with combined versus individual agent therapy. Thus, KGF combined with androgen blockade represents a novel approach to restore thymic function and facilitates the rapid recovery of peripheral T-cell function after allogeneic BMT.

Honokiol, a Natural Plant Product, Inhibits Inflammatory Signals and Alleviates Inflammatory Arthritis

Honokiol (HNK), a phenolic compound isolated and purified from magnolia, has been found to have a number of pharmacologic benefits, including anti-angiogenic and anti-inflammatory properties. HNK has long been used in traditional Asian medicine without toxic side effects. We and others have extensively studied signaling to B cells by CD40 and its Epstein Barr viral mimic, latent membrane protein 1 (LMP1), which has been implicated in exacerbation of chronic autoimmune disease. We asked whether HNK could inhibit CD40 and LMP1 inflammatory signaling mechanisms. In vivo, HNK stabilized the severity of symptomatic collagen-induced arthritis in both CD40-LMP1 transgenic mice and their congenic C57BL/6 counterparts. Ex vivo studies, including collagen-specific serum Ab and Ag recall responses, as well as CD40 or LMP1-mediated activation of splenic B cells, supported the anti-inflammatory effects of HNK. In mouse B cell lines expressing the human CD40-LMP1 chimeric receptor, CD40- and LMP1-mediated NF-kappaB and AP-1 activation were abrogated in a dose-dependent manner, with a concomitant decrease in TNF-alpha and IL-6. These promising findings suggest that the nontoxic anti-inflammatory properties of HNK could be valuable for blocking the autoimmune response.

Hematopoietic reconstitution by multipotent adult progenitor cells: precursors to long-term hematopoietic stem cells

For decades, in vitro expansion of transplantable hematopoietic stem cells (HSCs) has been an elusive goal. Here, we demonstrate that multipotent adult progenitor cells (MAPCs), isolated from green fluorescent protein (GFP)-transgenic mice and expanded in vitro for >40–80 population doublings, are capable of multilineage hematopoietic engraftment of immunodeficient mice. Among MAPC-derived GFP⁺CD45.2⁺ cells in the bone marrow of engrafted mice, HSCs were present that could radioprotect and reconstitute multilineage hematopoiesis in secondary and tertiary recipients, as well as myeloid and lymphoid hematopoietic progenitor subsets and functional GFP⁺ MAPC-derived lymphocytes that were functional. Although hematopoietic contribution by MAPCs was comparable to control KTLS HSCs, approximately 10³-fold more MAPCs were required for efficient engraftment. Because GFP⁺ host-derived CD45.1⁺ cells were not observed, fusion is not likely to account for the generation of HSCs by MAPCs.

Critical role for Stat3 in T-dependent terminal differentiation of IgG B cells

Stat proteins are latent cytoplasmic transcription factors that are crucial in many aspects of mammalian development. In the immune system, Stat3 has distinct roles in T-cell, neutrophil, and macrophage function, but a role for Stat3 in B-cell development, particularly in the terminal differentiation of B cells into antibody-secreting plasma cells, has never been directly tested. In this study, we used the Cre/lox system to generate a mouse strain in which Stat3 was conditionally deleted in the B-cell lineage (Stat3(fl/fl)CD19(Cre/+)). B-cell development, establishment of the peripheral B-cell compartment, and baseline serum antibody levels were unperturbed in Stat3(fl/fl)CD19(Cre/+) mice. Strikingly, Stat3(fl/fl)CD19(Cre/+) mice displayed profound defects in T-dependent (TD) IgG responses, but normal TD IgM, IgE, and IgA responses and T-independent (TI) IgM and IgG3 responses. In addition, germinal center (GC) formation, isotype switching, and generation of memory B cells, including IgG+ memory cells, were all intact in Stat3(fl/fl)CD19(Cre/+) mice, indicating that the requirement for Stat3 was limited to plasma cell differentiation. These results demonstrate a profound yet highly selective role for Stat3 in TD IgG plasma cell differentiation, and therefore represent a unique example of a transcription factor regulating isotype-specific terminal B-cell differentiation.

Expression of the Cytoplasmic Tail of LMP1 in Mice Induces Hyperactivation of B Lymphocytes and Disordered Lymphoid Architecture

The oncogenic EBV protein LMP1 mimics a dysregulated CD40 receptor in vitro. To compare CD40 and LMP1-mediated events in vivo, transgenic mice were engineered to express mouse CD40 (mCD40tg) or a protein with extracellular mCD40 and cytoplasmic LMP1 (mCD40-LMP1tg). Transgenic and CD40(-/-) mice were bred so that only the transgenic CD40 molecule is expressed in B cells, macrophages, and dendritic cells. mCD40-LMP1tg mice had normal lymphocyte subsets, and immunization elicited an antibody response featuring normal isotype switching, affinity maturation, and germinal center (GC) formation. However, unimmunized mCD40-LMP1tg mice had expanded immature and germinal center B cells, produced autoantibodies, exhibited marked splenomegaly and lymphadenopathy, and elevated serum IL-6. Thus, signaling through the LMP1 cytoplasmic tail results in amplified and abnormal mimicry of CD40 functions in vivo, indicating possible ways in which LMP1 contributes to the pathogenesis of EBV-associated human disease.