Reconstitution of Lethally Irradiated Adult Mice with Dominant Negative TGF-β Type II Receptor-Transduced Bone Marrow Leads to Myeloid Expansion and Inflammatory Disease

IL-2 and Anti-TGF-β Promote NK Cell Reconstitution and Anti-tumor Effects after Syngeneic Hematopoietic Stem Cell Transplantation

Simple Summary

Hematopoietic stem cell transplantation (HSCT) causes early immune deficiency and susceptibility to both opportunistic infections and cancer relapse. In this study, using a mouse model where donor cells can be tracked over time, we have observed that the combination of IL-2 (a cytokine which activates the immune system) combined with the blockade of TGF-β (a cytokine which suppresses the immune system) increased immune recovery and resulted in greater anti-tumor efficacy. The combination of IL-2 and anti-TGF-β accelerated NK cell and myeloid cell reconstitution after HSCT.

Abstract

The failure of autologous hematopoietic stem cell transplantation (HSCT) has been associated with a profound immunodeficiency that follows shortly after treatment, which renders patients susceptible to opportunistic infections and/or cancer relapse. Thus, given the additional immunosuppressive pathways involved in immune evasion in cancer, strategies that induce a faster reconstitution of key immune effector cells are needed. Natural killer (NK) cells mediate potent anti-tumor effector functions and are the first immune cells to repopulate after HSCT. TGF-β is a potent immunosuppressive cytokine that can impede both the development and function of immune cells. Here, we evaluated the use of an immunotherapeutic regimen that combines low dose of IL-2, an NK cell stimulatory signal, with TGF-β neutralization, in order to accelerate NK cell reconstitution following congenic HSCT in mice by providing stimulatory signals yet also abrogating inhibitory ones. This therapy led to a marked expansion of NK cells and accelerated NK cell maturation. Following HSCT, mature NK cells from the treated recipients displayed an activated phenotype and enhanced anti-tumor responses both in vitro and in vivo. No overt toxicities or adverse effects were observed in the treated recipients. However, these stimulatory effects on NK cell recovery were predicated upon continuous treatment as cessation of treatment led to return to baseline levels and to no improvement of overall immune recovery when assessed at later time-points, indicating strict regulatory control of the NK cell compartment. Overall, this study still demonstrates that therapies that combine positive and negative signals can be plausible strategies to accelerate NK cell reconstitution following HSCT and augment anti-tumor efficacy.

TGF-beta: a master immune regulator

Introduction: Transforming Growth Factor-Beta (TGF-β) is a master regulator of numerous cellular functions including cellular immunity. In cancer, TGF-β can function as a tumor promoter via several mechanisms including immunosuppression. Since the immune checkpoint pathways are co-opted in cancer to induce T cell tolerance, this review posits that TGF-β is a master checkpoint in cancer, whose negative regulatory influence overrides and controls that of other immune checkpoints.Areas Covered: This review examines therapeutic agents that target TGF-β and its signaling pathways for the treatment of cancer which may be classifiable as checkpoint inhibitors in the broadest sense. This concept is supported by the observations that 1) only a subset of patients benefit from current checkpoint inhibitor therapies, 2) the presence of TGF-β in the tumor microenvironment is associated with excluded or cold tumors, and resistance to checkpoint inhibitors, and 3) existing biomarkers such as PD-1, PD-L1, microsatellite instability and tumor mutational burden are inadequate to reliably and adequately identify immuno-responsive patients. By contrast, TGF-β overexpression is a widespread and profoundly negative molecular hallmark in multiple tumor types.Expert Opinion: TGF-β status may serve as a biomarker to predict responsiveness and as a therapeutic target to increase the activity of immunotherapies.

Keloids: The paradigm of skin fibrosis - Pathomechanisms and treatment

Keloids, fibroproliferative dermal tumors with effusive accumulation of extracellular matrix (ECM) components, particularly collagen, result from excessive expression of growth factors and cytokines. The etiology of keloids is unknown but they occur after dermal injury in genetically susceptible individuals, and they cause both physical and psychological distress for the affected individuals. Several treatment methods for keloids exist, including the combination therapy of surgical excision followed by intralesional steroid therapy, however, they have high recurrence rate regardless of the current treatment method. Improved understanding of the pathomechanisms leading to keloid formation will hopefully identify pathways that serve as specific targets to improve therapy for this devastating, currently intractable, disorder.

RCAN 1 and 3 proteins regulate thymic positive selection

Cooperation between calcineurin (CN)-NFATc and RAF-MEK-ERK signaling pathways is essential in thymocyte positive selection. It is known that the Regulators of Calcineurin (RCAN) proteins can act either facilitating or suppressing CN-dependent signaling events. Here, we show that RCAN genes are expressed in lymphoid tissues, and address the role of RCAN proteins in T cell development. Overexpression of human RCAN3 and RCAN1 can modulate T cell development by increasing positive selection-related surface markers, as well as the "Erk(hi) competence state" in double positive thymocytes, a characteristic molecular signature of positive selection, without affecting CN activity. We also found that RCAN1/3 interact with RAF kinases and CN in a non-exclusive manner. Our data suggests that the balance of RCAN interactions with CN and/or RAF kinases may influence T cell positive selection.

Induction of transplantation tolerance through regulatory cells: from mice to men

Organ transplantation results in the activation of both innate and adaptive immune responses to the foreign antigens. While these responses can be limited with the use of systemic immunosuppressants, the induction of regulatory cell populations may be a novel strategy for the maintenance of specific immunological unresponsiveness that can reduce the severity of the detrimental side effects of current therapies. Our group has extensively researched different regulatory T-cell induction protocols for use as cellular therapy in transplantation. In this review, we address the cellular and molecular mechanisms behind regulatory T-cell suppression and their stability following induction protocols. We further discuss the use of different hematopoietically derived regulatory cell populations, including regulatory B cells, regulatory macrophages, tolerogenic dendritic cells, and myeloid-derived suppressor cells, for the induction of transplantation tolerance in light of new clinical trials developing therapies with some of these populations.

Regulatory cells and transplantation tolerance

Transplantation tolerance is a continuing therapeutic goal, and it is now clear that a subpopulation of T cells with regulatory activity (Treg) that express the transcription factor foxp3 are crucial to this aspiration. Although reprogramming of the immune system to donor-specific transplantation tolerance can be readily achieved in adult mouse models, it has yet to be successfully translated in human clinical practice. This requires that we understand the fundamental mechanisms by which donor antigen-specific Treg are induced and function to maintain tolerance, so that we can target therapies to enhance rather than impede these regulatory processes. Our current understanding is that Treg act via numerous molecular mechanisms, and critical underlying components such as mTOR inhibition, are only now emerging.

In vivo knockdown of TAK1 accelerates bone marrow proliferation/differentiation and induces systemic inflammation

TAK1 (TGF-β Activated Kinase 1) is a MAPK kinase kinase, which activates the p38- and JNK-MAPK and NF-κB pathways downstream of receptors such as Toll-Like-, cytokine- and T-cell and B-cell receptors. Representing such an important node in the pro-inflammatory signal-transduction network, the function of TAK1 has been studied extensively. TAK1 knock-out mice are embryonic lethal, while conditional knock-out mice demonstrated either a pro- or anti-inflammatory function. To study the function of TAK1 protein in the adult immune system, we generated and characterized a transgenic mouse expressing TAK1 shRNA under the control of a doxycycline-inducible promoter. Following treatment of TAK-1 shRNA transgenic mice with doxycycline an effective knockdown of TAK1 protein levels was observed in lymphoid organs and cells in the peritoneal cavity (>50% down regulation). TAK1 knockdown resulted in significant changes in leukocyte populations in blood, bone marrow, spleen and peritoneal cavity. Upon TAK1 knockdown mice demonstrated splenomegaly, signs of systemic inflammation (increased levels of circulating cytokines and increase in cellularity of the B-cell areas and in germinal center development in the follicles) and degenerative changes in heart, kidneys and liver. Not surprisingly, TAK1-Tg mice treated with LPS or anti-CD3 antibodies showed enhanced cytokine/chemokine secretion. Finally, analysis of progenitor cells in the bone marrow upon doxycycline treatment showed increased proliferation and differentiation of myeloid progenitor cells. Given the similarity of the phenotype with TGF-β genetic models, our data suggest that in our model the function of TAK1 in TGF-β signal-transduction is overruling its function in pro-inflammatory signaling.

TGFβ signaling plays a critical role in promoting alternative macrophage activation

Background

Upon stimulation with different cytokines, macrophages can undergo classical or alternative activation to become M1 or M2 macrophages. Alternatively activated (or M2) macrophages are defined by their expression of specific gene products and play an important role in containing inflammation, removing apoptotic cells and repairing tissue damage. Whereas it is well-established that IL-4 can drive alternative activation, if lack of TGFβ signaling at physiological levels affects M2 polarization has not been addressed.

Results

Vav1-Cre x TβRII^fx/fx mice, lacking TβRII function in hematopoietic cells, exhibited uncontrolled pulmonary inflammation and developed a lethal autoimmune syndrome at young age. This was accompanied by significantly increased numbers of splenic neutrophils and T cells as well as elevated hepatic macrophage infiltration and bone marrow monocyte counts. TβRII^-/- CD4⁺ and CD8⁺ T-cells in the lymph nodes and spleen expressed increased cell surface CD44, and CD69 was also higher on CD4⁺ lymph node T-cells. Loss of TβRII in bone marrow-derived macrophages (BMDMs) did not affect the ability of these cells to perform efferocytosis. However, these cells were defective in basal and IL-4-induced arg1 mRNA and Arginase-1 protein production. Moreover, the transcription of genes that are typically upregulated in M2-polarized macrophages, such as ym1, mcr2 and mgl2, was also decreased in peritoneal macrophages and IL-4-stimulated TβRII^-/- BMDMs. We found that cell surface and mRNA expression of Galectin-3, which also regulates M2 macrophage polarization, was lower in TβRII^-/- BMDMs. Very interestingly, the impaired ability of these null mutant BMDMs to differentiate into IL-4 polarized macrophages was Stat6- and Smad3-independent, but correlated with reduced levels of phospho-Akt and β-catenin.

Conclusions

Our results establish a novel biological role for TGFβ signaling in controlling expression of genes characteristic for alternatively activated macrophages. We speculate that lack of TβRII signaling reduces the anti-inflammatory M2 phenotype of macrophages because of reduced expression of these products. This would cause defects in the ability of the M2 macrophages to negatively regulate other immune cells such as T-cells in the lung, possibly explaining the systemic inflammation observed in Vav1-Cre x TβRII^fx/fx mice.

TGF-β limits IL-33 production and promotes the resolution of colitis through regulation of macrophage function

Mϕs promote tissue injury or repair depending on their activation status and the local cytokine milieu. It remains unclear whether the immunosuppressive effects of transforming growth factor β (TGF-β) serve a nonredundant role in Mϕ function in vivo. We generated Mϕ-specific transgenic mice that express a truncated TGF-β receptor II under control of the CD68 promoter (CD68TGF-βDNRII) and subjected these mice to the dextran sodium sulfate (DSS) model of colitis. CD68TGF-βDNRII mice have an impaired ability to resolve colitic inflammation as demonstrated by increased lethality, granulocytic inflammation, and delayed goblet cell regeneration compared with transgene negative littermates. CD68TGF-βDNRII mice produce significantly less IL-10, but have increased levels of IgE and numbers of IL-33+ Mϕs than controls. These data are consistent with associations between ulcerative colitis and increased IL-33 production in humans and suggest that TGF-β may promote the suppression of intestinal inflammation, at least in part, through direct effects on Mϕ function.

TGF-β limits IL-33 production and promotes the resolution of colitis through regulation of macrophage function

Mϕs promote tissue injury or repair depending on their activation status and the local cytokine milieu. It remains unclear whether the immunosuppressive effects of transforming growth factor β (TGF-β) serve a nonredundant role in Mϕ function in vivo. We generated Mϕ-specific transgenic mice that express a truncated TGF-β receptor II under control of the CD68 promoter (CD68TGF-βDNRII) and subjected these mice to the dextran sodium sulfate (DSS) model of colitis. CD68TGF-βDNRII mice have an impaired ability to resolve colitic inflammation as demonstrated by increased lethality, granulocytic inflammation, and delayed goblet cell regeneration compared with transgene negative littermates. CD68TGF-βDNRII mice produce significantly less IL-10, but have increased levels of IgE and numbers of IL-33+ Mϕs than controls. These data are consistent with associations between ulcerative colitis and increased IL-33 production in humans and suggest that TGF-β may promote the suppression of intestinal inflammation, at least in part, through direct effects on Mϕ function.

Transforming growth factor-beta: recent advances on its role in immune tolerance

Transforming growth factor (TGF-β1) is a pleiotropic cytokine, secreted by immune and nonhematopoietic cells. TGF-β is involved in many different critical processes, such as embryonal development, cellular maturation and differentiation, wound healing, and immune regulation. It maintains immune homeostasis by acting as a potent immune suppressor through inhibition of proliferation, differentiation, activation, and effector function of immune cells. Paradoxically, depending on the context, it displays proinflammatory properties by being a potent chemoattractant for neutrophils and promoting inflammation. In addition, it does not only induce differentiation into the anti-inflammatory Treg cells, but also into the proinflammatory Th17 and Th9 cells and inhibits Th22 differentiation. TGF-β has been demonstrated to be involved in multiple pathologies. In infections, it protects against collateral damages caused by the immune system, but it also promotes immune evasion and chronic infections. In autoimmune diseases, a TGF-β dysfunction leads to the loss of tolerance to self-antigens. In cancer, TGF-β is a potent inhibitor of cell proliferation and acts as a tumor suppressor at the beginning of tumorogenesis. However, once the cells become resistant to TGF-β, it mainly supports tumor growth and metastasis by promoting immune evasion and angiogenesis. In asthma, it is assumed to promote allergen tolerance, but plays a detrimental role in irreversible remodeling of the airways. Despite the high numbers of TGF-β-targeted pathways, it is a promising drug target for treatment of autoimmunity, cancer, fibrosis, if cell specificity can be achieved.This review summarizes the progresses that have been accomplished on the understanding of TGF-β's signaling in the immune homeostasis and its role in pathogenesis.

Overexpression of transforming growth factor β1 in malignant prostate cells is partly caused by a runaway of TGF-β1 auto-induction mediated through a defective recruitment of protein phosphatase 2A by TGF-β type I receptor

OBJECTIVES

To elucidate the mechanism of transforming growth factor (TGF)-β1 overexpression in prostate cancer cells.

METHODS

Malignant (PC3, DU145) and benign (RWPE1, BPH1) prostate epithelial cells were used. Phosphatase activity was measured using a commercial kit. Recruitment of the regulatory subunit, Bα, of protein phosphatase 2A (PP2A-Bα) by TGF-β type I receptor (TβRI) was monitored by coimmunoprecipitation. Blockade of TGF-β1 signaling in cells was accomplished either by using TGF-β-neutralizing monoclonal antibody or by transduction of a dominant negative TGF-β type II receptor retroviral vector.

RESULTS

Basal levels of TGF-β1 in malignant cells were significantly higher than those in benign cells. Blockade of TGF-β signaling resulted in a significant decrease in TGF-β1 expression in malignant cells, but not in benign cells. Upon TGF-β1 treatment (10 ng/mL), TGF-β1 expression was increased in malignant cells, but not in benign cells. This differential TGF-β1 auto-induction between benign and malignant cells correlated with differential activation of extracellular signal-regulated kinase (ERK). Following TGF-β1 treatment, the activity of serine/threonine phosphatase and recruitment of PP2A-Bα by TβRI increased in benign cells, but not in malignant cells. Inhibition of PP2A in benign cells resulted in an increase in ERK activation and in TGF-β1 auto-induction after TGF-β1 (10 ng/mL) treatment.

CONCLUSIONS

These results suggest that TGF-β1 overexpression in malignant cells is caused, at least in part, by a runaway of TGF-β1 auto-induction through ERK activation because of a defective recruitment of PP2A-Bα by TβRI.

FGF-2, TGFbeta-1, PDGF-A and respective receptors expression in pleomorphic adenoma myoepithelial cells: an in vivo and in vitro study

Myoepithelial cells have an important role in salivary gland tumor development, contributing to a low grade of aggressiveness of these tumors. Normal myoepithelial cells are known by their suppressor function presenting increased expression of extracellular matrix genes and protease inhibitors. The importance of stromal cells and growth factors during tumor initiation and progression has been highlighted by recent literature. Many tumors result from the alteration of paracrine growth factors pathways. Growth factors mediate a wide variety of biological processes such as development, tissue repair and tumorigenesis, and also contribute to cellular proliferation and transformation in neoplastic cells.

OBJECTIVES

This study evaluated the expression of fibroblast growth factor-2 (FGF-2), transforming growth factor beta-1 (TGFbeta-1), platelet-derived growth factor-A (PDGF-A) and their respective receptors (FGFR-1, FGFR-2, TGFbetaR-II and PDGFR-alpha) in myoepithelial cells from pleomorphic adenomas (PA) by in vivo and in vitro experiments.

MATERIAL AND METHODS

Serial sections were obtained from paraffin-embedded PA samples obtained from the school's files. Myoepithelial cells were obtained from explants of PA tumors provided by surgery from different donors. Immunohistochemistry, cell culture and immunofluorescence assays were used to evaluate growth factor expression.

RESULTS

The present findings demonstrated that myoepithelial cells from PA were mainly positive to FGF-2 and FGFR-1 by immunohistochemistry and immunofluorescence. PDGF-A and PDGFR-alpha had moderate expression by immunohistochemistry and presented punctated deposits throughout cytoplasm of myoepithelial cells. FGFR-2, TGFbeta-1 and TGFbetaR-II were negative in all samples.

CONCLUSIONS

These data suggested that FGF-2 compared to the other studied growth factors has an important role in PA benign myoepithelial cells, probably contributing to proliferation of these cells through the FGFR-1.

Relative roles of TGF-beta1 and Wnt in the systemic regulation and aging of satellite cell responses

Muscle stem (satellite) cells are relatively resistant to cell-autonomous aging. Instead, their endogenous signaling profile and regenerative capacity is strongly influenced by the aged P-Smad3, differentiated niche, and by the aged circulation. With respect to muscle fibers, we previously established that a shift from active Notch to excessive transforming growth factor-beta (TGF-β) induces CDK inhibitors in satellite cells, thereby interfering with productive myogenic responses. In contrast, the systemic inhibitor of muscle repair, elevated in old sera, was suggested to be Wnt. Here, we examined the age-dependent myogenic activity of sera TGF-β1, and its potential cross-talk with systemic Wnt. We found that sera TGF-β1 becomes elevated within aged humans and mice, while systemic Wnt remained undetectable in these species. Wnt also failed to inhibit satellite cell myogenicity, while TGF-β1 suppressed regenerative potential in a biphasic fashion. Intriguingly, young levels of TGF-β1 were inhibitory and young sera suppressed myogenesis if TGF-β1 was activated. Our data suggest that platelet-derived sera TGF-β1 levels, or endocrine TGF-β1 levels, do not explain the age-dependent inhibition of muscle regeneration by this cytokine. In vivo, TGF-β neutralizing antibody, or a soluble decoy, failed to reduce systemic TGF-β1 and rescue myogenesis in old mice. However, muscle regeneration was improved by the systemic delivery of a TGF-β receptor kinase inhibitor, which attenuated TGF-β signaling in skeletal muscle. Summarily, these findings argue against the endocrine path of a TGF-β1-dependent block on muscle regeneration, identify physiological modalities of age-imposed changes in TGF-β1, and introduce new therapeutic strategies for the broad restoration of aged organ repair.

An anti-transforming growth factor beta antibody suppresses metastasis via cooperative effects on multiple cell compartments

Overexpression of transforming growth factor beta (TGF-beta) is frequently associated with metastasis and poor prognosis, and TGF-beta antagonism has been shown to prevent metastasis in preclinical models with surprisingly little toxicity. Here, we have used the transplantable 4T1 model of metastatic breast cancer to address underlying mechanisms. We showed that efficacy of the anti-TGF-beta antibody 1D11 in suppressing metastasis was dependent on a synergistic combination of effects on both the tumor parenchyma and microenvironment. The main outcome was a highly significant enhancement of the CD8+ T-cell-mediated antitumor immune response, but effects on the innate immune response and on angiogenesis also contributed to efficacy. Treatment with 1D11 increased infiltration of natural killer cells and T cells at the metastatic site, and enhanced expression of coactivators (NKG2D) and cytotoxic effectors (perforin and granzyme B) on CD8+ T cells. On the tumor cells, increased expression of an NKG2D ligand (Rae1gamma) and of a death receptor (TNFRSF1A) contributed to enhanced immune cell-mediated recognition and lysis. The data suggest that elevated TGF-beta expression in the tumor microenvironment modulates a complex web of intercellular interactions that aggregately promote metastasis and progression. TGF-beta antibodies reverse this effect, and the absence of a major effect of TGF-beta antagonism on any one cell compartment may be critical for a good therapeutic window and the avoidance of autoimmune complications.

Transforming growth factor beta (TGF-beta) and autoimmunity

TGF-beta1 deficient mice develop multifocal inflammatory autoimmune disease and serve as a valuable animal model of autoimmunity. Transgenic expression of a dominant negative form of TGF-beta receptor type II in T cells have enabled the study of cell lineage specific effects of TGF-beta providing clues to the potential etiology of autoimmunity. These studies suggest that TGF-beta deficiency may induce autoimmune disease by influencing a number of immunological phenomena including lymphocyte activation and differentiation, cell adhesion molecule expression, regulatory T cell function, the expression of MHC molecules and cytokines, and cell apoptosis. The spectrum of effects appears to be significant in mucosal immunity and may contribute to the pathogenesis of inflammatory bowel disease.

TGF-beta insensitive dendritic cells: an efficient vaccine for murine prostate cancer

Dendritic cells (DCs) are highly potent initiators of the immune response, but DC effector functions are often inhibited by immunosuppressants such as transforming growth factor beta (TGF-beta). The present study was conducted to develop a treatment strategy for prostate cancer using a TGF-beta-insensitive DC vaccine. Tumor lysate-pulsed DCs were rendered TGF-beta insensitive by dominant-negative TGF-beta type II receptor (TbetaRIIDN), leading to the blockade of TGF-beta signals to members of the Smad family, which are the principal cytoplasmic intermediates involved in the transduction of signals from TGF-beta receptors to the nucleus. Expression of TbetaRIIDN did not affect the phenotype of transduced DCs. Phosphorylated Smad-2 was undetectable and expression of surface co-stimulatory molecules (CD80/CD86) were upregulated in TbetaRIIDN DCs after antigen and TGF-beta1 stimulation. Vaccination of C57BL/6 tumor-bearing mice with the TbetaRIIDN DC vaccine induced potent tumor-specific cytotoxic T lymphocyte responses against TRAMP-C2 tumors, increased serum IFN-gamma and IL-12 level, inhibited tumor growth and increased mouse survival. Furthermore, complete tumor regression occurred in two vaccinated mice. These results demonstrate that blocking TGF-beta signals in DC enhances the efficacy of DC-based vaccines.

Effect of dominant negative transforming growth factor-beta receptor type II on cytotoxic activity of RAW 264.7, a murine macrophage cell line

Transforming growth factor-beta (TGF-beta) is a potent suppressor of the immune system. In the present study, we investigated the effect of TGF-beta resistance on a murine macrophage cell line, RAW 264.7, by overexpressing a dominant negative TGF-beta receptor type II (TbetaRIIDN) construct. As expected, TbetaRIIDN-expressing RAW cells, designated as RAW-TbetaRIIDN, were resistant to TGF-beta signaling. When these cells were cocultured with the murine renal cell carcinoma cell line, Renca, a dramatic increase in apoptosis of Renca cells was observed. Simultaneously, elevated levels of inducible nitric oxide synthase (iNOS) and tumor necrosis factor-alpha (TNF-alpha) in association with IFN-gamma were detected in RAW-TbetaRIIDN cells. When the effects of TNF-alpha and iNOS were neutralized through the use of neutralizing antibody and N(G)-methyl-L-arginine, respectively, the enhanced cytotoxicity of TbetaRIIDN-RAW cells was partially reversed. Taken together, these results show that TGF-beta-resistant RAW 264.7 murine macrophage cells have increased cytotoxic activity that is in part mediated by iNOS and TNF-alpha.

A knockout mouse approach reveals that TCTP functions as an essential factor for cell proliferation and survival in a tissue- or cell type-specific manner

Translationally controlled Tumor Protein (TCTP) is an evolutionally highly conserved protein which has been implicated in many cellular functions that are related to cell growth, death, and even the allergic response of the host. To address the physiological roles of TCTP, we generated TCTP knockout mice by targeted gene disruption. Heterozygous mutants appeared to be developmentally normal. However, homozygous mutants (TCTP(-/-)) were embryonic lethal. TCTP(-/-) embryos were smaller in size than the control littermates at all postimplantation stages examined. Although TCTP is widely expressed in both extraembryonic and embryonic tissues, the most prominent defect of the TCTP(-/-) embryo at embryonic stage day 5.5 (E5.5) was in its epiblast, which had a reduced number of cells compared with wild-type controls. The knockout embryos also suffered a higher incidence of apoptosis in epiblast starting about E6.5 and subsequently died around E9.5-10.5 with a severely disorganized structure. Last, we demonstrated that TCTP(-/-) and control mouse embryonic fibroblasts manifested similar proliferation activities and apoptotic sensitivities to various death stimuli. Taken together, our results suggest that despite that TCTP is widely expressed in many tissues or cell types, it appears to regulate cell proliferation and survival in a tissue- or cell type-specific manner.

Blockade of transforming growth factor-{beta} signaling in tumor-reactive CD8(+) T cells activates the antitumor immune response cycle

Transforming growth factor-beta (TGF-beta) is a potent immunosuppressant. Overproduction of TGF-beta by tumor cells leads to evasion of host immune surveillance and tumor progression. Results of our early studies showed that adoptive transfer of tumor-reactive, TGF-beta-insensitive CD8(+) T cells into immunocompetent mice was able to eradicate lung metastasis of mouse prostate cancer. The present study was conducted with three objectives. (a) We tested if this technology could be applied to the treatment of solid xenograft tumors in allogeneic immunodeficient hosts. (b) We determined relevant variables in the tumor microenvironment with the treatment. (c) We tested if immune cells other than CD8(+) T cells were required for the antitumor effect. Mouse prostate cancer cells, TRAMP-C2 of the C57BL/6 strain, grown in immunodeficient allogeneic hosts of BALB/c strain, were used as a xenograft model. Tumor-reactive CD8(+) T cells from C57BL/6 mice were isolated, expanded ex vivo, and rendered insensitive to TGF-beta by introducing a dominant-negative TGF-beta type II receptor vector. Seven days following s.c. injection of TRAMP-C2 cells (5 x 10(5)) into the flank of male BALB/c-Rag1(-/-) mice, tumor-reactive, TGF-beta-insensitive CD8(+) T cells (1.5 x 10(7)) were transferred with and without the cotransfer of an equal number of CD8-depleted splenocytes from C57BL/6 donors. Naive CD8(+) T cells or green fluorescent protein-empty vector-transfected tumor-reactive CD8(+) T cells were transferred as controls. Forty days following the transfer, the average tumor weight in animals that received cotransfer of tumor-reactive, TGF-beta-insensitive CD8(+) T cells and CD8-depleted splenocytes was at least 50% less than that in animals of all other groups (P < 0.05). Tumors in animals of the former group showed a massive infiltration of CD8(+) T cells. This was associated with secretion of relevant cytokines, decreased tumor proliferation, reduced angiogenesis, and increased tumor apoptosis. Based on these results, we postulated a concept of antitumor immune response cycle in tumor immunology.

TGF-beta in cancer and as a therapeutic target

Cancer develops through a series of genetic changes leading to malignant transformation. Numerous gene and pathways involved in stages of progression to frank malignancy have been elucidated. These genetic changes result in aberrations in fundamental cellular processes controlling proliferation, apoptosis, differentiation and genomic stability. Metastasis is the hallmark of malignancy. The process of metastasis is extremely complex and involves steps including dissemination of tumor cells from the primary tumor through the vascular and lymphatic system and growth selectively in distant tissues and organs. Transforming growth factor-beta which is a growth suppressive cytokine in many normal situations becomes an active and important participant in malignant disease including angiogenesis, extracellular matrix deposition, immuno-suppression and metastasis growth promotion. Transforming growth factor-beta and its receptors are targets for antibody therapeutics and small molecule kinase inhibitors.

Infiltration of tumor-reactive transforming growth factor-beta insensitive CD8+ T cells into the tumor parenchyma is associated with apoptosis and rejection of tumor cells

BACKGROUND

TGF-beta is a potent immunosuppressant. High levels of TGF-beta produced by cancer cells have a negative inhibition effect on surrounding host immune cells and leads to evasion of the host immune surveillance and tumor progression. In the present study, we report a distinct ability of tumor reactive, TGF-beta-insensitive CD8+ T cells to infiltrate into established tumors, secrete relevant cytokines, and induce apoptosis of tumor cells.

METHODS

CD8+ T cells were isolated from the spleens of C57BL/6 mice, which were primed with irradiated mouse prostate cancer cells, the TRAMP-C2 cells. After ex vivo expansion, these tumor reactive CD8+ cells were rendered TGF-beta-insensitive by infection with a retroviral (MSCV)-mediated dominant negative TGF-beta type II receptor (TbetaRIIDN). Control CD8+ cells consist of those transfected with the GFP-only empty vector and naïve CD8+ T cells. Recipient mice were challenged with a single injection of TRAMP-C2 cells 21 days before adoptive transfer of CD8+ T cells was performed. Forty days after the adoptive transfer, all animals were sacrificed. The presence of pulmonary metastases was evaluated pathologically. Serial slides of malignant tissues were used for immunofluorescent staining for different kinds of immune cell infiltration, cytokines, and apoptosis analysis.

RESULTS

Pulmonary metastases were either eliminated or significantly reduced in the group receiving adoptive transfer of tumor-reactive TGF-beta-insensitive CD8+ T cells (3 out of 12) when compared to GFP controls (9 out of 12), and naïve CD8+ T cells (12 out of 12). Results of immunofluorescent studies demonstrated that only tumor-reactive TGF-beta-insensitive CD8+ T cells were able to infiltrate into the tumor and mediate apoptosis when compared to CD4+ T cells, NK cells, and B cells. A large amount of cytokines such as perforin, nitric oxide, IFN-gamma, IL-2, TNF-alpha were secreted in tumor tissue treated with tumor-reactive TGF-beta-insensitive CD8+ T cells. No immune cells infiltration and cytokine secretion were detected in tumor tissues treated with naïve T cells and GFP controls.

CONCLUSIONS

Our results demonstrate the mechanism of anti-tumor effect of tumor-reactive TGF-beta-insensitive CD8+ T cells that adoptive transfer of these CD8+ T cells resulted in infiltration of these immune cells into the tumor parenchyma, secretion of relevant cytokines, and induction of apoptosis in tumor cells. These results support the concept that tumor-reactive TGF-beta-insensitive CD8+ T cells may prove beneficial in the treatment of advanced cancer patients.

Adoptive transfer of tumor-reactive transforming growth factor-beta-insensitive CD8+ T cells: eradication of autologous mouse prostate cancer

Transforming growth factor (TGF)-beta is a potent immunosuppressant. Overproduction of TGF-beta by tumor cells may lead to tumor evasion from the host immune surveillance and tumor progression. The present study was conducted to develop a treatment strategy through adoptive transfer of tumor-reactive TGF-beta-insensitive CD8+ T cells. The mouse TRAMP-C2 prostate cancer cells produced large amounts of TGF-beta1 and were used as an experimental model. C57BL/6 mice were primed with irradiated TRAMP-C2 cells. CD8+ T cells were isolated from the spleen of primed animals, were expanded ex vivo, and were rendered TGF-beta insensitive by infecting with a retrovirus containing dominant-negative TGF-beta type II receptor. Results of in vitro cytotoxic assay revealed that these CD8+ T cells showed a specific and robust tumor-killing activity against TRAMP-C2 cells but were ineffective against an irrelevant tumor line, B16-F10. To determine the in vivo antitumor activity, recipient mice were challenged with a single injection of TRAMP-C2 cells for a period up to 21 days before adoptive transfer of CD8+ T cells was done. Pulmonary metastasis was either eliminated or significantly reduced in the group receiving adoptive transfer of tumor-reactive TGF-beta-insensitive CD8+ T cells. Results of immunofluorescent studies showed that only tumor-reactive TGF-beta-insensitive CD8+ T cells were able to infiltrate into the tumor and mediate apoptosis in tumor cells. Furthermore, transferred tumor-reactive TGF-beta-insensitive CD8+ T cells were able to persist in tumor-bearing hosts but declined in tumor-free animals. These results suggest that adoptive transfer of tumor-reactive TGF-beta-insensitive CD8+ T cells may warrant consideration for cancer therapy.

Smad expression in human atherosclerotic lesions: evidence for impaired TGF-beta/Smad signaling in smooth muscle cells of fibrofatty lesions

OBJECTIVE

Transforming growth factor-beta (TGF-beta) has been implicated in the pathogenesis of human atherosclerosis but its actions during lesion progression are poorly understood. Smad2, Smad3, and Smad4 proteins are signaling molecules by which TGF-beta modulates gene transcription. Our objective was to define the actions of TGF-beta during lesion progression in humans by examining the expression of Smads in relation to TGF-beta-mediated responses.

METHODS AND RESULTS

Immunohistochemistry and reverse-transcription polymerase chain reaction demonstrated Smad2, Smad3, and Smad4 expression in macrophages of fibrofatty lesions and their upregulation after differentiation of monocytes to macrophages. The major Smad splice variants expressed by the macrophages were those that are transcriptionally most active. Macrophages also expressed cyclin inhibitors whose expression is induced via Smad proteins. The cytoplasmic location of p21(Waf1) suggests it may protect macrophages from apoptosis. Smooth muscle cells (SMCs) within the fibrofatty lesions did not express the Smad proteins or the cyclin inhibitors. SMCs of fibrous plaques expressed all 3 Smad proteins.

CONCLUSIONS

In human atherosclerotic lesions, the actions of TGF-beta appear restricted to SMCs in fibrous plaques and macrophages in fatty streaks/fibrofatty lesions. The lack of key TGF-beta signaling components in SMCs of fibrofatty lesions indicates impaired ability of these cells to initiate TGF-beta-mediated Smad-dependent transcriptional responses.

Anemia, thrombocytopenia, leukocytosis, extramedullary hematopoiesis, and impaired progenitor function in Pten+/-SHIP-/- mice: a novel model of myelodysplasia

The myeloproliferative disorder of mice lacking the Src homology 2 (SH2)-containing 5' phosphoinositol phosphatase, SHIP, underscores the need for closely regulating phosphatidylinositol 3-kinase (PI3K) pathway activity, and hence levels of phosphatidylinositol species during hematopoiesis. The role of the 3' phosphoinositol phosphatase Pten in this process is less clear, as its absence leads to embryonic lethality. Despite Pten heterozygosity being associated with a lymphoproliferative disorder, we found no evidence of a hematopoietic defect in Pten(+/-) mice. Since SHIP shares the same substrate (PIP(3)) with Pten, we hypothesized that the former might compensate for Pten haploinsufficiency in the marrow. Thus, we examined the effect of Pten heterozygosity in SHIP(-/-) mice, predicting that further dysregulation of PIP(3) metabolism would exacerbate the pheno-type of the latter. Indeed, compared with SHIP(-/-) mice, Pten(+/-)SHIP(-/-) animals developed a myelodysplastic phenotype characterized by increased hepatosplenomegaly, extramedullary hematopoiesis, anemia, and thrombocytopenia. Consistent with a marrow defect, clonogenic assays demonstrated reductions in committed myeloid and megakaryocytic progenitors in these animals. Providing further evidence of a Pten(+/-)SHIP(-/-) progenitor abnormality, reconstitution of irradiated mice with marrows from these mice led to a marked defect in short-term repopulation of peripheral blood by donor cells. These studies suggest that the regulation of the levels and/or ratios of PI3K-derived phosphoinositol species by these 2 phosphatases is critical to normal hematopoiesis.

TNF receptor-associated factor 6 deficiency during hemopoiesis induces Th2-polarized inflammatory disease

Toll-like receptors (TLR) initiate rapid innate immune responses by recognizing microbial products. These events in turn lead to the development of an efficient adaptive immune response through the up-regulation of a number of costimulatory molecules, including members of the TNF/TNFR superfamily, on the surface of an APC. TNFR-associated factor 6 (TRAF6) is a common signaling adapter used by members of both the TNFR and the TLR/IL-1R superfamilies, and as such plays a critical role in the development of immune responses. As TRAF6-deficient mice die prematurely, we generated chimeras reconstituted with TRAF6-deficient fetal liver cells to analyze functions of TRAF6 in vivo in the hemopoietic compartment. We found that TRAF6-deficient chimeras develop a progressive lethal inflammatory disease associated with massive organ infiltration and activation of CD4(+) T cells in a Th2-polarized phenotype, and a defect in IL-18 responsiveness. When recombination-activating gene 2(-/-) blastocysts were complemented with TRAF6-deficient embryonic stem cells, a marked elevation of activated CD4(+) T cells and progressive inflammatory disease were also observed. Moreover, T cell activation and lethal inflammation were not reversed in mixed chimeric mice generated from normal and TRAF6-deficient fetal liver cells. These results suggest that deletion of TRAF6 induces a dominant Th2-type polarized autoimmune response. Therefore, in addition to playing a critical role in innate and adaptive immunity, TRAF6 is likely to play a previously unrecognized role in the maintenance of self-tolerance.

Transforming growth factor-beta signaling in normal and malignant hematopoiesis

Transforming growth factor-beta (TGF-beta) is perhaps the most potent endogenous negative regulator of hematopoiesis. The intracellular signaling events mediating the effects of TGF-beta are multiple, involving extensive crosstalk between Smad-dependent and MAP-kinase-dependent pathways. We are only beginning to understand the importance of the balance between these cascades as a determinant of the response to TGF-beta, and have yet to determine the roles that disruption in TGF-beta signaling pathways might play in leukemogenesis. This review summarizes current knowledge regarding the function of TGF-beta in normal and malignant hematopoiesis. The principal observations made by gene targeting studies in mice are reviewed, with an emphasis on how a disruption of this pathway in vivo can affect blood cell development and immune homeostasis. We overview genetic alterations that lead to impaired TGF-beta signaling in hematopoietic neoplasms, including the suppression of Smad-dependent transcriptional responses by oncoproteins such as Tax and Evi-1, and fusion proteins such as AML1/ETO. We also consider mutations in genes encoding components of the core cell cycle machinery, such as p27(Kip1) and p15(INK4A), and emphasize their impact on the ability of TGF-beta to induce G1 arrest. The implications of these observations are discussed, and opinions regarding important directions for future research on TGF-beta in hematopoiesis are provided.