Broadly neutralizing antibodies targeting HIV: Progress and challenges

Anti-HIV broadly neutralizing antibodies (bNAbs) offer a novel approach to treating, preventing, or curing HIV. Pre-clinical models and clinical trials involving the passive transfer of bNAbs have demonstrated that they can control viremia and potentially serve as alternatives or complement antiretroviral therapy (ART). However, antibody decay, persistent latent reservoirs, and resistance impede bNAb treatment. This review discusses recent advancements and obstacles in applying bNAbs and proposes strategies to enhance their therapeutic potential. These strategies include multi-epitope targeting, antibody half-life extension, combining with current and newer antiretrovirals, and sustained antibody secretion.

Antiretrovirals to CCR5 CRISPR/Cas9 gene editing - A paradigm shift chasing an HIV cure

The evolution of drug-resistant viral strains and anatomical and cellular reservoirs of HIV pose significant clinical challenges to antiretroviral therapy. CCR5 is a coreceptor critical for HIV host cell fusion, and a homozygous 32-bp gene deletion (∆32) leads to its loss of function. Interestingly, an allogeneic HSCT from an HIV-negative ∆32 donor to an HIV-1-infected recipient demonstrated a curative approach by rendering the recipient's blood cells resistant to viral entry. Ex vivo gene editing tools, such as CRISPR/Cas9, hold tremendous promise in generating allogeneic HSC grafts that can potentially replace allogeneic ∆32 HSCTs. Here, we review antiretroviral therapeutic challenges, clinical successes, and failures of allogeneic and allogeneic ∆32 HSCTs, and newer exciting developments within CCR5 editing using CRISPR/Cas9 in the search to cure HIV.

PLD3 and PLD4 are single-stranded acid exonucleases that regulate endosomal nucleic-acid sensing

The sensing of microbial genetic material by leukocytes often elicits beneficial pro-inflammatory cytokines, but dysregulated responses can cause severe pathogenesis. Genome-wide association studies have linked the gene encoding phospholipase D3 (PLD3) to Alzheimer's disease and have linked PLD4 to rheumatoid arthritis and systemic sclerosis. PLD3 and PLD4 are endolysosomal proteins whose functions are obscure. Here, PLD4-deficient mice were found to have an inflammatory disease, marked by elevated levels of interferon-γ (IFN-γ) and splenomegaly. These phenotypes were traced to altered responsiveness of PLD4-deficient dendritic cells to ligands of the single-stranded DNA sensor TLR9. Macrophages from PLD3-deficient mice also had exaggerated TLR9 responses. Although PLD4 and PLD3 were presumed to be phospholipases, we found that they are 5' exonucleases, probably identical to spleen phosphodiesterase, that break down TLR9 ligands. Mice deficient in both PLD3 and PLD4 developed lethal liver inflammation in early life, which indicates that both enzymes are needed to regulate inflammatory cytokine responses via the degradation of nucleic acids.

Multiformat T-cell-engaging bispecific antibodies targeting human breast cancers

Four different formats of bispecific antibodies (bsAbs) were generated that consist of anti-Her2 IgG or Fab site-specifically conjugated to anti-CD3 Fab using the genetically encoded noncanonical amino acid. These bsAbs varied in valency or in the presence or absence of an Fc domain. Different valencies did not significantly affect antitumor efficacy, whereas the presence of an Fc domain enhanced cytotoxic activity, but triggered antigen-independent T-cell activation. We show that the bsAbs can efficiently redirect T cells to kill all Her2 expressing cancer cells, including Her2 1+ cancers, both in vitro and in rodent xenograft models. This work increases our understanding of the structural features that affect bsAb activity, and underscores the potential of bsAbs as a promising therapeutic option for breast cancer patients with low or heterogeneous Her2 expression.

An immunosuppressive antibody-drug conjugate

We have developed a novel antibody-drug conjugate (ADC) that can selectively deliver the Lck inhibitor dasatinib to human T lymphocytes. This ADC is based on a humanized antibody that selectively binds with high affinity to CXCR4, an antigen that is selectively expressed on hematopoietic cells. The resulting dasatinib-antibody conjugate suppresses T-cell-receptor (TCR)-mediated T-cell activation and cytokine expression with low nM EC50 and has minimal effects on cell viability. This ADC may lead to a new class of selective immunosuppressive drugs with improved safety and extend the ADC strategy to the targeted delivery of kinase inhibitors for indications beyond oncology.

A CXCR4-targeted site-specific antibody-drug conjugate

A chemically defined anti-CXCR4-auristatin antibody-drug conjugate (ADC) was synthesized that selectively eliminates tumor cells overexpressing the CXCR4 receptor. The unnatural amino acid p-acetylphenylalanine (pAcF) was site-specifically incorporated into an anti-CXCR4 immunoglobulin G (IgG) and conjugated to an auristatin through a stable, non-cleavable oxime linkage to afford a chemically homogeneous ADC. The full-length anti-CXCR4 ADC was selectively cytotoxic to CXCR4(+) cancer cells in vitro (half maximal effective concentration (EC50 )≈80-100 pM). Moreover, the anti-CXCR4 ADC eliminated pulmonary lesions from human osteosarcoma cells in a lung-seeding tumor model in mice. No significant overt toxicity was observed but there was a modest decrease in the bone-marrow-derived CXCR4(+) cell population. Because CXCR4 is highly expressed in a majority of metastatic cancers, a CXCR4-auristatin ADC may be useful for the treatment of a variety of metastatic malignancies.

Targeting human C-type lectin-like molecule-1 (CLL1) with a bispecific antibody for immunotherapy of acute myeloid leukemia

Acute myeloid leukemia (AML), which is the most common acute adult leukemia and the second most common pediatric leukemia, still has a poor prognosis. Human C-type lectin-like molecule-1 (CLL1) is a recently identified myeloid lineage restricted cell surface marker, which is overexpressed in over 90% of AML patient myeloid blasts and in leukemic stem cells. Here, we describe the synthesis of a novel bispecific antibody, αCLL1-αCD3, using the genetically encoded unnatural amino acid, p-acetylphenylalanine. The resulting αCLL1-αCD3 recruits cytotoxic T cells to CLL1 positive cells, and demonstrates potent and selective cytotoxicity against several human AML cell lines and primary AML patient derived cells in vitro. Moreover, αCLL1-αCD3 treatment completely eliminates established tumors in an U937 AML cell line xenograft model. These results validate the clinical potential of CLL1 as an AML-specific antigen for the generation of a novel immunotherapeutic for AML.

A regenerative approach to the treatment of multiple sclerosis

Progressive phases of multiple sclerosis are associated with inhibited differentiation of the progenitor cell population that generates the mature oligodendrocytes required for remyelination and disease remission. To identify selective inducers of oligodendrocyte differentiation, we performed an image-based screen for myelin basic protein (MBP) expression using primary rat optic-nerve-derived progenitor cells. Here we show that among the most effective compounds identifed was benztropine, which significantly decreases clinical severity in the experimental autoimmune encephalomyelitis (EAE) model of relapsing-remitting multiple sclerosis when administered alone or in combination with approved immunosuppressive treatments for multiple sclerosis. Evidence from a cuprizone-induced model of demyelination, in vitro and in vivo T-cell assays and EAE adoptive transfer experiments indicated that the observed efficacy of this drug results directly from an enhancement of remyelination rather than immune suppression. Pharmacological studies indicate that benztropine functions by a mechanism that involves direct antagonism of M1 and/or M3 muscarinic receptors. These studies should facilitate the development of effective new therapies for the treatment of multiple sclerosis that complement established immunosuppressive approaches.

Toll-like receptors and their role in renal pathologies

Toll-like receptors (TLRs) are the first identified and best studied family of pattern recognition receptors. Expressed in immunocytes, TLRs initiate innate immune responses and concurrently shape the subsequent adaptive immune response. They are sensors of both pathogens, through the exogenous pathogen-associated molecular patterns (PAMPs), and tissue injury, through the endogenous danger-associated molecular patterns (DAMPs). In addition to immunocytes, TLRs are widely distributed in various cell types, including renal cells where they contribute significantly to various pathologies. In particular, many experimental and emerging clinical data indicate that TLRs are involved in the pathogenesis of urinary tract infections, sepsis-induced renal failure, kidney ischemia/reperfusion injury, idiopathic or systemic autoimmunity-induced glomerulonephritis and ultimately is renal fibrosis, which leads to end-stage renal disease. This review summarizes the present data about the important role TLRs play in the above kidney diseases focusing on the specific role of PAMPs versus DAMPs and of local versus systemic TLR activation.

Role of nucleic acid-sensing TLRs in diverse autoantibody specificities and anti-nuclear antibody-producing B cells

Nucleic acid (NA)-sensing TLRs (NA-TLRs) promote the induction of anti-nuclear Abs in systemic lupus erythematosus. However, the extent to which other nonnuclear pathogenic autoantibody specificities that occur in lupus and independently in other autoimmune diseases depend on NA-TLRs, and which immune cells require NA-TLRs in systemic autoimmunity, remains to be determined. Using Unc93b1(3d) lupus-prone mice that lack NA-TLR signaling, we found that all pathogenic nonnuclear autoantibody specificities examined, even anti-RBC, required NA-TLRs. Furthermore, we document that NA-TLRs in B cells were required for the development of antichromatin and rheumatoid factor. These findings support a unifying NA-TLR-mediated mechanism of autoantibody production that has both pathophysiological and therapeutic implications for systemic lupus erythematosus and several other humoral-mediated autoimmune diseases. In particular, our findings suggest that targeting of NA-TLR signaling in B cells alone would be sufficient to specifically block production of a broad diversity of autoantibodies.

Critical role of transmethylation in TLR signaling and systemic lupus erythematosus

Post-translational protein modifications can play a significant role in immune cell signaling. Recently, we showed that inhibition of transmethylation curtails experimental autoimmune encephalomyelitis, notably by reducing T cell receptor (TCR)-induced activation of CD4(+) T cells. Here, we demonstrate that transmethylation inhibition by a reversible S-adenosyl-l-homocysteine hydrolase inhibitor (DZ2002) led to immunosuppression by reducing TLR-, B cell receptor (BCR)- and TCR-induced activation of immune cells, most likely by blocking NF-κB activity. Moreover, prophylactic treatment with DZ2002 prevented lupus-like disease from developing in both BXSB and MRL-Fas(lpr) mouse models. DZ2002 treatment initiated during active disease significantly improved outcomes in both in vivo models, suggesting methylation inhibition as a novel approach for the treatment of autoimmune/inflammatory diseases.

Anti-IFN-α/β receptor antibody treatment ameliorates disease in lupus-predisposed mice

The demonstration in humans and mice that nucleic acid-sensing TLRs and type I IFNs are essential disease mediators is a milestone in delineating the mechanisms of lupus pathogenesis. In this study, we show that Ifnb gene deletion does not modify disease progression in NZB mice, thereby strongly implicating IFN-α subtypes as the principal pathogenic effectors. We further document that long-term treatment of male BXSB mice with an anti-IFN-α/β receptor Ab of mouse origin reduced serologic, cellular, and histologic disease manifestations and extended survival, suggesting that disease acceleration by the Tlr7 gene duplication in this model is mediated by type I IFN signaling. The efficacy of this treatment in BXSB mice was clearly evident when applied early in the disease process, but only partial reductions in some disease characteristics were observed when treatment was initiated at later stages. A transient therapeutic effect was also noted in the MRL-Fas(lpr) model, although overall mortality was unaffected. The combined findings suggest that IFN-α/β receptor blockade, particularly when started at early disease stages, may be a useful treatment approach for human systemic lupus erythematosus and other autoimmune syndromes.

Transmethylation in immunity and autoimmunity

The activation of immune cells is mediated by a network of signaling proteins that can undergo post-translational modifications critical for their activity. Methylation of nucleic acids or proteins can have major effects on gene expression as well as protein repertoire diversity and function. Emerging data indicate that indeed many immunologic functions, particularly those of T cells, including thymic education, differentiation and effector function are highly dependent on methylation events. The critical role of methylation in immunocyte biology is further documented by evidence that autoimmune phenomena may be curtailed by methylation inhibitors. Additionally, epigenetic alterations imprinted by methylation can also exert effects on normal and abnormal immune responses. Further work in defining methylation effects in the immune system is likely to lead to a more detailed understanding of the immune system and may point to the development of novel therapeutic approaches.

Systemic autoimmunity and lymphoproliferation are associated with excess IL-7 and inhibited by IL-7Rα blockade

Lupus is characterized by disturbances in lymphocyte homeostasis, as demonstrated by the marked accumulation of activated/memory T cells. Here, we provide evidence that proliferation of the CD8⁺ precursors for the accumulating CD4^–CD8^– T cells in MRL-Fas^lpr lupus-predisposed mice is, in part, driven by commensal antigens. The ensuing lymphadenopathy is associated with increased production of IL-7 due to expansion of fibroblastic reticular cells, the primary source of this cytokine. The excess IL-7 is not, however, consumed by CD4^–CD8^– T cells due to permanent down-regulation of IL-7Rα (CD127), but instead supports proliferation of autoreactive T cells and progression of autoimmunity. Accordingly, IL-7R blockade reduced T cell activation and autoimmune manifestations even when applied at advanced disease stage. These findings indicate that an imbalance favoring production over consumption of IL-7 may contribute to systemic autoimmunity, and correction of this imbalance may be a novel therapeutic approach in lymphoproliferative and autoimmune syndromes.

An Slfn2 mutation causes lymphoid and myeloid immunodeficiency due to loss of immune cell quiescence

We describe a new form of inherited immunodeficiency revealed by an N-ethyl-N-nitrosourea (ENU)-induced mutation called elektra. Homozygotes showed enhanced susceptibility to bacterial and viral infections, and diminished numbers of T cells and inflammatory monocytes that failed to proliferate upon infection and died via the intrinsic apoptotic pathway in response to diverse proliferative stimuli. Elektra mice exhibited an increased proportion of T cells poised to replicate DNA and their T cells expressed a subset of activation markers, suggestive of a semi-activated state. The elektra phenotype was positionally ascribed to a mutation in the gene encoding Schlafen-2 (Slfn2). Our findings reveal a physiological role for Slfn2 in the defense against pathogens through regulation of quiescence in T cells and monocytes.

Toll-like receptors and kidney diseases

Toll like receptors (TLRs) have been extensively studied since their discovery in 1997, and an increasingly detailed picture is emerging about their role in health and disease. TLRs, the first identified family of pattern recognition receptors, can recognize invaders through the exogenous pathogen-associated molecular patterns (PAMPs) and tissue injury through the endogenous danger-associated molecular patterns (DAMPs). In addition to immunocytes, TLRs are widely distributed in various cell types, including renal cells where they are thought to play a significant role in immune activation to pathogens, as well as the development and course of various kidney pathologies. This review summarizes the present data about the important role TLRs play in kidney diseases focusing on the specific role of PAMPs versus DAMPs and of local versus systemic TLR activation.

The lupus-related Lmb3 locus contains a disease-suppressing Coronin-1A gene mutation

Here, we show that a lupus-suppressing locus is caused by a nonsense mutation of the filamentous actin-inhibiting Coronin-1A gene. This mutation was associated with developmental and functional alterations in T cells including reduced migration, survival, activation, and Ca2+ flux. T-dependent humoral responses were impaired, but no intrinsic B cell defects were detected. By transfer of T cells, it was shown that suppression of autoimmunity could be accounted for by the presence of the Coro1a(Lmb3) mutation in T cells. Our results demonstrate that Coronin-1A is required for the development of systemic lupus and identify actin-cytoskeleton regulatory proteins as potential targets for modulating autoimmune diseases.

Immunomodulation of murine collagen-induced arthritis by N, N-dimethylglycine and a preparation of Perna canaliculus

Background

Rheumatoid arthritis (RA) and its accepted animal model, murine collagen-induced arthritis (CIA), are classic autoimmune inflammatory diseases which require proinflammatory cytokine production for pathogenesis. We and others have previously used N, N-dimethylglycine (DMG) and extracts from the New Zealand green-lipped mussel Perna canaliculus (Perna) as potent immunomodulators to modify ongoing immune and/or inflammatory responses.

Methods

In our initial studies, we treated lipopolysaccahride (LPS) stimulated THP-1 monocytes in vitro with increasing concentrations of Perna extract or DMG. Additionally, we treated rat peripheral blood neutrophils with increasing concentrations of Perna extract and measured superoxide burst. In subsequent in vivo experiments, CIA was induced by administration of type II collagen; rats were prophylactically treated with either Perna or DMG, and then followed for disease severity. Finally, to test whether Perna and/or DMG could block or inhibit an ongoing pathologic disease process, we induced CIA in mice and treated them therapeutically with either of the two immunomodulators.

Results

Following LPS stimulation of THP-1 monocytes, we observed dose-dependent reductions in TNF-α and IL-12p40 production in Perna treated cultures. DMG treatment, however, showed significant increases in both of these cytokines in the range of 0.001–1 μM. We also demonstrate that in vitro neutrophil superoxide burst activity is dose-dependently reduced in the presence of Perna. Significant reductions in disease incidence, onset, and severity of CIA in rats were noted following prophylactic treatment with either of the two immunomodulators. More importantly, amelioration of mouse CIA was observed following therapeutic administration of Perna. In contrast, DMG appeared to have little effect in mice and may act in a species-specific manner.

Conclusion

These data suggest that Perna, and perhaps DMG, may be useful supplements to the treatment of RA in humans.

Inhibition of transmethylation down-regulates CD4 T cell activation and curtails development of autoimmunity in a model system

Transmethylation affects several cellular events, including T cell activation, and blockade of this pathway may curtail inflammatory/autoimmune responses. Here, we demonstrate that transmethylation inhibition by a novel reversible S-adenosyl-l-homocysteine hydrolase inhibitor leads to immunosuppression by reducing phosphorylation of several key proteins involved in TCR signaling, including Akt, Erk1/2, and NF-kappaB. Remarkably, this effect was largely restricted to CD4 T cells and correlated with reduced arginine methylation of Vav1, an essential guanine nucleotide exchange factor in T cell stimulation. Treatment with the transmethylation inhibitor averted, and even ameliorated, the CD4-mediated autoimmune disease, experimental autoimmune encephalomyelitis. The data suggest that transmethylation is required for CD4 T cell activation, and its inhibition may be a novel approach in the treatment of multiple sclerosis, and other CD4-mediated autoimmune diseases.

Intracellular protein modification associated with altered T cell functions in autoimmunity

Posttranslational protein modifications influence a number of immunologic responses ranging from intracellular signaling to protein processing and presentation. One such modification, termed isoaspartyl (isoAsp), is the spontaneous nonenzymatic modification of aspartic acid residues occurring at physiologic pH and temperature. In this study, we have examined the intracellular levels of isoAsp residues in self-proteins from MRL(+/+), MRL/lpr, and NZB/W F(1) mouse strains compared with nonautoimmune B10.BR mice. In contrast to control B10.BR or NZB/W mice, the isoAsp content in MRL autoimmune mice increased and accumulated with age in erythrocytes, brain, kidney, and T lymphocytes. Moreover, T cells that hyperproliferate to antigenic stimulation in MRL mice also have elevated intracellular isoAsp protein content. Protein l-isoaspartate O-methyltransferase activity, a repair enzyme for isoAsp residues in vivo, remains stable with age in all strains of mice. These studies demonstrate a role for the accumulation of intracellular isoAsp proteins associated with T cell proliferative defects of MRL autoimmune mice.

A ReversibleS-Adenosyl-l-Homocysteine Hydrolase Inhibitor Ameliorates Experimental Autoimmune Encephalomyelitis by Inhibiting T Cell Activation

The reversible S-adenosyl-l-homocysteine hydrolase inhibitor DZ2002 [methyl 4-(adenin-9-yl)-2-hydroxybutanoate] suppresses antigen-induced-specific immune responses, particularly type 1 helper T cell (Th1)-type responses. Experimental autoimmune encephalomyelitis (EAE) is thought to be a Th1 cell-mediated inflammatory demyelinating autoimmune disease model of human multiple sclerosis (MS). In this study, we examined the effects of DZ2002 on active EAE induced by myelin oligodendrocyte glycoprotein (MOG) 35-55 in female C57BL/6 mice. Administration of DZ2002 (50 mg/kg/day i.p.) significantly reduced the incidence and severity of EAE, which was associated with the inhibition of MOG35-55-specific T cell proliferation and Th1-type cytokine production. In vitro studies also demonstrated that DZ2002 inhibited anti-CD3/28-induced naive T cell activation concomitant with the down-regulation of cyclin-dependent kinase (CDK) 4, CDK6, cyclin D3, and the up-regulation or protection of the CDK inhibitor p27. These findings highlight the fact that DZ2002 likely prevents EAE by suppressing T cell activation and suggest its utility in the treatment of MS and other Th1-mediated inflammatory diseases.

S-adenosyl-L-homocysteine hydrolase inactivation curtails ovalbumin-induced immune responses

The reversible S-adenosyl-L-homocysteine (AdoHcy) hydrolase inhibitor methyl 4-(adenin-9-yl)-2-hydroxybutanoate (DZ2002) suppresses macrophage activation and function. The effects of DZ2002 on T cell function, however, are still unclear. Here, we examined whether DZ2002 alters type 1 helper T cell (Th1) and/or type 2 helper T cell (Th2) immune responses, and whether these effects are associated with both the inhibition of AdoHcy hydrolase and intracellular elevation of endogenous AdoHcy. Male C57BL/6 mice immunized with ovalbumin (OVA) were treated with DZ2002 (1, 5, and 25 mg/kg/day) after which lymphocyte proliferation, cytokine production, and IgG responses to OVA were monitored. Administration of DZ2002 dose dependently suppressed OVA-specific lymphocyte proliferation and anti-OVA IgG production compared with controls. Interleukin (IL)-2 and interferon (IFN)-gamma as well as anti-OVA IgG2a and IgG3, indicators of Th1 immune responses, were markedly decreased in mice treated with DZ2002, whereas IL-4 and anti-OVA IgG1, indicators of Th2 immune responses, were only mildly suppressed. AdoHcy hydrolase activity in spleens of DZ2002-treated mice was substantially blocked, and not surprisingly, AdoHcy levels were significantly elevated compared with controls. Finally, similar immunosuppressive effects were also observed in mice treated with AdoHcy. These data strongly indicate that DZ2002 suppresses antigen-induced specific immune responses, particularly Th1 responses, through inhibition of AdoHcy hydrolase and elevation of endogenous AdoHcy.

Inhibition ofS-Adenosyl-l-homocysteine Hydrolase Induces Immunosuppression

Lymphocytes depend on transmethylation reactions for efficient activation and function. These reactions are primarily catalyzed by S-adenosylmethionine-dependent methyltransferases, which convert S-adenosylmethionine to S-adenosyl-L-homocysteine. S-adenosyl-L-homocysteine is then hydrolyzed by S-adenosyl-L-homocysteine hydrolase to prevent feedback inhibition of transmethylation reactions. By impeding S-adenosyl-L-homocysteine hydrolase, a build-up of S-adenosyl-L-homocysteine occurs, and most intracellular transmethylation reactions cease. Thus, a nontoxic inhibitor of this enzyme might be a useful immunosuppressive therapeutic agent. We identified a potent reversible type III inhibitor of S-adenosyl-L-homocysteine hydrolase, DZ2002 [methyl 4-(adenin-9-yl)-2-hydroxybutanoate], and determined its cytotoxic and immunologic effects. We demonstrated that DZ2002 blocked S-adenosyl-L-homocysteine hydrolase more effectively than a type I inhibitor, but cytotoxicity from DZ2002 was greatly reduced. Although DZ2002 did not prevent concanavalin A-induced T cell proliferation or interleukin (IL)-2 production, it significantly reduced both a mixed lymphocyte reaction and IL-12 production from in vitro-stimulated splenocytes. In addition, levels of CD80 and CD86 on human monocytic THP-1 cells were decreased in a dose-dependent manner in the presence of 0.1 to 10 microM DZ2002, and decreases were also seen in IL-12 and tumor necrosis factor-alpha production from both mouse thioglycollate-stimulated peritoneal macrophages and THP-1 cells. In vivo, DZ2002 significantly suppressed a delayed-type hypersensitivity reaction as well as antibody secretion. We conclude that DZ2002's immunosuppressive effects are likely not solely attributed to T cell inhibition but also to the obstruction of macrophage activation and function through reductions in cytokine output and/or T cell costimulation. These data suggest an important dual role for the S-adenosyl-l-homocysteine hydrolase in both macrophage and T cell function.

Deficiency of the cyclin kinase inhibitor p21(WAF-1/CIP-1) promotes apoptosis of activated/memory T cells and inhibits spontaneous systemic autoimmunity

A characteristic feature of systemic lupus erythematosus is the accumulation of activated/memory T and B cells. These G₀/G₁-arrested cells express high levels of cyclin-dependent kinase inhibitors such as p21, are resistant to proliferation and apoptosis, and produce large amounts of proinflammatory cytokines. Herein, we show that ablation of p21 in lupus-prone mice allows these cells to reenter the cell cycle and undergo apoptosis, leading to autoimmune disease reduction. Absence of p21 resulted in enhanced Fas/FasL-mediated activation-induced T cell death, increased activation of procaspases 8 and 3, and loss of mitochondrial transmembrane potential. Increased apoptosis was also associated with p53 up-regulation and a modest shift in the ratio of Bax/Bcl-2 toward the proapoptotic Bax. Proliferation and apoptosis of B cells were also increased in p21^−/− lupus mice. Thus, modulation of the cell cycle pathway may be a novel approach to reduce apoptosis-resistant pathogenic lymphocytes and to ameliorate systemic autoimmunity.

T cell homeostatic proliferation elicits effective antitumor autoimmunity

Development of tumor immunotherapies focuses on inducing autoimmune responses against tumor-associated self-antigens primarily encoded by normal, unmutated genes. We hypothesized that such responses could be elicited by T cell homeostatic proliferation in the periphery, involving expansion of T cells recognizing self-MHC/peptide ligands. Herein, we demonstrate that sublethally irradiated lymphopenic mice transfused with autologous or syngeneic T cells showed tumor growth inhibition when challenged with melanoma or colon carcinoma cells. Importantly, the antitumor response depended on homeostatic expansion of a polyclonal T cell population within lymph nodes. This response was effective even for established tumors, was characterized by CD8(+) T cell-mediated tumor-specific cytotoxicity and IFN-gamma production, and was associated with long-term memory. The results indicate that concomitant induction of the physiologic processes of homeostatic T cell proliferation and tumor antigen presentation in lymph nodes triggers a beneficial antitumor autoimmune response.

Deletion of p21 (WAF-1/Cip1) does not induce systemic autoimmunity in female BXSB mice

Cell cycle, apoptosis, and replicative senescence are all influenced by the cyclin-dependent kinase inhibitor, p21. It was previously reported that deletion of p21 in 129/Sv x C57BL/6 mixed genetic background mice induced a severe lupus-like disease, almost exclusively in females. However, we did not confirm this finding in an independently derived stock of 129/Sv x C57BL/6 p21(-/-) mice. To further address this discrepancy, we examined the effects of p21 deletion in BXSB female mice that develop late-life, mild lupus-like disease. Survival, polyclonal Igs, anti-chromatin Abs, and kidney histopathology in these mice were unremarkable and identical to wild-type littermates for up to 14 mo of age. We conclude that p21 deficiency does not promote autoimmunity even in females of a predisposed strain. The findings indicate that the use of mixed background 129/Sv x C57BL/6 mice to study effects of gene deletions in systemic autoimmunity may be confounded by the genetic heterogeneity of this cross. We suggest that studies addressing gene deletion effects in systemic autoimmunity should use sufficiently backcrossed mice to attain genetic homogeneity, include wild-type littermate controls, and preferentially use congenic inbred strains with late-life lupus predisposition to emulate the polygenic nature of this disease.

Thymic dendritic cells traffic to thymi of allogeneic recipients and prolong graft survival

We have demonstrated that murine thymic dendritic cells (DCs) isolated from donor mice have the capability to home to thymi of fully allogeneic recipients after intravenous injections, where they induce T cell deletions and prolong donor-strain airway and skin graft survival. In contrast, infused splenic DCs immigrated poorly to thymi, and did not affect graft survival. These findings suggest that preferential homing may be an important mechanistic difference among subpopulations of DCs that mediate immune functions and illustrate a novel methodology that could have utility for induction of specific immunologic nonreactivity to allografts, or other disease-associated antigens.

Role of cyclin kinase inhibitor p21 in systemic autoimmunity

The cyclin kinase inhibitor protein p21 affects multiple processes relevant to the immune system, including cell cycle progression, replicative senescence, hemopoietic stem cell quiescence, and apoptosis. Therefore, malfunction of this protein may be a contributor to the pathogenesis of systemic autoimmunity. Here, we report that mixed background p21-deficient 129/Sv x C57BL/6 mice showed increased in vitro and in vivo T cell cycling and activation, moderate hypergammaglobulinemia and, at low penetrance, anti-chromatin autoantibodies. Homeostatic anti-self MHC/peptide ligand-induced proliferation of p21-deficient T cells was also enhanced. However, lymphoid organ enlargement was very mild, presumably due to increased apoptosis of the rapidly dividing cells. Moreover, the older p21-deficient mice had kidney pathology representing a similar, but slightly more advanced, state than that seen in the control mice. The timing and severity of the above serologic, cellular, and histologic manifestations in p21-deficient mice were unaffected by gender. Thus, p21 deficiency significantly enhances T cell activation and homeostatic proliferation, and can induce mild autoimmune manifestations at a low incidence without gender bias, but does not in itself generate the full spectrum of lupus-like disease.

Terminal deoxynucleotidyl transferase deficiency decreases autoimmune disease in MRL-Fas(lpr) mice

The neonatal Ab and TCR repertoires are much less diverse, and also very different from, the adult repertoires due to the delayed onset of terminal deoxynucleotidyl transferase (TdT) expression in ontogeny. TdT adds nontemplated N nucleotides to the junctions of Igs and TCRs, and thus its absence removes one of the major components of junctional diversity in complementarity-determining region 3 (CDR3). We have generated TdT-deficient MRL/lpr, Fas-deficient (MRL-Fas(lpr)) mice, and show that they have an increased lifespan, decreased incidence of skin lesions, and much lower serum levels of anti-dsDNA, anti-chromatin, and IgM rheumatoid factors. The generalized hypergammaglobulinemia characteristic of MRL-Fas(lpr) mice is also greatly reduced, as is the percentage of CD4(-)CD8(-)B220(+) (double-negative) T cells. IgG deposits in the kidney are significantly reduced, although evidence of renal disease is present in many mice at 6 mo. CDR3 regions of both IgH and TCR from peripheral lymphocytes of MRL-Fas(lpr) mice are shorter in the absence of TdT, and there is a paucity of arginines in the IgH CDR3 regions of the MRL-Fas(lpr) TdT(-/-) mice. Because the amelioration of symptoms is so widespread, it is likely that the absence of N regions has more of an affect than merely decreasing the precursor frequency of anti-dsDNA B cells. Hence, either the T or B cell repertoires, or more likely both, require N region diversity to produce the full spectrum of autoimmune lupus disease.

The role of alpha beta+ T cells and homeostatic T cell proliferation in Y-chromosome-associated murine lupus

Male BXSB mice develop an early life, severe lupus-like disease largely attributed to an undefined Y-chromosome-associated autoimmunity accelerator, termed YAA: Although the exact disease pathogenesis is uncertain, indirect evidence suggests that T cells play an important role in the male BXSB disease. We have developed TCR alpha-chain gene-deleted BXSB mice to directly examine the role of alphabeta+ T cells and the mode by which Yaa promotes disease in this strain. All disease parameters, including hypergammaglobulinemia, autoantibody production, glomerulonephritis, and the unique monocytosis of BXSB males, were severely reduced or absent in the alphabeta+ T cell-deficient mice. Adoptively transferred CD4+ T cells of either male or female BXSB origin showed equal homeostatic proliferation in alphabeta+ T cell-deficient male recipients. Moreover, deficient male mice eventually developed equally severe lupus-like disease after adoptive transfer and homeostatic expansion of T cells from wild-type BXSB males or females. The results directly demonstrate that the Yaa-mediated disease requires alphabeta+ T cells that are not, in themselves, abnormal in either composition or properties, but are engaged by a Yaa-encoded abnormality in a non-T cell component. In addition, homeostatic anti-self proliferation of mature T cells derived from a small number of precursors can induce systemic autoimmunity in an appropriate background.

Anticytokine gene therapy of autoimmune diseases

Viral and nonviral gene therapy vectors have been successfully employed to deliver inflammatory cytokine inhibitors (anticytokines), or anti-inflammatory cytokines, such as transforming growth factor beta-1 (TGF-beta 1), which protect against experimental autoimmune diseases. These vectors carry the relevant genes into a variety of tissues, for either localised or systemic release of the encoded protein. Administration of cDNA encoding soluble IFN-gamma receptor (IFN-gamma R)/IgG-Fc fusion proteins, soluble TNF-alpha receptors, or IL-1 receptor antagonist (IL-1ra), protects against either lupus, various forms of arthritis, autoimmune diabetes, or other autoimmune diseases. These inhibitors, unlike many cytokines, have little or no toxic potential. Similarly, TGF-beta 1 gene therapy protects against numerous forms of autoimmunity, though its administration entails more risk than anticytokine therapy. We have relied on the injection of naked plasmid DNA into skeletal muscle, with or without enhancement of gene transfer by in vivo electroporation. Expression plasmids offer interesting advantages over viral vectors, since they are simple to produce, non-immunogenic and nonpathogenic. They can be repeatedly administered and after each treatment the encoded proteins are produced for relatively long periods, ranging from weeks to months. Moreover, soluble receptors which block cytokine action, encoded by gene therapy vectors, can be constructed from non-immunogenic self elements that are unlikely to be neutralised by the host immune response (unlike monoclonal antibodies [mAbs]), allowing long-term gene therapy of chronic inflammatory disorders.

Immunotherapeutic gene transfer into muscle

Immuno-gene therapy can be advantageously performed with nonviral approaches. Genes that encode regulatory cytokines or inflammatory cytokine inhibitors can be delivered intramuscularly and expressed for weeks or months. This type of gene transfer into muscle has been shown to ameliorate several autoimmune diseases and is relevant to the development of effective DNA vaccines in autoimmune diseases, infectious diseases and cancer.

The role of IFN-gamma in systemic lupus erythematosus: a challenge to the Th1/Th2 paradigm in autoimmunity

The classification of T helper cells into type 1 (Th1) and type 2 (Th2) led to the hypothesis that Th1 cells and their cytokines (interleukin [IL]-2, interferon [IFN]-gamma) are involved in cell-mediated autoimmune diseases, and that Th2 cells and their cytokines (IL-4, IL-5, IL-10, IL-13) are involved in autoantibody(humoral)-mediated autoimmune diseases. However, this paradigm has been refuted by recent studies in several induced and spontaneous mouse models of systemic lupus erythematosus, which showed that IFN-gamma is a major effector molecule in this disease. These and additional findings, reviewed here, suggest that these two cross-talking classes of cytokines can exert autoimmune disease-promoting or disease-inhibiting effects without predictability or strict adherence to the Th1-versus-Th2 dualism.

Treatment of murine lupus with cDNA encoding IFN-gammaR/Fc

IFN-gamma, a pleiotropic cytokine, is a key effector molecule in the pathogenesis of several autoimmune diseases, including lupus. Importantly, deletion of IFN-gamma or IFN-gammaR in several lupus-predisposed mouse strains resulted in significant disease reduction, suggesting the potential for therapeutic intervention. We evaluated whether intramuscular injections of plasmids with cDNA encoding IFN-gammaR/Fc can retard lupus development and progression in MRL-Fas(lpr) mice. Therapy significantly reduced serum levels of IFN-gamma, as well as disease manifestations (autoantibodies, lymphoid hyperplasia, glomerulonephritis, mortality), when treatment was initiated at the predisease stage, particularly when IFN-gammaR/Fc expression was enhanced by electroporation at the injection site. Remarkably, disease was arrested and even ameliorated when this treatment was initiated at an advanced stage. This therapy represents a rare example of disease reversal and makes application of this nonviral gene therapy in humans with lupus (and perhaps other autoimmune/inflammatory conditions) highly promising.