Repeated administration of dapirolizumab pegol in a randomised phase I study is well tolerated and accompanied by improvements in several composite measures of systemic lupus erythematosus disease activity and changes in whole blood transcriptomic profiles.

OBJECTIVES: Systemic lupus erythematosus (SLE) is a heterogeneous autoimmune disease associated with diffuse immune cell dysfunction. CD40-CD40 ligand (CD40L) interaction activates B cells, antigen-presenting cells and platelets. CD40L blockade might provide an innovative treatment for systemic autoimmune disorders. We investigated the safety and clinical activity of dapirolizumab pegol, a polyethylene glycol conjugated anti-CD40L Fab' fragment, in patients with SLE. METHODS: This 32-week randomised, double-blind, multicentre study (NCT01764594) evaluated repeated intravenous administration of dapirolizumab pegol in patients with SLE who were positive for/had history of antidouble stranded DNA/antinuclear antibodies and were on stable doses of immunomodulatory therapies (if applicable). Sixteen patients were randomised to 30 mg/kg dapirolizumab pegol followed by 15 mg/kg every 2 weeks for 10 weeks; eight patients received a matched placebo regimen. Randomisation was stratified by evidence of antiphospholipid antibodies. Patients were followed for 18 weeks after the final dose. RESULTS: No serious treatment-emergent adverse events, thromboembolic events or deaths occurred. Adverse events were mild or moderate, transient and resolved without intervention. One patient withdrew due to infection.Efficacy assessments were conducted only in patients with high disease activity at baseline. Five of 11 (46%) dapirolizumab pegol-treated patients achieved British Isles Lupus Assessment Group-based Composite Lupus Assessment response (vs 1/7; 14% placebo) and 5/12 (42%) evaluable for SLE Responder Index-4 responded by week 12 (vs 1/7; 14% placebo). Mechanism-related gene expression changes were observed in blood RNA samples. CONCLUSIONS: Dapirolizumab pegol could be an effective biological treatment for SLE. Further studies are required to address efficacy and safety. TRIAL REGISTRATION NUMBER: NCT01764594.

Alterations in urinary collagen peptides in lupus nephritis subjects correlate with renal dysfunction and renal histopathology.

BACKGROUND: The excessive accumulation of extracellular matrix (ECM) in the renal tubulointerstitium is a key component of chronic renal damage in lupus nephritis (LN) and a critical determinant of the disease progression to renal failure. Detection of fibrosis requires renal biopsy and is therefore limited by high risks associated with an invasive procedure. This study explores whether a unique LN urinary peptidome can be identified and whether LN-specific alteration reflects the underlying fibrogenic process of altered ECM turnover. METHOD: Urinary peptides were analyzed for 36 LN and 35 nonrenal systemic lupus erythematosus (SLE) subjects and 58 healthy volunteers (HVs). RESULTS: In total, 70 collagen and 230 noncollagen peptides were significantly changed between LN and nonrenal SLE and between LN and HV and defined as 'LN peptides'; 14 proteases associated with observed LN collagen peptides were identified and activities in 9 proteases were significantly different between LN and nonrenal SLE; 28 collagen peptides were correlated with at least one parameter of clinical renal dysfunction or histolopathology. CONCLUSION: Urinary peptidomic alterations likely reflect pathogenic pathways involving ECM turnover in LN kidneys and potentially could be developed as biomarkers to monitor renal disease progression.

The lymphotoxin ß receptor is a potential therapeutic target in renal inflammation.

Accumulation of inflammatory cells in different renal compartments is a hallmark of progressive kidney diseases including glomerulonephritis (GN). Lymphotoxin ß receptor (LTßR) signaling is crucial for the formation of lymphoid tissue, and inhibition of LTßR signaling has ameliorated several non-renal inflammatory models. Therefore, we tested whether LTßR signaling could also have a role in renal injury. Renal biopsies from patients with GN were found to express both LTα and LTß ligands, as well as LTßR. The LTßR protein and mRNA were localized to tubular epithelial cells, parietal epithelial cells, crescents, and cells of the glomerular tuft, whereas LTß was found on lymphocytes and tubular epithelial cells. Human tubular epithelial cells, mesangial cells, and mouse parietal epithelial cells expressed both LTα and LTß mRNA upon stimulation with TNF in vitro. Several chemokine mRNAs and proteins were expressed in response to LTßR signaling. Importantly, in a murine lupus model, LTßR blockade improved renal function without the reduction of serum autoantibody titers or glomerular immune complex deposition. Thus, a preclinical mouse model and human studies strongly suggest that LTßR signaling is involved in renal injury and may be a suitable therapeutic target in renal diseases.

Donor B-cell alloantibody deposition and germinal center formation are required for the development of murine chronic GVHD and bronchiolitis obliterans.

Chronic GVHD (cGVHD) poses a significant risk for HSCT patients. Preclinical development of new therapeutic modalities has been hindered by models with pathologic findings that may not simulate the development of human cGVHD. Previously, we have demonstrated that cGVHD induced by allogeneic HSCT after a conditioning regimen of cyclophosphamide and total-body radiation results in pulmonary dysfunction and airway obliteration, which leads to bronchiolitis obliterans (BO), which is pathognomonic for cGVHD of the lung. We now report cGVHD manifestations in a wide spectrum of target organs, including those with mucosal surfaces. Fibrosis was demonstrated in the lung and liver and was associated with CD4(+) T cells and B220(+) B-cell infiltration and alloantibody deposition. Donor bone marrow obtained from mice incapable of secreting IgG alloantibody resulted in less BO and cGVHD. Robust germinal center reactions were present at the time of cGVHD disease initiation. Blockade of germinal center formation with a lymphotoxin-receptor-immunoglobulin fusion protein suppressed cGVHD and BO. We conclude that cGVHD is caused in part by alloantibody secretion, which is associated with fibrosis and cGVHD manifestations including BO, and that treatment with a lymphotoxin-ß receptor-immunoglobulin fusion protein could be beneficial for cGVHD prevention and therapy.

Results from a Phase 1 Study of ACTR707 in Combination with Rituximab in Patients with Relapsed or Refractory CD20+ B Cell Lymphoma.

The antibody-coupled T cell receptor (ACTR) platform is an autologous engineered T cell therapy combining the cell-killing ability of T cells and the tumor-targeting ability of coadministered antibodies. Activation of the T cell product ACTR707 is dependent on the engagement of antibody bound to target cells via the CD16 domain of the chimeric receptor (CD16V-CD28-CD3ζ). ACTR707 in combination with the anti-CD20 monoclonal antibody rituximab was evaluated in the ATTCK-20-03 study, a multisite, single-arm, open-label phase I trial in B cell non-Hodgkin lymphoma (NHL). The primary objectives of this study were to evaluate the safety of the combination of ACTR707 and rituximab and to determine a recommended phase 2 dose (RP2D). Secondary objectives included evaluation of antitumor activity and ACTR T cell persistence. The study design included an ACTR707 cell dose escalation phase and an expansion phase at the RP2D. Escalating dose levels of ACTR707 in combination with rituximab were explored in 5 dose cohorts, with 25 subjects receiving study treatment. Subjects received lymphodepleting chemotherapy (cyclophosphamide 400 mg/m2/day and fludarabine 30 mg/m2/day) for 3 days, followed by rituximab 375 mg/m2 and, 24 to 48 hours later, a single dose of ACTR707. Additional doses of rituximab were administered every 3 weeks until disease progression, unacceptable toxicity, or investigator decision. Blood samples were collected at various time points to assess levels of rituximab, cytokines, inflammatory markers, and ACTR707 T cells. The overall response rate of ACTR707 plus rituximab was 56% (14 of 25) across all dose levels. Ten subjects (40.0%) achieved a complete response, with the longest duration of 586 days (range, 85 to 586 days), and 4 subjects (16.0%) experienced a partial response, with the longest duration of 130 days (range, 44 to 130 days). Only 1 case of cytokine release syndrome (grade 2) and no events of neurotoxicity were reported. There were no dose-limiting toxicities or events leading to death. ACTR707 plus rituximab resulted in only 1 adverse event (neutropenia), leading to study discontinuation of rituximab. The ATTCK-20-03 trial serves as proof of principle regarding the ACTR approach that potentially could be used with other antibodies targeting other markers in other malignancies. Although the ACTR707 program has been discontinued, these results may support other programs in the use of similar novel approaches of antibody-coupled T cell activation.

BAD and glucokinase reside in a mitochondrial complex that integrates glycolysis and apoptosis.

Glycolysis and apoptosis are considered major but independent pathways that are critical for cell survival. The activity of BAD, a pro-apoptotic BCL-2 family member, is regulated by phosphorylation in response to growth/survival factors. Here we undertook a proteomic analysis to assess whether BAD might also participate in mitochondrial physiology. In liver mitochondria, BAD resides in a functional holoenzyme complex together with protein kinase A and protein phosphatase 1 (PP1) catalytic units, Wiskott-Aldrich family member WAVE-1 as an A kinase anchoring protein, and glucokinase (hexokinase IV). BAD is required to assemble the complex in that Bad-deficient hepatocytes lack this complex, resulting in diminished mitochondria-based glucokinase activity and blunted mitochondrial respiration in response to glucose. Glucose deprivation results in dephosphorylation of BAD, and BAD-dependent cell death. Moreover, the phosphorylation status of BAD helps regulate glucokinase activity. Mice deficient for BAD or bearing a non-phosphorylatable BAD(3SA) mutant display abnormal glucose homeostasis including profound defects in glucose tolerance. This combination of proteomics, genetics and physiology indicates an unanticipated role for BAD in integrating pathways of glucose metabolism and apoptosis.

Survival factor-mediated BAD phosphorylation raises the mitochondrial threshold for apoptosis.

Growth factor suppression of apoptosis correlates with the phosphorylation and inactivation of multiple proapoptotic proteins, including the BCL-2 family member BAD. However, the physiological events required for growth factors to block cell death are not well characterized. To assess the contribution of BAD inactivation to cell survival, we generated mice with point mutations in the BAD gene that abolish BAD phosphorylation at specific sites. We show that BAD phosphorylation protects cells from the deleterious effects of apoptotic stimuli and attenuates death pathway signaling by raising the threshold at which mitochondria release cytochrome c to induce cell death. These findings establish a function for endogenous BAD phosphorylation, and elucidate a mechanism by which survival kinases block apoptosis in vivo.

Association between changes in gene signatures expression and disease activity among patients with systemic lupus erythematosus.

BACKGROUND: We assessed the stability of BAFF, interferon, plasma cell and LDG neutrophil gene expression signatures over time, and whether changes in expression coincided with changes in SLE disease activity. METHODS: Two hundred forty-three patients with SLE were evaluated for disease activity, serological parameters and peripheral blood gene signatures in clinic visits (2 or more per patient) that occurred between 2009 and 2012. Levels of the BAFF gene transcript, plasma cell signature, Interferon (IFN) signature and the low density granulocytes (LDG)-associated neutrophil gene signature were assessed in PAX-gene-preserved peripheral blood by global microarray. The stability of repeated measures of gene expression was quantified using intra-class correlation coefficients. SLE disease activity was measured using the Physicians Global Assessment and the SELENA-SLEDAI index and its components. Using a mixed effects regression model we assessed: 1) the association between a patient's average gene signature expression over time and disease activity, and 2) the association between a patient's changes in gene expression over time and changes in disease activity. RESULTS: Gene expression signatures showed more within-person stability than systolic blood pressure. The IFN signature exhibited the most stability. Patients with high levels of BAFF and IFN transcripts tended to have significantly higher levels of musculoskeletal disease, skin disease, anti-dsDNA, and erythrocyte sedimentation rate, and lower levels of complement. However, changes in BAFF or IFN gene signatures were not associated with changes in disease activity. Similar associations were seen between the LDG gene signature and disease activity. However, when LDG increased, complement tended to increase. Patients with high levels of plasma cell gene signature tended to have higher levels of anti-dsDNA and lower levels of complement. However, unlike the other gene signatures, changes in plasma cell gene signature significantly coincided with changes in anti-dsDNA and complement. CONCLUSIONS: The gene expression signatures were relatively stable within patients over time. BAFF and interferon gene expression were markers of patients with generally higher disease activity, but changes in these gene signatures did not coincide with changes in disease activity. Plasma Cell gene signature expression tracked with the traditional SLE serologic markers of anti-dsDNA and complement.

Anti-LINGO-1 has no detectable immunomodulatory effects in preclinical and phase 1 studies.

OBJECTIVE: To evaluate whether the anti-LINGO-1 antibody has immunomodulatory effects. METHODS: Human peripheral blood mononuclear cells (hPBMCs), rat splenocytes, and rat CD4+ T cells were assessed to determine whether LINGO-1 was expressed and was inducible. Anti-LINGO-1 Li81 (0.1-30 µg/mL) effect on proliferation/cytokine production was assessed in purified rat CD4+ T cells and hPBMCs stimulated with antibodies to CD3 +/- CD28. In humans, the effect of 2 opicinumab (anti-LINGO-1/BIIB033; 30, 60, and 100 mg/kg) or placebo IV administrations was evaluated in RNA from blood and CSF samples taken before and after administration in phase 1 clinical trials; paired samples were assessed for differentially expressed genes by microarray. RNA from human CSF cell pellets was analyzed by quantitative real-time PCR for changes in transcripts representative of cell types, activation markers, and soluble proteins of the adaptive/innate immune systems. ELISA quantitated the levels of CXCL13 protein in human CSF supernatants. RESULTS: LINGO-1 is not expressed in hPBMCs, rat splenocytes, or rat CD4+ T cells; LINGO-1 blockade with Li81 did not affect T-cell proliferation or cytokine production from purified rat CD4+ T cells or hPBMCs. LINGO-1 blockade with opicinumab resulted in neither significant changes in immune system gene expression in blood and CSF, nor changes in CXCL13 CSF protein levels (clinical studies). CONCLUSIONS: These data support the hypothesis that LINGO-1 blockade does not affect immune function. CLASSIFICATION OF EVIDENCE: This study provides Class II evidence that in patients with MS, opicinumab does not have immunomodulatory effects detected by changes in immune gene transcript expression.

Clinical Application of a Modular Genomics Technique in Systemic Lupus Erythematosus: Progress towards Precision Medicine.

Monitoring disease activity in a complex, heterogeneous disease such as lupus is difficult. Both over- and undertreatment lead to damage. Current standard of care serologies are unreliable. Better measures of disease activity are necessary as we move into the era of precision medicine. We show here the use of a data-driven, modular approach to genomic biomarker development within lupus-specifically lupus nephritis.

Pristane-Accelerated Autoimmune Disease in (SWR X NZB) F1 Mice Leads to Prominent Tubulointerstitial Inflammation and Human Lupus Nephritis-Like Fibrosis.

Mouse models lupus nephritis (LN) have provided important insights into disease pathogenesis, although none have been able to recapitulate all features of the human disease. Using comprehensive longitudinal analyses, we characterized a novel accelerated mouse model of lupus using pristane treatment in SNF1 (SWR X NZB F1) lupus prone mice (pristane-SNF1 mice). Pristane treatment in SNF1 mice accelerated the onset and progression of proteinuria, autoantibody production, immune complex deposition and development of renal lesions. At week 14, the pristane-SNF1 model recapitulated kidney disease parameters and molecular signatures seen in spontaneous disease in 36 week-old SNF1 mice and in a traditional IFNα-accelerated NZB X NZW F1 (BWF1) model. Blood transcriptome analysis revealed interferon, plasma cell, neutrophil, T-cell and protein synthesis signatures in the pristane-SNF1 model, all known to be present in the human disease. The pristane-SNF1 model appears to be particularly useful for preclinical research, robustly exhibiting many characteristics reminiscent of human disease. These include i) a stronger upregulation of the cytosolic nucleic acid sensing pathway, which is thought to be key component of the pathogenesis of the human disease, and ii) more prominent kidney interstitial inflammation and fibrosis, which have been both associated with poor prognosis in human LN. To our knowledge, this is the only accelerated model of LN that exhibits a robust tubulointerstitial inflammatory and fibrosis response. Taken together our data show that the pristane-SNF1 model is a novel accelerated model of LN with key features similar to human disease.

BAFF (B cell activating factor) transcript level in peripheral blood of patients with SLE is associated with same-day disease activity as well as global activity over the next year.

OBJECTIVES: Quantitating gene expression is a potential method of developing biomarkers in systemic lupus erythematosus (SLE). Because of the known pathological role of B cell activating factor (BAFF) in SLE, we explored the association between BAFF gene expression and clinical activity in SLE. METHODS: A total of 275 patients with SLE completed this phase of a prospective observational study. At entry into the study, the BAFF gene expression levels were determined in peripheral blood RNA. Serum concentration of BAFF protein was also measured. We then determined clinical associations with SLE disease history, SLE activity on the same day and SLE activity over the course of the next year. RESULTS: Elevated BAFF gene expression was associated with a history of more leucopenia and serologically with more autoantibodies (anti-dsDNA, anti-Sm, anti-Ro, anti-La and anti-RNP) and low complement. Patients with higher amounts of BAFF transcript had higher measured levels of clinical disease activity. Initial high levels of BAFF gene expression also predicted increased disease activity over the course of the next year. In contrast, serum concentration of BAFF protein was not strongly associated with same-day global disease activity or with future disease activity. CONCLUSIONS: BAFF gene expression level is associated with clinical and serological SLE activity on the same day and predictive of clinical activity over the next year. BAFF gene expression is a better measure and predictor of SLE disease activity than the serum BAFF protein level.

Longitudinal analysis of peripheral blood T cell receptor diversity in patients with systemic lupus erythematosus by next-generation sequencing.

INTRODUCTION: T cells play an important role in the pathogenesis of systemic lupus erythematosus (SLE). Clonal expansion of T cells correlating with disease activity has been observed in peripheral blood (PB) of SLE subjects. Recently, next-generation sequencing (NGS) of the T cell receptor (TCR) ß loci has emerged as a sensitive way to measure the T cell repertoire. In this study, we utilized NGS to assess whether changes in T cell repertoire diversity in PB of SLE patients correlate with or predict changes in disease activity. METHODS: Total RNA was isolated from the PB of 11 SLE patients. Each subject had three samples, collected at periods of clinical quiescence and at a flare. Twelve age-matched healthy controls (HC) were used for reference. NGS was used to profile the complementarity-determining region 3 (CDR3) of the rearranged TCR ß loci. RESULTS: Relative to the HC, SLE patients (at quiescence) demonstrated a 2.2-fold reduction in repertoire diversity in a given PB volume (P <0.0002), a more uneven distribution of the repertoire (Gini coefficient, HC vs SLE, P = 0.015), and a trend toward increased percentage of expanded clones in the repertoire (clone size >1.0%, HC vs SLE, P = 0.078). No significant correlation between the overall repertoire diversity and clinical disease activity was observed for most SLE patients with only two of eleven SLE patients showing a decreasing trend in repertoire diversity approaching the flare time point. We did not observe any overlap of CDR3 amino acid sequences or a preferential Vß or Jß gene usage among the top 100 expanded clones from all SLE patients. In both HC and SLE, the majority of the expanded clones were remarkably stable over time (HC = 5.5 ±0.5 months, SLE = 7.2 ±2.4 months). CONCLUSIONS: A significant decrease in T cell repertoire diversity was observed in PB of SLE patients compared to HC. However, in most SLE patients, repertoire diversity did not change significantly with increases in disease activity to a flare. Thus, without a priori knowledge of disease-specific clones, monitoring TCR repertoire in PB from SLE patients is not likely to be useful to predict changes in disease activity.

Anti-BDCA2 monoclonal antibody inhibits plasmacytoid dendritic cell activation through Fc-dependent and Fc-independent mechanisms.

Type I interferons (IFN-I) are implicated in the pathogenesis of systemic lupus erythematosus (SLE). In SLE, immune complexes bind to the CD32a (FcγRIIa) receptor on the surface of plasmacytoid dendritic cells (pDCs) and stimulate the secretion of IFN-I from pDCs. BDCA2 is a pDC-specific receptor that, when engaged, inhibits the production of IFN-I in human pDCs. BDCA2 engagement, therefore, represents an attractive therapeutic target for inhibiting pDC-derived IFN-I and may be an effective therapy for the treatment of SLE. In this study, we show that 24F4A, a humanized monoclonal antibody (mAb) against BDCA2, engages BDCA2 and leads to its internalization and the consequent inhibition of TLR-induced IFN-I by pDCs in vitro using blood from both healthy and SLE donors. These effects were confirmed in vivo using a single injection of 24F4A in cynomolgus monkeys. 24F4A also inhibited pDC activation by SLE-associated immune complexes (IC). In addition to the inhibitory effect of 24F4A through engagement of BDCA2, the Fc region of 24F4A was critical for potent inhibition of IC-induced IFN-I production through internalization of CD32a. This study highlights the novel therapeutic potential of an effector-competent anti-BDCA2 mAb that demonstrates a dual mechanism to dampen pDC responses for enhanced clinical efficacy in SLE.

Feasibility of the use of combinatorial chemokine arrays to study blood and CSF in multiple sclerosis.

Meningeal inflammation, including the presence of semi-organized tertiary lymphoid tissue, has been associated with cortical pathology at autopsy in secondary progressive multiple sclerosis (SPMS). Accessible and robust biochemical markers of cortical inflammation for use in SPMS clinical trials are needed. Increased levels of chemokines in the cerebrospinal fluid (CSF) can report on inflammatory processes occurring in the cerebral cortex of MS patients. A multiplexed chemokine array that included BAFF, a high sensitivity CXCL13 assay and composite chemokine scores were developed to explore differences in lymphoid (CXCL12, CXCL13, CCL19 and CCL21) and inflammatory (CCL2, CXCL9, CXCL10 and CXCL11) chemokines in a small pilot study. Paired CSF and serum samples were obtained from healthy controls (n=12), relapsing-remitting MS (RRMS) (n=21) and SPMS (N=12). A subset of the RRMS patients (n = 9) was assessed upon disease exacerbation and 1 month later following iv methylprednisone. SPMS patients were sampled twice to ascertain stability. Both lymphoid and inflammatory chemokines were elevated in RRMS and SPMS with the highest levels found in the active RRMS group. Inflammatory and lymphoid chemokine signatures were defined and generally correlated with each other. This small exploratory clinical study shows the feasibility of measuring complex and potentially more robust chemokine signatures in the CSF of MS patients during clinical trials. No differences were found between stable RRMS and SPMS. Future trials with larger patient cohorts with this chemokine array are needed to further characterize the differences, or the lack thereof, between stable RRMS and SPMS.

Mice overexpressing BAFF develop a commensal flora-dependent, IgA-associated nephropathy.

B cell activation factor of the TNF family (BAFF) is a potent B cell survival factor. BAFF overexpressing transgenic mice (BAFF-Tg mice) exhibit features of autoimmune disease, including B cell hyperplasia and hypergammaglobulinemia, and develop fatal nephritis with age. However, basal serum IgA levels are also elevated, suggesting that the pathology in these mice may be more complex than initially appreciated. Consistent with this, we demonstrate here that BAFF-Tg mice have mesangial deposits of IgA along with high circulating levels of polymeric IgA that is aberrantly glycosylated. Renal disease in BAFF-Tg mice was associated with IgA, because serum IgA was highly elevated in nephritic mice and BAFF-Tg mice with genetic deletion of IgA exhibited less renal pathology. The presence of commensal flora was essential for the elevated serum IgA phenotype, and, unexpectedly, commensal bacteria-reactive IgA antibodies were found in the blood. These data illustrate how excess B cell survival signaling perturbs the normal balance with the microbiota, leading to a breach in the normal mucosal-peripheral compartmentalization. Such breaches may predispose the nonmucosal system to certain immune diseases. Indeed, we found that a subset of patients with IgA nephropathy had elevated serum levels of a proliferation inducing ligand (APRIL), a cytokine related to BAFF. These parallels between BAFF-Tg mice and human IgA nephropathy may provide a new framework to explore connections between mucosal environments and renal pathology.

Activation of BAD by therapeutic inhibition of epidermal growth factor receptor and transactivation by insulin-like growth factor receptor.

Novel cancer chemotherapeutics are required to induce apoptosis by activating pro-apoptotic proteins. Both epidermal growth factor (EGF) and insulin-like growth factor (IGF) provide potent survival stimuli in many epithelia, and activation of their receptors is commonly observed in solid human tumors. Here we demonstrate that blockade of the EGF receptor by a new drug in phase III clinical trails for cancer, ZD1839, potently induces apoptosis in mammary epithelial cell lines and primary cultures, as well as in a primary pleural effusion from a breast cancer patient. We identified the mechanism of apoptosis induction by ZD1839. We showed that it prevents cell survival by activating the pro-apoptotic protein BAD. Moreover, we demonstrate that IGF transactivates the EGF receptor and that ZD1839 blocks IGF-mediated phosphorylation of MAPK and BAD. Many cancer therapies kill tumor cells by inducing apoptosis as a consequence of targeting DNA; however, the threshold at which apoptosis can be triggered through DNA damage is often different from that in normal cells. Our results indicate that by targeting a growth factor-mediated survival signaling pathway, BAD phosphorylation can be manipulated therapeutically to induce apoptosis.

BAD is a pro-survival factor prior to activation of its pro-apoptotic function.

The mammalian BAD protein belongs to the BH3-only subgroup of the BCL-2 family. In contrast to its known pro-apoptotic function, we found that endogenous and overexpressed BAD(L) can inhibit cell death in neurons and other cell types. Several mechanisms regulate the conversion of BAD from an anti-death to a pro-death factor, including alternative splicing that produces the N-terminally truncated BAD(S). In addition, caspases convert BAD(L) into a pro-death fragment that resembles the short splice variant. The caspase site that is selectively cleaved during cell death following growth factor (interleukin-3) withdrawal is conserved between human and murine BAD. A second cleavage site that is required for murine BAD to promote death following Sindbis virus infection, gamma-irradiation, and staurosporine treatment is not conserved in human BAD, consistent with the inability of human BAD to promote death with these stimuli. However, loss of the BAD N terminus by any mechanism is not always sufficient to activate its pro-death activity, suggesting that the N terminus is a regulatory domain rather than an anti-death domain. These findings suggest that BAD is more than an inert death factor in healthy cells; it is also a pro-survival factor, prior to its role in promoting cell death.

Bad-deficient mice develop diffuse large B cell lymphoma.

The proapoptotic activity of the "BH3-only" molecule BAD can be differentially regulated by survival factor signaling. Bad-deficient mice lacking both BAD long and BAD short proteins proved viable, and most cell types appeared to develop normally. BAD did not exclusively account for cell death after withdrawal of survival factors, but it was an intermediate for epidermal growth factor- or insulin-like growth factor I-countered apoptosis, consistent with a "sensitizing" BH3-only molecule. Lymphocytes developed normally with no premalignant hyperplasia, but they displayed subtle abnormalities in proliferation and IgG production. Despite the minimal phenotype, Bad-deficient mice progressed, with aging, to diffuse large B cell lymphoma of germinal center origin. Exposure of Bad-null mice to sublethal gamma-irradiation resulted in an increased incidence of pre-T cell and pro-/pre-B cell lymphoblastic leukemia/lymphoma. Thus, proapoptotic BAD suppresses tumorigenesis in the lymphocyte lineage.