Efficacy and safety of sequential therapy with subcutaneous belimumab and one cycle of rituximab in patients with systemic lupus erythematosus: the phase 3, randomised, placebo-controlled BLISS-BELIEVE study.

OBJECTIVES: Disease activity control in patients with systemic lupus erythematosus (SLE) with corticosteroid and immunosuppressant withdrawal is a treatment goal. We evaluated whether this could be attained with sequential subcutaneous belimumab (BEL) and one cycle of rituximab (RTX). METHODS: In this phase 3, double-blind BLISS-BELIEVE trial (GSK Study 205646), patients with active SLE initiating subcutaneous BEL 200 mg/week for 52 weeks were randomised to intravenous placebo (BEL/PBO) or intravenous RTX 1000 mg (BEL/RTX) at weeks 4 and 6 while stopping concomitant immunosuppressants/tapering corticosteroids; standard therapy for 104 weeks (BEL/ST; reference arm) was included. PRIMARY ENDPOINT: proportion of patients achieving disease control (SLE Disease Activity Index-2000 (SLEDAI-2K) ≤2; without immunosuppressants; prednisone equivalent ≤5 mg/day) at week 52 with BEL/RTX versus BEL/PBO. Major (alpha-controlled) secondary endpoints: proportion of patients with clinical remission (week 64; clinical SLEDAI-2K=0, without immunosuppressants/corticosteroids); proportion of patients with disease control (week 104). Other assessments: disease control duration, anti-dsDNA antibody, C3/C4 and B cells/B-cell subsets. RESULTS: The modified intention-to-treat population included 263 patients. Overall, 16.7% (12/72) of BEL/PBO and 19.4% (28/144) of BEL/RTX patients achieved disease control (OR (95% CI) 1.27 (0.60 to 2.71); p=0.5342) at week 52. For major secondary endpoints, differences between BEL/RTX and BEL/PBO were not statistically significant. Anti-dsDNA antibodies and most assessed B cells/B-cell subsets were lower with BEL/RTX versus BEL/PBO. Mean disease control duration through 52 weeks was significantly greater with BEL/RTX versus BEL/PBO. CONCLUSIONS: BEL/RTX showed no superiority over BEL/PBO for most endpoints analysed; however, it led to significant improvements in disease activity markers compared with BEL/PBO. Further investigation of combination treatment is warranted. TRIAL REGISTRATION NUMBER: NCT03312907.

Disruption of memory B-cell trafficking by belimumab in patients with systemic lupus erythematosus.

OBJECTIVES: Autoreactive memory B cells (MBCs) contribute to chronic and progressive courses in autoimmune diseases like SLE. The efficacy of belimumab (BEL), the first approved biologic treatment for SLE and LN, is generally attributed to depletion of activated naïve B cells and inhibition of B-cell activation. BEL's effect on MBCs is currently unexplained. We performed an in-depth cellular and transcriptomic analysis of BEL's impact on the blood MBC compartment in patients with SLE. METHODS: A retrospective meta-analysis was conducted, pooling flow cytometry data from four randomized trials involving 1245 patients with SLE treated with intravenous BEL or placebo. Then, extensive MBC phenotyping was performed using high-sensitivity flow cytometry in patients with mild/moderate SLE and severe SLE/LN treated with subcutaneous BEL. Finally, transcriptomic characterization of surging MBCs was performed by single-cell RNA sequencing. RESULTS: In BEL-treated patients, a significant increase in circulating MBCs, in a broad range of MBC subsets, was established at week 2, gradually returning to baseline by week 52. The increase was most prominent in patients with higher SLE disease activity, serologically active patients and patients aged ≤18 years. MBCs had a non-proliferating phenotype with a prominent decrease in activation status and downregulation of numerous migration genes. CONCLUSION: Upon BEL initiation, an increase of MBCs was firmly established. In the small cohort investigated, circulating MBCs were de-activated, non-proliferative and demonstrated characteristics of disrupted lymphocyte trafficking, expanding on our understanding of the therapeutic mechanism of B-cell-activating factor inhibition by BEL. TRIAL REGISTRATION: ClinicalTrials.gov, http://clinicaltrials.gov, NCT00071487, NCT00410384, NCT01632241, NCT01649765, NCT03312907, NCT03747159.

10 Years of belimumab experience: What have we learnt?

Systemic lupus erythematosus (SLE) is a chronic autoimmune inflammatory disease affecting both adults and children. Belimumab is the only biologic approved for SLE, and the first in a class of drugs known as B-lymphocyte stimulator-specific inhibitors. The introduction of intravenous belimumab in 2011 was a major advance, being the first new therapy approved for SLE in over 50 years. As of April 2021, more than 7200 people with SLE have received belimumab in clinical studies, and it is approved in over 75 countries for the treatment of adults with SLE. A subcutaneous, self-injectable belimumab formulation was licensed in 2017 by both the US Food and Drug Administration (FDA) and European Medicines Agency (EMA). Belimumab was then approved for use in children in Europe, the USA and Japan in 2019, and China and Brazil in 2020. Recently, belimumab became the first FDA-approved drug for the treatment of adults with active lupus nephritis (LN), the most-common severe manifestation of SLE.Over the past 10 years, belimumab has established its position as a disease modifier in the SLE treatment paradigms. Robust evidence from randomised clinical studies and observational, real-world studies has demonstrated the tolerability and efficacy of belimumab for reducing disease activity and the risk of new, severe SLE flares. This enables patients to taper their glucocorticoid use, which limits damage accumulation. Significantly more patients with active LN met the criteria for renal responses and were at less risk of a renal-related event or death after receiving belimumab plus standard therapy, compared with standard therapy on top of mandatory steroid reduction. Ongoing clinical studies are evaluating belimumab's effectiveness in various indications beyond SLE. Post-marketing and registry studies are gathering additional data on key areas such as pregnancy outcomes after belimumab exposure and belimumab co-administration with other biologics.

Treating Opioid Use Disorder With a Monthly Subcutaneous Buprenorphine Depot Injection: 12-Month Safety, Tolerability, and Efficacy Analysis.

BACKGROUND: BUP-XR (RBP-6000 or SUBLOCADE) is the first Food and Drug Administration-approved subcutaneously administered monthly extended-release buprenorphine medication for the treatment of moderate or severe opioid use disorder. The primary objective of this phase III study was to assess the long-term safety, tolerability, and efficacy of BUP-XR. METHODS: This open-label multicenter study in adults with moderate or severe opioid use disorder enrolled 257 participants from a previously conducted placebo-controlled, double-blind phase III study (rollover group) and 412 de novo participants not previously treated with BUP-XR. Participants received an initial injection of BUP-XR 300 mg and subsequent monthly 300 mg or 100 mg flexible doses. By study end, participants received up to 12 injections. RESULTS: Overall, 66.8% of participants reported more than 1 treatment-emergent adverse event (TEAE). Injection-site TEAEs (13.2% of participants) were mostly mild or moderate in severity. There were no clinically meaningful changes in safety assessments. An integrated analysis of the double-blind and open-label study participants showed that the incidence of TEAEs, including injection-site TEAEs, was lower in the second 6 months of treatment versus the first 6 months. After 12 months of treatment, 61.5% of the rollover participants and 75.8% of the de novo participants were abstinent. Retention rates after 12 months were 50.6% for the participants who initiated BUP-XR in the double-blind study and 50.5% for de novo participants. CONCLUSIONS: This study demonstrates that the clinical benefits and acceptable safety profile of BUP-XR demonstrated in the 6-month double-blind study are sustained over a 12-month open-label study, with lower incidence of TEAEs in the second 6 months of treatment.

Fine-tuning p53 activity through C-terminal modification significantly contributes to HSC homeostasis and mouse radiosensitivity.

Cell cycle regulation in hematopoietic stem cells (HSCs) is tightly controlled during homeostasis and in response to extrinsic stress. p53, a well-known tumor suppressor and transducer of diverse stress signals, has been implicated in maintaining HSC quiescence and self-renewal. However, the mechanisms that control its activity in HSCs, and how p53 activity contributes to HSC cell cycle control, are poorly understood. Here, we use a genetically engineered mouse to show that p53 C-terminal modification is critical for controlling HSC abundance during homeostasis and HSC and progenitor proliferation after irradiation. Preventing p53 C-terminal modification renders mice exquisitely radiosensitive due to defects in HSC/progenitor proliferation, a critical determinant for restoring hematopoiesis after irradiation. We show that fine-tuning the expression levels of the cyclin-dependent kinase inhibitor p21, a p53 target gene, contributes significantly to p53-mediated effects on the hematopoietic system. These results have implications for understanding cell competition in response to stresses involved in stem cell transplantation, recovery from adverse hematologic effects of DNA-damaging cancer therapies, and development of radioprotection strategies.

JAK2V617F-positive endothelial cells contribute to clotting abnormalities in myeloproliferative neoplasms.

The Janus kinase 2 (JAK2) V617F mutation is the primary pathogenic mutation in patients with Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs). Although thrombohemorrhagic incidents are the most common causes of morbidity and mortality in patients with MPNs, the events causing these clotting abnormalities remain unclear. To identify the cells responsible for the dysfunctional hemostasis, we used transgenic mice expressing JAK2V617F in specific lineages involved in thrombosis and hemostasis. When JAK2V617F was expressed in both hematopoietic and endothelial cells (ECs), the mice developed a significant MPN, characterized by thrombocytosis, neutrophilia, and splenomegaly. However, despite having significantly higher platelet counts than controls, these mice showed severely attenuated thrombosis following injury. Interestingly, platelet activation and aggregation in response to agonists was unaltered by JAK2V617F expression. Subsequent bone marrow transplants revealed the contribution of both endothelial and hematopoietic compartments to the attenuated thrombosis. Furthermore, we identified a potential mechanism for this phenotype through JAK2V617F-regulated inhibition of von Willebrand factor (VWF) function and/or secretion. JAK2V617F(+) mice display a condition similar to acquired von Willebrand syndrome, exhibiting significantly less high molecular weight VWF and reduced agglutination to ristocetin. These findings greatly advance our understanding of thrombohemorrhagic events in MPNs and highlight the critical role of ECs in the pathology of hematopoietic malignancies.

Evaluation of a novel autoinjector for subcutaneous self-administration of belimumab in systemic lupus erythematosus
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OBJECTIVE: To study self-administration and pharmacokinetics (PK) of subcutaneous (SC) belimumab in patients with systemic lupus erythematosus (SLE). METHODS: Patients previously treated with belimumab self-administered belimumab 200 mg SC weekly for 8 weeks using an autoinjector. The primary endpoint was the proportion of patients able to self-administer their first and second dose (weeks 1 and 2) in the clinic. The proportion able to self-administer at weeks 4 and 8 (clinic) and weeks 3, 5, 6, and 7 (home) were secondary endpoints. Belimumab PK, safety, and injection-site pain were assessed. RESULTS: 91/95 patients completed the study (withdrawals: adverse events (AEs): 3; lost to follow-up: 1). 93% were female, and mean (SD) age was 44.8 (12.50) years. The majority (99%, 89/90; no attempt, n = 5) successfully self-administered belimumab SC at weeks 1 and 2 (5 had clinic staff assistance), and 98% (85/87) successfully self-administered at weeks 4 and 8. Home-administration success rates were high (93%, (81/87) at weeks 3, 5, 6, and 7). Week 8 median trough concentration was 113 µg/mL. For patients with a ≤ 1.5-week interval between IV SC administration, week-1 concentrations were higher vs. week 8 (+ 51% median) but within a range observed with IV dosing; those with a ≥ 2.5-week interval had median differences close to 0. AEs and serious AEs were low, with no deaths; pain levels were low and decreased with subsequent injections. CONCLUSION: Patients with SLE successfully self-administered belimumab SC using a novel autoinjector; the PK profile was stable following a switch from IV with acceptable AE and pain levels. The recommended dosing interval between IV to SC dosing is 1 - 4 weeks.
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Impact of Belimumab on Organ Damage in Systemic Lupus Erythematosus.

Organ damage is a key determinant of poor long-term prognosis and early death in patients with systemic lupus erythematosus (SLE). Prevention of damage is a key treatment goal of the 2019 update of the European Alliance of Associations for Rheumatology (EULAR) recommendations for SLE management. Belimumab is a monoclonal antibody that inhibits B lymphocyte stimulator (BLyS) and is the only therapy approved for both SLE and lupus nephritis. Here, we review the clinical trial and real-world data on the effects of belimumab on organ damage in adult patients with SLE. Across 4 phase III studies, belimumab in combination with background SLE therapy demonstrated consistent reductions in key drivers of organ damage including disease activity, risk of new severe flares, and glucocorticoid exposure compared to background therapy alone. Long-term belimumab use in SLE also reduced organ damage progression measured by the Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index, as reported in open-label extension studies, and propensity score-matched comparative analyses to background therapy alone. Results from a clinical trial showed that in patients with active lupus nephritis, belimumab treatment improved renal response, reduced the risk of renal-related events, and impacted features related to kidney damage progression compared to background therapy alone. The decrease of organ damage accumulation observed with belimumab treatment in SLE, including lupus nephritis, suggest a disease-modifying effect.

Blocking the alpha 4 integrin-paxillin interaction selectively impairs mononuclear leukocyte recruitment to an inflammatory site.

Antagonists to alpha4 integrin show promise for several autoimmune and inflammatory diseases but may exhibit mechanism-based toxicities. We tested the capacity of blockade of alpha4 integrin signaling to perturb functions involved in inflammation, while limiting potential adverse effects. We generated and characterized mice bearing a Y991A mutation in alpha4 integrin [alpha4(Y991A) mice], which blocks paxillin binding and inhibits alpha4 integrin signals that support leukocyte migration. In contrast to the embryonic-lethal phenotype of alpha4 integrin-null mice, mice bearing the alpha4(Y991A) mutation were viable and fertile; however, they exhibited defective recruitment of mononuclear leukocytes into thioglycollate-induced peritonitis. Alpha4 integrins are essential for definitive hematopoiesis; however, the alpha4(Y991A) mice had intact lymphohematopoiesis and, with the exception of reduced Peyer's patches, normal architecture and cellularity of secondary lymphoid tissues. We conclude that interference with alpha4 integrin signaling can selectively impair mononuclear leukocyte recruitment to sites of inflammation while sparing vital functions of alpha4 integrins in development and hematopoiesis.

A phase 1 study of mapatumumab (fully human monoclonal antibody to TRAIL-R1) in patients with advanced solid malignancies.

PURPOSE: Mapatumumab (TRM-1, HGS-ETR1) is a fully human agonistic monoclonal antibody that targets and activates tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor 1 (death receptor 4). Mapatumumab functions like the natural receptor ligand, TRAIL, a tumor necrosis factor superfamily member that is an important mediator of apoptosis in cancer cell lines. Promising preclinical activity with mapatumumab has been observed. EXPERIMENTAL DESIGN: This phase I, open-label, dose-escalation study assessed the tolerability and toxicity profile of > or =2 doses of mapatumumab administered i.v. in patients with advanced solid tumors. Patients received mapatumumab every 28 days until progression or dose-limiting toxicity. RESULTS: There were escalation levels from 0.01 to 20.0 mg/kg. Forty-one patients, 27 female, with a median age of 55 years (range, 23-81) were entered into the study and received 143 courses. The most common diagnoses were colorectal (10 patients) and ovarian cancer (9 patients). Patients received a median of two cycles (range, 1-33). Mapatumumab was well tolerated. Adverse events considered at least possibly related to mapatumumab that occurred most frequently included fatigue (36.2%), hypotension (34.1%), nausea (29.3%), and pyrexia (12.2%). The majority of adverse events were grade 1 or 2. The maximum tolerated dose was not reached. Linear pharmacokinetics was observed for doses up to 0.3 mg/kg and for the 20 mg/kg level, whereas exposure at 3 and 10 mg/kg increased less than proportionally. No objective responses were observed, but 12 patients had stable disease for 1.9 to 29.4 months. CONCLUSIONS: Mapatumumab is well tolerated and further evaluation of this TRAIL-R1 targeting agent is warranted.

Phase 1 and pharmacokinetic study of lexatumumab in patients with advanced cancers.

PURPOSE: To assess the safety and tolerability, pharmacokinetics, and early evidence of antitumor activity of escalating doses of lexatumumab (HGS-ETR2), a fully human agonistic monoclonal antibody which targets and activates the tumor necrosis factor-related apoptosis-inducing ligand receptor 2 (TRAIL-R2) in patients with advanced solid malignancies. EXPERIMENTAL DESIGN: In this phase 1, open label study, patients with advanced solid malignancies were treated with escalating doses of lexatumumab administered i.v. over 30 to 120 min every 21 days. A cohort of four patients, which could be expanded to six patients, was studied at each dose level. The dose-limiting toxicity (DLT) dose was defined as the dose at which the incidence of DLT in the first two cycles was >or=33%. The maximum tolerated dose was defined as the highest dose at which <33% of subjects experienced DLT. The pharmacokinetics and immunogenicity of lexatumumab were also characterized. Tumor specimens from historical or current biopsies, when available, were stained for TRAIL-R2 using immunohistochemistry techniques. RESULTS: Thirty-seven patients received 120 cycles of lexatumumab at doses ranging from 0.1 to 20 mg/kg every 21 days as of May 2006. The 20 mg/kg dose was identified as the DLT dose based on DLTs in three of seven patients treated with this dose; DLTs included asymptomatic elevations of serum amylase, transaminases, and bilirubin. The 10 mg/kg dose cohort was expanded to 12 patients and the 10 mg/kg dose was identified as the maximum tolerated dose. The mean (+/-SD) clearance and apparent terminal half-life values at the 10 mg/kg dose averaged 6.0 (2.9) mL/d/kg and 16.4 (10.9) days, respectively. Twelve patients had durable stable disease that lasted a median of 4.5 months, including three patients with sarcoma having prolonged stable disease (>or=6.7 months). Immunohistochemistry for TRAIL-R2 showed specific staining in >10% of tumor cells for 16 of the 20 evaluable specimens submitted (80%). CONCLUSIONS: Lexatumumab was safe and well tolerated at doses up to and including 10 mg/kg every 21 days. Lexatumumab was associated with sustained stable disease in several patients. Pharmacokinetics were linear over the dose range studied, and consistent with a two-compartment model with first-order elimination from the central compartment. Additional evaluation of this novel apoptosis-inducing agent, particularly in combination with chemotherapy agents, is warranted and ongoing.

Clinical response beyond the Systemic Lupus Erythematosus Responder Index: post-hoc analysis of the BLISS-SC study.

OBJECTIVE: The Systemic Lupus Erythematosus (SLE) Responder Index (SRI), developed as a primary outcome measure for use in clinical trials, captures improvement in SLE disease activity without concomitant worsening in disease manifestations. This study investigated the relationships between the SRI and clinical/laboratory correlates of SRI response in patients with SLE. METHODS: This was a post-hoc analysis of the phase III, double-blind, placebo-controlled study of subcutaneous BeLimumab in Subjects with Systemic lupus erythematosus - SubCutaneous (BLISS-SC). Patients were randomised to weekly belimumab 200 mg subcutaneously or placebo, plus standard SLE therapy. Changes from baseline to week 52 in clinical and laboratory parameters were compared among SRI responders and non-responders, irrespective of the treatment received. RESULTS: SRI responders (n=475) had significantly better (p<0.0001) outcomes compared with non-responders (n=358), including (by definition) higher proportions achieving ≥4-point improvement in Safety of Estrogens in Lupus Erythematosus National Assessment-SLE Disease Activity Index (100.0% vs 2.0%), no worsening in British Isles Lupus Assessment Group (BILAG; 0 new BILAG A or ≤1 new BILAG B score; 100.0 % vs 50.3%) and no worsening (<0.3-point increase) in Physician's Global Assessment score (100.0% vs 49.7%). Among patients receiving >7.5 mg/day corticosteroids at baseline, significantly more SRI responders had reductions in prednisone dose to ≤7.5 mg/day than non-responders. SRI responders reported lower flare rates and improvements in serological markers and Functional Assessment of Chronic Illness Therapy-Fatigue score than non-responders. CONCLUSION: SRI response is associated with improvements in clinical and laboratory measures, strengthening its value as a clinically meaningful primary endpoint in clinical trials.

Thrombopoietin expands hematopoietic stem cells after transplantation.

Multiple lines of evidence indicate that thrombopoietin (TPO) contributes to the development of hematopoietic stem cells (HSC), supporting their survival and proliferation in vitro. To determine whether TPO supports the impressive expansion of HSC observed following transplantation, we transplanted normal marrow cells into lethally irradiated Tpo(-/-) and Tpo(+/+) mice and quantified HSC self-renewal and expansion and hematopoietic progenitor cell homing. Although essentially identical numbers of marrow-associated colony forming unit-culture (a surrogate measure of stem cell homing) were observed in each type of recipient 24 hours following transplantation, we found that a minimum of fourfold greater numbers of marrow cells were required to radioprotect Tpo-null mice than to radioprotect controls. To assess whether long-term repopulating (LTR) HSCs self-renew and expand in Tpo(-/-) recipients or controls, we performed limiting-dilution secondary transplants using donor cells from the Tpo(-/-) or Tpo(+/+) recipients 5-7.5 weeks following primary transplantation. We found that LTR HSCs expand to levels 10-20 times greater within this time period in normal recipients than in Tpo-null mice and that physiologically relevant amounts of TPO administered to the Tpo(-/-) recipients could substantially correct this defect. Our results establish that TPO greatly promotes the self-renewal and expansion of HSCs in vivo following marrow transplantation.

Thrombopoietin (TPO) induces c-myc expression through a PI3K- and MAPK-dependent pathway that is not mediated by Akt, PKCzeta or mTOR in TPO-dependent cell lines and primary megakaryocytes.

Thrombopoietin (TPO) and its receptor (c-Mpl) are the major regulators of megakaryocyte and platelet production and serve a critical and non-redundant role in hematopoietic stem cell (HSC) biology. TPO signals through the Jak-STAT, Ras-Raf-MAPK, and PI3K pathways, and promotes survival, proliferation, and polyploidization in megakaryocytes. The proto-oncogene c-myc also plays an important role in many of these same processes. In this work we studied the regulated expression of c-myc in megakaryocytic cell lines and primary cells by quantitative real-time RT-PCR. We found that TPO induced expression of c-myc in 1 h in both hematopoietic cell lines (UT-7 and BaF3/Mpl) and mature murine megakaryocytes. The TPO-induced expression of c-myc was blocked by a phosphatidylinositol 3-kinase (PI3K) inhibitor, suggesting that TPO stimulated c-myc expression through a PI3K-dependent pathway. Of interest, our study showed that overexpression of active Akt did not rescue the effect of PI3K blockade on c-myc expression, rather, enhanced it. In addition, inhibitors of protein kinase C (PKC)zeta and the target of rapamycin (mTOR) also failed to affect c-myc mRNA expression, while c-myc mRNA expression was reduced by inhibition of the mitogen activated protein kinase (MAPK) pathway. Therefore, we conclude that TPO stimulates c-myc expression in primary megakaryocytes through a PI3K- and MAPK-dependent pathway that is not mediated by Akt, PKCzeta or mTOR.

Thrombopoietin induces HOXA9 nuclear transport in immature hematopoietic cells: potential mechanism by which the hormone favorably affects hematopoietic stem cells.

Members of the homeobox family of transcription factors are major regulators of hematopoiesis. Overexpression of either HOXB4 or HOXA9 in primitive marrow cells enhances the expansion of hematopoietic stem cells (HSCs). However, little is known of how expression or function of these proteins is regulated during hematopoiesis under physiological conditions. In our previous studies we demonstrated that thrombopoietin (TPO) enhances levels of HOXB4 mRNA in primitive hematopoietic cells (K. Kirito, N. Fox, and K. Kaushansky, Blood 102:3172-3178, 2003). To extend our studies, we investigated the effects of TPO on HOXA9 in this same cell population. Although overall levels of the transcription factor were not affected, we found that TPO induced the nuclear import of HOXA9 both in UT-7/TPO cells and in primitive Sca-1(+)/c-kit(+)/Gr-1(-) hematopoietic cells in a mitogen-activated protein kinase-dependent fashion. TPO also controlled MEIS1 expression at mRNA levels, at least in part due to phosphatidylinositol 3-kinase activation. Collectively, TPO modulates the function of HOXA9 by leading to its nuclear translocation, likely mediated by effects on its partner protein MEIS1, and potentially due to two newly identified nuclear localization signals. Our data suggest that TPO controls HSC development through the regulation of multiple members of the Hox family of transcription factors through multiple mechanisms.

The Mpl receptor expressed on endothelial cells does not contribute significantly to the regulation of circulating thrombopoietin levels.

OBJECTIVE: Blood levels of thrombopoietin (TPO) are regulated in part by cellular degradation following its binding to the cell surface receptor c-mpl. Previous reports have demonstrated that in addition to hematopoietic cells, c-mpl is expressed on and functions in several types of endothelial cells (ECs). We hypothesized that the c-mpl expressed on ECs would contribute to the regulation of circulating TPO levels. METHODS: To test this hypothesis we transplanted c-mpl-null and wild-type (WT) control mice with WT marrow stem cells, resulting in two groups of posttransplant chimeric animals, one expressing c-mpl on megakaryocytes and platelets only and one in which the receptor is expressed on both hematopoietic and ECs. Should EC c-mpl take up TPO and degrade it, we predicted that c-mpl-null mice reconstituted with WT cells would display increased TPO levels and an increased steady state platelet count compared to the WT recipients. RESULTS: Contrary to our prediction, for up to 6 months posttransplantation both platelet counts and TPO levels in both groups of transplanted mice were virtually identical. CONCLUSIONS: Our results indicate that the EC c-mpl receptor does not contribute significantly to the regulation of TPO levels or to steady-state platelet counts. These results also imply that patients with congenital amegakaryocytic thrombocytopenia, lacking the c-mpl receptor, who have successfully been engrafted with normal hematopoietic stem cells should have normal (not elevated) TPO levels and that gene replacement strategies designed to restore c-mpl in these patients do not need to target ECs to establish the normal regulation of TPO.

Efficacy and Safety of Subcutaneous Belimumab in Systemic Lupus Erythematosus: A Fifty-Two-Week Randomized, Double-Blind, Placebo-Controlled Study.

OBJECTIVE: To assess the efficacy and safety of subcutaneous (SC) belimumab in patients with systemic lupus erythematosus (SLE). METHODS: Patients with moderate-to-severe SLE (score of ≥8 on the Safety of Estrogens in Lupus Erythematosus National Assessment [SELENA] version of the SLE Disease Activity Index [SLEDAI]) were randomized 2:1 to receive weekly SC belimumab 200 mg or placebo by prefilled syringe in addition to standard SLE therapy for 52 weeks. The primary end point was the SLE Responder Index (SRI4) at week 52. Secondary end points were reduction in the corticosteroid dosage and time to severe flare. Safety was assessed according to the adverse events (AEs) reported and the laboratory test results. RESULTS: Of 839 patients randomized, 836 (556 in the belimumab group and 280 in the placebo group) received treatment. A total of 159 patients withdrew before the end of the study. At entry, mean SELENA-SLEDAI scores were 10.5 in the belimumab group and 10.3 in the placebo group. More patients who received belimumab were SRI4 responders than those who received placebo (61.4% versus 48.4%; odds ratio [OR] 1.68 [95% confidence interval (95% CI) 1.25-2.25]; P = 0.0006). In the belimumab group, both time to and risk of severe flare were improved (median 171.0 days versus 118.0 days; hazard ratio 0.51 [95% CI 0.35-0.74]; P = 0.0004), and more patients were able to reduce their corticosteroid dosage by ≥25% (to ≤7.5 mg/day) during weeks 40-52 (18.2% versus 11.9%; OR 1.65 [95% CI 0.95-2.84]; P = 0.0732), compared with placebo. AE incidence was comparable between treatment groups; serious AEs were reported by 10.8% of patients taking belimumab and 15.7% of those taking placebo. A worsening of IgG hypoglobulinemia by ≥2 grades occurred in 0.9% of patients taking belimumab and 1.4% of those taking placebo. CONCLUSION: In patients with moderate-to-severe SLE, weekly SC doses of belimumab 200 mg plus standard SLE therapy significantly improved their SRI4 response, decreased severe disease flares as compared with placebo, and had a safety profile similar to placebo plus standard SLE therapy.

Engagement of integrin alpha4beta1 enhances thrombopoietin-induced megakaryopoiesis.

OBJECTIVE: Studies in numerous adherent cell systems have indicated that engagement of integrins is required for cell survival and proliferation. Although not classically thought of as an adherent cell type, megakaryocytes in the marrow develop in juxtaposition to endothelial cells which display a number of integrin counter-receptors. Moreover, a number of other hematopoietic cell types, including stem cells and erythroid progenitors, have been shown to engage and be affected by integrin ligands. METHODS: The role of beta1 integrins in thrombopoietin-mediated megakaryopoiesis was studied using both gain-of-function and loss-of-function strategies. RESULTS: We found that pan-blockade of integrins with a relatively nonspecific disintegrin blocked TPO-induced MK growth, but that an alpha5beta1 disintegrin, and a function-blocking monoclonal antibody, failed to affect megakaryopoiesis in vitro. In contrast, a neutralizing alpha4beta1 monoclonal antibody blocked TPO-induced MK growth, and an integrin alpha4beta1 ligand, the H296 fragment of fibronectin, enhanced MK growth at all concentrations of TPO. CONCLUSIONS: These findings have important implications for thrombopoiesis in general, and potentially for the enhanced platelet production found in states of systemic inflammation and following the use of therapeutic strategies designed to block alpha4beta1 integrin engagement in states of chronic inflammation and autoimmunity.

Relative Bioavailability of a Single Dose of Belimumab Administered Subcutaneously by Prefilled Syringe or Autoinjector in Healthy Subjects.

Intravenous belimumab is approved for the treatment of systemic lupus erythematosus; subcutaneous self-administration would enable greater patient access. This study assessed relative bioavailability, tolerability, and safety of 1 subcutaneous dose of self-administered belimumab by healthy subjects using a single-use autoinjector or prefilled syringe. Subjects (randomized 1:1:1:1) self-administered belimumab 200 mg subcutaneously (abdomen or thigh) by prefilled syringe or autoinjector. Pharmacokinetics, adverse events (AEs), injection-site pain, and administration errors were recorded. Of 81 subjects, 5 experienced administration errors and were excluded from pharmacokinetic analyses. Mean serum belimumab concentration profiles were similar for both devices, with a weak trend toward higher concentrations for thigh injection compared with abdominal injections. Maximum observed serum concentration was slightly higher with the autoinjector (27.0 vs 25.3 µg/mL) and area under the concentration-time curve slightly lower (701 vs 735 day · µg/mL), compared with the prefilled syringe. Incidence of AEs was 51% (41 of 81 subjects; headache was most common), with no serious or severe AEs. Median injection-site pain scores were low (0 after 1 hour). Device handling was reported as acceptable by ≥95% of autoinjector users and ≥90% of prefilled syringe users for each characteristic assessed. These results support the use of either device for belimumab subcutaneous administration.

Quality of life after coronary artery bypass graft: results from the POST CABG Trial.

OBJECTIVES: The POST CABG (Post Coronary Artery Bypass Graft) Trial showed that aggressive lowering of low-density lipoprotein (LDL) cholesterol levels reduced the progression of atherosclerosis in saphenous vein grafts. In the extended follow-up phase, aggressive lowering of LDL cholesterol levels was associated with reduced rates of clinical events. Low-dose anticoagulation therapy did not reduce the progression of atherosclerosis. We conducted this analysis to determine the effects of both lipid-lowering and low-dose anticoagulation therapy on health-related quality of life (HRQL). DESIGN: Randomized clinical trial, factorial design. SETTING: Outpatients in five tertiary care medical centers. PATIENTS: A cohort of 852 patients enrolled in the POST CABG Trial completed an HRQL questionnaire at baseline, and at the year 2 and year 4 follow-up visits. INTERVENTION: Aggressive LDL cholesterol lowering vs moderate LDL cholesterol lowering, and low-dose warfarin vs placebo. MEASUREMENTS: Domains included emotional status, basic physical and social functioning, perceived health status, symptoms of pain, a variety of physical symptoms, and global life satisfaction. RESULTS: Overall, there were no indications of systematic differences among treatment groups for any of the HRQL parameters at baseline, year 2, or year 4. CONCLUSIONS: These data indicate that patients did not experience detrimental or beneficial effects on HRQL parameters while receiving LDL cholesterol-lowering therapy that had demonstrable benefits for treatment of atherosclerosis.