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Introduction: Patients (pts) with MDS/MPN-RS-T have limited treatment options for anemia due to ineffective erythropoiesis. Luspatercept, the first-in-class erythroid maturation agent that enhances late-stage erythropoiesis, is approved by the FDA for treatment of anemia in adult pts with lower-risk (LR) MDS with ring sideroblasts (RS) or MDS/MPN-RS-T after erythroid-stimulating agent (ESA) failure. In the randomized, double-blind, phase 3 MEDALIST study, luspatercept significantly reduced transfusion burden vs placebo in pts with LR-MDS (NCT02631070; Fenaux P, et al. N Engl J Med 2020;382:140-51). Here, we assess the efficacy and safety of luspatercept in pts with MDS/MPN-RS-T enrolled in the MEDALIST study. Methods: Eligible pts were ≥ 18 years; had IPSS-R-defined Very low-, Low-, or Intermediate-risk MDS with RS; were refractory, intolerant, or unlikely to respond to ESAs (serum erythropoietin > 200 U/L); and required regular RBC transfusions. Pts were randomized 2:1 to luspatercept (1.0 mg/kg, titration to 1.75 mg/kg) or placebo administered subcutaneously every 3 wks. The primary endpoint was achievement of RBC transfusion independence (RBC-TI) ≥ 8 wks during Wks 1-24. Results: A retrospective analysis identified 23/229 (10.0%) pts enrolled in the MEDALIST trial who had MDS/MPN-RS-T, per WHO 2016 criteria (Arber DA, et al. Blood 2016;127:2391-405); 14 received luspatercept and 9 received placebo. Pts in this subgroup received a median of 4.0 RBC units/8 wks (range 2.0-11.5) during the 16 wks prior to treatment. At baseline, pts had a median hemoglobin (Hb) level of 7.7 g/dL (range 7.0-9.0), a median leukocyte count of 5.1 × 109/L, a median platelet count of 447.0 × 109/L, and 18 (78.3%) pts had serum erythropoietin levels < 200 U/L (Table). In the luspatercept arm, 9/14 (64.3%) pts with MDS/MPN-RS-T achieved the primary endpoint of RBC-TI for ≥ 8 wks during Wks 1-24, compared with 2/9 pts (22.2%) receiving placebo (odds ratio 11.3; 95% confidence interval [CI] 1.19, 106.12; P = 0.028). Pts receiving luspatercept were significantly more likely to achieve clinical benefit (achieving RBC-TI ≥ 8 wks and/or modified hematologic improvement-erythroid [mHI-E] per IWG 2006 criteria [≥ 4 units/8 wks reduction in RBC transfusion in pts with ≥ 4 units/8 wks baseline RBC transfusion burden; Hb increase by ≥ 1.5 g/dL] during Wks 1-24 in pts with < 4 units/8 wks baseline RBC transfusion burden), compared with pts receiving placebo (78.6% vs 33.3%; P = 0.034). Median time from the start of clinical benefit response to end of treatment was 94.6 wks (range 8.0-150.0) in the luspatercept arm and 23.9 wks (range 23.7-57.9) in the placebo arm. During Wks 1-24, mHI-E was achieved by 10 luspatercept pts (6 were high transfusion burden [HTB; defined as baseline transfusion burden ≥ 4 units/8 wks] and 4 were low transfusion burden [LTB; defined as baseline transfusion burden < 4 units/8 wks]) and 1 placebo pt (1/5 HTB). RBC-TI ≥ 8 wks was achieved by 4/8 HTB pts receiving luspatercept (vs 0/5 placebo) and 5/6 LTB pts (vs 2/4 placebo). After 24 wks, pts in the luspatercept arm had a mean Hb increase of +1.7 g/dL compared with an increase of +0.9 g/dL in pts in the placebo arm (least squares [LS] mean difference +0.85 g/dL; 95% CI −1.13, +2.82). Greater reductions from baseline in mean serum ferritin levels were seen with luspatercept (−121.8 μg/L) compared with placebo (−91.9 μg/L) over Wks 9-24 (LS mean difference −90.1; 95% CI −758.4, 578.2). Pts in the luspatercept arm had median platelet counts of 467.5 × 109/L and median leukocyte counts of 6.5 × 109/L post 24 wks of treatment, compared with pts in the placebo arm with 514.0 × 109/L and 6.2 × 109/L, respectively. The incidence of specific TEAEs (occurring in ≥ 1 patient) are as follows: fatigue (1/14 [7.1%] luspatercept vs 1/9 [11.1%] placebo), dizziness (7/14 [50.0%] vs 0/9), dyspnea (3/14 [21.4%] vs 0/9), nausea (6/14 [42.9%] vs 2/9 [22.2%]), arthralgia (1/14 [7.1%] vs 0/9), diarrhea (6/14 [42.9%] vs 1/9 [11.1%]), and hypertension (3/14 [21.4%] vs 0/9). In the luspatercept arm, 1/14 (7.1%) pts experienced ≥ 1 thromboembolic event (transient ischemic attack) and 1/9 (11.1%) pts in the placebo arm progressed to AML (as of July 1, 2019). Conclusions: Luspatercept demonstrated clinical efficacy in pts with MDS/MPN-RS-T with a generally well-tolerated safety profile. These data support the clinical benefits of luspatercept in this patient population with otherwise limited treatment options. Disclosures Komrokji: Geron: Honoraria; Novartis: Honoraria; Incyte: Honoraria; JAZZ: Honoraria, Speakers Bureau; AbbVie: Honoraria; Agios: Honoraria, Speakers Bureau; Acceleron: Honoraria; BMS: Honoraria, Speakers Bureau. Platzbecker:Janssen: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria; Geron: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; BMS: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Research Funding; Amgen: Honoraria, Research Funding. Fenaux:BMS: Honoraria, Research Funding; Abbvie: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Jazz: Honoraria, Research Funding. Garcia-Manero:Helsinn Therapeutics: Consultancy, Honoraria, Research Funding; AbbVie: Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding; Amphivena Therapeutics: Research Funding; Jazz Pharmaceuticals: Consultancy; H3 Biomedicine: Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Acceleron Pharmaceuticals: Consultancy, Honoraria; Novartis: Research Funding; Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Onconova: Research Funding; Astex Pharmaceuticals: Consultancy, Honoraria, Research Funding; Merck: Research Funding. Mufti:Abbvie, Novartis: Consultancy; BMS, Novartis: Research Funding. Santini:Janssen: Research Funding; BMS, J&J, Novartis: Honoraria; Acceleron, BMS, Menarini, Novartis: Consultancy; Takeda, Pfizer: Membership on an entity's Board of Directors or advisory committees. Diez-Campelo:Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Finelli:BMS: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees. Jurcic:AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Syros Pharmaceuticals: Research Funding; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Consultancy, Research Funding; Daiichi-Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Arog Pharmaceuticals: Research Funding; Astellas: Research Funding; Forma Therapeutics: Research Funding; Genentech: Research Funding; Kura Oncology: Research Funding; PTC Therapeutics: Research Funding. Greenberg:BMS: Research Funding; Aprea: Research Funding; Notable Labs: Research Funding; H3 Biotech: Research Funding. Sekeres:BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda/Millenium: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees. Zeidan:Abbvie: Consultancy, Honoraria, Research Funding; Otsuka: Consultancy, Honoraria; Trovagene: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding; Boehringer-Ingelheim: Consultancy, Honoraria, Research Funding; Leukemia and Lymphoma Society: Other; CCITLA: Other; Astex: Research Funding; MedImmune/Astrazeneca: Research Funding; Ionis: Consultancy, Honoraria; Epizyme: Consultancy, Honoraria; Aprea: Research Funding; ADC Therapeutics: Research Funding; Taiho: Consultancy, Honoraria; Seattle Genetics: Consultancy, Honoraria; Cardinal Health: Consultancy, Honoraria; Daiichi Sankyo: Consultancy, Honoraria; Astellas: Consultancy, Honoraria; Jazz: Consultancy, Honoraria; Cardiff Oncology: Consultancy, Honoraria, Other; Agios: Consultancy, Honoraria; BeyondSpring: Consultancy, Honoraria; Incyte: Consultancy, Honoraria, Research Funding; Acceleron: Consultancy, Honoraria; Celgene / BMS: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding. DeZern:Astex: Research Funding; Celgene: Consultancy, Honoraria; MEI: Consultancy; Abbvie: Consultancy. Savona:Incyte: Consultancy, Research Funding; Sunesis: Consultancy, Research Funding; TG Therapeutics: Consultancy, Research Funding; BMS: Consultancy; AbbVie: Consultancy; Gilead: Consultancy; Karyopharm: Consultancy, Current equity holder in publicly-traded company; Ryvu: Consultancy; Boehringer Ingelheim: Patents & Royalties; Astex: Consultancy, Research Funding; Takeda: Consultancy, Research Funding. Shetty:BMS: Current Employment, Current equity holder in publicly-traded company. Ito:BMS: Current Employment, Current equity holder in publicly-traded company. Zhang:BMS: Current Employment. Ha:BMS: Current Employment. Sinsimer:BMS: Current Employment, Current equity holder in publicly-traded company. Backstrom:BMS: Current equity holder in publicly-traded company; Acceleron Pharma: Current Employment, Current equity holder in publicly-traded company. Verma:BMS: Consultancy, Research Funding; acceleron: Consultancy, Honoraria; Janssen: Research Funding; Medpacto: Research Funding; stelexis: Current equity holder in private company.

Introduction: β-thalassemia is an inherited hemoglobinopathy characterized by ineffective erythropoiesis and anemia. Luspatercept is a first-in-class erythroid maturation agent that binds to select TGF-β superfamily ligands to reduce aberrant Smad2/3 signaling and enhance late-stage erythropoiesis. We aim to evaluate in detail the number of response episodes, duration of clinical benefit, and safety in luspatercept responders during the phase 3 BELIEVE study (NCT02604433). Methods: Eligible pts were aged ≥ 18 years, with β-thalassemia or hemoglobin (Hb) E/β-thalassemia (compound β-thalassemia mutation and/or multiplication of α-globin genes was allowed), requiring regular transfusions of 6-20 RBC units in the 24 weeks (wks) prior to randomization, with no transfusion-free period > 35 days. Pts were randomized 2:1 to luspatercept 1.0 mg/kg (up to 1.25 mg/kg allowed), or placebo, subcutaneously every 3 wks for ≥ 48 wks. Pts in both treatment arms continued RBC transfusions to maintain baseline Hb level and iron chelation therapy. Achievement and number of response episodes (defined as ≥ 33% reduction in RBC transfusion from baseline over any consecutive 24 wks) were assessed at a median follow-up of 64.1 wks. Duration of clinical benefit, defined as the time of first response (≥ 33% reduction in RBC transfusion over any 24 wks) to discontinuation due to any cause at that episode, was also assessed. Results:A total of 336 pts were randomized. In the ITT population, 224 pts in the luspatercept arm had a median baseline RBC transfusion burden in the 12 wks prior to randomization of 6.12 U RBCs (average 0.51 U/wk; range 3-14) and the 112 pts in the placebo arm had a median baseline transfusion burden of 6.27 U (average 0.52 U/wk; range 3-12). A total of 194 (57.7%) luspatercept and 65 (58%) placebo pts had prior splenectomy. As of the May 11, 2018 cutoff date, 92/224 (41.1%) luspatercept-treated pts and 3/112 (2.7%) placebo-treated pts had achieved ≥ 33% reduction in RBC transfusion over any 24 wks; of these luspatercept responders, 55 (59.8%) had ≥ 2 separate responses (over the treatment period up to data cutoff), 42 (45.7%) had ≥ 3, 29 (31.5%) had ≥ 4, and 19 (20.7%) had ≥ 5. Three (1.3%) pts receiving luspatercept re-responded at the same dose level after initially losing response. Median duration of clinical benefit (as defined above) for luspatercept responders was 53.5 wks (range 24-93.7). Forty-seven (21.0%) pts receiving luspatercept had no loss of response within the entire study period. Five luspatercept responders achieved RBC transfusion independence for ≥ 24 wks (median total duration was 60.1 wks) and 3 achieved RBC transfusion independence for ≥ 48 wks (median duration was 66 wks). The average number of RBC units saved over any 24 wks in all luspatercept responders was 6.55 U (0.27 U/wk) and was 8.16 U (0.34 U/wk) with transfusion burden > 15 U/24 wks, compared to baseline. As of the May 11, 2018 cutoff date, the safety population consisted of 243 pts (including 92 pts who crossed over from the placebo arm to the luspatercept arm). Frequent adverse events (AEs) in the luspatercept and placebo arms included bone pain (19.7% vs 8.3%, respectively), arthralgia (19.3% vs 11.9%), and dizziness (11.2% vs 4.6%). The safety profile for pts who crossed over from placebo to luspatercept was consistent with that observed for pts receiving luspatercept from baseline. The incidence of bone pain, arthralgia, and dizziness was largely non-severe grade 1-2, tended to decrease over time during the study, was not associated with dose level, and was not associated with treatment modification or discontinuation. Pts continue to be monitored for safety outcomes. Conclusions: Most β-thalassemia pts who were luspatercept responders experienced multiple response periods and had durable clinical benefit over the 64.1 wk follow-up period. The incidence of frequent AEs was consistent with the previously reported 48 wk safety profile for luspatercept, was not associated with dose level, and decreased over time with no impact on treatment modification or continuation. Disclosures Viprakasit: Celgene Corporation: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; Protagonist: Consultancy, Research Funding; Vifor: Consultancy, Research Funding; Agios: Consultancy, Research Funding; Ionis: Consultancy, Research Funding; La Jolla: Consultancy, Research Funding. Taher:Celgene Corporation: Research Funding; Protagonist Therapeutics: Consultancy, Research Funding; Abfero: Consultancy; Novartis: Consultancy, Honoraria, Research Funding; La Jolla Pharmaceuticals: Consultancy, Research Funding; Ionis Pharmaceuticals: Consultancy. Hermine:AB Science: Consultancy, Equity Ownership, Honoraria, Research Funding; Celgene: Research Funding; Novartis: Research Funding. Porter:Vifor: Honoraria; Agios: Consultancy, Honoraria; Protagonist: Honoraria; La Jolla: Honoraria; Bluebird Bio: Consultancy, Honoraria; Celgene Corporation: Consultancy, Honoraria; Silence Therapeutics: Honoraria. Piga:Acceleron Pharma: Research Funding; Celgene Corporation: Consultancy, Research Funding; Novartis: Consultancy, Research Funding. Kuo:Agios: Consultancy; Alexion: Consultancy, Honoraria; Apellis: Consultancy; Bioverativ: Other: Data Safety Monitoring Board; Bluebird Bio: Consultancy; Celgene: Consultancy; Novartis: Consultancy, Honoraria; Pfizer: Consultancy. Coates:agios pharma: Consultancy, Honoraria; celgene: Consultancy, Honoraria, Other: steering committee of clinical study; apo pharma: Consultancy, Honoraria, Speakers Bureau; vifor: Consultancy, Honoraria. Voskaridou:Genesis: Consultancy, Research Funding; Protagonist: Research Funding; Celgene Corporation: Consultancy, Research Funding; Acceleron: Consultancy, Research Funding; Addmedica: Membership on an entity's Board of Directors or advisory committees. Perrotta:Acceleron Pharma: Research Funding; Novartis: Honoraria, Research Funding. Kattamis:Celgene Corporation: Honoraria, Membership on an entity's Board of Directors or advisory committees; Apopharma: Honoraria; Vertex: Membership on an entity's Board of Directors or advisory committees; ViFOR: Membership on an entity's Board of Directors or advisory committees; Ionis: Membership on an entity's Board of Directors or advisory committees; Novartis Oncology: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Laadem:Celgene Corporation: Employment, Equity Ownership. Shetty:Celgene Corporation: Employment, Equity Ownership. Kuo:Celgene Corporation: Employment, Equity Ownership. Miteva:Celgene International: Employment. Zinger:Celgene Corporation: Employment. Sinsimer:Celgene Corporation: Employment, Equity Ownership. Linde:Acceleron Pharma: Employment, Equity Ownership; Abbott Laboratories, Inc.: Equity Ownership; Fibrogen, Inc.: Equity Ownership. Cappellini:CRISPR Therapeutics: Membership on an entity's Board of Directors or advisory committees; Genzyme/Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Celgene Corporation: Honoraria; Vifor Pharmaceutical: Membership on an entity's Board of Directors or advisory committees. OffLabel Disclosure: Luspatercept is an investigational therapy that is not approved for any use in any country. Luspatercept is currently being evaluated for potential use in patients with anemia due to myelodysplastic syndromes, beta-thalassemia, or myelofibrosis.

Introduction: Lower-risk MDS is characterized by anemia and ineffective erythropoiesis leading to RBC transfusion dependence. Effective treatment for anemia remains an unmet medical need. Patients with MDS may also experience additional cytopenias that may complicate treatment and contribute to infections and bleeding events. Here, we report hematologic improvement (HI) outcomes for patients in the MEDALIST trial (ClinicalTrials.gov identifier: NCT02631070), a phase 3, randomized, double-blind, placebo-controlled study evaluating the efficacy and safety of luspatercept, a first-in-class erythroid maturation agent that binds select TGF-β superfamily ligands to reduce aberrant Smad2/3 signaling and enhance late-stage erythropoiesis. Methods: Eligible patients in the MEDALIST trial were adults with anemia due to Very low-, Low-, or Intermediate-risk MDS with RS according to the Revised International Prognostic Scoring System; were refractory, intolerant, or ineligible to receive erythropoiesis-stimulating agents (ESAs); and required RBC transfusions. Patients received luspatercept (starting dose of 1.0 mg/kg and titration up to 1.75 mg/kg, if needed) or placebo subcutaneously every 3 weeks for ≥ 24 weeks. Platelet and neutrophil counts were assessed by the central laboratory. Secondary endpoints included HI-neutrophil (HI-N) and -platelet (HI-P) responses, using International Working Group 2006 criteria, over any consecutive 56-day period. Mean changes from baseline in platelets and neutrophils were also evaluated. Results*: A total of 94.8% patients in the luspatercept arm and 97.4% in the placebo arm had refractory cytopenia with multilineage dysplasia and RS at baseline. Mean neutrophil and platelet counts at baseline for patients in the luspatercept arm were 2.8 x 109/L and 259 x 109/L, respectively, and in the placebo arm were 2.7 x 109/L and 252 x 109/L, respectively. Neutropenia (< 1 x 109/L) was confirmed at baseline in 15 (9.8%) and 10 (13.2%) patients in the luspatercept and placebo arms, respectively. Fifty-one (33.3%) patients in the luspatercept arm and 22 (28.9%) in the placebo arm received granulocyte colony-stimulating factor in combination with ESAs prior to randomization. A total of 8 (5.2%) and 6 (7.9%) patients receiving luspatercept and placebo, respectively, had baseline thrombocytopenia (< 100 x 109/L); no patients received prior platelet transfusions. Fifteen (9.8%) and 10 (13.2%) patients in the luspatercept and placebo arms, respectively, were evaluable for HI-N (i.e. baseline neutrophils < 1 x 109/L); 3/15 (20%) of those receiving luspatercept and 1/10 (10%) of those receiving placebo achieved HI-N in Weeks 1-48. Among patients who were evaluable for HI-P (i.e. baseline platelets < 100 x 109/L), 5/8 (62.5%) of those receiving luspatercept and 2/6 (33%) of those receiving placebo achieved HI-P in Weeks 1-48 (Table). None of the luspatercept HI-P responders received platelet transfusions. Mean changes from baseline in neutrophils of 0.94 x 109/L with luspatercept and 0.04 x 109/L with placebo were observed at Week 15, with early increases reported for luspatercept by Day 8 (0.86 vs 0.08 x 109/L for placebo). Mean increases in neutrophils at Day 8 occurred in both luspatercept responders (by MEDALIST primary endpoint; 1.0 x 109/L) and non-responders (0.8 x 109/L). Mean changes from baseline in platelets of 29 x 109/L were observed with luspatercept and 0.9 x 109/L with placebo by Week 12, but early increases were observed with luspatercept by Day 8 (18 vs 3 x 109/L for placebo) and mean increases in platelets at Day 8 occurred in both luspatercept responders (21.4 x 109/L) and non-responders (16.5 x 109/L). No patients in either arm experienced grade 3 or 4 treatment-emergent thrombocytopenia. Treatment-related grade 3 or 4 neutropenia was reported in 1 (0.7%) patient receiving luspatercept and 1 (1.3%) patient receiving placebo. Conclusions: Although only a minority of patients were evaluable for HI-P/HI-N response based on entry criteria for the study, luspatercept treatment resulted in a mean increase from baseline in platelet and neutrophil counts in most patients overall vs placebo, regardless of response status. These improvements were observed early following treatment initiation and then stabilized. Luspatercept did not contribute to the worsening of cytopenias vs placebo. *Data cutoff: May 8, 2018. Disclosures Garcia-Manero: Amphivena: Consultancy, Research Funding; Helsinn: Research Funding; Novartis: Research Funding; AbbVie: Research Funding; Celgene: Consultancy, Research Funding; Astex: Consultancy, Research Funding; Onconova: Research Funding; H3 Biomedicine: Research Funding; Merck: Research Funding. Mufti:Celgene Corporation: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Cellectis: Membership on an entity's Board of Directors or advisory committees, Research Funding. Fenaux:Celgene Corporation: Honoraria, Research Funding; Astex: Honoraria, Research Funding; Jazz: Honoraria, Research Funding; Aprea: Research Funding. Buckstein:Takeda: Research Funding; Celgene: Consultancy, Honoraria, Research Funding. Santini:Acceleron: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Menarini: Membership on an entity's Board of Directors or advisory committees; Celgene Corporation: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Johnson & Johnson: Honoraria. Díez-Campelo:Celgene Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Finelli:Celgene Corporation: Consultancy, Research Funding, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; Janssen: Consultancy, Speakers Bureau. Sekeres:Syros: Membership on an entity's Board of Directors or advisory committees; Millenium: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees. List:Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding. Laadem:Celgene Corporation: Employment, Equity Ownership. Ito:Celgene Corporation: Employment, Equity Ownership. Zhang:Celgene Corporation: Employment, Equity Ownership. Rampersad:Celgene Corp: Employment, Equity Ownership. Sinsimer:Celgene Corporation: Employment, Equity Ownership. Linde:Fibrogen, Inc.: Equity Ownership; Abbott Laboratories, Inc.: Equity Ownership; Acceleron Pharma: Employment, Equity Ownership. Platzbecker:Celgene: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria. Komrokji:Alexion: Speakers Bureau; Incyte: Consultancy; Janssen: Consultancy; Agios: Consultancy; Celgene: Consultancy; Pfizer: Consultancy; Jazz: Speakers Bureau; DSI: Consultancy; Novartis: Speakers Bureau. OffLabel Disclosure: Luspatercept is an investigational therapy that is not approved for any use in any country. Luspatercept is currently being evaluated for potential use in patients with anemia due to myelodysplastic syndromes, beta-thalassemia, or myelofibrosis.

Introduction: BELIEVE is an ongoing phase 3, randomized, double-blind, placebo-controlled study evaluating the efficacy and safety of luspatercept, a first-in-class erythroid maturation agent, in adults with β-thalassemia requiring regular RBC transfusions (ClinicalTrials.gov identifier: NCT02604433). Treatment with luspatercept significantly reduced RBC transfusion burden and was associated with a favorable safety profile in this patient (pt) population (Piga A, et al. Blood. 2019;133:1279-89). Here we report iron-related efficacy endpoints of the BELIEVE study, including change from baseline in serum ferritin, liver iron concentration (LIC), and myocardial iron, as determined by T2*-weighted magnetic resonance imaging (MRI), and the effect of baseline iron levels on response to luspatercept. Methods: Adults with β-thalassemia or hemoglobin (Hb) E/β-thalassemia who required regular transfusions of 6-20 RBC units in the 24 weeks (wks) prior to randomization (with no transfusion-free period ≥ 35 days during that period) were randomized 2:1 to luspatercept (starting dose level 1.0 mg/kg; titration up to 1.25 mg/kg) or placebo, administered subcutaneously every 3 wks for ≥ 48 wks. Pts in both arms could receive RBC transfusions and iron chelation therapy (ICT) throughout the study to maintain their baseline Hb levels. Results: 332/336 randomized pts received treatment with luspatercept or placebo; 209/223 (93.7%) and 104/109 (95.4%) pts in the luspatercept and placebo arms had history of iron overload, defined as serum ferritin > 1,000 µg/L or LIC > 7 mg/g dry weight. 97.3% of luspatercept-treated and 97.2% of placebo-treated pts received ICT at baseline; 62.3%, 41.3%, and 37.2% received deferasirox, deferiprone, and deferoxamine, respectively, in the luspatercept arm, vs 57.8%, 36.7%, and 35.8% in the placebo arm. Fewer pts received ICT as combination therapy vs monotherapy (luspatercept arm: 28.6% vs 68.8%; placebo arm: 24.1% vs 72.3%, respectively). Mean baseline serum ferritin, LIC, and myocardial iron (by T2* MRI) for luspatercept vs placebo arms were 2,096.91 vs 1,845.05 μg/L, 12.04 vs 10.09 mg/g, and 33.52 vs 34.76 ms, respectively. As of Jan 7, 2019, 157 (70.4%) continue to receive luspatercept and 92 (84.4%) crossed over from the placebo arm. During the last 12 wks of the 48-wk randomized treatment period, mean change from baseline in serum ferritin was −248.02 μg/L vs +106.62 μg/L for pts in the luspatercept and placebo arms, respectively (least squares mean [LSM] difference: −347.80; P < 0.0001). 158/224 (70.5%) and 33/112 (29.5%) pts in the luspatercept and placebo treatment arms achieved a ≥ 33% reduction in RBC transfusion burden of ≥ 2 RBC units during any 12-wk interval. Among the responders, mean change from baseline in serum ferritin was −343.22 μg/L and +47.30 μg/L for pts receiving luspatercept and placebo, respectively (LSM difference: −389.50; P = 0.0047). Of 140 luspatercept-treated pts with baseline ferritin ≥ 1,000 μg/L, 29 (20.7%) achieved post baseline ferritin of < 1,000 μg/L when assessed over the entire treatment period; results were similar in responders and non-responders. During the treatment phase, mean change in myocardial MRI iron signal (T2*) from baseline to Wk 48 was −1.83 ms for luspatercept and +0.02 ms for placebo (LSM difference: −2.39; P = 0.0391). Over 96 wks, 6 (20%) luspatercept-treated pts with baseline myocardial iron ≤ 20 ms had post-baseline results > 20 ms; results were similar between responders and non-responders. Mean LIC changes from baseline to Wk 48 (mg/g dry weight) were +0.10 and +0.08 for luspatercept and placebo arms, respectively (LSM difference: +0.11; P = 0.8685). Over 96 wks, mean change in LIC among luspatercept-treated patients overall was −0.5 mg/g and −1.1 mg/g among responders. When assessing impact of baseline iron loading there was a general consistency in achievement of ≥ 33% reduction in RBC transfusion with luspatercept over any 12 wks, regardless of iron loading subgroup (baseline serum ferritin, LIC, and myocardial iron) (Table). Conclusions: Luspatercept treatment resulted in clinically meaningful reductions in serum ferritin levels. Baseline iron overload did not seem to affect response to luspatercept; treatment resulted in clinically meaningful reductions in RBC transfusion burden regardless of baseline serum ferritin level, LIC, or myocardial iron loading. Disclosures Porter: Celgene Corporation: Consultancy, Honoraria; Protagonist: Honoraria; Vifor: Honoraria; La Jolla: Honoraria; Agios: Consultancy, Honoraria; Silence Therapeutics: Honoraria; Bluebird Bio: Consultancy, Honoraria. Cappellini:Novartis: Membership on an entity's Board of Directors or advisory committees; Celgene Corporation: Honoraria; Genzyme/Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Vifor Pharmaceutical: Membership on an entity's Board of Directors or advisory committees; CRISPR Therapeutics: Membership on an entity's Board of Directors or advisory committees. Coates:apo pharma: Consultancy, Honoraria, Speakers Bureau; agios pharma: Consultancy, Honoraria; celgene: Consultancy, Honoraria, Other: steering committee of clinical study; vifor: Consultancy, Honoraria. Hermine:AB Science: Consultancy, Equity Ownership, Honoraria, Research Funding; Novartis: Research Funding; Celgene: Research Funding. Viprakasit:Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; Celgene Corporation: Consultancy, Honoraria, Research Funding; Agios: Consultancy, Research Funding; Protagonist: Consultancy, Research Funding; Vifor: Consultancy, Research Funding; Ionis: Consultancy, Research Funding; La Jolla: Consultancy, Research Funding. Voskaridou:Genesis: Consultancy, Research Funding; Protagonist: Research Funding; Celgene Corporation: Consultancy, Research Funding; Acceleron: Consultancy, Research Funding; Addmedica: Membership on an entity's Board of Directors or advisory committees. Perrotta:Acceleron Pharma: Research Funding; Novartis: Honoraria, Research Funding. Kattamis:Celgene Corporation: Honoraria, Membership on an entity's Board of Directors or advisory committees; Apopharma: Honoraria; Vertex: Membership on an entity's Board of Directors or advisory committees; ViFOR: Membership on an entity's Board of Directors or advisory committees; Ionis: Membership on an entity's Board of Directors or advisory committees; Novartis Oncology: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Laadem:Celgene Corporation: Employment, Equity Ownership. Shetty:Celgene Corporation: Employment, Equity Ownership. Kuo:Celgene Corporation: Employment, Equity Ownership. Miteva:Celgene International: Employment. Zinger:Celgene Corporation: Employment. Linde:Acceleron Pharma: Employment, Equity Ownership; Fibrogen, Inc.: Equity Ownership; Abbott Laboratories, Inc.: Equity Ownership. Sinsimer:Celgene Corporation: Employment, Equity Ownership. Taher:Protagonist Therapeutics: Consultancy, Research Funding; La Jolla Pharmaceuticals: Consultancy, Research Funding; Celgene Corporation: Research Funding; Abfero: Consultancy; Novartis: Consultancy, Honoraria, Research Funding; Ionis Pharmaceuticals: Consultancy. OffLabel Disclosure: Luspatercept is an investigational therapy that is not approved for any use in any country. Luspatercept is currently being evaluated for potential use in patients with anemia due to myelodysplastic syndromes, beta-thalassemia, or myelofibrosis.

Introduction: Few treatment options are available to RBC transfusion-dependent pts with lower-risk MDS (LR-MDS) who are refractory/ineligible for erythropoiesis-stimulating agents (ESAs). Luspatercept is a first-in-class erythroid maturation agent that binds select TGF-β superfamily ligands to reduce aberrant Smad2/3 signaling and enhance late-stage erythropoiesis. In the phase 3, randomized, double-blind, placebo-controlled MEDALIST study (NCT02631070), luspatercept significantly reduced transfusion burden vs placebo. Longer-term efficacy analyses of the MEDALIST study (data cutoff Jan 7, 2019), including multiple responses, and safety are presented here. Methods: Eligible pts were ≥ 18 years of age with IPSS-R-defined Very low-, Low-, or Intermediate-risk MDS with RS (World Health Organization 2016 criteria); were refractory, intolerant, or unlikely to respond to ESAs (serum erythropoietin > 200 U/L); and required regular RBC transfusions. Pts were randomized 2:1 to luspatercept (1.0 mg/kg titrated up to 1.75 mg/kg, if needed) or placebo, subcutaneously every 3 weeks (wks). This analysis assessed the achievement and number of individual response periods of RBC transfusion independence (RBC-TI) ≥ 8 wks. Clinical benefit, defined as achieving RBC-TI ≥ 8 wks and/or modified hematologic improvement-erythroid (HI-E) response per International Working Group 2006 criteria, was also assessed, along with total duration of clinical benefit (time from achieving clinical benefit to discontinuation due to loss of benefit, adverse events [AEs], or other reasons). Longer-term efficacy and safety were also evaluated. Results: Pts were assessed for RBC transfusion burden/8 wks in the 16 wks before randomization: 66 pts received 2 to < 4 U RBCs (30.1% and 26.3% of pts receiving luspatercept and placebo, respectively), 64 received ≥ 4 to < 6 U (26.8% and 30.2%, respectively), and 99 received ≥ 6 U (43.1% and 43.4%, respectively); both arms had a median baseline burden of 5 RBC U/8 wks. Compared with our previous analysis and earlier data cutoff of May 8, 2018 (Fenaux P, et al. Blood. 2018;132:1), we now report that as of Jan 7, 2019, 72 (47.1%) pts treated with luspatercept and 12 (15.8%) treated with placebo achieved RBC-TI ≥ 8 wks. Analysis of multiple response periods of RBC-TI ≥ 8 wks in the luspatercept responders (i.e. initial RBC-TI ≥ 8 wks, followed by transfusion, followed by another period of RBC-TI ≥ 8 wks) demonstrated that 48 (66.7%) pts had ≥ 2 separate response periods, 22 (30.6%) had ≥ 3, 12 (16.7%) had ≥ 4 , and 7 (9.7%) had ≥ 5. Of the 12 pts achieving RBC-TI ≥ 8 wks with placebo, 4 (33.3%) had ≥ 2 responses; none had > 3. Overall, 48 (31.4%) pts receiving luspatercept and none receiving placebo remained on treatment as of the Jan 7, 2019 data cutoff. Median treatment duration was 50.9 (range 5.9-147.0) wks in pts receiving luspatercept vs 24.0 (range 7.4-103.0) wks in pts receiving placebo. Median duration of the longest period of RBC-TI ≥ 8 wks during Wks 1-48 was 30.6 (95% confidence interval [CI] 20.6-50.9) wks with luspatercept and 18.6 (95% CI 10.9-not evaluable) wks with placebo. Median total duration of clinical benefit was 83.6 and 26.8 wks for pts responding to luspatercept (n = 97) and placebo (n = 20), respectively. Of the 97 luspatercept-treated pts evaluable for clinical benefit, median duration of clinical benefit in pts with baseline transfusion burden of 4 to < 6 U/8 wks was 87.9 (range 13-125) wks, of < 4 U/8 wks was 84.7 (range 21-147) wks, and of ≥ 6 U/8 wks was 64.9 (range 8-122) wks. Twelve luspatercept-treated pts did not require a transfusion after the first dose of luspatercept up to Wk 48 or until time of analysis; as of Jan 7, 2019 data cutoff, 3 (25%) of those pts maintained response. AEs occurring more frequently with luspatercept vs placebo (fatigue, diarrhea, asthenia, dizziness) occurred early (Cycles 1-4), were mainly grade 1 or 2, decreased over time, and were not associated with a higher dose level. Progression to acute myeloid leukemia was similar in pts receiving luspatercept (n = 3 [2.0%]) and those receiving placebo (n = 1 [1.3%]). Conclusions: Most LR-MDS pts achieving RBC-TI and/or HI-E with luspatercept in the MEDALIST study had multiple responses with durable clinical benefit superior to that of pts receiving placebo, including those with a high baseline transfusion burden. AEs were mainly grade 1 or 2, decreased over time, and were not correlated with a higher dose level. Disclosures Fenaux: Aprea: Research Funding; Jazz: Honoraria, Research Funding; Astex: Honoraria, Research Funding; Celgene Corporation: Honoraria, Research Funding. Mufti:Cellectis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene Corporation: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Buckstein:Celgene: Consultancy, Honoraria, Research Funding; Takeda: Research Funding. Santini:Celgene Corporation: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Johnson & Johnson: Honoraria; Acceleron: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Menarini: Membership on an entity's Board of Directors or advisory committees. Díez-Campelo:Celgene Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Finelli:Celgene Corporation: Consultancy, Research Funding, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; Janssen: Consultancy, Speakers Bureau. Ilhan:Roche: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Alexion: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Sekeres:Celgene: Membership on an entity's Board of Directors or advisory committees; Syros: Membership on an entity's Board of Directors or advisory committees; Millenium: Membership on an entity's Board of Directors or advisory committees. Komrokji:DSI: Consultancy; JAZZ: Consultancy; celgene: Consultancy; Agios: Consultancy; pfizer: Consultancy; Novartis: Speakers Bureau; JAZZ: Speakers Bureau; Incyte: Consultancy. List:Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding. Zeidan:Trovagene: Consultancy, Honoraria, Research Funding; Incyte: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding; ADC Therapeutics: Research Funding; Jazz: Honoraria; Ariad: Honoraria; Agios: Honoraria; Novartis: Honoraria; Astellas: Honoraria; Daiichi Sankyo: Honoraria; Cardinal Health: Honoraria; Seattle Genetics: Honoraria; BeyondSpring: Honoraria; Boehringer-Ingelheim: Consultancy, Honoraria, Research Funding; Abbvie: Consultancy, Honoraria, Research Funding; Acceleron Pharma: Consultancy, Honoraria, Research Funding; Celgene Corporation: Consultancy, Honoraria, Research Funding; Medimmune/AstraZeneca: Research Funding; Otsuka: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding. Verma:Stelexis: Equity Ownership, Honoraria; Acceleron: Honoraria; Celgene: Honoraria; BMS: Research Funding; Janssen: Research Funding. Laadem:Celgene Corporation: Employment, Equity Ownership. Ito:Celgene Corporation: Employment, Equity Ownership. Zhang:Celgene Corporation: Employment, Equity Ownership. Rampersad:Celgene Corp: Employment, Equity Ownership. Sinsimer:Celgene Corporation: Employment, Equity Ownership. Linde:Acceleron Pharma: Employment, Equity Ownership; Fibrogen, Inc.: Equity Ownership; Abbott Laboratories, Inc.: Equity Ownership. Garcia-Manero:Amphivena: Consultancy, Research Funding; Helsinn: Research Funding; Novartis: Research Funding; AbbVie: Research Funding; Celgene: Consultancy, Research Funding; Astex: Consultancy, Research Funding; Onconova: Research Funding; H3 Biomedicine: Research Funding; Merck: Research Funding. Platzbecker:Novartis: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; Celgene: Consultancy, Honoraria. OffLabel Disclosure: Luspatercept is an investigational therapy that is not approved for any use in any country. Luspatercept is currently being evaluated for potential use in patients with anemia due to myelodysplastic syndromes, beta-thalassemia, or myelofibrosis.

BackgroundInteractions between host immune cells and gut microbiota are crucial for the integrity and function of the intestine. How these interactions regulate immune cell responses in the intestine remains a major gap in the field.AimWe have identified the signalling lymphocyte activation molecule family member 4 (SLAMF4) as an immunomodulator of the intestinal immunity. The aim is to determine how SLAMF4 is acquired in the gut and what its contribution to intestinal immunity is.MethodsExpression of SLAMF4 was assessed in mice and humans. The mechanism of induction was studied using GFPtgbone marrow chimaera mice, lymphotoxin α and TNLG8A-deficient mice, as well as gnotobiotic mice. Role in immune protection was revealed using oral infection withListeria monocytogenesandCytobacter rodentium.ResultsSLAMF4 is a selective marker of intestinal immune cells of mice and humans. SLAMF4 induction occurs directly in the intestinal mucosa without the involvement of the gut-associated lymphoid tissue. Gut bacterial products, particularly those of gut anaerobes, and gut-resident antigen-presenting cell (APC)TNLG8Aare key contributors of SLAMF4 induction in the intestine. Importantly, lack of SLAMF4 expression leads the increased susceptibility of mice to infection by oral pathogens culminating in their premature death.ConclusionsSLAMF4 is a marker of intestinal immune cells which contributes to the protection against enteric pathogens and whose expression is dependent on the presence of the gut microbiota. This discovery provides a possible mechanism for answering the long-standing question of how the intertwining of the host and gut microbial biology regulates immune cell responses in the gut.

In this work we describe the identification of a copper-inducible regulon in Mycobacterium tuberculosis (Mtb). Among the regulated genes was Rv0190/MT0200, a paralogue of the copper metalloregulatory repressor CsoR. The five-locus regulon, which includes a gene that encodes the copper-protective metallothionein MymT, was highly induced in wild-type Mtb treated with copper, and highly expressed in an Rv0190/MT0200 mutant. Importantly, the Rv0190/MT0200 mutant was hyper-resistant to copper. The promoters of all five loci share a palindromic motif that was recognized by the gene product of Rv0190/MT0200. For this reason we named Rv0190/MT0200 RicR for regulated in copper repressor. Intriguingly, several of the RicR-regulated genes, including MymT, are unique to pathogenic Mycobacteria. The identification of a copper-responsive regulon specific to virulent mycobacterial species suggests copper homeostasis must be maintained during an infection. Alternatively, copper may provide a cue for the expression of genes unrelated to metal homeostasis, but nonetheless necessary for survival in a host.

Despite our knowledge of the protective role of antibodies passed to infants through breast milk, our understanding of immunity transfer via maternal leukocytes is still limited. To emulate the immunological interface between the mother and her infant while breast-feeding, we used murine pups fostered after birth onto MHC-matched and MHC-mismatched dams. Overall, data revealed that: 1) Survival of breast milk leukocytes in suckling infants is possible, but not significant after the foster-nursing ceases; 2) Most breast milk lymphocytes establish themselves in specific areas of the intestine termed Peyer's patches (PPs); 3) While most leukocytes in the milk bolus were myeloid cells, the majority of breast milk leukocytes localized to PPs were T lymphocytes, and cytotoxic T cells (CTLs) in particular; 4) These CTLs exhibit high levels of the gut-homing molecules α4β7 and CCR9, but a reduced expression of the systemic homing marker CD62L; 5) Under the same activation conditions, transferred CD8 T cells through breast milk have a superior capacity to produce potent cytolytic and inflammatory mediators when compared to those generated by the breastfed infant. It is therefore possible that maternal CTLs found in breast milk are directed to the PPs to compensate for the immature adaptive immune system of the infant in order to protect it against constant oral infectious risks during the postnatal phase.

Drug resistance, particularly vancomycin and methicillin resistance, in Staphylococcus aureus continues to emerge as a significant public health threat in both the hospital and community settings. In addition to the limited treatment options, S. aureus strains acquire and express numerous virulence factors that continue to increase its ability to cause a wide spectrum of human disease. As a result, empirical treatment decisions are confounded and there is a heightened need for a diagnostic test (or assay) to rapidly identify antibiotic resistance and specific virulence determinants and indicate the appropriate treatment. To that end we developed a platform using multiplex molecular beacon probes with real-time PCR for the rapid detection of drug resistance-determining genes and virulence factors in S. aureus . In this study, we demonstrate the specificity and sensitivity of our platform for detection of the genes conferring methicillin ( mecA ) and vancomycin ( vanA ) resistance as well as a gene encoding the virulence factor Panton-Valentine leucocidin ( lukF ) in S. aureus isolates.

Introduction and objective The role of secreted gut microbial components in the initiation of systemic inflammation and consequences of antibiotic therapies on this inflammatory process are poorly elucidated. We investigate whether peripheral innate cells mount an inflammatory response to gut microbial components, the immune cells that are the primary drivers of systemic inflammation, the bacterial populations that are predominantly responsible, and whether perioperative antibiotics affect these processes. Method and experimental design Conditioned supernatants from gut microbes were used to stimulate murine innate cell types in vitro and in vivo , and proinflammatory responses were characterised. Effects of antibiotic therapies on these responses were investigated using a model of experimental intestinal barrier damage induced by dextran sodium sulfate. Results Proinflammatory responses in the periphery are generated by components of anaerobes from the Bacteroidetes phylotype and these responses are primarily produced by myeloid dendritic cells. We found that the common prophylactic therapy for sepsis (oral neomycin and metronidazole administered to patients the day prior to surgery) is ineffective for clearing Bacteroidetes from the murine intestine. A point of critical consequence of this result is the increased systemic inflammation and premature death observed in treated mice, and these outcomes appear to be independent of gut bacterial spread in the initial phase of intestinal barrier damage. Importantly, spillage of gut microbial products, rather than dissemination of gut microbes, may underlay the initiation of systemic inflammation leading to death. Conclusions Our data further affirm the importance of a balanced gut microflora biodiversity in host immune homeostasis and reinforce the notion that inadequate antibiotic therapy can have detrimental effects on overall immune system.

Leprosy is a chronic but treatable infectious disease caused by the intracellular pathogen Mycobacterium leprae . Host immunity to M. leprae determines the diversity of clinical manifestations seen in patients, from tuberculoid leprosy with robust production of Th1-type cytokines to lepromatous disease, characterized by elevated levels of Th2-type cytokines and a suboptimal proinflammatory response. Previous reports have indicated that M. leprae is a poor activator of macrophages and dendritic cells in vitro. To understand whether M. leprae fails to elicit an optimal Th1 immune response or actively interferes with its induction, we have examined the early interactions between M. leprae and monocytes from healthy human donors. We found that, in naïve monocytes, M. leprae induced high levels of the negative regulatory molecules MCP-1 and interleukin-1 (IL-1) receptor antagonist (IL-1Ra), while suppressing IL-6 production through phosphoinositide-3 kinase (PI3K)-dependent mechanisms. In addition, low levels of proinflammatory cytokines were observed in association with reduced activation of nuclear factor-κB (NF-κB) and delayed activation of IL-1β-converting enzyme, ICE (caspase-1), in monocytes stimulated with M. leprae compared with Mycobacterium bovis BCG stimulation. Interestingly, although in itself a weak stimulator of cytokines, M. leprae primed the cells for increased production of tumor necrosis factor alpha and IL-10 in response to a strongly inducing secondary stimulus. Taken together, our results suggest that M. leprae plays an active role to control the release of cytokines from monocytes by providing both positive and negative regulatory signals via multiple signaling pathways involving PI3K, NF-κB, and caspase-1.

Mycobacterium tuberculosispossesses a diversity of potential virulence factors including complex branched lipids such as the phenolic glycolipid PGL-tb. PGL-tb expression by the clinicalM. tuberculosisisolate HN878 has been associated with a less efficient Th1 response and increased virulence in mice and rabbits. It has been suggested that the W-Beijing family is the only group ofM. tuberculosisstrains with an intactpks1-15gene, required for the synthesis of PGL-tb and capable of producing PGL-tb. We have found that some strains with an intactpks1-15do not produce PGL-tb while others may produce a variant of PGL-tb. We examined the early host cytokine response to infection with these strains in vitro to better understand the effect of PGL-tb synthesis on immune responses. In addition, we generated a PGL-tb-producing H37Rv in order to determine the effect of PGL-tb production on the host immune response during infection by a strain normally devoid of PGL-tb synthesis. We observed that PGL-tb production by clinicalM. tuberculosisisolates affected cytokine production differently depending on the background of the strain. Importantly, while ectopic PGL-tb production by H37Rv suppressed the induction of several pro- and anti-inflammatory cytokines in vitro in human monocytes, it did not lead to increased virulence in infected mice and rabbits. Collectively, our data indicate that, while PGL-tb may play a role in the immunogenicity and/or virulence ofM. tuberculosis, it probably acts in concert with other bacterial factors which seem to be dependent on the background of the strain.

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is an emerging threat worldwide. CA-MRSA strains differ from hospital-acquired MRSA strains in their antibiotic susceptibilities and genetic backgrounds. Using several genotyping methods, we clearly define CA-MRSA at the genetic level and demonstrate that the prototypic CA-MRSA strain, MW2, has spread as a homogeneous clonal strain family that is distinct from other CA-MRSA strains. The Panton-Valentine leucocidin (PVL)-encoding genes, lukF and lukS , are prevalent among CA-MRSA strains and have previously been associated with CA-MRSA infections. To better elucidate the role of PVL in the pathogenesis of CA-MRSA, we first analyzed the distribution and expression of PVL among different CA-MRSA strains. Our data demonstrate that PVL genes are differentially distributed among CA-MRSA strains and, when they are present, are always transcribed, albeit with strain-to-strain variability of transcript levels. To directly test whether PVL is critical for the pathogenesis of CA-MRSA, we evaluated the lysis of human polymorphonuclear leukocytes (PMNs) during phagocytic interaction with PVL-positive and PVL-negative CA-MRSA strains. Unexpectedly, there was no correlation between PVL expression and PMN lysis, suggesting that additional virulence factors underlie leukotoxicity and, thus, the pathogenesis of CA-MRSA.