No abstract

Neutrophils are a major component of the innate immune response. Their homeostasis is maintained, in part, by the regulated release of neutrophils from the bone marrow. Constitutive expression of the chemokine CXCL12 by bone marrow stromal cells provides a key retention signal for neutrophils in the bone marrow through activation of its receptor, CXCR4. Attenuation of CXCR4 signaling leads to entry of neutrophils into the circulation through unknown mechanisms. We investigated the role of CXCR2-binding ELR + chemokines in neutrophil trafficking using mouse mixed bone marrow chimeras reconstituted with Cxcr2 -/-and WT cells. In this context, neutrophils lacking CXCR2 were preferentially retained in the bone marrow, a phenotype resembling the congenital disorder myelokathexis, which is characterized by chronic neutropenia. Additionally, transient disruption of CXCR4 failed to mobilize Cxcr2 -/-neutrophils. However, neutrophils lacking both CXCR2 and CXCR4 displayed constitutive mobilization, showing that CXCR4 plays a dominant role in neutrophil trafficking. With regard to CXCR2 ligands, bone marrow endothelial cells and osteoblasts constitutively expressed the ELR + chemokines CXCL1 and CXCL2, and CXCL2 expression was induced in endothelial cells during G-CSF-induced neutrophil mobilization. Collectively, these data suggest that CXCR2 signaling is a second chemokine axis that interacts antagonistically with CXCR4 to regulate neutrophil release from the bone marrow.

No abstract

Recent studies demonstrate that inflammatory signals regulate hematopoietic stem cells (HSCs). Granulocyte-colony stimulating factor (G-CSF) is often induced with infection and plays a key role in the stress granulopoiesis response. However, its effects on HSCs are less clear. Herein, we show that treatment with G-CSF induces expansion and increased quiescence of phenotypic HSCs, but causes a marked, cell-autonomous HSC repopulating defect associated with induction of toll-like receptor (TLR) expression and signaling. The G-CSF-mediated expansion of HSCs is reduced in mice lacking TLR2, TLR4 or the TLR signaling adaptor MyD88. Induction of HSC quiescence is abrogated in mice lacking MyD88 or in mice treated with antibiotics to suppress intestinal flora. Finally, loss of TLR4 or germ free conditions mitigates the G-CSF-mediated HSC repopulating defect. These data suggest that low level TLR agonist production by commensal flora contributes to the regulation of HSC function and that G-CSF negatively regulates HSCs, in part, by enhancing TLR signaling.

Methods and Results: This study was a phase I, open-label, dose-escalating registry control group study.Nineteen patients received MultiStem (20 million, n‫;6؍‬ 50 million, n‫;7؍‬ or 100 million, n‫)6؍‬ and 6 subjects were assigned to the registry control group. Two to 5 days after AMI, we delivered MultiStem to the adventitia of the infarct-related vessel in patients with first-time STEMI. All patients underwent primary percutaneous coronary intervention with resulting Thrombolysis In Myocardial Infarction grade 3 flow and with ejection fraction (EF) <45% as determined by echocardiogram or left ventriculogram within 12 hours of primary percutaneous coronary intervention. The cell product (20 million, 50 million, or 100 million) was well tolerated, and no serious adverse events were deemed related to MultiStem. There was no increase in creatine kinase-MB or troponin associated with the adventitial delivery of MultiStem. In patients with EF determined to be <45% by a core laboratory within 24 hours before the MultiStem injection, we observed a 0.9 (n‫,)4؍‬ 3.9 (n‫,)4؍‬ 13.5 (n‫,)5؍‬ and 10.9 (n‫)2؍‬ percent absolute increases in EF in the registry, 20 million, 50 million, and 100 million dose groups, respectively. The increases in EF in the 50 million and 100 million groups were accompanied by 25.4 and 8.4 mL increases in left ventricular stroke volume. Conclusions:In this study, the delivery of MultiStem to the myocardium in patients with recent STEMI was well tolerated and safe. In patients who exhibited significant myocardial damage, the delivery of >50 million MultiStem resulted in improved EF and stroke volume 4 months later. These findings support further development of MultiStem in patients with AMI and they validate the potential of a system for delivery of adult stem cells at any time after primary percutaneous coronary intervention. (Circ Res. 2012;110:304-311.)

No abstract

2390 Osteoblast lineage cells have been shown to play an important role in regulating hematopoietic stem cells (HSCs), and there is intense interest in identifying HSC regulatory molecules they produce. It has been reported that HSCs lie adjacent to spindle-shaped N-cadherin+ osteoblasts (SNO cells) and home to them in irradiated recipients, suggesting that N-cadherin may tether HSCs to their niche. Studies of N-cadherin expression in HSCs and its role in regulating HSC function have yielded conflicting results. Conditional deletion of Cdh2 (encoding N-cadherin) in HSCs had no affect on HSC number or function. On the other hand, silencing of N-cadherin using shRNA or expression of a dominant negative N-cadherin mutant resulted in the loss of HSC quiescence and repopulating activity. In addition to forming homodimers, N-cadherin is able to interact with other cadherins such E-cadherin, C-cadherin, and R-cadherin as well as non-cadherins such as KLRG1. Thus it is possible that expression of other cadherins in HSCs may compensate for the loss of N-cadherin. Rather than attempt to reconcile the conflicting results involving HSC production of N-cadherin, we chose to investigate what role that osteolineage production of N-cadherin plays in the regulation of hematopoiesis. Specifically, we conditionally deleted N-cadherin from osteoblast lineage cells using transgenic mice expressing Cre-recombinase under control of the osterix promoter (Osx-Cre mice). Our lineage mapping studies using the Osx-Cre mice demonstrated that this transgene directs recombination in SNO cells in the bone marrow. Accordingly, we intercrossed the Osx-Cre mice with Cdh2flox mice to generate N-cadherin-deleted (Cdh2flox/flox Osx-Cre) and control (Cdh2flox/flox) mice. N-cadherin expression was efficiently ablated in osteoblast lineage cells as assessed by mRNA expression (20-fold lower than control mice) and immunostaining of bone sections. Blood counts, bone marrow and spleen cellularity, and leukocyte differentials in N-cadherin-deleted mice were no different from control mice, indicating that basal hematopoiesis is normal. Moreover, the number of phenotypic HSCs (defined as lin− c-kit+ sca+ CD41− CD48− CD150+ cells) and their cell cycle status was normal. HSC long-term repopulating activity and self-renewal capacity were assessed by competitive repopulation assays and serial transplantation, respectively; we show that loss of osteoblast N-cadherin had no effect on these parameters. N-cadherin has been implicated in the homing and retention of HSCs to the bone marrow. However, we show that homing and engraftment of wildtype cells into N-cadherin-deleted recipients was normal. Finally, we tested the response to G-CSF, a potent HSC mobilizing stimulus, which leads to a profound loss of osteoblasts. N-cadherin-deleted mice showed normal mobilization of progenitors to the blood and spleen. Together, our data show that N-cadherin expression on SNO cells (and other osteoblast-lineage cells) is dispensable for HSC maintenance and trafficking. Disclosures: No relevant conflicts of interest to declare.

Background: Chimeric antigen receptor T-cells (CAR-T) targeting CD19 have shown clinical efficacy in high-risk B-cell lymphomas, which has led to approval of 2 such therapies (axicabtagene ciloleucel and tisagenlecleucel) for large B-cell lymphoma after 2 lines of treatment. Despite the promising results, complete remission (CR) is achieved in ~ 50% of patients, and with longer follow-up progression-free survival is around 40%. Therefore, finding effective treatments for high-risk B-NHLs remains an unmet need. CD20 is a proven therapeutic target for B-Cell Non-Hodgkin Lymphomas (B-NHL), supported by previously approved naked and radiolabeled anti-CD20 monoclonal antibodies and a number of studies investigating novel bispecific antibodies targeting this antigen. CD20-targeted CAR-T is another potential adoptive immunotherapy option that could be utilized in combination or sequentially before or after CD19 CAR-T, depending on efficacy. Here, we present our ongoing phase I/II clinical trial investigating safety and efficacy of CD20 CAR-T for high-risk B-NHLs (NCT03277729). Methods: MB-106 is a fully human third-generation CD20 targeted CAR-T with both 4-1BB and CD28 costimulatory domains. In the phase I portion of the study we use a continual reassessment method dose escalation design to find the maximally tolerated dose. Lymphodepletion (LD) chemotherapy consists of fludarabine and cyclophosphamide. Patients (pts) will undergo a mandatory biopsy before LD to confirm the diagnosis and CD20 expression. A repeat research biopsy will be done between 10-16 days after CAR-T infusion (Figure 1). Except for the first patient of each dose cohort, treatment is given in the outpatient setting (Fred Hutch/Seattle Cancer Care Alliance) and pts will only be admitted to the University of Washington Medical Center if clinically indicated after CAR-T infusion. Response to treatment will be assessed on day 28 using Lugano criteria. Patients with relapsed or refractory CD20 positive B-NHL are eligible, including but not limited to DLBCL, primary mediastinal lymphoma, follicular lymphoma or other indolent histologies, and mantle cell lymphoma. Prior treatment with CD19 CAR-T is permitted as long as there is evidence of B-cell recovery in peripheral blood (≥ 20 B cells/µl) as a functional test to rule out persistent CD19 CAR-Ts. Patients need to meet standard organ function criteria and have adequate blood counts (ANC >750, Hb >8.5, Plts >50,000). Patients with significant neurologic conditions, active CNS lymphoma, or need for systemic immunosuppressive therapy are excluded from the study. Disclosures Shadman: Mustang Bio: Research Funding; Verastem: Consultancy; Genentech: Consultancy, Research Funding; Atara Biotherapeutics: Consultancy; Pharmacyclics: Consultancy, Research Funding; ADC Therapeutics: Consultancy; Celgene: Research Funding; Sound Biologics: Consultancy; TG Therapeutic: Research Funding; Acerta Pharma: Research Funding; Sunesis: Research Funding; Gilead: Consultancy, Research Funding; AbbVie: Consultancy, Research Funding; BeiGene: Research Funding; Astra Zeneca: Consultancy. Gopal:Seattle Genetics, Pfizer, Janssen, Gilead, Sanofi, Spectrum, Amgen, Aptevo, BRIM bio, Acerta, I-Mab-pharma, Takeda, Compliment, Asana Bio, and Incyte: Honoraria; Seattle Genetics, Pfizer, Janssen, Gilead, Sanofi, Spectrum, Amgen, Aptevo, BRIM bio, Acerta, I-Mab-pharma, Takeda, Compliment, Asana Bio, and Incyte.: Consultancy; Teva, Bristol-Myers Squibb, Merck, Takeda, Seattle Genetics, Pfizer, Janssen, Takeda, and Effector: Research Funding. Smith:Pharmacyclics: Research Funding; Genentech: Research Funding; Ignyta (spouse): Research Funding; Portola Pharmaceuticals: Research Funding; Bristol-Myers Squibb (spouse): Research Funding; Ayala (spouse): Research Funding; AstraZeneca: Membership on an entity's Board of Directors or advisory committees, Research Funding; Acerta Pharma BV: Research Funding; Merck Sharp & Dohme Corp: Consultancy, Research Funding; Incyte Corporation: Research Funding; Seattle Genetics: Research Funding; Denovo Biopharma: Research Funding. Lynch:Juno Therapeutics: Research Funding; Rhizen Pharmaceuticals S.A: Research Funding; Takeda Pharmaceuticals: Research Funding; Johnson Graffe Keay Moniz & Wick LLP: Consultancy; Incyte Corporation: Research Funding; T.G. Therapeutics: Research Funding. Ujjani:Pharmacyclics: Honoraria; PCYC: Research Funding; Gilead: Consultancy; Astrazeneca: Consultancy; Atara: Consultancy; Genentech: Honoraria; AbbVie: Honoraria, Research Funding. Turtle:T-CURX: Membership on an entity's Board of Directors or advisory committees; Humanigen: Other: Ad hoc advisory board member; Eureka Therapeutics: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Precision Biosciences: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Caribou Biosciences: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Allogene: Other: Ad hoc advisory board member; Juno Therapeutics: Patents & Royalties: Co-inventor with staff from Juno Therapeutics; pending, Research Funding; Nektar Therapeutics: Other: Ad hoc advisory board member, Research Funding; Kite/Gilead: Other: Ad hoc advisory board member; Novartis: Other: Ad hoc advisory board member. Yeung:Pfizer: Research Funding; OBI Pharmaceutical: Research Funding; Merck: Consultancy; DiaCarta: Consultancy. Sersch:Mustang Bio: Employment. Maloney:Juno Therapeutics: Honoraria, Patents & Royalties: patients pending , Research Funding; Celgene,Kite Pharma: Honoraria, Research Funding; BioLine RX, Gilead,Genentech,Novartis: Honoraria; A2 Biotherapeutics: Honoraria, Other: Stock options . Till:Mustang Bio: Patents & Royalties, Research Funding.