Class I PI3K regulatory subunits control differentiation of dendritic cell subsets and regulate Flt3L mediated signal transduction.

Dendritic cells (DCs) play pivotal roles in initiating and shaping both innate and adaptive immune responses. The spatiotemporal expression of transcription factor networks and activation of specific signal transduction pathways determine the specification, distribution and differentiation of DC subsets. Even though pioneering studies have established indispensable roles for specific catalytic subunits (p110δ and p110γ) in immune cells, functions of the regulatory subunits, particularly of Class I PI3K, within the hematopoietic system remain incompletely understood. In the study presented here, we deleted the key regulatory subunits-p85α and p85ß of the Class IA PI3K in hematopoietic cells and studied its impact on DC differentiation. Our studies identify that a deficiency of p85 causes increased differentiation of conventional DC (cDC) 2 and plasmacytoid DC (pDC) subsets in the spleen. On the other hand, DC numbers in the bone marrow (BM), thymus and lymph nodes were decreased in p85 mutant mice. Analysis of DC-specific progenitors and precursors indicated increased numbers in the BM and spleen of p85 deficient mice. In-vitro differentiation studies demonstrated augmented DC-differentiation capacities of p85 deficient BM cells in the presence of GM-CSF and Flt3L. BM chimera studies established that p85 deficiency affects DC development through cell intrinsic mechanisms. Molecular studies revealed increased proliferation of DCs and common DC progenitors (CDPs) in the absence of p85 and altered signal transduction pathways in p85 mutant DC subsets in response to Flt3L. In essence, data presented here, for the first time, unequivocally establish that the P85α subunit of class IA PI3Ks has an indispensable role in the development and maintenance of DCs.

Lentiviral globin gene therapy with reduced-intensity conditioning in adults with ß-thalassemia: a phase 1 trial.

ß-Thalassemias are inherited anemias that are caused by the absent or insufficient production of the ß chain of hemoglobin. Here we report 6-8-year follow-up of four adult patients with transfusion-dependent ß-thalassemia who were infused with autologous CD34+ cells transduced with the TNS9.3.55 lentiviral globin vector after reduced-intensity conditioning (RIC) in a phase 1 clinical trial ( NCT01639690) . Patients were monitored for insertional mutagenesis and the generation of a replication-competent lentivirus (safety and tolerability of the infusion product after RIC-primary endpoint) and engraftment of genetically modified autologous CD34+ cells, expression of the transduced ß-globin gene and post-transplant transfusion requirements (efficacy-secondary endpoint). No unexpected safety issues occurred during conditioning and cell product infusion. Hematopoietic gene marking was very stable but low, reducing transfusion requirements in two patients, albeit not achieving transfusion independence. Our findings suggest that non-myeloablative conditioning can achieve durable stem cell engraftment but underscore a minimum CD34+ cell transduction requirement for effective therapy. Moderate clonal expansions were associated with integrations near cancer-related genes, suggestive of non-erythroid activity of globin vectors in stem/progenitor cells. These correlative findings highlight the necessity of cautiously monitoring patients harboring globin vectors.

Depletion of high-content CD14+ cells from apheresis products is critical for successful transduction and expansion of CAR T cells during large-scale cGMP manufacturing.

With the US Food and Drug Administration (FDA) approval of four CD19- and one BCMA-targeted chimeric antigen receptor (CAR) therapy for B cell malignancies, CAR T cell therapy has finally reached the status of a medicinal product. The successful manufacturing of autologous CAR T cell products is a key requirement for this promising treatment modality. By analyzing the composition of 214 apheresis products from 210 subjects across eight disease indications, we found that high CD14+ cell content poses a challenge for manufacturing CAR T cells, especially in patients with non-Hodgkin's lymphoma and multiple myeloma caused by the non-specific phagocytosis of the magnetic beads used to activate CD3+ T cells. We demonstrated that monocyte depletion via rapid plastic surface adhesion significantly reduces the CD14+ monocyte content in the apheresis products and simultaneously boosts the CD3+ content. We established a 40% CD14+ threshold for the stratification of apheresis products across nine clinical trials and demonstrated the effectiveness of this procedure by comparing manufacturing runs in two phase 1 clinical trials. Our study suggests that CD14+ content should be monitored in apheresis products, and that the manufacturing of CAR T cells should incorporate a step that lessens the CD14+ cell content in apheresis products containing more than 40% to maximize the production success.

APOBEC3H structure reveals an unusual mechanism of interaction with duplex RNA.

The APOBEC3 family of cytidine deaminases cause lethal hypermutation of retroviruses via deamination of newly reverse-transcribed viral DNA. Their ability to bind RNA is essential for virion infiltration and antiviral activity, yet the mechanisms of viral RNA recognition are unknown. By screening naturally occurring, polymorphic, non-human primate APOBEC3H variants for biological and crystallization properties, we obtained a 2.24-Å crystal structure of pig-tailed macaque APOBEC3H with bound RNA. Here, we report that APOBEC3H forms a dimer around a short RNA duplex and, despite the bound RNA, has potent cytidine deaminase activity. The structure reveals an unusual RNA-binding mode in which two APOBEC3H molecules at opposite ends of a seven-base-pair duplex interact extensively with both RNA strands, but form no protein-protein contacts. CLIP-seq analysis revealed that APOBEC3H preferentially binds to sequences in the viral genome predicted to contain duplexes, a property that may facilitate both virion incorporation and catalytic activity.

A single gp120 residue can affect HIV-1 tropism in macaques.

Species-dependent variation in proteins that aid or limit virus replication determines the ability of lentiviruses to jump between host species. Identifying and overcoming these differences facilitates the development of animal models for HIV-1, including models based on chimeric SIVs that express HIV-1 envelope (Env) glycoproteins, (SHIVs) and simian-tropic HIV-1 (stHIV) strains. Here, we demonstrate that the inherently poor ability of most HIV-1 Env proteins to use macaque CD4 as a receptor is improved during adaptation by virus passage in macaques. We identify a single amino acid, A281, in HIV-1 Env that consistently changes during adaptation in macaques and affects the ability of HIV-1 Env to use macaque CD4. Importantly, mutations at A281 do not markedly affect HIV-1 Env neutralization properties. Our findings should facilitate the design of HIV-1 Env proteins for use in non-human primate models and thus expedite the development of clinically relevant reagents for testing interventions against HIV-1.

Slicer Endonuclease Argonaute 2 Is a Negative Regulator of Hematopoietic Stem Cell Quiescence.

Hematopoietic stem cells (HSCs) are capable of both self-renewing throughout the lifetime of an organism and differentiating into all lineages of the blood system. A proper balance between quiescence and proliferation is critical for the self-renewal and functions of HSCs. The choice of HSCs to remain quiescent or to enter proliferation has been tightly regulated by a variety of cell intrinsic and extrinsic pathways. Identifying molecular players that control HSC quiescence and proliferation may lead to new treatment strategies and therapeutic interventions for hematologic disorders. To identify the functions of the slicer endonuclease Argonaute (Ago) 2 in the physiology of HSCs, we generated Ago2(Hem-KO) mice, that are deficient for Ago2 in HSCs and in their progeny. Analysis of Ago2(Hem-KO) mice indicated that a loss of Ago2 results in reduced HSC pool size and altered frequencies of hematopoietic progenitors. Ago2 deficient HSCs exhibit defective multilineage differentiation capacities and diminished repopulation abilities, in a cell intrinsic manner. Interestingly, Ago2 mutant HSCs remain largely quiescent and show reduced entry into cell cycle. Genome-wide transcriptome studies and gene set enrichment analysis revealed that Ago2 deficient HSCs downregulate the "HSC signature" and upregulate the "lineage signature." Moreover, our analysis on transcription factors (TFs) identified that a loss of Ago2 is sufficient to alter the "molecular signature" and "TF networks" that control the quiescent and proliferative states of HSCs. In essence, our study identified Ago2 as a key determinant of quiescence exit in HSCs. Stem Cells 2016;34:1343-1353.

Lack of the ubiquitin-editing enzyme A20 results in loss of hematopoietic stem cell quiescence.

A balance between quiescence and proliferation is critical for proper maintenance of the hematopoietic stem cell (HSC) pool. Although a lot is known about hematopoiesis, molecular mechanisms that control HSC quiescence remain largely unknown. The ubiquitin-editing enzyme A20 functions as a central regulator of inflammation and adaptive immunity. Here, we show that a deficiency of A20 in the hematopoietic system causes anemia, lymphopenia, and postnatal lethality. Lack of A20 in HSCs results in diminished pool size, impaired radioprotection, defective repopulation, and loss of quiescence. A20-deficient HSCs display increased IFN-γ signaling, caused by augmented NF-κB activation. Strikingly, deletion of both IFN-γ and A20 in hematopoietic cells results in partial rescue of the HSC phenotype. We anticipate that our experiments will facilitate the understanding of mechanisms through which A20-mediated inflammatory signals control HSC quiescence and functions.