Showing papers by "David Baltimore published in 2011"

miR-146a is a significant brake on autoimmunity, myeloproliferation, and cancer in mice

Abstract: Excessive or inappropriate activation of the immune system can be deleterious to the organism, warranting multiple molecular mechanisms to control and properly terminate immune responses. MicroRNAs (miRNAs), ∼22-nt-long noncoding RNAs, have recently emerged as key posttranscriptional regulators, controlling diverse biological processes, including responses to non-self. In this study, we examine the biological role of miR-146a using genetically engineered mice and show that targeted deletion of this gene, whose expression is strongly up-regulated after immune cell maturation and/or activation, results in several immune defects. Collectively, our findings suggest that miR-146a plays a key role as a molecular brake on inflammation, myeloid cell proliferation, and oncogenic transformation.

Cell-to-cell spread of HIV permits ongoing replication despite antiretroviral therapy

Abstract: Latency and ongoing replication have both been proposed to explain the drug-insensitive human immunodeficiency virus (HIV) reservoir maintained during antiretroviral therapy. Here we explore a novel mechanism for ongoing HIV replication in the face of antiretroviral drugs. We propose a model whereby multiple infections per cell lead to reduced sensitivity to drugs without requiring drug-resistant mutations, and experimentally validate the model using multiple infections per cell by cell-free HIV in the presence of the drug tenofovir. We then examine the drug sensitivity of cell-to-cell spread of HIV, a mode of HIV transmission that can lead to multiple infection events per target cell. Infections originating from cell-free virus decrease strongly in the presence of antiretrovirals tenofovir and efavirenz whereas infections involving cell-to-cell spread are markedly less sensitive to the drugs. The reduction in sensitivity is sufficient to keep multiple rounds of infection from terminating in the presence of drugs. We examine replication from cell-to-cell spread in the presence of clinical drug concentrations using a stochastic infection model and find that replication is intermittent, without substantial accumulation of mutations. If cell-to-cell spread has the same properties in vivo, it may have adverse consequences for the immune system, lead to therapy failure in individuals with risk factors, and potentially contribute to viral persistence and hence be a barrier to curing HIV infection.

NF-κB dysregulation in microRNA-146a–deficient mice drives the development of myeloid malignancies

Abstract: MicroRNA miR-146a has been implicated as a negative feedback regulator of NF-κB activation. Knockout of the miR-146a gene in C57BL/6 mice leads to histologically and immunophenotypically defined myeloid sarcomas and some lymphomas. The sarcomas are transplantable to immunologically compromised hosts, showing that they are true malignancies. The animals also exhibit chronic myeloproliferation in their bone marrow. Spleen and marrow cells show increased transcription of NF-κB–regulated genes and tumors have higher nuclear p65. Genetic ablation of NF-κB p50 suppresses the myeloproliferation, showing that dysregulation of NF-κB is responsible for the myeloproliferative disease.

MicroRNA-125b Potentiates Macrophage Activation

Abstract: MicroRNA (miR)-125b expression is modulated in macrophages in response to stimulatory cues. In this study, we report a functional role of miR-125b in macrophages. We found that miR-125b is enriched in macrophages compared with lymphoid cells and whole immune tissues. Enforced expression of miR-125b drives macrophages to adapt an activated morphology that is accompanied by increased costimulatory factor expression and elevated responsiveness to IFN-y, whereas anti–miR-125b treatment decreases CD80 surface expression. To determine whether these alterations in cell signaling, gene expression, and morphology have functional consequences, we examined the ability of macrophages with enhanced miR-125b expression to present Ags and found that they better stimulate T cell activation than control macrophages. Further indicating increased function, these macrophages were more effective at killing EL4 tumor cells in vitro and in vivo. Moreover, miR-125b repressed IFN regulatory factor 4 (IRF4), and IRF4 knockdown in macrophages mimicked the miR-125b overexpression phenotype. In summary, our evidence suggests that miR-125b is at least partly responsible for generating the activated nature of macrophages, at least partially by reducing IRF4 levels, and potentiates the functional role of macrophages in inducing immune responses.

NF-κB is 25

Abstract: NF-κB-mediated inflammatory biology can be formulated as the following five states: latency, induction, response, resolution and pathology. The first four involve carefully tuned molecular processes; pathology is the loss of control.

Antitumor activity from antigen-specific CD8 T cells generated in vivo from genetically engineered human hematopoietic stem cells

Abstract: The goal of cancer immunotherapy is the generation of an effective, stable, and self-renewing antitumor T-cell population. One such approach involves the use of high-affinity cancer-specific T-cell receptors in gene-therapy protocols. Here, we present the generation of functional tumor-specific human T cells in vivo from genetically modified human hematopoietic stem cells (hHSC) using a human/mouse chimera model. Transduced hHSC expressing an HLA-A*0201–restricted melanoma-specific T-cell receptor were introduced into humanized mice, resulting in the generation of a sizeable melanoma-specific naive CD8+ T-cell population. Following tumor challenge, these transgenic CD8+ T cells, in the absence of additional manipulation, limited and cleared human melanoma tumors in vivo. Furthermore, the genetically enhanced T cells underwent proper thymic selection, because we did not observe any responses against non–HLA-matched tumors, and no killing of any kind occurred in the absence of a human thymus. Finally, the transduced hHSC established long-term bone marrow engraftment. These studies present a potential therapeutic approach and an important tool to understand better and to optimize the human immune response to melanoma and, potentially, to other types of cancer.

A Computational-Experimental Approach Identifies Mutations That Enhance Surface Expression of an Oseltamivir-Resistant Influenza Neuraminidase

Abstract: The His274Tyr (H274Y) oseltamivir (Tamiflu) resistance mutation causes a substantial decrease in the total levels of surface-expressed neuraminidase protein and activity in early isolates of human seasonal H1N1 influenza, and in the swine-origin pandemic H1N1. In seasonal H1N1, H274Y only became widespread after the occurrence of secondary mutations that counteracted this decrease. H274Y is currently rare in pandemic H1N1, and it remains unclear whether secondary mutations exist that might similarly counteract the decreased neuraminidase surface expression associated with this resistance mutation in pandemic H1N1. Here we investigate the possibility of predicting such secondary mutations. We first test the ability of several computational approaches to retrospectively identify the secondary mutations that enhanced levels of surface-expressed neuraminidase protein and activity in seasonal H1N1 shortly before the emergence of oseltamivir resistance. We then use the most successful computational approach to predict a set of candidate secondary mutations to the pandemic H1N1 neuraminidase. We experimentally screen these mutations, and find that several of them do indeed partially counteract the decrease in neuraminidase surface expression caused by H274Y. Two of the secondary mutations together restore surface-expressed neuraminidase activity to wildtype levels, and also eliminate the very slight decrease in viral growth in tissue-culture caused by H274Y. Our work therefore demonstrates a combined computational-experimental approach for identifying mutations that enhance neuraminidase surface expression, and describes several specific mutations with the potential to be of relevance to the spread of oseltamivir resistance in pandemic H1N1.

Anti-apoptotic effect of hyperglycemia can allow survival of potentially autoreactive T cells.

Abstract: Thymocyte development is a tightly controlled multi-step process involving selective elimination of self-reactive and non-functional T cells by apoptosis. This developmental process depends on signaling by Notch, IL-7 and active glucose metabolism. In this study, we explored the requirement of glucose for thymocyte survival and found that in addition to metabolic regulation, glucose leads to the expression of anti-apoptotic genes. Under hyperglycemic conditions, both mouse and human thymocytes demonstrate enhanced survival. We show that glucose-induced anti-apoptotic genes are dependent on NF-κB p65 because high glucose is unable to attenuate normal ongoing apoptosis of thymocytes isolated from p65 knockout mice. Furthermore, we demonstrate that in vivo hyperglycemia decreases apoptosis of thymocytes allowing for survival of potentially self-reactive thymocytes. These results imply that hyperglycemic conditions could contribute to the development of autoimmunity through dysregulated thymic selection.

Treatment of autoimmune inflammation using mir-155

Abstract: The present disclosure relates to the finding that microRNA- 155 plays a role in the development and activity of CD4+ T cells. CD4+ T cell development and function, particularly T H 17 and T H 1 T cell development, can be modulated by delivery of microRNA- 155 (miR-155) or antisense miR-155 to target CD4+ cells or precursor cells. In some embodiments, antisense miR-155 is used to reduce tissue specific autoimmune inflalmmation and to treat autoimmune disease. In addition, miR155 and antisense miR-155 can be used to modulate expression of cytokines from dendritic cells.

Regulation of hematopoietic stem cell functions through microRNAs

Abstract: The present disclosure relates to regulation of functions of hematopoietic stem cells (HSCs) by delivering of miRNAs, including miR-125b, miR-126, and miR-155, to HSCs. For example, in some embodiments, blood output in a mammal can be increased by administering miR-125b, miR-126, and/or miR-155 oligonucleotides. Also disclosed are methods for promoting hematopoietic stem cell engraftment and method for treating a myeloproliferative disorder.

Lennart Philipson (1929-2011): A Warrior Has Passed Obituary

Abstract: Lennart Philipson died on June 26, 2011. His passing is a great loss to the worldwide biomedical research community. He was a big man—physically, emotionally and operationally, dominating rooms, psyches and institutions. He was my wonderful friend, and when Lennart became your friend, it filled a big need in your life.

Use of sam68 for modulating signaling through the tnf receptor

Abstract: Sam68 plays a role in TNF-dependent signaling, including NF-kB signaling and extrinsic activation of apoptosis. In some embodiments, inhibitors of Sam68 are administered to inhibit TNF-dependent signaling, for example to inhibit NF-kB signaling or apoptosis in a patient in need. In some embodiments, functional Sam68 is administered to increase TNF-dependent signaling, for example to induce apoptosis in a patient in need. In some embodiments, methods are provided determining whether the TNF-dependent or TNF- independent branch of a signaling pathway is active in a cell or cells, or for drug screening applications.