Factors affecting long-term expression of a secreted transgene product after intravenous administration of a retroviral vector

We have studied parameters affecting in vivo expression of human growth hormone (hGH) in mice after intravenous administration of a retroviral vector encoding the protein as a model system for clotting factor VIII gene therapy. Such treatment results in a brief burst of high-level expression followed by lower level sustained expression of the hGH in the circulation. The major targets for transduction in the mouse are liver and spleen. Such direct transduction (i.e., without surgical or chemical induction of cell division) requires vector at high titer (>/=10(8) cfu/ml) and is dose dependent. Transduction efficiency decreases with increasing age of the recipient. Nevertheless, long-term expression in adults is observed after administration of vector as a split dose on 2 consecutive days. We also show that anti-vector immune responses may enhance long-term expression and that both anti-vector and anti-transgene immunity can be modulated. This work provides a framework for the rational development of means to enhance the efficiency of retroviral vectors for use in clinical gene replacement therapy.

Approaches to enhancing the retroviral transduction of human synoviocytes

This report concerns a clinical trial for rheumatoid arthritis (RA), approved by the US National Institutes of Health and the Food and Drug Administration. An amphotropic retrovirus (MFG-IRAP) was used ex vivo to transfer a cDNA encoding human interleukin-1 receptor antagonist (IL-1Ra) to synovium. The protocol required the transduced cells to secrete at least 30 ng IL-1Ra/10(6) cells per 48 h before reimplantation. Here we have evaluated various protocols for their efficiency in transducing cultures of human rheumatoid synoviocytes. The most reliably efficient methods used high titer retrovirus (approximately 10(8) infectious particles/ml). Transduction efficiency was increased further by exposing the cells to virus under flow-through conditions. The use of dioctadecylamidoglycylspermine (DOGS) as a polycation instead of Polybrene (hexadimethrine bromide) provided an additional small increment in efficiency. Under normal conditions of static transduction, standard titer, clinical grade retrovirus (approximately 5 x 10(5) infectious particles/ml) failed to achieve the expression levels required by the clinical trial. However, the shortfall could be remedied by increasing the time of transduction under static conditions, transducing under flow-through conditions, or transducing during centrifugation.

Generation of retroviral packaging and producer cell lines for large-scale vector production and clinical application: improved safety and high titer

For many applications, human clinical therapies using retroviral vectors still require many technological improvements in key areas of vector design and production. These improvements include higher unprocessed manufacturing titers, complement-resistant vectors, and minimized potential to generate replication-competent retrovirus (RCR). To address these issues, we have developed a panel of human packaging cell lines (PCLs) with reduced homology between retroviral vector and packaging components. These reduced-homology PCLs allowed for the use of a novel high multiplicity of transduction ("high m.o. t.") method to introduce multiple copies of provector within vector-producing cell lines (VPCLs), resulting in high-titer vector without the generation of RCR. In a distinct approach to increase vector yields, we integrated manufacturing parameters into screening strategies and clone selection for large-scale vector production. Collectively, these improvements have resulted in the development of diverse VPCLs with unprocessed titers exceeding 2 x 10(7) CFU/ml. Using this technology, human Factor VIII VPCLs yielding titers as high as 2 x 10(8) CFU/ml unprocessed supernatant were generated. These cell lines produce complement-resistant vector particles (N. J. DePolo et al., J. Virol. 73: 6708-6714, 1999) and provide the basis for an ongoing Factor VIII gene therapy clinical trial.

Intra-articular IL-4 gene therapy in arthritis: anti-inflammatory effect and enhanced th2activity

Gene therapy has been explored as a potential method for treating chronic inflammatory diseases such as rheumatoid arthritis. To determine the efficacy of intra-articular IL-4 gene therapy in an animal model of arthritis using a retroviral vector, a retrovirus encoding rat IL-4 (DA-IL-4) was engineered, purified and concentrated to high titer (>/=109 CFU/ml). Infectivity and expression levels were demonstrated in vitro using cultured fibroblast-like synoviocytes. Efficacy was evaluated in the rat adjuvant arthritis model. DA-IL-4 or DA-beta-gal retrovirus was injected into the intra-articular joint space of the right ankle on day 12 after immunization. Three days after joint injection, the injected paw contained increased levels of IL-4 compared with control or with the contralateral uninjected paw, demonstrating successful transgene expression. Surprisingly, 8 days after treatment IL-4 levels continued to increase in the injected and contralateral paw compared with DA-beta-gal-treated animals. Serum IL-4 levels were also elevated in DA-IL-4-treated rats. RT-PCR studies demonstrated that the transgene was expressed in the injected ankle but not in the contralateral joint. IL-4 gene therapy resulted in a significant reduction in paw swelling and decreased radiographic evidence of bone destruction. This is the first demonstration of successful intra-articular retroviral gene treatment using a therapeutic gene. In addition to its anti-inflammatory effect, this study supports the potential application of intra-articular gene therapy as a method for enhancing systemic Th2 function.

Critical analysis of injuries sustained in the TWA flight 800 midair disaster

BACKGROUND

Previous reports of commercial airline disasters have reviewed incidents occurring at takeoff and landing. The purpose of the present study, which represents the first analysis of aviation injuries incurred during a midflight incident, was to examine the injuries sustained by the victims of the TWA Flight 800 disaster and to determine any correlation of injuries with structural damage and seat location.

METHODS

Complete autopsy records, toxicology screening, and forensic analysis were reviewed. Injuries were assessed by anatomic region and severity by using the Abbreviated Injury Scale. The National Transportation Safety Board report of the investigation was applied to correlate individual injuries with seat location and structural damage. A comparison was performed against injury data from takeoff and landing incidents.

RESULTS

All 230 passengers of TWA Flight 800 were recovered as fatalities. Head, thoracic, and abdominal injuries were multiple and severe, contributing to the mortality of the occupants. Analysis revealed that the severity of injury and anatomic injury pattern did not generally correlate with seating position or structural damage. A comparison of these injuries with those of takeoff and landing crashes showed differences in injury pattern and severity.

CONCLUSION

Passengers of Flight 800 sustained instantaneous fatal blunt force injury. Analysis of the data revealed no global correlation between seat position and pattern of injury. In contrast to injuries incurred during crashes at takeoff and landing, these midflight injuries were too extreme to warrant a reappraisal of current passenger protective safety measures or standards.

Direct synovial gene transfer with retroviral vectors in rat adjuvant arthritis

OBJECTIVE

To evaluate the feasibility of direct in vivo gene transfer in an animal model of arthritis using a retroviral vector.

METHODS

The timing and dose of retroviral vector was examined using very high titer retroviral vector (> or = 10(9) CFU) in rat adjuvant arthritis. Retroviral vector expressing beta-galactosidase (beta-gal) or vehicle alone was injected into the right ankle of rats with adjuvant arthritis. Ankles were injected either on Day 7 (pre-arthritis), Day 10 (early arthritis), Day 15 (accelerating arthritis), or Day 28 (chronic arthritis) after adjuvant immunization. Joints were harvested 3 days later and extracts were assayed for beta-gal activity.

RESULTS

Synovial beta-gal expression was minimal in the Day 7 group and elevated in the Day 10, Day 15, and Day 28 groups. Gene transfer with retroviral vector did not exacerbate the local inflammatory response. Minimal or no beta-gal expression was observed in the contralateral uninjected paw or in the spleen, lung, liver, and kidneys. Frozen sections of retroviral vector injected joints were stained with X-gal and revealed transduced cells in the lining and superficial sublining layers. To determine the longevity of gene expression, ankle joints were injected with vector on Day 15 post-adjuvant, harvested, and assayed for beta-gal activity for up to 49 days after injection. Expression of the enzyme peaked from Day 3 to 7 and was still readily detected up to 49 days after retrovirus infection.

CONCLUSION

This is the first report of successful direct in vivo gene transfer in the rat adjuvant arthritis model using a retroviral vector. Appropriate timing of administration and very high titer retroviral vector preparations are key determinants of adequate gene transduction.

DNA immunization against herpes simplex virus: enhanced efficacy using a Sindbis virus-based vector

Previously we reported the development of a plasmid DNA expression vector system derived from Sindbis virus (T. W. Dubensky, Jr., et al., J. Virol. 70:508-519, 1996). In vitro, such vectors exhibit high-level heterologous gene expression via self-amplifying cytoplasmic RNA replication. In the present study, we demonstrated the in vivo efficacy of the Sindbis virus-based pSIN vectors as DNA vaccines. A single intramuscular immunization of BALB/c mice with pSIN vectors expressing the glycoprotein B of herpes simplex virus type 1 induced a broad spectrum of immune responses, including virus-specific antibodies, cytotoxic T cells, and protection from lethal virus challenge in two different murine models. In addition, dosing studies demonstrated that the pSIN vectors were superior to a conventional plasmid DNA vector in the induction of all immune parameters tested. In general, 100- to 1,000-fold-lower doses of pSIN were needed to induce the same level of responsiveness as that achieved with the conventional plasmid DNA vector. In some instances, significant immune responses were induced with a single dose of pSIN as low as 10 ng/mouse. These results indicate the potential usefulness of alphavirus-based vectors for DNA immunization in general and more specifically as a herpes simplex virus vaccine.

Direct retrovirus-mediated gene transfer to the synovium of the rabbit knee: implications for arthritis gene therapy

We have investigated the feasibility of using high-titer murine leukemia virus-based retroviral vectors to deliver exogenous genes to naive and chronically inflamed knee joints of rabbits in vivo. Intraarticular injection of retrovirus encoding beta-galactosidase (beta-gal or lacZ) was found to transduce synoviocytes in both naive and inflamed joints, but a significantly higher number of lacZ+ cells were found in inflamed knees. Using a retrovirus encoding a secretable marker, human growth hormone (hGH), quantitative comparison of ex vivo and in vivo gene delivery methods demonstrated that transgene expression following in vivo gene transfer was at least equivalent to that of the ex vivo method in inflamed knees. In addition, hGH transgene expression was maintained for at least 4 weeks. These experiments suggest that high-titer retroviral vector could be used for efficient in vivo gene transfer to inflamed joints in patients with rheumatoid arthritis (RA).

Evaluation of PCR and ELISA assays for screening clinical trial subjects for replication-competent retrovirus

Gene delivery via murine-based recombinant retroviral vectors is currently widely used in gene therapy clinical trials. The vectors are engineered to be replication defective by replacing the structural and nonstructural genes of a cloned infectious retrovirus with a therapeutic gene of interest. The retroviral particles are currently generated in packaging cell lines, which supply all retroviral proteins in trans. Recombination between short homologous regions of the retroviral vector and packaging cell line elements can theoretically generate replication-competent retrovirus (RCR) and hence the Food and Drug Administration (FDA) requires the monitoring of clinical trial subjects for the presence of RCR. Sensitive polymerase chain reaction (PCR) assays have been used for the detection of murine leukemia virus (MLV) nucleotide sequences in peripheral blood mononuclear cells (PBMCs). A novel serological enzyme-linked immunosorbent assay (ELISA) for the detection of anti-MLV specific immunoglobulin (Ig) has been developed to be used as an alternative to the PCR assay. Both assays were used to monitor human immunodeficiency virus (HIV)-positive clinical trial subjects who had received multiple injections of HIV-IT (V), a retroviral vector encoding HIV-1 IIIBenv/rev. Western blot analysis and an in vitro vector neutralization assay were used to characterize further a subset of serum samples tested by ELISA. Results show no evidence of RCR infection in clinical trial subjects. PCR and ELISA assays are discussed in terms of their advantages and limitations as routine screening assays for RCR. The PCR assay is our current choice for monitoring clinical trial subjects receiving direct administration of vector, and the ELISA is our choice for those receiving ex vivo treatment regimens.

Anti-vector immunoglobulin induced by retroviral vectors

Replication-incompetent retroviruses have been employed as gene therapy vectors in experimental settings for more than a decade. More recently, these vectors have been tested in the clinic as immunotherapeutic agents and anticancer agents. One potential problem with the use of such vectors is the possible development of immune responses directed against the vector particles themselves. Here, we examine immunoglobulin (Ig) responses specific for retroviral vectors derived from murine leukemia virus (MLV). Anti-MLV Ig is seen following intramuscular (i.m.) administration of retroviral vectors in mice, and in nonhuman primates; as expected, these responses are dependent upon the vector dose delivered. Furthermore, serum from vector-treated animals is capable of partially neutralizing vector-mediated transduction of target cells in an in vitro assay. Nevertheless, even in the presence of significant levels of anti-vector Ig in vivo, i.m. administration of retroviral vector is still capable of driving both Ig and cytotoxic T lymphocyte (CTL) responses specific for vector-encoded gene products. This work suggests that although retroviral vectors may readily induce immune responses directed against the vector particles themselves, such responses will not significantly affect the efficiency of these vectors in an immunotherapeutic protocol.

Sudden death and the tasks of mourning: a case report

Trauma nurses are frequently without formal training in grief support or bereavement models. They may be unequal to the task of offering support to families who must cope with death from traumatic injury. Trauma nurses should consider the theoretical model of tasks to understand grief when dealing with sudden death. Through application of this model, we can develop specific nursing strategies that can help survivors of sudden death through this difficult time.

Lipopolysaccharide interferes with the induction of peripheral T cell death

In mice injected with superantigens, T cells specific for that antigen proliferate and then die. It has been suggested that the target cells die because they encounter superantigen on the surfaces of nonprofessional presenting cells, such as B cells, which cannot deliver costimulatory signals to T cells. A number of reagents that induce costimulatory molecules on B cells were tested. Lipopolysaccharide very effectively prevented T cell death driven by superantigen. Perhaps surprisingly, the action of lipopolysaccharide was not mediated through the expected costimulatory molecule, B7. Rather, the effects of lipopolysaccharide involved the production of inflammatory cytokines, in particular TNF alpha. The rescued cells survived in vitro culture and were resistant to Fas-induced killing. These data demonstrate that LPS can block antigen-induced T cell death perhaps by interfering with Fas signaling.

Reconstitution of TCR alpha-chain expression in deletion mutants restores dinitrophenyl-specific/class I MHC-restricted suppressor molecule production

A population of CD8+ T cells from dinitrobenzene sulfonate-primed mice produce soluble effector molecules that down-regulate the magnitude of dinitrophenol-specific contact hypersensitivity reactions. These soluble molecules express the binding specificity and serologic determinants of alpha/beta TCR. To examine the requirement for the TCR-alpha chain in the production of these molecules, we have cloned the alpha-chain gene used to encode the surface TCR of MTs 79.1, a T cell hybridoma producing a DNP/Kd-specific soluble suppressive molecule, and tested the ability of this gene to reconstitute the production of the regulatory molecule in TCR alpha-chain gene deletion mutants. Transfection and expression of the alpha-chain construct into an alpha-chain deletion mutant of the parental hybridoma that expressed the parental beta-chain gene resulted in reconstitution of both surface TCR expression and production of the soluble suppressive molecule. As with the molecule produced by the MTs 79.1 parental cells, the inhibitory activity produced by these alpha-chain gene transfectants was DNP-specific and expressed determinants bound by anti-V beta 8 Abs. Transfection of the alpha-chain gene construct into an alpha-/beta- chain gene deletion mutant did not restore the production of the soluble regulatory molecule. These results indicate that in addition to the TCR beta-chain gene, expression of the TCR alpha-chain gene is also required for the production of these molecules. Our results strongly support the hypothesis that some forms of immunosuppression are mediated by soluble forms of the TCR.

Reconstitution of TCR alpha-chain expression in deletion mutants restores dinitrophenyl-specific/class I MHC-restricted suppressor molecule production

A population of CD8+ T cells from dinitrobenzene sulfonate-primed mice produce soluble effector molecules that down-regulate the magnitude of dinitrophenol-specific contact hypersensitivity reactions. These soluble molecules express the binding specificity and serologic determinants of alpha/beta TCR. To examine the requirement for the TCR-alpha chain in the production of these molecules, we have cloned the alpha-chain gene used to encode the surface TCR of MTs 79.1, a T cell hybridoma producing a DNP/Kd-specific soluble suppressive molecule, and tested the ability of this gene to reconstitute the production of the regulatory molecule in TCR alpha-chain gene deletion mutants. Transfection and expression of the alpha-chain construct into an alpha-chain deletion mutant of the parental hybridoma that expressed the parental beta-chain gene resulted in reconstitution of both surface TCR expression and production of the soluble suppressive molecule. As with the molecule produced by the MTs 79.1 parental cells, the inhibitory activity produced by these alpha-chain gene transfectants was DNP-specific and expressed determinants bound by anti-V beta 8 Abs. Transfection of the alpha-chain gene construct into an alpha-/beta- chain gene deletion mutant did not restore the production of the soluble regulatory molecule. These results indicate that in addition to the TCR beta-chain gene, expression of the TCR alpha-chain gene is also required for the production of these molecules. Our results strongly support the hypothesis that some forms of immunosuppression are mediated by soluble forms of the TCR.

Stimulation with specific antigen can block superantigen-mediated deletion of T cells in vivo

The T-cell response to pigeon cytochrome c peptide, residues 88-104 (pcytC), in B10.BR mice is mediated largely by cells bearing both V beta 3 and V alpha 11 variable regions of the T-cell antigen receptor. These cells are, therefore, reactive with the superantigen staphylococcal enterotoxin A (SEA). Recent reports have shown that in vivo exposure to superantigen can lead to deletion of superantigen-reactive T cells from the pool of mature T cells in the periphery. Here we show that upon cotreatment of animals with both SEA and pcytC, bulk deletion of the population of SEA-reactive cells is maintained, while the subpopulation of SEA-reactive T cells that also responds to pcytC is not deleted but instead proliferates in response to pcytC. These results are discussed with regard to mechanisms regulating the balance between T-cell tolerance and T-cell activation in vivo.

Fibroblasts can induce thymocyte positive selection in vivo

During development in the thymus, thymocytes bearing alpha beta T-cell receptors are selected to mature if the receptors they bear are able to interact in some way with major histocompatibility complex (MHC) proteins expressed on thymic stromal cells. It has been shown that thymus cortical epithelial cells are usually the cells presenting the MHC molecules involved in this process of so-called positive selection. Here we tested the ability of fibroblasts to mediate positive selection in vivo. Fibroblasts transfected with the genes for the MHC I-Ab proteins were injected intrathymically into irradiated H-2k animals reconstituted with H-2bxk F1 fetal liver cells. Eight weeks later, the recipient mice were immunized and shown to contain peptide-specific I-Ab-restricted T cells. This demonstrates the ability of I-Ab-transfected fibroblasts to participate in positive selection. Thus a cell type that is not specialized to process and present antigens in the context of MHC class II molecules can mediate positive selection when transfected with an appropriate MHC molecule. The data also support the idea that the ability to mediate positive selection may not be limited to thymic cortical epithelium.

Profound deletion of mature T cells in vivo by chronic exposure to exogenous superantigen

It has been noted previously that superantigens can under different circumstances stimulate activation, expansion, anergy, and/or deletion of reactive T cells in vivo and in vitro. Here, we present a detailed examination of the expansion and deletion of T cells in vivo in response to the superantigens staphylococcal enterotoxin A (SEA) in the B10.BR mouse. Mice were either acutely or chronically exposed to varying doses of SEA, and the relative level of T cells bearing SEA-reactive V beta elements was followed over time in lymphocytes purified from peripheral blood, lymph nodes, mesenteric lymph nodes, and spleen. In most cases, an initial sharp rise in the proportion of reactive T cells was followed by a dramatic decline. Cells of the CD4+ and CD8+ lineages displayed subtle differences in their kinetics of activation and deletion, as well as their sensitivity to different doses of SEA. Furthermore, cells bearing either of two V beta elements previously characterized as SEA-reactive showed some differences in their responses to SEA treatment. Acute exposure usually caused the disappearance of only 50% to 70% of reactive T cells; however, chronic exposure to SEA caused almost complete deletion of target T cells. Deletion was evident even in animals treated with very low doses of SEA, doses that were too small to cause any apparent T cell proliferation. Thus, proliferation does not appear to be a prerequisite for peripheral deletion of T cells.

Profound deletion of mature T cells in vivo by chronic exposure to exogenous superantigen

It has been noted previously that superantigens can under different circumstances stimulate activation, expansion, anergy, and/or deletion of reactive T cells in vivo and in vitro. Here, we present a detailed examination of the expansion and deletion of T cells in vivo in response to the superantigens staphylococcal enterotoxin A (SEA) in the B10.BR mouse. Mice were either acutely or chronically exposed to varying doses of SEA, and the relative level of T cells bearing SEA-reactive V beta elements was followed over time in lymphocytes purified from peripheral blood, lymph nodes, mesenteric lymph nodes, and spleen. In most cases, an initial sharp rise in the proportion of reactive T cells was followed by a dramatic decline. Cells of the CD4+ and CD8+ lineages displayed subtle differences in their kinetics of activation and deletion, as well as their sensitivity to different doses of SEA. Furthermore, cells bearing either of two V beta elements previously characterized as SEA-reactive showed some differences in their responses to SEA treatment. Acute exposure usually caused the disappearance of only 50% to 70% of reactive T cells; however, chronic exposure to SEA caused almost complete deletion of target T cells. Deletion was evident even in animals treated with very low doses of SEA, doses that were too small to cause any apparent T cell proliferation. Thus, proliferation does not appear to be a prerequisite for peripheral deletion of T cells.

Characterization of defective I-A surface expression in a mixed isotype expressing murine B cell lymphoma: continued expression of E alpha d A beta d despite competition from restored A alpha d A beta d pairs

The BALB/c-derived mouse B cell lymphoma line, 2PK3, expresses mixed isotype E alpha dA beta d and classical I-E class II molecules on its surface, but normal surface I-A expression is not detectable. Northern blot analysis showed comparable amounts of A alpha mRNA in 2PK3 as compared to another Iad expressing B cell lymphoma, A20, which predominantly expresses I-A and I-E. Sequence analysis of 2PK3 A alpha cDNA revealed a single nucleotide difference in the signal sequence that would result in a proline for leucine substitution at position - 12. In vitro translation of 2PK3 A alpha mRNA gave results suggesting that the signal peptide mutation prevented translocation of the A alpha protein across the rough endoplasmic reticulum which would provide an explanation for the lack of I-A expression in 2PK3. I-A expression was restored by transfecting a functional A alpha d gene into 2PK3. Although I-A was expressed at high levels in some transfectants, in all cases significant levels of mixed isotype were still detected. Functional studies performed using antigen-specific I-A(d)-restricted and E alpha d-A beta d-specific T cell hybridomas confirmed the levels of expression of I-A(d) and E alpha dA beta d respectively on the transfectants and showed that these molecules were functional. An interesting observation from this study is the continued expression of significant levels of E alpha dA beta d in spite of competition from restored expression of I-A(d).

Analysis of class II MHC structure in thymic nurse cells

During the course of thymocyte maturation, the processes of positive selection and tolerance induction are mediated by interactions between thymocyte T-cell receptors and MHC molecules on thymic stromal cells. The means by which these seemingly contrary processes can be mediated by interactions between the same molecules has long been a source of controversy. One idea which has been put forward is that the MHC molecules in different microenvironments of the thymus are not the same. We have tested this hypothesis by examining class II transcripts derived from thymic cortical epithelial cells known as thymic nurse cells, reasoning that alternative splicing of primary transcripts might give rise to a positively selecting MHC molecule. However, we found no evidence for alternative splicing of these transcripts. These results are presented and discussed with regard to implications for possible mechanisms of positive selection.

Changes in phosphorylation of myc oncogene and RB antioncogene protein products during growth arrest of the murine lymphoma WEHI 231 cell line

The expression of the protein products of the c-myc oncogene and retinoblastoma susceptibility gene (RB) was investigated during either goat anti-mouse immunoglobulin (GaMIg)- or phorbol ester (TPA)-induced growth arrest of the murine B-lymphoma cell line WEHI 231. Previously we have demonstrated that c-myc mRNA levels increase within 1-2 h of treatment, return to control levels by 4 h, and decline below these values by 24 h of treatment. Here we demonstrate that the level of c-myc protein synthesis and mRNA change in parallel. The predominant c-myc protein expressed during the time course is the one initiated at the AUG codon (P2). The myc protein synthesized following 1-2 h of anti-immunoglobulin or TPA treatment migrates more slowly in a polyacrylamide gel as a result of increased phosphorylation. This hyperphosphorylation was no longer detectable by 4-6 h of treatment. Furthermore, the hyperphosphorylated myc protein appears to be more readily extractable with salt than the hypophosphorylated form. The product of the RB gene is present in multiple phosphorylation states in exponentially growing WEHI 231 cells. By 8 h of GaMIg or TPA treatment, a hypophosphorylated form begins to be detectable and significant levels were seen by 15 h. Thus post-translational control of both c-myc and RB expression occurs during the growth arrest of WEHI 231 cells. These changes in phosphorylation may play a role in mediating the cessation of proliferation of these cells.

Production of prostaglandin E2 and prostacyclin by thymic nurse cells in culture

To better define the thymic microenvironment, we have examined a specific population of thymic stromal cells, thymic nurse cells (TNC) for production of eicosanoids. TNC were prepared from BALB/c mice, cultured in complete medium, and culture supernatants were analyzed for the presence of various metabolites of arachidonic acid. Freshly isolated TNC produced large quantities of PGE2 and 6-keto PGF1 alpha (a stable metabolite of prostacyclin, PGI2). Both of these eicosanoids were produced continuously in culture, after an initial lag period of approximately 2 h. No significant production of the eicosanoids PGD2, thromboxane B2, or leukotrienes B4, C4/D4/E4 was seen in these cultures. Production of PGE2 and PGI2 by TNC was not stimulated by treatment with the calcium ionophore A23187, or by cell-cell interactions resulting from coculture of the TNC with free thymocytes. Eicosanoid production in these cultures was not due to production of these substances by cells likely to be present as contaminants, such as T rosettes or free thymocytes. These findings raise the possibility that PGE2 and/or PGI2 may provide signals to thymocytes at a specific developmental stage.

Production of prostaglandin E2 and prostacyclin by thymic nurse cells in culture

To better define the thymic microenvironment, we have examined a specific population of thymic stromal cells, thymic nurse cells (TNC) for production of eicosanoids. TNC were prepared from BALB/c mice, cultured in complete medium, and culture supernatants were analyzed for the presence of various metabolites of arachidonic acid. Freshly isolated TNC produced large quantities of PGE2 and 6-keto PGF1 alpha (a stable metabolite of prostacyclin, PGI2). Both of these eicosanoids were produced continuously in culture, after an initial lag period of approximately 2 h. No significant production of the eicosanoids PGD2, thromboxane B2, or leukotrienes B4, C4/D4/E4 was seen in these cultures. Production of PGE2 and PGI2 by TNC was not stimulated by treatment with the calcium ionophore A23187, or by cell-cell interactions resulting from coculture of the TNC with free thymocytes. Eicosanoid production in these cultures was not due to production of these substances by cells likely to be present as contaminants, such as T rosettes or free thymocytes. These findings raise the possibility that PGE2 and/or PGI2 may provide signals to thymocytes at a specific developmental stage.

Independent regulation of transcription of the two strands of the c-myc gene

Previously we demonstrated the existence of transcripts from the noncoding strand of a rearranged, truncated c-myc gene in murine plasmacytomas in which this oncogene is translocated to an immunoglobulin constant-region gene element (M. Dean, R. B. Kent, and G. E. Sonenshein, Nature [London] 305:443-446, 1983). Here we report on the transcription of the two strands of a normal, unrearranged c-myc gene. We examined the effects of gene rearrangements, growth state transitions, and differentiation on the relative levels of usage of the two strands. Transcription from intron 1 to exon 3 of the murine c-myc gene was studied in in vitro nuclear runoff assays. The level of transcription of the noncoding strand across this region of a germ line c-myc gene in a murine B-cell lymphoma line was comparable to the level observed in plasmacytomas with translocated c-myc genes. Rapid changes in transcription of the coding strand of the c-myc gene could be seen during growth arrest of WEHI 231 cells and during activation of splenic T lymphocytes. Transcription of the noncoding strand was constitutive during these growth state transitions and during activation of primary cultures of quiescent calf aortic smooth muscle cells as well. In contrast, differentiation of murine erythroleukemia cells was accompanied by an early drop in transcription of the two strands of this gene. The ramifications of these findings with respect to measurements of c-myc gene transcription and to the regulation of this gene are discussed.

Transcriptional and posttranscriptional control of c-myc gene expression in WEHI 231 cells

Incubation of WEHI 231 cells, derived from a murine B-cell lymphoma, with antisera directed against its surface immunoglobulin results in the inhibition of growth within 24 h. Previously, we demonstrated that this treatment selectively affects cytoplasmic levels of c-myc mRNA (J. E. McCormack, V. H. Pepe, R. B. Kent, M. Dean, A. Marshak-Rothstein, and G. E. Sonenshein, Proc. Natl. Acad. Sci. USA 81:5546-5550, 1984). An initial increase in the cytoplasmic mRNA level is followed by a precipitous drop. We now show that the early increase results from a dramatic increase in the rate of c-myc gene transcription, as well as from partial stabilization of the mRNA in the cytoplasm. The later decrease results from a shutdown in transcription of the c-myc gene and a return to the normal lability of the cytoplasmic c-myc mRNA. Treatment with phorbol ester, like treatment with anti-immunoglobulin sera, inhibited WEHI 231 cell growth and caused similar changes in cytoplasmic c-myc mRNA levels, which can also be related to alterations in c-myc gene transcription. These results indicate that the control of c-myc gene expression in B cells is effected through regulation at multiple levels.

Specific regulation of c-myc oncogene expression in a murine B-cell lymphoma

The c-myc oncogene has been implicated in a wide spectrum of B-cell neoplasias. In normal cells, the level of expression of the c-myc gene correlates with growth status. In the present study, we examined the effect of receptor-mediated inhibition of growth on c-myc expression in a B-cell lymphoma. The murine lymphoma line WEHI 231 has been characterized as an early B cell; it bears surface-bound IgM and has unrearranged c-myc genes. Following treatment of a WEHI 231 culture with anti-mouse Ig antiserum, the cells undergo one round of division and further proliferation is inhibited. We observed that this treatment specifically affected cytoplasmic levels of c-myc mRNA. An initial early increase is followed by a precipitous drop such that by 4 hr (after exposure) the amount of c-myc mRNA is below control values by a factor of approximately equal to 10. The drop in c-myc precedes cessation of DNA synthesis. During the 2- to 4-hr period, c-myc mRNA had a maximal half-life of between 20 and 30 min. In contrast, even 24 hr after anti-Ig exposure, the amounts of most major mRNAs, including mu heavy chain and actin, were not significantly altered. These results indicate that expression of an unrearranged c-myc gene can be selectively responsive to receptor-mediated regulatory events.

Personal sampling impactor with respirable aerosol penetration characteristics

Single stage impactors with penetration characteristics approximating those of the BMRC, AEC and ACGIH respirable criteria have been developed for use as personal samplers. Three impactors were built for flow rates of 2 L/min. Experimental calibration data of these impactors are compared to the respective respirable criteria for which they were designed. Oil soaked impaction plates were used in these impactors so particles impacting on the plates would always strike an oiled surface and not bounce from the plate. Experiments with coal dust using these plates showed little particle bounce. Finally, a procedure is introduced by which samplers can be designed with penetration characteristics that differentiate between the AEC and ACGIH respirable criteria.

Presentation of academy plaque to Edward Elliot Fischel, M.D

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Presentation of academy plaque to John L. Madden, M. D

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Presentation of the Academy Plaque to George A. Perera, M.D

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Presentation of the Academy Plaque to Albert Christy Santy, M.D

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Presentation of the Academy Plaque to Miss Janet Doe

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Presentation of the Academy plaque to Frank B. Berry, M.D

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Presentation of the Academy medal to Harold W. Brown, M.D

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The Treatment of Lobar Pneumonia and Pneumococcal Empyema with Penicillin

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