Phase I study in melanoma patients of a vaccine with peptide-pulsed dendritic cells generated in vitro from CD34(+) hematopoietic progenitor cells

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that can be used for vaccination purposes, to induce a specific T-cell response in vivo against melanoma-associated antigens. We have shown that the sequential use of early-acting hematopoietic growth factors, stem cell factor, IL-3 and IL-6, followed by differentiation with IL-4 and granulocyte-macrophage colony-stimulating factor allows the in vitro generation of large numbers of immature DCs from CD34(+) peripheral blood progenitor cells. Maturation to interdigitating DCs could specifically be induced within 24 hr by addition of TNF-alpha. Here, we report on a phase I clinical vaccination trial in melanoma patients using peptide-pulsed DCs. Fourteen HLA-A1(+) or HLA-A2(+) patients received at least 4 i.v. infusions of 5 x 10(6) to 5 x 10(7) DCs pulsed with a pool of peptides including either MAGE-1, MAGE-3 (HLA-A1) or Melan-A, gp100, tyrosinase (HLA-A2), depending on the HLA haplotype. A total of 83 vaccinations were performed. Clinical side effects were mild and consisted of low-grade fever (WHO grade I-II). Clinical and immunological responses consisted of anti-tumor responses in 2 patients, increased melanoma peptide-specific delayed-type hypersensitivity reactions in 4 patients, significant expansion of Melan-A- and gp100-specific cytotoxic T lymphocytes in the peripheral blood lymphocytes of 1 patient after vaccination and development of vitiligo in another HLA-A2(+) patient. Our data indicate that the vaccination of peptide-pulsed DCs is capable of inducing clinical and systemic tumor-specific immune responses without provoking major side effects.

Enhanced susceptibility to cytotoxic T lymphocytes without increase of MHC class I antigen expression after conditional overexpression of heat shock protein 70 in target cells

Antigenic peptides have been found associated with heat shock proteins (HSP) including cytoplasmic HSP70 and heat shock cognate protein 70 as well as the endoplasmic reticulum-resident glucose-regulated protein 94. Recently, HSP70 transfection has been reported to increase MHC class I cell surface expression and antigen presentation on mouse melanoma B16 cells (Wells et al., Int. Immunol. 1998. 10: 609). To analyze the effect of HSP70 on MHC class I cell surface expression and lysability of target cells we transfected a human melanoma cell line with the rat Hsp70-1 gene using the Tet-On system for conditional overexpression of HSP70. Induction of HSP70 did not increase cell surface expression of HLA class I molecules in general or individual HLA-A and B antigens in particular. Nonetheless, induction of HSP70 enhanced susceptibility of these cells to lysis by allospecific CTL. The same effect was observed using an HLA-A2-restricted tyrosinase-specific CTL clone after pulsing the tyrosinase-negative target cells with the specific peptide. Thus, HSP70 induction can increase killing by CTL without affecting MHC class I cell surface expression or antigen processing. This effect of HSP70 appears to be different from the commonly found protection exerted by HSP70 against stress like heat shock, and might be mediated by improving CTL-induced apoptosis.

Melan-A/MART-1(51-73) represents an immunogenic HLA-DR4-restricted epitope recognized by melanoma-reactive CD4(+) T cells

The human Melan-A/MART-1 gene encodes an HLA-A2-restricted peptide epitope recognized by melanoma-reactive CD8(+) cytotoxic T lymphocytes. Here we report that this gene also encodes at least one HLA-DR4-presented peptide recognized by CD4(+) T cells. The Melan-A/MART-1(51-73) peptide was able to induce the in vitro expansion of specific CD4(+) T cells derived from normal DR4(+) donors or from DR4(+) patients with melanoma when pulsed onto autologous dendritic cells. CD4(+) responder T cells specifically produced IFN-gamma in response to, and also lysed, T2.DR4 cells pulsed with the Melan-A/MART-1(51-73) peptide and DR4(+) melanoma target cells naturally expressing the Melan-A/MART-1 gene product. Interestingly, CD4(+) T cell immunoreactivity against the Melan-A/MART-1(51-73) peptide typically coexisted with a high frequency of anti-Melan-A/MART-1(27-35) reactive CD8(+) T cells in freshly isolated blood harvested from HLA-A2(+)/DR4(+) patients with melanoma. Taken together, these data support the use of this Melan-A/MART-1 DR4-restricted melanoma epitope in future immunotherapeutic trials designed to generate, augment, and quantitate specific CD4(+) T cell responses against melanoma in vivo.

Enhanced susceptibility to cytotoxic T lymphocytes without increase of MHC class I antigen expression after conditional overexpression of heat shock protein 70 in target cells

Antigenic peptides have been found associated with heat shock proteins (HSP) including cytoplasmic HSP70 and heat shock cognate protein 70 as well as the endoplasmic reticulum-resident glucose-regulated protein 94. Recently, HSP70 transfection has been reported to increase MHC class I cell surface expression and antigen presentation on mouse melanoma B16 cells (Wells et al., Int. Immunol. 1998. 10: 609). To analyze the effect of HSP70 on MHC class I cell surface expression and lysability of target cells we transfected a human melanoma cell line with the rat Hsp70-1 gene using the Tet-On system for conditional overexpression of HSP70. Induction of HSP70 did not increase cell surface expression of HLA class I molecules in general or individual HLA-A and B antigens in particular. Nonetheless, induction of HSP70 enhanced susceptibility of these cells to lysis by allospecific CTL. The same effect was observed using an HLA-A2-restricted tyrosinase-specific CTL clone after pulsing the tyrosinase-negative target cells with the specific peptide. Thus, HSP70 induction can increase killing by CTL without affecting MHC class I cell surface expression or antigen processing. This effect of HSP70 appears to be different from the commonly found protection exerted by HSP70 against stress like heat shock, and might be mediated by improving CTL-induced apoptosis.

Dendritic cells transduced with an adenovirus vector encoding Epstein-Barr virus latent membrane protein 2B: a new modality for vaccination

Epstein-Barr virus (EBV) is a herpesvirus commonly associated with several malignancies, particularly in immunocompromised hosts. As a strategy for stimulating immunity against EBV for the treatment of EBV-associated tumors, we have genetically engineered dendritic cells (DC) to express EBV antigens, such as latent membrane protein 2B (LMP2B), using recombinant adenovirus vectors. CD8(+) T lymphocytes from HLA-A2.1(+), EBV-seropositive healthy donors were cultured with autologous DC infected with recombinant adenovirus vector AdEGFP, encoding an enhanced green fluorescent protein (EGFP), or AdLMP2B at a multiplicity of infection of 250. After 48 h, >95% of the DC were positive for EGFP expression as assessed by fluorescence-activated cell sorting analysis, indicating efficient gene transfer. AdLMP2-transduced DC were used to stimulate CD8(+) T cells. Responder CD8(+) T cells were tested for gamma interferon (IFN-gamma) release by enzyme-linked spot (ELISPOT) assay and cytotoxic activity. Prior to in vitro stimulation, the frequencies of T-cells directed against two HLA-A2-presented LMP2 peptides (LMP2 329-337 and LMP2 426-434) were very low as assessed by IFN-gamma spot formation (T-cell frequency, <0.003%). IFN-gamma ELISPOT assays performed at day 14 showed a significant (2-log) increase of the day 0 frequency of T cells reactive against the LMP2 329-337 peptide, from 0.003 to 0.3 (P < 0.001). Moreover, specific cytolytic activity was observed against the autologous EBV B-lymphoblastoid cell lines after 21 days of stimulation of T-cell responders with AdLMP2-transduced DC (P < 0.01). In summary, autologous mature DC genetically modified with an adenovirus encoding EBV antigens stimulate the generation of EBV-specific CD8(+) effector T cells in vitro, supporting the potential application of EBV-based adenovirus vector vaccination for the immunotherapy of the EBV-associated malignancies.

Identification of naturally processed and HLA-presented Epstein-Barr virus peptides recognized by CD4(+) or CD8(+) T lymphocytes from human blood

The broad clinical implementation of cancer vaccines targeting the induction of specific T cell-mediated immunity is hampered because T cell defined tumor-associated peptides are currently available for only a restricted range of tumor types. Current epitope identification strategies require a priori the generation of T "indicator" cell lines that specifically recognize the tumor antigenic epitope in in vitro assay systems. An alternative to this strategy is the use of "memory" T cells freshly isolated from the peripheral blood of patients with cancer in concert with sensitive effector cell readout assays (such as the cytokine enzyme-linked immunospot assay) and MS to identify relevant peptide epitopes. In a model system, we have evaluated the capacity of natural Epstein-Barr virus (EBV)-transformed B-lymphoblastoid cell line-extracted peptides to activate "memory" viral-specific CD4(+) or CD8(+) T cells freshly isolated from the blood of an EBV-seropositive individual using the IFN-gamma enzyme-linked immunospot assay. After HPLC fractionation and loading onto autologous dendritic cells, multiple naturally processed HLA class I and II-associated lymphoblastoid cell line-derived peptides were isolated that were capable of inducing IFN-gamma spot production by "memory" T lymphocytes. Using MS analysis on a HPLC fraction recognized by CD8(+) T cells, we were able to sequence natural 9-, 10-, and 11-mer peptides naturally processed from the latent EBV antigen LMP-2 (latent membrane protein-2) and presented in the context of HLA-A2. This approach provides a useful methodology for the future identification of MHC-presented viral and tumor epitopes using freshly isolated patient materials.

Crystal structure of the conserved core of the herpes simplex virus transcriptional regulatory protein VP16

On infection, the herpes simplex virus (HSV) virion protein VP16 (Vmw65; alphaTIF) forms a transcriptional regulatory complex-the VP16-induced complex-with two cellular proteins, HCF and Oct-1, on VP16-responsive cis-regulatory elements in HSV immediate-early promoters called TAATGARAT. Comparison of different HSV VP16 sequences reveals a conserved core region that is sufficient for VP16-induced complex formation. The crystal structure of the VP16 core has been determined at 2.1 A resolution. The results reveal a novel, seat-like protein structure. Together with the activity of mutant VP16 proteins, the structure of free VP16 suggests that it contains (1) a disordered carboxy-terminal region that associates with HCF, Oct-1, and DNA in the VP16-induced complex, and (2) a structured region involved in virion assembly and possessing a novel DNA-binding surface that differentiates among TAATGARAT VP16-response elements.

Selected elements of herpes simplex virus accessory factor HCF are highly conserved in Caenorhabditis elegans

HCF is a mammalian nuclear protein that undergoes proteolytic processing and is required for cell proliferation. During productive herpes simplex virus (HSV) infection, the viral transactivator VP16 associates with HCF to initiate HSV gene transcription. Here, we show that the worm Caenorhabditis elegans possesses a functional homolog of mammalian HCF that can associate with and activate the viral protein VP16. The pattern of sequence conservation, however, is uneven. Sequences required for mammalian HCF processing are not present in C. elegans HCF. Furthermore, not all elements of mammalian HCF that are required for promoting cell proliferation are conserved. Nevertheless, unexpectedly, C. elegans HCF can promote mammalian cell proliferation because a region of HCF that is conserved can promote mammalian cell proliferation better than its human counterpart. These results suggest that HCF possesses a highly conserved role in metazoan cell proliferation which is targeted by VP16 to regulate HSV infection. The precise mechanisms, however, by which HCF functions in mammals and worms appear to differ.

Quantitative and functional analysis of core-specific T-helper cell and CTL activities in acute and chronic hepatitis B

AIMS/BACKGROUND

CD4+ T-helper cell (Th) responses to hepatitis B virus (HBV) core antigen (HBc) are increased during exacerbations in acute and chronic hepatitis B (AHB, CHB) and might influence the induction of CD8+ cytotoxic T lymphocytes (CTL) that are important for viral clearance.

METHODS

HBc-specific proliferative responses and cytokine release of blood mononuclear cells (PBMC) were studied in patients with AHB or CHB, as well as responders and non-responders to interferon-alpha treatment (IFN-R, IFN-NR), by [3H]-thymidine-uptake, enzyme-linked immunosorbent assay (ELISA) and Elispot assay and were compared to peptide HBc18 27-specific CTL precursor frequencies among CD8+ T cells derived from HLA-A2+ patients.

RESULTS

HBc-specific proliferative PBMC responses and Th frequencies were significantly increased in AHB patients compared with untreated CHB patients. PBMC derived from IFN-R showed stronger cellular responses than IFN-NR. Stimulated PBMC from all patient groups secreted significantly more IFN-gamma than IL-4 indicating Th1/Th0 cell responses. Furthermore, in AHB and IFN-R patients, high peptide HBc18-27-specific CTL precursor frequencies closely correlated with strong HBc-specific Th responses, whereas in untreated CHB and IFN-NR patients lower CTL frequencies were observed without correlation to Th activities.

CONCLUSIONS

HBV core-specific Th-cell responses appeared to support efficient CTL induction in patients with viral clearance, whereas in chronic HBV carriers quantitatively insufficient Th and CTL responses were observed. This observation could be important for future therapeutic strategies.

Quantification of CD8+ T lymphocytes responsive to human immunodeficiency virus (HIV) peptide antigens in HIV-infected patients and seronegative persons at high risk for recent HIV exposure

The combination of a tumor necrosis factor (TNF)-alpha enzyme-linked immunospot (ELISPOT) assay and computer-assisted video image analysis was used to detect and quantitate in peripheral blood CD8+ T cells reactive with known human immunodeficiency virus type 1 (HIV-1) peptide antigens presented by HLA-A2 or HLA-A3. T lymphocyte responsiveness to at least one HIV peptide was found in 10 (83%) of 12 HIV-1-infected patients and in 5 (45%) of 11 persons who had no serologic and virologic signs of HIV infection but who were at high risk for recent sexual exposure to HIV-1. CD8+ T cells responding to HIV-1 peptides were observed in none of 11 HIV-seronegative donors without a history of HIV exposure. ELISPOT assays are relatively fast and easy to perform and appear to reliably detect T cell reactivity due to previous exposure to HIV. These findings support the use of the ELISPOT assay for monitoring T cell responsiveness to HIV peptides.

Transforming growth factor-beta1 in autoimmune hepatitis: correlation of liver tissue expression and serum levels with disease activity

BACKGROUND/AIMS

Transforming growth factor-beta1 (TGF-beta1) is considered the most important mediator of hepatic fibrogenesis. At the same time, TGF-beta1 is an immunosuppressive cytokine. Development of fibrosis, often rapid, is a characteristic of autoimmune hepatitis, as is spontaneous systemic immunosuppression. The aim of our study was therefore to define the role of TGF-beta1 in autoimmune hepatitis.

METHODS/RESULTS

Using the MV 1Lu bioassay, we found markedly elevated serum levels of TGF-beta1 (median 109 ng/ml) in active autoimmune hepatitis, which normalised when patients reached biochemical remission following immunosuppressive therapy (median 34 ng/ml; p=0.0001 compared to active disease). With a newly established ELISPOT-assay for TGF-beta1-producing cells, we could exclude an increase in TGF-beta1-producing peripheral blood cells as a source of the elevated TGF-beta1. However, by in situ hybridisation and immunohistochemistry, we found strong TGF-beta1 expression in the inflamed liver. In addition to non-parenchymal and infiltrating cells, many hepatocytes showed strong staining for TGF-beta1. TGF-beta1 expression in the liver normalised in remission, yet was still somewhat increased in patients with biochemical remission but remaining histological disease activity.

CONCLUSIONS

These results suggest that TGF-beta1 is an important mediator in active autoimmune hepatitis. They support the theory that immunosuppressive therapy needs to be guided by histology, as prevention of the development of cirrhosis presumably requires near complete suppression of TGF-beta1 in the liver; this is only found when there is no longer any histological evidence of inflammation.

The mouse telomerase RNA 5"-end lies just upstream of the telomerase template sequence

Telomerase is a ribonucleoprotein enzyme with an essential RNA component. Embedded within the telomerase RNA is a template sequence for telomere synthesis. We have characterized the structure of the 5' regions of the human and mouse telomerase-RNA genes, and have found a striking difference in the location of the template sequence: Whereas the 5'-end of the human telomerase RNA lies 45 nt from the telomerase-RNA template sequence, the 5'-end of the mouse telomerase RNA lies just 2 nt from the telomerase-RNA template sequence. Analysis of genomic sequences flanking the 5'-end of the human and mouse telomerase RNA-coding sequences reveals similar promoter-element arrangements typical of mRNA-type promoters: a TATA box-like element and an upstream region containing a consensus CCAAT box. This putative promoter structure contrasts with that of the ciliate telomerase-RNA genes whose structure resembles RNA polymerase III U6 small nuclear RNA (snRNA) promoters. These and other comparisons suggest that, during evolution, both the RNA-polymerase specificity of telomerase RNA-gene promoters and, more recently, the position of the template sequence in the telomerase RNA changed.

OCA-B is a functional analog of VP16 but targets a separate surface of the Oct-1 POU domain

OCA-B is a B-cell-specific coregulator of the broadly expressed POU domain transcription factor Oct-1. OCA-B associates with the Oct-1 POU domain, a bipartite DNA-binding structure containing a POU-specific (POU[S]) domain joined by a flexible linker to a POU homeodomain (POU[H]). Here, we show that OCA-B alters the activity of Oct-1 in two ways. It provides a transcriptional activation domain which, unlike Oct-1, activates an mRNA-type promoter effectively, and it stabilizes Oct-1 on the Oct-1-responsive octamer sequence ATGCAAAT. These properties of OCA-B parallel those displayed by the herpes simplex virus Oct-1 coregulator VP16. OCA-B, however, interacts with a different surface of the DNA-bound Oct-1 POU domain, interacting with both the POU(S) and POU(H) domains and the center of the ATGCAAAT octamer sequence. The OCA-B and VP16 interactions with the Oct-1 POU domain are sufficiently different to permit OCA-B and VP16 to bind the Oct-1 POU domain simultaneously. These results emphasize the structural versatility of the Oct-1 POU domain in its interaction with coregulators.

Viral mimicry: common mode of association with HCF by VP16 and the cellular protein LZIP

Upon infection of human cells, the herpes simplex virus protein VP16 associates with the endogenous cell-proliferation factor HCF. VP16 can also associate with HCFs from invertebrates, suggesting that VP16 mimics a cellular protein whose interaction with HCF has been conserved. Here, we show that VP16 mimics the human basic leucine-zipper protein LZIP, which, through association with HCF, may control cell-cycle progression. VP16 and LZIP share a tetrapeptide motif-D/EHXY-used to associate with human HCF. The LZIP-related Drosophila protein BBF-2/dCREB-A contains this HCF-binding motif, indicating that the LZIP-HCF interaction has been conserved during metazoan evolution.

VP16 targets an amino-terminal domain of HCF involved in cell cycle progression

The herpes simplex virus (HSV) regulatory protein VP16 activates HSV immediate-early gene transcription through formation of a multiprotein-DNA complex on viral promoters that includes the preexisting nuclear proteins HCF and Oct-1. The HCF protein is a complex of amino- and carboxy-terminal polypeptides derived from a large (approximately 2,000-amino-acid) precursor by proteolytic processing. Here we show that a 361-residue amino-terminal region of HCF is sufficient to bind VP16, stabilize VP16-induced complex assembly with Oct-1 and DNA, and activate transcription in vivo. This VP16 interaction region contains six kelch-like repeats, a degenerate repeat motif that is likely to fold as a distinctive beta-propeller structure. The third HCF kelch repeat includes a proline residue (P134) that is mutated to serine in hamster tsBN67 cells, resulting in a temperature-sensitive defect in cell proliferation. This missense mutation also prevents direct association between HCF and VP16, suggesting that VP16 mimics a cellular factor required for cell proliferation. Rescue of the tsBN67 cell proliferation defect by HCF, however, requires both the VP16 interaction domain and an adjacent basic region, indicating that HCF utilizes multiple regions to promote cell cycle progression.

Structural flexibility in transcription complex formation revealed by protein-DNA photocrosslinking

The Oct-1 POU domain binds diverse DNA-sequence elements and forms a higher-order regulatory complex with the herpes simplex virus coregulator VP16. The POU domain contains two separate DNA-binding domains joined by a flexible linker. By protein-DNA photocrosslinking we show that the relative positioning of the two POU DNA-binding domains on DNA varies depending on the nature of the DNA target. On a single VP16-responsive element, the POU domain adopts multiple conformations. To determine the structure of the Oct-1 POU domain in a multiprotein complex with VP16, we allowed VP16 to interact with previously crosslinked POU-domain-DNA complexes and found that VP16 can associate with multiple POU-domain conformations. These results reveal the dynamic potential of a DNA-binding domain in directing transcriptional regulatory complex formation.

Interdigitated residues within a small region of VP16 interact with Oct-1, HCF, and DNA

Upon infection, the herpes simplex virus (HSV) activator of immediate-early (IE) gene transcription VP16 forms a multiprotein-DNA complex with two cellular proteins, Oct-1 and HCF. First, VP16 associates with HCF independently of DNA, and this association stimulates subsequent association with Oct-1 on the DNA target of VP16 activation, the TAATGARAT motif found in HSV IE promoters. We have analyzed the involvement of VP16 residues lying near the carboxy-terminal transcriptional activation domain of VP16 in associating with HCF, Oct-1, and DNA. To assay VP16 association with HCF, we developed an electrophoretic mobility retardation assay in which HCF is used to retard the mobility of a hybrid VP16-GAL4 DNA-binding domain fusion protein bound to a GAL4 DNA-binding site. Analysis of an extensive set of individual and combined alanine substitutions over a 61-amino-acid region of VP16 shows that, even within a region as small as 13 amino acids, there are separate residues involved in association with either HCF, DNA, or Oct-1 bound to DNA; indeed, of two immediately adjacent amino acids in VP16, one is important for DNA binding and the other is important for HCF binding. These results suggest that a small region in VP16 is important for linking in close juxtaposition the four components of the VP16-induced complex and support the hypothesis that the structure of the Oct-1-VP16 interaction in this complex is similar to that formed by the yeast transcriptional regulatory proteins MATa1 and MAT alpha2. We propose that HCF stabilizes this Oct-1-VP16 interaction.

The use of computer-assisted video image analysis for the quantification of CD8+ T lymphocytes producing tumor necrosis factor alpha spots in response to peptide antigens

Enzyme-linked immunospot (ELISPOT) analysis is a sensitive technique for the detection and quantification of single T lymphocytes forming cytokine spots after antigen contact in vitro. Herein computer-assisted video image analysis (CVIA) was applied to automatically determine the number and size of tumor necrosis factor alpha (TNF-alpha) spots formed by single blood-derived CD8+ T cells after contact with peptide-loaded target cells. With CVIA and TNF-alpha ELISPOT analysis we quantified CD8+ T cells responsive to HLA-A2.1-binding tyrosinase and influenza matrix peptides in healthy donors. We followed the course of the virus-specific T cell response in two HLA-A2-positive patients with reactivation of latent cytomegalovirus (CMV) infection during immunosuppressive therapy. The test proved sufficiently sensitive to detect in the blood of both patients a temporary expansion of CD8+ T lymphocytes reactive with a known immunogenic HLA-A2.1-binding peptide from glycoprotein B of CMV. Reactivity to peptide antigens was not only reflected by numeric increases of spot formation, but also by the appearance of larger spot areas, presumably formed by strongly peptide-reactive CD8+ T cells. We conclude that the combined use of the TNF-alpha ELISPOT assay and CVIA allows reliable monitoring of the T cell responsiveness to peptide antigens in peripheral blood.

[Prostate carcinoma associated spontaneous factor VIII:C inhibitor hemophilia. Successful therapy of severe hemorrhagic complication with porcine factor VIII in a 75-year-old patient]

Inhibitors of factor VIII are a rare condition in non-hemophiliacs, but they are frequently responsible for life threatening hemorrhage. Acquired factor VIII:C inhibitors represent the spontaneous development of autoantibodies that partially or completely neutralize the plasma coagulant activity of the clotting factor. The autoantibodies can arise in diverse clinical settings, in older adults they are frequently associated with immunologic disorders or malignancies. We report of a 75-year-old man with acquired factor VIII:C inhibitor associated with adenocarcinoma of the prostate and a successful treatment of a severe bleeding complication with porcine factor VIII. A 75-year-old man was admitted because of a hematoma of his right cheek and an isolated prolonged aPTT. Acquired factor VIII:C inhibitor was identified as the cause and immuno-suppressive therapy was begun. In the clinical course severe hemorrhaging occurred and was successfully treated with porcine factor VIII (Hyate:C). The initially high inhibitor titer of 32 Bethesda Units (BU) disappeared. As the cause of acquired factor VIII:C inhibitor a newly diagnosed adenocarcinoma of the prostate is likely. After complete remission of acquired factor VIII:C inhibitor radiation therapy was begun. Six months after severe hemorrhaging the patient was clinically stable and PSA levels were normal. This case demonstrates the necessity of a precise diagnosis and therapy regimen of this coagulopathy based on clinical and laboratory data. In the absence of hemorrhage immuno-suppressive therapy with corticosteroids is indicated, in a patient with severe bleeding and high inhibitor titer (> or = 5 BU) porcine factor VIII should be administered.

N-Oct 5 is generated by in vitro proteolysis of the neural POU-domain protein N-Oct 3

The neural POU-domain proteins N-Oct 3 and N-Oct 5 were first identified in electrophoretic mobility retardation assays through their ability to bind to the octamer sequence ATGCAAAT. These two N-Oct factors are detected in extracts from tumor-derived and normal neural cells. They are present differentially, however, in extracts from melanocytes and melanoma cells: N-Oct 3 is present in extracts from both melanocytes and melanoma cells, whereas N-Oct 5 is more evident in extracts from metastatic melanoma cells. We show here that a cDNA encoding N-Oct 3 directs synthesis of both the N-Oct 3 and N-Oct 5 proteins and that the N-Oct 5 protein in neural and melanoma-cell extracts is also related to N-Oct 3. N-Oct 5, however, is apparently not expressed in vivo: It is not detected if cells are rapidly lysed in SDS or if extracts are prepared with a cocktail of protease inhibitors that includes the serine-protease inhibitor 4-(2-Aminoethyl)benzenesulfonyl fluoride hydrochloride (AEBSF). These data suggest that N-Oct 5 is a specific in vitro proteolytic cleavage product of N-Oct 3 and is not directly related to melanocyte malignancy.

A single-point mutation in HCF causes temperature-sensitive cell-cycle arrest and disrupts VP16 function

The temperature-sensitive BHK21 hamster cell line tsBN67 ceases to proliferate at the nonpermissive temperature after a lag of one to a few cell divisions, and the arrested cells display a gene expression pattern similar to that of serum-starved cells. The temperature-sensitive phenotype is reversible and results from a single missense mutation--proline to serine at position 134--in HCF, a cellular protein that, together with the viral protein VP16, activates transcription of herpes simplex virus (HSV) immediate-early genes. The tsBN67 HCF mutation also prevents VP16 activation of transcription at the nonpermissive temperature. The finding that the same point mutation in HCF disrupts both VP16 function and the cell cycle suggests that HCF plays a role in cell-cycle progression in addition to VP16-dependent transcription.

Selective use of TBP and TFIIB revealed by a TATA-TBP-TFIIB array with altered specificity

Interaction between the TATA box-binding protein TBP and TFIIB is critical for transcription in vitro. An altered-specificity TBP-TFIIB interaction was rationally designed and linked in sequence to an altered-specificity TATA box-TBP interaction to study how TBP and TFIIB function together to support transcription in human cells. The activity of this altered-specificity TATA-TBP-TFIIB array demonstrated that many activators use the known TBP-TFIIB interaction to stimulate transcription. One activator, however, derived from a glutamine-rich activation domain of Sp1, activated transcription independently of this interaction. These results reveal that selectivity in activator function in vivo can be achieved through differential use of TBP and TFIIB.