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Biomedical subjects

P Björk

Publications and source records attributed to P Björk.

At least 19 recordsLinked to original sources
PubMed2003

A comparison of T-, B- and NK-cell reconstitution following conventional or nonmyeloablative conditioning and transplantation with bone marrow or peripheral blood stem cells from human leucocyte antigen identical sibling donors.

This retrospective study compares the reconstitution of T, B and NK cells in three groups of patients transplanted for haematological malignancies with grafts from their HLA-identical sibling donors. In all, 15 patients received PBSC after a nonmyeloablative conditioning regimen consisting of fludarabine and 200 cGy TBI, 13 patients received PBSC after myeloablative conditioning and 37 patients received BM after myeloablative conditioning. In the nonmyeloablative group, the NK cells normalised after 1 month, the CD8+ T cells normalised after 3 months, the CD4+ T cells reached near normal values after 9 months and the B cell values were reduced until 12 months after transplant. In the two myeloablative groups, recipients of PBSC had a significantly higher number of CD4+ T cells after 4 months (P=0.004) and after 12 months (P=0.001), than recipients of BM. We found no differences in the T cell reconstitution between the two PBSC groups. This was of interest as the recipients of nonmyeloablative conditioning were older (P<0.001) and had a higher occurrence of chronic GVHD (P<0.05) than the recipients of myeloablative conditioning. In contrast, the recipients of nonmyeloablative conditioning had a delayed B cell recovery when compared to the patients who received myeloablative conditioning (P=0.04).

Adolescent↗
PubMed2001

Therapy of human non-small-cell lung carcinoma using antibody targeting of a modified superantigen.

Superantigens activate T-cells by linking the T-cell receptor to MHC class II on antigen-presenting cells, and novel reactivity can be introduced by fusing the superantigen to a targeting molecule. Thus, an antibody-targeted superantigen, which activates T cells to destroy tumour cells, might be used as cancer therapy. A suitable target is the 5T4 oncofetal antigen, which is expressed on many carcinomas. We constructed a fusion protein from a Fab of a monoclonal antibody recognizing the 5T4 antigen, and an engineered superantigen. The recombinant product 5T4FabV13-SEA(D227A)bound the 5T4 antigen expressed on the human non-small-cell lung cancer cell line Calu-1 with a Kd of 1.2 nM while the substitution of Asp227 to Ala in the superantigen moiety reduced binding activity to MHC class II. 5T4FabV13-SEA(D227A)tumour reactivity was demonstrated in 7/7 NSCLC samples by immunohistochemistry, while normal tissue reactivity was low to moderate. 5T4FabV13-SEA(D227A)induced significant T-cell-dependent in vitro killing of sensitive 5T4 bearing Calu-1 cells, with maximum lysis at 10(-10)M, while the capacity to lyse MHC class II expressing cells was approximately 1000 times less effective. Immunotherapy of 5T4FabV13-SEA(D227A)against human NSCLC was investigated in SCID mice reconstituted with human peripheral blood mononuclear cells. Mice carrying intreperitoneally growing Calu-1 cells showed significant reduction in tumour mass and number after intravenous therapy with 5T4FabV13-SEA(D227A). Thus, 5T4FabV13-SEA(D227A)has highly attractive properties for therapy of human NSCLC.

Animals↗
PubMed2001

Cooperative zinc binding in a staphylococcal enterotoxin A mutant mimics the SEA-MHC class II interaction.

The structure of a mutant form of staphylococcal enterotoxin A (SEA) has been determined to 2.1 A resolution. The studied SEA substitution H187-->A187 (SEAH187A) leads to an almost 10-fold reduction of the binding to major histocompatibility complex (MHC) class II. H187 is important for this interaction since it coordinates Zn2+. The zinc ion is thought to hold MHC class II and SEA together in a complex. Interestingly, only one of two molecules in the asymmetric unit binds Zn2+. H225, D227, a water molecule, and H44 from a symmetry-related molecule ligate Zn2+. The symmetry-related histidine is necessary for this substituted Zn2+ site to bind to Zn2+ at low zinc concentration (no Zn2+ added). Since a water molecule replaces the missing H187, H44 binds Zn2+ at the position where betaH81 from MHC class II probably will bind. Dynamic light scattering analysis reveals that in solution as well as in the crystal lattice the SEA(H187A) mutant forms aggregates. The substitution per se does not cause aggregation since wild-type SEA also forms aggregates. Addition of EDTA reduces the size of the aggregates, indicating a cross-linking function of Zn2+. In agreement with the biological function, the aggregation is weak (i.e. not revealed by gel filtration) and non-specific.

Crystallography, X-Ray↗
PubMed2000

The crystal structure of staphylococcal enterotoxin H: implications for binding properties to MHC class II and TcR molecules.

The X-ray structure of the superantigen staphylococcal enterotoxin H (SEH) has been determined at 1.69 A resolution. In this paper we present two structures of zinc-free SEH (apoSEH) and one zinc-loaded form of SEH (ZnSEH). SEH exhibits the conventional superantigen (SAg) fold with two characteristic domains. In ZnSEH one zinc ion per SEH molecule is bound to the C-terminal beta-sheet in the region implicated for major histocompatibility complex class II (MHC class II) binding in SEA, SED and SEE. Surprisingly, the zinc ion has only two ligating amino acid residues His206 and Asp208. The other ligands to the zinc ion are two water molecules. An extensive packing interaction between two symmetry-related molecules in the crystal, 834 A(2)/molecule, forms a cavity that buries the zinc ions of the molecules. This dimer-like interaction is found in two crystal forms. Nevertheless, zinc-dependent dimerisation is not observed in solution, as seen in the case of SED. A unique feature of SEH as compared to other staphylococcal enterotoxins is a large negatively charged surface close to the Zn(2+) site. The interaction of SEH with MHC class II is the strongest known among the staphylococcal enterotoxins. However, SEH seems to lack a SEB-like MHC class II binding site, since the side-chain properties of structurally equivalent amino acid residues in SEH and those in SEB-binding MHC class II differ dramatically. There is also a structural flexibility between the domains of SEH. The domains of two apoSEH structures are related by a 5 degrees rotation leading to at most 3 A difference in C(alpha) positions. Since the T-cell receptor probably interacts with both domains, SEH by this rotation may modulate its binding to different TcR Vbeta-chains.

Amino Acid Sequence↗
PubMed2000

Design and dosimetry characteristics of a soft-docking system for intraoperative radiation therapy.

PURPOSE: The design concept and the dosimetric characteristics of an applicator system for intraoperative radiation therapy (IORT) with special emphasis on alignment methods, the effect of a plastic scatterer in the beam, radiation leakage, and misalignment dosimetry, are presented in this paper. MATERIALS AND METHODS: A soft-docking system for a linear accelerator, which enables collimation of electron beams (4-22 MeV) for IORT has been developed. The system includes twenty-one circular polymethylmethacrylate (PMMA) treatment cones of different lengths, diameters and end angles. All in-water measurements are made using p-type silicon diode detectors. RESULTS: The effect of introducing a PMMA scatterer in the therapeutic beam includes increased surface dose values (above 83% for all nominal electron energies and for all cones) and improved dose homogeneity within the therapeutic range. Electrons scattered from the inside wall of the cone result in dose profile horns at depth of dose maximum always lower than 109%. The radiation leakage outside the cone is less than 13%. Large changes in the dose profiles occur if the intraoperative cone is misaligned more than 0.5. CONCLUSION: The alignment procedure of the soft-docking system is easy to handle and the applicator design provides adequate collimation of electron beams for IORT.

Combined Modality Therapy↗
PubMed2000

The spectral and thermodynamic properties of staphylococcal enterotoxin A, E, and variants suggest that structural modifications are important to control their function.

The superantigens staphylococcal enterotoxin A and E (SEA and SEE) can activate a large number of T-cells. SEA and SEE have approximately 80% sequence identity but show some differences in their biological function. Here, the two superantigens and analogues were characterized biophysically. SEE was shown to have a substantially higher thermal stability than SEA. Both SEA and SEE were thermally stabilized by 0.1 mM Zn(2+) compared with Zn(2+)-reduced conditions achieved using 1 mM EDTA or specific replacements that affect Zn(2+) coordination. The higher stability of SEE was only partly caused by the T-cell receptor (TCR) binding regions, whereas regions in the vicinity of the major histocompatibility complex class II binding sites affected the stability to a greater extent. SEE exhibited a biphasic denaturation between pH 5.0-6.5, influenced by residues in the TCR binding regions. Interestingly, enzyme-linked immunosorbent assay, isoelectric focusing, and circular dichroism analysis indicated that conformational changes had occurred in the SEA/E chimerical constructs relative to SEA and SEE. Thus, it is proposed that the Zn(2+) binding site is very important for the stability and potency of SEA and SEE, whereas residues in the TCR binding site have a substantial influence on the molecular conformation to control specificity and function.

Amino Acid Sequence↗
PubMed2000

Estramustine-binding protein in malignant glioma in rat.

Estramustine is a chemotherapeutic drug, used in the treatment of prostatic carcinoma. In the prostate, it binds specifically to a 46 kDa glycoprotein called estramustine-binding protein (EMBP), which consists of three polypeptide components; C1, C2, and C3, each coded for by a specific gene. Expression of EMBP and binding of estramustine has also been detected in malignant glioma in both rats and humans. Elevated levels of this protein in astrocytoma have proved to correlate with poor prognosis. In the present work, expression of all three polypeptide components of EMBP was confirmed in an orthotopic rat glioma model with nested reverse transcriptase PCR and Western blot (molecular weights of 8, 10, and 12 kDa). Specific binding of estramustine with a Kd of 40 for male and 50 for female rats, and a total number of binding sites of 0.7 and 0.4 pmol/mg proteins for male and female rats respectively, was demonstrated with Scatchard plot analysis. These binding characteristics are similar to those of prostatic EMBP. Further studies to elucidate how EMBP expression affects the effect of estramustine treatment, and its putative prognostic value is of special clinical interest. The confirmation of BMBP expression in BT4C rat glioma demonstrates its suitability as a model system for such studies.

Animals↗
PubMed2000

Chemical cross-linking with thiol-cleavable reagents combined with differential mass spectrometric peptide mapping--a novel approach to assess intermolecular protein contacts.

The intermolecular contact regions between monomers of the homodimeric DNA binding protein ParR and the interaction between the glycoproteins CD28 and CD80 were investigated using a strategy that combined chemical cross-linking with differential MALDI-MS analyses. ParR dimers were modified in vitro with the thiol-cleavable cross-linker 3,3'-dithio-bis(succinimidylproprionate) (DTSSP), proteolytically digested with trypsin and analyzed by MALDI-MS peptide mapping. Comparison of the peptide maps obtained from digested cross-linked ParR dimers in the presence and absence of a thiol reagent strongly supported a "head-to-tail" arrangement of the monomers in the dimeric complex. Glycoprotein fusion constructs CD28-IgG and CD80-Fab were cross-linked in vitro by DTSSP, characterized by nonreducing SDS-PAGE, digested in situ with trypsin and analyzed by MALDI-MS peptide mapping (+/- thiol reagent). The data revealed the presence of an intermolecular cross-link between the receptor regions of the glycoprotein constructs, as well as a number of unexpected but nonetheless specific interactions between the fusion domains of CD28-IgG and the receptor domain of CD80-Fab. The strategy of chemical cross-linking combined with differential MALDI-MS peptide mapping (+ thiol reagent) enabled localization of the interface region(s) of the complexes studied and clearly demonstrates the utility of such an approach to obtain structural information on interacting noncovalent complexes.

Amino Acid Sequence↗
PubMed2000

Comparative dosimetry of diode and diamond detectors in electron beams for intraoperative radiation therapy.

The aim of the present study is to examine the validity of using silicon semiconductor detectors in degraded electron beams with a broad energy spectrum and a wide angular distribution. A comparison is made with diamond detector measurements, which is the dosimeter considered to give the best results provided that dose rate effects are corrected for. Two-dimensional relative absorbed dose distributions in electron beams (6-20 MeV) for intraoperative radiation therapy (IORT) are measured in a water phantom. To quantify deviations between the detectors, a dose comparison tool that simultaneously examines the dose difference and distance to agreement (DTA) is used to evaluate the results in low- and high-dose gradient regions, respectively. Uncertainties of the experimental measurement setup (+/- 1% and +/- 0.5 mm) are taken into account by calculating a composite distribution that fails this dose-difference and DTA acceptance limit. Thus, the resulting area of disagreement should be related to differences in detector performance. The dose distributions obtained with the diode are generally in very good agreement with diamond detector measurements. The buildup region and the dose falloff region show good agreement with increasing electron energy, while the region outside the radiation field close to the water surface shows an increased difference with energy. The small discrepancies in the composite distributions are due to several factors: (a) variation of the silicon-to-water collision stopping-power ratio with electron energy, (b) a more pronounced directional dependence for diodes than for diamonds, and (c) variation of the electron fluence perturbation correction factor with depth. For all investigated treatment cones and energies, the deviation is within dose-difference and DTA acceptance criteria of +/- 3% and +/- 1 mm, respectively. Therefore, p-type silicon diodes are well suited, in the sense that they give results in close agreement with diamond detectors, for practical measurements of relative absorbed dose distributions in degraded electron beams used for IORT.

Diamond↗
PubMed1999

Staphylococcal enterotoxin H displays unique MHC class II-binding properties.

Staphylococcal enterotoxin H (SEH) has been described as a superantigen by sequence homology with the SEA subfamily and briefly characterized for its in vivo activity. In this study, we demonstrate that SEH is a potent T cell mitogen and inducer of T cell cytotoxicity that possesses unique MHC class II-binding properties. The apparent affinity of SEH for MHC class II molecules is the highest affinity ever measured for a staphylococcal enterotoxin (Bmax1/2 approximately 0.5 nM for MHC class II expressed on Raji cells). An excess of SEA or SEAF47A, which has reduced binding to the MHC class II alpha-chain, is able to compete for binding of SEH to MHC class II, indicating an overlap in the binding sites at the MHC class II beta-chain. The binding of SEH to MHC class II is like SEA, SED, and SEE dependent on the presence of zinc ions. However, SEH, in contrast to SEA, binds to the alanine-substituted DR1 molecule, betaH81A, believed to have impaired zinc-bridging capacity. Furthermore, alanine substitution of residues D167, D203, and D208 in SEH decreases the affinity for MHC class II as well as its in vitro potency. Together, this indicates an MHC class II binding site on SEH with a different topology as compared with SEA. These unique binding properties will be beneficial for SEH to overcome MHC class II isotype variability and polymorphism as well as to allow an effective presentation on APCs also at low MHC class II surface expression.

Alanine↗
PubMed1999

[Umbilical cord blood from unrelated donor. An alternative to bone marrow transplantation].

Unrelated umbilical cord blood (UCB) as a source of haematopoietic stem/progenitor cells has been used for the first time in Sweden for allografting two boys (6 and 11 1/2 years old) with acute leukaemia in complete remission. Double class-II HLA-mismatch UCB units, from the Milan and New York cord blood banks, respectively, were used. Pre-transplant preparation consisted in fractionated total body irradiation in both cases, followed by cytoreductive high-dose cyclophosphamide for the 6-year-old with acute lymphocytic leukaemia (ALL) and fludarabine-melphalan for the 11 1/2-year-old with acute non-lymphocytic leukaemia (ANLL). Despite delayed haematopoietic recovery (probably due to HLA disparity) or reactivated cytomegalovirus infection in one boy, the immediate post-graft course was uneventful and extramedullary toxicity mild in both cases. Only transient acute graft-versus-host disease occurred, and complete donor chimerism was confirmed. Unfortunately, the out-come was unfavourable in both cases, the ANLL patient succumbing on day 96 due to pneumonia followed by multiorgan failure, and the ALL patient on day 140 due to combined medullar and central nervous system relapse. Although UCB transplantation needs further evaluation, it may contribute substantially to successful salvage procedures. Thus the introduction of cord blood banking in Sweden merits consideration.

Blood Banks↗
PubMed1999

Estramustine-binding protein in meningioma.

The presence of estramustine-binding protein has been suggested to positively correlate with the effect of the cytotoxic drug estramustine, a combination of estradiol and nornitrogen mustard used in the treatment of prostatic carcinoma. This study demonstrates expression of estramustine-binding protein in a series of meningioma using different ligand-based and immunological techniques. Scatchard plot analysis showed specific binding sites for [3H]lestramustine in meningioma tissue with a dissociation constant of 22-26 nM. Immunohistochemistry revealed an immunoreactivity in meningioma comparable to that demonstrated in prostatic carcinoma. The mean concentration (n = 6) of estramustine-binding protein in meningioma, as determined by radioimmunoassay was 159 ng/g tissue (range 18-274 ng/g). Moreover, partial characterization using size exclusion chromatography of [3H]estramustine-labeled tumor extracts and Western blot analysis of immunoprecipitated samples indicated that the structure of the estramustine-binding protein in meningioma is similar to that in rat prostate, with three polypeptide components of 10, 14, and 16 kDa, as compared to 8, 10-11, and 12 kDa in rat prostate. In conclusion, the novel observation of estramustine-binding protein and specific binding of estramustine in meningioma justify further evaluation regarding the role of estramustine-binding protein in the growth behavior of meningioma and the potential for estramustine and similar hormone-related drugs in the treatment of relapsing meningioma.

Blotting, Western↗
PubMed1999

Verification of a pencil beam based treatment planning system: output factors for open photon beams shaped with MLC or blocks.

The accuracy of monitor unit calculations from a pencil beam based, three-dimensional treatment planning system (3D TPS) has been evaluated for open irregularly shaped photon fields. The dose per monitor unit was measured in water and in air for x-ray beam qualities from 6 to 15 MV. The fields were shaped either with a multileaf collimator (MLC) or with customized alloy blocks. Calculations from the 3D TPS were compared with measurements. The agreement between calculated and measured dose per monitor unit depended on field size and the amount of blocking and was within 3% for the MLC-shaped fields. The deviation could be traced to limitations in head scatter modelling for the MLC. For fields shaped with alloy blocks, the dose per monitor unit was calculated to be within 1.6% of measured values for all fields studied. The measured and calculated relative phantom scatter for fields with the same equivalent field size were identical for MLC and alloy shaped fields. These results indicate that the accuracy in the TPS calculations for open irregular fields, shaped with MLC or blocks, is satisfactory for clinical situations.

Algorithms↗
PubMed1998

Differential uptake of estramustine phosphate metabolites and its correlation with the levels of estramustine binding protein in prostate tumor tissue.

Estracyt (EMP) has been used for the treatment of hormone refractory prostate cancer for many years. Recently, new data from combination studies have given rise to new interest in this old drug. Explanations for the synergy found in the clinic are many, but one major factor may be the previous indication that the drug accumulates in the prostate tumor. We have, therefore, examined the level of the four metabolites, estromustine (EoM), estramustine (EaM), estrone, and estradiol in the tumor and serum of 14 patients with T2 and T3 prostate cancer receiving a single i.v. dose of 600 mg of EMP, about 12 h before radical prostatectomy. Because it has been suggested that the uptake into the prostate tumor is due to binding to the estramustine binding protein (EMBP), we have in addition measured the level of EMBP in the prostate tumor tissue. The main serum and tissue metabolite in all patients was EoM followed by EaM, estrone, and estradiol. The levels for EoM ranged from 63.8-162.8 ng/ml in the serum and from 64.8-1209 ng/ml in the prostate tumor, resulting in a mean ratio for serum to tumor of 1:5. The levels for EaM ranged from 8.3-51.4 ng/ml in the serum and 73.9-563.4 ng/ml in the tumor, giving a mean ratio for serum to tumor of 1:13. The levels of EMBP were higher in T3 tumors than in T2 tumors, 54.1 and 40.7 ng/g tissue, respectively. A significant correlation was found between the levels of EaM (r = 0.60) and the levels of EMBP in the tumor. These data demonstrate that 12 h after a single i.v. dose of 600 mg of EMP the levels of the cytotoxic metabolites EoM and EaM are substantially higher in the tumor than in the serum of the same patient and that a correlation exists between the levels of EaM in the tumor and the levels of EMBP. Thus, this supports the hypothesis that the EMBP is responsible for the retention of EoM and EaM in the prostate tumor.

Aged↗
PubMed1997

The macrophage migration inhibitory factor MIF is a phenylpyruvate tautomerase.

A macrophage migration inhibitory factor (MIF), originally described as a product of activated lymphocytes, has been defined as a 12 kDa protein, expressed in a wide variety of tissues. Here MIF is identified as a phenylpyruvate tautomerase (EC 5.3.2.1) having p-hydroxyphenylpyruvate and phenylpyruvate as its natural substrates. The definition of MIF as an enzyme may yield insight into the mechanism of action of this proinflammatory and immunomodulating cytokine.

Amino Acids↗
PubMed1997

Identification of framework residues in a secreted recombinant antibody fragment that control production level and localization in Escherichia coli.

The monoclonal antibody 5T4, directed against a human tumor-associated antigen, was expressed as a secreted Fab superantigen fusion protein in Escherichia coli. The product is a putative agent for immunotherapy of non-small cell lung cancer. During fermentation, most of the fusion protein leaked out from the periplasm to the growth medium at a level of approximately 40 mg/liter. This level was notably low compared with similar products containing identical CH1, CL, and superantigen moieties, and the Fv framework was therefore engineered. Using hybrid molecules, the light chain was found to limit high expression levels. Substituting five residues in VL increased the level almost 15 times, exceeding 500 mg/liter in the growth medium. Here, the substitutions Phe-10 --> Ser, Thr-45 --> Lys, Thr-77 --> Ser, and Leu-78 --> Val were most powerful. In addition, replacing four VH residues diminished cell lysis during fermentation. Thereby the product was preferentially located in the periplasm instead of the growth medium, and the total yield was more than 700 mg/liter. All engineered products retained a high affinity for the tumor-associated antigen. It is suggested that at least some of the identified framework residues generally have to be replaced to obtain high level production of recombinant Fab products in E. coli.

Amino Acid Sequence↗