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Biomedical subjects

W Rowan

Publications and source records attributed to W Rowan.

8 recordsLinked to original sources
PubMed1998

Cross-linking of the CAMPATH-1 antigen (CD52) mediates growth inhibition in human B- and T-lymphoma cell lines, and subsequent emergence of CD52-deficient cells.

The CAMPATH-1H (CD52) antigen is a 21 000-28 000 MW glycopeptide antigen that is highly expressed on T and B lymphocytes and is coupled to the membrane by a glycosylphosphatidylinositol (GPI) anchoring structure. The humanized CAMPATH-1H anti-CD52 antibody is extremely effective at mediating depletion of both normal and tumorigenic lymphocytes in vivo and has been used in clinical trials for lymphoid malignancy and rheumatoid arthritis. Cross-linking GPI-anchored molecules, including CD52, on the surface of T lymphocytes in the presence of phorbol 12-myristate 13-acetate or anti-CD3, results in cellular activation. In the present study we have investigated the functional effects of cross-linking CD52 on T and B tumour cell lines. Cross-linking CD52 on either a B-cell line, Wien 133, which expresses high levels of endogenous CD52 or Jurkat T cells transfected and selected to express high levels of CD52 resulted in growth inhibition. This effect showed slower kinetics and occurred in a lower percentage of cells than growth inhibition stimulated via T- or B-cell receptors. Growth inhibition of the Wien 133 line was followed by the induction of apoptosis, which appeared independent of the Fas/Fas L pathway. Wien 133 cells surviving anti-CD52 treatment were selected and cloned and found to have down-regulated CD52 expression, with a characteristic biphasic pattern of 10% CD52-positive, 90% negative by fluorescence-activated cell sorter analysis. Interestingly, surface expression of other GPI-linked molecules, such as CD59 and CD55, was also down-regulated, but other transmembrane molecules such as surface IgM, CD19, CD20, HLA-DR were unaffected. The present study and previous work show that this is due to a defect in the synthesis of mature GPI precursors. Separation of CD52-positive and negative populations in vitro resulted in a rapid redistribution to the mixed population. Injection of CD52-negative cells into nude mice to form a subcutaneous tumour resulted in a substantial increase in expression of CD52. These results suggest that the defect in the Wien 133 cells is reversible, although the molecular mechanism is not clear. These observations have relevance to the clinical situation as a similar GPI-negative phenotype has been reported to occur in lymphocytes following CAMPATH-1H treatment in vivo.

Animals↗
PubMed1997

Differential functional effects of a humanized anti-CD4 antibody on resting and activated human T cells.

A fully humanized immunoglobulin G1 (IgG1) anti-CD4 monoclonal antibody is currently being evaluated in phase I/II clinical trials for rheumatoid arthritis. In order to understand the mode of action of this antibody in vivo, we have carried out a detailed functional analysis in vitro of the effects of this antibody on T-cell activation. The anti-CD4 antibody was found to inhibit both antigen-specific responses involving recognition of human leucocyte antigen (HLA) class II and processed antigenic peptides as well as non-class II dependent responses via anti-CD3 antibodies. The antibody did not cause total blockade of T-cell proliferation, but rather induced a shift in the dose-response curve, decreasing the sensitivity of cells to antigen or anti-CD3-mediated stimulation. The antibody appears to allow at least a partial early signal into the T cell as it does not inhibit the increase in tyrosine phosphorylation induced by anti-CD3 antibodies. A comparison of the intact antibody with that of either the F(ab')2 fragment or an engineered non-Fc receptor (FcR) binding form revealed that the intact antibody was the most effective at inhibiting proliferation of resting peripheral blood CD4+ T cells. However, this difference was only apparent when excess antibody was removed from culture prior to antigen or anti-CD3 mediated stimulation. The intact antibody induced both CD4 down-modulation and increases in CD4-associated tyrosine phosphorylation of resting CD4+ T cells, which were not seen with the non-FcR binding versions, which may account for the enhanced potency of the intact antibody at inhibiting T-cell activation. Interestingly, the anti-CD4 antibody induced a differential effect on activated CD4+ T cell clones compared with resting CD4+ T cells with respect to degree of CD4 cross-linking required to induce functional effects in the T cell. Both intact and non-FcR binding antibodies were equally effective at inhibiting T-cell proliferation of activated T-cell clones. In addition CD4 down-modulation and increased CD4-associated tyrosine phosphorylation were observed with T-cell clones in the absence of secondary cross-linking. Such observations may be of relevance when studying the effects of the antibody at sites of inflammation, where there will be CD4+ T cells of differing activation states as well as varying numbers of FcR positive cells.

Antibodies, Monoclonal↗
PubMed1996

Emergence of CD52-, glycosylphosphatidylinositol-anchor-deficient lymphocytes in rheumatoid arthritis patients following Campath-1H treatment.

CD52 is a glycosylphosphatidyl-inositol (GPI)-linked glycoprotein expressed at high levels on normal T and B lymphocytes and at lower levels on monocytes, while being absent on granulocytes and bone marrow stem cell precursors. The emergence of CD52- lymphocytes of both T and B cell lineages was observed in three out of 25 rheumatoid arthritis patients treated with teh humanized antibody Campath-1H in phase II clinical trial. Whereas the majority of CD52- B cells had disappeared from the peripheral blood by 3 months post-treatment, both CD52- CD4+ and CD8+ T cells persisted in the circulation for at least 20 months. In the two patients that were tested, the GPI-anchored surface molecules CD55 and CD59 were also absent on the CD52- cells, although expression of other cell surface transmembrane, proteins (CD3, CD4 and CD2) was unaffected. The CD52- cells maintained a stable phenotype in vitro despite repeated re-stimulation in culture. Both CD52- and C52+ clones, established from one of the patients, responded to a similar extent to several T cell mitogens, as assessed by proliferation, suggesting that a general defect in expression of GPI-linked molecules does not impair T cell activation. These data show that an immune attack against a GPI-anchored surface molecule can result in the selection of a GPI-anchor-deficient cell population. Despite the persistence of CD52- T cells in the peripheral blood, no adverse reactions associated with the presence of these cells were noted in any of the patients; in fact they responded with longer remission times after Campath-1H treatment than the other patients in the trial.

Adult↗
PubMed1995

Coronary angioplasty of branch vessels associated with an extreme angle take-off.

Stenoses in branch vessels which originate at acute angle to the main vessel represent a technically challenging anatomy for the performance of balloon angioplasty [PTCA]. We report a novel technique utilizing a distally placed perfusion balloon that facilitated guidewire placement and subsequent balloon angioplasty of a branch vessel stenosis.

Aged↗
PubMed1993

A humanized CD18 antibody can block function without cell destruction.

Leukocyte integrins are intimately involved in transient adherence of leukocytes to endothelium and to each other in the processes of extravasation and cell activation. In this study, seven mAb directed against human CD11a and two mAb directed against human CD18, the alpha- and beta-chains of the leukocyte functional Ag-1 molecule, respectively, were analyzed for their ability to inhibit several leukocyte functional Ag-1-mediated interactions. The best blocking mAb in these studies, a rat anti-human CD18, YFC51.1, was subsequently humanized by complementarily-determining region grafting, associated with human C regions and expressed. The humanized mAb was shown to maintain binding for human CD18. Even though the humanized mAb was an IgG1 isotype it still retained the functional blocking characteristics of the rat mAb while failing to mediate cell killing. The IgG1 mAb was unable to bind human Clq and could block but did not mediate antibody-dependent cellular cytotoxicity.

Animals↗
PubMed1993

Immunogenicity of a hybrid Plasmodium falciparum malaria antigen.

A recombinant baculovirus-expressed hybrid protein containing epitopes for the C-terminal fragment of the Plasmodium falciparum precursor to the major merozoite surface antigens (PMMSA) and the tetrapeptide repeats of the circumsporozoite protein (CSP) was assessed for its immunogenicity. Murine MHC-II restriction of the antibody response to the CSP repeats was not overcome by the PMMSA component, the response to which showed no restriction. In an adjuvant trial the highest antibody titres in rabbits to both components of the hybrid were obtained using Freund's adjuvant. Lack of a boosting antibody response to the CSP repeats appeared to be linked to the conformation of the PMMSA component. Formulation of the hybrid protein into Iscoms gave antibody titres of only short duration to both components.

Adjuvants, Immunologic↗
PubMed1982

Resolution and contrast recovery at depth in planar nuclear images.

Resolution and contrast recovery in planar nuclear images at depth with a high purity germanium (HPGe) camera has been achieved through use of a weighted back projection (WBP) method. The algorithm can be derived from Bayes' theorem using the point spread function of the camera. The variations in the formulation of WBP (one single pass and two iterative procedures) are presented with the characteristics and performance of each method. The evaluation procedure determines the behaviour of signal-to-noise ratio, contrast and texture after application of the algorithm. Both real and simulated cold lesions obtained with the HPGe camera are studied with sizes ranging from 3 mm to 17 mm and background count densities from 100 to 6400 counts cm2. Application of WBP is shown to increase spatial resolution and contrast without a concomitant reduction in signal-to-noise ratio. Images obtained with the HPGe camera and processed with WBP are presented. The algorithm has been applied to the scintillation camera, yielding significant resolution and contrast recovery despite the presence of scatter and textured noise present in the HPGe images.

Animals↗