PubMed Health⌕ Search

Biomedical subjects

P Cowburn

Publications and source records attributed to P Cowburn.

8 recordsLinked to original sources
PubMed2002

Induction of viral and tumour specific CTL responses using antibody targeted HLA class I peptide complexes.

The production of cytotoxic T cells with specificity for cancer cells is a rapidly evolving branch of cancer therapeutics. A variety of approaches aim to amplify anti-tumour cytotoxic T cell responses using purified peptides, tumour cell lysates or recombinant HLA/peptide complexes in differing antigen presenting systems. Using a two-step biotin-streptavidin antibody targeting system, recombinant HLA-class I/peptide complexes were attached to the surface of B cells via the anti-CD20 B9E9-scFvSA antibody-streptavidin fusion protein. Flow cytometry with a conformation dependant monoclonal antibody to HLA class I indicated that targeted HLA-class I/peptide complexes remain on the surface of B cells in culture for periods in excess of 72 h. PBMCs were stimulated in vitro for 8-14 days using the autologous B cells as antigen presenting cells. Following a single cycle of stimulation specific cytotoxic T cell responses to targeted HLA-A2 complexes containing the M1, BMLF1 and Melan A peptides could be demonstrated by tetramer staining and Cr release assays. With the HLA-A2/BMLF1 complex up to 2.99% of CD8+ve cells were tetramer positive producing 20% lysis (E : T 10 : 1) of CIR-A2 target cells in an in vitro cytotoxicity assay compared to baseline levels of 0.09% tetramer +ve and 2% lysis in the unstimulated population. PBMCs from a healthy donor treated with two cycles of stimulations with targeted HLA-A2/Melan A complexes, demonstrated expansion of the melanA tetramer +ve population from 0.03% to 1.4% producing 15% lysis of Melan A pulsed target cells. With further consideration to the key variables of HLA/peptide complex density, the ratio of stimulator to effector cells and optimum cytokine support, this system should offer an easy and effective method for the in vitro amplification of specific cytotoxic T cell responses and warrants development for the in vivo induction of cytotoxic T cell responses in cancer therapy.

Antibodies↗
PubMed2000

In vitro and in vivo effects of a cyclic peptide with affinity for the alpha(nu)beta3 integrin in human melanoma cells.

Expression of the integrin alpha(nu)beta3 has been shown to be associated with increasing metastatic potential in malignant melanoma. It also has a functional role on vascular endothelial cells during angiogenesis. The cyclic oligopeptide cRGDfV is known to bind with high affinity to alpha(nu)beta3. We have investigated the cellular effects of cRGDfV on a panel of human melanoma cell lines in vitro and also on the A375 melanoma cell line growing as xenografts in nude mice. cRGDfV is a potent inhibitor of alpha(nu)beta3-mediated cell adhesion, however, we have found no convincing evidence that integrin ligation by cRGDfV induces apoptosis in melanoma cell lines. However, cRGDfV when administered subcutaneously into nude mice did inhibit the growth of A375 melanoma xenografts. Histological examination of the tumours indicated that this effect was primarily one of angiogenesis inhibition. The results suggest that agents which target the alpha(nu)beta3 integrin may have a useful role as anti-angiogenesis agents in clinical oncology, but that they may not exert a direct effect on alphavbeta3-expressing tumour cells.

Animals↗
PubMed2000

Effect of photodynamic therapy in combination with ionizing radiation on human squamous cell carcinoma cell lines of the head and neck.

Photodynamic therapy (PDT) is a promising treatment modality for head and neck, and other tumours, using drugs activated by light. A second generation drug, 5-aminolaevulinic acid (5-ALA), is a precursor of the active photosensitizer protoporphyrin IX (PpIX) and has fewer side-effects and much more transient phototoxicity than previous photosensitizers. We have investigated the effect of 5-ALA mediated PDT in combination with gamma-irradiation on the colony forming ability of several human head and neck tumour cell lines. The effect of treatments on the DNA cell cycle kinetics was also investigated. Our results indicate that the combination of 5-ALA mediated PDT and gamma-irradiation results in a level of cytotoxicity which is additive and not synergistic. 5-ALA mediated PDT had no discernible effect on DNA cell cycle distributions. gamma-irradiation-induced cell cycle arrest in G2 did not enhance the phototoxicity of 5-ALA.

Aminolevulinic Acid↗
PubMed1996

Detection of microemboli by transcranial Doppler ultrasound.

Doppler ultrasound detection of abnormally high-pitched signals within the arterial waveform offers a new method for diagnosis, and potentially for prediction, of embolic complications in at-risk patients. The nature of Doppler "microembolic" signals is of particular interest in patients with prosthetic heart valves, where a high prevalence of these signals is observed. Monitoring the middle cerebral artery with 2-MHz transcranial Doppler ultrasound (TC-2000, Nicolet Biomedical; Warwick, UK), we looked for microemboli signals in 150 patients (95 women and 55 men), and found 1 or more signals during a 30-min recording in 89% of 70 patients with Bjork-Shiley valves (principally monostrut), 54% of 50 patients with Medtronic-Hall valves, and 50% of 30 patients with Carpentier-Edwards valves (p < 0.001, chi 2). In the patients with Bjork-Shiley valves, the mean number of signals per hour was 59 (range, 42-86; 95% confidence interval), which was significantly higher than the mean in patients with Medtronic-Hall and Carpentier-Edwards valves (1.5[range, 0.5-2.5] and 1 [range, 0-5.3], respectively; both p < 0.04, multiple comparisons. Bonferroni correction). In the patients undergoing serial pre- and postoperative studies, the causative role of the valve implant was emphasized. There was no correlation between the number of emboli signals and a prior history of neurologic deficit, cardiac rhythm, previous cardiac surgery, or the intensity of oral anticoagulation, in patients with prosthetic heart valves. In Bjork-Shiley patients, dual (mitral and aortic) valves were associated with more signals than were single valves. In Medtronic-Hall patients, the signal count was greater for valves in the aortic position than it was for valves in the mitral position. Comparative studies of Doppler emboli signals in other clinical settings suggest a difference in composition or size of the underlying maternal between prosthetic valve patients and patients with carotid stenosis. These studies also suggest that the signals are of gaseous origin in valve patients. The clinical significance of continuing microembolism remains to be determined.

Carotid Stenosis↗
PubMed1994

Subclinical embolism in patients undergoing cardiac valve implantation and coronary artery bypass surgery.

Patients undergoing prosthetic valve insertion and coronary artery bypass surgery were examined with transcranial Doppler ultrasound, recently shown to be capable of detecting continuing subclinical emboli in patients with embolic sources. In 30 patients examined at least 1 year after valve surgery, and in whom warfarinisation was stable within defined limits, 20 of 24 patients (83%) with mechanical valves and 3 of 6 patients (50%) with porcine valves had embolic signals. In a serial preoperative and postoperative study in a further 30 patients, of whom 29 had native or bioprosthetic valves, only the one patient with a previous mechanical mitral valve prosthesis had embolic signals preoperatively. The incidence of embolic signals increased to 9 (30%) on the first postoperative day, and 20 (67%) on day 5. In a similar serial study in 25 patients undergoing coronary bypass surgery, 8 (32%) had preoperative embolic signals, which were explicable by cardiac and/or carotid disease in 6 cases. The embolus signal incidence and count did not increase postoperatively in this group. No embolic signals were found in 15 volunteer controls. The results indicate that prosthetic valves cause continuing microembolisation, detectable by transcranial Doppler; coronary artery bypass cases may have incidental embolic signals which are unaffected by cardiac surgery. This new application of Doppler ultrasound may improve the clinical assessment of embolic risk of new prosthetic valve types and deserves further examination.

Adult↗
PubMed1994

Ultrasound detection of cerebral emboli in patients with prosthetic heart valves.

This study was undertaken in 64 patients, 50 with mechanical and 14 with porcine prosthetic valves, to evaluate the incidence of intracranial emboli and their distribution in the basal cerebral arteries. The patients were studied using transcranial Doppler (EME TC2-64B, Uberlingen, Germany), with a monitoring time of two minutes over each of the internal carotid arteries, middle and anterior cerebral arteries, vertebral arteries and the basilar artery. Sixty-three of the 64 patients were stabilized on warfarin at the time of the study. The incidence of emboli signals was significantly higher in patients with mechanical compared to porcine cardiac valves (88% versus 14%, p < 0.01). The number of emboli signals was significantly higher in the anterior compared with the posterior circulation, with a median of eight signals in the internal carotid arteries (95% confidence interval 5-15), 2.5 in the vertebral arteries (95% confidence interval 1-5.5)(p < 0.03). It was also significantly higher in those patients who had undergone double (aortic and mitral) as opposed to those who had undergone single aortic valve replacement: 18 versus two signals per minute (confidence intervals 5-30.5 versus 0.5-3.5) (p < 0.01). It is concluded that subclinical emboli signals are readily detectable using transcranial Doppler and are common in patients with prosthetic heart valves. Their number depends on both the type and the number of the prosthesis, while their distribution in the basal cerebral arteries is consistent with their cardiac source.

Adult↗