Abstract-The glycoprotein IIb/IIIa receptor inhibitor abciximab has been shown to facilitate the rate and the extent of pharmacological thrombolysis with recombinant tissue plasminogen activator (rtPA) in patients with acute myocardial infarction. However, the underlying mechanisms remain not fully determined. We sought to demonstrate that this facilitating effect of abciximab could be related to its potential to modify the clot architecture and the clot physical properties. Compared with fibrin-rich clots, platelets dramatically modified the in vitro properties of the fibrin network, leading to a significant increase of the permeability (K s ) and the viscoelasticity (GЈ) indexes but also leading to the appearance of platelet aggregates (surface area [S.ag]). These modifications resulted in a 2.6-fold decrease of the fibrinolysis rate when rtPA (1 nmol/L) was added before the initiation of clotting. Adding aspirin (100 g/mL) or abciximab (0.068 mol/L) before the clotting of platelet-rich clots (PRCs) lowered K s by 50% and 70%, respectively (PϽ0.01), GЈ by 41% and 66%, respectively (PϽ0.01), and S.ag by 32% and 61%, respectively (PϽ0.01). As a consequence, the lysis speed was increased by 21% with aspirin (PϽ0.01) and 45% with abciximab (PϽ0.01). However, unlike aspirin, permeation of preformed PRCs with abciximab (0.068 mol/L) decreased GЈ (37%, PϽ0.01), K s (35%, PϽ0.001) and S.ag (25%, PϭNS) and resulted in a 27% (PϽ0.01) increase of the lysis speed when abciximab and rtPA (0.2 mol/L) were simultaneously permeated. This effect was found to be time dependent and was observed only with early permeation, starting within the first 10 minutes of clotting. These changes in the physical properties of the PRC architecture suggest that fibrin is removed from the platelet-fibrin aggregates and reexposed into the surrounding fibrin network, increasing rtPA access to fibrin and therefore the fibrinolysis rate. The superiority of abciximab over aspirin in accelerating fibrinolysis of forming and preformed PRCs is related to its ability to modulate the interactions of fibrinogen and fibrin with platelets. These findings provide new mechanistic information on reperfusion therapy. by abciximab (Reopro) can restore coronary flow, 1 as shown in randomized trials combining abciximab with either primary angioplasty or thrombolysis in acute myocardial infarction. [2][3][4][5] However, the comprehensive mechanisms remain to be fully understood. In the present study, we sought to demonstrate that this effect of abciximab is related to its potential to modify platelet-fibrin(ogen) interactions, leading to changes of clot architecture and clot physical properties and facilitating pharmacological thrombolysis.For the first step in our experiments, differences between the physical properties of fibrin-rich clots (FRCs) and platelet-rich clots (PRC) were studied to delineate the mechanical impact of platelets on the fibrin network properties and their consequences for the fibrinolysis rate. The second step in our experiments evaluated ...

Virions of filamentous bacteriophage fd are capable of displaying multiple copies of peptide epitopes and generating powerful immune responses to them. To investigate the antigen processing mechanisms in human B cell lines used as antigen presenting cells, the major coat protein (pVIII) in intact virions was fluorescently labeled, and its localization in various intracellular compartments was followed using confocal microscopy. We show that the virions were taken up and processed to yield peptides that reach both the major histocompatibility complex (MHC) class II compartment and the endoplasmic reticulum. Moreover, when exposed to bacteriophages displaying a cytotoxic T lymphocyte (CTL) epitope from the reverse transcriptase of human immunodeficiency virus type-1 (HIV-1), B cells were lysed by specific cytotoxic lymphocytes. This confirms that filamentous bacteriophage virions are capable of being taken up and processed efficiently by MHC class I and class II pathways, even in nonprofessional antigen presenting cells. These remarkable features explain, at least in part, the unexpected ability of virions displaying foreign T-cell epitopes to prime strong T-helper-dependent CTL responses. These findings have important implications for the development of peptide-based vaccines, using filamentous bacteriophage virions as scaffolds.

Endostatin has been considered a highly specific inhibitor of endothelial cell proliferation and/or migration. To explore the use of endostatin in antiangiogenic gene therapy, we generated a recombinant adenovirus, AdEndo, carrying the gene for mouse endostatin. Injection of 10(9) PFU of AdEndo resulted in a low but significant suppression (25%) of preestablished tumor growth in murine models involving murine Lewis lung carcinoma (LLC) and human breast cancer MDA-MB-231 tumors. Greater anticancer activity was observed when the same dose of AdEndo was injected into two other preestablished murine models involving C51 murine colon cancer and HT29 human colon cancer (55 and 47% tumor growth reduction, respectively). In vitro, endostatin derived from AdEndo-infected MRC-5 fibroblasts inhibited the growth of C51 and HT29 cell lines (72 and 61%, respectively). The extent of this inhibition was comparable to that observed in endothelial cells: 75% for microcapillary endothelial cell line HMEC-1, 52% for human dermal microvascular endothelial cells, 46% for human umbilical vein endothelial cells, and 67% for calf pulmonary arterial endothelial cells. Both endothelial and colon cancer cells showed a clear increase in cell apoptosis (4- to 5-fold for endothelial cells and 5- to 10-fold for colon cancer cells) and an accumulation in the G(1) phase of the cell cycle. This antiproliferative activity was not observed in other tumor cell lines: LLC, MDA-MB-231, murine colon adenocarcinoma MC38, human prostate cancer cell line DU145, and human breast cancer cell line CAL51. Taken together, these results provide evidence that, in addition to its antiangiogenic activity, endostatin exerts a direct anticancer action that appears to be restricted to some tumor cell lines. Thus, endostatin could be used in some colon cancer treatments and its clinical efficacy would depend on the response of tumor cells themselves.