Induction of CD8+ T cell-mediated protective immunity against Trypanosoma cruzi.
(17/13590)
Trypanosoma cruzi was transformed with the Plasmodium yoelii gene encoding the circum-sporozoite (CS) protein, which contains the well-characterized CD8+ T cell epitope, SYVPSAEQI. In vivo and in vitro assays indicated that cells infected with the transformed T. cruzi could process and present this malaria parasite-derived class I MHC-restricted epitope. Immunization of mice with recombinant influenza and vaccinia viruses expressing the SYVPSAEQI epitope induced a large number of specific CD8+ T cells that strongly suppressed parasitemia and conferred complete protection against the acute T. cruzi lethal infection. CD8+ T cells mediated this immunity as indicated by the unrelenting parasitemia and high mortality observed in immunized mice treated with anti-CD8 antibody. This study demonstrated, for the first time, that vaccination of mice with vectors designed to induce CD8+ T cells is effective against T. cruzi infection. (+info)
Characterization of the culture filtrate-specific cytotoxic T lymphocyte response induced by Bacillus Calmette-Guerin vaccination in H-2b mice.
(18/13590)
Although CD8+ T cells are supposed to play an important role in protective immunity to mycobacteria, cytotoxic T lymphocyte (CTL) responses in this infection remain poorly characterized. We previously demonstrated that bacillus Calmette-Guerin (BCG) immunization of H-2b mice induced CTL able to recognize and kill macrophages incubated with proteins from mycobacterial culture supernatant [culture filtrate (CF) antigens]. In the present study, we have further characterized the lytic activity of these CTL and the processing pathway used for the presentation of CF proteins. We show that they use the degranulation pathway (secretion of perforins and granzymes) as the main lytic mechanism of cytotoxicity and also secrete IFN-gamma upon incubation with CF-pulsed macrophages. The in vitro presentation of CF proteins to CTL required a processing step inhibited in the cold but insensitive to Brefeldin A. Transporter-associated protein (TAP)-2-deficient RMA-S cells were efficiently recognized and killed by CF-specific CTL, demonstrating the lack of TAP requirement for this presentation. However, recognition of target cells by CTL was abolished when carried out in the presence of chloroquine. These results indicate that a non-classical MHC class I-processing pathway allows the recognition of a CF protein by CTL in BCG-vaccinated H-2b mice. (+info)
Differentiation of human CD8 T cells: implications for in vivo persistence of CD8+ CD28- cytotoxic effector clones.
(19/13590)
CD8 T cells contain a distinct subset of CD8+ CD28- cells. These cells are not present at birth and their frequency increases with age. They frequently contain expanded clones using various TCRalphabeta receptors and these clones can represent >50% of all CD8 cells, specially in old subjects or patients with chronic viral infections such as HIV-1. Herein, it is shown that a large fraction of CD8+ CD28- cells expresses intracellular perforin by three-color flow cytometry, in particular when this subset is expanded. Together with their known ability to exert potent re-directed cytotoxicity, this indicates that CD8+ CD28- T cells comprise cytotoxic effector cells. With BrdU labeling, we show that CD8+ CD28- cells derive from CD8+ CD28+ precursors in vitro. In addition, sorted CD8+ CD28+ cells gave rise to a population of CD8+ CD28- cells after allo-stimulation. Moreover, ex vivo CD8+ CD28+ cells contain the majority of CD8 blasts, supporting the notion that they contain the proliferative precursors of CD8+ CD28- cells. CD95 (Fas) expression was lower in CD8+ CD28- cells, and this subset was less prone to spontaneous apoptosis in ex vivo samples and more resistant to activation-induced cell death induced by a superantigen in vitro. Thus, the persistence of expanded clones in vivo in the CD8+ CD28- subset may be explained by antigen-driven differentiation from CD8+ CD28+ memory precursors, with relative resistance to apoptosis as the clones become perforin(+) effector cells. (+info)
A comparative study of the effects of ketotifen, disodium cromoglycate, and beclomethasone dipropionate on bronchial mucosa and asthma symptoms in patients with atopic asthma.
(20/13590)
Asthma is a chronic inflammatory disorder of the airways that is characterized by infiltration of many inflammatory cells into the bronchial mucosa. We compared the effects of ketotifen, disodium cromoglycate (DSCG), and beclomethasone dipropionate (BDP) on inflammatory cells in the bronchial mucosa and on the asthma symptoms of patients with atopic asthma. In this 12-week parallel study, 32 patients were randomly allocated to either the ketotifen group (2 mg day-1, n = 13), DSCG group (8 mg day-1, n = 9) or BDP (400 micrograms day-1, n = 10). Each subject recorded daily asthma symptoms and peak expiratory flow (PEF). Before and after treatment, pulmonary function and bronchial responsiveness to methacholine were evaluated, and fibreoptic bronchoscopy and biopsy were performed before and after treatment. Biopsy specimens were obtained by bronchoscopy. We performed immunohistochemistry using specific monoclonal antibodies for activated eosinophils (EG2), mast cells (AA1), and T cells (CD3, CD4, and CD8). Our clinical findings showed significant improvement in symptom score and bronchial responsiveness (P < 0.01) each) in all groups. Both the DSCG and the BDP groups had significantly better symptom scores than the ketotifen group (P < 0.05, both groups). PEF significantly increased in the DSCG group in comparison to the ketotifen (P < 0.01) and BDP (P < 0.05) groups, FEV1% increased significantly in the DSCG (P < 0.01) and BDP (P < 0.05) groups in comparison to the ketotifen group. Compared with their baseline values, treatment significantly decreased EG2+ activated eosinophils, and CD3+ and CD4+ T cells, in each group (P < 0.01). Both the DSCG (P < 0.05) and the BDP groups (P < 0.01) exhibited significant decreases in AA1+ mast cell count, but this was not observed in the ketotifen group. Comparing before- and after-treatment values, only the DSCG group exhibited a significant decrease in the number of CD8+ T cells (P < 0.01). Ketotifen, DSCG, and BDP all showed anti-inflammatory activity as determined by examination of the bronchial mucosa of asthmatic patients; and both the DSCG and BDP groups had better clinical responses than the ketotifen group. (+info)
T-cell receptor transgenic analysis of tumor-specific CD8 and CD4 responses in the eradication of solid tumors.
(21/13590)
The role of tumor-specific CD8 and CD4 lymphocytes in rejecting solid tumors has been difficult to determine because of the lack of models in which tumor antigen, specific CD8 cells, and specific CD4 cells can be monitored and controlled. To investigate the minimal components required for the induction and maintenance of CTL activity sufficient to reject a solid tumor in vivo, we transfected the influenza hemagglutinin (HA) gene into a nonimmunogenic class I+/class II- murine malignant mesothelioma (MM) tumor line to generate an endogenous tumor antigen and used TCR transgenic mice with class I- or class II-restricted specificities for HA as sources of naive, tumor-specific T cells. The data show that the presence of a strong tumor antigen is not in itself sufficient to induce an effective CTL response, nor does the presence of a high frequency of precursor cells guarantee tumor rejection. We also show that tumor-specific CD4 cells, when CTL numbers are suboptimal, greatly enhance the eradication of tumor, confirming the importance of antigen-presenting cell presentation of tumor antigens to class II-restricted cells. These data confirm that T-cell receptor transgenic cells, combined with nominal tumor antigen transfection, represent powerful tools to analyze tumor-specific T-cell responses. (+info)
Evidence for involvement of B lymphocytes in the surveillance of lung metastasis in the rat.
(22/13590)
These studies examined the composition of lymphocytes within the lung after the introduction of tumor cells that metastasize to the lung in rats. i.v. delivery of MADB106 tumor cells into syngeneic Fischer 344 rats caused dose- and time-dependent development of lung tumors, with surface metastases evident 7 days after injection and markedly increased 11 days after injection. The total number of lymphocytes recovered from the lung was increased 11 days after injection but not 7 days after injection. When lymphocytes from the lung, spleen, and blood were subjected to fluorescence-activated cell sorting analysis, the most conspicuous change was an increase in the percentage of CD45RA+ cells (i.e., B lymphocytes in the rat) in the lung, with no changes seen in the percentage of natural killer (NKR-P1+), CD4+, or CD8+ cells in the lung. Analysis of the time course showed that B lymphocytes increased in the lung soon after i.v. tumor injection, with an initial peak seen 6 h after injection. Rapid influx of B lymphocytes into lung after i.v. tumor cell injection was also observed in another syngeneic tumor model, i.e., after injection of CC531 cells into WAG rats. To determine whether the influx of B lymphocytes into the lung might participate in tumor surveillance, a high dose of antibody (100 microg) to rat B lymphocytes was given to immunoneutralize these cells; this produced an increase in lung tumors in both models. Finally, Fischer 344 rats were given a s.c. injection of MADB106 tumor cells that made them resistant to lung tumors when given a later i.v. injection of these tumor cells. These animals were found to have an elevated level of B lymphocytes residing in the lung associated with the resistance to lung tumor. These findings suggest that early responses of B lymphocytes are important in protection against tumor development in two rat models of cancer. (+info)
Cancer vaccines.
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It has been more than 100 years since the first reported attempts to activate a patient's immune system to eradicate developing cancers. Although a few of the subsequent vaccine studies demonstrated clinically significant treatment effects, active immunotherapy has not yet become an established cancer treatment modality. Two recent advances have allowed the design of more specific cancer vaccine approaches: improved molecular biology techniques and a greater understanding of the mechanisms involved in the activation of T cells. These advances have resulted in improved systemic antitumor immune responses in animal models. Because most tumor antigens recognized by T cells are still not known, the tumor cell itself is the best source of immunizing antigens. For this reason, most vaccine approaches currently being tested in the clinics use whole cancer cells that have been genetically modified to express genes that are now known to be critical mediators of immune system activation. In the future, the molecular definition of tumor-specific antigens that are recognized by activated T cells will allow the development of targeted antigen-specific vaccines for the treatment of patients with cancer. (+info)
Tolerance to antigen-presenting cell-depleted islet allografts is CD4 T cell dependent.
(24/13590)
Pretreatment of pancreatic islets in 95% oxygen culture depletes graft-associated APCs and leads to indefinite allograft acceptance in immunocompetent recipients. As such, the APC-depleted allograft represents a model of peripheral alloantigen presentation in the absence of donor-derived costimulation. Over time, a state of donor-specific tolerance develops in which recipients are resistant to donor APC-induced graft rejection. Thus, persistence of the graft is sufficient to induce tolerance independent of other immune interventions. Donor-specific tolerance could be adoptively transferred to immune-deficient SCID recipient mice transplanted with fresh immunogenic islet allografts, indicating that the original recipient was not simply "ignorant" of donor antigens. Interestingly, despite the fact that the original islet allograft presented only MHC class I alloantigens, CD8+ T cells obtained from tolerant animals readily collaborated with naive CD4+ T cells to reject donor-type islet grafts. Conversely, tolerant CD4+ T cells failed to collaborate effectively with naive CD8+ T cells for the rejection of donor-type grafts. In conclusion, the MHC class I+, II- islet allograft paradoxically leads to a change in the donor-reactive CD4 T cell subset and not in the CD8 subset. We hypothesize that the tolerant state is not due to direct class I alloantigen presentation to CD8 T cells but, rather, occurs via the indirect pathway of donor Ag presentation to CD4 T cells in the context of host MHC class II molecules. (+info)