CD4+, CD8+ and CD4- CD8- T cell-subsets can confer protection against Leishmania m. mexicana infection

We studied the role of CD4+, CD8+, CD4- CD8- T cells and IgG anti-Leishmania after infection or vaccination in the CBA/ca mouse. Mice were either infected with L. m. mexicana promastigotes or vaccinated with parasite-membrane antigens incorporated into liposomes. Successfully vaccinated mice were used as cell-donors in adoptive transfer experiments. Naive, syngeneic recipients received highly-enriched CD4+, CD8+ or CD4- CD8- T cells from those two set of donors and challenged with live parasites. Our results showed that, both CD4+ and CD8+ T cells from infected or vaccinated donors conferred significant disease-resistance to naive recipients. In addition, adoptive transfer of CD4- CD8- T cells from vaccinated donors significantly delayed lesion growth in recipient mice. We concluded that vaccination of CBA mice correlates with the induction of protective CD4+, CD8+ and CD4- CD8- T cells and the synthesis of IgG anti-Leishmania.

Tuberculin Skin Test and CD4+/CD8+ T Cell Counts in Adults Infected with the Human Immunodeficiency Virus in Medellín, Colombia

To evaluate the effect of BCG vaccination and T lymphocyte subpopulations on the reactivity to the tuberculin skin test, 113 asymtomatic HIV+ individuals were tuberculin tested by intradermal injection of 5TU of purified protein derivative and the levels of circulating lymphocyte (CD3, CD4 and CD8) subpopulations determined by indirect immunofluorescence. Ninety-two percent of the subjects included in the study were males. The mean age of the group was 32.1±7.4 years. Sixty-two percent presented a BCG scar. However, only 22% exhibited positive tuberculin reactions (³5mm) irrespective of the presence of the BCG scar. Tuberculin positive individuals exhibited higher CD4+ cell counts (p=0.004) and CD4+/CD8+ ratios (p=0.006) than tuberculin negative (<5mm) HIV+ individuals. The number of individuals with positive tuberculin reactions was significantly higher in subjects with more than 500 CD4+ lymphocytes/ml (p=0.02) or CD4+/CD8+ ratios ³1.12 (p=0.002). These results suggest that a prior BCG vaccination does not influence the reactivity to the tuberculin skin test in HIV+ asymptomatic individuals and that the number of CD4+ lymphocytes and the CD4+/CD8+ ratio positively correlate with the tuberculin reactivity

Protective CD8+ T cell responses against the pre-erythrocytic stages of malaria parasites: an overview

CD8+ T cells have been implicated as critical effector cells in protection against the pre-erythrocytic stage of malaria in mice and humans following irradiated sporozoite immunization. Immunization experiments in animal models by several investigators have suggested different strategies for vaccination against malaria and many of the targets from liver stage malaria antigens have been shown to be immunogenic and to protect mice from the sporozoite challenge. Several prime/boost protocols with replicating vectors, such as vaccinia/influenza, with non-replicating vectors, such as recombinant particles derived from yeast transposon (Ty-particles) and modified vaccinia virus Ankara, and DNA, significantly enhanced CD8+ T cell immunogenicity and also the protective efficacy against the circumsporosoite protein of Plasmodium berghei and P. yeti. Based on these experimental results the development of a CD8+ T cell inducing vaccine has moved forward from epitope identification to planning stages of safety and immunogenicity trials of candidate vaccines.

Trypanosoma cruzi-elicited CD8+ T cell-mediated myocarditis: chemokine receptors and adhesion molecules as potential therapeutic targets to control chronic inflammation?

In Chagas disease, during the acute phase, the establishment of inflammatory processes is crucial for Trypanosoma cruzi control in target tissues and for the establishment of host/parasite equilibrium. However, in about 30% of the patients, inflammation becomes progressive, resulting in chronic disease, mainly characterized by myocarditis. Although several hypothesis have been raised to explain the pathogenesis of chagasic myocardiopathy, including the persistence of the parasite and/or participation of autoimmune processes, the molecular mechanisms underlying the establishment of the inflammatory process leading to parasitism control but also contributing to the maintenance of T. cruzi-elicited chronic myocarditis remain unsolved. Trying to shed light on these questions, we have for several years been working with murine models for Chagas disease that reproduce the acute self-resolving meningoencephalitis, the encephalitis resulting of reactivation described in immunodeficient individuals, and several aspects of the acute and chronic myocarditis. In the present review, our results are summarized and discussed under the light of the current literature. Furthermore, rational therapeutic intervention strategies based on integrin-mediated adhesion and chemokine receptor-driven recruitment of leukocytes are proposed to control T. cruzi-elicited unbalanced inflammation.

Detection of early apoptosis and cell death in T CD4+ and CD8+ cells from lesions of patients with localized cutaneous leishmaniasis

Human localized cutaneous leishmaniasis (LCL), induced by Leishmania braziliensis, ranges from a clinically mild, self-healing disease with localized cutaneous lesions to severe forms which can present secondary metastatic lesions. The T cell-mediated immune response is extremely important to define the outcome of the disease; however, the underlying mechanisms involved are not fully understood. A flow cytometric analysis of incorporation of 7-amino actinomycin D and CD4+ or CD8+ T cell surface phenotyping was used to determine whether different frequencies of early apoptosis or accidental cell death occur at different stages of LCL lesions. When all cells obtained from a biopsy sample were analyzed, larger numbers of early apoptotic and dead cells were observed in lesions from patients with active disease (mean = 39.5 ± 2.7%) as compared with lesions undergoing spontaneous healing (mean = 17.8 ± 2.2%). Cells displaying normal viability patterns obtained from active LCL lesions showed higher numbers of early apoptotic events among CD8+ than among CD4+ T cells (mean = 28.5 ± 3.8 and 15.3 ± 3.0%, respectively). The higher frequency of cell death events in CD8+ T cells from patients with LCL may be associated with an active form of the disease. In addition, low frequencies of early apoptotic events among the CD8+ T cells were observed in two patients with self-healing lesions. Although the number of patients in the latter group was small, it is possible to speculate that, during the immune response, differences in apoptotic events in CD4+ and CD8+ T cell subsets could be responsible for controlling the CD4/CD8 ratio, thus leading to healing or maintenance of disease.

Role of CD8+ T cells in endogenous interleukin-10 secretion associated with visceral leishmaniasis

This study examined the role and source of endogenous interleukin-10 (IL) secretion in visceral leishmaniasis (VL). The amounts of endogenous and Leishmania specific IL-10 and interferon-gamma (IFN) secreted by peripheral blood mononuclear cells (PBMC) from VL patients were compared. The correlation coefficient between endogenous IL-10 secretion and Leishmania specific IFN-gamma was -0.77, suggesting a major role for endogenous IL-10 secretion in VL. The effects of CD4+ and CD8+ T cell clones, isolated from a treated VL patient, on IL-10 secretion were assayed by mixing the clones with autologous, inactivated PBMC. The CD8+ clones mediated increased levels of IL-10 secretion in the presence of PBMC alone suggesting that CD8+ T cells may mediate endogenous IL-10 secretion.

Induction and maintenance of protective CD8+ T cells against malaria liver stages: implications for vaccine development

CD8+ T cells against malaria liver stages represent a major protective immune mechanism against infection. Following induction in the peripheral lymph nodes by dendritic cells (DCs), these CD8+ T cells migrate to the liver and eliminate parasite infected hepatocytes. The processing and presentation of sporozoite antigen requires TAP mediated transport of major histocompatibility complex class I epitopes to the endoplasmic reticulum. Importantly, in DCs this process is also dependent on endosome-mediated cross presentation while this mechanism is not required for epitope presentation on hepatocytes. Protective CD8+ T cell responses are strongly dependent on the presence of CD4+ T cells and the capacity of sporozoite antigen to persist for a prolonged period of time. While human trials with subunit vaccines capable of inducing antibodies and CD4+ T cell responses have yielded encouraging results, an effective anti-malaria vaccine will likely require vaccine constructs designed to induce protective CD8+ T cells against malaria liver stages.

The role of CD8+ T cells during allograft rejection

Organ transplantation can be considered as replacement therapy for patients with end-stage organ failure. The percent of one-year allograft survival has increased due, among other factors, to a better understanding of the rejection process and new immunosuppressive drugs. Immunosuppressive therapy used in transplantation prevents activation and proliferation of alloreactive T lymphocytes, although not fully preventing chronic rejection. Recognition by recipient T cells of alloantigens expressed by donor tissues initiates immune destruction of allogeneic transplants. However, there is controversy concerning the relative contribution of CD4+ and CD8+ T cells to allograft rejection. Some animal models indicate that there is an absolute requirement for CD4+ T cells in allogeneic rejection, whereas in others CD4-depleted mice reject certain types of allografts. Moreover, there is evidence that CD8+ T cells are more resistant to immunotherapy and tolerance induction protocols. An intense focal infiltration of mainly CD8+CTLA4+ T lymphocytes during kidney rejection has been described in patients. This suggests that CD8+ T cells could escape from immunosuppression and participate in the rejection process. Our group is primarily interested in the immune mechanisms involved in allograft rejection. Thus, we believe that a better understanding of the role of CD8+ T cells in allograft rejection could indicate new targets for immunotherapy in transplantation. Therefore, the objective of the present review was to focus on the role of the CD8+ T cell population in the rejection of allogeneic tissue.

Longitudinal comparison between plasma and seminal HIV-1 viral loads during antiretroviral treatment

This study was designed to investigate the impact of anti-retroviral therapy on both plasma and seminal HIV-1 viral loads and the correlation between viral loads in these compartments after treatment. Viral load, CD4+ and CD8+ T-cell counts were evaluated in paired plasma and semen samples from 36 antiretroviral therapy-naïve patients at baseline and on days 45, 90, and 180 of treatment. Slopes for blood and seminal viral loads in all treated patients were similar (p = 0.21). Median HIV-1 RNA titers in plasma and semen at baseline were 4.95 log10 and 4.48 log10 copies/ml, respectively. After 180 days of therapy, the median viral load declined to 3.15 log10 copies/ml (plasma) and 3.2 log10 copies/ml (semen). At this timepoint 22 patients presented HIV-1 viral load below 400 copies/ml in either plasma or semen, but only 9 had viral loads below 400 copies/ml in both compartments.

Immunopathology of giardiasis: the role of lymphocytes in intestinal epithelial injury and malfunction

T lymphocyte-mediated pathogenesis is common to a variety of enteropathies, including giardiasis, cryptosporidiosis, bacterial enteritis, celiac's disease, food anaphylaxis, and Crohn's disease. In giardiasis as well as in these other disorders, a diffuse loss of microvillous brush border, combined or not with villus atrophy, is responsible for disaccharidase insufficiencies and malabsorption of electrolytes, nutrients, and water, which ultimately cause diarrheal symptoms. Other mucosal changes may include crypt hyperplasia and increased infiltration of intra-epithelial lymphocytes. Recent studies using models of giardiasis have shed new light on the immune regulation of these abnormalities. Indeed, experiments using an athymic mouse model of infection have found that these epithelial injuries were T cell-dependent. Findings from further research indicate that that the loss of brush border surface area, reduced disaccharidase activities, and increase crypt-villus ratios are mediated by CD8+ T cells, whereas both CD8+ and CD4+ small mesenteric lymph node T cells regulate the influx of intra-epithelial lymphocytes. Future investigations need to characterize the CD8+ T cell signaling cascades that ultimately lead to epithelial injury and malfunction in giardiasis and other malabsorptive disorders of the intestine.

Effect of surgical treatment on the cellular immune response of gastric cancer patients

Patients with gastric cancer have a variety of immunological abnormalities. In the present study the lymphocytes and their subsets were determined in the peripheral blood of patients with gastric cancer (N = 41) both before and after surgical treatment. The percent of helper/inducer CD4 T cells (43.6 ± 8.9) was not different after tumor resection (43.6 ± 8.2). The percent of the cytotoxic CD8+ T cell population decreased significantly, whether patients were treated surgically (27.2 ± 5.8%, N = 20) or not (27.3 ± 7.3%, N = 20) compared to individuals with inflammatory disease (30.9 ± 7.5%) or to healthy individuals (33.2 ± 7.6%). The CD4/CD8 ratio consequently increased in the group of cancer patients. The peripheral blood lymphocytes of gastric cancer patients showed reduced responsiveness to mitogens. The defective blastogenic response of the lymphocytes was not associated with the production of transforming growth factor beta (TGF-ß) since the patients with cancer had reduced production of TGF-ß1 (269 ± 239 pg/ml, N = 20) in comparison to the normal individuals (884 ± 175 pg/ml, N = 20). These results indicate that the immune response of gastric cancer patients was not significantly modified by surgical treatment when evaluated four weeks after surgery and that the immunosuppression observed was not due to an increase in TGF-ß1 production by peripheral leukocytes.

Enhanced anti-tumor effect of a gene gun-delivered DNA vaccine encoding the human papillomavirus type 16 oncoproteins genetically fused to the herpes simplex virus glycoprotein D

Anti-cancer DNA vaccines have attracted growing interest as a simple and non-invasive method for both the treatment and prevention of tumors induced by human papillomaviruses. Nonetheless, the low immunogenicity of parenterally administered vaccines, particularly regarding the activation of cytotoxic CD8+ T cell responses, suggests that further improvements in both vaccine composition and administration routes are still required. In the present study, we report the immune responses and anti-tumor effects of a DNA vaccine (pgD-E7E6E5) expressing three proteins (E7, E6, and E5) of the human papillomavirus type 16 genetically fused to the glycoprotein D of the human herpes simplex virus type 1, which was administered to mice by the intradermal (id) route using a gene gun. A single id dose of pgD-E7E6E5 (2 µg/dose) induced a strong activation of E7-specific interferon-γ (INF-γ)-producing CD8+ T cells and full prophylactic anti-tumor effects in the vaccinated mice. Three vaccine doses inhibited tumor growth in 70% of the mice with established tumors. In addition, a single vaccine dose consisting of the co-administration of pgD-E7E6E5 and the vector encoding interleukin-12 or granulocyte-macrophage colony-stimulating factor further enhanced the therapeutic anti-tumor effects and conferred protection to 60 and 50% of the vaccinated mice, respectively. In conclusion, id administration of pgD-E7E6E5 significantly enhanced the immunogenicity and anti-tumor effects of the DNA vaccine, representing a promising administration route for future clinical trials.

Characterization of T cell clones from chagasic patients: predominance of CD8 surface phenotype in clones from patients with pathology

Human Chagas' disease, caused by the protozoan Trypanosoma cruzi, is associated with pathological processes whose mechanisms are not known. To address this question, T cell lines were developed from chronic chagasic patients peripheral blood mononuclear cells (PBMC) and cloned. These T cell clones (TCC) were analyzed phenotypically with monoclonal antibodies by the use of a fluorescence microscope. The surface phenotype of the TCC from the asymptomatic patient were predominantly CD4 positive (86%). On the contrary, the surface phenotype CD8 was predominant in the TCC from the patients suffering from cardiomegaly with right bundle branch block (83%), bradycardia with megacolon (75 %) and bradycardia (75%). Future studies will be developed in order to identify the antigens eliciting these T cell subpopulations.