IFN-γ ELISPOT Analysis Research Articles

4-1BB (CD137) or CD40 Signaling Fails To Improve the Expansion of Antigen Specific T Cells Demonstrated with Engagement of TCR, CD28 and CD83 Ligand.

Following the engagement of the T cell receptor by HLA class I and antigenic peptide, naïve CD8+ T cells are primed to receive one or more costimulatory signals. Some of these signals, which are upregulated on and delivered by mature dendritic cells, include members of the immunoglobulin superfamily such as CD80 and CD83. Using a K562 derived artificial antigen presenting cell (aAPC) that expresses HLA-A2, CD80, and CD83, we have shown that the coengagement of CD83 ligand:CD83 and CD28:CD80 induces prolonged and preferential expansion of antigen specific CD8+ T cells. Furthermore, we have found that CD28:CD80 signaling is required for the induction of CD83 ligand expression on peripheral T cells. In order to identify additional immunoaccessory molecules that can augment this response, we have developed a system to efficiently transfer any chosen molecule into aAPC. This provides an excellent platform for studying a potentially immunogenic molecule given the relative lack of immunoaccessory molecules expressed by K562 (i.e. no expression of CD40, CD40 ligand, CD83, CD86, 4-1BB, 4-1BB ligand, OX40, OX40 ligand, HLA class I, or HLA class II). Following the transduction of a candidate molecule under study, the stimulatory capacity of a supertransduced aAPC can be compared to parental aAPC. Attractive candidates include members of the TNF superfamily since they have been shown to deliver important costimulatory signals to T cells. It has been suggested that 4-1BB signaling supports the survival of newly generated effector CD8+ T cells and that CD40 signaling confers “CD4+ T cell-like” help directly to CD8+ T cells. However, the impact of each of these molecules on the stimulation and expansion of antigen specific T cells has not been exhaustively studied. In this report, we transfected aAPC with either 4-1BB ligand or CD40 ligand, allowing us to compare the stimulatory capacity of aAPC/CD40 ligand, aAPC/4-1BB ligand and parental aAPC. We stimulated HLA-A2 positive CD8+ T cells from healthy donors three times at weekly intervals with A2-restricted MART1 peptide pulsed onto either irradiated aAPC/CD40 ligand, aAPC/4-1BB ligand or parental aAPC. Between the stimulations, cells were treated with IL2 and IL15 every three days. When MART1 peptide pulsed aAPC/CD40 ligand were used as stimulators, the total number of CD8+ T cells and number of MART1 specific CD8+ T cells was slightly smaller. IFN-γ ELISPOT analysis revealed that functional avidity of T cell receptors on MART1 specific CD8+ T cells was similar whether they were stimulated by aAPC/CD40 ligand or parental aAPC. These results indicate that CD40 ligand, at least in the human setting, does not directly provide “CD4+ T cell-like” help to antigen-specific CD8+ T cells. In contrast, stimulation with peptide pulsed aAPC/4-1BB ligand did generate a larger total number of CD8+ T cells. Surprisingly, however, most of these T cells were not antigen specific. In fact, significantly fewer MART1 specific CD8+ T cells were generated by aAPC/4-1BB ligand compared to aAPC alone. These results suggest that, unlike CD80 and CD83, 4-1BB ligand delivers a costimulatory signal resulting in the non-specific expansion of CD8+ T cells. This work demonstrates the versatility of our system to dissect the function of particular immunoaccessory molecules and determine the optimal conditions in the stimulation and expansion of antigen-specific human CD8+ T cells ex vivo.

Potent immune response against HIV-1 and protection from virus challenge in hu-PBL-SCID mice immunized with inactivated virus-pulsed dendritic cells generated in the presence of IFN-alpha.

A major challenge of AIDS research is the development of therapeutic vaccine strategies capable of inducing the humoral and cellular arms of the immune responses against HIV-1. In this work, we evaluated the capability of DCs pulsed with aldrithiol-2–inactivated HIV-1 in inducing a protective antiviral human immune response in SCID mice reconstituted with human PBL (hu-PBL-SCID mice). Immunization of hu-PBL-SCID mice with DCs generated after exposure of monocytes to GM-CSF/IFN-α (IFN-DCs) and pulsed with inactivated HIV-1 resulted in a marked induction of human anti–HIV-1 antibodies, which was associated with the detection of anti-HIV neutralizing activity in the serum. This vaccination schedule also promoted the generation of a human CD8+ T cell response against HIV-1, as measured by IFN-γ Elispot analysis. Notably, when the hu-PBL-SCID mice immunized with antigen-pulsed IFN-DCs were infected with HIV-1, inhibition of virus infection was observed as compared with control animals. These results suggest that IFN-DCs pulsed with inactivated HIV-1 can represent a valuable approach of immune intervention in HIV-1–infected patients.

Generation of CD8(+) T cell memory in response to low, high, and excessive levels of epitope.

The magnitude of a virus-specific memory CTL population can dramatically influence the outcome of secondary infections, yet little is known about the determinants of memory size. We investigated the impact of epitope levels on CTL memory generation by using a recombinant vaccinia virus system that allows for a broad range of epitope expression with the same infectious dose of virus. The size of the memory pool was examined using MHC class I/peptide tetramer staining and IFN-gamma ELISPOT analysis following priming with viruses expressing low, high, or excessive epitope levels. The size of the epitope-specific CD8(+) T cell memory population correlates with Ag dose at the low and high levels of epitope expression. However, at excessive epitope levels, the number of functional, IFN-gamma-producing, epitope-specific memory cells is significantly reduced compared with the number of tetramer(+) cells. These results demonstrate that the level of epitope expressed during an acute viral infection in vivo can dramatically influence CTL memory size. Furthermore, when epitope is overexpressed, the quality of the response can be adversely affected. Therefore, epitope expression level is an important consideration when developing approaches to optimize CTL memory induction.

Impaired T cell immunity in B cell-deficient mice following viral central nervous system infection.

CD8(+) T cells are required to control acute viral replication in the CNS following infection with neurotropic coronavirus. By contrast, studies in B cell-deficient (muMT) mice revealed Abs as key effectors in suppressing virus recrudescence. The apparent loss of initial T cell-mediated immune control in the absence of B cells was investigated by comparing T cell populations in CNS mononuclear cells from infected muMT and wild-type mice. Following viral recrudescence in muMT mice, total CD8(+) T cell numbers were similar to those of wild-type mice that had cleared infectious virus; however, virus-specific T cells were reduced at least 3-fold by class I tetramer and IFN-gamma ELISPOT analysis. Although overall T cell recruitment into the CNS of muMT mice was not impaired, discrepancies in frequencies of virus-specific CD8(+) T cells were most severe during acute infection. Impaired ex vivo cytolytic activity of muMT CNS mononuclear cells, concomitant with reduced frequencies, implicated IFN-gamma as the primary anti viral factor early in infection. Reduced virus-specific CD8(+) T cell responses in the CNS coincided with poor peripheral expansion and diminished CD4(+) T cell help. Thus, in addition to the lack of Ab, limited CD8(+) and CD4(+) T cell responses in muMT mice contribute to the ultimate loss of control of CNS infection. Using a model of virus infection restricted to the CNS, the results provide novel evidence for a role of B cells in regulating T cell expansion and differentiation into effector cells.

Cross-staining of cytotoxic T lymphocyte populations with peptide-MHC class I multimers of natural HIV-1 variant antigens.

Multimeric soluble peptide-MHC class I complexes bind to T cell receptors (TCR) on the surface of CD8 cytotoxic T lymphocytes (CTL) with sufficient avidity to enable the labelling of CTL according to their antigen specificity [1]. Visualization of antigen-specific CD8+T lymphocytes with fluorogen-conjugated peptide-MHC class I multimers enables both the physical quantification and the phenotypic characterization of CTL responses directly ex vivo, and these properties have led to the widespread adoption of this technique throughout the field of experimental immunology. However, it is well documented that TCR can exhibit a degree of promiscuity in terms of ligand recognition [2]. We recently demonstrated that the multimerization of peptide-MHC class I can allow binding to TCR with affinities that are too low to generate ligand-induced physiological responses, and result in crossreactive staining of HIV-specific CTL lines and clones by unrecognized natural variant antigens [3]. These results suggest that crossreactivity between peptide-MHC class I multimers and low avidity CTL could be relevant to the interpretation of direct ex-vivo staining. The possibility of such cross-staining is likely to be considerably greater when using peptide-MHC class I multimers to stain CTL specific for epitopes derived from antigenically variable pathogens such as HIV-1 [4]. Here we extend our previous study with the demonstration that the cross-staining of CTL populations with peptide-MHC class I multimers can complicate analyses performed directly ex vivo.

Natural T-helper immunity against human papillomavirus type 16 (HPV16) E7-derived peptide epitopes in patients with HPV16-positive cervical lesions: identification of 3 human leukocyte antigen class II-restricted epitopes.

Tumor-specific T-helper (Th) immunity was found to play a pivotal role in the natural and vaccine-induced immune defense against tumors. Since the majority of cervical cancers express human papillomavirus type 16 (HPV16) E7 oncoprotein, it is important to investigate the Th response against this target antigen in detail. By means of PBMC cultures from HLA-typed healthy donors, we identified the central part of HPV16 E7 (E7(41-72)) as the major immunogenic region within this antigen. Furthermore, we mapped 3 distinct Th epitopes within this region (DR15/E7(50-62), DR3/E7(43-77), DQ2/E7(35-50)). In a parallel approach, employing IFN-gamma ELISPOT analysis, we detected Th immunity against HPV16 E7 in subjects with HPV16+ lesions. Several of these responses matched with the 3 Th epitopes defined in our study. A number of other HPV16+ subjects did not display any E7-specific type 1 cytokine-producing T-cell immunity, indicating failure of the immune response. Our combined data argue for more extensive as well as longitudinal analysis of HPV16-specific T-cell immunity using the ELISPOT assay described, as well as for HPV-specific vaccination of individuals with HPV+ lesions.

Intracellular staining for TNF and IFN-γ detects different frequencies of antigen-specific CD8 + T cells

CD8 + T lymphocytes are important mediators of adaptive immunity against certain viral, protozoan and bacterial pathogens. Activated CD8 + T cells are able to induce cytolysis of infected cells (perforin and CD95–CD95L mediated pathways) and also elaborate cytokines, including IFN-γ and TNF after appropriate MHC class I-peptide recognition. New technologies for the detection of antigen-specific CD8 + T cells, including tetrameric MHC class I-peptide complexes, intracellular IFN-γ staining and IFN-γ ELISPOT analysis have revised our understanding of the magnitude of the CD8 + T cell response to infection. Here, using intracellular cytokine staining, we compare detection of IFN-γ and TNF in the analysis of pathogen-specific CD8 + T cell lines and CD8 + T cells after primary viral infection (LCMV) or secondary bacterial infection ( Listeria monocytogenes). Under multiple conditions and with multiple epitopes, we find that staining for intracellular IFN-γ consistently detects a higher frequency of antigen-specific CD8 + T cells than detection of intracellular TNF. However, (a) intracellular staining for TNF can be used to detect antigen-specific CD8 + T cell responses and (b) intracellular staining for cytokines is a useful approach for in vitro characterization of antigen-specific CD8 + T cell lines.