Helper function of cytolytic lymphocytes: Switching roles in the immune response

A registry of HLA-typed donors for production of virus-specific CD4 and CD8 T lymphocytes for adoptive reconstitution of immune-compromised patients

BACKGROUND

Virus-specific CD4 and CD8 T lymphocytes from HLA-matched donors are effective for treatment and prophylaxis of viral infections in immune-compromised recipients of hematopoietic stem cell transplant recipients. Adoptive immune reconstitution is based on selection of specific T cells or on generation of specific T-cell lines from the graft donor. Unfortunately, the graft donor is not always immune to the relevant pathogen or the graft donor may not be available (registry-derived or cord blood donors).

STUDY DESIGN AND METHODS

Since the possibility of using T cells from a third-party subject is now established, we screened potential donors for T-cell responses against cytomegalovirus (CMV), Epstein-Barr virus (EBV), and adenovirus, the viruses most frequently targeted by adoptive immune reconstitution. Specific T-cell responses against viral antigens were analyzed in 111 donors using a miniaturized interferon-γ release assay.

RESULTS

Responders to CMV were 64%, to EBV 40%, and to adenovirus 51%. Simultaneous responders to the three viruses were 49%. CMV-specific CD4 and CD8 T-cell lines could be generated from 11 of 12 donors defined as positive responders according to the T-cell assay.

CONCLUSIONS

These data demonstrate that a large fraction of volunteers can be recruited in a donor registry for selection or expansion of virus specific T cells and that our T-cell assay predicts the donors' ability to give rise to established T-cell lines endowed with proliferative potential and effector function for adoptive immune reconstitution.

Miniaturized and high-throughput assays for analysis of T-cell immunity specific for opportunistic pathogens and HIV

Monitoring of antigen-specific T-cell responses is valuable in numerous conditions that include infectious diseases, vaccinations, and opportunistic infections associated with acquired or congenital immune defects. A variety of assays that make use of peripheral lymphocytes to test activation markers, T-cell receptor expression, or functional responses are currently available. The last group of assays calls for large numbers of functional lymphocytes. The number of cells increases with the number of antigens to be tested. Consequently, cells may be the limiting factor, particularly in lymphopenic subjects and in children, the groups that more often require immune monitoring. We have developed immunochemical assays that measure secreted cytokines in the same wells in which peripheral blood mononuclear cells (PBMC) are cultured. This procedure lent itself to miniaturization and automation. Lymphoproliferation and the enzyme-linked immunosorbent spot (ELISPOT) assay have been adapted to a miniaturized format. Here we provide examples of immune profiles and describe a comparison between miniaturized assays based on cytokine secretion or proliferation. We also demonstrate that these assays are convenient for use in testing antigen specificity in established T-cell lines, in addition to analysis of PBMC. In summary, the applicabilities of miniaturization to save cells and reagents and of automation to save time and increase accuracy were demonstrated in this study using different methodological approaches valuable in the clinical immunology laboratory.

GP120-specific exosome-targeted T cell-based vaccine capable of stimulating DC- and CD4(+) T-independent CTL responses

The limitations of highly active anti-retroviral therapy (HAART) have necessitated the development of alternative therapeutics. In this study, we generated ovalbumin (OVA)-pulsed and pcDNAgp120-transfected dendritic cell (DC)-released exosomes (EXOova and EXOgp120) and ConA-stimulated C57BL/6 CD8(+) T cells. OVA- and Gp120-Texo vaccines were generated from CD8(+) T cells with uptake of EXOova and EXOgp120, respectively. We demonstrate that OVA-Texo stimulates in vitro and in vivo OVA-specific CD4(+) and CD8(+) cytotoxic T lymphocyte (CTL) responses leading to long-term immunity against OVA-expressing BL6-10(OVA) melanoma. Interestingly, CD8(+) T cell responses are DC and CD4(+) T cell independent. Importantly, Gp120-Texo also stimulates Gp120-specific CTL responses and long-term immunity against Gp120-expressing B16 melanoma. Therefore, this novel HIV-1-specific EXO-targeted Gp120-Texo vaccine may be useful in induction of efficient CTL responses in AIDS patients with DC dysfunction and CD4(+) T cell deficiency.

Biomarkers of immunoregulatory status in stable liver transplant recipients undergoing weaning of immunosuppressive therapy

Biomarkers that reflect immune response recovery and predict clinical events during withdrawal or minimization of immunosuppressive therapy have not been evaluated. This study aimed to evaluate whether immune response recovers after withdrawal of long-term immunosuppressive treatment in stable liver transplant patients and to determine whether specific biomarkers reflect immune response reactivity and predict rejection. Pharmacokinetic-pharmacodynamic profiles were determined in 24 patients and 80 healthy donors before immunosuppressive treatment reduction began, at 50%, and at complete withdrawal. In patients who rejected, effector-T-cell response mediated by soluble IFN-γ, %CD4(+)IFN-γ and %CD8(+)IL-2/IFN-γ were significantly increased, while TGF-β1 production and the TGF-β1/IFN-γ ratio were significantly decreased. In patients with rejection, soluble IFN-γ and %CD8(+)IL-2 were significantly higher before immunosuppressive treatment was reduced. Further studies are required, but this battery of biomarkers performed in whole blood could be a useful tool to monitor immunosuppressive treatment minimization or withdrawal protocols and identify patients at increased risk of rejection.

Evaluation of antigen-specific T-cell responses with a miniaturized and automated method

The evaluation of antigen-specific T-cell responses is helpful for both research and clinical settings. Several techniques can enumerate antigen-responsive T cells or measure their products, but they require remarkable amounts of peripheral blood mononuclear cells (PBMCs). Since screening numerous antigens or testing samples from pediatric or lymphopenic patients is hampered in clinical practice, we refined a miniaturized, high-throughput assay for T-cell immunity. Antigens and cells in 10-microl volumes were dispensed into 1,536-well culture plates precoated with anti-gamma interferon (anti-IFN-gamma) antibodies. After being cultured, the wells were developed by enzyme-linked immunosorbent assay for bound cytokine. Miniaturization and automation allowed quantitation of antigen-specific responses on 10(4) PBMCs. This method was applied for epitope mapping of mycobacterial antigens and was used in the clinic to evaluate T-cell immunity to relevant opportunistic pathogens by using small blood samples. A comparison with conventional methods showed similar sensitivity. Therefore, current flow cytometric methods that provide information on frequency and phenotype of specific T cells can be complemented by this assay that provides extensive information on cytokine concentrations and profiles and requires 20- to 50-fold fewer PBMCs than other analytical methods.

CD40L-expressing CD8 T cells prime CD8alpha(+) DC for IL-12p70 production

CD8alpha(+) DC are implicated as the principle DC subset for cross-presentation and cross-priming of cytotoxic CD8 T cell responses. In this study, we demonstrate another unique facet of the CD8alpha(+) DC and CD8 T cell relationship, by showing that CD8 T cells reciprocally activate CD8alpha(+) DC, but not CD8alpha(-) DC, for IL-12p70 production, the key Th1-promoting cytokine. This effect was observed during an antigen-specific interaction between DC and activated CD8 T cells, along with secondary TLR stimulation of DC by LPS. Activated CD8 T cells use a combination of IFN-gamma and CD40L, which is rapidly up-regulated post-stimulation, to prime DC for IL-12p70 production during an antigen-specific response. Our results suggest that the interaction between CD8alpha(+) DC and antigen-primed CD8 T cells may form an important component of Th1-mediated immunity through the induction of IL-12p70.

Antigenic properties of HCMV peptides displayed by filamentous bacteriophages vs. synthetic peptides

Several efforts have been invested in the identification of CTL and Th epitopes, as well as in the characterization of their immunodominance and MHC restriction, for the generation of a peptide-based HCMV vaccine. Small synthetic peptides are, however, poor antigens and carrier proteins are important for improving the efficacy of synthetic peptide vaccines. Recombinant bacteriophages appear as promising tools in the design of subunit vaccines. To investigate the antigenicity of peptides carried by recombinant bacteriophages we displayed different HCMV MHCII restricted peptides on the capsid of filamentous bacteriophage (fd) and found that hybrid bacteriophages are processed by human APC and activate HCMV-specific CD4 T-cells. Furthermore we constructed a reporter T-cell hybridoma expressing a chimeric TCR comprising murine alphabeta constant regions and human variable regions specific for the HLA-A2 restricted immunodominant NLV peptide of HCMV. Using the filamentous bacteriophage as an epitope carrier, we detected a more robust and long lasting response of the reporter T-cell hybridoma compared to peptide stimulation. Our results show a general enhancement of T-cell responses when antigenic peptides are carried by phages.

High throughput functional microdissection of pathogen-specific T-cell immunity using antigen and lymphocyte arrays

The analysis of the human T-cell response specific for relevant pathogens is useful for diagnostic purposes and for research. Several methods enumerate antigen specific T-cells and measure their functions. Since screening of numerous antigens from pathogens is often needed to evaluate immunocompetence, lymphocytes, labor and cost are limiting factors. To examine pathogen-specific T-cell immunity, we have miniaturized the analysis of T-cell responses using an array approach in 384- and 1536-well plates with as few as 10 x 10(3) PBMC per well instead of the 500 x 10(3) PBMC used for current assays. Secreted cytokines were detected in the same wells used for lymphocyte cultures. The method can detect about ten CMV specific T-cells diluted into 50 x 10(3) PBMC (0.02%), and can quantify secreted cytokines. The microarray approach allowed evaluation of T-cell immunity in children with a sensitivity higher than current methods. When applied to CMV epitope mapping, the data obtained with conventional methods were confirmed. The assay could be automated, allowing high throughput processing. The assay provides quantitative information on cytokines induced by antigen stimulation and can be applied in a simplified format as a field test to monitor T-cell immunity in vaccine trials or in veterinary medicine.

Measurement of antigen specific immune responses: 2006 update

Measuring antigen-specific immune responses (MASIR) is essential for basic immunological research and in the clinical setting. Numerous techniques have been used and the recent years have witnessed a flourishing of flow cytometry based methods for the identification of antigen specific T cells, in addition to other methodologies. The second MASIR conference held in Santorini, Greece, from 14 to 18 June 2006 has been a forum for the discussion of methodological issues and for research or clinical applications of these techniques, as reviewed here. In addition to flow cytometry based techniques, other emerging techniques with different degrees of complexity can be applied. These novel methods are highly promising in numerous conditions to look for correlates of protection, to test responses to natural infections or to vaccination trials, to evaluate the immune status of immunocompromised patients and to monitor persistence and function of specific T cells administered as adoptive therapy.