A sensitive ELISPOT assay to detect low-frequency human T lymphocytes

Human T cell responses to HPV 16 E2 generated with monocyte-derived dendritic cells

Persistent infection with human papillomavirus (HPV) type 16 has been implicated in the etiology of cervical cancer. The E2 protein is required early in viral infection and therefore may serve as a useful immune target for a vaccine aimed at prevention or therapy of premalignant lesions. Dendritic cells (DC) prepared from monocytes and pulsed with bacterially produced HPV 16 E2 C-terminus protein were used to stimulate autologous T cells over several rounds of stimulation. T cells were tested for gamma-interferon release by ELISPOT and for cytotoxic activity by (51)chromium release assays. To generate E2-expressing target cells for cytotoxicity assays, we constructed a recombinant vaccinia virus encoding HPV 16 E2, which was used to infect autologous Epstein-Barr virus-transformed lymphoblastoid cell lines (LCL). The results show that DC pulsed with E2 C-terminus protein induce gamma-interferon-releasing T cells as demonstrated by ELISPOT. Furthermore, we demonstrate E2-specific lysis of vaccinia-E2 infected autologous LCL by CD8+ cytotoxic T lymphocytes (CTL). E2-specific CTL did not lyse untreated autologous LCL or LCL infected with wild-type vaccinia and showed low levels of cytotoxicity against natural killer cell-sensitive K562 cells. In addition, T cells stimulated with DC in the absence of E2 failed to demonstrate lysis of vaccinia-E2-labeled targets. Phenotypically, CTL populations were CD3+/CD8+. These results will facilitate the study of naturally occurring T-cell responses to HPV E2 in patients with cervical intraepithelial neoplasia and the development of immunotherapeutic strategies designed to treat this and other HPV-associated diseases.

Cellular immune response against tropomyosin isoform 5 in ulcerative colitis

We have reported an autoantibody response in ulcerative colitis (UC) against human tropomyosin isoform 5 (hTM5), the predominant colonic epithelial cell hTM isoform. In this report, we determined the number of IFN-gamma-secreting cells (spot-forming cells, SFC) against hTM5 by an enzyme-linked immunospot (ELISPOT) assay. Another cytoskeletal protein, caldesmon, CaD40, was used as a control antigen. Peripheral blood mononuclear cells were separated by a Ficoll density gradient from 28 patients with UC, 13 patients with Crohn's disease (CD), and 9 healthy subjects (HS). The mean (+/-SEM) SFC values against hTM5 in UC, CD, and HS were 48.8 +/- 8.1, 18.6 +/- 4.6, and 20.8 +/- 8.6, respectively. The value in UC was significantly higher than those in CD (P < 0.005) and HS (P < 0.025). SFC values in CD did not differ from those in HS. None of the 50 samples (except 1 UC) reacted to the CaD40 antigen. This study demonstrates, for the first time, a defined colon epithelial cell antigen, hTM5, that is capable of inducing a significant T cell response in UC but not in CD.

Opposing effects of anti-activation-inducible lymphocyte-immunomodulatory molecule/inducible costimulator antibody on the development of acute versus chronic graft-versus-host disease

The functional role of inducible costimulator (ICOS)-mediated costimulation was examined in an in vivo model of alloantigen-driven Th1 or Th2 cytokine responses, the parent-into-F(1) model of acute or chronic graft-vs-host disease (GVHD), respectively. When the Ab specific for mouse ICOS was injected into chronic GVHD-induced mice, activation of B cells, production of autoantibody, and development of glomerulonephritis were strongly suppressed. In contrast, the same treatment enhanced donor T cell chimerism and host B cell depletion in acute GVHD induced host mice. Blocking of B7-CD28 interaction by injection of anti-B7-1 and anti-B7-2 Abs inhibited both acute and chronic GVHD. These observations clearly indicate that the costimulatory signal mediated by CD28 caused the initial allorecognition resulting in the clonal expansion of alloreactive T cells, whereas the costimulatory signal mediated by ICOS played a critical role in the functional differentiation and manifestation of alloreactive T cells. Furthermore, treatment with anti-ICOS Ab selectively suppresses Th2-dominant autoimmune disease.

Development and validation of a gamma interferon ELISPOT assay for quantitation of cellular immune responses to varicella-zoster virus

Cell-mediated immunity appears to be critical for the prevention and control of varicella-zoster virus (VZV) infection and complications arising from zoster. Current assays of VZV-specific cell-mediated immunity are cumbersome or lack sensitivity. We have developed a gamma interferon ELISPOT assay that provides a direct measure of the number of T cells secreting a cytokine following stimulation with antigen. This assay is extremely sensitive and specific, with the ability to detect gamma interferon spot-forming cells (SFC) in the range of 10 to 1,000 SFC per million peripheral blood mononuclear cells (PBMCs). This assay has been validated by demonstrating the following: (i) the response detected is mediated almost entirely by CD4+ T cells, (ii) ELISPOT responses from fresh-frozen PBMCs are equivalent to those from freshly isolated cells, (iii) frozen PBMCs can be shipped on dry ice for up to 48 h without loss of activity, (iv) frozen PBMC samples can be stored in liquid nitrogen over long periods (>22 months) without any significant change in response, and (v) the numbers of ELISPOTs counted using a computer-based imaging system are equivalent to those counted by humans but have lower variability. The ability to use frozen cells is facilitated by the use of a recombinant nuclease (Benzonase) that can prevent cell clumping when samples are thawed. Frozen PBMC samples can be cycled through multiple changes in storage between liquid nitrogen and dry ice without any change in response being detected. This facilitates collection of samples at one site and testing performed at a remote location. This VZV ELISPOT assay provides a new versatile tool for monitoring cellular immune responses either during a herpes zoster disease outbreak or following vaccination.

Serum and mucosal immune responses to an inactivated influenza virus vaccine induced by epidermal powder immunization

Both circulating and mucosal antibodies are considered important for protection against infection by influenza virus in humans and animals. However, current inactivated vaccines administered by intramuscular injection using a syringe and needle elicit primarily circulating antibodies. In this study, we report that epidermal powder immunization (EPI) via a unique powder delivery system elicits both serum and mucosal antibodies to an inactivated influenza virus vaccine. Serum antibody responses to influenza vaccine following EPI were enhanced by codelivery of cholera toxin (CT), a synthetic oligodeoxynucleotide containing immunostimulatory CpG motifs (CpG DNA), or the combination of these two adjuvants. In addition, secretory immunoglobulin A (sIgA) antibodies were detected in the saliva and mucosal lavages of the small intestine, trachea, and vaginal tract, although the titers were much lower than the IgG titers. The local origin of the sIgA antibodies was further shown by measuring antibodies released from cultured tracheal and small intestinal fragments and by detecting antigen-specific IgA-secreting cells in the lamina propria using ELISPOT assays. EPI with a single dose of influenza vaccine containing CT or CT and CpG DNA conferred complete protection against lethal challenges with an influenza virus isolated 30 years ago, whereas a prime and boost immunizations were required for protection in the absence of an adjuvant. The ability to elicit augmented circulating antibody and mucosal antibody responses makes EPI a promising alternative to needle injection for administering vaccines against influenza and other diseases.

Detection and quantification of HIV-1 specific CD4 helper and CD8 cytotoxic cells: their role in HIV-1-infected individuals and vaccine recipients

There is a strong link between virus specific CD8 T-cell function and the efficiency of regulatory CD4 helper T cells. Controlling viraemia in HIV-1-infected individuals requires the maintenance of strong CD4 and CD8 T-cell responses. These responses should be elicited by prophylactic vaccination and by postexposure immunotherapy. This review will examine the methods that are available for the detection and quantification of HIV-1 specific CD4 and CD8 T-cell responses. We will also discuss the methods that should be used to identify these responses in HIV-1-infected individuals, seropositive recipients of immunotherapy and seronegative vaccinees. Finally, we will give examples of how responses observed in vitro relate to those known to occur in vivo.

Influenza vaccination in MS: absence of T-cell response against white matter proteins

BACKGROUND

Natural infections bear the risk of triggering MS bouts, whereas epidemiologic studies have not delineated an increased risk for disease activity after influenza virus vaccination.

OBJECTIVE

To examine influenza A virus-specific and myelin protein-reactive T-cell frequencies by interferon gamma (IFNgamma)-enzyme-linked immunospot and the response of these cells by IFNgamma-reverse transcription (RT) PCR after immunization and any incidental upper respiratory tract infection (URI) in 12 patients with MS (seven with a relapsing-remitting course; five with a secondary progressive course; Kurtzke Expanded Disability Status Scale [EDSS] score from 1.0 to 6.5, without immunosuppressive treatment) and 28 healthy volunteers.

RESULTS

A cellular immune response against influenza A virus was mounted in both populations at 2 weeks after vaccination. Patients with MS showed a higher relative increase (p = 0.008) than controls with respect to the number of influenza-specific T cells. Mean antibody responses against influenza A virus were increased in both populations after 2 weeks (p < 0.01). Despite these virus-specific reactions, no increase in T-cell frequencies responsive to human myelin basic protein (MBP) or recombinant human myelin oligodendrocyte protein (MOG) was observed after immunization, arguing against a general immune stimulation by influenza vaccination. In contrast, MBP-specific T-cell responses became detectable in several individuals after febrile infection.

CONCLUSION

These data support the clinical observations that influenza vaccination is effective and safe in patients with MS with respect to cellular immunoreactivity against two main CNS myelin proteins.

Adjuvantation of epidermal powder immunization

The skin is an immunologically active site and an attractive vaccination route. All current vaccines, however, are administered either orally, intramuscularly, or subcutaneously. We previously reported that epidermal powder immunization (EPI) with an extremely small dose of powdered influenza vaccine induces protective immunity in mice. In this study, we report that commonly used adjuvants can be used in EPI to further enhance the immune responses to an antigen. The IgG antibody response to diphtheria toxoid (DT) following EPI was augmented by 25- and 250-fold, when 1 microg DT was co-delivered with aluminum phosphate (alum) and a synthetic oligonucleotide containing CpG DNA motifs (CpG DNA), respectively. These antibodies had toxin-neutralization activity and were long lasting. Furthermore, EPI using an adjuvant selectively activated different subsets of T helper cells and gave either a Th1 or a Th2 type of immune response. Similar to needle injection into deeper tissues, EPI with alum adsorbed DT promoted a predominantly IgG1 subclass antibody response and elevated level of IL-4 secreting cells. These are indicative of Th2-type immunity. In contrast, co-delivery of CpG DNA adjuvant via EPI led to Th-1 type of response as characterized by the increased production of IgG2a antibodies and IFN-gamma secreting cells. This study indicated that EPI using appropriate adjuvants can produce an augmented antibody response and desirable cellular immune responses. EPI is a promising immunization method that may be used to administer a broad range of vaccines including vaccines with adjuvants.

Expansion of HER2/neu-specific T cells ex vivo following immunization with a HER2/neu peptide-based vaccine

The identification and characterization of tumor antigens has facilitated the development of immune-based cancer prophylaxis and therapy. Cancer vaccines, like viral vaccines, may be effective in cancer prevention. Adoptive T-cell therapy, in contrast, may be more efficacious for the eradication of existing malignancies. Our group is examining the feasibility of antigen-specific adoptive T-cell therapy for the treatment of established cancer in the HER2/neu model. Transgenic mice overexpressing rat neu in mammary tissue develop malignancy, histologically similar to human HER2/neu-overexpressing breast cancer. These mice can be effectively immunized against a challenge with neu-positive tumor cells. Adoptive transfer of neu-specific T cells into tumor-bearing mice eradicates malignancy. Effective T-cell therapy relies on optimization of the ex vivo expansion of antigen-specific T cells. Two important elements of ex vivo antigen-specific T-cell growth that have been identified are (1) the preexisting levels of antigen-specific T cells and (2) the cytokine milieu used during ex vivo expansion of the T cells. Phase I clinical trials of HER2/neu-based peptide vaccination in human cancer patients have demonstrated that increased levels of HER2/neu-specific T-cells can be elicited after active immunization. Initiating cultures with greater numbers of antigen-specific T cells facilitates expansion. In addition, cytokines, such as interleukin-12, when added during ex vivo culturing along with interleukin-2 can selectively expand antigen-specific T-cells. Interleukin-12 also enhances antigen-specific functional measurements such as interferon-gamma and tumor necrosis factor-alpha release. Refinements in ex vivo expansion techniques may greatly improve the feasibility of tumor-antigen T-cell-based therapy for the treatment of advanced-stage HER2/neu-overexpressing breast malignancy.

Direct detection of cellular immune responses to cancer vaccines

The evaluation of cancer immunotherapy is predicated on the hypothesis that markers of tumor antigen-specific T-cell immunity will cone-late with clinical efficacy. Establishing which candidate vaccines should enter large-scale clinical trials will necessitate optimal application of immunologic monitoring assays. Evidence suggests that available techniques are adequate for the direct detection of clinically significant antigen-specific T-cell responses from tissue specimens. To achieve this goal, it is important to have an understanding of individual methods and their limitations, to include appropriate control antigens in the monitoring strategy, and to incorporate statistical considerations into the design and analysis of such studies.

Immunization with a HER-2/neu helper peptide vaccine generates HER-2/neu CD8 T-cell immunity in cancer patients

CD4 T-cell help is required during the generation and maintenance of effective antitumor CD8 T cell-mediated immunity. The goal of this study was to determine whether HER-2/neu-specific CD8 T-cell immunity could be elicited using HER-2/neu-derived MHC class II "helper" peptides, which contain encompassed HLA-A2-binding motifs. Nineteen HLA-A2 patients with HER-2/neu-overexpressing cancers received a vaccine preparation consisting of putative HER-2/neu helper peptides p369-384, p688-703, and p971-984. Contained within these sequences are the HLA-A2-binding motifs p369-377, p689-697, and p971-979. After vaccination, the mean peptide-specific T-cell precursor frequency to the HLA-A2 peptides increased in the majority of patients. In addition, the peptide-specific T cells were able to lyse tumors. The responses were long-lived and detectable for more than 1 year after the final vaccination in select patients. These results demonstrate that HER-2/neu MHC class II epitopes containing encompassed MHC class I epitopes are able to induce long-lasting HER-2-specific IFN-gamma-producing CD8 T cells.

Correlation of human CD56+ cell cytotoxicity and IFN-gamma production

The use of an IFN-gamma ELISPOT assay to evaluate cellular immune responses has gained increasing popularity, especially as a surrogate measure for cytotoxic T lymphocyte (CTL) responses. We have compared the IFN-gamma ELISPOT assay and the traditional(51)Cr release assay for detection of human natural killer (NK) cell activity. The cell populations used for evaluation of these assays included freshly isolated and IL-2-activated peripheral blood mononuclear cells (PBMC). CD56-positive cells were demonstrated to be the primary source of the IFN-gamma signal when PBMC were evaluated with NK-sensitive targets in the IFN-gamma ELISPOT assay. IFN-gamma ELISPOT and(51)Cr release assays showed excellent correlation suggesting that NK activity can be reliably evaluated with methods other than the traditional(51)Cr release assays.

Characterization of early immunological responses in primary cultures of differentially activated human peripheral mononuclear cells

Specific immune cell activation is a hallmark of infections and autoimmune disorders. Quantification of proliferative cell responses by (3)H-thymidine incorporation is a slow process and describes only one type of cellular reaction. We here investigated early immunological responses of purified human peripheral blood mononuclear cells to the direct stimulus alpha CD3 and antigen specific stimulation (human myelin basic protein (hMBP), tetanus toxoid, and influenza vaccine) and compared them to polyclonal LPS stimulation. Cytokine mRNA levels were quantified using real-time quantitative reverse transcriptase polymerase chain reaction (RT PCR) 4 h, 16 h, and 48 h after activation. Proliferation was measured 96 h after initiation of the cultures. Antigen specific responses were detected as early as 4 h after stimulation and followed different kinetics depending on the mode of activation. We demonstrated significant correlations of cytokine mRNA and protein expression for TNF alpha, IL10, and IFN gamma. Expression of IL2 mRNA at 16 h was correlated with proliferation indices at 96 h whereas IL4 mRNA levels were negatively correlated. Early cytokine mRNA expression in stimulated immune cells provides important functional data and is a powerful tool with which to study immunological reactions.

Pre-existent immunity to the HER-2/neu oncogenic protein in patients with HER-2/neu overexpressing breast and ovarian cancer

Immunomodulatory strategies, such as antibody therapy and cancer vaccines, are increasingly being considered as potential adjuvant therapies in patients with advanced stage breast cancer to either treat minimal residual disease or prevent relapse. However, little is known concerning the incidence and magnitude of the pre-existent breast cancer specific immune response in this patient population. Using the HER-2/neu oncogenic protein as a model, a well-defined tumor antigen in breast cancer, we questioned whether patients with advanced stage HER-2/neu overexpressing breast and ovarian cancers (III/IV) had evidence of pre-existent immunity to HER-2/neu. Forty-five patients with stage III or IV HER-2/neu overexpressing breast or ovarian cancer were evaluated for HER-2/neu specific T cell and antibody immunity. Patients enrolled had not received immunosuppressive chemotherapy for at least 30 days (median 5 months, range 1-75 months). All patients were documented to be immune competent prior to entry by DTH testing using a skin test anergy battery. Five of 45 patients (11%) were found to have a significant HER-2/neu specific T cell response as defined by a stimulation index > or = 2.0 (range 2.0-7.9). None of eight patients who were HLA-A2 had a detectable IFNgamma secreting T-cell precursor frequency to a well-defined HER-2/neu HLA-A2 T cell epitope, p369-377. Three of 45 patients (7%) had detectable HER-2/neu specific IgG antibodies, range 1.2-8.9 microg/ml. These findings suggest that patients with advanced stage HER-2/neu overexpressing breast and ovarian cancer can mount a T cell and/or antibody immune response to their tumor. However, in the case of the HER-2/neu antigen, the pre-existent tumor specific immune response is found only in a minority of patients.

Antigen-specific immunotherapy for human papillomavirus 16 E7-expressing tumors grown in the liver

BACKGROUND/AIMS

We have previously reported a recombinant vaccinia-based vaccine (vac-Sig/E7/LAMP-1) that demonstrated a significant anti-tumor effect in a subcutaneous tumor challenge model. Since the liver is one of the most common sites for tumor metastasis and organ microenvironments may modulate tumor cell responses to therapies, the aim of the present study was to evaluate the potency of vac-Sig/E7/LAMP-1 in treating E7-expressing tumors grown in the liver.

METHODS

For in vivo tumor prevention experiments, mice were vaccinated intraperitoneally with vac-Sig/E7/LAMP-1 followed by intrahepatic tumor challenge. For in vivo tumor regression experiments, mice were first challenged with tumor cells and then vaccinated with vac-Sig/E7/LAMP-1 intraperitoneally. In addition, enzyme-linked immunospot assays were used to determine the frequency of E7-specific T cell precursors.

RESULTS

For in vivo tumor protection experiments, tumor growth was observed in all of the mice vaccinated with wild-type vaccinia and 60% of the mice vaccinated with wild-type E7 vaccinia. All of the mice vaccinated with vac-Sig/E7/LAMP-1 remained tumor-free 30 days after tumor challenge. For the tumor regression assays, all of the mice vaccinated with vac-Sig/E7/LAMP-1 remained tumor-free 30 days after vaccination. In contrast, all of those mice receiving culture medium, wild-type vaccinia, or wild-type E7 vaccinia developed tumors in the liver. In addition, mice vaccinated with vac-Sig/E7/LAMP-1 had the highest E7-specific CD8+ T cell precursors.

CONCLUSIONS

Our data suggest that vac-Sig/E7/LAMP-1 is an effective vaccine for controlling E7-expressing tumors grown in the liver and our model suggests that antigen-specific immunotherapy may represent a powerful tool for treating liver tumors with characterized tumor-specific antigens. In addition, our data indicate that the number of E7-specific CD8+ T cell precursors directly correlated with the anti-tumor effect generated by Sig/E7/LAMP-1 vaccinia.

CD8(+) T-cell autoreactivity to an HLA-B27-restricted self-epitope correlates with ankylosing spondylitis

HLA-B27 is highly associated with ankylosing spondylitis (AS), but the mechanism is unknown. Among the HLA-B27 alleles, B*2709, which differs by one amino acid from the susceptible B*2705, is not associated with the disease. Here, we analyze the reactivity, in patients with AS and in healthy controls carrying the B*2709 or B*2705 alleles, to an EBV epitope derived from LMP2 (236-244) and to a sequence-related self-peptide from vasoactive intestinal peptide receptor 1 (VIP1R 400-408). We found that both B*2705(+) and B*2709(+) subjects possess LMP2 236-244-specific, HLA-B27-restricted T cells, whereas only the B*2705(+) individuals respond significantly to VIP1R 400-408. These results prompted us to compare, by IFN-gamma ELISPOT analysis, the T-cell response to VIP1R 400-408 in patients with AS versus B*2705 healthy controls. The data show that VIP1R 400-408-specific reactivity is a major feature of the patients with AS. These findings show, for the first time to our knowledge, a widespread reactivity in patients with AS against a self-epitope that exhibits some features of a putative "arthritogenic" peptide.

Boosting with recombinant vaccinia increases HPV-16 E7-specific T cell precursor frequencies of HPV-16 E7-expressing DNA vaccines

We have previously linked the sorting signals of the lysosome-associated membrane protein-1 (LAMP-1) to HPV-16 E7 antigen, creating a chimera, Sig/E7/LAMP-1. We found that both Sig/E7/LAMP-1-containing recombinant vaccinia virus (Vac-Sig/E7/LAMP-1) and Sig/E7/LAMP-1 DNA can generate strong antitumor immunity. To determine whether combination of Sig/E7/LAMP-1 DNA and Vac-Sig/E7/LAMP-1 can further enhance immune responses, sequential vaccination with Sig/E7/LAMP-1 DNA and Vac-Sig/E7/LAMP-1 was given. We found that priming with Sig/E7/LAMP-1 DNA and boosting with Vac-Sig/E7/LAMP-1 generated the strongest E7-specific CD8(+) T cell responses. Our results encourage the use of the DNA prime/vaccinia booster regimen in future clinical trials.

Characterization of an in situ IFN-gamma ELISA assay which is able to detect specific peptide responses from freshly isolated splenocytes induced by DNA minigene immunization

An in situ IFN-gamma ELISA assay has been developed and optimized for both freshly isolated and peptide-restimulated splenocytes. This assay is based on the ELISPOT assay, but utilizes a soluble chromagen, making it readily adaptable to high-throughput analysis. We show that in both the primary and restimulation assays this technique is more sensitive than either a traditional supernatant ELISA or the 51Cr-release assay, in that responses are observed in the in situ ELISA that are not detectable in these other assays. On a per-cell basis, the sensitivity of the in situ ELISA is approximately one IFN-gamma secreting cell/10(4) plated cells. The in situ IFN-gamma ELISA was utilized to describe the kinetics of the IFN-gamma response to DNA vaccination with pMin.1. For freshly isolated splenocytes, the peak response for all the peptides tested was observed from 10 to 12 days after immunization, with responses seen to some peptides as early as 7 days. When a 6-day in vitro peptide restimulation step was added, responses were seen for all the peptides tested after 7 days of in vivo immunization. This data demonstrates that a single intramuscular administration of a DNA vaccine can induce T-cell responses that can be detected in freshly isolated splenocytes.

Gene gun-mediated DNA vaccination induces antitumor immunity against human papillomavirus type 16 E7-expressing murine tumor metastases in the liver and lungs

DNA vaccination has emerged as an attractive approach for tumor immunotherapy. The aim of this study was to evaluate the potency of DNA vaccines in preventing and treating the liver and lung metastases of a human papillomavirus-16 (HPV-16) E7-expressing murine tumor (TC-1). We used the gene gun method to vaccinate C57BL/6 mice intradermally with DNA vaccines containing the HPV-16 E7 gene, the E7 gene linked to the sorting signals of the lysosome-associated membrane protein-1 (Sig/E7/ LAMP-1), or the 'empty' plasmid vector. The in vivo antitumor immunity was analyzed in both tumor prevention and tumor regression experiments. In addition, cytotoxic T lymphocyte (CTL) assays, enzyme-linked immunospot assay and enzyme-linked immunoabsorbent assay were used to assess the E7-specific T cell-mediated and humoral immunity. Mice vaccinated with Sig/E7/LAMP-1 DNA generated the strongest E7-specific CTL activities, the highest numbers of E7-specific CD8+ cell precursors and the highest titers of E7-specific antibodies. While both E7 DNA and Sig/E7/LAMP-1 DNA generated potent antitumor immunity in the liver and lung metastases models, the Sig/E7/LAMP-1 DNA was more potent under stringent conditions. DNA vaccination with E7-expressing plasmids was effective in controlling liver and lung metastases of an E7-expressing murine tumor. Our data suggest that antigen-specific DNA vaccination can potentially be applied to control liver and lung metastases of tumors with defined tumor-specific antigens.

Presentation of epstein-barr virus latency antigens to CD8(+), interferon-gamma-secreting, T lymphocytes

Epstein-Barr virus (EBV) infects more than 95 % of the human population and causes an asymptomatic life-long infection in the majority of EBV carriers. Cell-mediated immunity provides resistance to EBV, as demonstrated by the occurrence of EBV-induced post-transplant lymphoproliferative disease in immunosuppressed patients. Here we looked for IFN-gamma-producing T lymphocytes in the blood of healthy donors with a rapid enzyme-linked immunospot (ELISPOT) assay, comparing as antigen presenting cells monocytes and dendritic cells (DC) infected with recombinant vaccinia virus (rVV). We found a strong CD8(+) ELISPOT response to one or more of the EBNA 3A, 3B and 3C antigens in the PBMC from 14 / 18 donors. The sensitivity of the overnight ELISPOT assay was increased using DC as antigen-presenting cells, including 3 / 3 individuals who lacked ELISPOT in PBMC. In addition, DC could markedly expand EBV-specific spots after a 7-day culture. In a smaller number of donors, we documented recognition of the subdominant LMP 1, LMP 2 and EBNA 1 antigens that are expressed in a variety of EBV-associated malignancies. Therefore our data provide more evidence for the efficacy of DC in eliciting rapid responses to EBV latency antigens in circulating CD8(+) T cells.

A flow cytometric method to estimate the precursor frequencies of cells proliferating in response to specific antigens

Fluorescent dyes that stain cell membranes or cytoplasm and then partition between daughter cells at division have been used in conjunction with flow cytometry to measure the proliferation of cells. In this paper, using peripheral blood mononuclear cells responding to tetanus toxoid, we describe an extension of this dye methodology to calculate the precursor frequency of antigen-specific T-cells. With mathematical deconvolution of the fluorescence histograms providing information about the proportion of cells in each of the daughter generations, information can be derived about the precursor frequency of cells in the original population that responded to the specific stimulus. Data from a model system with different proportions of fixed and viable cells indicate that the flow method returns accurate values for precursor frequency. Based on the characteristics of flow cytometric data acquisition, it is estimated that the flow method could detect proliferation of cells that represented, before addition of the stimulus, approximately 1/10(5) of the population. When comparing results to those from the limiting dilution technique, the flow cytometric method returns values that indicate higher precursor frequencies. Possible reasons for this discrepancy are discussed. The flow cytometric method offers the advantage of simplicity as well as the additional ability to phenotype the responding cells and determine their rate of proliferation. The flow method may find use as a simple, routine assay in the fields of allergy, transplant rejection, and autoimmunity and for quantitating responses to vaccination and cancer immunotherapy.

Identification of Three HLA-A*0201-Restricted Cytotoxic T Cell Epitopes in the Cytomegalovirus Protein pp65 That Are Conserved Between Eight Strains of the Virus

The Ag specificity of the CTL response against CMV is directed almost entirely to a single CMV tegument protein, the phosphoprotein pp65. We report the identification of three peptides derived from the protein pp65 that displayed a high or intermediate binding to HLA-A*0201 molecules, which were also able to induce an in vitro CTL response in peripheral blood lymphocytes from CMV seropositive individuals. The peptide-specific CTLs generated were capable of recognizing the naturally processed pp65 either presented by CMV-infected cells or by cells infected with an adenovirus construct expressing pp65 in an HLA-A*0201-restricted manner. Thus, we were able to demonstrate responses to subdominant CTL epitopes in CMV-pp65 that were not detected in polyclonal cultures obtained by conventional stimulations. We also found that the amino acid sequences of the three peptides identified as HLA-A*0201-restricted CTL epitopes were conserved among different wild-type strains of CMV obtained from renal transplant patients, an AIDS patient, and a congenitally infected infant, as well as three laboratory strains of the virus (AD169, Towne and Davis). These observations suggest that these pp65 CTL peptide epitopes could potentially be used as synthetic peptide vaccines or for other therapeutic strategies aimed at HLA-A*0201-positive individuals, who represent ∼40% of the European Caucasoid population. However, strain variation must be taken in consideration when the search for CTL epitopes is extended to other HLA class I alleles, because these mutations may span potential CTL epitopes for other HLA molecules, as it is described in this study.

Presence of Effector CD8+ T Cells in Hepatitis C Virus-Exposed Healthy Seronegative Donors

CTL responses against multiple hepatitis C virus (HCV) epitopes were detected in 7 of 29 (24.1%) healthy family members (HFM) persistently exposed to chronically HCV-infected patients (HCV-HFM). These precursor CTL were at very low or undetectable frequencies, as determined by limiting dilution analysis. However, when HCV-specific effector CD8+ T cells, freshly isolated from PBMC of HCV-HFM, were assessed by a sensitive enzyme-linked immunospot assay, their frequencies were severalfold higher than those of precursor CTL. These results indicate that the two assays detect two functionally distinct T cell populations and that the effector cells are not assayed by the 51Cr-release assay. Furthermore, the combination of cell depletion and enzyme-linked immunospot analyses showed that the effector cells were confined into a CD8+ CD45RO+ CD28− population. The persistence of effector CD8+ T cells specific for both the structural and nonstructural viral proteins in uninfected HCV-HFM, suggest that: 1) an immunological memory is established upon a subclinical infection without any evidence of hepatitis, in a large cohort of HCV-exposed individuals; 2) because these cells required neither restimulation nor the addition of particular cytokines in vitro for differentiating in effectors, they should be capable of prompt HCV-specific effector function in vivo, possibly providing antiviral protection; and 3) the maintenance of effector T cell responses may be sustained by persisting low-level stimulation induced by inapparent infections.

A recombinant vaccinia virus based ELISPOT assay detects high frequencies of Pol-specific CD8 T cells in HIV-1-positive individuals

OBJECTIVES

HIV-1-specific CD8 T cells are considered to be critical in anti-HIV responses. It is important to quantify these cells and to determine their antigenic targets. Here quantification of interferon (IFN)-gamma secreting, virus-specific cells was achieved with an enzyme linked immuno spot (ELISPOT) assay.

METHODS

Peripheral blood mononuclear cells (PBMC) were infected with recombinant vaccinia vectors expressing HIV-1 genes (gag, pol, env or nef) and added to wells precoated with anti-IFN-gamma monoclonal antibodies. Spot forming cells (SFC), i.e. antigen-specific T cells were detected 24 h later by the addition of biotinylated anti-IFN-gamma monoclonal antibodies, followed by avidin-bound biotinylated horseradish peroxidase.

RESULTS

In a cohort of 19 patients, of whom 15 were on highly active antiretroviral therapy, 18 had primed T cells directed against one or more HIV-1 antigens (P < 0.0001). Pol-specific T cells routinely dominated the CD8 response with frequencies up to 2000 SFC per 10(6) PBMC. In HLA A*0201-positive patients, the vaccinia vectors detected much higher frequencies of SFC than haplotype-restricted peptides. Elimination of CD8 T cells resulted in > 90% loss of antigen-specific SFC when vaccinia virus was used as a vector. The number of CD8 SFC exceeded the number of memory cells detected in limiting dilution assays by > 1 log10, whereas a correlation was found between the frequency of effector cells detected by both ELISPOT and MHC class I peptide tetramer assays.

CONCLUSIONS

Vaccinia virus vectors used in ELISPOT assays are useful for determining the frequency and specificity of CD8 T cells for individual HIV-1 gene products. The dominance of cytolytic T lymphocytes (CTL) recognizing pol proteins suggests that this antigen should be considered in vaccine strategies.

Impaired apoptotic deletion of myelin basic protein-reactive T cells in patients with multiple sclerosis

T cell responses to myelin basic protein (MBP) may play an important role in the pathogenesis of multiple sclerosis (MS). If MBP-reactive T cells are involved in the disease processes and undergo clonal activation and expansion, their precursor frequency would be increased in patients with MS. The frequency of MBP-reactive T cells is also influenced by regulatory mechanisms in vivo, including apoptotic deletion. In this study, we examined changes in the frequency of MBP-reactive T cells in patients with MS as a function of the apoptotic deletional mechanism in vivo, using a cell culture-based assay. A significantly increased frequency of MBP-reactive T cells was found in patients with MS relative to healthy individuals only when Fas-ligand antibody was used to block apoptosis. This result indicates that a significant proportion of MBP-reactive T cells are sensitive to apoptosis and are not deleted in vivo in patients with MS, as opposed to healthy individuals, thus suggesting a functional deficit in apoptotic deletional mechanism. Surviving Fas-sensitive MBP-reactive T cell lines represent distinct subpopulations preferentially recognizing the 111-139 region of MBP and exhibiting a Th2 cytokine profile. The findings are relevant to our understanding of regulation of MBP-reactive T cells in vivo in MS.

Self glycolipids as T-cell autoantigens

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system characterized by discrete areas of demyelination. An autoimmune response against components of myelin is thought to contribute to disease pathogenesis. Here we identify glycolipids as new targets recognized by T cells in multiple sclerosis patients. Circulating T cells reactive with glycolipids are more frequent in MS patients than in control donors as shown by enzyme-linked immunospot assay. They specifically recognize different types of glycolipids, such as gangliosides, sulfatide and galactosylceramide and release IFN-gamma and TNF-alpha. T cells specific for gangliosides were found to be CD8+, TCR alphabeta+, restricted by the MHC-like CD1b molecule and specific for epitopes residing in the carbohydrate moiety of gangliosides. Our findings suggest that in addition to self proteins, self glycolipids may represent potential source of autoantigens recognized by T cells in autoimmune diseases.

Immune markers for monitoring the progression of autoimmune disease

The incidence of immune-mediated diseases is increasing worldwide. Reliable immune markers for monitoring disease progression and also the effect of therapeutic interventions are urgently needed in order to investigate preventive or therapeutic measures effectively. At a recent workshop held on 5 December 1998 in Copenhagen, the state of research on surrogate markers in Type 1 diabetes was discussed and compared with the experience in multiple sclerosis, inflammatory bowel disease and transplantation.