Characterization of circulating T cells specific for tumor-associated antigens in melanoma patients

Recombinant human single-chain MHC-peptide complexes made from E. coli By in vitro refolding: functional single-chain MHC-peptide complexes and tetramers with tumor associated antigens

Soluble recombinant MHC-peptide complexes are valuable tools for molecular characterization of immune responses as well as for other functional and structural studies. In this study, soluble recombinant single-chain human MHC (scMHC)-peptide complexes were generated by in vitro refolding of inclusion bodies from bacterially expressed engineered HLA-A2 in the presence of tumor-associated or viral peptides. The scMHC molecule was composed of beta2-microglobulin connected to the first three domains of the HLA-A2 heavy chain through a 15-amino acid flexible linker. Highly purified scMHC-peptide complexes were obtained in high yield using several peptides derived from the melanoma antigens gp100 and MART-1 or a viral peptide derived from HTLV-1. The scMHC complexes were characterized in detail and were found to be correctly folded and able to specifically bind HLA-A2-restricted peptides. We also generated scMHC-peptide tetramers, which were biologically functional; they induced a peptide-specific CTL clone to be activated and secrete IFN-gamma, and were able to stain specifically CTL lines. Such recombinant soluble scMHC-peptide complexes and tetramers should prove of great value for characterization of immune responses involving CTL, for visualization of antigen-specific immune responses, for in vitro primary CTL induction, and for peptide binding assays and structural studies.

Artificial antigen-presenting cells as a tool to exploit the immune 'synapse'

Recent progress in molecular medicine has provided important tools to identify antigen-specific T cells. In most cases, the approach is based on oligomeric combinations of recombinant major histocompatibility complex-peptide complexes fixed to various rigid supports available for binding by the T-cell receptor. These tools have greatly increased our insight into mechanisms of immune responses mediated by CD8+ T cells. Examples of the diverse fields of application for this technology include immunization, viral infections and oral tolerance induction.

Induction of tolerance to immunogenic tumor antigens associated with lymphomagenesis in HOX11 transgenic mice

Transgenic mice expressing human HOX11 in B lymphocytes die prematurely from lymphomas that initiate in the spleen and frequently disseminate to distant sites. Preneoplastic hematopoiesis in these mice is unperturbed. We now report that expression of the HOX11 transgene does not affect the ability of dendritic cells (DCs) to process and present foreign peptides and activate antigen-specific T cell responses. We also show that nontransgenic DCs presenting peptides derived from the human HOX11 protein are highly efficient stimulators of autologous T cells, whereas transgenic T cells are nonresponsive to peptides derived from the HOX11 transgene and the murine Meis1 protein. HOX11 transgenic mice thus show normal development of tolerance to immunogenic antigens expressed throughout B cell maturation. DCs pulsed with cell lysates prepared from lymphomas, obtained from HOX11 transgenic mice with terminal lymphoma, activate T cells from nontransgenic and premalignant transgenic mice, whereas T cells isolated from lymphomatous transgenic mice are nonresponsive to autologous tumor cell antigens. These data indicate that HOX11 lymphoma cells express tumor-rejection antigens that are recognized as foreign in healthy transgenic mice and that lymphomagenesis is associated with the induction of anergy to tumor antigen-specific T cells. These findings are highly relevant for the development of immunotherapeutic protocols for the treatment of lymphoma.

Impaired function of circulating HIV-specific CD8+ T cells in chronic human immunodeficiency virus infection

The functional status of circulating human immunodeficiency (HIV)-specific CD8 T cells in chronically infected subjects was evaluated. By flow cytometry, only 5 of 7 subjects had detectable CD8 T cells that produced IFN-γ after stimulation with HIV-infected primary CD4 T cells. In 2 subjects, the frequency of IFN-γ–producing cells increased 4-fold when IL-2 was added to the culture medium; in another subject, IFN-γ–producing cells could be detected only after IL-2 was added. IFN-γ–producing cells ranged from 0.4% to 3% of CD8 T cells. Major histocompatibility complex–peptide tetramer staining, which identifies antigen-specific T cells irrespective of function, was used to evaluate the proportion of HIV-specific CD8 T cells that may be nonfunctional in vivo. CD8 T cells binding to tetramers complexed to HIV gag epitope SLYNTVATL and reverse transcriptase epitope YTAFTIPSI were identified in 9 of 15 and 5 of 12 HLA-A2–expressing seropositive subjects at frequencies of 0.1% to 1.1% and 0.1 to 0.7%, respectively. Freshly isolated tetramer-positive cells expressed a mixed pattern of memory and effector markers. On average, IFN-γ was produced by less than 25% of tetramer-positive CD8 T cells after stimulation with the relevant gag or reverse transcriptase peptide. In all subjects tested, freshly isolated CD8 T cells were not cytolytic against peptide-pulsed B lymphoblastoid cell line or primary HIV-infected CD4 T-cell targets. Exposure to IL-2 enhanced the cytotoxicity of CD8 T cells against primary HIV-infected CD4 targets in 2 of 2 subjects tested. These results suggest that a significant proportion of HIV-specific CD8 T cells may be functionally compromised in vivo and that some function can be restored by exposure to IL-2.

A significant number of human immunodeficiency virus epitope-specific cytotoxic T lymphocytes detected by tetramer binding do not produce gamma interferon

Despite the seemingly important role of cytotoxic T-lymphocyte (CTL) responses in human immunodeficiency virus (HIV) disease pathogenesis, their measurement has relied on a variety of different techniques. We utilized three separate methodologies for the detection of CTLs in a cohort of HIV-infected individuals who were also human leukocyte antigen A2 (HLA-A2) positive. Among the different CTL assays, a correlation was seen only when the Gag epitope-specific HLA A*0201-restricted tetramer assay was compared with the ELISPOT assay performed after stimulation with the Gag epitope; however, this correlation was of borderline statistical significance. On average, the tetramer reagent detected a 10-fold-higher number of cells than were seen to produce gamma interferon by the ELISPOT assay. The implications of this CTL assay comparison and the possibility of phenotypic differences in HIV-specific CD8(+) T lymphocytes are discussed.

Antibody-conjugated MHC class I tetramers can target tumor cells for specific lysis by T lymphocytes

To demonstrate that antibody-guided targeting of antigenic MHC class I-peptide tetramer on tumor cells can render them susceptible to lysis by relevant cytotoxic T lymphocytes (CTL), biotinylated HLA-A*0201/Flu matrix peptide complexes were tetramerized on streptavidin molecules previously coupled to Fab' fragments from monoclonal antibodies (mAb) specific for cell surface markers such as carcinoembryonic antigen (CEA), ErbB-2 or CD20. Flow cytometry analysis showed that coating of the HLA-A2-peptide complexes on the four HLA-A2-negative human cancer lines tested (including a CEA-positive colon carcinoma, an ErbB-2(+) breast carcinoma and two CD20(+) B lymphomas) was entirely dependent upon the specificity of the conjugated antibody fragments. More importantly, HLA-A2-restricted Flu matrix peptide-specific CTL were then found to lyse specifically and efficiently the MHC-coated target cells. These results open the way to the development of new immunotherapy strategies based on antibody targeting of MHC class I-peptide complexes.

Immunofluorescence analysis of T-cell responses in health and disease

The use of flow cytometry to study the functional responses of T cells by immunofluorescent staining for intracellular cytokines and other markers is a growing field of clinical interest. In this article, we describe methods for the rapid evaluation of T-cell responses to mitogens and specific antigens and explore how these assays might be valuable in various clinical settings.

Impaired function of circulating HIV-specific CD8+ T cells in chronic human immunodeficiency virus infection

The functional status of circulating human immunodeficiency (HIV)-specific CD8 T cells in chronically infected subjects was evaluated. By flow cytometry, only 5 of 7 subjects had detectable CD8 T cells that produced IFN-γ after stimulation with HIV-infected primary CD4 T cells. In 2 subjects, the frequency of IFN-γ–producing cells increased 4-fold when IL-2 was added to the culture medium; in another subject, IFN-γ–producing cells could be detected only after IL-2 was added. IFN-γ–producing cells ranged from 0.4% to 3% of CD8 T cells. Major histocompatibility complex–peptide tetramer staining, which identifies antigen-specific T cells irrespective of function, was used to evaluate the proportion of HIV-specific CD8 T cells that may be nonfunctional in vivo. CD8 T cells binding to tetramers complexed to HIV gag epitope SLYNTVATL and reverse transcriptase epitope YTAFTIPSI were identified in 9 of 15 and 5 of 12 HLA-A2–expressing seropositive subjects at frequencies of 0.1% to 1.1% and 0.1 to 0.7%, respectively. Freshly isolated tetramer-positive cells expressed a mixed pattern of memory and effector markers. On average, IFN-γ was produced by less than 25% of tetramer-positive CD8 T cells after stimulation with the relevant gag or reverse transcriptase peptide. In all subjects tested, freshly isolated CD8 T cells were not cytolytic against peptide-pulsed B lymphoblastoid cell line or primary HIV-infected CD4 T-cell targets. Exposure to IL-2 enhanced the cytotoxicity of CD8 T cells against primary HIV-infected CD4 targets in 2 of 2 subjects tested. These results suggest that a significant proportion of HIV-specific CD8 T cells may be functionally compromised in vivo and that some function can be restored by exposure to IL-2.

Design and evaluation of antigen-specific vaccination strategies against cancer

After studies in preclinical mouse models, the efficacy and safety of tumor-specific vaccination strategies is currently being evaluated in cancer patients. The first wave of clinical trials has shown that in general such vaccination strategies are safe. However examples of clinical responses, especially in conjunction with vaccine-induced immune responses, are still scarce. The fact that most trials have so far been performed with end-stage cancer patients can largely account for this deficit. Greater efficacy of anticancer vaccines is expected in patients with less-progressed disease. In addition, the detection of both natural and vaccine-induced T cell immunity needs further improvement.

Tumor antigen pulsed dendritic cells enhance the cytolytic activity of tumor infiltrating lymphocytes in human hepatocellular cancer

OBJECTIVE

Tumor infiltrating lymphocytes (TILs) stimulated with interleukin-2 (IL-2) ex vivo have been successfully used therapeutically in some cancer patients, but their potency in eliciting an effective anti-tumor response is variable. We have tried to augment killing activity of tumor infiltrating lymphocytes derived from hepato-cellular carcinoma (HCC) using autologous monocytes derived dendritic cells.

METHODS

Tumor infiltrating lymphocytes (TILs) from 6 patient with hepatocellular carcinoma were isolated and the phenotype were further characterized. From the same patients, autologous dendritic cells were generated from CD14+ monocytes that were cultured for 6 days in the presence of granulocyte macrophage colony-stimulating factor (GM-CSF) and interleukin 4 (IL-4). Those professional antigen presenting cells were pulsed with whole autologous hepatoma tumor lysates (pDC). TILs were cocultured with pDC or unpulsed DC. To assess the cytotoxic potency of TILs, the ability to lyse the tumor cell targets K652, Daudi and an allogeneic HCC celline was determined in a standard cytotoxic assay.

RESULTS

Tumor cells targets in vitro are poorly lysed by tumor infiltrating lymphocytes indicating T-cell hyporesponsiveness. In contrast, the killing activity of HCC derived TILs against Daudi (9.15% +/- 7.5) and allogeneic HCC tumor target (18.2% +/- 9.2) could be significantly augmented when stimulated with pDC (Daudi: 38% +/- 6.8 and allogeneic HCC: 55% +/- 10). The killing activity of TILs against K562 was unaffected by pDC.

CONCLUSION

The low cytotoxic activity profile of HCC derived TILs in vitro can be increased by tumor lysate pulsed dendritic cells and may therefore be more effective in vivo when used for adoptive immunotherapy.

Cross-presentation of tumor antigens to effector T cells is sufficient to mediate effective immunotherapy of established intracranial tumors

The systemic adoptive transfer of tumor-sensitized T cells, activated ex vivo, can eliminate established intracranial tumors. Regression of MHC class II negative MCA 205 fibrosarcomas occurs optimally following adoptive transfer of both CD4 and CD8 tumor-sensitized T cells, indicating an important function for tumor-infiltrating APC. Here, we demonstrate that during an effector response, indirect presentation of tumor Ags to transferred T cells is sufficient to mediate intracranial tumor regression. BALB/c --> CB6F1 (H-2bxd) bone marrow chimeras were challenged with the MCA 205 fibrosarcoma (H-2b). The tumor grew progressively in the H-2b-tolerant chimeras and stimulated an immune response in tumor-draining lymph nodes. Tumor-sensitized lymph node T cells were activated ex vivo with anti-CD3 and IL-2, then adoptively transferred to sublethally irradiated BALB/c or C57BL/6 recipients bearing established intracranial MCA 205 tumors. The transferred T cells eradicated MCA 205 tumors in BALB/c recipients and demonstrated tumor specificity, but had no therapeutic efficacy in the C57BL/6 recipients. These data establish that tumor-associated host cell constituents provide sufficient Ag presentation to drive effector T cell function in the complete absence of direct tumor recognition. This effector mechanism has an evident capacity to remain operative in circumstances of immune escape, where the tumor does not express the relevant MHC molecules, and may have importance even at times when direct CTL recognition also remains operative.

Enhanced antigen-specific antitumor immunity with altered peptide ligands that stabilize the MHC-peptide-TCR complex

T cell responsiveness to an epitope is affected both by its affinity for the presenting MHC molecule and the affinity of the MHC-peptide complex for TCR. One limitation of cancer immunotherapy is that natural tumor antigens elicit relatively weak T cell responses, in part because high-affinity T cells are rendered tolerant to these antigens. We report here that amino acid substitutions in a natural MHC class I-restricted tumor antigen that increase the stability of the MHC-peptide-TCR complex are significantly more potent as tumor vaccines. The improved immunity results from enhanced in vivo expansion of T cells specific for the natural tumor epitope. These results indicate peptides that stabilize the MHC-peptide-TCR complex may provide superior antitumor immunity through enhanced stimulation of specific T cells.

A practical approach to multicolor flow cytometry for immunophenotyping

Through a series of novel developments in flow cytometry hardware, software, and dye-chemistry it is now possible to simultaneously measure up to 11 distinct fluorescences and two scattered light parameters on each cell. Such advanced multicolor systems have a number of advantages over current two- and three-color flow cytometric measurements. They provide a large amount of novel information for each sample studied, an exquisitely accurate quantitation of even rare cell populations, and allow identification and characterization of novel cell subsets. In particular, this technology is proving crucial to identifying functionally homogeneous subsets of cells within the enormously complex immune system; such identification and enumeration is important for understanding disease pathogenesis. However, multicolor flow cytometry comes with a new and sometimes difficult set of technical problems that must be overcome by users to derive meaningful results. In this manuscript, we describe the basic aspects of multicolor flow cytometry, including the technical hurdles and artefacts that may occur, and provide some suggestions for how to best overcome these hurdles. While inspired by the 11-color technology that we currently use, these principles apply to all flow cytometric experiments in which more than one fluorescent dye is used.

Adoptive immunotherapy to lower postsurgical recurrence rates of hepatocellular carcinoma: a randomised trial

BACKGROUND

Postsurgical recurrence of hepatocellular carcinoma (HCC) is frequent and fatal. Adoptive immunotherapy is active against HCC. We assessed whether postoperative immunotherapy could lower the frequency of recurrence.

METHODS

Between 1992 and 1995, we did a randomised trial in which 150 patients who had undergone curative resection for HCC were assigned adoptive immunotherapy (n=76) or no adjuvant treatment (n=74). Autologous lymphocytes activated vitro with recombinant interleukin-2 and antibody to CD3 were infused five times during the first 6 months. Primary endpoints were time to first recurrence and recurrence-free survival and analyses were by intention to treat.

FINDINGS

76 patients received 370 (97%) of 380 scheduled lymphocyte infusions (mean cell number per patient 7.1x10(10) [SD 2.1]; CD3 and HLA-DR cells 78% [16]), and none had grade 3 or 4 adverse events. After a median follow-up of 4.4 years (range 0.2-6.7), adoptive immunotherapy decreased the frequency of recurrence by 18% compared with controls (45 [59%] vs 57 [77%]) [corrected] patients. Time to first recurrence in the immunotherapy group was significantly longer than that in the control group (48% [37-59] vs 33% [22-43] at 3 years, 38% [22-54] vs 22% [11-34] at 5 years; p=0.008). The immunotherapy group had significantly longer recurrence-free survival (p=0.01) and disease-specific survival (p=0.04) than the control group. Overall survival did not differ significantly between groups (p=0.09).

INTERPRETATION

Adoptive immunotherapy is a safe, feasible treatment that can lower recurrence and improve recurrence-free outcomes after surgery for HCC.

Evidence that specific T lymphocytes may participate in the elimination of chronic myelogenous leukemia

Although the immune system has long been implicated in the control of cancer, evidence for specific and efficacious immune responses in human cancer has been lacking. In the case of chronic myelogenous leukemia (CML), either allogeneic bone marrow transplant (BMT) or interferon-alpha2b (IFN-alpha2b) therapy can result in complete remission, but the mechanism for prolonged disease control is unknown and may involve immune anti-leukemic responses. We previously demonstrated that PR1, a peptide derived from proteinase 3, is a potential target for CML-specific T cells. Here we studied 38 CML patients treated with allogeneic BMT, IFN- alpha2b or chemotherapy to look for PR1-specific T cells using PR1/HLA-A*0201 tetrameric complexes. There was a strong correlation between the presence of PR1-specific T cells and clinical responses after IFN-alpha and allogeneic BMT. This provides for the first time direct evidence of a role for T-cell immunity in clearing malignant cells.

Detection and quantification of CD4(+) T cells with specificity for a new major histocompatibility complex class II-restricted influenza A virus matrix protein epitope in peripheral blood of influenza patients

FVFTLTVPS was identified as the core sequence of a new major histocompatibility complex class II-restricted T-cell epitope of influenza virus matrix protein. Epitope-specific CD4(+) T cells were detected in the peripheral blood of patients with frequencies of up to 0.94%, depending on the number of additional terminal amino acids.

Cytolytic mechanisms and expression of activation-regulating receptors on effector-type CD8+CD45RA+CD27- human T cells

Circulating CD8+ T cells with a CD45RA+CD27- phenotype resemble cytolytic effector cells because they express various cytolytic mediators and are able to execute cytotoxicity without prior stimulation in vitro. We here demonstrate that CD8+CD45RA+CD27- T cells can use both granule exocytosis and Fas/Fas ligand pathways to induce apoptosis in target cells. The availability of these cytolytic mechanisms in circulating T cells suggests that the activity of these cells must be carefully controlled to prevent unwanted tissue damage. For this reason, we analyzed the expression of surface receptors that either enhance or inhibit T cell function. Compared with memory-type cells, effector cells were found to express normal levels of CD3epsilon and TCRzeta and relatively high levels of CD8. CTLA-4 was absent from freshly isolated effector cells, whereas a limited number of unstimulated memory cells expressed this molecule. In line with recent findings on CD8+CD28- T cells, CD45RA+CD27- T cells were unique in the abundant expression of NK cell-inhibitory receptors, both of Ig superfamily and C-type lectin classes. Binding of NK cell-inhibitory receptors to classical and nonclassical MHC class I molecules may inhibit the activation of the cytolytic machinery induced by either Ag receptor-specific or nonspecific signals in CD8+CD45RA+CD27- T cells.

Status of activation of circulating vaccine-elicited CD8+ T cells

Selective blunting of the status of activation of circulating tumor-specific T cells was invoked to explain their paradoxical coexistence with unhampered tumor growth. By analogy, lack of tumor regression in the face of observable melanoma vaccine-induced T cell responses might be attributed to their status of activation. We enumerated with HLA-A*0201/peptide tetramers (tHLA) vaccine-elicited T cell precursor frequency directly in PBMC of patients with melanoma undergoing vaccination with the HLA-A*0201-associated gp100:209-217(210 M) epitope (g209-2 M). Furthermore, we tested by intracellular (IC)-FACS analysis and quantitative real-time PCR (qRT-PCR) the ability of postvaccination PBMC to produce cytokine in response to challenge with vaccine-related epitopes or vaccine-matched (HLA-A*0201) melanoma cells. Vaccine-induced enhancement of T cell precursor frequency could be detected with tHLA in PBMC from six of eight patients studied at frequencies ranging between 0.3 and 2.3% of the total CD8+ population. Stimulation with vaccine-related epitopes induced IFN-gamma expression detectable by IC-FACS or qRT-PCR, respectively, in five and six of these patients. Furthermore, down-regulation of tHLA staining was noted upon cognate stimulation that could be utilized as an additional marker of T cell responsiveness. Finally, we observed in six patients an enhancement of reactivity against vaccine-matched tumor targets that was partly independent of documented vaccine-specific immune responses. A strong correlation was noted between tHLA staining of postvaccination PBMC and IFN-gamma expression by the same samples upon vaccine-relevant stimulation and assessed either by IC-FACS or qRT-PCR. Thus, blunting of the status of T cell activation on itself cannot easily explain the lack of clinical responses observed with vaccination.

Human immunodeficiency virus-specific circulating CD8 T lymphocytes have down-modulated CD3zeta and CD28, key signaling molecules for T-cell activation

Although human immunodeficiency virus (HIV)-infected subjects without AIDS have a high frequency of HIV-specific CD8 T lymphocytes, cellular immunity is unable to control infection. Freshly isolated lymphocytes often do not lyse HIV-infected targets in 4-h cytotoxicity assays. A large fraction of circulating CD8 T cells from HIV-infected donors down-modulate CD3zeta, the signaling component of the T-cell receptor complex, which is reexpressed in vitro coincident with the return of cytotoxic function. To investigate further the link between CD3zeta down-modulation and possible CD8 T-cell functional defects, we used flow cytometry to characterize further the properties of the CD3zeta-down-modulated subset. HIV-specific CD8 T cells, identified by tetramer staining, are CD3zeta(-). CD8 T cells with down-modulated CD3zeta also do not express the key costimulatory receptor CD28 and have the cell surface phenotype of activated or memory T cells (HLA-DR(+) CD62L(-)). After T-cell activation, CD3zeta-down-modulated cells express the activation marker CD69 but not the high-affinity interleukin 2 (IL-2) receptor alpha-chain CD25 and produce gamma interferon but not IL-2. Therefore HIV-specific CD8 T cells have down-modulated key signaling molecules for T-cell activation and costimulation and require exogenous cytokine stimulation. The typical impairment of HIV-specific CD4 T helper cells, which would normally provide specific CD8 T-cell stimulation, means that in vivo CTL function in vivo is compromised in most HIV-infected individuals. In AIDS patients, the functional defect is more severe, since CD3zeta is not reexpressed even after IL-2 exposure.

Simplified method to generate large quantities of dendritic cells suitable for clinical applications

The present study describes the optimization of an in vitro culture method for generating large amounts of dendritic cells (DC) in serum-free conditions from leukapheresis containing a mixed population of peripheral blood mononuclear cells (PBMC) which are cultured in the presence of GM-CSF and IL-13. Initial comparisons between the generation of DC from bulk and monocyte-enriched leukapheresis products showed that the presence of lymphocytes during the culture favors the differentiation of monocytes into DC. DC yields obtained from mixed mononuclear cell cultures were between 38 and 54% higher than yields obtained from monocyte-enriched cultures. Both types of cultures resulted in the generation of DC with an immature phenotype (CD83- and high phagocytic activity), which have been previously shown to be good stimulators for T cell responses. DC yields of bulk cultures in serum-free conditions were significantly higher than those obtained in the presence of 2% human serum. The cytokines of the supernatants of serum-free cultures comprised a significant content of pro-inflammatory cytokines such as IL-1, IL-12 and TNF-alpha. Maturation of DC generated by this method can be induced by treatment with double-stranded RNA, LPS or TNF-alpha, resulting in enhanced surface expression of CD80, CD86, CD40, CD83 and MHC molecules on the DC. The methodology described here offers the possibility for generating large amounts of clinical grade DC from bulk leukapheresis products, thus avoiding DC precursor purification steps, and thereby minimizing the risks of contamination. This culture process may be applied to cell-based therapeutic approaches for the treatment of cancer or chronic viral infections.

Monoclonal antibodies and the FACS: complementary tools for immunobiology and medicine

The histories of monoclonal antibodies and the fluorescence activated cell sorter (FACS) are as closely intertwined as their current uses in biology and medicine. Here, Leonore Herzenberg, Stephen De Rosa and Leonard Herzenberg recount the meeting and the mating of these two technologies, whose offspring now populate clinical and research laboratories throughout the world.

Role of CD8 T cells in mycobacterial infections

The interaction between IFN-gamma-secreting CD4+ T cells and macrophages has long been established as integral in the protective immune response against tuberculosis. More recently, evidence from murine experiments and human studies has begun to demonstrate an essential role for MHC class I restricted CD8+ T cells in this immune response. CD8+ T cells can produce the protective cytokines IFN-gamma and TNF-alpha in addition to their classical cytolytic functions. However, the exact protective mechanisms and antigens recognized by these important cells remain poorly characterized.

Functions of tetramer-stained HIV-specific CD4(+) and CD8(+) T cells

Significant insight has been gained into constraints on the sensitivity and specificity of staining with class I tetramers. The function of the populations that are defined varies with the clinical situation. Insight has also been gained into the determinants of the CD8(+) T cell response during primary and chronic HIV infection. Human class II tetramers have been synthesised but their role in defining CD4(+) T cell function in HIV infection remains to be determined.

Eradication of established tumors by CD8+ T cell adoptive immunotherapy

We generated the DUC18 T cell receptor transgenic mouse expressing an H-2Kd -restricted transgenic T cell receptor specific for the syngeneic CMS5 fibrosarcoma rejection antigen mutated ERK2(136-144). DUC18 mice were capable of specifically eliminating lethal CMS5 tumor challenges, and transfer of DUC18 splenocytes to naive nontransgenic recipients conferred protection from subsequent and established CMS5 tumor burdens. Eradication of established tumor burdens by adoptive transfer of DUC18 splenocytes was dose and time dependent. Transferred tumor-specific T cells remained functional in vivo and capable of rejecting small tumors even in the presence of large, established tumor burdens. These findings highlight the kinetic battle between tumor growth and the production of a tumor-specific response and have critical implications for effective adoptive immunotherapy.

Evaluation of CD8(+) T-cell frequencies by the Elispot assay in healthy individuals and in patients with metastatic melanoma immunized with tyrosinase peptide

The lack of reproducible, quantitative assays for T-cell responses has been a limitation in the development of cancer vaccines to elicit T-cell immunity. We utilized the Elispot assay, which allows a quantitative and functional assessment of T cells directed against specific peptides after only brief in vitro incubations. CD8(+) T-cell reactivity was determined with an interferon (IFN)-gamma Elispot assay detecting T cells at the single cell level that secrete IFN-gamma. We studied both healthy individuals and patients with melanoma. Healthy HLA-A*0201-positive individuals showed a similar mean frequency of CD8(+) cells recognizing a tyrosinase peptide, YMDGTMSQV, when compared with melanoma patients prior to immunization. The frequencies of CD8(+) cells recognizing the tyrosinase peptide remained relatively constant over time in healthy individuals. Nine HLA-A*0201-positive patients with stage IV metastatic melanoma were immunized intradermally with the tyrosinase peptide together with the immune adjuvant QS-21 in a peptide dose escalation study with 3 patients per dose group. Two patients demonstrated a significant increase in the frequency of CD8(+) cells recognizing the tyrosinase peptide during the course of immunization, from approx. 1/16,000 CD8(+) T cells to approx. 1/4,000 in the first patient and from approx. 1/14,000 to approx. 1/2,000 in the second patient. These results demonstrate that modest expansion of peptide-specific CD8(+) T cells can be generated in vivo by immunization with peptide plus QS-21 in at least a subset of patients with melanoma.

Dynamics of HIV-specific CD8+ T lymphocytes with changes in viral load.The RESTIM and COMET Study Groups

The influence of HIV burden variations on the frequencies of Ag-specific CD8+ T cell responses was evaluated before and during highly active antiretroviral therapy by analyzing the number, diversity, and function of these cells. The frequencies of HLA-A2-restricted CD8+ PBL binding HLA-A2/HIV-epitope tetramers or producing IFN-gamma were below 1%. A panel of 16 CTL epitopes covering 15 HLA class I molecules in 14 patients allowed us to test 3.8 epitopes/patient and to detect 2.2 +/- 1.8 HIV epitope-specific CD8+ subsets per patient with a median frequency of 0.24% (0.11-4. 79%). During the first month of treatment, viral load rapidly decreased and frequencies of HIV-specific CD8 PBL tripled, eight new HIV specificities appeared of 11 undetectable at entry, while CMV-specific CD8+ PBL also appeared. With efficient HIV load control, all HIV specificities decayed involving a reduction of the CD8+CD27+CD11ahigh HIV-specific effector subset. Virus rebounds triggered by scheduled drug interruptions or transient therapeutic failures induced four patterns of epitope-specific CD8+ lymphocyte dynamics, i.e., peaks or disappearance of preexisting specificities, emergence of new specificities, or lack of changes. The HIV load rebounds mobilized both effector/memory HIV- and CMV-specific CD8+ lymphocytes. Therefore, frequencies of virus-specific CD8 T cells appear to be positively correlated to HIV production in most cases during highly active antiretroviral therapy, but an inverse correlation can also be observed with rapid virus changes that might involve redistribution, sequestration, or expansion of these Ag-specific CD8 T cells. Future strategies of therapeutic interruptions should take into account these various HIV-specific cell dynamics during HIV rebounds.

CD3ζ and CD28 down-modulation on CD8 T cells during viral infection

Down-modulation of CD3ζ expression on CD8 T lymphocytes occurs, independently of other T-cell receptor (TCR)-CD3 components, in tumor-infiltrating lymphocytes, human immunodeficiency virus infection, and autoimmune disease. These associations suggest that it might be related to chronic antigenic stimulation. CD3ζ down-modulation was found, however, in CD8 T cells that proliferate in response to acute viral infections. In 3 otherwise healthy donors with acute gastroenteritis, infectious mononucleosis, and Epstein–Barr virus/cytomegalovirus/mononucleosis, 30% to 60% of circulating CD8 T cells had down-modulated CD3ζ to below the level of detection. The CD3ζ-T cells were also CD28− but expressed the activation markers HLA-DR and CD57. CD3ζ–CD28– T cells are effector CTL because they express perforin and produce IFN-γ, but not IL-2, on activation and contain the viral-specific cytotoxic T lymphocyte (CTL). However, CD3ζ–CD28–T cells generally do not express CD25 after anti-CD3 and anti-CD28 stimulation and are not cytotoxic until they are cultured with IL-2 overnight. Cytotoxicity coincides with the re-expression of CD3ζ but not CD28. Down-modulation of CD3ζ and CD28 on effector CTL may control CTL triggering and proliferation to prevent immunopathogenesis.

CD3ζ and CD28 down-modulation on CD8 T cells during viral infection

Down-modulation of CD3ζ expression on CD8 T lymphocytes occurs, independently of other T-cell receptor (TCR)-CD3 components, in tumor-infiltrating lymphocytes, human immunodeficiency virus infection, and autoimmune disease. These associations suggest that it might be related to chronic antigenic stimulation. CD3ζ down-modulation was found, however, in CD8 T cells that proliferate in response to acute viral infections. In 3 otherwise healthy donors with acute gastroenteritis, infectious mononucleosis, and Epstein–Barr virus/cytomegalovirus/mononucleosis, 30% to 60% of circulating CD8 T cells had down-modulated CD3ζ to below the level of detection. The CD3ζ-T cells were also CD28− but expressed the activation markers HLA-DR and CD57. CD3ζ–CD28– T cells are effector CTL because they express perforin and produce IFN-γ, but not IL-2, on activation and contain the viral-specific cytotoxic T lymphocyte (CTL). However, CD3ζ–CD28–T cells generally do not express CD25 after anti-CD3 and anti-CD28 stimulation and are not cytotoxic until they are cultured with IL-2 overnight. Cytotoxicity coincides with the re-expression of CD3ζ but not CD28. Down-modulation of CD3ζ and CD28 on effector CTL may control CTL triggering and proliferation to prevent immunopathogenesis.

Dendritic cells in cancer immunotherapy

The potential to harness the potency and specificity of the immune system underlies the growing interest in cancer immunotherapy. One such approach uses bone marrow-derived dendritic cells, phenotypically distinct and extremely potent antigen-presenting cells, to present tumor-associated antigens and thereby generate tumor-specific immunity. Support for this strategy comes from animal studies that have demonstrated that dendritic cells, when loaded ex vivo with tumor antigens and administered to tumor-bearing hosts, can elicit T cell-mediated tumor destruction. These observations have led to clinical trials designed to investigate the immunologic and clinical effects of antigen-loaded dendritic cells administered as a therapeutic vaccine to patients with cancer. In the design and conduct of such trials, important considerations include antigen selection, methods for introducing the antigen into MHC class I and II processing pathways, methods for isolating and activating dendritic cells, and route of administration. Although current dendritic cell-based vaccination methods are cumbersome, promising results from clinical trials in patients with malignant lymphoma, melanoma, and prostate cancer suggest that immunotherapeutic strategies that take advantage of the antigen presenting properties of dendritic cells may ultimately prove both efficacious and widely applicable to human tumors.

Maintenance of large numbers of virus-specific CD8+ T cells in HIV-infected progressors and long-term nonprogressors

The virus-specific CD8+ T cell responses of 21 HIV-infected patients were studied including a unique cohort of long-term nonprogressors with low levels of plasma viral RNA and strong proliferative responses to HIV Ags. HIV-specific CD8+ T cell responses were studied by a combination of standard cytotoxic T cell (CTL) assays, MHC tetramers, and TCR repertoire analysis. The frequencies of CD8+ T cells specific to the majority of HIV gene products were measured by flow cytometric detection of intracellular IFN-gamma in response to HIV-vaccinia recombinant-infected autologous B cells. Very high frequencies (0.8-18.0%) of circulating CD8+ T cells were found to be HIV specific. High frequencies of HIV-specific CD8+ T cells were not limited to long-term nonprogressors with restriction of plasma virus. No correlation was found between the frequency of HIV-specific CD8+ T cells and levels of plasma viremia. In each case, the vast majority of cells (up to 17.2%) responded to gag-pol. Repertoire analysis showed these large numbers of Ag-specific cells were scattered throughout the repertoire and in the majority of cases not contained within large monoclonal expansions. These data demonstrate that high numbers of HIV-specific CD8+ T cells exist even in patients with high-level viremia and progressive disease. Further, they suggest that other qualitative parameters of the CD8+ T cell response may differentiate some patients with very low levels of plasma virus and nonprogressive disease.

Direct measurement of CD8+ T cell responses in macaques infected with simian immunodeficiency virus

The simian immunodeficiency virus (SIV) macaque model system has been used extensively to study AIDS pathogenesis and to test candidate vaccines for their ability to protect against homologous or heterologous challenge with pathogenic SIV or SHIV. Recent studies suggest that stimulation of HIV-1-specific CTL responses is important for effective vaccination against HIV-1. While quantitative measurements of SIV-specific cytotoxic T lymphocyte (CTL) responses have been facilitated by the use of tetrameric peptide complexes, this technique is currently limited to the study of Mamu-A*01-positive rhesus macaques. Furthermore, very few SIV-specific CTL epitopes have been identified, and there is limited identification of other MHC alleles in macaques. In this study, cytokine flow cytometry (CFC) was used to quantify SIV-specific CD8+ antigen-reactive T cells in macaques infected with SIV. We found a strong correlation (r = 0.96, P < 0.001) between CD8+ antigen-reactive T cells stained with the Mamu-A*01 p11C, C-M tetramer and production of intracellular TNF-alpha in the CFC assay. Furthermore, the CFC assay was used to identify a novel SIV-specific CTL epitope in Envelope (SIV Env, a.a. 486-494, sequence AEVAELYRL). The use of the CFC assay facilitates the study of antigen-reactive T cell responses in SIV infection and vaccination.

HIV-specific CD8(+) T cells produce antiviral cytokines but are impaired in cytolytic function

The use of peptide-human histocompatibility leukocyte antigen (HLA) class I tetrameric complexes to identify antigen-specific CD8(+) T cells has provided a major development in our understanding of their role in controlling viral infections. However, questions remain about the exact function of these cells, particularly in HIV infection. Virus-specific cytotoxic T lymphocytes exert much of their activity by secreting soluble factors such as cytokines and chemokines. We describe here a method that combines the use of tetramers and intracellular staining to examine the functional heterogeneity of antigen-specific CD8(+) T cells ex vivo. After stimulation by specific peptide antigen, secretion of interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, macrophage inflammatory protein (MIP)-1beta, and perforin is analyzed by FACS((R)) within the tetramer-positive population in peripheral blood. Using this method, we have assessed the functional phenotype of HIV-specific CD8(+) T cells compared with cytomegalovirus (CMV)-specific CD8(+) T cells in HIV chronic infection. We show that the majority of circulating CD8(+) T cells specific for CMV and HIV antigens are functionally active with regards to the secretion of antiviral cytokines in response to antigen, although a subset of tetramer-staining cells was identified that secretes IFN-gamma and MIP-1beta but not TNF-alpha. However, a striking finding is that HIV-specific CD8(+) T cells express significantly lower levels of perforin than CMV-specific CD8(+) T cells. This lack of perforin is linked with persistent CD27 expression on HIV-specific cells, suggesting impaired maturation, and specific lysis ex vivo is lower for HIV-specific compared with CMV-specific cells from the same donor. Thus, HIV-specific CD8(+) T cells are impaired in cytolytic activity.

The evolving role of dendritic cell therapy in urologic oncology

The recognition that dendritic cells, the most potent antigen-presenting cells, play a pivotal role in the induction of antitumor immunity has reshaped the development of tumor vaccines in clinical medicine. Early clinical trials of administration of dendritic cell-based vaccines to patients with genitourinary malignancies showed low toxicity profiles, and provided evidence for immunologic and clinical responses in some patients. Although the development of dendritic cell-based vaccines is still in its infancy, the prospects of ultimately generating clinically effective cancer vaccines have become more realistic.

Long-term survival of anti-tumor lymphocytes generated by vaccination of patients with melanoma with a peptide vaccine

Immunization with the modified gp100 melanoma peptide gp100:109-217 (210M) in Incomplete Freund's Adjuvant (IFA) results in the generation of antipeptide and antitumor lymphocytes in the patients' circulation. In this study, the authors have evaluated the persistence of these immune cells. Reactivity against the native peptide persisted for 138 to 403 days after immunization. Reactivity also persisted in three of five patients that received external beam radiotherapy and in both patients who received systemic chemotherapy after the completion of peptide immunization. Thus, immune lymphocytes with anti gp100:209-217 peptide activity appear to persist for prolonged periods after vaccination with modified peptide in IFA.

Characterization of CMVpp65-specific CD8+ T lymphocytes using MHC tetramers in kidney transplant patients and healthy participants

BACKGROUND

Cytomegalovirus (CMV) is a ubiquitous herpesvirus that infects 50-90% of individuals in different populations. After primary infection, the virus persists latently in myeloid cells under the control of specific T-cells. Reactivation of CMV infection may cause lethal organ dysfunction and is frequently seen in immunosuppressed individuals. CD8+ cytotoxic T-cells (CTL) have a primary role in suppressing CMV reactivation, and the dominating CTL response is directed against pp65.

METHODS

MHC tetramers, that is, complexes between HLA class I (or class II) molecules and antigenic peptides conjugated to fluorochromes allow the direct visualization of antigen-specific receptor-carrying T-cells using flow cytometry. We constructed a novel MHC tetramer for identification of CMVpp65-specific CD8+ T-cells using HLA-A2 molecules folded with the immunodominant NLVPMVATV peptide.

RESULTS

The A2/pp65 tetramer specifically stained CMV-directed T-cell lines, and sorted cells showed CMV-specific cytotoxicity. High proportions (0.1-9%) of the CD8+ T-cells were A2/pp65 tetramer+ in healthy HLA-A2+ CMV carriers and in immunosuppressed kidney transplant patients with latent infection. Patients with reactivated CMV infection exhibited up to 15% A2/pp65 tetramer+ cells, which seemed to correlate with CMV load over time. A2/pp65 tetramer+ cells expressed T-cell activation markers.

CONCLUSIONS

The construction of a novel A2/pp65 MHC tetramer enabled the design of a rapid and precise flow cytometric method allowing quantitative and qualitative analysis of CMV-specific T-cells. The number of A2/pp65 tetramer binding CTLs in blood may prove to be clinically relevant in assessing the immune response to CMV.

An overview of cancer immunotherapy

The survival of patients with cancer has improved steadily but incrementally over the last century, with the advent of effective anticancer treatments such as chemotherapy and radiotherapy. However, the majority of patients with metastatic disease will not be cured by these measures and will eventually die of their disease. New and more effective methods of treating these patients are required urgently. The immune system is a potent force for rejecting transplanted organs or microbial pathogens, but effective spontaneous immunologically induced cancer remissions are very rare. In recent years, much has been discovered about the mechanisms by which the immune system recognizes and responds to cancers. The specific antigens involved have now been defined in many cases. Improved adjuvants are available. Means by which cancer cells overcome immunological attack can be exploited and overcome. Most importantly, the immunological control mechanisms responsible for initiating and maintaining an effective immune response are now much better understood. It is now possible to manipulate immunological effector cells or antigen-presenting cells ex vivo in order to induce an effective antitumour response. At the same time, it is possible to recruit other aspects of the immune system, both specific (e.g. antibody responses) and innate (natural killer cells and granulocytes).

Immune selection in neoplasia: towards a microevolutionary model of cancer development

The dual properties of genetic instability and clonal expansion allow the development of a tumour to occur in a microevolutionary fashion. A broad range of pressures are exerted upon a tumour during neoplastic development. Such pressures are responsible for the selection of adaptations which provide a growth or survival advantage to the tumour. The nature of such selective pressures is implied in the phenotype of tumours that have undergone selection. We have reviewed a range of immunologically relevant adaptations that are frequently exhibited by common tumours. Many of these have the potential to function as mechanisms of immune response evasion by the tumour. Thus, such adaptations provide evidence for both the existence of immune surveillance, and the concept of immune selection in neoplastic development. This line of reasoning is supported by experimental evidence from murine models of immune involvement in neoplastic development. The process of immune selection has serious implications for the development of clinical immunotherapeutic strategies and our understanding of current in vivo models of tumour immunotherapy.

High frequency of autologous anti-melanoma CTL directed against an antigen generated by a point mutation in a new helicase gene

We have identified an Ag recognized by autologous CTL on the melanoma cells of a patient who enjoyed an unusually favorable clinical evolution. The antigenic peptide, which is presented by HLA-A28 molecules, is encoded by a mutated sequence in a new gene. This gene, which was named MUM-3, is expressed ubiquitously and shows homology with the RNA helicase gene family. Limiting dilution analysis indicated that at least 0.15% of the blood CD8 T cells were tumor-specific CTL precursors. The MUM-3 Ag was recognized by 90% of these CTL, indicating that it is the dominant target Ag of the tumor-specific CTL response. The high frequency of anti-MUM-3 CTL was confirmed with tetramers of soluble HLA-A28 molecules loaded with the antigenic peptide. MUM-3 tetramers stained 1.2% of blood CD8 cells, a frequency that has never been reported for T cells directed against a strictly tumor-specific Ag. To confirm these results, the CD8 T cells that were clearly labeled with tetramers were restimulated in clonal conditions. About 90% of these cells proliferated, and all the resulting clones proved lytic and MUM-3 specific. By improving the conditions used for the in vitro restimulation of CTL precursors by the tumor cells, the same frequency could be obtained in limiting dilution analysis. These results show that some cancer patients have a high frequency of circulating CTL that are directed against a strictly tumor-specific Ag. These CTL are responsive to restimulation in vitro and are easily detected with tetramers. Such responses may therefore be an achievable goal for therapeutic vaccination with tumor-specific Ags.

Phase I study in melanoma patients of a vaccine with peptide-pulsed dendritic cells generated in vitro from CD34(+) hematopoietic progenitor cells

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that can be used for vaccination purposes, to induce a specific T-cell response in vivo against melanoma-associated antigens. We have shown that the sequential use of early-acting hematopoietic growth factors, stem cell factor, IL-3 and IL-6, followed by differentiation with IL-4 and granulocyte-macrophage colony-stimulating factor allows the in vitro generation of large numbers of immature DCs from CD34(+) peripheral blood progenitor cells. Maturation to interdigitating DCs could specifically be induced within 24 hr by addition of TNF-alpha. Here, we report on a phase I clinical vaccination trial in melanoma patients using peptide-pulsed DCs. Fourteen HLA-A1(+) or HLA-A2(+) patients received at least 4 i.v. infusions of 5 x 10(6) to 5 x 10(7) DCs pulsed with a pool of peptides including either MAGE-1, MAGE-3 (HLA-A1) or Melan-A, gp100, tyrosinase (HLA-A2), depending on the HLA haplotype. A total of 83 vaccinations were performed. Clinical side effects were mild and consisted of low-grade fever (WHO grade I-II). Clinical and immunological responses consisted of anti-tumor responses in 2 patients, increased melanoma peptide-specific delayed-type hypersensitivity reactions in 4 patients, significant expansion of Melan-A- and gp100-specific cytotoxic T lymphocytes in the peripheral blood lymphocytes of 1 patient after vaccination and development of vitiligo in another HLA-A2(+) patient. Our data indicate that the vaccination of peptide-pulsed DCs is capable of inducing clinical and systemic tumor-specific immune responses without provoking major side effects.

Analysis of successful immune responses in persons infected with hepatitis C virus

Although hepatitis C virus (HCV) infection is very common, identification of patients during acute infection is rare. Consequently, little is known about the immune response during this critical stage of the disease. We analyzed the T lymphocyte response during and after acute resolving HCV infection in three persons, using interferon (IFN)-gamma enzyme-linked immunospot (ELISPOT) and human histocompatibility leukocyte antigen (HLA) peptide tetramer assays. Acute infection was associated with a broadly directed T helper and cytotoxic T lymphocyte (CTL) response, which persisted after resolution of clinical hepatitis and clearance of viremia. At the earliest time point studied, highly activated CTL populations were observed that temporarily failed to secrete IFN-gamma, a "stunned" phenotype, from which they recovered as viremia declined. In long-term HCV-seropositive persons, CTL responses were more common in persons who had cleared viremia compared with those with persistent viremia, although the frequencies of HCV-specific CTLs were lower than those found in persons during and after resolution of acute HCV infection. These studies demonstrate a strong and persistent CTL response in resolving acute HCV infection, and provide rationale to explore immune augmentation as a therapeutic intervention in chronic HCV infection.

Immunotherapy with dendritic cells directed against tumor antigens shared with normal host cells results in severe autoimmune disease

Vaccination with dendritic cells (DCs) presenting tumor antigens induces primary immune response or amplifies existing cytotoxic antitumor T cell responses. This study documents that antitumor treatment with DCs may cause severe autoimmune disease when the tumor antigens are not tumor-specific but are also expressed in peripheral nonlymphoid organs. Growing tumors with such shared tumor antigens that were, at least initially, strictly located outside of secondary lymphoid organs were successfully controlled by specific DC vaccination. However, antitumor treatment was accompanied by fatal autoimmune disease, i.e., autoimmune diabetes in transgenic mice expressing the tumor antigen also in pancreatic beta islet cells or by severe arteritis, myocarditis, and eventually dilated cardiomyopathy when arterial smooth muscle cells and cardiomyocytes expressed the transgenic tumor antigen. These results reveal the delicate balance between tumor immunity and autoimmunity and therefore point out important limitations for the use of not strictly tumor-specific antigens in antitumor vaccination with DCs.

T-cell recognition of melanoma-associated antigens

In this review, we summarize the significant progress that has been made in the identification of melanoma-associated antigens (MAA) recognized by cytotoxic T-lymphocytes (CTL). These antigens belong to three main groups: tumor-associated testis-specific antigens (e.g. , MAGE, BAGE, and GAGE); melanocyte differentiation antigens (e.g., tyrosinase, Melan-A/MART-1); and mutated or aberrantly expressed molecules (e.g, CDK4, MUM-1, beta-catenin). Although strong CTL activity may be induced ex vivo against most of these antigens, often in the presence of excess cytokines and antigen, a clear understanding of the functional status of CTL in vivo and their impact on tumor growth, is still lacking. Several mechanisms are described that potentially contribute to tumor cell evasion of the immune response, suggesting that any antitumor efficacy achieved by immune effectors may be offset by factors that result ultimately in tumor progression. Nevertheless, most of these MAA are currently being investigated as immunizing agents in clinical studies, the conflicting results of which are reviewed. Indeed, the therapeutic potential of MAA has still to be fully exploited and new strategies have to be found in order to achieve an effective and long-lasting in vivo immune control of melanoma growth and progression.