Peptide-pulsed dendritic cells induce tumoricidal cytotoxic T lymphocytes from healthy donors against stably HLA-A*0201-binding peptides from the Melan-A/MART-1 self antigen

Dendritic Cell Vaccination in Non-Small Cell Lung Cancer: Remodeling the Tumor Immune Microenvironment

Non-small-cell lung cancer (NSCLC) remains one of the leading causes of death worldwide. While NSCLCs possess antigens that can potentially elicit T cell responses, defective tumor antigen presentation and T cell activation hinder host anti-tumor immune responses. The NSCLC tumor microenvironment (TME) is composed of cellular and soluble mediators that can promote or combat tumor growth. The composition of the TME plays a critical role in promoting tumorigenesis and dictating anti-tumor immune responses to immunotherapy. Dendritic cells (DCs) are critical immune cells that activate anti-tumor T cell responses and sustain effector responses. DC vaccination is a promising cellular immunotherapy that has the potential to facilitate anti-tumor immune responses and transform the composition of the NSCLC TME via tumor antigen presentation and cell-cell communication. Here, we will review the features of the NSCLC TME with an emphasis on the immune cell phenotypes that directly interact with DCs. Additionally, we will summarize the major preclinical and clinical approaches for DC vaccine generation and examine how effective DC vaccination can transform the NSCLC TME toward a state of sustained anti-tumor immune signaling.

Predicting peptide binding affinities to MHC molecules using a modified semi-empirical scoring function

The Major Histocompatibility Complex (MHC) plays an important role in the human immune system. The MHC is involved in the antigen presentation system assisting T cells to identify foreign or pathogenic proteins. However, an MHC molecule binding a self-peptide may incorrectly trigger an immune response and cause an autoimmune disease, such as multiple sclerosis. Understanding the molecular mechanism of this process will greatly assist in determining the aetiology of various diseases and in the design of effective drugs. In the present study, we have used the Fresno semi-empirical scoring function and modify the approach to the prediction of peptide-MHC binding by using open-source and public domain software. We apply the method to HLA class II alleles DR15, DR1, and DR4, and the HLA class I allele HLA A2. Our analysis shows that using a large set of binding data and multiple crystal structures improves the predictive capability of the method. The performance of the method is also shown to be correlated to the structural similarity of the crystal structures used. We have exposed some of the obstacles faced by structure-based prediction methods and proposed possible solutions to those obstacles. It is envisaged that these obstacles need to be addressed before the performance of structure-based methods can be on par with the sequence-based methods.

Impact of transfection with total RNA of K562 cells upon antigen presenting, maturation, and function of human dendritic cells from peripheral blood mononuclear cells

BACKGROUND

Vaccination of dendritic cells (DCs) with tumor antigens is a potential strategy to induce tumor-specific immunity in tumor-bearing patients. The purpose of this study was to investigate whether human monocyte-derived DCs were able to present P210(Bcr-Ab1) protein and induce antigen-specific cytotoxic T lymphocyte (CTL) responses in vitro after transfected with total RNA of K562 cells (K562-RNA).

STUDY DESIGN AND METHODS

DCs derived from human peripheral blood mononuclear cells were transfected with K562-RNA with electroporation or DOTAP lipofection. The successful transfection was determined by reverse transcription-polymerase chain reaction and Western blot. The phenotypes of the DCs were analyzed by flow cytometry (FCM), and cytotoxicity of CTL was assessed by propidium iodide staining followed by FCM analysis. The CD1a expression and purity of DCs were measured by FCM.

RESULTS

The Bcr-Abl fusion gene was detected in the DCs with 24 hours after the transfection. The transfected cell expressed increased levels of CD80, CD83, CD86, and HLA-DR. Moreover, the transfected DCs strongly stimulated the T lymphocytes to gain cytotoxic activity against K562 cells. Culture medium containing 1 percent human plasma was the most effective for DC growth.

CONCLUSION

Human DCs transfected with K562-RNA effectively induce specific immune responses. This method can be used to induce tumor-specific immune response and may have potential application in immunotherapy of tumors.

Identification of a major histocompatibility complex class I-restricted T-cell epitope in the tumour-associated antigen, 5T4

5T4 is a surface glycoprotein expressed on placental trophoblasts and also on a wide range of human carcinomas. Its highly restricted expression on normal tissues and broad distribution on many carcinomas make 5T4 a promising target for cancer immunotherapy. In the current study, we set out to investigate whether a 5T4-specific cytotoxic T lymphocyte (CTL) repertoire exists in healthy individuals. CD4-depleted peripheral blood mononuclear cells (PBMCs) from blood donors were screened using an ex vivo interferon-gamma (IFN-gamma) enzyme-linked immunospot (ELISPOT) assay. A panel of overlapping peptides, spanning the full length of the 5T4 protein, was used as a source of antigen. In the process of screening, one out of 30 blood donors demonstrated a positive ex vivo IFN-gamma ELISPOT response to a single 5T4 peptide. A polyclonal T-cell line was derived from this donor by culturing PBMCs with autologous peptide-pulsed dendritic cells (DCs). The resulting polyclonal T-cell line and clones were tested in a 51Cr-release assay and by ELISPOT and were shown to be peptide specific. Furthermore, antigen-presenting cells (APCs), infected with a viral vector expressing 5T4, were able to stimulate IFN-gamma production by the peptide-specific T-cell clones. A minimal CD8 epitope, PLADLSPFA, has been identified and found to be restricted through human leucocyte antigen (HLA) Cw7. Subsequently, we have demonstrated that HLA-Cw7-positive colorectal cancer patients vaccinated with a recombinant vaccinia viral vector encoding 5T4 (TroVax) are capable of mounting a strong IFN-gamma ELISPOT response to this novel CTL epitope. These findings have potential application in cancer immunotherapy in terms of subunit vaccine design and the monitoring of immune responses induced in patients by 5T4-based therapies.

Adoptive transfer of tumor-reactive Melan-A-specific CTL clones in melanoma patients is followed by increased frequencies of additional Melan-A-specific T cells

In this study, we report the adoptive transfer of highly tumor-reactive Melan-A-specific T cell clones to patients with metastatic melanoma, and the follow-up of these injected cells. These clones were generated from HLA-A*0201 patients by in vitro stimulations of total PBMC with the HLA-A*0201-binding Melan-A peptide analog ELAGIGILTV. Ten stage IV melanoma patients were treated by infusion of these CTL clones with IL-2 and IFN-alpha. The generated T cell clones, of effector/memory phenotype were selected on the basis of their ability to produce IL-2 in response to HLA-A*0201 Melan-A-positive melanoma lines. Infused clones were detected, by quantitative PCR, in the blood of three patients for periods ranging from 7 to 60 days. Six patients showed regression of individual metastases or disease stabilization, and one patient experienced a complete response, but no correlation was found between the detection of the infused clones in PBMC or tumor samples and clinical responses. Nonetheless, frequencies of Melan-A/A2-specific lymphocytes, measured by tetramer labeling, increased after treatment in most patients. In one of these patients, who showed a complete response, this increase corresponded to the expansion of new clonotypes of higher avidity than those detected before treatment. Together, our results suggest that infused CTL clones may have initiated an antitumor response that may have resulted in the expansion of a Melan-A-specific CTL repertoire.

Development and validation of a fluorescence polarization-based competitive peptide-binding assay for HLA-A*0201--a new tool for epitope discovery

Various approaches are currently proposed to successfully develop therapies for the prevention and treatment of infectious diseases and cancer. One of the most promising approaches is the development of vaccines that elicit cytotoxic T lymphocyte (CTL) responses. Consequently, identification and exact definition of molecular parameters involved in peptide-MHC class-I interactions of putative CTL epitopes are of prime importance for the development of immunomodulating compounds. To better facilitate epitope discovery, we developed and validated a novel state-of-the-art biochemical HLA-A0201 assay, which is comprised of technologically advanced cutting edge reagents. The technique is based on competition and uses a FITC-labeled reference peptide and highly purified soluble HLA-A0201 molecules to quantitatively measure the binding capacity of nonlabeled peptide candidates. Detection by fluorescence polarization allows real-time measurement of binding ratios without separation steps. During standardization, the problem of assay parameter variation is discussed, showing the dramatic influence of HLA and reference peptide concentrations as well as the choice of the reference peptide itself on IC(50) determinations. For validation, a panel of 15 well-defined HLA-A0201 ligands from various sources covering a broad range of binding affinities was tested. Binding data were used to compare against pre-existing quantitative assay systems. The results obtained demonstrated significant correlation among assay procedures, suggesting that the application of fluorescence polarization in combination with recombinant sHLA molecules is highly advantageous for the accurate assessment of peptide binding. Furthermore, the assay also features high-throughput screening capacity, providing uniquely efficient means of identifying and evaluating immune target molecules.

Modulation of the CD8+-T-cell response by CD4+ CD25+ regulatory T cells in patients with hepatitis B virus infection

CD4+ CD25+ regulatory T cells have been shown to maintain peripheral tolerance against self and foreign antigens. In this study we analyzed the effect of circulating CD4+ CD25+ T cells on CD8+-T-cell responses of patients with chronic and resolved hepatitis B virus (HBV) infection. We demonstrated that circulating CD4+ CD25+ T cells modulate the function and expansion of HBV-specific CD8+ cells ex vivo in all patients, regardless of whether they have chronic or resolved HBV infection. The possible role of CD4+ CD25+ T cells in the pathogenesis of chronic HBV infection is not supported by these data. However, these results might have implications for optimizing future immunotherapeutic approaches to HBV treatment.

A pilot clinical trial of vaccination with dendritic cells pulsed with autologous tumor cells derived from malignant pleural effusion in patients with late-stage lung carcinoma

BACKGROUND

The authors conducted a pilot clinical trial to explore the vaccination of patients with late-stage lung carcinoma with dendritic cells (DCs) pulsed with necrotic tumor cells derived from malignant pleural effusion specimens, and to evaluate the antitumor immune response induced by this therapy.

METHODS

Autologous DCs were generated by culturing adherent mononuclear cells with interleukin-4 and granulocyte-macrophage-colony-stimulating factor for 7 days. Day-7 DCs were cocultured overnight with autologous necrotic tumor cells derived from pleural effusion specimens to allow internalization of tumor antigens. DCs were then treated with tumor necrosis factor-alpha for 16 hours. The antigen-loaded DCs were injected into each patient's inguinal lymph nodes under sonographic guidance. Eight patients with late-stage nonsmall cell lung carcinoma were treated in this manner. Patients were vaccinated once weekly for 4 weeks and then boosted twice biweekly.

RESULTS

The authors found that there was no Grade II/III toxicity and autoimmune response in all patients after intranodal injection of the DC vaccine. Minor to moderate increases in T-cell responses against tumor antigens were observed after DC vaccination in six of eight patients. Five patients had progressive disease. One patient had minor tumor response and two patients had stable disease. The two patients who had longer disease control also had better T-cell responses.

CONCLUSIONS

The results indicated that it was feasible to immunize patients with lung carcinoma intranodally with DCs pulsed with necrotic tumor cells enriched from pleural effusion specimens, and this approach may generate T-cell responses and provide clinical benefit in some patients.

In vivo expansion of the residual tumor antigen-specific CD8+ T lymphocytes that survive negative selection in simian virus 40 T-antigen-transgenic mice

Mice that express the viral oncoprotein simian virus 40 (SV40) large T antigen (T-Ag) as a transgene provide useful models for the assessment of the state of the host immune response in the face of spontaneous tumor progression. Line SV11 (H2(b)) mice develop rapidly progressing choroid plexus tumors due to expression of full-length T-Ag from the SV40 promoter. In addition, T-Ag expression in the thymus of SV11 mice results in the deletion of CD8(+) T cells specific for the three H2(b)-restricted immunodominant epitopes of T-Ag. Whether CD8(+) T cells specific for the immunorecessive H2-D(b)-restricted epitope V of T-Ag survive negative selection in SV11 mice has not been determined. Immunization of SV11 mice with rVV-ES-V, a recombinant vaccinia virus expressing epitope V as a minigene, resulted in the induction of weak, but reproducible, epitope V-specific cytotoxic T-lymphocyte (CTL) responses. This weak lytic response corresponded with a decreased frequency of epitope V-specific CTL that could be recruited in SV11 mice. In addition, CTL lines derived from rVV-ES-V-immunized SV11 mice had reduced avidities compared to that seen with CTL derived from healthy mice. Despite this initial weak response, significant numbers of epitope V-specific CD8(+) T cells were detected in SV11 mice ex vivo following a priming-boosting approach and these cells demonstrated high avidity for epitope V. The results suggest that low numbers of tumor-reactive CD8(+) T cells with high avidity for epitope V survive negative selection in SV11 mice but can be expanded by specific boosting approaches in the tumor bearing host.

Early Adenoviral Gene Expression Mediates Immunosuppression by Transduced Dendritic Cell (DC): Implications for Immunotherapy Using Genetically Modified DC

Long-lasting, high-level gene expression in the absence of a toxic or inflammatory response to viral Ags is necessary for the successful application of genetically modified dendritic cell (DC). We previously demonstrated that efficient transduction of mature DC using DeltaE1DeltaE3 adenoviruses suppressed their stimulatory capacity for T cells. The current study was designed to investigate in more detail the suppressive effect of Ad-DC. We demonstrate that immunosuppression is not mediated by alterations in the T cell phenotype or cytokine profiles released by stimulated T cells. Also DC phenotypes are not affected. However, we demonstrate a cell cycle arrest of the T cell population stimulated by adenovirally transduced DC. Surprisingly, only freshly transduced DC are perturbed in their stimulatory capacity. Experiments using cycloheximide to block early intracellular viral gene expression showed that viral genes expressed in DC are responsible for this transient immunosuppression. In agreement with these findings, high-capacity (gutless) Ad-vectors that differ in viral gene expression from conventional DeltaE1DeltaE3 adenovirus are suitable for an efficient transduction of human DC. DC transduced with gutless Ad-vectors showed a high allostimulatory capacity for CD4(+) and CD8(+) T cells. Thus, the immunosuppressive effect of DeltaE1DeltaE3 Ad-transduced mature DC seems to be the result of early viral gene expression in DC that can be prevented using gutless Ad-vectors for transduction. These results have important implications for the use of genetically modified DC for therapeutic application.

Generation of melanoma-specific cytotoxic T lymphocytes for allogeneic immunotherapy

To exploit alloreactive T-cell responses known as the graft-versus-tumor effect, allogeneic hematopoietic stem cell transplantation is being explored as experimental therapy in selected solid tumors, including metastatic melanoma. However, donor T-cell responses are often delayed and associated with severe graft-versus-host disease. Posttransplant adoptive immunotherapy using tumor-specific cytotoxic T lymphocytes (CTL) of donor origin might provide immediate graft-versus-tumor effects but not graft-versus-host disease. Therefore, the aim of the current study was to define in vitro conditions for the expansion of allogeneic major histocompatibility complex-matched CTLs targeting melanoma-associated antigens (MAA). The CTLs were generated from peripheral blood mononuclear cells (PBMCs) of HLA-A*0201+ healthy donors by repetitive stimulations with HLA-A*0201-restricted MAA-derived peptides. Melanoma reactivity, as determined by lysis of peptide-pulsed T2 cells and HLA-A2+/Ag+ melanoma cells, was detected using in vitro expanded CTL targeting MAA peptides AAGIGILTV(MT(27-35)), IMDQVPFSV(G(209-2M)), and YMDGTMSQV(T(368-376)). In contrast, FLWGPRALV(MAGE3(271)-(279)) and VLPDVFIRCV(GnT-V(nt38-67)) induced peptide-specific recognition of T2 target cells only, whereas ITDQVPFSV(G(209-217)), KTWGQYWQV(G9(154)), MLLAVLYCL(T(1-9)), and tumor lysate could not induce specific CTLs. Specific cytolytic activity was accompanied by interferon-gamma secretion. Peptide-pulsed dendritic cells were required only for the initial stimulation of CTLs and could be substituted by PBMCs during restimulations. The median expansion rate of CTL was five to six times, regardless of whether dendritic cells or PBMCs were used after the initial stimulation. The results delineate the conditions for effective ex vivo expansion of melanoma-specific CTLs from PBMCs of healthy donors to be used as an adjunct in allogeneic cell therapy of metastatic melanoma.

Priming of T cells with Ad-transduced DC followed by expansion with peptide-pulsed DC significantly enhances the induction of tumor-specific CD8+ T cells: implications for an efficient vaccination strategy

In recent years, vaccination strategies using antigen-presenting cells (APC) have been under investigation. Antigen delivery using genetic immunization through ex vivo transduction of dendritic cells (DC) is supposed to enhance the induction of antitumor responses in humans by activating a broad range of peptide-specific CD8+ T cells. In this study, we compared the potential of adenoviral (Ad)-transduced versus peptide-pulsed DC to induce melanoma-antigen (Ag)-specific T-cell responses in vitro. Whereas gp100-peptide-pulsed DC induced long-lasting specific CD8+ T-cell responses against single peptides, Ad-transduced DC induced broad and strong, specific immunity against various peptides of the gp100-Ag. Surprisingly, several restimulations led to decreasing gp100-specific and in parallel to increasing anti-adenoviral T-cell responses. Nevertheless, those anti-adenoviral T-cell responses provided an "adjuvant" effect by inducing an early release of high amounts of IL-2/IFN-gamma, therewith enhancing CTL induction in the initiation phase. Based on these data, we suggest a prime/boost vaccination strategy in melanoma patients--combining the use of Ad-DC and peptide-pulsed DC--to obtain efficient and long-term antitumor T-cell responses.

In vitro dendritic cell-induced T cell responses to B cell chronic lymphocytic leukaemia enhanced by IL-15 and dendritic cell-B-CLL electrofusion hybrids

HLA class II-restricted proliferative and cytotoxic T cell (CTL) responses to B cell chronic lymphocytic leukaemia (B-CLL) can be generated using autologous dendritic cells (DCs) pulsed with tumour cell lysate. In this study a number of different approaches were used to optimize further the in vitro system. First, the effects of a variety of maturation agents were studied. The addition of TNF-alpha, polyriboinosinic polyribocytidylic acid (Poly(I:C)) and LPS to autologous DCs resulted in the emergence of only a small percentage of CD83+ DCs, IFN-alpha having no demonstrable effect. Only the addition of Poly(I:C) to DCs resulted in modestly increased specific cytotoxicity to B-CLL targets, IFN-alpha and LPS having no effect. Secondly, T cells were pretreated with IL-15, prior to culturing with lysate-pulsed autologous DCs. A significant increase in T cell activation (P = 0.038), IFN-gamma secretion (P = 0.030) and specific cytotoxicity to B-CLL targets (P = 0.006) was demonstrated compared to untreated T cells. Thirdly, monocyte derived DCs electrofused with B-CLL B cells were compared with lysate-pulsed DCs. T cells stimulated by fused DCs generated higher levels of specific cytotoxicity to autologous B-CLL B cell targets than those stimulated by lysate pulsed DCs (P = 0.013). Blocking studies demonstrated inhibition of this cytotoxicity by both anti-CD4 (P = 0.062) and anti-CD8 monoclonal antibodies (P = 0.018), suggesting the generation of both HLA class I- and HLA class II-restricted CTL responses. In summary, in vitro B-CLL-specific T cell responses can be enhanced further by preincubating T cells with IL-15 and using autologous fused DC-B-CLL hybrids instead of autologous lysate-pulsed DCs. These preliminary data require confirmation with larger numbers of patients. Such an approach, however, may eventually provide effective immunotherapy for treatment of B-CLL.

Cytotoxic T-lymphocyte responses in melanoma through in vitro stimulation with the Melan-A peptide analogue A27L: a qualitative analysis

Modifications in tumour antigen-derived epitopes that stabilize the major histocompatibility complex (MHC)-peptide complex result in enhanced stimulatory capacity and improved immunogenicity of the altered peptide. These epitope analogues are attractive candidates for the development of peptide-based vaccine trials. Any modification, however, in tumour antigens may induce T-cell responses that could either fail to react against the naturally occurring peptides or represent only a subset of the total antigen-specific repertoire. In the present study, we performed a critical analysis of the ability of cytotoxic T-lymphocyte (CTL) clones, derived from two melanoma patients through stimulation with the A27L peptide analogue, to cross-react with the naturally processed Melan-A/MART-1 (Melan-A) peptides in terms of T-cell receptor (TCR) affinity, functional avidity and fine antigen specificity. We found that all the A27L-specific clones analysed possessed a very low avidity for the natural Melan-A peptides, and that their binding affinity for human leukocyte antigen (HLA) tetramers complexed with both the modified and the natural Melan-A peptides did not strictly correlate with their functional avidity. We also observed that these clones were able to cross-recognize both natural Melan-A peptides in one patient, but only one peptide in the second patient. We discuss the capability of the A27L peptide analogue to stimulate all the available Melan-A-specific repertoire.

Inhibiting effects on the induction of cytotoxic T lymphocytes by dendritic cells pulsed with lysates from acute myeloid leukemia blasts

Dendritic cells (DCs) were established from 25 patients in complete remission of acute myeloid leukemia (AML). In patients during hematopoietic regeneration following chemotherapy the yield of DC was comparable to that of healthy donors. In patients, more than 2 months after chemotherapy, significantly less DC were generated. Comparison of the antigen-presenting capacity using tetanus toxoid of six AML patients and six healthy volunteers did not show significant differences. In six AML patients, lymphocytes stimulated with blast cell lysate pulsed DC were analyzed for cytotoxic activity against autologous blast cells. 8.4-35.6% of autologous blast cells were lysed by DC stimulated lymphocytes. In three of the six patients maximum lysis of target cells was achieved by unpulsed DC. Thus, it seems that in some patients blast cell lysates mediate inhibitory effects, which may explain to some extend immune escape mechanisms in AML.

Efficient discovery of immune response targets by cyclical refinement of QSAR models of peptide binding

Peptides that induce and recall T-cell responses are called T-cell epitopes. T-cell epitopes may be useful in a subunit vaccine against malaria. Computer models that simulate peptide binding to MHC are useful for selecting candidate T-cell epitopes since they minimize the number of experiments required for their identification. We applied a combination of computational and immunological strategies to select candidate T-cell epitopes. A total of 86 experimental binding assays were performed in three rounds of identification of HLA-A11 binding peptides from the six preerythrocytic malaria antigens. Thirty-six peptides were experimentally confirmed as binders. We show that the cyclical refinement of the ANN models results in a significant improvement of the efficiency of identifying potential T-cell epitopes.

Rapid induction of cytotoxic T-cell response against cervical cancer cells by human papillomavirus type 16 E6 antigen gene delivery into human dendritic cells by an adeno-associated virus vector

We have shown that the pulsing of dendritic cells (DCs) with human papillomavirus type 16 (HPV-16) antigen proteins by lipofection stimulates class I-restricted cytotoxic T lymphocyte (CTL) response against primary cervical cancer cells. Also, we have shown that adeno-associated virus (AAV) was able to effectively deliver a cytokine gene into DCs. It has been our hypothesis that the delivery of antigen genes into DCs, resulting in endogenous and continuous antigen protein expression, may result in an improvement in T-cell priming by DCs. Here, DCs are pulsed (infected) with an AAV vector containing the HPV-16 E6 gene. After infection, transduced E6 gene mRNA expression and vector chromosomal integration could be identified in infected DCs. Furthermore, priming rosettes formed at early times when the AAV/E6 vector was used. Most importantly, AAV/E6 vector pulsing of DCs induced, after only 7 days of priming, a strong CTL response against primary cervical cancer cell lines, compared to bacterial E6 protein lipofection. Killing was significantly blocked by the addition of anti-MHC class I antibodies. Fluorescence-activated cell sorter (FACS) analysis of resulting primed cell populations revealed higher levels of CD8+ T cells by AAV-based pulsing, with little evidence of CD56 (NK). FACS analysis of the DC populations revealed that AAV/E6 vector-pulsed DCs had higher levels of CD80 and lower levels of CD86 than protein-pulsed DCs. These data suggest that rAAV may be appropriate for antigen pulsing of DCs for immunotherapy protocols. Finally, our protocol represents an advance in regards to the time needed for generating a CTL response compared to other techniques.

Generation in vitro of B-cell chronic lymphocytic leukaemia-proliferative and specific HLA class-II-restricted cytotoxic T-cell responses using autologous dendritic cells pulsed with tumour cell lysate

Immunotherapy using dendritic cells has shown encouraging results in both haematological and non-haematological malignancies. In this study, monocyte-derived dendritic cells from patients with B-CLL were cultured for 6 days in the presence of IL-4 and GM-CSF. Autologous B-CLL T-cells were cultured alone or with B-CLL lysate-pulsed and unpulsed autologous dendritic cells. IFN-gamma secretion was assessed using ELISA. Cytotoxicity was assessed, after 21 days in culture and re-stimulation, using flow cytometry with and without blockade by anti-HLA class I, anti-HLA class II, anti-CD4, anti-CD8 and anti-TCRalphabeta monoclonal antibodies. B-CLL T cells stimulated with B-CLL lysate-pulsed autologous dendritic cells showed a significant (P = 0.0004) increase in IFN-gamma secretion and a significant (P = 0.0008) increase in specific cytotoxicity to autologous B-cell targets, but none to autologous T cell or B cell targets from healthy individuals. B-CLL T cells cultured with (non-B-CLL) B-cell lysate-pulsed B-CLL dendritic cells showed no significant response. Pulsing dendritic cells from healthy volunteers with an autologous (non-B-CLL) B-cell lysate did not stimulate proliferation, cytokine production or cytotoxicity by autologous T cells. Pulsing B-CLL dendritic cells with allogeneic B-CLL lysates and culturing with autologous T-cells elicited cytotoxicity against autologous B-CLL targets in some cases, but not in others. Cytotoxicity was significantly reduced by blocking with anti-HLA class II (P = 0.001), anti-TCRalphabeta (P = 0.03) and anti-CD4 (P = 0.046) antibodies. Phenotyping of the responding T-cell population demonstrated the majority to be CD4 positive. Our data demonstrate that HLA class II-restricted proliferative and cytotoxic T-cell responses to B-CLL can be generated using autologous dendritic cells pulsed with tumour cell lysate.

Autologous and allogeneic high-dose therapy for melanoma

Opportunities for the treatment of melanoma with high-dose chemotherapy have been inadequately explored because of the failure of early studies to demonstrate an advantage for high doses of those agents with disease activity that could also be safely dose-escalated without excessive extramedullary toxicities. However, emerging concepts of tumor and transplantation immunology have recently coincided, providing the rationale for new strategies that exploit principles of allogeneic transplant to overcome immunologic tolerance and escape mechanisms in the tumor-bearing individual. It is hoped that this setting will provide an improved milieu for donor-derived immunotherapeutic intervention that takes advantage of shared tumor antigens with therapeutic potential shown in a variety of tumor vaccination studies.

Immunotherapy of prostate cancer

The realization that prostate cancer is an immunogenic tumor, in conjunction with the discovery of novel methods for priming the immune system to generate an antitumor response, has resulted in several new approaches for prostate cancer immunotherapy. Based on these various approaches, several human clinical trials have begun using immune-based therapies for prostate cancer. These approaches can be divided into cytokine-based therapies, tumor-associated antigen-based therapies, tumor vaccines, and dendritic cell-based therapies. This review summarizes the latest findings from each of these approaches and gives results from the few completed human clinical trials.

Generation of hepatitis C virus-specific cytotoxic T lymphocytes from healthy individuals with peptide-pulsed dendritic cells

BACKGROUND AND AIMS

In hepatitis C virus (HCV) infection, cytotoxic T lymphocytes (CTL) are involved in liver inflammation and contribute to the reduction of viral load. Antibodies for HCV-CTL precursor frequencies (CTLpf) are relatively low in chronic hepatitis C, and this may be related to the poor CTL response in vivo. The aim of this study was to assess the efficacy of dendritic cells (DC) as antigen-presenting cells in CTL generation from low CTLpf.

METHODS

To confirm the rationale of using DC to prime naive T cells, five HCV-uninfected individuals were enrolled in the study. We obtained DC by maturation from peripheral progenitors under stimulation with granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-4 and IL-1alpha. Autologous T cells were cultured with DC or concanavalin-A-induced blasts loaded with four HCV-derived peptides bearing human leukocyte antigen (HLA)-A*0201 or -A24 motifs for 28 days under IL-7 and IL-2 stimulation. The lytic activity against peptide-pulsed targets was assessed by using a [51Cr]-releasing assay.

RESULTS

The DC strongly expressed HLA class I, II, B7-1 and B7-2, but not phenotypic markers of T-, B-, natural killer (NK)-cells or monocytes. The CD8-positive, HLA-class I-restricted and HCV peptide-specific CTL were generated with DC from HLA-A antigen-matched subjects, whereas no CTL activity was detected with concavalin (Con-A) blasts. We were thus able to generate HCV specific CTL from naive precursors with peptide-pulsed DC.

CONCLUSIONS

This DC-based system can be used to generate CTL of desired antigen specificity, even from a source with low CTLpf.

Synthesis and antigenic properties of reduced peptide bond analogues of an immunodominant epitope of the melanoma MART-1 protein

Backbone modifications have been introduced into the melanoma derived peptide MART-1(27-35) to increase its binding to class I major histocompatibility complex HLA-A2 molecule, and ultimately to enhance its immunogenicity. Each analogue was obtained by replacing one peptide bond at a time in the natural epitope by the aminomethylene (CH2-NH) surrogate. All analogues displayed an increased resistance to proteolysis. Interestingly, the comparative results showed that five analogues bound more efficiently to HLA-A2 than the parent peptide. On the other hand, two pseudopeptide/HLA-A2 complexes were recognized by one melanoma-specific T cell clone. Close examination of the impact of such modifications at the molecular level provides useful supports for the rational design of stable compounds with applications in anti-tumour specific immunotherapy and in vaccine development.

Human dendritic cells transfected with either RNA or DNA encoding influenza matrix protein M1 differ in their ability to stimulate cytotoxic T lymphocytes

The use of tumor antigen loaded dendritic cells (DC) is one of the most promising approaches to induce a tumor specific immune response in vivo. Several strategies have been designed to load DC with tumor antigens. In this study, we investigated the delivery of in vitro transcribed RNA and plasmid DNA into monocyte-derived, ie non-proliferating human DC, using several nonviral transfection methods including electroporation and lipofection. Green fluorescent protein (GFP) was used as a reporter gene and influenza matrix protein 1 (M1) as a model antigen for HLA class I restricted antigen presentation. Using electroporation in combination with DNA or with RNA, up to 11% of DC were GFP-positive. Using liposomes as a vehicle for DNA transport up to 10% of the DC were GFP-positive. A significant increase in transfection efficacy, of up to 20%, was observed when GFP RNA was used in combination with liposomes. Importantly, the RNA transfected DC retained their typical morphological and immunophenotypical characteristics. In addition, DC transfected with M1 RNA were able to stimulate autologous peripheral M1-specific memory cytotoxic T lymphocytes (CTL), as well as M1-specific CTL clones. Furthermore, comparison of DNA-transfected DC with RNA-transfected DC revealed the latter to be far better stimulators of antigen-specific T cells. This RNA transfection technique consequently represents a very promising tool for future immunotherapy strategies.

Identification of a new HLA-A(*)0201-restricted T-cell epitope from the tyrosinase-related protein 2 (TRP2) melanoma antigen

For the development of peptide-based immunotherapies, the identification of additional tumor antigens and T-cell epitopes is required. Because HLA-A(*)0201 is the most common allele in Caucasians, who represent the majority of patients with melanomas, 6 peptides carrying an HLA-A(*)0201 motif were synthesized from tyrosinase-related protein-2 (TRP2) melanoma antigen and tested for binding affinity to the HLA allele using processing-defective T2 cells. These peptides were then pulsed onto autologous dendritic cells and used to stimulate in vitro CD8(+)-enriched T cells isolated from peripheral blood of HLA-A(*)02(+) healthy donors or melanoma patients for the induction of specific cytotoxic T lymphocytes (CTLs). One peptide, TRP2(288-296) (SLDDYNHLV), the best HLA-A(*)0201 binder, elicited specific CTLs from 1 of 4 patients and 3 of 4 healthy donors. The induced CTLs from the patient and from 1 donor efficiently recognized HLA-A(*)02(+) TRP2(+) melanomas as well as COS-7 cells expressing HLA-A(*)0201 and TRP2 in an HLA class I-restricted manner, as assessed by cytokine production and direct cytolysis. The remaining 2 CTL lines derived from 2 donors displayed low T-cell receptor avidity, which could lyse melanoma cells in the presence of exogenous peptide. Since TRP2 is an antigen expressed in most melanomas, identification of the TRP2/HLA-A(*)0201 peptide SLDDYNHLV may facilitate the design of present peptide-based immunotherapies for the treatment of a large fraction of melanoma patients.

Induction of cytotoxic T lymphocytes from peripheral blood of human histocompatibility antigen (HLA)-A31(+) gastric cancer patients by in vitro stimulation with antigenic peptide of signet ring cell carcinoma

Antigenic peptides have been used as a cancer vaccine in melanoma patients and have led to a drastic regression of metastatic tumors. However, few antigens have been identified in non-melanoma tumors. We recently purified a new natural antigenic peptide, designated F4. 2, by biochemical elution from a human gastric signet cell carcinoma cell line and showed that it is recognized by an autologous human histocompatibility antigen (HLA)-A31-restricted cytotoxic T lymphocyte (CTL) clone. Here we describe in vitro induction of F4. 2-specific CTLs from peripheral blood T lymphocytes of HLA-A31( +) gastric cancer patients. The T cells of seven HLA-A31( +) patients with gastric cancers were stimulated in vitro by F4.2-pulsed autologous dendritic cells which had been induced from peripheral blood of each patient by incubation in the presence of granulocyte macrophage colony-stimulating factor (GM-CSF) and IL-4. We tested the cytotoxicity of the T cells against F4.2-loaded C1R-A*31012 by a 6-h (51)Cr release assay after 3 stimulations with F4.2-pulsed dendritic cells. F4.2-specific cytotoxicity was detectable in the stimulated T cells from two of the seven HLA-A31( +) patients. Further, both F4.2-specific CTLs also lysed the gastric cancer cell line, HST-2, from which F4.2 was derived. These results suggest that F4.2 peptide may be useful as an HLA-A31-restricted peptide vaccine in certain patients with gastric cancer.

Efficient transduction of mature CD83+ dendritic cells using recombinant adenovirus suppressed T cell stimulatory capacity

We have developed a culture method for the foreign serum-free generation of highly immunostimulatory, CD83+ human dendritic cells (DC). In this study, we evaluated the feasibility and consequences of endogenously expressing antigens in mature DC using adenoviral vectors. Transduction of DC with Ad-EGFP demonstrated endogenous fluorescence in 50-85% of CD83+ DC. Ad-transduced DC stimulated the proliferation of allogeneic CD8+ and CD4+ T cells at low DC: T cell ratios. However, at high DC: T cell ratios the stimulatory capacity of Ad-transduced DC was suppressed. This immunosuppressive effect was confirmed by demonstrating that the stimulatory function of untreated DC could be suppressed in a dose-dependent manner by addition of Ad-transduced DC. Furthermore, transwell experiments suggested that direct cell contact was required. Taken together, our results demonstrate the feasibility of efficiently expressing antigens in CD83+ DC using adenoviruses. However, immunosuppressive effects must be considered and carefully studied before Ad-transduced DC are employed for clinical trials. Gene Therapy (2000) 7, 249-254.

Identification of subdominant cytotoxic T lymphocyte epitopes encoded by autologous HIV type 1 sequences, using dendritic cell stimulation and computer-driven algorithm

Conventional analysis of the cytotoxic T lymphocyte (CTL) response to HIV-1 may underestimate the true breadth of CTL epitopes recognized. This underestimation could be due to several reasons, including (1) the use of laboratory-adapted stains of HIV or consensus sequences, which would lead to the identification of only highly conserved epitopes, (2) the use of EBV-transformed B cells (B-LCLs) and vaccinia virus constructs in standard assays that may obscure low level CTL responses due to high EBV or vaccinia reactivity, and (3) relatively insensitive assays wherein PBMCs instead of professional APCs are used to stimulate CTL responses. To address these problems, we first identified an immunodominant HLA-B7-restricted CTL epitope, by standard cloning methods, in a long-term nonprogressor (LTNP). To determine whether the patient had CTLs specific for autologous viral sequences other than the dominant epitope, proviral DNA was cloned and sequenced. A matrix-based epitope algorithm (EpiMatrix) was used to identify the top 2% of peptides from the viral sequences with the highest likelihood of binding to HLA-B7. These 55 peptides were synthesized and tested for HLA-B7 binding in a T2/B7 cell line; 10 peptides were able to stabilize HLA-B7 on the cell surface. By using peptide-pulsed autologous dendritic cells as a more sensitive method of CTL stimulation, we found three additional subdominant CTL epitopes.

Immunomodulatory dendritic cells generated from nonfractionated bulk peripheral blood mononuclear cell cultures induce growth of cytotoxic T cells against renal cell carcinoma

Dendritic cells (DCs) loaded with tumor antigens have the potential to become a powerful tool for clinical cancer treatment. Recently, the authors showed that a tumor-specific immune response can be elicited in culture via stimulation with autologous renal tumor lysate (Tuly)-loaded DCs that were generated from cytokine-cultured adherent peripheral blood mononuclear cells (PBMCs). Here, the authors show that immunomodulatory DCs can be generated directly from nonfractionated bulk PBMC cultures. Kinetic studies of DC differentiation and maturation in PBMC cultures were performed by monitoring the acquisition of DC-associated molecules using fluorescence-activated cell sorting analysis to determine the percentage of positive immunostained cells and the mean relative linear fluorescence intensity (MRLFI). Compared with conventional adherent CD14+ cultures, which have mostly natural killer, T, and B cells removed before cytokine culture, bulk PBMC cultures exhibited an early loss of CD14+ cells (day 0 = 78.8%, day 2 = 29.6% versus day 0 = 74%, day 2 = 75%) with an increase in yield of mature DCs (DC19- CD83+) (day 5 = 17%, day 6 = 21%, day 7 = 22% versus day 5 = 11%, day 6 = 15%, day 7 = 23%). Although a comparable percentage of DCs expressing CD86+ (B7-2), CD40+, and HLA-DR+ were detected in both cultures, higher expression levels were detected in DCs derived from bulk culture (CD86 = MRLFI 3665.1 versus 2662.1 on day 6; CD40 = MRLFI 1786 versus 681.2 on day 6; HLA-DR = MRLFI 6018.2 versus 3444.9 on day 2). Cytokines involved in DC maturation were determined by polymerase chain reaction demonstrating interleukin-6 (IL-6), IL-12, interferon-gamma, granulocyte-macrophage colony-stimulating factor, and tumor necrosis factor-alpha mRNA expression by bulk culture cells during the entire 9-day culture period. This same cytokine mRNA profile was not found in the conventional adherent DC culture. Autologous renal Tuly (30 micrograms protein/10(7) PBMCs) enhanced human leukocyte antigen expression by DCs (class I = 7367.6 versus 4085.4 MRFLI; class II = 8277.2 versus 6175.7 MRFLI) and upregulated cytokine mRNAs levels. Concurrently, CD3+ CD56-, CD3+ CD25+, and CD3+ TCR+ cell populations increased and cytotoxicity against autologous renal cell carcinoma tumor target was induced. Specific cytotoxicity was augmented when cultures were boosted continuously with IL-2 (20 U/mL biological response modifier program) plus Tuly stimulation. These results suggest that nonadherent PBMCs may participate in enhancing DC maturation. Besides the simplicity of this culture technique, bulk DC cultures potentially may be used with the same efficiency as conventional purified DCs. Furthermore, bulk culture-derived DCs may be used directly in vivo as a tumor vaccine, or for further ex vivo expansion of co-cultured cytotoxic T cells to be used for adoptive immunotherapy.

Melanoma peptide vaccines: from preclinical background to clinical trials

The discovery that immune T-cells recognize intracellularly processed peptides associated with major histocompatibility locus molecules has revolutionized the cancer vaccine field by providing new reagents for the generation of immune responses against cancer. The cloning of tumor antigen genes has proceeded most rapidly in melanoma because of the ease with which melanoma-specific T-cells can be propagated in vitro. The cloning and identification of tumor regression antigens and data from the initial clinical trials with peptides vaccines derived from those antigens are presented here.

High frequencies of naive Melan-A/MART-1-specific CD8(+) T cells in a large proportion of human histocompatibility leukocyte antigen (HLA)-A2 individuals

Using fluorescent HLA-A*0201 tetramers containing the immunodominant Melan-A/MART-1 (Melan-A) tumor-associated antigen (Ag), we previously observed that metastatic lymph nodes of melanoma patients contain high numbers of Ag-experienced Melan-A-specific cytolytic T lymphocytes (CTLs). In this paper, we enumerated and characterized ex vivo Melan-A-specific cells in peripheral blood samples from both melanoma patients and healthy individuals. High frequencies (>/=1 in 2,500 CD8(+) T cells) of Melan-A-specific cells were found in 10 out of 13 patients, and, surprisingly, in 6 out of 10 healthy individuals. Virtually all Melan-A-specific cells from 6 out of 6 healthy individuals and from 7 out of 10 patients displayed a naive CD45RA(hi)/RO(-) phenotype, whereas variable proportions of Ag-experienced CD45RA(lo)/RO(+) Melan-A-specific cells were observed in the remaining 3 patients. In contrast, ex vivo influenza matrix-specific CTLs from all individuals exhibited a CD45RA(lo)/RO(+) memory phenotype as expected. Ag specificity of tetramer-sorted A2/Melan-A(+) cells from healthy individuals was confirmed after mitogen-driven expansion. Likewise, functional limiting dilution analysis and interferon gamma ELISPOT assays independently confirmed that most of the Melan-A-specific cells were not Ag experienced. Thus, it appears that high frequencies of naive Melan-A-specific CD8(+) T cells can be found in a large proportion of HLA-A*0201(+) individuals. Furthermore, as demonstrated for one patient followed over time, dramatic phenotype changes of circulating Melan-A-specific cells can occur in vivo.

Generation of tumor-specific cytotoxic T lymphocytes by stimulation with HPV type 16 E7 peptide-pulsed dendritic cells: an approach to immunotherapy of cervical cancer

OBJECTIVE

The aim of this study was to generate HPV-16 E7 peptide-specific cytotoxic T lymphocytes (CTLs) in vitro for future adoptive immunotherapy of cervical cancer.

METHODS

Peripheral blood mononuclear cells (PBMC) were isolated from HLA-A2+ healthy donors. The PBMCs were incubated with HPV-16 E7(11-20) peptide and varying cytokines in the primary culture. Restimulation was performed weekly with peptide-pulsed, irradiated autologous PBMCs. Alternatively, the PBMCs were depleted of abundant CD4+ cells and stimulated with HPV-16 E7(11-20) peptide-pulsed dendritic cells. Cytolytic activity was determined by a standard 4-h (51)Cr-release assay.

RESULTS

After 6 weeks in culture, we were able to establish peptide-specific CTL lines in one of seven donors by incubating PBMCs with HPV-16 E7(11-20) peptide. When we employed autologous peptide-pulsed dendritic cells to stimulate CD8+ cell-enriched PBMCs, we obtained CTL lines in four of seven donors. The primed CTLs were able to lyse the HLA-A2+ and HPV-16+ cervical cancer cell line Caski. SiHa, an HLA-A2-, but HPV 16+, cervical cancer cell line could be lysed only after transfection with HLA-A2. In addition, a high cytotoxicity (>80%) was obtained against peptide-pulsed, but not unpulsed, targets such as autologous Ebstein-Barr virus-immortalized B cells or allogeneic lipopolysaccaride-stimulated PBMCs. DCs were clearly the most potent of all tested antigen presenting cells to stimulate a CTL response in a proliferation assay.

CONCLUSION

HPV-16 E7 peptide-specific CTLs could be generated in vitro. A practical protocol to expand the CTLs to a sufficient number for an application in a clinical trial is in progress.

Autoimmune disease induced by dendritic cell immunization against leukemia

Induction of an optimal immune response will likely be a prerequisite for successful immunotherapy of human leukemias and other malignancies. Dendritic cells are highly effective at inducing an immune response to antigens to which the host is unresponsive, while transgenic expression of the costimulator molecule CD40 ligand (gp39/CD154) and the T cell growth factor interleukin 2 (IL2) are also able to augment immune responsiveness. We therefore investigated whether a combination of these two distinctive approaches to immunostimulation could safely increase the anti-tumor immune response compared to each stimulus alone. We injected BALB/CBYJ mice with syngeneic dendritic cells (DC) exposed to A20 lymphoblastic leukemia cell-derived peptides and proteins which had been acid-eluted from the cell surface. In additional mice, the pulsed DC were mixed with genetically modified syngeneic fibroblasts that were expressing CD40 ligand or secreting interleukin 2 (IL2). Three days after their third, weekly, vaccination, they were challenged with parental A20 cells. Tumor growth was suppressed by responses to pulsed DC alone (P < 0.02). This suppression was further enhanced when pulsed DC were coinjected with fibroblasts expressing CD40 ligand and IL2 (P < 0.0005 compared to DC alone) even though CD40 ligand and IL2-expressing fibroblasts alone offered no significant protection in this model. Mice receiving the full complement of immunostimulants either failed to develop visible tumors or developed small tumors which quickly necrosed and regressed, allowing the mice to become long term tumor-free survivors. Antibody mediated depletion of either CD4+ or CD8+ T-cell subset significantly reduced the level of protection afforded by the vaccination. However, it became evident that this intensive stimulation of the immune system lead not only to tumor eradication but also to destruction of cells bearing normal self antigens. Hence, 60 days after challenge with A20 cells all mice in the DC/IL2/CD40 ligand group developed a severe, systemic autoimmune disorder that resembled graft versus host disease and manifest itself by significant peripheral blood cytotoxicity against autologous fibroblasts, blood dyscrasias, gross hepatosplenomegaly, cachexia and fur loss. This phenomenon depended on CD8+ cytotoxic T lymphocytes. Our results therefore suggest that the most effective strategies of immunotherapy against leukemia may also exceed the threshold of anergic cells, leading to a loss of self tolerance to normal self-antigens and the induction of an CD8+ anti-self effector response.

Covalent Linkage to β2-Microglobulin Enhances the MHC Stability and Antigenicity of Suboptimal CTL Epitopes

Many CTL epitopes of clinical importance, particularly those derived from tumor Ags, display relatively poor MHC binding affinity and stability. Because in vivo immunogenicity, and thus the efficacy of peptide-based vaccines, is thought to be determined by MHC/peptide complex stability, there is a need to develop a simple strategy for enhancing the binding of suboptimal epitopes. Toward this goal, the ability to enhance suboptimal peptides through covalent linkage to β2-microglobulin (β2m) was explored. Two suboptimal variants of a high-affinity Db-restricted influenza nucleoprotein peptide were covalently linked, via a polypeptide spacer, to the amino terminus of human β2m and the recombinant fusion proteins expressed in Escherichia coli. When compared with their uncoupled counterparts, the β2m-linked epitopes display enhanced MHC stabilization and antigenicity. Thus, tethering epitopes to β2m provides a simple method for augmenting the biological activity of suboptimal peptides and could be useful in the design of peptide-based vaccines or immunotherapeutics.

Vaccine therapy for prostate cancer

Vaccine therapy may provide an alternative for prostate cancer patients whose disease no longer responds to hormone therapy. Administration of dendritic cells pulsed with prostate-specific membrane antigen (PSMA) induces cellular immune responses against the tumor with virtually no adverse effects. About 30% of the evaluable patients were identified as partial responders, based on the National Prostate Cancer Project (NPCP) criteria. In addition, there was a 50% decrease of serum prostate-specific antigen or resolution of previously measurable lesions on imaging. Dendritic cell vaccine therapy may have a synergistic effect, when combined with other therapies.

Feasibility of Immunotherapy of Relapsed Leukemia With Ex Vivo–Generated Cytotoxic T Lymphocytes Specific for Hematopoietic System-Restricted Minor Histocompatibility Antigens

Allogeneic bone marrow transplantation (BMT) is a common treatment of hematologic malignancies. Recurrence of the underlying malignancy is a major cause of treatment failure. Donor-derived cytotoxic T lymphocytes (CTLs) specific for patients’ minor histocompatibility antigens (mHags) play an important role in both graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) reactivities. mHags HA-1 and HA-2 induce HLA-A*0201-restricted CTLs in vivo and are exclusively expressed on hematopoietic cells, including leukemic cells and leukemic precursors, but not on fibroblasts, keratinocytes, or liver cells. The chemical nature of the mHags HA-1 and HA-2 is known. We investigated the feasibility of ex vivo generation of mHag HA-1– and HA-2–specific CTLs from unprimed mHag HA-1– and/or HA-2–negative healthy blood donors. HA-1 and HA-2 synthetic peptide-pulsed dendritic cells (DCs) were used as antigen-presenting cells (APC) to stimulate autologous unprimed CD8+ T cells. The ex vivo–generated HA-1– and HA-2–specific CTLs efficiently lyse leukemic cells derived from acute myeloid leukemia (AML) and acute lymphoid leukemia (ALL) patients. No lytic reactivity was detected against nonhematopoietic cells. Sufficient numbers of the CTLs can be obtained for the adoptive immunotherapy purposes. In conclusion, we present a feasible, novel therapy for the treatment for relapsed leukemia after BMT with a low risk of GVHD.

Feasibility of Immunotherapy of Relapsed Leukemia With Ex Vivo–Generated Cytotoxic T Lymphocytes Specific for Hematopoietic System-Restricted Minor Histocompatibility Antigens

Allogeneic bone marrow transplantation (BMT) is a common treatment of hematologic malignancies. Recurrence of the underlying malignancy is a major cause of treatment failure. Donor-derived cytotoxic T lymphocytes (CTLs) specific for patients’ minor histocompatibility antigens (mHags) play an important role in both graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) reactivities. mHags HA-1 and HA-2 induce HLA-A*0201-restricted CTLs in vivo and are exclusively expressed on hematopoietic cells, including leukemic cells and leukemic precursors, but not on fibroblasts, keratinocytes, or liver cells. The chemical nature of the mHags HA-1 and HA-2 is known. We investigated the feasibility of ex vivo generation of mHag HA-1– and HA-2–specific CTLs from unprimed mHag HA-1– and/or HA-2–negative healthy blood donors. HA-1 and HA-2 synthetic peptide-pulsed dendritic cells (DCs) were used as antigen-presenting cells (APC) to stimulate autologous unprimed CD8+ T cells. The ex vivo–generated HA-1– and HA-2–specific CTLs efficiently lyse leukemic cells derived from acute myeloid leukemia (AML) and acute lymphoid leukemia (ALL) patients. No lytic reactivity was detected against nonhematopoietic cells. Sufficient numbers of the CTLs can be obtained for the adoptive immunotherapy purposes. In conclusion, we present a feasible, novel therapy for the treatment for relapsed leukemia after BMT with a low risk of GVHD.

Immunophenotypical and functional heterogeneity of dendritic cells generated from murine bone marrow cultured with different cytokine combinations: implications for anti-tumoral cell therapy

Dendritic cells (DC) are professional antigen-presenting cells that can be used as immune adjuvant for anti-tumoural therapies. This approach requires the generation of large quantities of DC that are fully characterized on the immunophenotypical and functional levels. In a murine model, we analysed the in vitro effects of granulocyte-macrophage colony-stimulating factor (GM-CSF) alone or combined with interleukin-4 (IL-4) or Flt3 ligand (Flt3-L) on the number, immunophenotype and functions of bone marrow-derived DC. In GM-CSF cultures, we have identified two populations based on their level of expression of major histocompatibility complex (MHC) class II molecules: MHC-IIhi cells, exhibiting the typical morphology and immunophenotype of myeloid DC (CD11c+ 33D1+ DEC-205+ F4/80+), and MHC-IIlo cells, heterogeneous for DC markers (30% CD11c+; 50% 33D1+; DEC-205-; F4/80+). The addition of Flt3-L to GM-CSF induced a twofold increase in MHC-IIhi DC number; besides, the MHC-IIlo cells lost all DC markers. In contrast, after addition of IL-4 to GM-CSF, the two populations displayed a very similar phenotype (CD11c+ 33D1- DEC-205+ F4/80-), differing only in their expression levels of MHC class II and costimulatory molecules, and showed similar stimulatory activity in mixed leucocyte reaction. We next analysed the migration of these cultured cells after fluorescent labelling. Twenty-four hours after injection into the footpads of mice, fluorescent cells were detected in the draining popliteal lymph nodes, with an enhanced migration when cells were cultured with GM-CSF+Flt3-L. Finally, we showed that MHC-IIhi were more efficient than MHC-IIlo cells in an anti-tumoral vaccination protocol. Altogether, our data highlight the importance of characterizing in vitro-generated DC before use in immunotherapy.

Assessment of Immunogenicity of Human Melan-A Peptide Analogues in HLA-A*0201/Kb Transgenic Mice

Previous studies have shown that substitution of single amino acid residues in human Melan-A immunodominant peptides Melan-A27–35 and Melan-A26–35 greatly improved their binding and the stability of peptide/HLA-A*0201 complexes. In particular, one Melan-A peptide analogue was more efficient in the generation of Melan-A peptide-specific and melanoma-reactive CTL than its parental peptide in vitro from human PBL. In this study, we analyzed the in vivo immunogenicity of Melan-A natural peptides and their analogues in HLA-A*0201/Kb transgenic mice. We found that two human Melan-A natural peptides, Melan-A26–35 and Melan-A27–35, were relatively weak immunogens, whereas several Melan-A peptide analogues were potent immunogens for in vivo CTL priming. In addition, induced Melan-A peptide-specific mouse CTL cross-recognized natural Melan-A peptides and their analogues. More interestingly, these mouse CTL were also able to lyse human melanoma cell lines in vitro in a HLA-A*0201-restricted, Melan-A-specific manner. Our results indicate that the HLA-A*0201/Kb transgenic mouse is a useful animal model to perform preclinical testing of potential cancer vaccines, and that Melan-A peptide analogues are attractive candidates for melanoma immunotherapy.

Circulating Melan-A/Mart-1 specific cytolytic T lymphocyte precursors in HLA-A2+ melanoma patients have a memory phenotype

Melan-A/MART-1 is a melanoma differentiation antigen that is recognized by a high proportion of cytolytic T lymphocyte (CTL) clones derived from human leukocyte antigen (HLA)-A2+ melanoma patients. Whereas peptide Melan-A/ MART-1(27-35) was originally defined as the immunodominant CTL epitope, we have previously reported that peptide Melan-A/MART-1(26-35) was recognized more efficiently by the majority of tumor-reactive CTL clones. As demonstrated here, CTL populations generated from blood lymphocytes of either melanoma patients or healthy individuals after in vitro stimulation with peptide Melan-A/MART-1(26-35) killed specifically HLA-A2+ Melan-A+ allogeneic melanoma cells, thus suggesting their potential use in adoptive immunotherapy. We characterized the surface phenotype of the circulating CTL precursors (CTLp), which respond to in vitro stimulation with peptide Melan-A/MART-1(26-35). In melanoma patients, these CTLp predominantly expressed the CD45RO memory marker. In contrast, they were mainly, although not exclusively, found in the CD45RA subpopulation of CD8 T cells in healthy individuals. The demonstration that Melan-A/MART-1-specific CTLp in peripheral blood lymphocytes from HLA-A2+ patients with metastatic melanoma express a memory phenotype provides direct evidence that in vivo priming of this antigen may occur during tumor progression.

High Titer, Prostate Specific Antigen-Specific Human IgG Production by hu-PBL-SCID Mice Immunized with Antigen-Mouse IgG2a Complex-Pulsed Autologous Dendritic Cells

We report here that immunization of human PBMC reconstituted SCID mice (hu-PBL-SCID mice) with in vitro cultured autologous dendritic cells (DC) pulsed with prostate specific antigen (PSA) complexed to a PSA-specific mouse IgG2a (PSA-IgG2a) consistently and reproducibly stimulates PSA-specific human IgG production. On day 0, female PBMC were used to reconstitute SCID mice and to generate DC in vitro. DC cultures were pulsed with PSA or PSA-IgG2a on day 6. The previously reconstituted hu-PBL-SCID mice were immunized with either PSA-pulsed DC and PSA, PSA-IgG2a-pulsed DC and PSA-IgG2a, or additional PBMC and PSA-IgG2a on day 7. Mice immunized with PSA-IgG2a-pulsed DC had, on the average, up to 31.5 times greater PSA-specific IgG serum concentrations than control mice. Competition ELISA confirmed the PSA specificity of serum IgG. Immunoblot analysis suggested that sera IgG preferentially recognized conformational epitopes on PSA. Therefore, our results represent a major step toward cloning human tumor-associated Ag-specific human mAbs from hu-PBL-SCID mice. In addition, flow cytometry showed that PSA-pulsed DC express significantly more B7.1, B7.2, CD40, and MHC class II surface molecules than mock-treated DC, but PSA-IgG2a-pulsed DC only had significantly enhanced B7.2 surface expression. Interestingly, PSA-specific IgG responses were reproducibly stimulated by DC expressing more B7.2, a molecule associated with Th2-type immune deviation, but not by those expressing more B7.1 and CD40, molecules associated with Th1-type immune deviation. Thus, our results show that stimulation with either Ag or Ag complexed to mAb yields DC with different phenotypes and APC effector functions.

Generation of Melanoma-Specific Cytotoxic T Lymphocytes by Dendritic Cells Transduced with a MART-1 Adenovirus

Dendritic cells (DC) are potent stimulators of primary T cell responses. In this study, we demonstrate that DC, genetically engineered to express the MART-1/Melan-A (MART-1) tumor-associated Ag, express MART-1 mRNA and protein, correctly process and present the HLA-A2.1-restricted immunodominant MART-1 peptide (MART-127–35), and serve as potent stimulators of MART-1-specific CTL in vitro. A replication-defective E1-deleted adenovirus (AdV) was constructed that expresses MART-1 (AdVMART1). Transduced DC produce full length MART-1 mRNA as well as MART-1 protein. AdVMART1 does not significantly down-regulate cell surface class I expression despite having an intact E3 region. Transduction of an HLA-A2-positive/MART-1-negative cell line with AdVMART1 renders these cells sensitive to lysis by CTL specific for the MART-127–35 immunodominant peptide. In addition, DC transduced with AdVMART1 stimulated MART-127–35-specific tumor-infiltrating lymphocytes to synthesize IFN-γ. Finally, AdVMART1-transduced DC were able to generate MART-127–35 peptide-specific, class I-restricted CTL in PBL cultures from normal donors. This study supports the use of tumor Ag-engineered DC in genetic immunotherapy.

High frequency of skin-homing melanocyte-specific cytotoxic T lymphocytes in autoimmune vitiligo

Vitiligo is an autoimmune condition characterized by loss of epidermal melanocytes. Using tetrameric complexes of human histocompatibility leukocyte antigen (HLA) class I to identify antigen-specific T cells ex vivo, we observed high frequencies of circulating MelanA-specific, A*0201-restricted cytotoxic T lymphocytes (A2-MelanA tetramer+ CTLs) in seven of nine HLA-A*0201-positive individuals with vitiligo. Isolated A2-MelanA tetramer+ CTLs were able to lyse A*0201-matched melanoma cells in vitro and their frequency ex vivo correlated with extent of disease. In contrast, no A2-MelanA tetramer+ CTL could be identified ex vivo in all four A*0201-negative vitiligo patients or five of six A*0201-positive asymptomatic controls. Finally, we observed that the A2-MelanA tetramer+ CTLs isolated from vitiligo patients expressed high levels of the skin homing receptor, cutaneous lymphocyte-associated antigen, which was absent from the CTLs seen in the single A*0201-positive normal control. These data are consistent with a role of skin-homing autoreactive melanocyte-specific CTLs in causing the destruction of melanocytes seen in autoimmune vitiligo. Lack of homing receptors on the surface of autoreactive CTLs could be a mechanism to control peripheral tolerance in vivo.

Stringent Allele/Epitope Requirements for MART-1/Melan A Immunodominance: Implications for Peptide-Based Immunotherapy

The exclusiveness of the relationship between peptide and HLA alleles, combined with their extensive polymorphism, emphasizes the need for immunization strategies based on endogenous processing of full length proteins (containing multiple epitopic determinants) for presentation to T cells. This could allow vaccination regardless of the patient’s HLA phenotype, assuming that individual molecules can be efficient T cell Ags in association with various HLA alleles. An endogenous system of Ag presentation was developed using dendritic cells infected with recombinant viral vectors expressing the melanoma-associated Ag MART-1/Melan A. CD8+ T cells from melanoma patients were activated in vitro by coincubation with infected dendritic cells and tested for recognition of HLA-A-matched melanoma targets. This allowed the analysis of T cell induction in association with any HLA-A allele of a given patient’s phenotype. In this system, MART-1/Melan A could not efficiently immunize in association with HLA-A alleles other than A*0201, including the one residue variant from A*0201: HLA-A*0226. Clonal analysis of MART-1/Melan A-specific CTL confirmed that MART-1/Melan A immunodominance is strongly restricted to the AAGIGILTV/HLA-A*0201 combination. The stringent epitope/allele requirements for MART-1/Melan A/TCR interactions were not associated with limitations in the TCR repertoire. In conclusion, autologous induction of MART-1/Melan A CTL by whole Ag processing and presentation is restricted to a unique allele/ligand combination and is excluded by minimal changes in HLA structure. Thus, whole protein vaccination for small m.w. Ags may provide no further advantage over a peptide-based approach.

Melanoma-associated antigens recognized by cytotoxic T lymphocytes

During the last 7 years significant progress has been made in the identification of melanoma-associated antigens recognized by cytotoxic T lymphocytes (CTL). These antigens belong to three main groups: cancer/testis-specific antigens (MAGE, BAGE, GAGE, PRAME and NY-ESO-1), melanocyte differentiation antigens (tyrosinase, Melan-A/MART-1, gp100, TRP-1 and TRP-2), and mutated or aberrantly expressed antigens (MUM-1, CDK4, beta-catenin, gp100-in4, p15 and N-acetylglucosaminyltransferase V). In this review we have summarized the available data concerning the characterization of melanoma-associated antigens, focusing on their immunogenic and protective properties. The development of a strong immune response to differentiation antigens is limited by the existence of tolerance to these "self"-antigens, permitting the involvement of only T cells with low affinity T-cell receptors. Among the melanoma differentiation antigens, only gp100 has been shown to be a tumor regression antigen. The cancer/testis-specific antigens such as MAGE and PRAME should potentially be highly immunogenic antigens. They contain several potential HLA class I binding epitopes and are present only in the testes, which are not accessible to the cells of the immune system owing to the lack of direct contact with the immune cells and the lack of HLA class I expression on the surface of germ cells. But only two patients have been found who responded to these antigens in vivo, indicating their genuinely low immunogenicity. A comparison of the predicted secondary structures of these two groups of antigens (cancer/testis-specific and differentiation antigens) revealed enrichment of long alpha-helical stretches in the cancer/testis-specific antigens. We hypothesize that such highly organized stable structures could, first, reduce denaturation of the protein and, thus, ubiquitinylation as a degradation signal, and, second, diminish the efficiency of the protein unfolding - a necessary step in the proteolytic cleavage by proteasomes. High structural stability could therefore be responsible for the low immunogenicity of these proteins. In this case, modifications decreasing the stability of these proteins might be a means of improving the immune response to these potentially therapeutically useful antigens.