Extranodal induction of therapeutic immunity in the tumor microenvironment after intratumoral delivery of Tbet gene-modified dendritic cells.

Murine dendritic cells (DC) transduced to express the Type-1 transactivator T-bet (i.e. mDC.Tbet) and delivered intratumorally as a therapy are superior to control wild-type DC in slowing the growth of established subcutaneous MCA205 sarcomas in vivo. Optimal antitumor efficacy of mDC.Tbet-based gene therapy was dependent on host natural killer (NK) cells and CD8(+) T cells, and required mDC.Tbet expression of major histocompatibility complex class I molecules, but was independent of the capacity of the injected mDC.Tbet to produce proinflammatory cytokines (interleukin-12 family members or interferon-γ) or to migrate to tumor-draining lymph nodes based on CCR7 ligand chemokine recruitment. Conditional (CD11c-DTR) or genetic (BATF3(-/-)) deficiency in host antigen-crosspresenting DC did not diminish the therapeutic action of intratumorally delivered wild-type mDC.Tbet. Interestingly, we observed that intratumoral delivery of mDC.Tbet (versus control mDC.Null) promoted the acute infiltration of NK cells and naive CD45RB(+) T cells into the tumor microenvironment (TME) in association with elevated expression of NK- and T-cell-recruiting chemokines by mDC.Tbet. When taken together, our data support a paradigm for extranodal (cross)priming of therapeutic Type-1 immunity in the TME after intratumoral delivery of mDC.Tbet-based gene therapy.

Therapeutic effectiveness of intratumorally delivered dendritic cells engineered to express the pro-inflammatory cytokine, interleukin (IL)-32.

Interleukin-32 (IL-32) is a pro-inflammatory cytokine conditionally produced by T cells, natural killer (NK) cells, monocytes, epithelial cells and keratinocytes, which has an important role in host resistance against infectious disease. Interestingly, elevated levels of IL-32 transcripts in fine needle aspirates of tumor tissue have also been correlated with objective clinical responses in cancer patients receiving immunotherapy. To evaluate the antitumor impact of IL-32 gene therapy, we treated BALB/c mice bearing established subcutaneous CMS4 sarcomas with intratumoral (i.t.) injections of syngenic dendritic cells (DCs) engineered to express human IL-32ß complementary DNA (that is, DC.IL32). Although ectopic expression of IL-32ß by DC resulted in only modest phenotypic changes in these antigen-presenting cells, DC.IL32 produced higher levels of IL-12p70 than control DC. DC.IL32 were more potent activators of type-1 T-cell responses in vitro and in vivo, with i.t. administration of DC.IL32 leading to the CD8(+) T-cell-dependent (but CD4(+) T-cell- and NK cell-independent) suppression of tumor growth. Effective DC.IL32-based therapy promoted infiltration of tumors by type-1 (that is, CXCR3(+)VLA-4(+)GrB(+)) CD8(+) T cells and CD11b(+)CD11c(+) host myeloid DC, but led to reductions in the prevalence of CD11b(+)Gr1(+) myeloid-derived suppressor cells and CD31(+) blood vessels.

Conditional interleukin-12 gene therapy promotes safe and effective antitumor immunity.

We and others have previously demonstrated that (chronic) interleukin (IL)-12 gene therapy delivered intratumorally through ex vivo gene-engineered dendritic cell (DC) is competent to promote the regression of established murine tumors. In this report, we have developed a conditional expression system (rAd.RheoIL12) to determine the temporal requirements of transgenic IL-12p70 production by administered DC on therapeutic outcome in a subcutaneous B16 melanoma model. DCs infected with rAd.RheoIL12 (DC.RheoIL12) secreted IL-12p70 in a tightly regulated fashion in response to a synthetic diacylhydrazine small molecule ligand in vitro, and the treatment benefit of DC.RheoIL12 delivered into B16 lesions was strictly ligand dependent in vivo. Indeed, DC.RheoIL12-based therapy promoted the regression of established day 7 B16 tumor lesions after intratumoral injection, provided that ligand administration occurred within 24 h of DC injection and was sustained for approximately 5 or more days. Treatment efficacy was correlated to the magnitude of systemic anti-B16 CD8(+) T cells cross-primed in vivo, which in turn, appeared dependent on the early enhanced in vivo survival of adoptively transferred DC.RheoIL12 in tumor and tumor-draining lymph nodes. The unique safety feature of DC.RheoIL12 application was emphasized in a combined treatment model with rIL-2, where profound TNF-alpha-associated toxicity could be ameliorated upon discontinuation of activating ligand administration.

Dysfunctional DC subsets in RCC patients: ex vivo correction to yield an effective anti-cancer vaccine.

Dendritic cells (DCs) are potent antigen-presenting cells responsible for the activation and functional polarization of specific T cells. In patients with renal cell carcinoma (RCC) and other cancers, coordinate DC and T cell defects have been reported. In particular, DC and T cell functional subsets that are not conducive to tumor clearance are hypothesized to predominate in patients with advanced-stage disease. Two major peripheral blood DC subsets have been identified in humans: myeloid dendritic cells (mDCs) and plasmacytoid dendritic cells (pDCs) that are believed to mediate contrasting effects on cancer immunity. Given the lack of information regarding DC subsets in patients with RCC, in the present study we have investigated the comparative frequencies and activation states of mDC and pDC in peripheral blood, cancer tissues and lymph nodes of patients with RCC using flow cytometry and immunohistochemistry. Three monoclonal antibodies (mAbs) reactive against specific DC subsets (BDCA-2 or BDCA-4 for pDC and BDCA-1 and BDCA-3 which represent two distinct subsets of mDC, mDC1 and mDC2, respectively) were employed. We observed a significant reduction of both DC subsets in the peripheral blood of patients as compared to normal donors. Similarly, both mDC and pDC were recruited in large numbers into RCC tumor tissues, where they displayed an immature phenotype (DC-LAMP(-)) and appeared unable to differentiate into mature DC (CD83(+)) that were competent to migrate to draining lymph nodes. However, we were readily able to generate ex vivo mDC from RCC patients. These DC stimulated robust anti-tumor CTL in vitro and would be envisioned for use in DC-based vaccines applied in patients with RCC whose existing immune system is judged dysfunctional, anergic or prone to undergo apoptosis.

Killer dendritic cells: mechanisms of action and therapeutic implications for cancer.

Dendritic cells (DC) are essential for the development and regulation of adaptive host immune responses against tumors. DC are heterogeneous and comprised of diverse cellular subsets. They are best known for mediating a crucial role in the initiation of acquired immunity by serving as professional antigen presenting cells (APC) that take up antigens in their local microenvironment, which are then processed and presented to naïve T cells in the context of major histocompatibility complex (MHC) class I and II molecules. In addition to these functions, DC can modulate the types of T cell responses they generate, and can also influence the responses of innate effectors, such as NK cells. There is also now evidence that they may mediate a more primordial role as innate, effector cells that are tumoricidal. 'Killer' DC (KDC) may represent a true 'multi-tasking' cell type that can sequentially act as a 'hunter-gatherer' of antigens; as well as, an instructor, then enforcer/regulator, of antigen-specific anti-tumor T-cell responses in vivo. In this review, we will critically examine the published record regarding KDC, their mechanism(s) of action, and then consider the potential integration of KDC into novel immunotherapies for patients with cancer.

EBV-specific CD8+ T cell reactivation in transplant patients results in expansion of CD8+ type-1 regulatory T cells.

Posttransplantation lymphoproliferative disorders (PTLD) are life-threatening complications of solid organ transplantation, triggered by EBV infection in chronically immunosuppressed (IS) patients. Our goal is to establish DC-based protocols for adoptive immunotherapy of refractory PTLD, while understanding how the immunosuppressive drug environment may subvert DC-EBV-specific T cell interactions. Type-1 CD8(+) T cells are critical for efficient immune surveillance and control of EBV infection, whereas type-2 or Treg/type-3 responses may provide an environment conductive to disease progression. We have recently reported that chronic IS inhibits DC function in transplant patients. Here, we have analyzed the comparative ability of mature, type-1 polarized DCs (i.e. DC1) generated from quiescent transplant patients or healthy controls, to boost type-1 EBV-specific CD8(+) T cells in vitro. Our results show that unlike healthy controls, where DC1 loaded with MHC class I EBV peptides preferentially reactivate specific type-1 CD8(+) T cells, DC1 generated from transplant patients reactivate EBV-specific CD8(+) T cells that produce both IFN-gamma and IL-10, up-regulate FOXP3 mRNA, and suppress noncognate CD4(+) T-cell proliferation via cell-cell contact. These data support a novel regulatory pathway for anti-EBV T-cell-mediated responses in IS transplant patients, with implications for the design of adoptive immunotherapies in this setting.

Injection of IL-12 gene-transduced dendritic cells into mouse liver tumor lesions activates both innate and acquired immunity.

Dendritic cell (DC)-based vaccines have been applied clinically in the setting of advanced-stage cancer. To date, the clinical efficacy of these vaccines has been limited, possibly owing to the impairment of transferred DC function in cancer-bearing patients. In this study, we examined the therapeutic efficacy of interleukin-12 (IL-12) gene-transfected DCs isolated from tumor-bearing hosts against liver tumor. The endogenous DCs isolated from subcutaneous (s.c.) CMS4 tumor-bearing mice (CMS4DC) exhibited decreased expression levels of antigen-presenting molecules and low-allostimulatory capacity. CMS4DC produced less IL-12p70 than DCs isolated from normal mice. Adenoviral transfection of IL-12 gene into CMS4DC (AdIL12DC) restored the expression of antigen-presenting molecules and allostimulatory capacity. Intratumoral (i.t.) delivery of AdIL12DC resulted in complete rejection of intrahepatic CMS4 tumors and activation of innate and acquired immune cells. Antibody depletion studies revealed that both CD4(+) and CD8(+) T cells as well as natural killer cells play critical roles in mediating liver tumor rejection. I.t. treatment of AdIL12DC resulted in long-term protection against s.c. rechallenge with CMS4 tumor cells. These results revealed that IL-12 gene transfer is capable of improving the impaired functions of DC isolated from tumor-bearing hosts, and support the preclinical therapeutic efficacy of intrahepatic injection of AdIL12DC.

Translational mini-review series on vaccines: Dendritic cell-based vaccines in renal cancer.

Renal cancer is a relatively uncommon solid tumor, accounting for about 3% of all adult malignancies, however this rate incidence is rising. The most common histological renal cell carcinoma (RCC) subtype is clear cell carcinoma that makes up approximately 70-80% of all renal neoplasms and appears to be the only histological subtype that is responsive to immunotherapeutic approaches with any consistency. Therefore, it has been hypothesized that immune-mediated mechanisms play important roles in limiting tumor growth and that dendritic cells (DC), the most potent APC in the body, and T cells are the dominant effector cells that regulate tumor progression in situ. In this context, the development of clinically effective DC-based vaccines is a major focus for active specific immunotherapy in renal cancer. In the current review we have not focused on the results of recently published RCC clinical trials, as several excellent reviews have already performed this function. Instead, we turned our attention to how the perception and practical application of DC-based vaccinations are evolving.

IL-12p70 and IL-18 gene-modified dendritic cells loaded with tumor antigen-derived peptides or recombinant protein effectively stimulate specific Type-1 CD4+ T-cell responses from normal donors and melanoma patients in vitro.

Although CD4(+) Type-1T helper (Th1) cells secreting interferon-gamma (IFN-gamma) appear to play an essential role in promoting durable antitumor immunity, we have previously shown that patients with cancer exhibit dysfunctional Th1-type responses against epitopes derived from tumor antigens, such as MAGE-A6. Here, we engineered human dendritic cells (DCs) to secrete high levels of the IFN-gamma-inducing cytokines, interleukin (IL)-12p70 and IL-18, via recombinant adenoviral infection to generate an in vitro stimulus capable of promoting previously deficient patient Th1-type responses. Dendritic cells co-infected with Ad.IL-12 and Ad.IL-18 (DC.IL-12/18) were more effective at stimulating MAGE-A6-specific Th1-type CD4(+) T-cell responses than DCs infected with either of the cytokine vectors alone, control Ad.Psi5 virus or uninfected DCs. Furthermore, we show that DC.IL-12/18 loaded with recombinant MAGE-A6 protein (rMAGE) and used as in vitro stimulators promote Th1-type immunity that is frequently directed against multiple MAGE-A6-derived epitopes. The superiority of DC.IL-12/18-based stimulations in melanoma patients was independent of disease stage or current disease status. Based on these results, we believe this modality may prove clinically useful as a vaccine platform to promote the recovery of tumor antigen-specific, Th1-type CD4(+) T-cell responses in patients with cancer.

gp100/pmel17 and tyrosinase encode multiple epitopes recognized by Th1-type CD4+T cells.

CD4+ T cells modulate the magnitude and durability of CTL responses in vivo, and may serve as effector cells in the tumour microenvironment. In order to identify the tumour epitopes recognized by tumour-reactive human CD4+ T cells, we combined the use of an HLA-DR4/peptide binding algorithm with an IFN-gamma ELISPOT assay. Two known and three novel CD4+ T cell epitopes derived from the gp 100/pmel17 and tyrosinase melanocyte-associated antigens were confirmed or identified. Of major interest, we determined that freshly-isolated PBMC frequencies of Th1-type CD4+ T recognizing these peptides are frequently elevated in HLA-DR4+ melanoma patients (but not normal donors) that are currently disease-free as a result of therapeutic intervention. Epitope-specific CD4+ T cells from normal DR4+ donors could be induced, however, after in vitro stimulation with autologous dendritic cell pulsed with antigens (peptides or antigen-positive melanoma lysates) or infected with recombinant vaccinia virus encoding the relevant antigen. Peptide-reactive CD4+ T cells also recognized HLA-DR4+ melanoma cell lines that constitutively express the relevant antigen. Based on these data, these epitopes may serve as potent vaccine components to promote clinically-relevant Th1-type CD4+ T cell effector function in situ.

Direct transfection and activation of human cutaneous dendritic cells.

Gene therapy techniques can be important tools for the induction and control of immune responses. Antigen delivery is a critical challenge in vaccine design, and DNA-based immunization offers an attractive method to deliver encoded transgenic protein antigens. In the present study, we used a gene gun to transfect human skin organ cultures with a particular goal of expressing transgenic antigens in resident cutaneous dendritic cells. Our studies demonstrate that when delivered to human skin, gold particles are observed primarily in the epidermis, even when high helium delivery pressures are used. We demonstrate that Langerhans cells resident in the basal epidermis can be transfected, and that biolistic gene delivery is sufficient to stimulate the activation and migration of skin dendritic cells. RT-PCR analysis of dendritic cells, which have migrated from transfected skin, demonstrates the presence of transgenic mRNA, indicating direct transfection of cutaneous dendritic cells. Importantly, transfected epidermal Langerhans cells can efficiently present a peptide derived from the transgenic melanoma antigen MART-1 to a MART-1-specific CTL. Taken together, our results demonstrate direct transfection, activation, and antigen-specific stimulatory function of in situ transduced human Langerhans cells.

Proinflammatory cytokines and CD40 ligand enhance cross-presentation and cross-priming capability of human dendritic cells internalizing apoptotic cancer cells.

Human monocyte-derived dendritic cells (DC) can ingest apoptotic tumor cells (ATC) and present tumor-associated antigens (TAA) to T cells, leading to the generation of tumor-specific cytotoxic effector cells (Cancer Res 2000;60:3542-9). To further augment antitumor effector cell responses, attempts were made to modify antigen presentation and cross-priming of T cells by DC fed with ATC. Proinflammatory cytokines (PC), CD40 ligand (CD40L) and/or interferon-gamma (IFN-gamma) were found to markedly enhance the immunogenicity of TAA presented by DC. While PC upregulated expression of major histocompatibility complex class I/II and costimulatory molecules on the surface of DC, CD40L +/- IFN-gamma increased interleukin (IL)- 12 and to a lesser extent, IL-15 production by DC. Additionally, lactacystin, a specific proteasome inhibitor, significantly abrogated the effects of IFN-gamma and, in part, also those of CD40L or PC. The ability of DC + ATC to cross-prime TAA-inexperienced ("naive") T cells was significantly enhanced by PC and CD40L or CD40L + IFN-gamma, but not by IFN-gamma alone. These results indicate that future vaccines for patients with cancer incorporating DC fed with ATC could be made more effective by the addition of proinflammatory cytokines or CD40L +/- IFN-gamma to improve the DC function.

Human thymic epithelial cells inhibit IL-15- and IL-2-driven differentiation of NK cells from the early human thymic progenitors.

T/NK progenitors are present in the thymus; however, the thymus predominantly promotes T cell development. In this study, we demonstrated that human thymic epithelial cells (TEC) inhibit NK cell development. Most ex vivo human thymocytes express CD1a, indicating that thymic progenitors are predominantly committed to the T cell lineage. In contrast, the CD1a(-)CD3(-)CD56(+) NK population comprises only 0.2% (n = 7) of thymocytes. However, we observed increases in the percentage (20- to 25-fold) and absolute number (13- to 71-fold) of NK cells when thymocytes were cultured with mixtures of either IL-2, IL-7, and stem cell factor or IL-15, IL-7, and stem cell factor. TEC, when present in the cultures, inhibited the increases in the percentage (3- to 10-fold) and absolute number (3- to 25-fold) of NK cells. Furthermore, we show that TEC-derived soluble factors inhibit generation of NK-CFU and inhibit IL15- or IL2-driven NK cell differentiation from thymic CD34(+) triple-negative thymocytes. The inhibitory activity was found to be associated with a 8,000- to 30,000 Da fraction. Thus, our data demonstrate that TEC inhibit NK cell development from T/NK CD34(+) triple negative progenitors via soluble factor(s), suggesting that the human thymic microenvironment not only actively promotes T cell maturation but also controls the development of non-T lineage cells such as the NK lineage.

Melanoma antigens recognised by CD8+ and CD4+ T cells.

The field of melanoma immunobiology has made tremendous strides in the past decade, resulting in the molecular identification of a vast array of tumour-expressed antigens that contain determinants that are recognised by patient T cells or immunoglobulins. The integration of these antigens, their derivative peptides or improved analogues in vaccine trials allows for the augmentation of melanoma-specific CD4+ and CD8+ T cells in situ that may prove clinically efficacious in the adjuvant or therapeutic setting. Indeed, melanoma peptide-based immunotherapies targeting the activation of anti-tumour CD8+ cytotoxic T lymphocytes have proven successful (i.e. yielding objective clinical responses), particularly when combined with T cell growth factors or potent antigen-presenting cells, such as dendritic cells. Vaccine approaches implementing poly-epitope and/or melanoma peptides recognised by CD4+ T cells are anticipated to yield still better clinical outcomes due to the in vivo promotion and maintenance of a diversified, poly-specific effector T cell repertoire directed against resident tumours.

NY-ESO-1 encodes DRB1*0401-restricted epitopes recognized by melanoma-reactive CD4+ T cells.

The NY-ESO-1 gene is expressed by a range of human tumors and encodes HLA-A2-restricted melanoma peptides recognized by CD8+ CTLs. Here we report that the NY-ESO-1 gene also encodes two overlapping, but non-cross-reactive, HLA-DRB1*0401-presented peptides that are recognized by CD4+ T cells. The NY-ESO-1(119-143) peptide was able to induce specific CD4+ T cells in vitro from both an HLA-DRB1*0401+ normal donor and an HLA-DRB1*0401+ patient with melanoma. Bulk and cloned CD4+ T cells produced IFN-gamma specifically in response to, and also lysed, T2.DR4 cells pulsed with peptide NY-ESO-1(119-143) and the autologous tumor cell line, but not a DRB1*0401+ melanoma cell line that does not express NY-ESO-1. Interestingly, the NY-ESO119-143 peptide contains two overlapping putative "core" epitopes recognized by non-cross-reactive anti-NY-ESO-1(119-143) CD4+ T-cell clones. Taken together, these data support the use of this novel DR4-restricted tumor peptide, NY-ESO-1(119-143), or its two "sub-epitopes" in immunotherapeutic trials designed to generate or enhance specific CD4+ T-cell responses against tumors expressing NY-ESO-1 in vivo.

Mature dendritic cells pulsed with freeze-thaw cell lysates define an effective in vitro vaccine designed to elicit EBV-specific CD4(+) and CD8(+) T lymphocyte responses.

Immunotherapy trials targeting the induction of tumor-reactive T-cell responses in cancer patients appear to hold significant promise. Because nonmutated lineage-specific antigens and mutated idiotypic antigens may be coexpressed by tumor cells, the use of autologous tumor material to promote the broadest range of antitumor T-cell specificities has significant clinical potential in cancer vaccination trials. As a model for vaccination in the cancer setting, we chose to analyze the promotion of T-cell responses against Epstein-Barr virus (EBV)-transformed B-lymphoblastoid cell line (B-LCL)-derived antigens in vitro. A series of bulk antigenic formats (freeze-thaw lysate, trifluoroacetic acid lysate, extracted membranes, affinity-purified MHC class I- and class II-presented peptides, acid-eluted peptides) prepared from EBV B-LCLs were tested for their ability to stimulate EBV B-LCL-reactive CD4(+) and CD8(+) T lymphocytes in vitro when pulsed onto autologous dendritic cells (DCs). DC presentation of freeze-thaw lysate material derived from (either autologous or allogeneic) EBV B-LCLs with an Mr of 10 kd or larger stimulated optimal anti-EBV B-LCL responsiveness from freshly isolated CD4(+) and CD8(+) peripheral blood T cells. These in vivo "memory" T-cell responses were observed only in EBV-seropositive donors. CD4(+) T-cell responses to lysate-pulsed DCs were Th1 type (ie, strong interferon-gamma and weak interleukin-5 responses). While CD8(+) T-cell responses were also observed in interferon-gamma Elispot assays and in cytotoxicity assays, these responses were of low frequency unless the DC stimulators were induced to "mature" after being fed with tumor lysates. Optimal-length, naturally processed, and MHC class I- or class II-presented tumor peptides were comparatively poorly immunogenic in this model system. (Blood. 2000;96:1857-1864)

Evaluation of the modified ELISPOT assay for gamma interferon production in cancer patients receiving antitumor vaccines.

Frequencies of vaccine-responsive T-lymphocyte precursors in peripheral blood mononuclear cells (PBMC) prior to and after administration of peptide-based vaccines in patients with cancer can be measured by limiting-dilution assays (LDA) or by ELISPOT assays. We have used a modified version of the ELISPOT assay to monitor changes in the frequency of gamma interferon (IFN-gamma)-producing T cells in a population of lymphocytes responding to a relevant peptide or a nonspecific stimulator, such as phorbol myristate acetate-ionomycin. Prior to its use for monitoring of patient samples, the assay was validated and found to be comparable to the LDA performed in parallel, using tumor-reactive cytolytic T-lymphocyte (CTL) lines. The sensitivity of the ELISPOT assay was found to be 1/100,000 cells, with an interassay coefficient of variation of 15%, indicating that it could be reliably used for monitoring of changes in the frequency of IFN-gamma-secreting responder cells in noncultured or cultured lymphocyte populations. To establish that the assay is able to detect the T-cell precursor cells responsive to the vaccine, we used CD8(+) T-cell populations positively selected from PBMC of HLA-A2(+) patients with metastatic melanoma, who were treated with dendritic cell-based vaccines containing gp100, MELAN-A/MART-1, tyrosinase, and influenza virus matrix peptides. The frequency of peptide-specific responder T cells ranged from 0 to 1/2,600 before vaccination and increased by at least 1 log unit after vaccination in two patients, one of whom had a clinical response to the vaccine. However, no increases in the frequency of peptide-responsive T cells were observed in noncultured PBMC or PBMC cultured in the presence of the relevant peptides after the melanoma patients enrolled in another trial were treated with the intramuscular peptide vaccine plus MF59 adjuvant. Thus, while the ELISPOT assay was found to be readily applicable to assessments of frequencies of CTL precursors of established CTL lines and ex vivo-amplified PBMC, its usefulness for monitoring of fresh PBMC in patients with cancer was limited. In many of these patients antitumor effector T cells are present at frequencies of lower than 1/100,000 in the peripheral circulation. Serial monitoring of such patients may require prior ex vivo amplification of specific precursor cells.

Melan-A/MART-1(51-73) represents an immunogenic HLA-DR4-restricted epitope recognized by melanoma-reactive CD4(+) T cells.

The human Melan-A/MART-1 gene encodes an HLA-A2-restricted peptide epitope recognized by melanoma-reactive CD8(+) cytotoxic T lymphocytes. Here we report that this gene also encodes at least one HLA-DR4-presented peptide recognized by CD4(+) T cells. The Melan-A/MART-1(51-73) peptide was able to induce the in vitro expansion of specific CD4(+) T cells derived from normal DR4(+) donors or from DR4(+) patients with melanoma when pulsed onto autologous dendritic cells. CD4(+) responder T cells specifically produced IFN-gamma in response to, and also lysed, T2.DR4 cells pulsed with the Melan-A/MART-1(51-73) peptide and DR4(+) melanoma target cells naturally expressing the Melan-A/MART-1 gene product. Interestingly, CD4(+) T cell immunoreactivity against the Melan-A/MART-1(51-73) peptide typically coexisted with a high frequency of anti-Melan-A/MART-1(27-35) reactive CD8(+) T cells in freshly isolated blood harvested from HLA-A2(+)/DR4(+) patients with melanoma. Taken together, these data support the use of this Melan-A/MART-1 DR4-restricted melanoma epitope in future immunotherapeutic trials designed to generate, augment, and quantitate specific CD4(+) T cell responses against melanoma in vivo.