Increased CD8+ T-cell function following castration and immunization is countered by parallel expansion of regulatory T cells

Although androgen ablation therapy is effective in treating primary prostate cancers, a significant number of patients develop incurable castration-resistant disease. Recent studies have suggested a potential synergy between vaccination and androgen ablation, yet the enhanced T-cell function is transient. Using a defined tumor antigen model, UV-8101-RE, we found that concomitant castration significantly increased the frequency and function of antigen-specific CD8(+) T cells early after the immunization of wild-type mice. However, at a late time point after immunization, effector function was reduced to the same level as noncastrated mice and was accompanied by a concomitant amplification in CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg) following immunization. We investigated whether Treg expansion occurred following castration of prostate tumor-bearing mice. In the prostate-specific Pten(-/-) mouse model of prostate cancer, we observed an accelerated Treg expansion in mice bearing the castration-resistant endogenous prostate tumor, which prevented effector responses to UV-8101-RE. Treg depletion together with castration elicited a strong CD8(+) T-cell response to UV-8101-RE in Pten(-/-) mice and rescued effector function in castrated and immunized wild-type mice. In addition, Treg expansion in Pten(-/-) mice was prevented by in vivo interleukin (IL)-2 blockade suggesting that increased IL-2 generated by castration and immunization promotes Treg expansion. Our findings therefore suggest that although effector responses are augmented by castration, the concomitant expansion of Tregs is one mechanism responsible for only transient immune potentiation after androgen ablation.     

CD4+ T cells are able to promote tumor growth through inhibition of tumor-specific CD8+ T-cell responses in tumor-bearing hosts

Modulation of the immune response by established tumors may contribute to the limited success of therapeutic vaccination for the treatment of cancer compared with vaccination in a preventive setting. We analyzed the contribution of the CD4+ T-cell population to the induction or suppression of tumor-specific CD8+ T cells in a tumor model in which eradication of tumors crucially depends on CD8+ T cell-mediated immunity. Vaccine-mediated induction of protective antitumor immunity in the preventive setting (i.e., before tumor challenge) was CD4+ T cell dependent because depletion of this T-cell subset prevented CD8+ T-cell induction. In contrast, depletion of CD4+ cells in mice bearing established E1A+ tumors empowered the mice to raise strong CD8+ T-cell immunity capable of tumor eradication without the need for tumor-specific vaccination. Spontaneous eradication of tumors, which had initially grown out, was similarly observed in MHC class II-deficient mice, supporting the notion that the tumor-bearing mice harbor a class II MHC-restricted CD4+ T-cell subset capable of suppressing a tumor-specific CD8+ T-cell immune response. The deleterious effects of the presence of CD4+ T cells in tumor-bearing hosts could be overcome by CD40-triggering or injection of CpG. Together these results show that CD4+ T cells with a suppressive activity are rapidly induced following tumor development and that their suppressive effect can be overcome by agents that activate professional antigen-presenting cells. These observations are important for the development of immune interventions aiming at treatment of cancer.     

Simultaneous generation of CD8+ and CD4+ melanoma-reactive T cells by retroviral-mediated transfer of a single T-cell receptor

Adoptive immunotherapy of cancer requires the generation of large numbers of tumor antigen-reactive T cells for transfer into cancer patients. Genes encoding tumor antigen-specific T-cell receptors can be introduced into primary human T cells by retroviral mediated gene transfer as a potential method of providing any patient with a source of autologous tumor-reactive T cells. A T-cell receptor-specific for a class I MHC (HLA-A2)-restricted epitope of the melanoma antigen tyrosinase was isolated from a CD4(+) tumor-infiltrating lymphocyte (TIL 1383I) and introduced into normal human peripheral blood lymphocytes by retroviral transduction. T-cell receptor-transduced T cells secreted various cytokines when cocultured with tyrosinase peptide-loaded antigen-presenting cells as well as melanoma cells in an HLA-A2-restricted manner, and could also lyse target cells. Furthermore, T-cell clones isolated from these cultures showed both CD8(+) and CD4(+) transduced T cells could recognize HLA-A2(+) melanoma cells, giving us the possibility of engineering class I MHC-restricted effector and T helper cells against melanoma. The ability to confer class I MHC-restricted tumor cell recognition to CD4(+) T cells makes the TIL 1383I TCR an attractive candidate for T-cell receptor gene transfer-based immunotherapy.     

In vitro peptide immunization of target tax protein human T-cell leukemia virus type 1-specific CD4+ helper T lymphocytes.

PURPOSE: Adult T-cell leukemia/lymphoma induced by human T-cell leukemia virus type 1 (HTLV-1) is usually a fatal lymphoproliferative malignant disease. HTLV-1 Tax protein plays a critical role in HTLV-1-associated leukemogenesis and is an attractive target for vaccine development. Although HTLV-1 Tax is the most dominant antigen for HTLV-1-specific CD8(+) CTLs in HTLV-1-infected individuals, few epitopes recognized by CD4(+) helper T lymphocytes in HTLV-1 Tax protein have been described. The aim of the present study was to study T-helper-cell responses to HTLV-1 Tax and to identify naturally processed MHC class II-restricted epitopes that could be used for vaccine development. EXPERIMENTAL DESIGN: An MHC class II binding peptide algorithm was used to predict potential T-helper cell epitope peptides from HTLV-1 Tax. We assessed the ability of the corresponding peptides to elicit helper T-cell responses by in vitro vaccination of purified CD4(+) T lymphocytes. RESULTS: Peptides Tax(191-205) and Tax(305-319) were effective in inducing T-helper-cell responses. Although Tax(191-205) was restricted by the HLA-DR1 and DR9 alleles, responses to Tax(305-319) were restricted by either DR15 or DQ9. Both these epitopes were found to be naturally processed by HTLV-1(+) T-cell lymphoma cells and by autologous antigen-presenting cells that were pulsed with HTLV-1 Tax(+) tumor lysates. Notably, the two newly identified helper T-cell epitopes are found to lie proximal to known CTL epitopes, which will facilitate the development of prophylactic peptide-based vaccine capable of inducing simultaneous CTL and T-helper responses. CONCLUSION: Our data suggest that HTLV-1 Tax protein could serve as tumor-associated antigen for CD4(+) helper T cells and that the present epitopes might be used for T-cell-based immunotherapy against tumors expressing HTLV-1.     

High frequencies of circulating melanoma-reactive CD8+ T cells in patients with advanced melanoma

To determine whether circulating tumor-reactive T cells are present in melanoma patients, unstimulated T cells from peripheral blood were tested for recognition of HLA-A2- or HLA-A1-matched melanoma cell lines using the ELISPOT assay. Eleven out of 19 patients with metastatic melanoma had a T-cell response with up to 0.81%, 0.78%, 0. 53%, 0.12%, 0.10%, 0.09%, 0.07%, 0.06%, 0.06%, 0.04%, and 0.04% of peripheral blood mononuclear cells (PBMC) secreting IFNgamma upon exposure to various HLA-A2- or HLA-A1-matched melanoma cell lines. These T-cell responses were mediated by CD8+ T cells and could specifically be blocked by an anti-HLA-A2 antibody in HLA-A2-positive patients. Separation experiments performed in one melanoma patient showed tumor-reactive T cells in both the CD8+ effector T cell (CD45RA+/IFNgamma+) as well as the CD8+ memory T-cell compartment (CD45RO+/IFNgamma+). In 3 out of 5 patients, in whom autologous cell lines were available, similar frequencies of T cells in response to HLA-A1- or HLA-A2-matched allogeneic and autologous tumor cells were observed, while 2 patients had a T-cell response restricted to either the autologous or the allogeneic cell lines. These results give evidence for the presence of tumor-reactive CD8+ T cells in more than half of melanoma patients tested. Although some of these patients have clinical evidence for an immunological-mediated tumor control, several patients have growing tumors suggesting presence of escape mechanisms.     

Role of IL-2, IL-4 and IL-6 in the growth and differentiation of tumor-specific CD4+ T helper and CD8+ T cytotoxic cells

We have earlier observed that 1,3-bis (2-chloroethyl)-1-nitrosourea (BCNU), a chemotherapeutic drug, cured 90-100% of mice bearing a syngeneic Ia- T-cell lymphoma (LSA) and furthermore, 100% of the BCNU-cured mice could reject homologous tumor rechallenge. In the present study, purified CD4+ and CD8+ T cells isolated from BCNU-cured mice were used to investigate the mechanism by which such T cells recognized and responded to the tumor-specific antigens. The responsiveness of CD4+ T cells to LSA was dependent on processing and presentation of tumor-specific antigens by syngenic Ia+ splenic antigen-presenting cells (APC). Such activated CD4+ T cells endogenously produced IL-2 but not IL-4 and only IL-2 acted as an autocrine growth factor inasmuch as anti-IL-2 receptor antibodies but not anti-IL-4 antibodies inhibited the CD4+ T cell proliferation. In contrast, the CD8+ T cells failed to produce endogenous growth factors when stimulated with LSA alone or with LSA plus APC, and therefore failed to proliferate. However, in the presence of exogenous recombinant IL-2 (rIL-2), CD8+ T cells could proliferate directly in response to LSA-stimulation, even in the absence of APC. Addition of exogenous rIL-4 alone to cultures induced CD4+ but not CD8+ T cells to proliferate. However, rIL-4 in the presence of rIL-2, could synergize and induce tumor-specific proliferation of CD8+ cells. These data suggested that for IL-4 to act as a T-cell growth factor, the presence of IL-2 was essential, either in the form of endogenously secreted IL-2 (CD4+ T cells) or exogenous IL-2 (for CD8+ T cells). In contrast to rIL-2 and rIL-4, rIL-6 failed to induce growth when used alone or in combination with rIL-2 or rIL-4. Furthermore, when tested individually, only rIL-2 but not rIL-4 or rIL-6 could support the cytotoxic differentiation of CD8+ T cells. The present study suggests that the early events in responsiveness to LSA tumor may involve activation of the IL-2-producing Th1 subpopulation of CD4+ helper cells which in turn activate IL-2 dependent CD8+ cytotoxic T cells. IL-4 if produced subsequently, may act synergistically with IL-2 to promote the growth of CD4+ and CD8+ T cells.     

CD4+ T cells inhibit the neu-specific CD8+ T-cell exhaustion during the priming phase of immune responses against breast cancer

Studies conducted in animal model of infectious diseases or H-Y antigen model suggest a crucial role for CD4+ T cells in providing help for CD8+ T-cell memory responses. This concept suggests that inclusion of T helper epitopes in vaccine formulation will result in improved CD8+ T-cell responses. Although this concept has been applied to cancer vaccine design, the role of CD4+ T cells in the memory differentiation of CD8+ T cells and retention of their anti-tumor function have never been tested in breast cancer model. Using the FVB mouse model of neu-positive breast carcinoma we report for the first time that helpless T cells showed cytostatic or tumor inhibitory effects during primary tumor challenge whereas, helped T cells showed cytotoxic effects and resulted in complete tumor rejection. Such differential effects, in vivo, were associated with higher frequency of CD8+PD-L1+ and CD8+PD-1+ T cells in animals harboring helpless T cells as well as higher titer of IL-2 in the sera of animals harboring helped T cells. However, depletion of CD4+ T cells did not alter the ability of neu-specific CD8+ T cells to differentiate into memory cells and to retain their effector function against the tumor during recall challenge. These results suggest the inhibitory role of CD4+ T cells on CD8+ T-cell exhaustion without substantial effects on the differentiation of memory T cells during priming phase of the immune responses against breast cancer.     

Antigen-specific CD4+ T-cell help is required to activate a memory CD8+ T cell to a fully functional tumor killer cell

Although the importance of CD4+ T-cell help for generation of an effective CD8+ effector cytotoxic T cell (CTL) response is well established, the role of T-cell help in the activation of memory T cells to become fully functional tumor killer cells is undefined. Using synthetic peptide immunizations corresponding to the major CTLs and T-helper epitopes of ovalbumin, adoptive transfers of ovalbumin-specific memory CTLs (mCTLs), and ovalbumin as the tumor-specific antigen in a mouse tumor model, we have determined that T help is essential for the activation of mCTLs to kill tumors. Our data show that T-helper cells specific for the tumor-associated antigen are required for the reactivation of mCTLs by antigen presented indirectly from tumor. In contrast, effector CTLs do not need T help to kill tumors. These results have implications for induction of tumor immunotherapy by immunization.     

CD4+ T cells support polyfunctionality of cytotoxic CD8+ T cells with memory potential in immunological control of tumor

Polyfunctionality/multifunctionality of effector T cells at the single cell level has been shown as an important parameter to predict the quality of T cell response and immunological control of infectious disease and malignancy. However, the fate of polyfunctional CD8⁺ CTLs and the factors that control the polyfunctionality of T cells remain largely unknown. Here we show that the acquisition of polyfunctionality on the initial stimulation is a sensitive immune correlate of CTL survival and memory formation. CD8⁺ T cells with high polyfunctionality, assessed with γ‐interferon and tumor necrosis factor‐α production and surface mobilization of the degranulation marker CD107a, showed enhanced Bcl‐2 expression, low apoptosis, and increased CD127^highKLRG1^low memory precursor phenotype. Consistent with these observations, CD8⁺ T cells were found to acquire high frequency of cells with polyfunctionality when stimulated in conditions known to enhance memory formation, such as the presence of CD4⁺ T cells, interleukin (IL)‐2, or IL‐21. Utilizing T‐cell receptor (TCR) transgenic mouse‐derived CD8⁺ T cells that express a TCR specific for a tumor‐derived neoantigen, we showed that polyfunctional tumor‐specific CTLs generated in the presence of CD4⁺ T cells showed long persistence in vivo and induced enhanced tumor regression when adoptively transferred into mice with progressing tumor. Acquisition of polyfunctionality thus impacts CTL survival and memory formation associated with immunological control of tumor.     

Peripheral T-cell tolerance associated with prostate cancer is independent from CD4+CD25+ regulatory T cells

CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg) are thought to suppress the natural and vaccine-induced immune response against tumor-associated antigens (TAA). Here, we show that Treg accumulate in tumors and tumor-draining lymph nodes of aging transgenic adenocarcinoma of the mouse prostate (TRAMP) male mice, which spontaneously develop prostate cancer. TAA overexpression and disease progression associate also with induction of TAA-specific tolerance. TAA-specific T cells were found in the lymphoid organs of tumor-bearing mice. However, they had lost the ability to release IFN-gamma and kill relevant targets. Neither in vivo depletion of Treg by PC61 monoclonal antibody followed by repeated vaccinations with antigen-pulsed dendritic cells nor the combined treatment with 1-methyl-L-tryptophan inhibitor of the enzyme indoleamine 2,3-dyoxigenase, PC61 antibody, and dendritic cell vaccination restored the TAA-specific immune response. Treg did not seem to control the early phases of tolerance induction, as well. Indeed, depletion of Treg, starting at week 6, the age at which TRAMP mice are not yet tolerant, and prolonged up to week 12, did not avoid tolerance induction. A similar accumulation of Treg was found in the lymph nodes draining the site of dendritic cell vaccination both in TRAMP and wild-type animals. Hence, we conclude that Treg accrual is a phenomenon common to the sites of an ongoing immune response, and in TRAMP mice in particular, Treg are dispensable for induction of tumor-specific tolerance.     

CD4+ and CD8+ T cells cooperate to improve prognosis of patients with esophageal squamous cell carcinoma

The purpose of this study is to clarify the roles of immune cell types, both individually and synergistically, in esophageal squamous cell carcinoma (ESCC). One hundred and twenty-two patients (105 males and 17 females; mean age, 62.3 years) with primary ESCC underwent surgical tumor resection at the Department of Surgical Oncology, School of Medicine, Hokkaido University and two affiliated hospitals between 1989 and 1999. Immunohistochemical analyses were performed for CD4, CD8, and CD57 (surface markers for natural killer cells). Patient prognosis was found to correlate with the number of CD4(+) and CD8(+) T cells in the stroma and the number of CD8(+) T cells within the cancer cell nest. Furthermore, the number of CD8(+) T cells in the stroma and within the cancer cell nest was found to be correlated [correlation coefficient (r) = 0.790; P < 0.0001). However, no correlation was observed between the number of natural killer cells and patient prognosis. Patients were classified into the following four groups based on CD4(+) and CD8(+) T-cell count: CD4/8(+/+), CD4/8(+/-), CD4/8(-/+), CD4/8(-/-). For the general patient pool, as well as for selected p-stage III and IV cases (n = 48), the survival rate for CD4/8(+/+) patients was significantly higher than that for the other three groups (log-rank test, P = 0.0012 and 0.0088, respectively). Multivariate analysis identified CD4/8(+/+) status, T classification, and N classification as independent prognostic factors. In conclusion, cooperation between CD4(+) and CD8(+) T cells correlates strongly with ESCC patient prognosis.     

Concurrent infiltration by CD8+ T cells and CD4+ T cells is a favourable prognostic factor in non-small-cell lung carcinoma

The purpose of this study was to clarify the relationship between the number of tumour-infiltrating T lymphocytes and the clinicopathological features and clinical outcome in patients with non-small-cell lung cancer (NSCLC). Tissue specimens from 109 patients who underwent surgical resection for NSCLC were immunohistochemically analysed for CD4 and CD8 expression. Patients were classified into two groups according to whether their tumours exhibited a 'high' or 'low' level of CD8(+) or CD4(+) lymphocyte infiltration. Although the level of infiltration by CD8(+) T cells alone had no prognostic significance, the survival rate for patients with both 'high' CD8(+) and 'high' CD4(+) T-cell infiltration was significantly higher than that for the other groups (log-rank test, P=0.006). Multivariate analysis indicated that concomitant high CD8(+) and high CD4(+) T-cell infiltration was an independent favourable prognostic factor (P=0.0092). In conclusion, the presence of high levels of both CD8(+) T cells and CD4(+) T cells is a significant indicator of a better prognosis for patients with NSCLC, and cooperation between these cell populations may allow a significantly more potent antitumour response than either population alone.     

CD8+ T cell-mediated control of distant tumours following local photodynamic therapy is independent of CD4+ T cells and dependent on natural killer cells

Cancer survival rates decrease in the presence of disseminated disease. However, there are few therapies that are effective at eliminating the primary tumour while providing control of distant stage disease. Photodynamic therapy (PDT) is an FDA-approved modality that rapidly eliminates local tumours, resulting in cure of early disease and palliation of advanced disease. Numerous pre-clinical studies have shown that local PDT treatment of tumours enhances anti-tumour immunity. We hypothesised that enhancement of a systemic anti-tumour immune response might control the growth of tumours present outside the treatment field. To test this hypothesis we delivered PDT to subcutaneous (s.c.) tumours of mice bearing both s.c. and lung tumours and monitored the growth of the untreated lung tumours. Our results demonstrate that PDT of murine tumours provided durable inhibition of the growth of untreated lung tumours. The inhibition of the growth of tumours outside the treatment field was tumour-specific and dependent on the presence of CD8(+) T cells. This inhibition was accompanied by an increase in splenic anti-tumour cytolytic activity and by an increase in CD8(+) T cell infiltration into untreated tumours. Local PDT treatment led to enhanced anti-tumour immune memory that was evident 40 days after tumour treatment and was independent of CD4(+) T cells. CD8(+) T cell control of the growth of lung tumours present outside the treatment field following PDT was dependent upon the presence of natural killer (NK) cells. These results suggest that local PDT treatment of tumours lead to induction of an anti-tumour immune response capable of controlling the growth of tumours outside the treatment field and indicate that this modality has potential in the treatment of distant stage disease.     

CD4+CD25+CCR6+调节性T细胞在小鼠乳腺癌模型中对CD8+T细胞的抑制作用

目的：观察CD4+CD25+CCR6+调节性T细胞（简称CCR6+Tregs）体内对CD8+T细胞功能的抑制作用,并探讨其与肿瘤免疫逃逸的关系。方法：建立4T1乳腺癌细胞荷瘤裸鼠模型,FACS分选CCR6+Tregs,检测其Foxp3的表达;FACS分选4T1特异性CD8+T细胞,CFSE标记后分别与CCR6+Tregs或CCR6Tregs共同过继转输入4T1荷瘤裸鼠体内,观察荷瘤裸鼠肿瘤生长情况和小鼠存活时间;FACS检测肿瘤组织中CD8+T细胞的增殖、细胞因子IFNγ的产生和颗粒酶B的表达情况。结果：CCR6+Tregs和CCR6Tregs均高表达Foxp3;CCR6+Tregs和CD8+T细胞共转输组4T1荷瘤裸鼠肿瘤的生长明显快于CCR6Tregs共转输组和CD8+T细胞单转输组,同时该组荷瘤裸鼠生存时间也明显缩短（P<0.05）;CCR6+Tregs和CD8+T细胞共转输组CD8+T细胞的增殖、IFNγ的产生和颗粒酶B的表达均明显低于CCR6Tregs共转输组和CD8+T细胞单转输组（P<0.05）。结论：CCR6+Tregs在体内可以有效抑制CD8+T细胞的功能,其在肿瘤免疫逃逸和肿瘤发生、发展中发挥重要作用。     

In vitro stimulation of CD8 and CD4 T cells by dendritic cells loaded with a complex of cholesterol-bearing hydrophobized pullulan and NY-ESO-1 protein: Identification of a new HLA-DR15-binding CD4 T-cell epitope.

PURPOSE: NY-ESO-1 belongs to a class of cancer/testis antigens and has been shown to be immunogenic in cancer patients. We synthesized a complex of cholesterol-bearing hydrophobized pullulan and NY-ESO-1 protein (CHP/ESO) and investigated the in vitro stimulation of CD8 and CD4 T cells from peripheral blood mononuclear cells in healthy donors with autologous CHP/ESO-loaded dendritic cells as antigen-presenting cells. EXPERIMENTAL DESIGN: In vitro stimulation of CD8 or CD4 T cells was determined by IFNgamma ELISPOT assays against autologous EBV-B cells infected with vaccinia/NY-ESO-1 recombinant virus or wild-type vaccinia virus as targets and by ELISA measuring secreted IFNgamma. RESULTS: NY-ESO-1-specific CD8 and CD4 T cells were induced. In a donor expressing HLA-A2, CD8 T cells stimulated with CHP/ESO-loaded dendritic cells recognized naturally processed NY-ESO-1(157-165), an HLA-A2-binding CD8 T cell epitope. NY-ESO-1 CD4 T cells were Th1-type. We identified a new HLA-DR15-binding CD4 T cell epitope, NY-ESO-1(37-50). CONCLUSIONS: These findings indicate that CHP/ESO is a promising polyvalent cancer vaccine targeting NY-ESO-1.     

CD4+ CD25+调节性T细胞及其与肿瘤的关系

CD4+CD25+调节性T细胞是体内自然存在的,能够分泌IL-4、IL-10、转化生长因子-β(TGF-β),表达IL-2Rα(CD25)、细胞毒性T淋巴细胞抗原4(CTLA-4)分子,对效应性T细胞具有抑制作用,是调节性T细胞的重要亚群,参与肿瘤的生长、自身免疫性疾病的发生及耐受移植排斥.现就该类细胞抑制作用机制的研究近况及相关免疫治疗主要是肿瘤免疫治疗的研究进展作一综述.     

Recognition of adult T-cell leukemia/lymphoma cells by CD4+ helper T lymphocytes specific for human T-cell leukemia virus type I envelope protein.

PURPOSE: Human T-cell leukemia virus type I (HTLV-I) can cause an adult T-cell leukemia/lymphoma (ATLL). Because ATLL is a life-threatening lymphoproliferative disorder and is resistant to chemotherapy, the establishment and enhancement of T-cell immunity to HTLV-I through the development of therapeutic vaccines could be of value. Thus, the identification of HTLV-I epitopes for both CD8(+) and CD4(+) T cells should facilitate the development of effective vaccines. Although numerous HTLV-I epitopes for CTLs have been identified, few epitopes recognized by CD4(+) helper T cells against this virus have been described. EXPERIMENTAL DESIGN: Synthetic peptides prepared from several regions of the HTLV-I envelope (Env) sequence that were predicted to serve as helper T-cell epitopes were prepared with use of computer-based algorithms and tested for their capacity to trigger in vitro helper T-cell responses using lymphocytes from normal volunteers. RESULTS: The results show that the HTLV-I-Env(317-331), and HTLV-I-Env(384-398)-reactive helper T lymphocytes restricted by HLA-DQw6 and HLA-DR15, respectively, could recognize intact HTLV-I+ T-cell lymphoma cells and, as a consequence, secrete lymphokines. In addition, HTLV-I Env(196-210)-reactive helper T lymphocytes restricted by HLA-DR9 were able to directly kill HTLV-I+ lymphoma cells and recognize naturally processed antigen derived from killed HTLV-I+ lymphoma cells, which was presented to the helper T cells by autologous antigen-presenting cells. CONCLUSIONS: The present findings hold relevance for the design and optimization of T-cell epitope-based immunotherapy against HTLV-I-induced diseases such as ATLL.     

Inhibition of melanoma growth after treatment with dendritic cells in a Tyr-SV40E murine model requires CD4+ T cells but not CD8+ T cells

Melanomas are promising targets for immunotherapy, as they express a number of tissue-specific antigens against which immune responses can be elicited. We have previously described transgenic mice in which malignant cutaneous melanomas are produced. The 1042 melanoma cell line, derived from a primary melanoma in one of these mice, was used here to generate tumours by subcutaneous inoculation in syngeneic animals. All mice injected with 1 x 10(6) cells of the 1042 cell line developed a tumour. CD4+ T cells, CD8+ T cells and macrophages infiltrated the tumours. Treatment with dendritic cells pulsed with peptides from melanogenic proteins slowed tumour growth and resulted in increased numbers of infiltrating lymphocytes and macrophages, expansion of CD4+ T cells specific for 1042 cell antigens, and increased levels of 1042-specific immunoglobulin G1 (IgG1) and IgM in serum. The frequency of cytotoxic T lymphocytes (CTLs) specific for the MART-1 melanocytic antigen did not increase after dendritic cell treatment. Indeed, the presence of CD8+ T cells was apparently not required for the anti-tumour effects: slowing of tumour growth was not abrogated in animals depleted of CD8+ T cells using antibodies, or in syngeneic CD8-/- animals. In contrast, treatment with dendritic cells + peptides was ineffective after depletion of CD4+ T cells and in syngeneic CD4-/- mice. This experimental system therefore provides an opportunity to investigate CD4-dependent anti-tumour effector mechanisms, and for studies designed to activate the quiescent CTLs which infiltrate melanomas.