Depletion of CD4+ CD25+ regulatory cells augments the generation of specific immune T cells in tumor-draining lymph nodes

Antigen quality determines the efficiency of antitumor immune responses generated in the absence of regulatory T cells

The observation that depletion or inhibition of regulatory T cells (Tregs) unleashes efficient antitumor effector immune responses that can lead to tumor eradication in mice has opened new perspectives for the development of cancer immunotherapy. The quality and overall efficiency of the effector immune responses induced in the absence of Tregs seem to depend on multiple factors that determine the result of a battle involving effector T cells (Teffs), Tregs and tumor cells. In this study, we investigated the quality of tumor-associated antigens (TAAs) as one such factor. We show that the presence of a strong dominant antigen is required for the induction of effector responses capable of tumor eradication in the absence of Tregs. The sole addition of a dominant antigen on tumor cells does not change tumor growth in unmanipulated mice, but improves tumor eradication rate from a few to almost 100% in the absence of Tregs. This eradication can be shown to result from the recruitment and activation of specific Teffs recognizing this antigen. We also show that the presence of such dominant antigens has the side effect of restricting the breadth of the immune response to other TAAs, which could favor the generation of escape mutant by tumor editing. Taken together, our results highlight the potential, and some requirements for cancer immunotherapy based on Treg depletion. They also show that, ultimately, tumor fate depends on multiple factors that should all be taken into consideration for the design of more efficient immunotherapy.

Breaking tolerance in a mouse model of multiple myeloma by chemoimmunotherapy

A unique mouse model of multiple myeloma (MM), namely 5T2MM-bearing mouse, was useful for elucidating the pathophysiological mechanisms underlying the disease. Increased accumulation of suppressive CD4(+)CD25(High)Foxp3(+) regulatory T cells (Tregs) was observed in the thymus and lymphoid peripheral organs during disease progression. Adoptive transfer of Tregs, but not other thymocytes, from 5T2MM-bearing mice led to increased progression of disease manifestations in young syngeneic mice. Depletion of Tregs, a proposed strategy in cancer immunotherapy, was tested using cyclophosphamide (CYC), an alkylating agent with selective cytotoxicity. Both low- and high-dose CYC, administered to sick mice with hind limb paralysis, caused the paralysis to disappear, the plasma tumor cells in the bone marrow (BM) cavity to be replaced by normal cell populations, and the survival of the mice to be significantly prolonged. Low-dose CYC, which selectively depletes Tregs, decreased MM incidence, in contrast to high-dose CYC, which was generally cytotoxic, and did not reduce MM incidence. In contrast, low-dose CYC induced Tregs to become susceptible to apoptosis by downregulating Bcl-xL and CTLA-4 in these cells, and by decreasing the production of IL-2 by effector CD4 cells. This treatment consequently triggered the recovery of IFN-gamma-producing natural killer T cells and the maturation of dendritic cells. Transient gradual depletion of Tregs in low-dose CYC-treated 5T2MM mice was maintained beyond 45 days. Thus, less frequent injections of low-dose CYC enabled us to recruit compatible immune-derived cells that would reduce tumor load and delay or prevent tumor recurrence, hence breaking immune tolerance toward MM tumor cells.

Regulatory T cells in cancer

At the present time, regulatory T cells (Tregs) are an integral part of immunology but the route from discovery of "suppressive" lymphocytes in the 1980s to the current established concept of Tregs almost 20 years later has been a rollercoaster ride. Tregs are essential for maintaining self-tolerance as defects in their compartment lead to severe autoimmune diseases. This vitally important function exists alongside the detrimental effects on tumor immunosurveillance and antitumor immunity. Beginning with the identification of CD4(+)CD25(+) Tregs in 1995, the list of Treg subsets, suppressive mechanisms, and knowledge about their various origins is steadily growing. Increase in Tregs within tumors and circulation of cancer patients, observed in early studies, implied their involvement in pathogenesis and disease progression. Several mechanisms, ranging from proliferation to specific trafficking networks, have been identified to account for their systemic and/or local accumulation. Since various immunotherapeutic approaches are being utilized for cancer therapy, various strategies to overcome the antagonistic effects exerted by Tregs are being currently explored. An overview on the biology of Tregs present in cancer patients, their clinical impact, and methods for modulating them is given in this review. Despite the extensive studies on Tregs in cancer many questions still remain unanswered. Even the paradigm that Tregs generally are disadvantageous for the control of malignancies is now under scrutiny. Insight into the specific role of Tregs in different types of neoplasias is the key for targeting them in a way that is beneficial for the clinical outcome.

Depletion of tumor-induced Treg prior to reconstitution rescues enhanced priming of tumor-specific, therapeutic effector T cells in lymphopenic hosts

We reported previously that vaccination of reconstituted, lymphopenic mice resulted in a higher frequency of tumor-specific effector T cells with therapeutic activity than vaccination of normal mice. Here, we show that lymphopenic mice reconstituted with spleen cells from tumor-bearing mice (TBM), a situation that resembles the clinical condition, failed to generate tumor-specific T cells with therapeutic efficacy. However, depletion of CD25(+) Treg from the spleen cells of TBM restored tumor-specific priming and therapeutic efficacy. Adding back TBM CD25(+) Treg to CD25(-) naïve and TBM donor T cells prior to reconstitution confirmed their suppressive role. CD25(+) Treg from TBM prevented priming of tumor-specific T cells since subsequent depletion of CD4(+) T cells did not restore therapeutic efficacy. This effect may not be antigen-specific as three histologically distinct tumors generated CD25(+) Treg that could suppress the T-cell immune response to a melanoma vaccine. Importantly, since ex vivo depletion of CD25(+) Treg from TBM spleen cells prior to reconstitution and vaccination fully restored the generation of therapeutic effector T cells, even in animals with established tumor burden, we have initiated a translational clinical trial of this strategy in patients with metastatic melanoma.

Gamma-ray resistance of regulatory CD4+CD25+Foxp3+ T cells in mice

Abstract CD4(+)CD25(+) regulatory T cells (Treg cells) are an important subset of T cells for keeping proper immune responses and tolerance. However, the effects of gamma radiation on CD4(+)CD25(high) Foxp3(+) Treg cells have not been examined previously. In the present study, we compared the sensitivity of mouse CD4(+)CD25(high) Foxp3(+) Treg cells and CD4(+)CD25(-) T cells to gamma radiation in vitro and in vivo. After C57BL/6 mice received a whole-body dose of 5 Gy gamma rays, the numbers of lymphocyte subsets in blood, lymph nodes, spleens and thymuses clearly decreased. However, gamma radiation significantly enhanced the ratios of CD4(+)CD25(high) Treg cells and CD4(+)CD25(high) Foxp3(+) Treg cells to CD4(+) T cells in the blood, lymph nodes, spleens and thymuses of mice. More dead cells were observed in CD4(+)CD25(-) T cells than in CD4(+)CD25(high) Treg cells or CD4(+)CD25(high) Foxp3(+) Treg cells when the cells were irradiated in vitro, indicating that CD4(+)CD25(high) Foxp3(+) Treg cells are more resistant to gamma radiation than other T cells. Moreover, a higher expression of Bcl-2 in CD4(+)CD25(high) Treg cells was detected compared with that in CD4(+)CD25(-) T cells. CD4(+)CD25(+) Treg cells from irradiated mice were functional, though their immunosuppressive ability was somewhat impaired compared to those from nonirradiated mice as determined by an in vitro assay. These results indicate that mouse CD4(+)CD25(+) Treg cells and CD4(+)CD25(-) T effector cells have different sensitivities to gamma radiation in mice.

Co-inhibitory molecules: Controlling the effectors or controlling the controllers?

Nearly forty years ago the concept was proposed that lymphocytes are negatively regulated by what are now called co-inhibitory signals. Nevertheless, it is only the more recent identification of numerous co-inhibitors and their critical functions that has brought co-inhibition to the forefront of immunologic research. Although co-inhibitory signals have been considered to directly regulate conventional T cells, more recent data has indicated a convergence between co-inhibitory signals and the other major negative control mechanism in the periphery that is mediated by regulatory T cells. Furthermore, it is now clear that lymphocytes are not the sole domain of co-inhibitory signals, as cells of the innate immune system, themselves controllers of immunity, are regulated by co-inhibitors they express. Thus, in order to better understand negative regulation in the periphery and apply this knowledge to the treatment of disease, a major focus for the future should be the definition of the conditions where co-inhibition controls effector cells intrinsically versus extrinsically (via regulatory or innate cells).

The role of regulatory T cells in cancer

There has been an explosion of literature focusing on the role of regulatory T (Treg) cells in cancer immunity. It is becoming increasingly clear that Treg cells play an active and significant role in the progression of cancer, and have an important role in suppressing tumor-specific immunity. Thus, there is a clear rationale for developing clinical strategies to diminish their regulatory influences, with the ultimate goal of augmenting antitimor immunity. Therefore, manipulation of Treg cells represent new strategies for cancer treatment. In this Review, I will summarize and review the explosive recent studies demonstrating that Treg cells are increased in patients with malignancies and restoration of antitumor immunity in mice and humans by depletion or reduction of Treg cells. In addition, I will discuss both the prognostic value of Treg cells in tumor progression in tumor-bearing hosts and the rationale for strategies for therapeutic vaccination and immunotherapeutic targeting of Treg cells with drugs and microRNA.

Targeting the tumor microenvironment with anti-neu/anti-CD40 conjugated nanoparticles for the induction of antitumor immune responses

Clinical and preclinical data indicate that immunotherapeutic interventions could induce immune responses capable of controlling or retard the tumor growth. However, immunotherapies need to be further optimized. We hypothesized that a more effective strategy for tumor eradication is to directly target the tumor microenvironment in order to generate a proinflammatory response and induce a localized antitumor immune response capable of eliminating the tumor cells. Nanoparticles have been proven to be an effective delivery system. In these studies we evaluated conjugated anti-RNEU and anti-CD40 antibodies onto PLA-(poly dl-lactic acid)-biodegradable nanoparticles (PLA-NP) for the induction of antitumor immune responses. The anti-neu/anti-CD40-NP were functional in vitro recognizing RNEU(+) tumors and activating dendritic cells. The delivery of anti-neu/anti-CD40-NP but not anti-neu-NP or anti-CD40-NP induced an antitumor response resulting in complete tumor elimination and generation of protective memory responses. The anti-neu/anti-CD40-NP specifically activated an antitumor response against RNEU(+) tumors but not against RNEU(-) tumors. The antitumor immune responses correlate with the induction of a Th1-proinflammatory response, reduction in the number of Tregs within the tumor and activation of a specific cytotoxic response. These results indicate that anti-neu/anti-CD40-NP with immunomodulatory properties are safe and can be used effectively as cancer vaccines strategy for the specific induction of antitumor immune responses.

Partial CD4 depletion reduces regulatory T cells induced by multiple vaccinations and restores therapeutic efficacy

PURPOSE

A single vaccination of intact or reconstituted-lymphopenic mice (RLM) with a granulocyte macrophage colony-stimulating factor-secreting B16BL6-D5 melanoma cell line induces protective antitumor immunity and T cells that mediate the regression of established melanoma in adoptive immunotherapy studies. We wanted to study if multiple vaccinations during immune reconstitution of the lymphopenic host would maintain a potent antitumor immune response.

EXPERIMENTAL DESIGN

RLM were vaccinated multiple times over a 40-day period. Spleens were isolated from these mice, activated in vitro, and adoptively transferred into mice bearing 3-day experimental pulmonary metastases.

RESULTS

Multiple vaccinations, rather than boosting the immune response, significantly reduced therapeutic efficacy of adoptive immunotherapy and were associated with an increased frequency and absolute number of CD3+CD4+Foxp3+ T regulatory (T(reg)) cells. Anti-CD4 administration reduced the absolute number of T(reg) cells 9-fold. Effector T-cells generated from anti-CD4-treated mice were significantly (P < 0.0001) more therapeutic in adoptive transfer studies than T cells from multiply vaccinated animals with a full complement of CD4+ cells.

CONCLUSION

These results suggest that CD4+ T(reg) cells limit the efficacy of multiple vaccinations and that timed partial depletion of CD4+ T cells may reduce suppression and "tip-the-balance" in favor of therapeutic antitumor immunity. The recent failure of large phase III cancer vaccine clinical trials, wherein patients received multiple vaccines, underscores the potential clinical relevance of these findings.

Skin melanoma development in ret transgenic mice despite the depletion of CD25+Foxp3+ regulatory T cells in lymphoid organs

CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg) known to mediate self-tolerance were also shown to contribute to tumor progression. In mouse melanoma transplantation models, Treg depletion resulted in the stimulation of antitumor immune responses and tumor eradication. To study Treg in conditions close to the clinical situation, we used a ret transgenic mouse spontaneous melanoma model, which, in contrast to transplantation models, resembles human melanoma regarding clinical development. Significantly higher numbers of Treg were found in skin tumors and metastatic lymph nodes at early stages of melanoma progression compared with more advanced stages accompanied by the elevated CCR4 expression on Treg and higher production of its ligand CCL2 in tumor lesions. Numbers of tumor infiltrating Treg inversely correlated with Treg amounts in the bone marrow, suggesting their possible recruitment to melanoma lesions from this organ. The immunosuppressive function of Treg from transgenic tumor-bearing mice was similar to that from transgenic tumor-free mice or nontransgenic littermates. Although anti-CD25 mAb injections resulted in the efficient Treg depletion from lymphoid organs of transgenic mice, melanoma development was not significantly delayed. Furthermore, the treatment of mice with macroscopical tumors also failed to inhibit tumor progression, which correlated with the inability to deplete intratumoral Treg. We suggest that in the autochthonous melanoma genesis, other immunosuppressive cells could play an important role and replace immunosuppressive, tumor-promoting functions of Treg. Therefore, effective melanoma immunotherapy should include the inhibition of Treg migration into the tumor combined with neutralization of other immunosuppressive cells and factors in the tumor microenvironment.

Enhancing immune responses to tumor-associated antigens

The goal of vaccine-based cancer immunotherapy is to induce a tumor-specific immune response that ultimately reduces tumor burden. However, the immune system is often tolerant to antigens presented by the tumor, as the cancer originates from within a patient and is therefore recognized as self. This article reviews selected clinical strategies for overcoming this immune tolerance, and approaches to enhance generation of immunity to tumor-associated antigens by activating innate immunity, potentiating adaptive immunity, reducing immunosuppression, and enhancing tumor immunogenicity. Success in the field of cancer vaccines has yet to be fully realized, but intelligent choice of immunomodulators, tumor antigens and patient populations will likely lead to clinically relevant uses for cancer vaccines.

CD4+CD25+ T cell depletion impairs tolerance induction in a murine model of asthma

BACKGROUND

Regulatory T cells (Tregs) are key players in controlling the development of airway inflammation. However, their role in the mechanisms leading to tolerance in established allergic asthma is unclear.

OBJECTIVE

To examine the role of Tregs in tolerance induction in a murine model of asthma.

METHODS

Ovalbumin (OVA) sensitized asthmatic mice were depleted or not of CD25(+) T cells by anti-CD25 PC61 monoclonal antibody (mAb) before intranasal treatment (INT) with OVA, then challenged with OVA aerosol. To further evaluate the respective regulatory activity of CD4(+)CD25(+) and CD4(+)CD25(-) T cells, both T cell subsets were transferred from tolerized or non-tolerized animals to asthmatic recipients. Bronchoalveolar lavage fluid (BALF), T cell proliferation and cytokine secretion were examined.

RESULTS

Intranasal treatment with OVA led to increased levels of IL-10, TGF-beta and IL-17 in lung homogenates, inhibition of eosinophil recruitment into the BALF and antigen specific T cell hyporesponsiveness. CD4(+)CD25(+)Foxp3(+) T cells were markedly upregulated in lungs and suppressed in vitro and in vivo OVA-specific T cell responses. Depletion of CD25(+) cells before OVA INT severely hampered tolerance induction as indicated by a strong recruitment of eosinophils into BALF and a vigorous T cell response to OVA upon challenge. However, the transfer of CD4(+)CD25(-) T cells not only suppressed antigen specific T cell responsiveness but also significantly reduced eosinophil recruitment as opposed to CD4(+)CD25(+) T cells. As compared with control mice, a significantly higher proportion of CD4(+)CD25(-) T cells from OVA treated mice expressed mTGF-beta.

CONCLUSION

Both CD4(+)CD25(+) and CD4(+)CD25(-) T cells appear to be essential to tolerance induction. The relationship between both subsets and the mechanisms of their regulatory activity will have to be further analyzed.

Prostvac-VF: a vector-based vaccine targeting PSA in prostate cancer

Prostvac is a prostate cancer vaccine regimen consisting of a recombinant vaccinia vector as a primary vaccination, followed by multiple booster vaccinations employing a recombinant fowlpox vector. Both vectors contain the transgenes for prostate-specific antigen (PSA) and multiple T-cell co-stimulatory molecules (TRICOM). The PSA-TRICOM vaccines infect antigen-presenting cells (APCs) and generate proteins that are expressed on the surface of the APCs in an immune context. The interaction of these APCs with T cells initiates a targeted immune response and T cell-mediated tumor cell destruction. Preliminary clinical trials have indicated negligible toxicity, and Phase II trials have suggested a survival benefit after treatment with Prostvac, especially in patients with indolent disease characteristics. Preclinical and clinical data indicate that radiation, hormonal therapy, and chemotherapy may be combined with Prostvac to enhance the vaccine's efficacy. Additional strategies are in development to further enhance the clinical benefits of Prostvac, and a Phase III trial is being planned in metastatic castration-resistant prostate cancer.

Effector/memory but not naive regulatory T cells are responsible for the loss of concomitant tumor immunity

The phenomenon of concomitant tumor immunity involves a tumor-bearing host rejecting another similar tumor at a distant site and suggests the existence of tumor-specific immunity. Loss of this immunity may contribute to tumor metastasis. However, mechanisms underlying the loss of concomitant immunity are largely unknown. We set up a concomitant tumor immunity model in which this immunity is gradually lost as the primary tumor progresses. We found that CD8(+) T cells, especially tumor-infiltrating CD8(+) T cells, from mice that lost concomitant tumor immunity, possessed potent antitumor properties and strongly expressed effector molecules. Furthermore, effector/memory regulatory T cells (Treg cells, CD103(+)CD4(+)Foxp3(+) T cells) increased as the primary tumor progressed. They initially accumulated around the tumor and in the spleen at later points. Not only did these cells more greatly express killing molecules, they also suppressed the functions of tumor-bearing CD8(+) T cells in vitro and in vivo. Finally, we show that these effector/memory Treg cells inhibit concomitant tumor immunity in vivo. Taken together, data suggest that effector/memory Treg cells are responsible for the loss of concomitant tumor immunity associated with tumor progression.

A key regulatory role of the transcription factor NFATc2 in bronchial adenocarcinoma via CD8+ T lymphocytes

The Ca(2+)-regulated calcineurin/nuclear factor of activated T cells (NFAT) cascade controls alternative pathways of T-cell activation and peripheral tolerance. Here, we describe reduction of NFATc2 mRNA expression in the lungs of patients with bronchial adenocarcinoma. In a murine model of bronchoalveolar adenocarcinoma, mice lacking NFATc2 developed more and larger solid tumors than wild-type littermates. The extent of central tumor necrosis was decreased in the tumors in NFATc2((-/-)) mice, and this finding was associated with reduced tumor necrosis factor-alpha and interleukin-2 (IL-2) production by CD8(+) T cells. Adoptive transfer of CD8(+) T cells of NFATc2((-/-)) mice induced transforming growth factor-beta(1) in the airways of recipient mice, thus supporting CD4(+)CD25(+)Foxp-3(+)glucocorticoid-induced tumor necrosis factor receptor (GITR)(+) regulatory T (T(reg)) cell survival. Finally, engagement of GITR in NFATc2((-/-)) mice induced IFN-gamma levels in the airways, reversed the suppression by T(reg) cells, and costimulated effector CD4(+)CD25(+) (IL-2Ralpha) and memory CD4(+)CD127(+) (IL-7Ralpha) T cells, resulting in abrogation of carcinoma progression. Agonistic signaling through GITR, in the absence of NFATc2, thus emerges as a novel possible strategy for the treatment of human bronchial adenocarcinoma in the absence of NFATc2 by enhancing IL-2Ralpha(+) effector and IL-7Ralpha(+) memory-expressing T cells.

The importance of the age factor in cancer vaccination at older age

Cancer is an age-related disease, and with the graying of the society there is an increasing need to optimize cancer management and therapy to elderly patients. Vaccine therapy for cancer is less toxic than chemotherapy or radiation and could be, therefore, especially effective in older, more frail cancer patients. However, it has been shown that older individuals do not respond to vaccine therapy as well as younger adults. This has been attributed to T cell unresponsiveness, a phenomenon also observed in cancer patients per se. Therefore, research is needed to establish whether age-specific tumor-immunological variables permit optimal use of cancer vaccines and therapy in the elderly. This review summarizes the current knowledge of T cell unresponsiveness in cancer patients and elderly, and the results of cancer vaccination in preclinical models at young and old age. Finally, new directions that may lead to effective cancer vaccination at older age will be proposed.

Gamma irradiation alters the phenotype and function of CD4+CD25+ regulatory T cells

To examine the effects of gamma irradiation on Tregs, changes in phenotype and suppression function in Tregs treated with or without gamma ray were analyzed. Purified CD4(+)CD25(+) regulatory T cells were irradiated at different dosages with a (137)Cs source gamma ray at 4.8 Gy/min. After culture, the phenotype and function changes were determined by flow cytometry and [(3)H]-thymidine incorporation, respectively. A dose-dependent reduction of Tregs proliferation in response to gamma irradiation was noted, which paralleled the apoptosis induction of Tregs. Gamma irradiation downregulated the Tregs expression of CD45RO, CD62L, FOXP3, membrane TGF-beta, but upregulated Bax and GITR. High dose gamma irradiation (30 Gy) significantly abolished the suppression of Tregs on CD4(+)CD25(-) T cells proliferation. Thus Tregs not only influences the phenotype but also alters their suppressive capacities. Our findings suggest that radiotherapy may be an important strategy to alter the immunologic balance of Tregs and effector cells in cancer therapy.

Multiple roles for CD4+ T cells in anti-tumor immune responses

Our understanding of the importance of CD4+ T cells in orchestrating immune responses has grown dramatically over the past decade. This lymphocyte family consists of diverse subsets ranging from interferon-gamma (IFN-gamma)-producing T-helper 1 (Th1) cells to transforming growth factor-beta (TGF-beta)-secreting T-regulatory cells, which have opposite roles in modulating immune responses to pathogens, tumor cells, and self-antigens. This review briefly addresses the various T-cell subsets within the CD4+ T-cell family and discusses recent research efforts aimed at elucidating the nature of the 'T-cell help' that has been shown to be essential for optimal immune function. Particular attention is paid to the role of Th cells in tumor immunotherapy. We review some of our own work in the field describing how CD4+ Th cells can enhance anti-tumor cytotoxic T-lymphocyte (CTL) responses by enhancing clonal expansion at the tumor site, preventing activation-induced cell death and functioning as antigen-presenting cells for CTLs to preferentially generate immune memory cells. These unconventional roles for Th lymphocytes, which require direct cell-to-cell communication with CTLs, are clear examples of how versatile these immunoregulatory cells are.

A study on the CD(4) (+) CD (25) (+) regulatory T cells in patients with gastrointestinal malignancies

OBJECTIVES

Regulatory T cells play an active role in the maintenance of the immune system's tolerance of both foreign and self antigens. Particularly, CD(4) (+) CD(25) (+) regulatory T cells participate in tumor immunity. The study provided further evidence on the involvement of CD(4) (+ )CD(25) (+) regulatory T cells in immune system impairment in patients with gastrointestinal malignancies.

METHODS

Using flow cytometry, CD(4) (+ )CD(25) (+) regulatory T cells were analyzed in peripheral blood from 114 patients with gastrointestinal malignancies and 15 healthy controls.

RESULTS

The prevalence of the CD(25) (+) subset in CD(4) (+) T cells was increased in patients with colorectal carcinoma compared with healthy controls. The phenotic characteristics of the CD(4) (+ )CD(25) (+) T cells in patient with malignancies were low expression of CD(45) RA and no expression of CD(69). Our results indicated that when compared with healthy control, the proportions of CD(4) (+) CD(25) (+) T cells in the peripheral blood of patients with colorectal, gastric, and esophageal carcinoma were significantly higher (P < 0.05) in colorectal carcinoma (22.11 +/- 9.65%), gastric carcinoma (17.74 +/- 4.24%), and esophageal carcinoma (24.37 +/- 4.82)%, respectively. Further analysis on the proportion of CD(4) (+ )CD(25) (+) T cells revealed that those patients with gastrointestinal malignancies in stages IV were higher than those of in stage I-III, though no significant difference was observed (P > 0.05). However, the proportion of CD(4) (+ )CD(25) (+) T cells in the patients with relapse gastric carcinoma (23.32 +/- 4.98%) was significantly higher than that of patients with primary gastric carcinoma (P < 0.01).

CONCLUSIONS

The increased CD(4) (+ )CD(25) (+) T cells in patients with gastrointestinal malignancies may be related to immunosuppression and tumor progression. This suggests that elimination or reduction of CD(4) (+ )CD(25) (+) regulatory T cells can improve effective tumor immunity for immunotherapy.

Immunosuppressive regulatory T cells are associated with aggressive breast cancer phenotypes: a potential therapeutic target

FoxP3 is a marker for immunosuppressive CD25+CD4+ regulatory T cells. These regulatory T cells are thought to play a role in inducing immune tolerance to antigens and may be selectively recruited by carcinomas. We investigated whether breast carcinomas had significant numbers of FoxP3-positive regulatory T cells by immunohistochemistry, and if their presence was associated with other prognostic factors, such as Nottingham grade, hormone receptor immunohistochemical profile, tumor size, or lymph node metastases. Ninety-seven needle core or excisional breast biopsies with invasive breast carcinoma diagnosed at the University of Washington were stained with antibodies to FoxP3, estrogen receptor, and Her2/neu. The numbers of FoxP3-positive cells present within the neoplastic epithelium, and immediately adjacent stroma were counted manually in three high-powered fields (HPFs; x 400) by two independent pathologists. The average scores were then correlated with the parameters of interest. A threshold of >or=15 FoxP3-positive cells/HPF was used to define a FoxP3-positive case in some analyses. Higher average numbers of FoxP3-positive cells present significantly correlated with higher Nottingham grade status (P=0.000229). In addition, the presence of significant numbers (>or=15/HPF) of FoxP3-positive cells in breast carcinoma was positively associated with higher Nottingham grade (P=0.00002585). Higher average numbers of FoxP3-positive cells were also significantly associated with larger tumor size (>2.0 cm; P=0.012824) and trended toward an association with estrogen receptor negativity. Interestingly, 'triple-negative' (estrogen and progesterone receptor negative and Her2/neu negative) Nottingham grade III cases were also significantly associated with high numbers of FoxP3 cells. These results argue that regulatory T cells may play a role in inducing immune tolerance to higher grade, more aggressive breast carcinomas, and are a potential therapeutic target for these cancers.

Depletion of CD4(+)CD25(+) regulatory T cells can promote local immunity to suppress tumor growth in benzo[a]pyrene-induced forestomach carcinoma

AIM

To elucidate the distribution of CD4(+)CD25(+) regulatory T cells (Tregs) in different lymphoid tissues and its local enhancement on tumor growth before and after depletion of CD4(+)CD25(+) Tregs.

METHODS

Female ICR mice were gavaged with benzo[a]pyrene (BaP) to induce forestomach carcinoma. CD4(+)CD25(+) Tregs were intraperitoneally depleted with monoclonal antibody PC61. These mice were divided into BaP-only, BaP + IgG, BaP + PC61, and control groups. The forestomach of mice was dissected for histological analysis, and tunnel test was performed for apoptosis of tumor cells. CD4(+)CD25(+) Tregs were sorted from different lymphoid tissues and expression of Foxp3, IL-10, and chemokine receptors was analyzed by flow cytometry, semi-quantitative and real-time polymerase chain reaction.

RESULTS

The mice gavaged with only BaP showed increased forestomach papilloma and carcinoma at wk 16 and 32. The proportion of CD4(+)CD25(+) Tregs was significantly higher in peri-stomach regional lymph nodes than in other lymphoid tissues. These CD4(+)CD25(+) Tregs in regional lymph nodes expressed higher levels of Foxp3 and IL-10, enriched in the CD62L-subset, and CCR1 and CCR5 chemokine receptors. In mice gavaged with BaP + PC61, the number of tumor nodules and tumor volume decreased significantly with massive infiltrating cells and apoptosis of tumor cells. In the draining regional lymph nodes, the number of CD4(+)CD25(+) Tregs also decreased significantly.

CONCLUSION

Inducible and activated CD4(+)CD25(+) Tregs in the draining regional lymph nodes suppress host local immunity during tumor growth. Depletion of CD4(+)CD25(+) Tregs can promote host local immunity to suppress tumor growth.

Differential impairment of regulatory T cells rather than effector T cells by paclitaxel-based chemotherapy

Characterized as a mitotic inhibitor, paclitaxel has gained importance as a promising agent for the treatment of advanced non-small cell lung cancer (NSCLC). However, whether paclitaxel has immune modulatory effects remains unclear. In this study, we analyzed 55 peripheral blood samples from NSCLC patients who underwent paclitaxel-based chemotherapy. We found that among the lymphocyte subsets, paclitaxel selectively decreased the size of the regulatory T cell (Treg) population rather than other subsets including effector T cells (Teff). Apoptosis by upregulating the expression of the cell death receptor Fas (CD95) contributed to the reduced cell number of Treg. Importantly, the inhibitory function of Treg was significantly impaired, while the production of Th1 cytokines IFN-gamma and IL-2 and the expression of the activation marker CD44 among CD4(+) and CD8(+) T cells were augmented after paclitaxel treatment. These results strongly demonstrated that paclitaxel-based chemotherapy played important roles in modulating immune responses.

Regulatory T cells as therapeutic target in Hodgkin's lymphoma

BACKGROUND

The clinical and pathological features of Hodgkin's lymphoma (HL) reflect an abnormal immune response that results from cytokines and chemokines secreted by Hodgkin/Reed-Sternberg (H/R-S) cells and/or the surrounding tissue.

OBJECTIVE

Increasing evidence indicates that H/R-S cells recruit and/or induce regulatory T (Treg) cells that contribute to an ineffective immune clearance of the malignant cell types and may also impair effects of adaptive cellular immunotherapy applied in HL.

METHODS

In this review we highlight advances in the understanding of immune regulation in HL, and discuss implications for immunotherapy in this disease by targeting Treg cells. However, the origin, development, migration and functional mechanism of these Treg cells are under discussion.

RESULTS/CONCLUSION

As studies demonstrate that the depletion and/or manipulation of Treg cells enhance antitumor immunity, these novel treatment approaches may improve the therapy especially for patients with refractory or relapsed HL.

Fusions of dendritic cells with breast carcinoma stimulate the expansion of regulatory T cells while concomitant exposure to IL-12, CpG oligodeoxynucleotides, and anti-CD3/CD28 promotes the expansion of activated tumor reactive cells

Vaccination of patients with dendritic cell (DC)/breast carcinoma fusions stimulated antitumor immune responses in a majority of patients with metastatic disease but only a subset demonstrate evidence of tumor regression. To define the factors that limit vaccine efficacy, we examined the biological characteristics of DC/breast carcinoma fusions as APCs and the nature of the vaccine-mediated T cell response. We demonstrate that fusion of DCs with breast carcinoma cells up-regulates expression of costimulatory and maturation markers and results in high levels of expression of IL-12 consistent with their role as activated APCs. Fusion cells also express the chemokine receptor CCR7, consistent with their ability to migrate to the draining lymph node. However, DC/breast cancer fusions stimulate a mixed T cell response characterized by the expansion of both activated and regulatory T cell populations, the latter of which is characterized by expression of CTLA-4, FOXP3, IL-10, and the suppression of T cell responses. Our results demonstrate that IL-12, IL-18, and TLR 9 agonist CpG oligodeoxynucleotides reduce the level of fusion-mediated regulatory T cell expansion. Our results also demonstrate that sequential stimulation with DC/breast carcinoma fusions and anti-CD3/CD28 results in the marked expansion of activated tumor-specific T cells. These findings suggest that DC/breast carcinoma fusions are effective APCs, but stimulate inhibitory T cells that limit vaccine efficacy. In contrast, exposure to TLR agonists, stimulatory cytokines, and anti-CD3/CD28 enhances vaccine efficacy by limiting the regulatory T cell response and promoting expansion of activated effector cells.

Regulatory T cells in colorectal cancer patients suppress anti-tumor immune activity in a COX-2 dependent manner

OBJECTIVE

Naturally occurring regulatory T (T(R)) cells suppress autoreactive T cells whereas adaptive T(R) cells, induced in the periphery, play an important role in chronic viral diseases and cancer. Several studies indicate that cyclooxygenase (COX) inhibitors prevent cancer development of colon adenomas and delay disease progression in patients with colorectal cancer (CRC). We have shown that adaptive T(R) cells express COX-2 and produce PGE(2) that suppress effector T cells in a manner that is reversed by COX-inhibitors.

METHODS AND RESULTS

Here we demonstrate that CRC patients have elevated levels of PGE(2) in peripheral blood, and CRC tissue samples and draining lymph nodes display increased numbers of FOXP3+ T(R) cells. Depletion of T(R) cells from PBMC enhanced anti-tumor T-cell responses to peptides from carcinoembryonic antigen. Furthermore, the COX inhibitor indomethacin and the PKA type I antagonist Rp-8-Br-cAMPS significantly improved the anti-tumor immune activity.

CONCLUSION

We suggest that adaptive T(R) cells contribute to an immunosuppressive microenvironment in CRC and inhibit effector T cells by a COX-2-PGE(2)-dependent mechanism and thereby facilitate tumor growth. Therapeutic strategies targeting T(R) cells and the PGE(2)-cAMP pathway may be interesting to pursue to enhance anti-tumor immune activity in CRC patients.

Cancer vaccination: manipulation of immune responses at old age

The incidence of cancer has increased over the last decade, mainly due to an increase in the elderly population. Vaccine therapy for cancer is less toxic than chemotherapy or radiation and could be, therefore, especially effective in older, more frail cancer patients. However, it has been shown that older individuals do not respond to vaccine therapy as well as younger adults. This has been attributed to T-cell unresponsiveness, a phenomenon also observed in cancer patients per se. This review summarizes the current knowledge of impaired T-cell responses in cancer patients and the elderly, and the results of cancer vaccination in preclinical models at young and old age. Finally, various approaches how to manipulate immune responses against cancer by vaccination at older age will be proposed.

Photodynamic therapy plus low-dose cyclophosphamide generates antitumor immunity in a mouse model

Photodynamic therapy (PDT) is a modality for the treatment of cancer involving excitation of nontoxic photosensitizers with harmless visible light-producing cytotoxic reactive oxygen species. PDT causes apoptosis and necrosis of tumor cells, destruction of the tumor blood supply, and activation of the immune system. The objective of this study was to compare in an animal model of metastatic cancer PDT alone and PDT combined with low-dose cyclophosphamide (CY) a treatment that has been proposed to deplete regulatory T cells (T-regs) and increase the immune response to some tumors. We used J774 tumors (a highly metastatic reticulum cell sarcoma line) and PDT with benzoporphyrin derivative monoacid ring A, verteporfin for injection (BPD; 1-mg/kg injected i.v. followed after 15 min by 150 J/cm(2) of 690-nm light). CY (50 or 150 mg/kg i.p.) was injected 48 h before light delivery. PDT alone led to tumor regressions and a survival advantage but no permanent cures were obtained. BPD-PDT in combination with low-dose CY (but not high-dose CY) led to 70% permanent cures. Low-dose CY alone gave no permanent cures but did provide a survival advantage and was shown to reduce CD4+FoxP3+ T-regs in lymph nodes, whereas high-dose CY reduced other lymphocyte classes as well. Cured animals were rechallenged with J774 cells, and the tumors were rejected in 71% of mice. Cured mice had tumor-specific T cells in spleens as determined by a (51)Cr release assay. We conclude that low-dose CY depletes T-regs and potentiates BPD-PDT, leading to tumor cures and memory immunity.

Infiltrating regulatory T cell numbers is not a factor to predict patient's survival in oesophageal squamous cell carcinoma

CD4/8 status has been previously reported to be a critical factor in the prognosis of oesophageal squamous cell carcinoma (OSCC). In the current study, we investigated the effect of regulatory T cells (T_reg; Foxp3⁺ lymphocytes) on the status of CD4⁺ and CD8⁺ T cells in 122 patients with OSCC. Immunohistochemical analysis of T_reg was performed using an antibody against Foxp3. The survival rate for low Foxp3 patients was significantly lower than for high Foxp3 patients (P=0.0028 by log-rank test), but Foxp3 status did not significantly correlate with prognosis in CD4/8(+/+) patients or CD4/8(+/−) or (−/+) patients (P=0.5185 and 0.8479, respectively, by log-rank test). We also found that Foxp3 status correlated with CD4/8 status (P=0.0002 by χ² test) and that the variance of CD8/CD4 ratio in patients with low Foxp3 was larger than in patients with high Foxp3 (P<0.0001 by F-test). Thus, the results do not support the idea that T_reg suppress anti-tumour immunity in patients with OSCC. Rather, the CD8/CD4 ratio and CD4/8 status appear to be critical factors in anti-tumour immunity. Furthermore, T_reg numbers correlate with both the CD8/CD4 ratio and the CD4/8 status, suggesting that T_reg number is not a factor to predict patient's survival in OSCC.

Depletion of CD4+ CD25+ regulatory T cells inhibits local tumour growth in a mouse model of B cell lymphoma

Regulatory T cells (T(regs)) may inhibit immunity against cancer. Induction and expansion of T(regs) in the immunosuppressive microenvironment created by a growing tumour appear to be one of the mechanisms by which it can evade host defence. We studied the impact of CD25+ T(regs) in a B cell lymphoma model in which Rag2-/- mice received adoptive transfer of wild-type spleen cells with or without CD25+ cells, and concurrently subcutaneous inoculation of the B cell lymphoma cell line A20. We also examined the effect of engaging the glucocorticoid-induced tumour necrosis factor receptor (GITR) - an approach reported previously to abrogate the suppressive effects of T(regs). Mice that received spleen cells depleted of CD25+ T(regs) showed significantly slower tumour growth and increased survival compared with mice that received unsorted spleen cells. The T(reg)-depleted group also had significantly more CD8+ T cells infiltrating the tumours and higher levels of serum immunoglobulin G subclasses. The anti-GITR treatment had no significant effect on tumour growth, survival or immunoglobulin production. In the CD25-depleted group four of 10 mice developed clinical signs of autoimmunity, in contrast to none in the non-depleted group. Forkhead box P3+ T cells were found in tumour-draining lymph nodes in mice in the CD25-depleted group, suggesting an in vivo induction or expansion of rare transferred donor T(regs). Thus, our study showed that removal of CD25+ T(regs) enhanced anti-tumour immunity against local growth of a B cell lymphoma and that induction or expansion of T(regs) could be one mechanism by which the growing tumour evades immune surveillance.

Comparative methodologies of regulatory T cell depletion in a murine melanoma model

There has been recent interest in the depletion of regulatory T cells (Tregs) as part of a multi-faceted approach to the immunotherapy of melanoma patients. This is in part due recent findings that convincingly show that Tregs are an integral part of regulating and even suppressing an immune response to growing tumor cells. We therefore compared three methods of Treg depletion and/or elimination, utilizing low dose cyclophosphamide (CY), a specific antibody directed against the IL-2 receptor found on Tregs (PC61) and the use of denileukin diftitox (DD), which is a fusion protein designed to have a direct cytocidal action on cells which express the IL-2 receptor. We show that CY administration resulted in the highest reduction in Tregs among the three reagents. However, the reduction in Tregs with CY was also associated with the concomitant reduction of CD8(+) T cells and a lack of tumor antigen priming. Utilization of DD resulted in a >50% Treg cell reduction without parallel cytocidal effects upon other T cell subsets but did not enhance anti-tumor immunity against B16 melanoma. Lastly, the PC61 showed a moderate reduction of Tregs that lasted longer than the other reagents, without a reduction in the total number of CD8(+) T cells. Furthermore, PC61 treatment did not abrogate tumor antigen-specific immunity elicited by dendritic cells (DC). We therefore conclude that PC61 administration was the most effective method of reducing Tregs in a murine melanoma model in addition to providing evidence of a synergistic effect when combined with DC-based immunotherapy.

Partial reduction of human FOXP3+ CD4 T cells in vivo after CD25-directed recombinant immunotoxin administration

The regulation of tolerance to self-proteins and the suppression of T-cell responses have in part been attributed to the activity of CD25+CD4+ T regulatory (Treg) cells. Further, Treg cells can inhibit the antitumor effectiveness of adoptive immunotherapy and active immunization approaches in preclinical models. In an effort to selectively eliminate Treg cells from human peripheral blood mononuclear cell to potentially bolster antitumor responses, we have evaluated the Treg-cell depleting capacity of the CD25-directed immunotoxin, RFT5-SMPT-dgA. In preclinical studies, incubation of human peripheral blood mononuclear cell with RFT5-SMPT-dgA mediated a partial reduction in the levels of CD25+, Foxp3-expressing CD4+ T cells in vitro. Administration of RFT5-SMPT-dgA to 6 patients with metastatic melanoma induced a transient but robust reduction in the number of CD25high CD4 T cells in vivo (a 97.5% mean reduction at nadir; from 69.4 +/- 12.4 cells/miroL to 1.7 +/- 0.3 cells/microL). The reduction in FOXP3+ CD4 T-cell number was less comprehensive (a 71.3% mean reduction at nadir; from 66.6 +/- 16.5 cells/microL to 14.2 +/- 3.9 cells/tL). This resulted in the selective persistence of a stable number of CD25(low/neg) FOXP3+ CD4+ T cells in vivo. No objective antitumor responses were seen in any patient. Our results indicate that the CD25-directed, RFT5-SMPT-dgA immunotoxin can mediate a transient, partial reduction in Treg-cell frequency and number in vitro and in vivo and suggest that comprehensive eradication of human Treg cells in vivo may require the ability to target and eliminate FOXP3+ CD4+ T cells expressing both high and low levels of CD25.

Cytokine, chemokine, and co-stimulatory fusion proteins for the immunotherapy of solid tumors

This chapter describes the generation of novel reagents for the treatment of cancer using fusion proteins constructed with natural ligands of the immune system. Immunotherapy is a powerful therapeutic modality that has not been fully harnessed for the treatment of cancer. We and others have hypothesized that if the proper immunoregulatory ligands can be targeted to the tumor, an effective immune response can be mounted to treat both established primary tumors and distant metastatic lesions. Though it is generally believed that immunotherapy has the potential to treat only residual disease, we offer evidence that this approach can, by itself, destroy large tumor masses and produce lasting remissions of experimental solid tumors. From these studies, three major classes of immune activators, namely, cytokines, chemokines, and costimulatory molecules, have been shown to generate antitumor responses in animal models. In addition, the reversal of immune tolerance by the deletion of T regulatory (Treg) cells has been shown to be equally important for effective immunotherapy. In an attempt to identify reagents that can provide an enhanced immune stimulation and treatment of cancer, our laboratory has developed a novel monoclonal antibody targeting approach, designated Tumor Necrosis Therapy (TNT), which utilizes stable intracellular antigens present in all cell types but which are only accessible in dead and/or dying cells. Since tumors contain necrotic and degenerating regions that account for 30-80% of the tumor mass, this targeting approach can be used to deliver therapeutic reagents to the core of tumors, a site abundant in tumor antigens. In our first set of reagents, a panel of cytokine fusion proteins was genetically engineered using monoclonal antibody chimeric TNT-3 (chTNT-3) directed against necrotic regions of tumors (single-stranded DNA) fused with IL-2, or GM-CSF, or TNFalphaa, or IFNgamma. Tested against different solid tumors, these reagents were found to mount an effective although transient immune response to tumor especially when used in combination. To improve upon these results, additional chTNT-3 fusion proteins using the liver-expression chemokine (LEC) and the costimulatory molecule B7.1 were constructed. Both of these reagents were found to work significantly better than the above cytokine fusion proteins due to their ability to stimulate multiple arms of the immune system deemed useful for cancer immunotherapy. Finally, the Tumor Necrosis Factor Superfamily (TNFSF) gene DC137L was used to generate chTNT-3 antibody (targeted) and soluble Fc (untargeted) fusion proteins. When used alone, both forms of costimulatory fusion proteins were found to produce in a s dose-dependent manner, complete regression of murine solid tumors. Evidence is presented to show that Treg cells play an important role in suppressing antitumor immunity since the deletion of these cells, when used in combination with LEC or costimulatory fusion proteins, produced profound and effective treatment with sustained memory. It is hoped that these data will further the preclinical development of soluble Fc and antibody based fusion proteins fro the immunotherapy of cancer.

How regulatory CD25+CD4+ T cells impinge on tumor immunobiology: the differential response of tumors to therapies

Aiming to get a better insight on the impact of regulatory CD25(+)CD4(+) T cells in tumor-immunobiology, a simple mathematical model was previously formulated and studied. This model predicts the existence of two alternative modes of uncontrolled tumor growth, which differ on their coupling with the immune system, providing a plausible explanation to the observation that the development of some tumors expand regulatory T cells whereas others do not. We report now the study of how these two tumor classes respond to different therapies, namely vaccination, immune suppression, surgery, and their different combinations. We show 1) how the timing and the dose applied in each particular treatment determine whether the tumor will be rejected, with or without concomitant autoimmunity, or whether it will continue progressing with slower or faster pace; 2) that both regulatory T cell-dependent and independent tumors are equally sensitive to vaccination, although the former are more sensitive to T cell depletion treatments and are unresponsive to partial surgery alone; 3) that surgery, suppression, and vaccination treatments, can synergistically improve their individual effects, when properly combined. Particularly, we predict rational combinations helping to overcome the limitation of these individual treatments on the late stage of tumor development.

Increase of CD4+ CD25+ regulatory T cells in the peripheral blood of patients with metastatic carcinoma: a Phase I clinical trial using cyclophosphamide and immunotherapy to eliminate CD4+ CD25+ T lymphocytes

We determined the number and functional status of CD4+ CD25(high) regulatory T cells (Treg) in blood samples from patients with metastatic carcinoma, and evaluated their sensitivity to a single intravenous infusion of cyclophosphamide. Treg numbers were significantly higher in 49 patients with metastatic cancer (9.2% of CD4+ T cells) compared to 24 healthy donors (7.1%). These cells expressed the transcription factor forkhead box P3 (FoxP3), glucocorticoid-induced tumour necrosis factor receptor family-related protein (GITR) and intracellular CD152, and demonstrated a suppressive activity in vitro against CD4+ CD25- autologous proliferation. At a single intravenous infusion, cyclophosphamide failed, in association with a non-specific immunotherapy by intratumoral bacille Calmette-Guérin (BCG), to modulate significantly Treg numbers or function. Metastatic cancer is associated with an expansion of peripheral blood CD4+ CD25(high) FoxP3+ GITR+ CD152+ Treg cells whose immunosuppressive properties do not differ from those of healthy subjects. Moreover, cyclophosphamide administration may not represent an optimal therapy to eliminate Treg, which further underlines the need to identify specific agents that would selectively deplete these cells.

RA8, a human anti-CD25 antibody against human Treg cells

Although anti-CD25 antibodies exist for clinical use in patients, there is a need for the development of a human Treg antibody that will abrogate the immunosuppressive function of this small but critical T cell subtype. Based upon mounting evidence that the level of Treg cells in the tumor microenvironment correlates with clinical prognosis and stage in man, it appears that Treg cells play an important role in the tumor's ability to overcome host immune responses. In mice, the rat anti-mouse CD25 antibody PC61 causes depletion of CD25-bearing Treg cells both peripherally in lymphatic tissues and in the tumor microenvironment, without inducing symptoms of autoimmunity. A similar antibody, though with the ability to delete Treg cells specifically, would be an important new tool for reversing tumor escape associated with Treg immunosuppression in man. To begin to generate such a reagent, we now describe the development of a human anti-CD25 antibody using a novel yeast display library. The target antigen CD25-Fc was constructed and used for five rounds of selection using a non-immune yeast display library that contained as many as 10(9) single chain variable fragments (scFv). Two unique clones with low K(D) values (RA4 and RA8) were then selected to construct fully human anti-CD25 antibodies (IgG1/kappa) for stable expression. One antibody, RA8, showed excellent binding to human CD25(+) cell lines and to human Treg cells and appears to be an excellent candidate for the generation of a human reagent that may be used in man for the immunotherapy of cancer.

Augmented induction of CD8+ cytotoxic T-cell response and antitumor effect by DCs pulsed with virus-like particles packaging with CpG

The present study aims at establishing a novel vaccine procedure based on HBc-VLP-pulsed DCs. Immature mice BMDCs could capture HBc-VLP or HBc-VLP packaging CpG efficiently and present the antigen to syngeneic mice spleen T cells in vitro. Immunization with DCs showed that compared to VLP-pulsed DCs, VLP packaging CpG-pulsed DCs elicit stronger T-cell responses in vivo, as measured by both intracellular production of IFN-gamma and in vivo killing assays by Ag-specific T cells. In the B16-pIR-HH tumor therapy model, the growth of established tumors was significantly inhibited by single immunization of DCs pulsed with HBc-VLP packaged with CpG, resulting in significantly longer survival of immunized animals and strikingly, high frequencies (>10% of CD8(+) cells) of protective CTL could be induced and maintained. The mice immunized with DCs treated with HBc-VLP, however, trigger an antitumor effect at the early phase of vaccination, after 20 days of tumor injection, the tumor growth inhibition of VLP-pulsed DCs vaccination was decreased gradually and the fact could be interpreted by the decreasing number of antigen-specific CD8(+) T-cell and IFN-gamma(+)-producing CD8(+) T cell. This study therefore shows that the use of HBc-VLP packaging CpG-pulsed DCs could facilitate the development of effective T-cell-based vaccines.

Association of cervical cancer with the presence of CD4+ regulatory T cells specific for human papillomavirus antigens

Because of their important role in the maintenance of self-tolerance, CD4(+) regulatory T cells prevent autoimmune diseases but also curtail the efficacy of T cell immune responses against cancers. We now show that this suppressive action of CD4(+) regulatory T cells is not limited to cancers displaying tumor-associated self antigens, such as melanomas, but also extends to human papillomavirus (HPV)-positive cervical cancers that express foreign tumor antigens. HPV-specific CD4(+) T cells isolated from lymph node biopsies of cervical cancer patients were found to suppress proliferation and cytokine (IFN-gamma, IL-2) production by responder T cells. The capacity of HPV-specific CD4(+) T cells to exert this suppressive effect depended on their activation by cognate HPV antigen and on close-range interactions with responder T cells. HPV-specific CD4(+) regulatory T cells were also retrieved from cervical cancer biopsies, suggesting that they interfere with the anti-tumor immune response at both the induction and effector levels. Our findings offer a plausible explanation for the observed failure of the tumor-specific immune response in patients with cervical carcinoma.

Tregs and rethinking cancer immunotherapy

Tumors express antigens that should induce immune-mediated rejection, but spontaneous rejection of established tumors is rare. Recent work demonstrates that one reason for the lack of tumor rejection is that tumors actively defeat host immunity. This concept forces us to rethink current approaches to harnessing potent, specific host immunity to battle cancer, most of which are based on the paradigm that inducing more antitumor immune cells alone is therapeutic. However, as I discuss in this Personal Perspective, a newer paradigm predicts that reducing tumor-driven immune suppression will be clinically beneficial. CD4+CD25+ Tregs are one mechanism of tumor-driven immune evasion that provide prototypical targets for testing novel anticancer treatment strategies within the newer paradigm.

CD4+CD25+T cells regulate the intensity of hypersensitivity responses to peanut, but are not decisive in the induction of oral sensitization

BACKGROUND

Naturally occurring CD4+CD25+ regulatory T cells (Tregs) play a critical role in the maintenance of self-tolerance and it has been suggested that these Tregs may also be involved in preventing allergic disease.

OBJECTIVE

The precise role of CD4+CD25+ T cells in the regulation of allergic responses to mucosal antigens remains to be elucidated. In the present study, it was investigated whether CD4+CD25+ T cells are involved in the induction of oral tolerance and whether they play a role in controlling hypersensitivity responses to food proteins.

METHODS

CD4+CD25+ T cells were depleted with PC61 mAb before the induction of low dose oral tolerance to peanut extract (PE). In addition, CD4+CD25+ T cell depletion was performed during sensitization or before oral challenge, using a C3H/HeOuJ mouse model of allergic sensitization to peanut.

RESULTS

Oral tolerance to PE could not be induced in CD4+CD25+ T cell-depleted mice. However, CD4+CD25+ T cell depletion during long-term exposure to PE alone did not result in allergic sensitization. In sensitized mice, anti-CD25 treatment during oral exposure resulted in higher levels of PE-specific IgE and increased mast cell degranulation upon an oral challenge. In contrast, anti-CD25 treatment of PE-sensitized mice before oral challenges did not affect the level of mast cell degranulation.

CONCLUSION

These results indicate that CD4+CD25+ Tregs are involved in maintaining tolerance to oral antigens and regulate the intensity of an IgE-mediated food hypersensitivity response, but are not crucial in preventing sensitization. Accordingly, CD4+CD25+ Tregs may represent a potential tool for the treatment of food allergic disorders.

T-regulatory cells are relatively deficient in squamous carcinomas undergoing regression in mice immunized with a squamous carcinoma vaccine enriched for immunotherapeutic cells

In a prior report (Int J Cancer 2006; 119: 339-348), we described a new vaccination strategy for squamous cell carcinoma (SCC). The vaccine was prepared by transfer of unfractionated DNA-fragments (25 kb) from KLN205 cells, a squamous carcinoma cell line (DBA/2 origin; H-2(d)) into LM cells, a highly immunogenic mouse fibroblast cell line (C3H/He origin; (H-2(k))). As only a small proportion of the transfected cell population was expected to have incorporated DNA segments that included genes specifying antigens associated with the squamous carcinoma cells, we devised a novel strategy to enrich the vaccine for immunotherapeutic cells. Enhanced immunity to squamous carcinoma was induced in tumor-bearing mice treated solely by immunization with the enriched vaccine, which translated into prolonged survival without toxicity. Here, we describe the characteristics of the cell populations infiltrating established squamous carcinomas undergoing regression in mice immunized with vaccines enriched for immunotherapeutic cells. The results indicated that CD8+ T cells were predominant and that T-regulatory cells (FoxP3+, CD4/CD25+, CD4/CD62L(high), CD4/CTLA-4e) were relatively deficient in the regressing tumors. Inflammatory infiltrates were not detected in various organs and tissues of mice immunized with the DNA-based vaccine.

Induction of immunity to neuroblastoma early after syngeneic hematopoietic stem cell transplantation using a novel mouse tumor vaccine

Autologous HSCT has resulted in improved event-free survival in patients with advanced neuroblastoma, but most of these patients still relapse. We previously reported that transient transfection of mouse neuroblastoma cells with plasmid DNA vectors encoding immune costimulatory molecules generates cell-based vaccines capable of inducing potent antitumor T cell immunity. In this study, we explored the effectiveness of tumor vaccine administration soon after HSCT. Soon after transplantation, only vaccinated mice that had received an adoptive transfer of syngeneic T cells survived tumor challenge. Tumor protective immunity in the transplant recipients was dependent on CD4(+) and CD8(+) T cells, and tumor-reactive T cells in the spleens of vaccinated mice could be detected in IFN-gamma enzyme-linked immunosorbent spot (ELISPOT) assays. Our data indicate that the adoptive transfer of T cells was absolutely required for induction of protective immunity by the tumor vaccine. Adoptive transfer of T cells accelerated T cell reconstitution, but it also resulted in increased percentages of CD4(+)CD25(+)Foxp3(+) cells soon after HSCT. Treatment of HSC transplant recipients with an anti-CD25 mAb before tumor vaccination inhibited antitumor immunity and significantly decreased the number of IFN-gamma-secreting tumor-specific CD4 T cells. However, physical depletion of CD25(+) cells from the adoptively transferred splenocytes appeared to increase the efficacy of tumor vaccination. Collectively, these results demonstrate that anti-neuroblastoma immunity can be induced soon after HSCT using a novel cell-based cancer vaccine. However, sufficient numbers of T cells must be added to the graft to achieve protective antitumor immunity, and depletion of CD25(+) T cells from adoptively transferred T cells might provide some additional benefit. These translational studies will aid in our development of post-HSCT vaccines for neuroblastoma.

Tumor Evasion of the Immune System by Converting CD4+CD25− T Cells into CD4+CD25+ T Regulatory Cells: Role of Tumor-Derived TGF-β

CD4+CD25+ T regulatory (T(reg)) cells were initially described for their ability to suppress autoimmune diseases in animal models. An emerging interest is the potential role of T(reg) cells in cancer development and progression because they have been shown to suppress antitumor immunity. In this study, CD4+CD25- T cells cultured in conditioned medium (CM) derived from tumor cells, RENCA or TRAMP-C2, possess similar characteristics as those of naturally occurring T(reg) cells, including expression of Foxp3, a crucial transcription factor of T(reg) cells, production of low levels of IL-2, high levels of IL-10 and TGF-beta, and the ability to suppress CD4+CD25- T cell proliferation. Further investigation revealed a critical role of tumor-derived TGF-beta in converting CD4+CD25- T cells into T(reg) cells because a neutralizing Ab against TGF-beta, 1D11, completely abrogated the induction of T(reg) cells. CM from a nontumorigenic cell line, NRP-152, or irradiated tumor cells did not convert CD4+CD25- T cells to T(reg) cells because they produce low levels of TGF-beta in CM. Finally, we observed a reduced tumor burden in animals receiving 1D11. The reduction in tumor burden correlated with a decrease in tumor-derived TGF-beta. Treatment of 1D11 also reduced the conversion of CD4+ T cells into T(reg) cells and subsequent T(reg) cell-mediated suppression of antitumor immunity. In summary, we have demonstrated that tumor cells directly convert CD4+CD25- T cells to T(reg) cells through production of high levels of TGF-beta, suggesting a possible mechanism through which tumor cells evade the immune system.

The role of regulatory T cells in ovarian cancer

Regulatory T cells (T(reg)), also termed suppressor T cells, control self-reactive T cells in the periphery, thereby conferring protection against immunologic self-destruction. While T(reg) are essential for the prevention of autoimmunity, they also inhibit immune responses against tumor antigens. This is corroborated by an increased mortality rate associated with the presence of a high number of intratumoral T(reg). Tumor infiltration by non-T(reg), on the other hand, is predictive for a substantially longer patient survival. These clinical data suggest that ovarian cancer patients can spontaneously mount effective antitumor immune responses that are undermined by T(reg)-mediated tolerization. The present article reviews clinical and experimental findings on T(reg) in ovarian cancer, with special regard to potential therapeutic implications, which may result from the existing evidence.

High accumulation of T regulatory cells prevents the activation of immune responses in aged animals

In our previous in vivo study we demonstrated that young BALB/c mice effectively rejected the BM-185 tumor cells expressing enhanced GFP (EGFP) as a surrogate tumor Ag. In contrast, old BALB/c mice succumbed to the BM-185-EGFP tumors, indicating that there is a deficiency in old animals preventing the rejection of immunogenic tumors. There is cumulative evidence indicating that regulatory T (T(reg)) cells control the activation of primary and memory T cell responses. However, very little is known about whether there is a relation between T(regs) and the lack of immune responses in the aged. We evaluated young and aged animals, and our results demonstrated that there are significantly more CD4+CD25+FoxP3+ and CD8+CD25+FoxP3+ T(regs) in the spleen and lymph nodes of old animals when compared with the young. Depletion of CD25+ cells with anti-CD25 mAb induces the rejection of BM-185-EGFP cells, restores antitumor T cell cytotoxic activity, and results in the generation of a protective memory response against the BM-185 wild-type tumors in old mice. Furthermore, vaccination with CpG-oligodeoxynucleotide decreases the number of T(reg) cells in old animals to the same levels as young mice, restoring the primary and memory antitumor immune responses against BM-185-EGFP tumors. Taken together, these results indicate that there is a direct correlation between the expansion of T(reg) cells and immune deficiency in the old, and that depletion of these cells might be critical for restoring immune responses in aged animals.

CD4+CD25high T cells are enriched in the tumor and peripheral blood of prostate cancer patients

In this study, we investigated whether CD4+CD25high regulatory T cells (Treg) are increased in the tumor tissue and peripheral blood of early-stage prostate cancer patients undergoing prostatectomy. We show that the prevalence of CD4+CD25high T cells inside the prostate was significantly higher in the tumor compared with benign tissue from the same prostate. Furthermore, the frequency of CD4+CD25high T cells in peripheral blood was significantly higher in prostate cancer patients compared with normal donors. A proportion of the CD4+CD25high T cells was also shown to be glucocorticoid-induced TNF receptor, ICOS, and FOXP3 positive. Moreover, CD4+CD25+ T cells from blood and supernatants from cultured prostate tumor tissue samples exhibited immunosuppressive function in vitro. Furthermore, supernatants from cultured prostate tissue samples and prostate cancer ascites fluid induced migration of CD4+CD25+ T cells and were shown to contain the regulatory T cell chemokine CCL22 by ELISA. Our findings indicate that Tregs are an important cellular component of early-stage prostate tumors, and thus new therapeutic strategies aimed at inhibition or depletion of Tregs may improve prostate cancer immunotherapy.

The tumor-draining lymph node as an immune-privileged site

Lymph nodes that lie immediately downstream of tumors [tumor-draining lymph nodes (TDLNs)] undergo profound alterations due to the presence of the upstream tumor. The antigen-presenting cell population in TDLNs becomes modified such that tumor-derived antigens are cross-presented by host cells in a tolerizing fashion. In addition, the number and suppressor activity of regulatory T cells (Tregs) are increased in the TDLN. Emerging evidence suggests that some of these Tregs may be generated de novo against specific tumor-derived antigens, and thus they arise as a direct consequence of antigen presentation in the TDLN. Others may represent Tregs against self-antigens, which undergo preferential activation in the tolerogenic milieu of the TDLN. The TDLN thus becomes an anatomic context in which presentation of new antigens not only fails to elicit a protective immune response but also actively creates systemic tolerance. In this regard, the TDLN displays features analogous to classical immune privilege. Accumulating evidence thus suggests that the TDLNs, although small in size, may exert a profound tolerizing influence on the rest of the immune system. These mechanisms will need to be interrupted in order for clinical anti-tumor immunotherapy to be successful.

CD4+CD25+ regulatory T-cell-inactivation in combination with adenovirus vaccines enhances T-cell responses and protects mice from tumor challenge

Cancer vaccines are a promising approach to treating tumors or preventing tumor relapse through induction of an immune response against tumor-associated antigens (TAA). One major obstacle to successful therapy is the immunological tolerance against self-antigens which limits an effective antitumor immune response. As a transient reduction of immunological tolerance may enable more effective vaccination against self-tumor antigens, we explored this hypothesis in a CEA tolerant animal model with an adenovirus expressing CEA vaccine in conjunction with inactivation of CD4(+)CD25(+) regulatory T cells. This vaccination modality resulted in increased CEA-specific CD8(+), CD4(+) T cells and antibody response. The appearance of a CD4(+) T-cell response correlated with a stronger memory response. The combined CD25(+) inactivation and genetic vaccination resulted in significant tumor protection in a metastatic tumor model. Non-invasive tumor visualization showed that not only primary tumors were reduced, but also hepatic metastases. Our results support the viability of this cancer vaccine strategy as an adjuvant treatment to prevent tumor relapse in cancer patients.