Administration of a CD25-directed immunotoxin, LMB-2, to patients with metastatic melanoma induces a selective partial reduction in regulatory T cells in vivo

Depletion of endogenous tumor-associated regulatory T cells improves the efficacy of adoptive cytotoxic T-cell immunotherapy in murine acute myeloid leukemia

Tumor-induced immune suppression can permit tumor cells to escape host immune resistance. To elucidate host factors contributing to the poor response of adoptively transferred tumor-reactive cytotoxic T lymphocytes (CTLs), we used a systemic model of murine acute myeloid leukemia (AML). AML progression resulted in a progressive regulatory T-cell (Treg) accumulation in disease sites. The adoptive transfer of in vitro-generated, potently lytic anti-AML-reactive CTLs failed to reduce disease burden or extend survival. Compared with non-AML-bearing hosts, transferred CTLs had reduced proliferation in AML sites of metastases. Treg depletion by a brief course of interleukin-2 diphtheria toxin (IL-2DT) transiently reduced AML disease burden but did not permit long-term survival. In contrast, IL-2DT prevented anti-AML CTL hypoproliferation, increased the number of transferred CTLs at AML disease sites, reduced AML tumor burden, and resulted in long-term survivors that sustained an anti-AML memory response. These data demonstrated that Tregs present at AML disease sites suppress adoptively transferred CTL proliferation, limiting their in vivo expansion, and Treg depletion before CTL transfer can result in therapeutic efficacy in settings of substantial pre-existing tumor burden in which antitumor reactive CTL infusion alone has proven ineffective.

Harnessing the physiology of lymphopenia to support adoptive immunotherapy in lymphoreplete hosts

Lymphopenia enhances the effectiveness of adoptive immunotherapy by facilitating expansion of transferred T cells but also limits the T-cell repertoire available to mediate immune responses and, in humans, is associated with chronic immune dysfunction. Previous studies concluded that lymphopenia augments adoptive immunotherapy by diminishing Tregs and increasing homeostatic cytokines. We sought to determine whether targeted therapies that replicate the physiology of lymphopenia in lymphoreplete hosts could provide a similarly supportive milieu. Pmel-1 T cells were transferred to B16-bearing lymphopenic versus lymphoreplete mice receiving alphaCD25 and/or recombinant human interleukin-7. Although CD25-based Treg depletion was inefficient because of peripheral expansion of CD4+CD25-FOXP3+ cells, outcomes were better in alphaCD25-treated lymphoreplete hosts than in lymphopenic hosts, and adoptive immunotherapy was most effective in lymphoreplete hosts receiving alphaCD25 plus recombinant human interleukin-7. Lymphopenic hosts supported increased proliferation of adoptively transferred antigen-specific T cells, but cells transferred to lymphoreplete recipients receiving targeted therapies showed superior function. Further, determinant spreading was substantial in lymphoreplete hosts but absent in lymphopenic hosts. These results demonstrate that targeted therapies delivered to mimic the "physiology of lymphopenia" enhance the efficacy of adoptive immunotherapy in lymphoreplete hosts and provide a potentially superior alternative to the induction of lymphopenia.

Pretreatment frequency of circulating IL-17+ CD4+ T-cells, but not Tregs, correlates with clinical response to whole-cell vaccination in prostate cancer patients

The aim of this study was to determine the prognostic implications of the pretreatment level of Th17 cells compared with regulatory T-cell status in prostate cancer patients receiving active whole cell immunotherapy. Ten-color flow cytometry was used to analyze IL-17-producing CD4(+) T-cells in the peripheral blood of hormone-resistant non-bone metastatic prostate cancer patients prior to immunotherapy with an allogeneic whole-cell vaccine. Surface expression of the chemokine receptors CCR4 and CCR6 was used to further subdivide IL-17-producing cells into subsets with distinct homing properties. The frequency of circulating regulatory T-cells (Tregs), defined as CD3(+)CD4(+)CD127(lo)Foxp3(+)CD25(+) was compared in the same patients. The frequency of CCR4(-)IL-17(+)CD4(+) T-cells prevaccination inversely correlated with time to disease progression (TTP) in 23 prostate cancer patients. Furthermore, responder (R) patients with statistically significant reductions in PSA velocity (PSAV) in response to the immunotherapy (n = 9), showed a Th17 profile similar to healthy male controls and significantly different from non-responder (NR) patients (n = 14) (i.e., those without any significant reduction in PSAV). In contrast, the frequency of Tregs in peripheral blood in PSA-R (n = 11) and -NR (n = 14) patients was similar (but in both cases, significantly higher than in age-matched healthy men). Accordingly, there was no significant correlation between frequency of Tregs and TTP in these late-stage prostate cancer patients undergoing active immunotherapy. These data imply an important role for IL-17-producing helper T-cells in cancer immunology and highlight their potential use as a pretreatment screen to ensure appropriate treatment is offered to hormone-resistant prostate cancer patients.

Regulatory T cells and the PD-L1/PD-1 pathway mediate immune suppression in malignant human brain tumors

The brain is a specialized immune site representing a unique tumor microenvironment. The availability of fresh brain tumor material for ex vivo analysis is often limited because large parts of many brain tumors are resected using ultrasonic aspiration. We analyzed ultrasonic tumor aspirates as a biosource to study immune suppressive mechanisms in 83 human brain tumors. Lymphocyte infiltrates in brain tumor tissues and ultrasonic aspirates were comparable with respect to lymphocyte content and viability. Applying ultrasonic aspirates, we detected massive infiltration of CD4+FoxP3+CD25(high) CD127(low) regulatory T cells (Tregs) in glioblastomas (n = 29) and metastatic brain tumors (n = 20). No Treg accumulation was observed in benign tumors such as meningiomas (n = 10) and pituitary adenomas (n = 5). A significant Treg increase in blood was seen only in patients with metastatic brain tumors. Tregs in high-grade tumors exhibited an activated phenotype as indicated by decreased proliferation and elevated CTLA-4 and FoxP3 expression relative to blood Tregs. Functional analysis showed that the tumor-derived Tregs efficiently suppressed cytokine secretion and proliferation of autologous intratumoral lymphocytes. Most tumor-infiltrating Tregs were localized in close proximity to effector T cells, as visualized by immunohistochemistry. Furthermore, 61% of the malignant brain tumors expressed programmed death ligand-1 (PD-L1), while the inhibitory PD-1 receptor was expressed on CD4+ effector cells present in 26% of tumors. In conclusion, using ultrasonic tumor aspirates as a biosource we identified Tregs and the PD-L1/PD-1 pathway as immune suppressive mechanisms in malignant but not benign human brain tumors.

Systematic analysis of immune infiltrates in high-grade serous ovarian cancer reveals CD20, FoxP3 and TIA-1 as positive prognostic factors

Background

Tumor-infiltrating T cells are associated with survival in epithelial ovarian cancer (EOC), but their functional status is poorly understood, especially relative to the different risk categories and histological subtypes of EOC.

Methodology/Principal Findings

Tissue microarrays containing high-grade serous, endometrioid, mucinous and clear cell tumors were analyzed immunohistochemically for the presence of lymphocytes, dendritic cells, neutrophils, macrophages, MHC class I and II, and various markers of activation and inflammation. In high-grade serous tumors from optimally debulked patients, positive associations were seen between intraepithelial cells expressing CD3, CD4, CD8, CD45RO, CD25, TIA-1, Granzyme B, FoxP3, CD20, and CD68, as well as expression of MHC class I and II by tumor cells. Disease-specific survival was positively associated with the markers CD8, CD3, FoxP3, TIA-1, CD20, MHC class I and class II. In other histological subtypes, immune infiltrates were less prevalent, and the only markers associated with survival were MHC class II (positive association in endometrioid cases) and myeloperoxidase (negative association in clear cell cases).

Conclusions/Significance

Host immune responses to EOC vary widely according to histological subtype and the extent of residual disease. TIA-1, FoxP3 and CD20 emerge as new positive prognostic factors in high-grade serous EOC from optimally debulked patients.

Cyclophosphamide resets dendritic cell homeostasis and enhances antitumor immunity through effects that extend beyond regulatory T cell elimination

Using a model of established malignancy, we found that cyclophosphamide (Cy), administered at a dose not requiring hematopoietic stem cell support, is superior to low-dose total body irradiation in augmenting antitumor immunity. We observed that Cy administration resulted in expansion of tumor antigen-specific T cells and transient depletion of CD4(+)Foxp3(+) regulatory T cells (Tregs). The antitumor efficacy of Cy was not improved by administration of anti-CD25 monoclonal antibody given to induce more profound Treg depletion. We found that Cy, through its myelosuppressive action, induced rebound myelopoiesis and perturbed dendritic cell (DC) homeostasis. The resulting DC turnover led to the emergence of tumor-infiltrating DCs that secreted more IL-12 and less IL-10 compared to those from untreated tumor-bearing animals. These newly recruited DCs, originating from proliferating early DC progenitors, were fully capable of priming T cell responses and ineffective in inducing expansion of Tregs. Together, our results show that Cy-mediated antitumor effects extend beyond the well-documented cytotoxicity and lymphodepletion and include resetting the DC homeostasis, thus providing an excellent platform for integration with other immunotherapeutic strategies.

Regulatory (FOXP3+) T cells as target for immune therapy of cervical intraepithelial neoplasia and cervical cancer

Regulatory (FOXP3+) T cells (Tregs) comprise a subpopulation of CD4+ T cells that suppress autoreactive immune cells, thereby protecting organs and tissues from autoimmunity. Tregs have also been detected in human malignancies and their depletion or inactivation substantially improves cellular antitumor immunity in preclinical studies. Novel therapeutic strategies for cervical cancer and precancerous cervical intraepithelial neoplasia (CIN) focus on immune-modulatory and cancer vaccination approaches. In this context, the frequency of Tregs in cervical cancer and precancerous CIN could influence therapeutic strategies. We determined the frequency of infiltrating CD4+ and CD8+ T cells as well as FOXP3+ Tregs in high-grade CIN lesions (CIN III) and cervical carcinoma compared to colon carcinoma, skin melanoma, and bronchial carcinoma. We show that human papilloma virus-derived lesions have a significantly higher number of infiltrating lymphocytes and FOXP3+ Tregs compared to three other common tumor entities. In addition we explored the therapeutic effect of agonistic anti-glucocorticoid-induced tumor necrosis factor receptor family-related protein antibodies that, by single systemic application, inactivate Tregs and induce strong intratumoral invasion of CD8+ T cells and complete tumor eradication in 70% of treated animals. The large number of Tregs in human papilloma virus-derived lesions suggests a pivotal role of Tregs for counteracting the host immune response. We therefore regard CIN and cervical cancer as prime targets for new immune-based non-invasive therapies.

Tumor-derived TGF-beta mediates conversion of CD4+Foxp3+ regulatory T cells in a murine model of pancreas cancer

CD4+25+Foxp3+ regulatory T cells (Treg) play a critical role in the induction of tolerance to tumor-associated antigens and suppression of antitumor immunity. How Treg are induced in cancer is poorly understood. We reported previously that Treg are significantly elevated in the peripheral blood of patients with pancreas cancer and that in a murine pancreas cancer model induction of Treg seems to be transforming growth factor (TGF)-beta dependent. Here we provide additional evidence that Treg are increased locally within the tumor microenvironment by a mechanism that seems dependent on TGF-beta receptor expression and the presence of tumor derived TGF-beta. The murine pancreas cancer cell line Pan02 produces high levels of TGF-beta both in vitro and in vivo. In contrast, the esophageal murine cancer cell line, Eso2, does not. Immunohistochemical staining of Foxp3 in explanted tumors shows an identifiable population of Treg in the Pan02 (TGF-beta positive) tumors but not Eso2 (TGF-beta negative). Naive CD4+25-Foxp3- T cells, when adoptively transferred into Rag-/- mice, are converted into Foxp3+ Treg in the presence of Pan02 but not Eso2 tumors. Induction of Treg in Pan02 mice is blocked by systemic injection of an anti-TGF-beta antibody. If Rag-/- mice are instead reconstituted with naive CD4+25- T cells expressing a mutated TGF-beta receptor, induction of Foxp3+ Treg in Pan02 bearing mice is blocked. Collectively, these observations further support the role of TGF-beta in the induction of Treg in pancreas adenocarcinoma.

T-regulatory cell modulation: the future of cancer immunotherapy?

T-regulatory cells suppress anti-tumour immunity in cancer patients and in murine tumour models. Furthermore, their activity is likely to have an effect on the effectiveness of immunotherapeutic treatments for cancer. Here we describe the current status of developing clinical strategies for modulating Treg activity in cancer patients.

Focus on TILs: prognostic significance of tumor infiltrating lymphocytes in human melanoma

Tumors contain variable numbers of lymphocytes, referred to as tumor infiltrating lymphocytes (TILs). In melanoma, the intensity of this lymphocytic infiltrate is believed to correlate with outcome, though there is some debate about the applicability of this finding for all melanomas. Much research has gone into classifying TILs with respect to antigen receptor structure and the antigen to which melanoma-specific T cells react. However, these studies for the most part did not immunophenotype TILs, and recent data has revealed that the composition of tumoral lymphocytes is not homogenous, but rather represents varying contributions from many lymphocytic subsets. Furthermore, the function of TILs is often compromised as a result of the accumulation of immunoregulatory cells and various tumor escape mechanisms. These recent insights stress the need to collect more data on the composition and function of TIL infiltrates before definitive conclusions about the prognostic significance of TILs can be drawn. Advances in immunology have also facilitated the development of immunotherapeutic strategies, examples of which will be discussed with a special emphasis on blocking antibodies against CTLA-4, which are prototypical immunotherapeutic agents. This flurry of novel "biological" therapies will undoubtedly complicate our already incomplete understanding of TIL immunobiology as each of these agents has the potential to uniquely distort the series of immunological events which normally occur in untreated melanoma. Therefore, considerable research is needed to better elucidate the function and prognostic significance of TILs in both untreated melanoma and tumors treated with "biological" therapy.

Acquired immune mediated aplastic anemia: is it antineoplastic?

There is increasing evidence that autoimmunity can inhibit growth of solid tumors. We propose that anti-tumor activity also operates in autoimmunity against hematopoietic stem cells in acquired aplastic anemia (AA). Reduction/dysfunction of regulatory T cells (T(REG)) in AA - rather than being the primary event - could be a response to insufficient or failing anti-tumor reactivity in predisposed individuals, causing elimination of tumor cells and collateral damage to adjacent normal hematopoietic tissue. This pathophysiological mechanism could also apply to otherwise unexplained pancytopenic syndromes which frequently occur in patients with leukemia and lymphoma and non-hematological malignancies. Observations supporting an anti-tumor effect of marrow hypoplasia/aplasia are presented and illustrated with case reports. The conclusion would be that pancytopenia occurring in AA or in AA-like syndromes reflects an ongoing immune reaction against underlying malignancy or infection.

Immunotherapy of malignant brain tumors

Despite aggressive multi-modality therapy including surgery, radiation, and chemotherapy, the prognosis for patients with malignant primary brain tumors remains very poor. Moreover, the non-specific nature of conventional therapy for brain tumors often results in incapacitating damage to surrounding normal brain and systemic tissues. Thus, there is an urgent need for the development of therapeutic strategies that precisely target tumor cells while minimizing collateral damage to neighboring eloquent cerebral cortex. The rationale for using the immune system to target brain tumors is based on the premise that the inherent specificity of immunologic reactivity could meet the clear need for more specific and precise therapy. The success of this modality is dependent on our ability to understand the mechanisms of immune regulation within the central nervous system (CNS), as well as counter the broad defects in host cell-mediated immunity that malignant gliomas are known to elicit. Recent advances in our understanding of tumor-induced and host-mediated immunosuppressive mechanisms, the development of effective strategies to combat these suppressive effects, and a better understanding of how to deliver immunologic effector molecules more efficiently to CNS tumors have all facilitated significant progress toward the realization of true clinical benefit from immunotherapeutic treatment of malignant gliomas.

Increased Intratumoral FOXP3-positive Regulatory Immune Cells during Interleukin-2 Treatment in Metastatic Renal Cell Carcinoma

Purpose: The administration of interleukin-2 (IL-2) may increase the frequency of peripherally circulating FOXP3-positive regulatory immune cells, thus potentially compromising this treatment option for patients with metastatic renal cell carcinoma. The impact of IL-2–based therapy on the accumulation of FOXP3-positive immune cells in the tumor microenvironment in metastatic renal cell carcinoma is unknown.

Experimental Design: Baseline (n = 58) and on-treatment (n = 42) tumor core biopsies were prospectively obtained from patients with clear cell metastatic renal cell carcinoma before and during IL-2–based immunotherapy. Immunohistochemical expression of FOXP3 was estimated by stereological counting technique and correlated with other immune cell subsets and overall survival.

Results: A significant increase in absolute intratumoral FOXP3-positive immune cells was observed comparing baseline (median 23 cells/mm2; range, 0-183) and on-treatment biopsies (median, 89 cells/mm2; range, 11-388; P < 0.001). The relative increase in individual patients was median 4.7-fold, range 0.3 to 230. FOXP3-positive cells were positively correlated with CD3-positive, CD4-positive, and CD8-positive tumor-infiltrating immune cells at baseline and during treatment (P < 0.05 in all comparisons). All patients achieving high numbers (>180 cells/mm2) of on-treatment FOXP3-positive intratumoral immune cells were dead within 22 months (n = 11), whereas patients with low numbers (<180 cells/mm2) of on-treatment FOXP3-positive cells (n = 31) had a 5-year survival rate of 19% (hazard ratio, 2.2; confidence interval, 1.03-4.5; P = 0.043). All long-term survivors were characterized by low-baseline FOXP3-positive cells and a modest absolute rise in FOXP3-positive cells.

Conclusion: Intratumoral FOXP3-positive regulatory immune cells significantly increased during IL-2–based immunotherapy, and high numbers of on-treatment FOXP3-positive cells were correlated with poor prognosis in patients with metastatic renal cell carcinoma.

Effects of high-dose IFNalpha2b on regional lymph node metastases of human melanoma: modulation of STAT5, FOXP3, and IL-17

PURPOSE

Signal transducer and activator of transcription 5 (STAT5) and STAT3 oppose one another in regulation of the reciprocal development of CD4+CD25+FOXP3+ regulatory T cells (Treg) and T helper 17 (Th17). A reduction in STAT3 is associated with up-regulation of Treg, and STAT5 activation promotes Treg differentiation or function while constraining Th17 generation. The effects of IFNalpha on STAT signaling in relation to tumor tissue Treg and Th17 have not been documented in humans beyond the observations that IFNalpha2b down-regulates STAT3.

EXPERIMENTAL DESIGN

Following diagnostic biopsy and before definitive surgery, 20 doses of high-dose IFNalpha2b (HDI) were administered to patients with stage IIIB melanoma who gave written informed consent. Lymph node biopsies, in which both total STAT3 and phosphorylated STAT3 were down-regulated by HDI, were probed with STAT5, FOXP3, CD4, and interleukin 17 (IL-17) with immunohistochemistry and/or immunofluorescence techniques.

RESULTS

The percentage of FOXP3+ lymphocytes determined by immunohistochemistry was up-regulated from 3.06 +/- 0.65% to 9.86 +/- 1.27% (n = 13, P = 0.0002), and this observation was confirmed by immunofluorescence evaluation of CD4+FOXP3+ Tregs. HDI induced STAT5 up-regulation (five cases observed) in melanoma cells and lymphocytes but did not induce the generation of IL-17-expressing lymphocytes. Increased STAT5 expression was associated with increased FOXP3 expression among lymphocytes, and STAT5 was constitutively activated among both melanoma cells and lymphocytes.

CONCLUSION

IFNalpha2b up-regulates STAT5 and down-regulates STAT3, in conjunction with up-regulation of Treg and inhibition of IL-17-expressing lymphocytes in melanoma tissues. These findings suggest that the effects of IFNalpha may be potentiated through interference with the response of Tregs and/or STAT5.

FOXP3 expression accurately defines the population of intratumoral regulatory T cells that selectively accumulate in metastatic melanoma lesions

Regulatory T (T(reg)) cells are often found in human tumors; however, their functional characteristics have been difficult to evaluate due to low cell numbers and the inability to adequately distinguish between activated and T(reg) cell populations. Using a novel approach, we examined the intracellular cytokine production capacity of tumor-infiltrating T cells in the single-cell suspensions of enzymatically digested tumors to differentiate T(reg) cells from effector T cells. Similar to T(reg) cells in the peripheral blood of healthy individuals, tumor-infiltrating FOXP3(+)CD4 T cells, unlike FOXP3(-) T cells, were unable to produce IL-2 and IFN-gamma upon ex vivo stimulation, indicating that FOXP3 expression is a valid biological marker for human T(reg) cells even in the tumor microenvironment. Accordingly, we enumerated FOXP3(+)CD4 T(reg) cells in intratumoral and peritumoral sections of metastatic melanoma tumors and found a significant increase in proportion of FOXP3(+)CD4 T(reg) cells in the intratumoral compared with peritumoral areas. Moreover, their frequencies were 3- to 5-fold higher in tumors than in peripheral blood from the same patients or healthy donors, respectively. These findings demonstrate that the tumor-infiltrating CD4 T(reg) cell population is accurately depicted by FOXP3 expression, they selectively accumulate in tumors, and their frequency in peripheral blood does not properly reflect tumor microenvironment.

Phosphoantigen-activated V gamma 2V delta 2 T cells antagonize IL-2-induced CD4+CD25+Foxp3+ T regulatory cells in mycobacterial infection

Although Foxp3(+) T regulatory cells (Tregs) are well documented for their ability to suppress various immune cells, T-cell subsets capable of counteracting Tregs have not been demonstrated. Here, we assessed phosphoantigen-activated Vgamma2Vdelta2 T cells for the ability to interplay with Tregs in the context of mycobacterial infection. A short-term IL-2 treatment regimen induced marked expansion of CD4(+)CD25(+)Foxp3(+) T cells and subsequent suppression of mycobacterium-driven increases in numbers of Vgamma2Vdelta2 T cells. Surprisingly, activation of Vgamma2Vdelta2 T cells by adding phosphoantigen Picostim to the IL-2 treatment regimen down-regulated IL-2-induced expansion of CD4(+)CD25(+)Foxp3(+) T cells. Consistently, in vitro activation of Vgamma2Vdelta2 T cells by phosphoantigen plus IL-2 down-regulated IL-2-induced expansion of CD4(+)CD25(+)Foxp3(+) T cells. Interestingly, anti-IFN-gamma-neutralizing antibody, not anti-TGF-beta or anti-IL-4, reduced the ability of activated Vgamma2Vdelta2 T cells to down-regulate Tregs, suggesting that autocrine IFN-gamma and its network contributed to Vgamma2Vdelta2 T cells' antagonizing effects. Furthermore, activation of Vgamma2Vdelta2 T cells by Picostim plus IL-2 treatment appeared to reverse Treg-driven suppression of immune responses of phosphoantigen-specific IFNgamma(+) or perforin(+) Vgamma2Vdelta2 T cells and PPD-specific IFNgamma(+)alphabeta T cells. Thus, phos-phoantigen activation of Vgamma2Vdelta2 T cells antagonizes IL-2-induced expansion of Tregs and subsequent suppression of Ag-specific antimicrobial T-cell responses in mycobacterial infection.

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.

Limited tumor infiltration by activated T effector cells restricts the therapeutic activity of regulatory T cell depletion against established melanoma

Interference with inhibitory immunological checkpoints controlling T cell activation provides new opportunities to augment cancer immunotherapies. Whereas cytotoxic T lymphocyte–associated antigen-4 blockade has shown promising preclinical and clinical results, therapeutic CD4⁺CD25⁺ T reg cell depletion has failed to consistently enhance immune-based therapies. Using B16/BL6, a transplantable murine melanoma model, we show a dichotomy between the effects of T reg cell depletion on tumor rejection dependent on whether depletion occurs before (prophylactic) or after (therapeutic) tumor engraftment. Failure to promote rejection with therapeutic depletion is not related to lack of T reg cell depletion, to elimination of CD25⁺ effector T cells, or to a failure to enhance systemic antitumor T cell responses, but correlates with failure of effector cells to infiltrate the tumor and increase the intratumor ratio of effector T cell/T reg cell. Finally, systemic antitumor responses generated upon therapeutic T reg cell depletion are significantly stronger than those generated in the presence of T reg cells, and are capable of eliciting rejection of established tumors after transfer into immunoablated recipients receiving combination immunotherapy. The data demonstrate a dissociation between measurable systemic responses and tumor rejection during CD25-directed T reg cell depletion, and suggest an alternative, clinically applicable strategy for the treatment of established tumors.

Combating immunosuppression in glioma

Despite maximal therapy, malignant gliomas have a very poor prognosis. Patients with glioma express significant immune defects, including CD4 lymphopenia, increased fractions of regulatory T cells in peripheral blood and shifts in cytokine profiles from Th1 to Th2. Recent studies have focused on ways to combat immunosuppression in patients with glioma as well as in animal models for glioma. We concentrate on two specific ways to combat immunosuppression: inhibition of TGF-beta signaling and modulation of regulatory T cells. TGF-beta signaling can be interrupted by antisense oligonucleotide technology, TGF-beta receptor I kinase inhibitors, soluble TGF-beta receptors and antibodies against TGF-beta. Regulatory T cells have been targeted with antibodies against T-cell markers, such as CD25, CTLA-4 and GITR. In addition, vaccination against Foxp3 has been explored. The results of these studies have been encouraging; combating immunosuppression may be one key to improving prognosis in malignant glioma.

Regulatory T cells and treatment of cancer

CD4+CD25+FOXP3+ regulatory T cells (Tregs) are elevated in cancers and can thwart protective antitumor immunity. Recent human cancer trials suggest that depleting Tregs can be clinically beneficial. Additional types of deleterious regulatory cells are also increased in cancer. Tregs also play unanticipated roles in cancer therapy in that some drugs unexpectedly increase (e.g. cancer vaccines or IL-2 treatment) or decrease (e.g. antineoangiogenesis agents or receptor tyrosine kinase inhibitors) their numbers or function. Managing deleterious effects of regulatory cells represents a novel and potentially effective way to give immunotherapy for cancer. New insights into molecular mechanisms governing trafficking, differentiation, and function of these cells suggest novel approaches to manipulating them as treatment strategies.

Immunotherapy for gastrointestinal cancer: current status and strategies for improving efficacy

BACKGROUND

Despite improvement in conventional strategies for treating gastrointestinal (GI) carcinoma, large numbers of patients still suffer from incurable or progressive disease.

OBJECTIVE

Here we consider the prospects for circumventing limitations and maximising the efficacy of different immunotherapies.

METHODS

We summarise different cancer vaccines and targeted drugs and highlight the scientific rationale of using immunotherapy for targeting GI cancers, in addition to the potential strategies for improving immunotherapeutic efficacy.

RESULTS/CONCLUSION

Many cancer vaccines and antibody-directed therapies have been tested in early phase clinical trials and demonstrated proof of concept and safety. As yet few have been properly evaluated for clinical efficacy; although adoptive transfer of tumour-associated-antigen-specific T cells has shown dramatic clinical responses in some patients. The recognition of a role for T regulatory cells in limiting anti-tumour immunity has provided momentum for developing strategies to over-ride such immunoinhibitory effects. There is some evidence that conventional therapies may work by influencing these negative factors and allowing expression of immune control mechanisms. An important developing area for clinical evaluation is the testing of combined conventional and immunotherapeutic modalities which may provide for synergy; thereby circumventing the limitations of individualised treatments and generating additional clinical benefits.

Cluster intradermal DNA vaccination rapidly induces E7-specific CD8+ T-cell immune responses leading to therapeutic antitumor effects

Intradermal administration of DNA vaccines via a gene gun represents a feasible strategy to deliver DNA directly into the professional antigen-presenting cells (APCs) in the skin. This helps to facilitate the enhancement of DNA vaccine potency via strategies that modify the properties of APCs. We have previously demonstrated that DNA vaccines encoding human papillomavirus type 16 (HPV-16) E7 antigen linked to calreticulin (CRT) are capable of enhancing the E7-specific CD+ T-cell immune responses and antitumor effects against E7-expressing tumors. It has also been shown that cluster (short-interval) DNA vaccination regimen generates potent immune responses in a minimal time frame. Thus, in the current study we hypothesize that the cluster intradermal CRT/E7 DNA vaccination will generate significant antigen-specific CD8+ T-cell infiltrates in E7-expressing tumors in tumor-bearing mice, leading to an increase in apoptotic tumor cell death. We found that cluster intradermal CRT/E7 DNA vaccination is capable of rapidly generating a significant number of E7-specific CD8+ T cells, resulting in significant therapeutic antitumor effects in vaccinated mice. We also observed that cluster intradermal CRT/E7 DNA vaccination in the presence of tumor generates significantly higher E7-specific CD8+ T-cell immune responses in the systemic circulation as well as in the tumors. In addition, this vaccination regimen also led to significantly lower levels of CD4+Foxp3+ T-regulatory cells and myeloid suppressor cells compared to vaccination with CRT DNA in peripheral blood and in tumor-infiltrating lymphocytes, resulting in an increase in apoptotic tumor cell death. Thus, our study has significant potential for future clinical translation.

Immunotherapy opportunities in ovarian cancer

Ovarian cancer is responsible for the majority of gynecologic cancer deaths and despite the highest standard of multimodality therapy with surgery and cytotoxic chemotherapy, long-term survival remains low. With compelling evidence that epithelial ovarian cancer is an immunogenic tumor capable of stimulating an antitumor immune response, renewed efforts to develop immune therapies to augment the efficacy of traditional therapies are underway. Current immunotherapies focus on varied modes of antitumor vaccine development, particularly with the use of dendritic cell vaccines, effective methods for adoptive T-cell transfer and combinatorial approaches with immune modulatory therapy subverting natural tolerance mechanisms or boosting effector mechanisms. Additional combinatorial approaches include the use of cytokines and/or chemotherapy with immune therapy.

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.