Sunitinib reverses type-1 immune suppression and decreases T-regulatory cells in renal cell carcinoma patients

Myeloid-derived suppressor cells: natural regulators for transplant tolerance

Myeloid derived suppressor cells (MDSC) contribute to the negative regulation of immune response in cancer patients. This review summarizes results on important issues related to MDSC biology, including expansion and activation of MDSC, phenotype, and subsets as well pathways and different mechanisms by which these cells exert their suppressive effect. Recent observations suggesting that MDSC may have roles in transplant tolerance are presented. Although therapeutic targeting and destruction of MDCS is of primary interest in cancer patients, in transplantation it will instead be necessary to induce, expand, and activate these cells; thus current possibilities for in vitro generation of MDSC are also discussed.

Mechanism of synergistic antitumor effect of sorafenib and interferon-α on treatment of renal cell carcinoma

PURPOSE

The multikinase and tyrosine kinase inhibitor sorafenib has antitumor activity in patients with advanced renal cell carcinoma. Recent reports show the ability of sorafenib to synergize with interferon-α, leading to greater antitumor activity. We examined the underlying mechanism of sorafenib and interferon-α synergism for renal cell carcinoma treatment in vitro and in tumor bearing murine models.

MATERIALS AND METHODS

We used murine and human renal cell carcinoma cell lines for in vitro cell proliferation assay. ACHN (ATCC®) and RENCA tumors were subcutaneously transplanted into NCr-nu/nu and syngeneic BALB/c mice (Charles River Laboratories, Yokohama, Japan), respectively. Mice were treated with sorafenib and/or interferon-α, and tumor growth was monitored. Immunological assays were done in the RENCA model.

RESULTS

In the ACHN and RENCA cell lines combination index analysis clearly revealed the synergistic antiproliferative effects of interferon-α and sorafenib in vitro. In the ACHN NCr-nu/nu model we clearly noted the synergistic antitumor effects of interferon-α and sorafenib, indicating the synergistic direct effects of each drug on tumor growth. In the RENCA BALB/c model flow cytometry showed no change in the proportion of lymphocytes. However, while sorafenib alone did not induce natural killer or cytotoxic T-lymphocyte activity against RENCA in that model, interferon-α alone or combined with sorafenib induced natural killer and cytotoxic T-lymphocyte activity.

CONCLUSIONS

Our results show the synergistic activity of interferon-α and sorafenib. These findings provided the rationale for combination therapy with interferon-α and sorafenib in patients with advanced renal cell carcinoma.

The effect of sunitinib on immune subsets in metastatic clear cell renal cancer

BACKGROUND

Sunitinib is standard first-line therapy for metastatic clear cell renal cancer (MCRC). It is associated with leucopenia; however, its effects on specific immune cell subsets are unclear. Alterations in immune cell subsets may contribute to tumour progression.

METHODS

Lymphocyte subsets (CD3, 4, 8, 19 and 56) were measured in 43 untreated MCRC patients who received sunitinib. The protocol included a structured treatment interruption of 5 weeks. Cell populations were measured at specific time points during sunitinib treatment and the treatment break.

RESULTS

Sunitinib was associated with significant declines in total leucocyte (-48%), neutrophil (-62%), CD3 total T cell (-31%) and CD4 counts (32%; p < 0.05). There was no significant change in CD19 B lymphocyte, CD8 or CD56 natural killer cells. During the sunitinib-free interval, all parameters recovered to baseline. No patients developed opportunistic infections or neutropenic sepsis. The level of specific immune subsets at presentation or occurrence of a fall in specific counts had an effect on progression-free survival (p > 0.05).

CONCLUSIONS

Sunitinib is associated with reversible inhibition of specific lymphocyte subsets which has implications for the immunological control of MCRC and its use in combination with other agents. Despite suppressive effects, there was no evidence of predisposition to immune suppressive-related infection.

Phase 1 dose-escalation trial of tremelimumab plus sunitinib in patients with metastatic renal cell carcinoma

BACKGROUND

On the basis of potential additive or synergistic immunostimulatory antitumor effects, in this phase 1 study, the authors evaluated the combination of sunitinib and tremelimumab (CP-675206; an antibody against cytotoxic T-lymphocyte-associated antigen 4 [CTLA4]) in patients with metastatic renal cell carcinoma (mRCC) was evaluated.

METHODS

Adult patients with mRCC who had received ≤ 1 previous systemic treatment received tremelimumab (6 mg/kg, 10 mg/kg, or 15 mg/kg) intravenously once every 12 weeks and oral sunitinib (50 mg daily for 4 weeks then 2 weeks off or 37.5 mg daily as a continuous dose). The primary objective was to determine the maximum tolerated dose (MTD). Secondary objectives were to assess antitumor activity, safety, and pharmacokinetics.

RESULTS

Twenty-eight patients were enrolled. Two of 5 patients who received 50 mg sunitinib plus tremelimumab 6 mg/kg experienced dose-limiting toxicities (DLTs), and no further enrollment to the combination with sunitinib 50 mg dosing was pursued. Among patients who received continuous sunitinib 37.5 mg daily, 1 of 7 patients who received tremelimumab 10 mg/kg plus sunitinib suffered a sudden death, and 3 of 6 patients who received tremelimumab 15 mg/kg plus sunitinib experienced DLTs. An expansion cohort (n = 7) was enrolled at tremelimumab 10 mg/kg plus sunitinib 37.5 mg daily; 3 of those patients experienced DLTs. Overall, rapid-onset renal failure was the most common DLT. Nine of 21 patients who were evaluable for response achieved partial responses (43%; 95% confidence interval, 22%-66%), and 4 of those responses were ongoing at the time of the current report.

CONCLUSIONS

In this study of tremelimumab plus sunitinib, rapid-onset acute renal failure was observed unexpectedly, and further investigation of tremelimumab doses > 6 mg/kg plus sunitinib 37.5 mg daily is not recommended. Preclinical investigation may be warranted to understand the mechanism of renal toxicity.

Exploratory analysis of early toxicity of sunitinib in advanced hepatocellular carcinoma patients: kinetics and potential biomarker value

PURPOSE

Sunitinib--a multitargeted tyrosine kinase inhibitor--can modulate circulating inflammatory factors in cancer patients that may be relevant for hepatocellular carcinoma (HCC) progression. However, a recent phase III study of sunitinib in HCC was halted due to its toxicity. Here, we studied the early kinetics of adverse events after sunitinib, and explored their association with circulating proteins and clinical outcome in advanced HCC in a single-arm phase II study.

EXPERIMENTAL DESIGN

Toxicity was evaluated every two weeks during the first cycle of therapy. Biomarker changes from baseline were tested after adjusting for multiple comparisons. Correlation between toxicities and overall survival (OS) or time-to-tumor progression (TTP) was evaluated in a Cox model using log-transformed levels or change in biomarkers, after stratifying by stage and adjusting for baseline level.

RESULTS

Myeloid and lymphoid blood cell counts decreased by 20% to 50% after sunitinib treatment (P < 0.05 for all). The extent of the early decrease in neutrophils and monocytes, and the development of nonhematologic toxicities (i.e., skin toxicities), were significantly associated with both OS and TTP (P < 0.05). Changes in circulating cells significantly associated with specific changes in plasma biomarkers (i.e., changes in platelets with changes in VEGF-C and soluble-VEGFR3; changes in neutrophils with changes in IL-8, TNF-α, and soluble-VEGFR2).

CONCLUSIONS

The adverse effects of sunitinib, particularly on the hematopoietic system, may be rapid and appear directly related to its activity in HCC. This exploratory study suggests that early hematopoietic toxicities may potentially predict outcome in advanced HCC after sunitinib treatment.

Inhibiting the inhibitors: evaluating agents targeting cancer immunosuppression

IMPORTANCE OF THE FIELD

Immunotherapy of cancer has not improved disease-free or overall patient survival. The lack of concordance between immunological and clinical responses in cancer immunotherapy trials is thought to result from the pervasive presence of tumor-driven immune suppression that allows tumor to escape and that has not been adequately targeted by current therapies.

AREAS COVERED IN THIS REVIEW

Because multiple mechanisms of tumor induced suppression have been identified and shown to contribute to tumor escape, the opportunity arises to interfere with these mechanisms. A range of known tumor-derived inhibitors can now be blocked or neutralized by biologic or metabolic agents. Used alone or in combination with each other or with conventional cancer therapies, these agents offer novel therapeutic strategies for the control of tumor escape.

WHAT THE READER WILL GAIN

This review deals with currently available inhibitors for counteracting tumor immune escape. The restoration of effective anti-tumor immunity in patients with cancer will require new approaches aiming at: i) protection of immune cells from adverse effects of myeloid-derived suppressor cells, regulatory T cells or inhibitory factors thus enhancing effector functions; and ii) prolonging survival of central memory T cells, thus ensuring long-term protection.

TAKE HOME MESSAGE

Inhibitors of mechanisms responsible for tumor escape could restore anti-tumor immune responses in patients with cancer.

Development and application of 'phosphoflow' as a tool for immunomonitoring

Flow cytometry has revolutionized our ability to monitor immune responses by allowing us to simultaneously track a variety of cell surface and intracellular markers in discrete cell subsets in a highly sensitive and reproducible manner. This is especially critical in this new era of vaccinology trying to tackle the growing problems of chronic viral infections and cancer that not only evade host immune responses, but can negatively manipulate vaccine-induced immune responses. Thus, understanding how lymphocyte signaling is altered under normal and pathological conditions has become more critical. Over the last decade, a new flow cytometry technology called 'phosphoflow' (also sometimes called 'phosflow'), is rapidly developing for tracking multiple intracellular signaling molecules in the immune system at a single-cell level. Antibodies and reagents for tracking both tyrosine-phosphorylated and serine/threonine-phosphorylated signaling intermediaries in key immune signaling pathways have been developed, and phosphoflow is now starting to be applied to a wide variety of both preclinical and clinical studies on lymphocyte responses, as well as the functioning of cancer cells and virally infected cells. Here, we review the development of phosphoflow technology, its modern applications in the field of immunomonitoring and its current limitations. We then provide a perspective on the future of phosphoflow and a vision of how it can be applied to emerging critical questions in human vaccinology and public health.

Renal cancer resistance to antiangiogenic therapy is delayed by restoration of angiostatic signaling

Treatment of metastatic renal cell cancer (RCC) with antiangiogenic agents that block vascular endothelial growth factor (VEGF) receptor 2 signaling produces tumor regression in a substantial fraction of patients; however, resistance typically develops within 6 to 12 months. The purpose of this study was to identify molecular pathways involved in resistance. Treatment of mice bearing either 786-0 or A498 human RCC xenografts with sorafenib or sunitinib produced tumor growth stabilization followed by regrowth despite continued drug administration analogous to the clinical experience. Tumors and plasma were harvested at day 3 of therapy and at the time of resistance to assess pathways that may be involved in resistance. Serial perfusion imaging, and plasma and tumor collections were obtained in mice treated with either placebo or sunitinib alone or in combination with intratumoral injections of the angiostatic chemokine CXCL9. Sunitinib administration led to an early downmodulation of IFNγ levels as well as reduction of IFNγ receptor and downstream angiostatic chemokines CXCL9 to 11 within the tumor. Intratumoral injection of CXCL9, although producing minimal effects by itself, when combined with sunitinib resulted in delayed resistance in vivo accompanied by a prolonged reduction of microvascular density and tumor perfusion as measured by perfusion imaging relative to sunitinib alone. These results provide evidence that resistance to VEGF receptor therapy is due at least in part to resumption of angiogenesis in association with reduction of IFNγ-related angiostatic chemokines, and that this resistance can be delayed by concomitant administration of CXCL9.

Update on vaccine development for renal cell cancer

Renal cell carcinoma (RCC) remains a significant health concern that frequently presents as metastatic disease at the time of initial diagnosis. Current first-line therapeutics for the advanced-stage RCC include antiangiogenic drugs that have yielded high rates of objective clinical response; however, these tend to be transient in nature, with many patients becoming refractory to chronic treatment with these agents. Adjuvant immunotherapies remain viable candidates to sustain disease-free and overall patient survival. In particular, vaccines designed to optimize the activation, maintenance, and recruitment of specific immunity within or into the tumor site continue to evolve. Based on the integration of increasingly refined immunomonitoring systems in both translational models and clinical trials, allowing for the improved understanding of treatment mechanism(s) of action, further refined (combinational) vaccine protocols are currently being developed and evaluated. This review provides a brief history of RCC vaccine development, discusses the successes and limitations in such approaches, and provides a rationale for developing combinational vaccine approaches that may provide improved clinical benefits to patients with RCC.

Anti-inflammatory M2 type macrophages characterize metastasized and tyrosine kinase inhibitor-treated gastrointestinal stromal tumors

We have made a detailed inventory of the immune infiltrate of gastrointestinal stromal tumors (GISTs), which originate from mesenchymal cells in the intestinal tract. These sarcomas are heavily infiltrated with macrophages and T cells, while immune cells of other lineages were much less abundant. Dissecting the functional subtypes of T cells with multicolor fluorescent microscopy revealed substantial populations of cytotoxic T cells, helper T cells and FoxP3(+) regulatory T cells. The balance of cytotoxic T cells and FoxP3(+) T cells was toward immune suppression. Analysis of the macrophage population also showed a dominance of anti-inflammatory cells, as the M2 type scavenger receptor CD163 was abundantly present. Other subsets of macrophages (CD14(+)CD163(-)) were occasionally detected. M2 type CD163(+) macrophages were associated with the number of infiltrating FoxP3(+) regulatory T cells and twice as many macrophages were found in metastatic GIST compared to primary lesions. Most metastatic GISTs had been treated with the tyrosine kinase inhibitors imatinib and sunitinib, but the high macrophage infiltrate was not related to this treatment. However, imatinib and sunitinib did induce secretion of anti-inflammatory IL-10 in macrophage cultures, indicating that treatment with these inhibitors might contribute to an immune suppressive microenvironment in GIST. Overall, our data reveal a picture of GIST as an active site of tumor-immune interaction in which suppressive mechanisms overrule potential antitumor responses. Tyrosine kinase inhibitors might promote this negative balance.

AACR centennial series: the biology of cancer metastasis: historical perspective

Metastasis resistant to therapy is the major cause of death from cancer. Despite almost 200 years of study, the process of tumor metastasis remains controversial. Stephen Paget initially identified the role of host-tumor interactions on the basis of a review of autopsy records. His "seed and soil" hypothesis was substantiated a century later with experimental studies, and numerous reports have confirmed these seminal observations. An improved understanding of the metastatic process and the attributes of the cells selected by this process is critical for the treatment of patients with systemic disease. In many patients, metastasis has occurred by the time of diagnosis, so metastasis prevention may not be relevant. Treating systemic disease and identifying patients with early disease should be our goal. Revitalized research in the past three decades has focused on new discoveries in the biology of metastasis. Even though our understanding of molecular events that regulate metastasis has improved, the contributions and timing of molecular lesion(s) involved in metastasis pathogenesis remain unclear. Review of the history of pioneering observations and discussion of current controversies should increase understanding of the complex and multifactorial interactions between the host and selected tumor cells that contribute to fatal metastasis and should lead to the design of successful therapy.

AACR centennial series: the biology of cancer metastasis: historical perspective

Metastasis resistant to therapy is the major cause of death from cancer. Despite almost 200 years of study, the process of tumor metastasis remains controversial. Stephen Paget initially identified the role of host-tumor interactions on the basis of a review of autopsy records. His "seed and soil" hypothesis was substantiated a century later with experimental studies, and numerous reports have confirmed these seminal observations. An improved understanding of the metastatic process and the attributes of the cells selected by this process is critical for the treatment of patients with systemic disease. In many patients, metastasis has occurred by the time of diagnosis, so metastasis prevention may not be relevant. Treating systemic disease and identifying patients with early disease should be our goal. Revitalized research in the past three decades has focused on new discoveries in the biology of metastasis. Even though our understanding of molecular events that regulate metastasis has improved, the contributions and timing of molecular lesion(s) involved in metastasis pathogenesis remain unclear. Review of the history of pioneering observations and discussion of current controversies should increase understanding of the complex and multifactorial interactions between the host and selected tumor cells that contribute to fatal metastasis and should lead to the design of successful therapy.

Direct and differential suppression of myeloid-derived suppressor cell subsets by sunitinib is compartmentally constrained

The antiangiogenic drug sunitinib is a receptor tyrosine kinase inhibitor with significant, yet not curative, therapeutic effects in metastatic renal cell carcinoma (RCC). Sunitinib is also an immunomodulator, potently reversing myeloid-derived suppressor cell (MDSC) accumulation and T-cell inhibition in the blood even of nonresponder RCC patients. We observed that sunitinib similarly prevented MDSC accumulation and restored normal T-cell function to the spleens of tumor-bearing mice, independent of the capacity of sunitinib to inhibit tumor progression (RENCA>CT26>4T1). Both monocytic and neutrophilic splenic MDSC were highly repressible by sunitinib. In contrast, MDSC within the microenvironment of 4T1 tumors or human RCC tumors proved highly resistant to sunitinib and ambient T-cell function remained suppressed. Proteomic analyses comparing tumor to peripheral compartments showed that granulocyte macrophage colony-stimulating factor (GM-CSF) predicted sunitinib resistance and recombinant GM-CSF conferred sunitinib resistance to MDSC in vivo and in vitro. MDSC conditioning with GM-CSF uniquely inhibited signal transducers and activators of transcription (STAT3) and promoted STAT5 activation. STAT5ab(null/null) MDSC were rendered sensitive to sunitinib in the presence of GM-CSF in vitro. We conclude that compartment-dependent GM-CSF exposure in resistant tumors may account for the regionalized effect of sunitinib upon host MDSC modulation and hypothesize that ancillary strategies to decrease such regionalized escape will enhance the potency of sunitinib as an immunomodulator and a cancer therapy.

Targeting immune suppressing myeloid-derived suppressor cells in oncology

Emerging data suggests that host immune cells with a suppressive phenotype represent a significant hurdle to successful therapy for metastatic cancer. Among the suppressor cells, T regulatory cells (Treg) and myeloid-derived suppressor cells (MDSC) are significantly increased in hosts with advanced malignancies. MDSC mediate the suppression of the tumor antigen-specific T cell response through the induction of T cell anergy and the development of Treg in tumor-bearing mice. These results provide robust evidence of an in vivo immunoregulatory function of MDSC in the establishment of tumor antigen-specific tolerance and the development of Treg in tumor-bearing hosts. To achieve effective anti-tumor immunity, tumor-induced immunosuppression must be reversed. Our preliminary results indicate that c-kit ligand (stem cell factor) expressed by tumor cells may be required for MDSC accumulation in tumor-bearing mice, and that blocking the c-kit ligand/c-kit receptor interaction can prevent the development of Treg and reverse immune tolerance induced by MDSC. Since c-kit can be readily inhibited by several small molecule inhibitors including imatinib, sunitinib and dasatinib, targeting immune suppressing cells can be readily accomplished in the clinic.

Practical strategies for suppressing hypoxia-inducible factor activity in cancer therapy

The utility of anti-angiogenic strategies for cancer control is strongly compromised by hypoxia-driven phenotypic changes in cancer cells, which make cancer cells more invasive and more prone to give rise to metastases. A key mediator of this phenotypic shift is the transcription factor hypoxia-inducible factor-1 (HIF-1), which acts directly and indirectly to promote the epidermal-mesenchymal transition, boost cancer invasiveness, increase production of angiogenic factors, and induce chemoresistance. In some cancers, HIF-1 activity is constitutively elevated even in aerobic environments, making the cancer harder to treat and control. Practical strategies for suppressing HIF-1 activation may include the following: inhibiting NF-kappaB activation with salicylic acid and/or silibinin, which should decrease transcription of the HIF-1alpha gene; suppressing translation of HIF-1alpha mRNA with drugs that inhibit mTOR or topoisomerase I; supporting the effective activity of prolyl hydroxylases - which promote proteasomal degradation of HIF-1alpha under aerobic conditions - with antioxidant measures, alpha-ketoglutarate, and possibly dichloroacetate; promoting the O(2)-independent proteasomal degradation of HIF-1alpha with agents that inhibit the chaperone protein Hsp90; and blocking HIF-1 binding to its DNA response elements with anthracyclines. The utility of various combinations of these strategies should be tested in cancer cell cultures and rodent xenograft models; initial efforts in this regard have yielded encouraging results. Comprehensive strategies for suppressing HIF-1 activity can be expected to complement the efficacy of cancer chemotherapy and of effective anti-angiogenic regimens.

Sunitinib impairs the proliferation and function of human peripheral T cell and prevents T-cell-mediated immune response in mice

Sunitinib (sunitinib malate; SU11248; SUTENT) is a novel multi-targeted receptor tyrosine kinase inhibitor currently approved for the treatment of metastatic renal cell carcinoma. To analyze the possible use of this compound in combination with immunotherapeutic approaches, we investigated the effects of sunitinib on the human peripheral T cells and the induction of primary immune responses in mice. Sunitinib inhibited the proliferation of primary human T cells from normal healthy volunteers as well as from renal cell carcinoma (RCC) and other cancer patients. The inhibition was recoverable after drug withdrawal because sunitinib did not induce T-cell apoptosis even at 0.8 muM. In addition, sunitinib led to accumulation in G(0)/G(1) phase of the cell cycle, inhibition of cytokine production, downregulation of activation markers expression and blockade of Zap-70 signaling in the T cells. Sunitinib significantly reduced the ear swelling induced by picryl chloride in mice. In light of these findings, the effects of sunitinib on the immune system should be emphasized for the therapy of metastatic renal cell carcinoma patients to avoid the impairment of T lymphocytes.

Simultaneous infiltration of polyfunctional effector and suppressor T cells into renal cell carcinomas

Renal cell carcinoma is frequently infiltrated by cells of the immune system. This makes it important to understand interactions between cancer cells and immune cells so they can be manipulated to bring clinical benefit. Here, we analyze subsets and functions of T lymphocytes infiltrating renal cell tumors directly ex vivo following mechanical disaggregation and without any culture step. Subpopulations of memory and effector CD4(+) Th1, Th2, and Th17 and CD8(+) Tc1 cells were identified based on surface phenotype, activation potential, and multicytokine production. Compared with the same patient's peripheral blood, T lymphocytes present inside tumors were found to be enriched in functional CD4(+) cells of the Th1 lineage and in effector memory CD8(+) cells. Additionally, several populations of CD4(+) and CD8(+) regulatory T cells were identified that may synergize to locally dampen antitumor T-cell responses.

Therapeutic activity of sunitinib for Her2/neu induced mammary cancer in FVB mice

Mouse mammary tumor virus-Neu (MMTV/neu) transgenic mice on an FVB-background (FVB-neuN) have increased numbers of myeloid derived suppressor cells (MDSCs) and regulatory T-cells (T-regs) in the spleen during mammary tumor induction and progression. Using this transgenic tumor model, we assessed the therapeutic activity of sunitinib, a multi-targeted, tyrosine kinase (TK) inhibitor and its effects on immune-regulatory cells. Our preliminary results show that sunitinib at 40mg/kg/day, p.o. (per os), delayed the time to tumor induction and reduced the incidence and growth of tumors in FVB-neuN mice. In association with its therapeutic activity, sunitinib reduced the absolute number of splenic T-reg cells (CD4(+)CD25(+)CD62L(+)) and MDSCs (CD11b(+)Gr1(+)) that were increased during tumor progression with less activity in mice with gross tumors. A significant decrease in the absolute number of splenic T-regs, dendritic cells (DCs), MDSCs and hematopoietic progenitors (Lin(-)Sca1(+)CD90(dull)) was observed following sunitinib treatment. The frequency of splenic T-regs and hematopoietic progenitors, but not MDSCs was also reduced by sunitinib treatment. Additionally immune-regulatory cytokines and enzymes were down regulated by sunitinib treatment, including TGFbeta and NOS2 in the spleen cells of sunitinib treated mice as compared to untreated tumor bearing (TB) mice. We conclude that sunitinib has therapeutic activity, in association with the down regulation of MDSCs and T-regs and has a trend towards the normalization of the inflammatory cytokine levels induced by tumor progression and growth. Based on these results, we suggest that sunitinib reduction of immune suppressive cells is a critical part of its adjuvant immune therapeutic activity.

A phase I pharmacokinetic and biological correlative study of IMP321, a novel MHC class II agonist, in patients with advanced renal cell carcinoma

PURPOSE

To evaluate the safety, tolerability, pharmacokinetics, and pharmacodynamics of IMP321, a recombinant soluble LAG-3Ig fusion protein which agonizes MHC class II-driven dendritic cell activation.

EXPERIMENTAL DESIGN

Patients with advanced renal cell carcinoma were treated with escalating doses of IMP321 s.c. Blood samples were assayed to determine plasma pharmacokinetic parameters, detect human anti-IMP321 antibody formation, and determine long-lived CD8 T cell responses.

RESULTS

Twenty-one advanced renal cell carcinoma patients received 119 injections of IMP321 at doses ranging from 0.050 to 30 mg/injection s.c. biweekly for 6 injections. No clinically significant adverse events were observed. Good systemic exposure to the product was obtained following s.c. injections of doses above 6 mg. IMP321 induced both sustained CD8 T-cell activation and an increase in the percentage of long-lived effector-memory CD8 T cells in all patients at doses above 6 mg. Tumor growth was reduced and progression-free survival was better in those patients receiving higher doses (>6 mg) of IMP321: 7 of 8 evaluable patients treated at the higher doses experienced stable disease at 3 months compared with only 3 of 11 in the lower dose group (P = 0.015).

CONCLUSION

The absence of toxicity and the demonstration of activity at doses above 6 mg warrant further disease-directed studies of IMP321 in combined regimens (e.g., chemoimmunotherapy).

Therapeutic targeting of myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) represent a subset of myeloid cells that expand under pathological conditions, such as cancer development, acute and chronic infections, trauma, bone marrow transplantations, and some autoimmune diseases. MDSCs mediate a negative regulation of the immune response by affecting different T lymphocyte subsets. Potential mechanisms, which underlie this inhibitory activity range from those requiring direct cell-to-cell contact with others, more indirect, and mediated by the modification of the microenvironment. Pharmacological inhibition of MDSC suppressive pathways is a promising strategy to overcome disease-induced immune defects, which might be a key step in enhancing the effectiveness of immune-based therapies.

Vaccination strategies in patients with renal cell carcinoma

Although new treatment options for patients with advanced renal cell cancer (RCC) have been developed within recent years, vaccination is still a promising emerging treatment option. An increasing number of tumor-associated antigens (TAA) available for RCC are currently used and analyzed for their efficacy for antigen-specific vaccine strategies. Recently, antigen-specific vaccination with dendritic cells in patients with metastatic RCC was shown to induce cytotoxic T cell response associated with objective clinical responses in some of the patients. Furthermore, current studies focus on the development of more effective vaccine regimes, such as the application of polyvalent, HLA-independent RNA coding for multiple TAA and adjuvants. First results demonstrate promising clinical and immunological efficacy. The efficacy of antigen-specific vaccination might be improved by a combination of tyrosine kinase inhibitors, since sunitinib was shown to promote T cell induction following vaccination in a mouse model and elimination of regulatory T cells.

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.

Immunotherapeutic strategies in kidney cancer--when TKIs are not enough

FDA approval of the multitargeted, antiangiogenic tyrosine kinase inhibitors (TKIs) sunitinib and sorafenib, and the serine and threonine mammalian target of rapamycin inhibitor, temsirolimus, has revolutionized the management of metastatic clear-cell renal-cell carcinoma (CC-RCC). The inability of these targeted therapies to provide durable complete responses, however, is a serious limiting factor to their clinical usefulness. Although immunotherapeutic approaches in advanced disease are increasingly regarded as a historical treatment paradigm, we propose that a fundamental understanding of immunobiology in CC-RCC can improve the selection of patients for high-dose intravenous interleukin 2 and facilitate the development of novel immunotherapeutic strategies. In our opinion, immunotherapeutic strategies have an important place in the management of advanced CC-RCC in the era of biological targeted therapy.

Myeloid-derived suppressor cells: a novel therapeutic target

Immunotherapy and angiogenic inhibitors, used alone or in combination with chemotherapy, represent two promising cancer treatment programs. Each is limited by myeloid-derived suppressor cells (MDSCs), which accumulate in tumor-bearing hosts. MDSCs inhibit effector T-cell function and thus prevent the formation and execution of an effective antitumor immune response. Recently reported studies have shown that MDSCs also function to promote tumor-dependent angiogenesis as well as tumor metastasis, and to provide tumor resistance to antiangiogenic drugs. Insights into tumor-imposed dynamic changes in bone marrow function and myeloid cell development should fuel novel drug developments and novel applications of drugs currently in use. Such insights suggest that multitargeted receptor tyrosine kinase inhibitors, such as sunitinib, may be useful adjunctive agents for use in immunotherapy trials treating several tumor types.

The novel role of tyrosine kinase inhibitor in the reversal of immune suppression and modulation of tumor microenvironment for immune-based cancer therapies

In tumor-bearing hosts, myeloid-derived suppressor cells (MDSC) and T regulatory cells (Treg) play important roles in immune suppression, the reversal of which is vitally important for the success of immune therapy. We have shown that ckit ligand is required for MDSC accumulation and Treg development. We hypothesized that sunitinib malate, a receptor tyrosine kinase inhibitor, could reverse MDSC-mediated immune suppression and modulate the tumor microenvironment, thereby improving the efficacy of immune-based therapies. Treatment with sunitinib decreased the number of MDSC and Treg in advanced tumor-bearing animals. Furthermore, it not only reduced the suppressive function of MDSCs but also prevented tumor-specific T-cell anergy and Treg development. Interestingly, sunitinib treatment resulted in reduced expression of interleukin (IL)-10, transforming growth factor-beta, and Foxp3 but enhanced expression of Th1 cytokine IFN-gamma and increased CTL responses in isolated tumor-infiltrating leukocytes. A significantly higher percentage and infiltration of CD8 and CD4 cells was detected in tumors of sunitinib-treated mice when compared with control-treated mice. More importantly, the expression of negative costimulatory molecules CTLA4 and PD-1 in both CD4 and CD8 T cells, and PDL-1 expression on MDSC and plasmacytoid dendritic cells, was also significantly decreased by sunitinib treatment. Finally, sunitinib in combination with our immune therapy protocol (IL-12 and 4-1BB activation) significantly improves the long-term survival rate of large tumor-bearing mice. These data suggest that sunitinib can be used to reverse immune suppression and as a potentially useful adjunct for enhancing the efficacy of immune-based cancer therapy for advanced malignancies.

Sunitinib mediates reversal of myeloid-derived suppressor cell accumulation in renal cell carcinoma patients

PURPOSE

Immune dysfunction reported in renal cell carcinoma (RCC) patients may contribute to tumor progression. Myeloid-derived suppressor cells (MDSC) represent one mechanism by which tumors induce T-cell suppression. Several factors pivotal to the accumulation of MDSC are targeted by the tyrosine kinase inhibitor, sunitinib. The effect of sunitinib on MDSC-mediated immunosuppression in RCC patients has been investigated.

EXPERIMENTAL DESIGN

Patient peripheral blood levels of MDSC and regulatory T-cell (Treg) and T-cell production of IFN-gamma were evaluated before and after sunitinib treatment. Correlations between MDSC and Treg normalization as well as T-cell production of IFN-gamma were examined. The in vitro effect of sunitinib on patient MDSC was evaluated.

RESULTS

Metastatic RCC patients had elevated levels of CD33(+)HLA-DR(-) and CD15(+)CD14(-) MDSC, and these were partially overlapping populations. Treatment with sunitinib resulted in significant reduction in MDSC measured by several criteria. Sunitinib-mediated reduction in MDSC was correlated with reversal of type 1 T-cell suppression, an effect that could be reproduced by the depletion of MDSC in vitro. MDSC reduction in response to sunitinib correlated with a reversal of CD3(+)CD4(+)CD25(hi)Foxp3(+) Treg cell elevation. No correlation existed between a change in tumor burden and a change in MDSC, Treg, or T-cell production of IFN-gamma. In vitro addition of sunitinib reduced MDSC viability and suppressive effect when used at >/=1.0 microg/mL. Sunitinib did not induce MDSC maturation in vitro.

CONCLUSIONS

Sunitinib-based therapy has the potential to modulate antitumor immunity by reversing MDSC-mediated tumor-induced immunosuppression.

Influence of bevacizumab, sunitinib and sorafenib as single agents or in combination on the inhibitory effects of VEGF on human dendritic cell differentiation from monocytes

Vascular endothelial growth factor (VEGF) inhibits differentiation and maturation of dendritic cells (DC), suggesting a potential immunosuppressive role for this proangiogenic factor. Bevacizumab, sorafenib and sunitinib target VEGF-mediated angiogenesis and are active against several types of cancer, but their effects on the immune system are poorly understood. In this study, VEGF and supernatants of renal carcinoma cell lines cultured under hypoxia were found to alter the differentiation of human monocytes to DC. Resulting DC showed impaired activity, as assessed by the alloreactive mixed T-lymphocyte reaction. Bevacizumab and sorafenib, but not sunitinib, reversed the inhibitory effects of VEGF, but not of those mediated by tumour supernatants. Dendritic cells matured under the influence of VEGF expressed less human leukocyte antigen-DR (HLA-DR) and CD86, and this effect was restored by bevacizumab and sorafenib. Finally, tumour-cell supernatants decreased interleukin-12 (IL-12) production by mature DC, and such inhibition was not restored by any of the tested drugs, delivered either as single agents or in combination. The deleterious effects of tumour-cell supernatants were mainly mediated by thermostable molecules distinct from VEGF. These results indicate that inhibition of the differentiation of monocytes to DC is a multifactorial effect, and that they support the development of combinations of angiogenesis inhibitors with immunological modulators.

Clinical and biological efficacy of recombinant human interleukin-21 in patients with stage IV malignant melanoma without prior treatment: a phase IIa trial

PURPOSE

Human interleukin-21 (IL-21) is a class I cytokine that mediates activation of CD8(+) T cells, natural killer (NK) cells, and other cell types. We report final clinical and biological results of a phase II study of recombinant human IL-21 (rIL-21) in patients with metastatic melanoma.

EXPERIMENTAL DESIGN

Open-label, single-arm, two-stage trial.

ELIGIBILITY CRITERIA

unresectable metastatic melanoma, measurable disease by Response Evaluation Criteria in Solid Tumors, no prior systemic therapy (adjuvant IFN permitted), adequate major organ function, good performance status, no significant autoimmune disease, and life expectancy at least 4 months.

PRIMARY OBJECTIVE

antitumor efficacy (response rate).

SECONDARY OBJECTIVES

safety, blood biomarkers, and generation of anti-rIL-21 antibodies. rIL-21 (30 microg/kg/dose) was administered by intravenous bolus injection in 8-week cycles (5 dosing days followed by 9 days of rest for 6 weeks and then 2 weeks off treatment).

RESULTS

Stage I of the study comprised 14 patients. One confirmed complete response (CR) was observed, and as per protocol, 10 more patients were accrued to stage II (total n = 24: 10 female and 14 male). Best tumor response included one confirmed CR and one confirmed partial response, both with lung metastases. Treatment was overall well tolerated. Biomarker analyses showed increases in serum soluble CD25, frequencies of CD25(+) NK and CD8(+) T cells, and mRNA for IFN-gamma, perforin, and granzyme B in CD8(+) T and NK cells.

CONCLUSIONS

rIL-21 administered at 30 microg/kg/d in 5-day cycles every second week is biologically active and well tolerated in patients with metastatic melanoma. Confirmed responses, including one CR, were observed.

Sunitinib inhibition of Stat3 induces renal cell carcinoma tumor cell apoptosis and reduces immunosuppressive cells

The novel multitargeted tyrosine kinase inhibitor sunitinib is used as an antiangiogenic agent for the treatment of several types of cancer, including metastatic renal cell carcinoma (RCC). Sunitinib was shown to positively change the immunosuppressive phenotype in RCC patients. To improve its antitumor efficacy, and offer strategies for its combination with other approaches, it is critical to fully elucidate its mechanisms of action. We show that sunitinib induces tumor cell apoptosis and growth arrest in RCC tumor cells, which correlates with signal transducer and activator of transcription 3 (Stat3) activity inhibition. Sunitinib-mediated direct effects on tumor cells occur regardless of von Hippel-Lindau tumor suppressor gene status and hypoxia-inducible transcription factor-2alpha levels. Reduction of Stat3 activity enhances the antitumor effects of sunitinib, whereas expression of a constitutively activated Stat3 mutant rescues tumor cell death. Intravital multiphoton microscopy data show that sunitinib induces mouse Renca tumor cell apoptosis in vivo before tumor vasculature collapse. Sunitinib also inhibits Stat3 in Renca tumor-associated myeloid-derived suppressor cells (MDSC), down-regulates angiogenic gene expression, and reduces MDSCs and tumor T regulatory cells. These results suggest that Stat3 activity is important for RCC response to sunitinib, and Stat3 inhibition permits the direct proapoptotic activity of sunitinib on tumor cells and positive effects on tumor immunologic microenvironment.

Enhancing therapeutic HPV DNA vaccine potency through depletion of CD4+CD25+ T regulatory cells

Therapeutic human papillomavirus (HPV) vaccines targeting E6 and/or E7 antigens represent an opportunity to control HPV-associated lesions. We have previously generated several therapeutic DNA vaccines targeting HPV-16 E7 antigen and generated significant antitumor effects. Since regulatory T cells (Tregs) play an important role in suppressing immune responses against tumors by immunotherapy, such as DNA vaccines, we tested if the therapeutic effects of a DNA vaccine encoding E7 linked to heat shock protein 70 (Hsp70) can be improved by a strategy to deplete Tregs using a anti-CD25 monoclonal antibody (PC61) in vaccinated mice. We found that administration of PC61 prior to vaccination with E7/Hsp70 DNA was capable of generating higher levels of E7-specific CD8(+) T cells compared to the control antibody, leading to significantly improved therapeutic and long-term protective antitumor effects against an E7-expressing tumor, TC-1. Thus, a strategy to deplete CD4(+)CD25(+) Tregs in conjunction with therapeutic tumor antigen-specific DNA vaccine may represent a potentially promising approach to control tumor. The clinical implications of our study are discussed.