The critical role of IL-15 in the antitumor effects mediated by the combination therapy imatinib and IL-2

Biological effects of IL-15 on immune cells and its potential for the treatment of cancer

Interleukin-15 (IL-15) has recently emerged as a novel immunomodulatory cytokine in cancer immunotherapy. IL-15 has the potential to reject and destroy cancer cells in the tumor microenvironment by expanding and activating natural killer (NK), natural killer T (NKT), and memory (m) CD8+T cells. Due to the feasible outcomes obtained from preclinical studies and phase 1/2 clinical trials, IL-15-based therapy, including chimeric antigen receptor (CAR) T cell or CAR NK cell infusion following in vitro expansion in the presence of IL-15, used in combination with checkpoint inhibitors and other therapy may extend to clinical practice in the future. It is also important to understand the biological characteristics of IL-15 to ensure the maximal benefit of therapeutic strategies. Here, we summarize the current development of IL-15 in the following areas: anti-tumor mechanisms in the tumor microenvironment, advances in IL-15-based therapy itself or in combination with other methods, including biological agents, monoclonal antibodies, and adoptive immunotherapy.

Essential role of TNF-α in gamma c cytokine aided crosstalk between dendritic cells and natural killer cells in experimental murine lymphoma

Cooperative and cognitive interaction between the dendritic cells and natural killer cells was investigated for demonstrating the anti-tumor activity against an aggressive murine lymphoma, treated with doxorubicin. Crosstalk between the dendritic cells and the natural killer cells significantly reduced the proliferation of Dalton's lymphoma cells in a dose dependent manner. Treatment of Dalton's lymphoma cells with doxorubicin in vitro enhances the effects of crosstalk against the target cells. This crosstalk between the cells was regulated via stimulation with recombinant interleukin-15, and release of TNF-α which is critically important for the tumoricidal effects. Dendritic cells and the natural killer cells crosstalk activate both the cells and upregulate the expression of CD40, CD69 and CD86 on the dendritic cells. These findings provided new insight regarding these interactions and define a mechanism by which cellular immune response promotes tumoricidal activity against lymphoma in therapeutic setting.

Imatinib modulates pro-inflammatory microenvironment with angiostatic effects in experimental lung carcinogenesis

Lung cancer has second highest rate of incidence and mortality around the world. Smoking cigarettes is the main stream cause of lung carcinogenesis along with other factors such as spontaneous mutations, inactivation of tumor suppressor genes. The present study was aimed to identify the mechanistic role of Imatinib in the chemoprevention of experimental lung carcinogenesis in rat model. Gross morphological observations for tumor formation, histological examinations, RT-PCR, Western blotting, fluorescence spectroscopy and molecular docking studies were performed to elucidate the chemopreventive effects of Imatinib and support our hypothesis by various experiments. It is evident that immuno-compromised microenvironment inside solid tumors is responsible for tumor progression and drug resistance. Therefore, it is inevitable to modulate the pro-inflammatory signaling inside solid tumors to restrict neoangiogenesis. In the present study, we observed that Imatinib could downregulate the inflammatory signaling and also attributed angiostatic effects. Moreover, Imatinib also altered the biophysical properties of BAL cells such as plasma membrane potential, fluidity and microviscosity to restrict their infiltration and thereby accumulation to mount immuno-compromised environment inside the solid tumors during angiogenesis. Our molecular docking studies suggest that immunomodulatory and angiostatic properties of Imatinib could be either independent of each other or just a case of synergistic pleiotropy. Imatinib was observed to activate the intrinsic or mitochondrial pathway of apoptosis to achieve desired effects in cancer cell killings. Interestingly, binding of Imatinib inside the catalytic domain of PARP-1 also suggests that it has caspase-independent properties in promoting cancer cell deaths.

CXCR3-deficient natural killer cells fail to migrate to B16F10 melanoma cells

Natural killer (NK) cells eliminate cancer cells in a contact-dependent manner. However, how NK cells find cancer cells remain unclear. Here, using time-lapse imaging, we investigated how individual NK cells migrate toward cancer cells. Although naïve B16F10 cancer cells produce low levels of chemokines, IFN-γ-treated B16F10 cells secreted high levels of CXCL10, low levels of CCL5, but did not secrete CCL2, CCL7, or CXCL12. Wild-type NK cells migrated well toward cancer cells and killed them, whereas NK cells deficient in CXCR3 did not. CXCR3-deficient NK cells also showed slower migration speed than did wild-type NK cells. Taken together, our data show that NK cells find cancer cells, at least in part, by sensing CXCL10 produced by cancer cells and suggest that a strategy to increase CXCL10 secretion by cancer cells may improve the efficacy of NK cell-based immunotherapy.

Sunitinib does not impair natural killer cell function in patients with renal cell carcinoma

Although the available treatment options have expanded, the survival of patients with metastatic renal cell carcinoma (RCC) remains poor. As patients with RCC lack responsiveness to chemotherapy or radiation, therapeutic options predominantly include surgical interventions and immunomodulatory approaches, including the administration of tyrosine kinase inhibitors (TKIs) such as sunitinib. Natural killer (NK) cells have been reported to be key players in TKI-mediated off-target effects on the immune system. However, only limited information is available regarding the possible impact of sunitinib on the function of NK cells of individual patients. The present study reports on the immunomonitoring results of three patients with metastatic RCC who underwent sunitinib treatment. These results were compared with age-matched, healthy controls in terms of the immune status of T, B and NK cells, focusing on functional in vitro analyses of NK cells. In all three patients, NK cell number, subset distribution and function, as measured by cluster of differentiation 107a degranulation, did not exhibit any significant alterations as a result of sunitinib treatment. These results indicate that sunitinib does not negatively affect NK cell function, which supports the pursuit of therapeutic modalities that combine immunomodulation and NK cell-stimulating approaches.

Downregulation of STAT3 phosphorylation enhances tumoricidal effect of IL-15-activated dendritic cell against doxorubicin-resistant lymphoma and leukemia via TNF-α

Although disputed by some, increasing evidence suggests that TNF-α synergies with traditional chemotherapeutic drugs to exert a heightened antitumor effect. The present study investigated the antitumor efficacy of recombinant IL-15 in combination with the STAT3 inhibitor cucurbitacin-I in a doxorubicin-resistant murine lymphoma model. The significance of the work is to understand and design effective strategies in doxorubicin resistant lymphomas. TNF-α is downregulated in dendritic cells from mice with Dalton's lymphoma and shows an inverse relationship with disease progression. Doxorubicin-resistant DL cells have elevated levels of Bcl-2 and Mcl-1 and increased phosphorylation of STAT3. These cells are refractory to dendritic cell derived TNF-α. Doxorubicin resistant Dalton's lymphoma is susceptible to dendritic cell derived TNF-α upon stimulation with the STAT3 inhibitor cucurbitacin-I, which downregulates STAT3 and other survival molecules. The combined treatment of low dose of cucurbitacin-I and rIL-15 is ineffective in mice with doxorubicin resistant Dalton's lymphoma, but a similar therapy prolongs the survival of mice transplanted with parental Dalton's lymphoma. Doxorubicin resistant Dalton's lymphoma responds to therapy with high doses of cucurbitacin-I and rIL-15. Dendritic cell derived from mice responded positively to the therapy and regained their tumoricidal properties with respect to growth inhibition and killing of DL tumor cells. Similar to DL, DC derived from CML patients are impaired in TNF-α expression and are unable to restrict the growth of drug-resistant lymphoma and leukemia cells. This combination approach could be used as a new therapeutic strategy for aggressive and highly metastatic doxorubicin resistant lymphoma.

Trial Watch: Adoptive cell transfer for oncological indications

One particular paradigm of anticancer immunotherapy relies on the administration of (potentially) tumor-reactive immune effector cells. Generally, these cells are obtained from autologous peripheral blood lymphocytes (PBLs) ex vivo (in the context of appropriate expansion, activation and targeting protocols), and re-infused into lymphodepleted patients along with immunostimulatory agents. In spite of the consistent progress achieved throughout the past two decades in this field, no adoptive cell transfer (ACT)-based immunotherapeutic regimen is currently approved by regulatory agencies for use in cancer patients. Nonetheless, the interest of oncologists in ACT-based immunotherapy continues to increase. Accumulating clinical evidence indicates indeed that specific paradigms of ACT, such as the infusion of chimeric antigen receptor (CAR)-expressing autologous T cells, are associated with elevated rates of durable responses in patients affected by various neoplasms. In line with this notion, clinical trials investigating the safety and therapeutic activity of ACT in cancer patients are being initiated at an ever increasing pace. Here, we review recent preclinical and clinical advances in the development of ACT-based immunotherapy for oncological indications.

Classification of current anticancer immunotherapies

During the past decades, anticancer immunotherapy has evolved from a promising therapeutic option to a robust clinical reality. Many immunotherapeutic regimens are now approved by the US Food and Drug Administration and the European Medicines Agency for use in cancer patients, and many others are being investigated as standalone therapeutic interventions or combined with conventional treatments in clinical studies. Immunotherapies may be subdivided into "passive" and "active" based on their ability to engage the host immune system against cancer. Since the anticancer activity of most passive immunotherapeutics (including tumor-targeting monoclonal antibodies) also relies on the host immune system, this classification does not properly reflect the complexity of the drug-host-tumor interaction. Alternatively, anticancer immunotherapeutics can be classified according to their antigen specificity. While some immunotherapies specifically target one (or a few) defined tumor-associated antigen(s), others operate in a relatively non-specific manner and boost natural or therapy-elicited anticancer immune responses of unknown and often broad specificity. Here, we propose a critical, integrated classification of anticancer immunotherapies and discuss the clinical relevance of these approaches.

Phase I clinical trial combining imatinib mesylate and IL-2 in refractory cancer patients: IL-2 interferes with the pharmacokinetics of imatinib mesylate

Imatinib mesylate (IM) is a small molecule inhibitor of protein tyrosine kinases. In addition to its direct effect on malignant cells, it has been suggested IM may activate of natural killer (NK) cells, hence exerting immunomodulatory functions. In preclinical settings, improved antitumor responses have been observed when IM and interleukin-2 (IL-2), a cytokine that enhances NK cells functions, were combined. The goals of this study were to determine the maximum tolerated dose (MTD) of IL-2 combined with IM at a constant dose of 400 mg, the pharmacokinetics of IM and IL-2, as well as toxicity and clinical efficacy of this immunotherapeutic regimen in patients affected by advanced tumors. The treatment consisted in 50 mg/day cyclophosphamide from 21 d before the initiation of IM throughout the first IM cycle (from D-21 to D14), 400 mg/day IM for 14 d (D1 to D14) combined with escalating doses of IL-2 (3, 6, 9 and 12 MIU/day) from days 10 to 14. This treatment was administered at three week intervals to 17 patients. Common side effects of the combination were mild to moderate, including fever, chills, fatigue, nausea and hepatic enzyme elevation. IL-2 dose level II, 6 MIU/day, was determined as the MTD with the following dose-limiting toxicities: systemic capillary leak syndrome, fatigue and anorexia. Pharmacokinetic studies revealed that the area under the curve and the maximum concentration of IM and its main metabolite CGP74588 increased significantly when IM was concomitantly administered with IL-2. In contrast, IM did not modulate IL-2 pharmacokinetics. No objective responses were observed. The best response obtained was stable disease in 8/17 (median duration: 12 weeks). Finally, IL-2 augmented the impregnation of IM and its metabolite. The combination of IM (400 mg/day) and IL-2 (6 MIU/day) in tumors that express IM targets warrants further investigation.

Phase I clinical trial combining imatinib mesylate and IL-2: HLA-DR+ NK cell levels correlate with disease outcome

We performed a Phase I clinical trial from October 2007 to October 2009, enrolling patients affected by refractory solid tumors, to determine the maximum tolerated dose (MTD) of interleukin (IL)-2 combined with low dose cyclophosphamide (CTX) and imatinib mesylate (IM). In a companion paper published in this issue of OncoImmunology, we show that the MTD of IL-2 is 6 MIU/day for 5 consecutive days, and that IL-2 increases the impregnation of both IM and of its main metabolite, CGP74588. Among the secondary objectives, we wanted to determine immunological markers that might be associated with progression-free survival (PFS) and/or overall survival (OS). The combination therapy markedly reduced the absolute counts of B, CD4⁺ T and CD8⁺ T cells in a manner that was proportional to IL-2 dose. There was a slight (less than 2-fold) increase in the proportion of regulatory T cells (Tregs) among CD4⁺ T cells in response to IM plus IL-2. The natural killer (NK)-cell compartment was activated, exhibiting a significant upregulation of HLA-DR, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and CD56. The abundance of HLA-DR⁺ NK cells after one course of combination therapy positively correlated with both PFS and OS. The IL-2-induced rise of the CD4⁺:CD8⁺ T-cell ratio calculated after the first cycle of treatment was also positively associated with OS. Overall, the combination of IM and IL-2 promoted the rapid expansion of HLA-DR⁺ NK cells and increased the CD4⁺:CD8⁺ T-cell ratio, both being associated with clinical benefits. This combinatorial regimen warrants further investigation in Phase II clinical trials, possibly in patients affected by gastrointestinal stromal tumors, a setting in which T and NK cells may play an important therapeutic role.

Prospective study of the evolution of blood lymphoid immune parameters during dacarbazine chemotherapy in metastatic and locally advanced melanoma patients

Background

The importance of immune responses in the control of melanoma growth is well known. However, the implication of these antitumor immune responses in the efficacy of dacarbazine, a cytotoxic drug classically used in the treatment of melanoma, remains poorly understood in humans.

Methods

In this prospective observational study, we performed an immunomonitoring of eleven metastatic or locally advanced patients treated with dacarbazine as a first line of treatment. We assessed by flow cytometry lymphoid populations and their activation state; we also isolated NK cells to perform in vitro cytotoxicity tests.

Results

We found that chemotherapy induces lymphopenia and that a significantly higher numbers of naïve CD4⁺ T cells and lower proportion of Treg before chemotherapy are associated with disease control after dacarbazine treatment. Interestingly, NK cell cytotoxicity against dacarbazine-pretreated melanoma cells is only observed in NK cells from patients who achieved disease control.

Conclusion

Together, our data pinpoint that some immune factors could help to predict the response of melanoma patients to dacarbazine. Future larger scale studies are warranted to test their validity as prediction markers.

Trial Watch: Adoptive cell transfer for anticancer immunotherapy

The expression "adoptive cell transfer" (ACT) is commonly employed to indicate an immunotherapeutic regimen involving the isolation of autologous blood-borne or tumor-infiltrating lymphocytes, their selection/expansion/activation ex vivo, and their reinfusion into the patient, most often in the context of lymphodepleting pre-conditioning and in combination with immunostimulatory treatments. Optionally, the cellular material for ACT is genetically manipulated before expansion to (1) target specific tumor-associated antigens; (2) endogenously express immunostimulatory molecules; and/or (3) persist for long periods upon reinfusion. Consistent efforts have been dedicated at the amelioration of this immunotherapeutic regimen throughout the past decade, resulting in the establishment of ever more efficient and safer ACT protocols. Accordingly, the number of clinical trials testing ACT in oncological indications does not cease to increase. In this Trial Watch, we summarize recent developments in this exciting area of research, covering both high-impact studies that have been published during the last 12 months and clinical trials that have been launched in the same period to evaluate the safety and therapeutic potential of ACT in cancer patients.

Revisiting the Prominent Anti-Tumoral Potential of Pre-mNK Cells

Interferon-producing killer dendritic cells (IKDC) were first described for their outstanding anti-tumoral properties. The “IKDC” terminology implied the description of a novel DC subset and initiated a debate on their cellular lineage origin. This debate shifted the focus away from their notable anti-tumoral potential. IKDC were recently redefined as precursors to mature NK (mNK) cells and consequently renamed pre-mNK cells. Importantly, a putative human equivalent of pre-mNK cells was recently associated with improved disease outcome in cancer patients. It is thus timely to revisit the functional attributes as well as the therapeutic potential of pre-mNK cells in line with their newly defined NK-cell precursor function.

Bleomycin exerts ambivalent antitumor immune effect by triggering both immunogenic cell death and proliferation of regulatory T cells

Bleomycin (BLM) is an anticancer drug currently used for the treatment of testis cancer and Hodgkin lymphoma. This drug triggers cancer cell death via its capacity to generate radical oxygen species (ROS). However, the putative contribution of anticancer immune responses to the efficacy of BLM has not been evaluated. We make here the observation that BLM induces immunogenic cell death. In particular, BLM is able to induce ROS-mediated reticulum stress and autophagy, which result in the surface exposure of chaperones, including calreticulin and ERp57, and liberation of HMBG1 and ATP. BLM induces anti-tumor immunity which relies on calreticulin, CD8⁺ T cells and interferon-γ. We also find that, in addition to its capacity to trigger immunogenic cell death, BLM induces expansion of Foxp3+ regulatory T (Treg) cells via its capacity to induce transforming growth factor beta (TGFβ) secretion by tumor cells. Accordingly, Treg cells or TGFβ depletion dramatically potentiates the antitumor effect of BLM. We conclude that BLM induces both anti-tumor CD8⁺ T cell response and a counteracting Treg proliferation. In the future, TGFβ or Treg inhibition during BLM treatment could greatly enhance BLM anti-tumor efficacy.

Trial Watch: Adoptive cell transfer for anticancer immunotherapy

Adoptive cell transfer (ACT) represents a prominent form of immunotherapy against malignant diseases. ACT is conceptually distinct from dendritic cell-based approaches (which de facto constitute cellular vaccines) and allogeneic transplantation (which can be employed for the therapy of hematopoietic tumors) as it involves the isolation of autologous lymphocytes exhibiting antitumor activity, their expansion/activation ex vivo and their reintroduction into the patient. Re-infusion is most often performed in the context of lymphodepleting regimens (to minimize immunosuppression by host cells) and combined with immunostimulatory interventions, such as the administration of Toll-like receptor agonists. Autologous cells that are suitable for ACT protocols can be isolated from tumor-infiltrating lymphocytes or generated by engineering their circulating counterparts for the expression of transgenic tumor-specific T-cell receptors. Importantly, lymphocytes can be genetically modified prior to re-infusion for increasing their persistence in vivo, boosting antitumor responses and minimizing side effects. Moreover, recent data indicate that exhausted antitumor T lymphocytes may be rejuvenated in vitro by exposing them to specific cytokine cocktails, a strategy that might considerably improve the clinical success of ACT. Following up the Trial Watch that we published on this topic in the third issue of OncoImmunology (May 2012), here we summarize the latest developments in ACT-related research, covering both high-impact studies that have been published during the last 13 months and clinical trials that have been initiated in the same period to assess the antineoplastic profile of this form of cellular immunotherapy.

Cytokines: monitors of disease severity for the clinic

BACKGROUND

Cytokines communicate between the cells of the immune system and its targets to maintain homeostasis after injury or pathogenic events. They are involved in almost any pathological situation imaginable.

OBJECTIVE

To verify the importance of cytokines as biomarkers in current preclinical (aetiopathogenic, development of new therapies) and clinical studies (diagnosis, disease severity, prognosis and response to therapy).

METHOD/RESULTS

A Medline search with the query 'cytokine' AND 'biomarker' AND a variable for a variety of biomedical fields, followed by deeper-level searches, demonstrated the immense popularity of cytokines as biomarkers in almost any biomedical field.

CONCLUSION

As cytokines are not disease-specific they do not serve as single diagnostic biomarkers. The strength of the cytokines resides in monitoring disease severity, prognosis and response to treatment.

Liver gene transfer of interkeukin-15 constructs that become part of circulating high density lipoproteins for immunotherapy

Apolipoprotein A-I (Apo A-I) is a major component of high density lipoproteins (HDL) that transport cholesterol in circulation. We have constructed an expression plasmid encoding a chimeric molecule encompassing interleukin-15 (IL-15) and Apo A-I (pApo-hIL15) that was tested by hydrodynamic injections into mice and was co-administered with a plasmid encoding the sushi domain of IL-15Rα (pSushi) in order to enhance IL-15 trans-presentation and thereby bioactivity. The pharmacokinetics of the Apo A-I chimeric protein were much longer than non-stabilized IL-15 and its bioactivity was enhanced in combination with IL-15Rα Sushi. Importantly, the APO-IL-15 fusion protein was incorporated in part into circulating HDL. Liver gene transfer of these constructs increased NK and memory-phenotype CD8 lymphocyte numbers in peripheral blood, spleen and liver as a result of proliferation documented by CFSE dilution and BrdU incorporation. Moreover, the gene transfer procedure partly rescued the NK and memory T-cell deficiency observed in IL-15Rα^−/− mice. pApo-hIL15+ pSushi gene transfer to the liver showed a modest therapeutic activity against subcutaneously transplanted MC38 colon carcinoma tumors, that was more evident when tumors were set up as liver metastases. The improved pharmacokinetic profile and the strong biological activity of APO-IL-15 fusion protein holds promise for further development in combination with other immunotherapies.

How do cytokines trigger genomic instability?

Inflammation is a double-edged sword presenting a dual effect on cancer development, from one hand promoting tumor initiation and progression and from the other hand protecting against cancer through immunosurveillance mechanisms. Cytokines are crucial components of inflammation, participating in the interaction between the cells of tumor microenvironment. A comprehensive study of the role of cytokines in the context of the inflammation-tumorigenesis interplay helps us to shed light in the pathogenesis of cancer. In this paper we focus on the role of cytokines in the development of genomic instability, an evolving hallmark of cancer.

Trial Watch: Adoptive cell transfer immunotherapy

During the last two decades, several approaches for the activation of the immune system against cancer have been developed. These include rather unselective maneuvers such as the systemic administration of immunostimulatory agents (e.g., interleukin-2) as well as targeted interventions, encompassing highly specific monoclonal antibodies, vaccines and cell-based therapies. Among the latter, adoptive cell transfer (ACT) involves the selection of autologous lymphocytes with antitumor activity, their expansion/activation ex vivo, and their reinfusion into the patient, often in the context of lymphodepleting regimens (to minimize endogenous immunosuppression). Such autologous cells can be isolated from tumor-infiltrating lymphocytes or generated by manipulating circulating lymphocytes for the expression of tumor-specific T-cell receptors. In addition, autologous lymphocytes can be genetically engineered to prolong their in vivo persistence, to boost antitumor responses and/or to minimize side effects. ACT has recently been shown to be associated with a consistent rate of durable regressions in melanoma and renal cell carcinoma patients and holds great promises in several other oncological settings. In this Trial Watch, we will briefly review the scientific rationale behind ACT and discuss the progress of recent clinical trials evaluating the safety and effectiveness of adoptive cell transfer as an anticancer therapy.

The predictive value of pre-treatment inflammatory markers in advanced non-small-cell lung cancer

BACKGROUND

Accurate prediction of outcome in advanced non-small-cell lung cancer (NSCLC) remains challenging. Even within the same stage and treatment group, survival and response to treatment vary. We set out to determine the predictive value of inflammatory markers C-reactive protein (CRP) and white blood cells (WBCS) in patients with advanced NSCLC.

PATIENTS AND METHODS

Patients were assigned a prognostic index (PI): 0 for crp 10 mg/L or less and WBCS 11x10⁹/L or less, 1 if one of the two markers was elevated, and 2 if both markers were elevated. We then used chest computed tomography (CT) imaging to evaluate response after 2 cycles of chemotherapy treatment.

RESULTS

Of 134 patients, 46 had a PI of 0; 60, a PI of 1; and 28, a PI of 2. Disease progressed in 41 patients. Progression was significantly more frequent among patients with a PI of 2 (p = 0.008). Median survival was 20.0 months for the PI 0 group, 10.4 months for the PI 1 group, and 7.9 months for the PI 2 group (p < 0.001). The PI was the only significant prognostic factor for survival even after adjustment for performance status, smoking, and weight loss (hazard ratio: 1.57; 95% confidence interval: 1.2 to 2.14; p = 0.004).

CONCLUSIONS

Inflammatory state correlates significantly with both chemotherapy response and survival in stage IV NSCLC. The PI may provide additional guidance for therapeutic decision-making.

G-protein-coupled receptors in control of natural killer cell migration

Natural killer (NK) cells are highly motile cells that patrol lymphoid and non-lymphoid organs, and are poised to react to infectious or other inflammatory situations. Several NK cell subsets equipped with different sets of chemotactic G-protein-coupled receptors, and which display distinct distribution across lymphoid and non-lymphoid organs, have been described. These receptors detect various guidance cues including sphingosine-1-phosphate and chemokines that orchestrate NK cell trafficking. Here, we highlight recent advances regarding the receptors involved in NK cell migration, with a focus on bone marrow egress, entry into activated lymph nodes, extravasation into inflamed tissues, and motility within lymph nodes or tumors. Understanding NK cell migration could provide a rational basis for the design of novel therapies in various clinical conditions.

Small-molecule protein kinase inhibitors and their effects on the immune system: implications for cancer treatment

Oncogenic signaling pathways have emerged as key targets for the development of small-molecule inhibitors, with several protein kinase inhibitors already in clinical use for cancer patients. In addition to their role in tumorigenesis, many of the molecules and signaling pathways targeted by these inhibitors are also important in the signaling and interaction of immune cells, such as T cells and dendritic cells. Not surprisingly, there is increasing evidence that many of these inhibitors can have a substantial impact on immune function, both stimulating and downregulating an immune response. In order to illustrate the important role of signaling molecule inhibition in the modulation of immune function, we will discuss the exemplary pathways MAPK, AKT-PI3K-mTOR and VEGF-VEGFR, as well as selected small-molecule inhibitors, whose impact on immune cells has been studied more extensively.

Immunomodulatory effects of cyclophosphamide and implementations for vaccine design

Drug repositioning refers to the utilization of a known compound in a novel indication underscoring a new mode of action that predicts innovative therapeutic options. Since 1959, alkylating agents, such as the lead compound cyclophosphamide (CTX), have always been conceived, at high dosages, as potent cytotoxic and lymphoablative drugs, indispensable for dose intensity and immunosuppressive regimen in the oncological and internal medicine armamentarium. However, more recent work highlighted the immunostimulatory and/or antiangiogenic effects of low dosing CTX (also called "metronomic CTX") opening up novel indications in the field of cancer immunotherapy. CTX markedly influences dendritic cell homeostasis and promotes IFN type I secretion, contributing to the induction of antitumor cytotoxic T lymphocytes and/or the proliferation of adoptively transferred T cells, to the polarization of CD4(+) T cells into TH1 and/or TH17 lymphocytes eventually affecting the Treg/Teffector ratio in favor of tumor regression. Moreover, CTX has intrinsic "pro-immunogenic" activities on tumor cells, inducing the hallmarks of immunogenic cell death on a variety of tumor types. Fifty years after its Food and Drug Administration approval, CTX remains a safe and affordable compound endowed with multifaceted properties and plethora of clinical indications. Here we review its immunomodulatory effects and advocate why low dosing CTX could be successfully combined to new-generation cancer vaccines.

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.

Interleukin-2 treatment effect on imatinib pharmacokinetic, P-gp and BCRP expression in mice

The aim of this study was to investigate the effect that recombinant interleukin-2 (rIL-2) (0.16 MUI/injection) had on the pharmacokinetics of imatinib (IM) in plasma. In this study, IM was given orally to mice at a dose of 150 mg/kg once a day for 11 days (from day 1 to 11) either alone or in combination with intraperitoneal injections of rIL-2 twice a day from day 8 to 11. Pharmacokinetic parameters were determined using WinNonLin software. Areas under the curve were compared using Bailer's method. The repeated administration of the rIL-2+IM combination was shown to have two pharmacokinetic advantages compared with repeated IM doses alone. In addition to the pharmacodynamic interest of this treatment, we found that the combined treatment significantly increased the IM Cmax (P<0.05) and significantly increased the IM trough concentration (C(24 h)) (P<0.01), which was always above the minimum therapeutic IM concentration (1 mumol/l) in plasma. Those pharmacokinetic modifications may be explained, in part, by a decrease in the P-glycoprotein expression in the three intestinal segments of the mice (duodenum, P<0.01; jejunum, P<0.05; and ileum, P<0.05) and a decrease in BCRP expression in the duodenum segment (P<0.05) due to rIL-2. In another experiment, we found a significant induction of intestinal P-glycoprotein expression in mice that had been given IM orally (150 mg/kg) twice a day for 11 days. It would be interesting to further investigate the IM disposition associated with rIL-2 treatment for clinical applications.

Killer dendritic cells and their potential for cancer immunotherapy

Known for years as the principal messengers of the immune system, dendritic cells (DC) represent a heterogeneous population of antigen presenting cells critically located at the nexus between innate and adaptive immunity. DC play a central role in the initiation of tumor-specific immune responses as they are endowed with the unique ability to take up, process and present tumor antigens to naïve CD4(+) or CD8(+) effector T lymphocytes. By virtue of the cytokines they produce, DC also regulate the type, strength and duration of T cell immune responses. In addition, they can participate in anti-tumoral NK and NKT cell activation and in the orchestration of humoral immunity. More recent studies have documented that besides their primary role in the induction and regulation of adaptive anti-tumoral immune responses, DC are also endowed with the capacity to directly kill cancer cells. This dual role of DC as killers and messengers may have important implications for tumor immunotherapy. First, the direct killing of malignant cells by DC may foster the release and thereby the immediate availability of specific tumor antigens for presentation to cytotoxic or helper T lymphocytes. Second, DC may participate in the effector phase of the immune response, potentially augmenting the diversity of the killing mechanisms leading to tumor elimination. This review focuses on this non-conventional cytotoxic function of DC as it relates to the promotion of cancer immunity and discusses the potential application of killer DC (KDC) in tumor immunotherapy.

The dendritic cell-like functions of IFN-producing killer dendritic cells reside in the CD11b+ subset and are licensed by tumor cells

IFN producing killer dendritic cells (IKDC) were originally defined as CD11c(int) B220(+)NK1.1(+) (or CD49b(+)) cells that exert a potent tumoricidal activity in animals lacking B, T, and conventional natural killer effectors. MHC class II expression on tumor infiltrating IKDC prompted us to investigate their putative antigen presenting function. Here, we show that tumor cells license IKDC to acquire the properties of antigen presenting cells, i.e., expression of MHC class II and costimulatory CD86 molecules. We show that the CD11b(+) subset of IKDC are able to prime naïve CD4(+) T cells and cross-prime naïve CD8(+) T lymphocytes. Licensing of IKDC by tumor cells was mandatory for the full differentiation of T cells into polarized effectors. IKDC could engulf and process soluble Ova protein in a CD206-dependent manner. Finally, we show that CD11b(+)IKDC is selectively endowed with CTLA4Ig-inhibitable antigen presenting capacities and that targeting this subset with the detoxified adenylate cyclase toxin of Bordetella pertussis fused to antigen resulted in efficient cross-presentation of antigen by IKDC to specific TCR transgenic CD8(+)T cells in vivo. Collectively, our data indicate that upon exposure to tumor cells, IKDC subserve DC-like functions.

[Immunological evaluation for CML and its possibility for an immunotherapy]

Chronic myelogenous leukemia (CML) is associated with the Ph1 chromosome translocation, which produces a chimeric tyrosine-specific kinase gene, the product of the fusion of the BCR gene and the ABL gene. The immune system has long been implicated in the control of CML. We found oligoclonal T cell responses in treated patients with IFN-alpha or leukemic dendritic cells. Also other groups treated chronic phase CML (CP-CML) patients with various leukemic antigen peptides, resulted in apparent immune response and clinical response. Imatinib mesylate is currently used as the first line therapy for CP-CML patients. Although it selectively targets the ABL portion of BCR-ABL protein as a reversible tyrosine kinase inhibitor, it cannot kill the leukemic stem cells of CML. To find a possibility to enhance the immunity in imatinib-treated CML patients by combining it with immunotherapy, we summarized the immune response of innate and adaptive immunity in CML. Development of such immunotherapeutic strategies would be a promising approach to treat the imatinib-treated CML-CP patients.

Cytokines as Adjuvants for Vaccine and Cellular Therapies for Cancer

PROBLEM STATEMENT: The development of a potent vaccine that can help treat tumors resistant to conventional cytotoxic therapies remains elusive. While part of the problem may be that trials have focused on patients with bulky residual disease, the desire to maximize responses to the vaccine remains. APPROACH: The gamma(c) family of cytokines offer a unique opportunity to support the expansion and effector potential of vaccine-responding T-cells, as well as stimulate other effectors, such as natural killer (NK) cells, to become activated. RESULTS: Combining vaccines with cytokines seems logical but can bring unwanted toxicity, as has been observed with interleukin (IL)-2. In addition, the nonspecific activation or expansion of unwanted cell subsets, such as regulatory T-cells, can contribute to global immunosuppression and limit vaccine responses. The development of IL-7 and IL-21 for the clinic offers the promise of enhancing anti-tumor responses but with far less systemic toxicity and no expansion of regulatory T cells. Preclinical studies demonstrate that IL-15 could also improve T-cell, and especially NK-cell, responses as well. CONCLUSIONS/RECOMMENDATIONS: Future work should expand the use of vaccines with IL-7, IL-21 and hopefully IL-15 in high-risk patients, and consider treatment while in a state of minimal residual disease to maximize benefit. Identifying tumors that can signal through gamma(c) cytokines will also be essential so that induction of relapse will be avoided.

Trans-presentation of IL-15 dictates IFN-producing killer dendritic cells effector functions

IFN-producing killer dendritic cells (IKDC) were initially described as B220(+)CD11c(+)CD3(-)NK1.1(+) tumor-infiltrating cells that mediated part of the antitumor effects of the combination therapy with imatinib mesylate and IL-2. In this study, we show their functional dependency on IL-15 during homeostasis and inflammatory processes. Trans-presentation of IL-15 by IL-15Ralpha allows dramatic expansion of IKDC in vitro and in vivo, licenses IKDC for TRAIL-dependent killing and endows IKDC with immunizing potential, all three biological attributes not shared by B220(-)NK cells. However, IL-15 down-regulates the capacity of IKDC to induce MHC class I- or II-restricted T cell activation in vitro. Trans-presentation of IL-15 by IL-15Ralpha allows IKDC to respond to TLR3 and TLR4 ligands for the production of CCL2, a chemokine that is critical for IKDC trafficking into tumor beds (as described recently). We conclude that IKDC represent a unique subset of innate effectors functionally distinguishable from conventional NK cells in their ability to promptly respond to IL-15-driven inflammatory processes.