Regression of a mammary adenocarcinoma in STAT6-/- mice is dependent on the presence of STAT6-reactive T cells

ICRP Publication 131: Stem Cell Biology with Respect to Carcinogenesis Aspects of Radiological Protection

This report provides a review of stem cells/progenitor cells and their responses to ionising radiation in relation to issues relevant to stochastic effects of radiation that form a major part of the International Commission on Radiological Protection's system of radiological protection. Current information on stem cell characteristics, maintenance and renewal, evolution with age, location in stem cell 'niches', and radiosensitivity to acute and protracted exposures is presented in a series of substantial reviews as annexes concerning haematopoietic tissue, mammary gland, thyroid, digestive tract, lung, skin, and bone. This foundation of knowledge of stem cells is used in the main text of the report to provide a biological insight into issues such as the linear-no-threshold (LNT) model, cancer risk among tissues, dose-rate effects, and changes in the risk of radiation carcinogenesis by age at exposure and attained age. Knowledge of the biology and associated radiation biology of stem cells and progenitor cells is more developed in tissues that renew fairly rapidly, such as haematopoietic tissue, intestinal mucosa, and epidermis, although all the tissues considered here possess stem cell populations. Important features of stem cell maintenance, renewal, and response are the microenvironmental signals operating in the niche residence, for which a well-defined spatial location has been identified in some tissues. The identity of the target cell for carcinogenesis continues to point to the more primitive stem cell population that is mostly quiescent, and hence able to accumulate the protracted sequence of mutations necessary to result in malignancy. In addition, there is some potential for daughter progenitor cells to be target cells in particular cases, such as in haematopoietic tissue and in skin. Several biological processes could contribute to protecting stem cells from mutation accumulation: (a) accurate DNA repair; (b) rapidly induced death of injured stem cells; (c) retention of the DNA parental template strand during divisions in some tissue systems, so that mutations are passed to the daughter differentiating cells and not retained in the parental cell; and (d) stem cell competition, whereby undamaged stem cells outcompete damaged stem cells for residence in the niche. DNA repair mainly occurs within a few days of irradiation, while stem cell competition requires weeks or many months depending on the tissue type. The aforementioned processes may contribute to the differences in carcinogenic radiation risk values between tissues, and may help to explain why a rapidly replicating tissue such as small intestine is less prone to such risk. The processes also provide a mechanistic insight relevant to the LNT model, and the relative and absolute risk models. The radiobiological knowledge also provides a scientific insight into discussions of the dose and dose-rate effectiveness factor currently used in radiological protection guidelines. In addition, the biological information contributes potential reasons for the age-dependent sensitivity to radiation carcinogenesis, including the effects of in-utero exposure.

Adaptive Immune Regulation of Mammary Postnatal Organogenesis

Postnatal organogenesis occurs in an immune competent environment and is tightly controlled by interplay between positive and negative regulators. Innate immune cells have beneficial roles in postnatal tissue remodeling, but roles for the adaptive immune system are currently unexplored. Here we show that adaptive immune responses participate in the normal postnatal development of a non-lymphoid epithelial tissue. Since the mammary gland (MG) is the only organ developing predominantly after birth, we utilized it as a powerful system to study adaptive immune regulation of organogenesis. We found that antigen-mediated interactions between mammary antigen-presenting cells and interferon-γ (IFNγ)-producing CD4+ T helper 1 cells participate in MG postnatal organogenesis as negative regulators, locally orchestrating epithelial rearrangement. IFNγ then affects luminal lineage differentiation. This function of adaptive immune responses, regulating normal development, changes the paradigm for studying players of postnatal organogenesis and provides insights into immune surveillance and cancer transformation.

Signaling pathways involved in MDSC regulation

The immune system has evolved mechanisms to protect the host from the deleterious effects of inflammation. The generation of immune suppressive cells like myeloid derived suppressor cells (MDSCs) that can counteract T cell responses represents one such strategy. There is an accumulation of immature myeloid cells or MDSCs in bone marrow (BM) and lymphoid organs under pathological conditions such as cancer. MDSCs represent a population of heterogeneous myeloid cells comprising of macrophages, granulocytes and dendritic cells that are at early stages of development. Although, the precise signaling pathways and molecular mechanisms that lead to MDSC generation and expansion in cancer remains to be elucidated. It is widely believed that perturbation of signaling pathways involved during normal hematopoietic and myeloid development under pathological conditions such as tumorogenesis contributes to the development of suppressive myeloid cells. In this review we discuss the role played by key signaling pathways such as PI3K, Ras, Jak/Stat and TGFb during myeloid development and how their deregulation under pathological conditions can lead to the generation of suppressive myeloid cells or MDSCs. Targeting these pathways should help in elucidating mechanisms that lead to the expansion of MDSCs in cancer and point to methods for eliminating these cells from the tumor microenvironment.

STAT signaling in mammary gland differentiation, cell survival and tumorigenesis

The mammary gland is a unique organ that undergoes extensive and profound changes during puberty, menstruation, pregnancy, lactation and involution. The changes that take place during puberty involve large-scale proliferation and invasion of the fat-pad. During pregnancy and lactation, the mammary cells are exposed to signaling pathways that inhibit apoptosis, induce proliferation and invoke terminal differentiation. Finally, during involution the mammary gland is exposed to milk stasis, programmed cell death and stromal reorganization to clear the differentiated milk-producing cells. Not surprisingly, the signaling pathways responsible for bringing about these changes in breast cells are often subverted during the process of tumorigenesis. The STAT family of proteins is involved in every stage of mammary gland development, and is also frequently implicated in breast tumorigenesis. While the roles of STAT3 and STAT5 during mammary gland development and tumorigenesis are well studied, others members, e.g. STAT1 and STAT6, have only recently been observed to play a role in mammary gland biology. Continued investigation into the STAT protein network in the mammary gland will likely yield new biomarkers and risk factors for breast cancer, and may also lead to novel prophylactic or therapeutic strategies against breast cancer.

Cure of metastatic growth of EMT6 tumor cells in mice following manipulation of CD200:CD200R signaling

In previous studies, we observed that regulation of expression of CD200, both on cells of a transplantable breast cancer, EMT6, and of the host, as well as of the receptor, CD200R in host mice, regulated local tumor growth and metastasis in immunocompetent animals. This in turn led to an improved ability to document immunity to EMT6 in CD200R1KO mice. In the current study, we have explored the ability to cure BALB/c CD200KO or CD200R1KO mice of tumors ≤1 cm³ in size by surgical resection of localized tumor, followed by immunization with irradiated EMT6 cells along with CpG as adjuvant. While control animals treated in this fashion developed significant pulmonary and liver metastases within 30 days of surgery, significant protection was seen in both CD200KO or CD200R1KO mice, with no macroscopic lung/liver metastases observed in CD200R1KO mice on sacrifice at day 300. Following surgical resection and immunization, draining lymph nodes from control mice contained tumor cells cloned at limiting dilution in vitro even before pulmonary and hepatic metastasis was seen. In contrast, within the limits of detection of the assay used (sensitivity ~1 in 10⁷ cells), no tumor cells were detected at limiting dilution in similarly treated CD200R1KO mice, and significant reductions were seen in CD200KO mice. Infusion of anti-CD4, but less so anti-CD8, mAb into surgically treated and immunized CD200R1KO mice attenuated protection from both macroscopic (liver/lung) and microscopic (assayed by limiting dilution of DLN) metastasis. Adoptive transfer of lymphocytes from treated CD200R1KO mice to surgically treated control mice also attenuated metastatic growth of tumor, which was abolished by pretreatment of transferred cells with anti-CD4 mAb. Our data suggest that CD200:CD200R attenuates a potentially tumor-protective CD4 host response to breast cancer.

Anti-STAT6 CTL activity in Stat6 (-/-) mice: A cautionary tale

The generation of germline gene mutations in mice has been an invaluable tool for experimental biology. However, studying immune responses that develop in the absence of a specific protein that could alter thymic selection complicates experimental interpretations. We observed that CD8⁺ T cells from Stat6^−/− mice displayed “autoreactivity” to STAT6-expressing cells, associated with specific STAT6 peptides binding to MHC class I molecules. These results suggest caution in interpreting experiments where STAT6-expressing cells are transferred into Stat6^−/− mice, or where adoptive transfer of Stat6^−/− lymphocytes is performed. Our results further highlight additional considerations when studying immune responses involving cell transfer into gene-deficient mice.

STAT6 expression in glioblastoma promotes invasive growth

BACKGROUND

Glioblastoma (GBM) is a highly aggressive malignant primary brain tumor, characterized by rapid growth, diffuse infiltration of cells into both adjacent and remote brain regions, and a generalized resistance to currently available treatment modalities. Recent reports in the literature suggest that Signal Transducers and Activators of Transcription (STATs) play important roles in the regulation of GBM pathophysiology.

METHODS

STAT6 protein expression was analyzed by Western blotting in GBM cell lines and by immunohistochemistry in a tissue microarray (TMA) of glioma patient tissues. We utilized shRNA against STAT6 to investigate the effects of prolonged STAT6 depletion on the growth and invasion of two STAT6-positive GBM cell lines. Cell proliferation was assessed by measuring (3)H-Thymidine uptake over time. Invasion was measured using an in vitro transwell assay in which cells invade through a type IV collagen matrix toward a chemoattractant (Fetal Bovine Serum). Cells were then stained and counted. Kaplan-Meyer survival curves were generated to show the correlation between STAT6 gene expression and patient survival in 343 glioma patients and in a subset of patients with only GBM. Gene expression microarray and clinical data were acquired from the Rembrandt 1 public data depository (https://caintegrator.nci.nih.gov/rembrandt/). Lastly, a genome-wide expression microarray analysis was performed to compare gene expression in wild-type GBM cells to expression in stable STAT6 knockdown clones.

RESULTS

STAT6 was expressed in 2 GBM cell lines, U-1242MG and U-87MG, and in normal astrocytes (NHA) but not in the U-251MG GBM cell line. In our TMA study, STAT6 immunostaining was visible in the majority of astrocytomas of all grades (I-IV) but not in normal brain tissue. In positive cells, STAT6 was localized exclusively in the nuclei over 95% of the time. STAT6-deficient GBM cells showed a reduction in (3)H-Thymidine uptake compared to the wild-type. There was some variation among the different shRNA- silenced clones, but all had a reduction in (3)H-Thymidine uptake ranging from 35%- 70% in U-1242MG and 40- 50% in U-87MG cells. Additionally, STAT6- depleted cells were less invasive than controls in our in vitro transmembrane invasion assay. Invasiveness was decreased by 25-40% and 30-75% in U-1242MG and U-87MG cells, respectively. The microarray analysis identified matrix metalloproteinase 1 (MMP-1) and urokinase Plasminogen activator (uPA) as potential STA6 target genes involved in the promotion of GBM cell invasion. In a Kaplan-Meier survival curve based on Rembrandt 1 gene expression microarray and clinical data, there was a significant difference in survival (P < 0.05) between glioma patients with up- and down-regulated STAT6. Decreased STAT6 expression correlated with longer survival times. In two subsets of patients with either grade IV tumors (GBM) or Grade II/III astrocytomas, there was a similar trend that however did not reach statistical significance.

CONCLUSIONS

Taken together, these findings suggest a role for STAT6 in enhancing cell proliferation and invasion in GBM, which may explain why up-regulation of STAT6 correlates with shorter survival times in glioma patients. This report thus identifies STAT6 as a new and potentially promising therapeutic target.

Alternative activation of tumor-associated macrophages by IL-4: priming for protumoral functions

Although macrophages were originally recognized as major immune effector cells, it is now appreciated that they also play many important roles in the maintenance of tissue homeostasis, and are involved in a variety of pathological conditions including cancer. Several studies have demonstrated the contributions of tumor-associated macrophages (TAMs) to tumor initiation, progression, and metastasis. However, the detailed mechanisms underlying how TAMs differ molecularly from their normal counterparts and how the conversion to TAMs occurs have only just begun to be understood. TAMs have been proposed to exhibit phenotypes of 'alternatively activated' macrophages, though there has been limited evidence directly linking the phenotypes of TAMs to the alternative activation of macrophages. This review will focus on IL-4, the prototypic cytokine that induces the alternative activation of macrophages, and review current knowledge regarding the contributions of IL-4 to the phenotypes of TAMs and its effects on tumorigenesis.

Mammary gland growth factors: roles in normal development and in cancer

Normal development of the mammary gland proceeds via interactions between the epithelium and the mesenchyme that start during embryogenesis and continue during pubertal outgrowth and differentiation. The function of specific peptide growth factors that bind members of the receptor tyrosine kinase family and the cytokine receptor family are required at each stage. In many cases the peptides are produced in one compartment and act on receptors in the other compartment. One of the striking differences between normal development and cancer is the loss of this cross-talk. Mammary tumor cells often produce a peptide and express the receptor on the same cell leading to autocrine activation of signaling pathways, a mechanism that is characteristic for cancer cells. We will discuss different peptides in the context of normal development and cancer in this review.

Signal transducer and activator of transcription 6 (STAT6) is a novel interactor of annexin A2 in prostate cancer cells

Annexin A2 (AnxA2) is a multifunctional Ca(2+)-dependent phospholipid-binding protein, and its overexpression is implicated in malignant transformation of several cancers. In prostate cancer, however, the expression of AnxA2 is lost in prostate intraepithelial neoplasia and reappears in the high-grade tumors, suggesting a complex regulation of AnxA2 in the prostate microenvironment. Since a majority of the biological functions of AnxA2 are mediated by its interaction with other proteins, we performed a yeast two-hybrid assay to search for novel interactors of AnxA2. Our studies revealed that signal transducer and activator of transcription 6 (STAT6), a member of the STAT family of transcription factors, is a binding partner of AnxA2. We confirmed AnxA2-STAT6 interaction by in vitro co-immunoprecipitation and fluorescence resonance energy transfer (FRET) studies and demonstrated that AnxA2 interacts with phosphorylated STAT6. Furthermore, chromatin immunoprecipitation (ChIP) assay revealed that AnxA2 is associated with the STAT6 DNA-binding complex, and luciferase reporter assays demonstrated that AnxA2 upregulates the activity of STAT6. Upon interleukin-4 treatment, AnxA2 stabilizes the cytosolic levels of phosphorylated STAT6 and promotes its nuclear entry. These findings suggest that AnxA2-STAT6 interactions could have potential implications in prostate cancer progression. This report is the first to demonstrate the interaction of AnxA2 with STAT6 and suggests a possible mechanism by which AnxA2 contributes to the metastatic processes of prostate cancer.

Invariant natural killer T cells regulate breast cancer response to radiation and CTLA-4 blockade

PURPOSE

Immunoregulatory and suppressive mechanisms represent major obstacles to the success of immunotherapy in cancer patients. We have shown that the combination of radiotherapy to the primary tumor and CTL-associated protein 4 (CTLA-4) blockade induces antitumor immunity, inhibiting metastases and extending the survival of mice bearing the poorly immunogenic and highly metastatic 4T1 mammary carcinoma. Similarly to patients with metastatic cancer, however, mice were seldom cured. Here we tested the hypothesis that invariant natural killer T (iNKT) cells, a subset with unique regulatory functions, can regulate the response to radiotherapy and CTLA-4 blockade.

EXPERIMENTAL DESIGN

The growth of 4T1 primary tumors and lung metastases was compared in wild-type and iNKT cell-deficient (iNKT-/-) mice. Treatment was started on day 13 when the primary tumors were palpable. Mice received radiotherapy to the primary tumor in two doses of 12 Gy in combination or not with 9H10 monoclonal antibody against CTLA-4. Response to treatment was assessed by measuring primary tumor growth delay/regression, survival, and number of lung metastases.

RESULTS

The response to radiotherapy plus 9H10 was markedly enhanced in the absence of iNKT cells, with 50% of iNKT-/- versus 0% of wild-type mice showing complete tumor regression, long-term survival, and resistance to a challenge with 4T1 cells. Administration of the iNKT cell activator alpha-galactosylceramide did not enhance the response of wild-type mice to radiotherapy plus 9H10. Tumor-infiltrating iNKT cells were markedly reduced in wild-type mice treated with radiotherapy plus 9H10.

CONCLUSIONS

iNKT cells play a major role in regulating the response to treatment with local radiotherapy and CTLA-4 blockade.

The IL-4/IL-13/Stat6 signalling pathway promotes luminal mammary epithelial cell development

Naïve T helper cells differentiate into Th1 and Th2 subsets, which have unique cytokine signatures, activators and transcriptional targets. The Th1/Th2 cytokine milieu is a key paradigm in lineage commitment, and IL-4 (Il4), IL-13 (Il13) and Stat6 are important mediators of Th2 development. We show here, for the first time, that this paradigm applies also to mammary epithelial cells, which undergo a switch from Th1 to Th2 cytokine production upon the induction of differentiation. Thus, the Th1 cytokines IL-12 (Il12), interferon gamma (INFgamma; also known as Ifng) and Tnfalpha are downregulated concomitantly with the upregulation of the Th2 cytokines IL-4, IL-13 and IL-5 (Il5) as epithelial cells commit to the luminal lineage. Moreover, we show that Th2 cytokines play a crucial role in mammary gland development in vivo, because differentiation and alveolar morphogenesis are reduced in both Stat6 and IL-4/IL-13 doubly deficient mice during pregnancy. This unexpected discovery demonstrates a role for immune cell cytokines in epithelial cell fate and function, and adds an unexpected tier of complexity to the previously held paradigm that steroid and peptide hormones are the primary regulators of mammary gland development.

Inhibition of host signal transducer and activator of transcription factor 6 results in cure with cyclophosphamide and interleukin 12 immunotherapy

BACKGROUND

Interleukin (IL)-12 immunotherapy is highly effective against established immunogenic tumors. However, nonimmunogenic tumors fail to respond to IL-12 therapy. Analysis of tumor rejection of the immunogenic tumors shows that a preexisting antitumor immune response is required for an effective IL-12 response. It is not known whether this lack of a preexisting host antitumor immune response is a limiting factor for the lack of response to IL-12 therapy by nonimmunogenic tumors.

METHODS

Experiments were done using the spontaneously arising nonimmunogenic metastatic murine breast 4T1 carcinoma in normal and STAT6 knockout BALB/c mice.

RESULTS

4T1 is nonimmunogenic in normal mice, and established subcutaneous tumors are resistant to immunotherapy with cyclophosphamide (Cy) plus IL-12. However, in STAT6 knockout mice, 4T1 becomes immunogenic, and established 4T1 tumors are eradicated by Cy plus IL-12. Adoptive transfer of spleen cells from normal mice into STAT6 knockout mice before tumor inoculation reduces both the immunogenicity and response to Cy plus IL-12 immunotherapy of 4T1 in the recipient mice.

CONCLUSIONS

Cy plus IL-12 immunotherapy can eradicate nonimmunogenic tumors as long as a preexisting immunity is established in the tumor-bearing host. Furthermore, the STAT6 pathway is likely involved in the suppression of the development of host antitumor immunity.

Tumor immunity: a balancing act between T cell activation, macrophage activation and tumor-induced immune suppression

The mouse 4T1 mammary carcinoma is a BALB/c-derived tumor that spontaneously metastasizes and induces immune suppression. Although >95% of wild type BALB/c mice die from metastatic 4T1 tumor even if the primary mammary tumor is surgically removed, >65% of BALB/c mice with a deleted Signal Transducer Activator of Transcription 6 (STAT6) gene survive post-surgery. STAT6-deficiency also confers enhanced immunity against spontaneously developing breast cancer since NeuT+/- mice that are STAT6-deficient develop mammary tumors later and survive longer than NeuT+/- mice that are STAT6-competent. Rejection of metastastic disease and survival of STAT6-deficient mice after removal of primary tumor involve three mechanisms: (1) The generation of M1 type macrophages that produce nitric oxide and are tumoricidal; (2) A decrease to normal in the elevated levels of myeloid suppressor cells that accumulate during primary tumor growth; and (3) CD8+ tumor-specific T lymphocytes. STAT6-deficient, but not wild type BALB/c, mice generate nitric oxide producing macrophages because they lack the STAT6 transcription factor which is necessary for signaling through the type 2 IL-4Ralpha complex, and which induces the production of arginase instead of nitric oxide.

Δ-9-Tetrahydrocannabinol Enhances Breast Cancer Growth and Metastasis by Suppression of the Antitumor Immune Response

In the current study, we tested the central hypothesis that exposure to Delta-9-tetrahydrocannabinol (Delta9-THC), the major psychoactive component in marijuana, can lead to enhanced growth of tumors that express low to undetectable levels of cannabinoid receptors by specifically suppressing the antitumor immune response. We demonstrated that the human breast cancer cell lines MCF-7 and MDA-MB-231 and the mouse mammary carcinoma 4T1 express low to undetectable levels of cannabinoid receptors, CB1 and CB2, and that these cells are resistant to Delta9-THC-induced cytotoxicity. Furthermore, exposure of mice to Delta9-THC led to significantly elevated 4T1 tumor growth and metastasis due to inhibition of the specific antitumor immune response in vivo. The suppression of the antitumor immune response was mediated primarily through CB2 as opposed to CB1. Furthermore, exposure to Delta9-THC led to increased production of IL-4 and IL-10, suggesting that Delta9-THC exposure may specifically suppress the cell-mediated Th1 response by enhancing Th2-associated cytokines. This possibility was further supported by microarray data demonstrating the up-regulation of a number of Th2-related genes and the down-regulation of a number of Th1-related genes following exposure to Delta9-THC. Finally, injection of anti-IL-4 and anti-IL-10 mAbs led to a partial reversal of the Delta9-THC-induced suppression of the immune response to 4T1. Such findings suggest that marijuana exposure either recreationally or medicinally may increase the susceptibility to and/or incidence of breast cancer as well as other cancers that do not express cannabinoid receptors and are resistant to Delta9-THC-induced apoptosis.

Reduction of myeloid-derived suppressor cells and induction of M1 macrophages facilitate the rejection of established metastatic disease

More than 60% of STAT6(-/-) mice immunologically reject spontaneous metastatic mammary carcinoma and survive indefinitely if their primary tumors are removed, whereas 95% of STAT6-competent BALB/c mice succumb to metastatic disease. BALB/c and STAT6-deficient mice with primary tumors have elevated levels of Gr1(+)CD11b(+) myeloid suppressor cells (MSCs), which inhibit T cell activation. After removal of primary tumor, MSC levels revert to baseline in STAT6-deficient mice, but remain elevated in BALB/c mice. The decrease is IFN-gamma dependent, as is the reduction in metastatic disease. Neither BALB/c nor STAT6-deficient MSCs produce inducible NO synthase; however, both produce arginase and reactive oxygen species. STAT6-deficient mice produce M1 macrophages, which contain high levels of NO and are tumoricidal, whereas BALB/c mice produce M2 macrophages, which make arginase and are not tumoricidal. Immunity in STAT6-deficient mice requires the activation of NO-producing M1 macrophages that are tumoricidal, the reduction in MSC levels to baseline after surgical removal of primary tumor, and the activation of tumor-specific T cells. These mechanisms occur in STAT6(-/-) mice because STAT6 deficiency prevents signaling through the type 2 IL-4Ralpha, thereby blocking the production of arginase and promoting the synthesis of NO.

Prolonged Culture of Vaccine-Primed Lymphocytes Results in Decreased Antitumor Killing and Change in Cytokine Secretion

Adoptive transfer of effector T cells has been used successfully to eliminate metastases in animal models. Because antitumor activity depends on the number of effector cells transferred, some human trials have used in vitro-repetitive activation and expansion techniques to increase cell number. We hypothesized that the prolonged culture period might contribute to the lack of human trial success by decreasing the potency of the effector T cells. Lymph nodes draining a progressively growing murine melanoma tumor transduced to secrete granulocyte/macrophage colony-stimulating factor were harvested and activated in vitro with anti-CD3 monoclonal antibody followed by expansion in IL-2 for a total of 5 days in culture. Some lymphocytes were reactivated and further expanded for a total of 9 days in culture. In vivo activity of the effector T cells was measured by the reduction in lung metastases and is shown to be dose dependent. The prolonged culture period resulted in nearly 3-fold more T cells but at least 8-fold less antitumor activity. This was accompanied by decreased secretion of the proinflammatory cytokine, IFN-gamma, and increased secretion of the anti-inflammatory cytokine, IL-10. Thus, although increased cell number is important to maximize the effectiveness of adoptive immunotherapy, some culture conditions may actually be counterproductive in that decreases in cell potency can outweigh the benefits of increased cell numbers. The T-cell cytokine secretion pattern predicts decreased effector cell function and may explain the decreased antitumor effect.

Type 1 and type 2 tumor infiltrating effector cell subpopulations in progressive breast cancer

Effector T cells fall into two subpopulations based on cytokine-secretion. Type 1 cells secrete IFN-gamma, whereas type 2 cells secrete IL-4, IL-10, and GM-CSF. NKT cells represent a third subpopulation that secretes similar cytokines and have been associated with immunoregulation. Using the TS/A adenocarcinoma, we assessed the phenotype and kinetics of tumor-infiltrating lymphocytes (TIL) in mice challenged subcutaneously in the mammary region. Flow cytometric analysis shows that T cells do not infiltrate the primary tumor site until days 7-14 following tumor challenge. Both CD4 and CD8 TILs were predominantly CD44(High) and expressed CD25, CD69, and CD95 cell surface activation markers. Activated CD4/CD44(High) TIL numbers reached peak levels at day 21 that precipitously decreased by day 28 whereas corresponding CD8 cell numbers progressively increased, however, at lower levels and with later kinetics. Intracellular cytokine staining showed that greater numbers of IL-4-producing Th2 cells were elicited and with earlier kinetics than that of IFN-gamma-producing Th1 cells. T cells co-expressing DX5 (CD3(+)/DX5(+)) emerged (>21 days), suggesting a recruitment of NK-like T cells at later stages of tumor progression. Moreover, tumors selectively up-regulated TGF-beta, MIF, and IP-10 gene expression at times as early as day 4, with peak levels at day 7 in vivo. Such gene expression remained elevated and correlated with a continued progression in tumor growth suggesting that preferential effector cell recruitment and production of select factors during different stages of tumor maturation may aid in regulating effective endogenous antitumor responses in progressive breast cancer.

Intralesional Injection of Adenovirus Encoding CC Chemokine Ligand 16 Inhibits Mammary Tumor Growth and Prevents Metastatic-Induced Death after Surgical Removal of the Treated Primary Tumor

The CC chemokine ligand (CCL)16 exerts chemotactic activity on human monocytes and lymphocytes. Although no murine homologous has been defined, the TSA mouse adenocarcinoma cells engineered to express human CCL16 are rapidly rejected by syngenic mice. An adenovirus encoding CCL16 (AdCCL16) was generated using a Cre-Lox-based system and was used to determine whether this chemokine might also block pre-existing tumors. Both recombinant and viral CCL16 showed in vitro chemotactic activity for murine CD4(+) and CD8(+) lymphocytes and dendritic cells (DC). AdCCL16, but not the control empty vector, when injected in established nodules significantly delayed tumor growth. Immunohistochemistry revealed accumulation of CD4(+) and CD8(+) T cells and DC in the treated tumors as well as in draining lymph nodes. DC from such lymph nodes stimulated IFN-gamma by a T cell clone specific for the known TSA tumor-associated Ag (TAA), suggesting the tumor origin of these cells. Lymphocytes from the same nodes showed specific CTL activity against TSA tumor cells and their immunodominant TAA peptide. Antitumor activity required CD4, CD8, and IFN-gamma production, as shown using subset-depleted and knockout mice. Despite the robust and rapid immune response triggered by intratumoral injection of AdCCL16, the lesions were not completely rejected; however, the same treatment given before surgical excision of primary lesions prevented metastatic spread and cured 63% of mice bearing the 4T1 mammary adenocarcinoma, which is perhaps the most compelling model of spontaneous metastasis.