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T cell exhaustion is a state of dysfunction that frequently occurs during chronic infections and cancer due to persistent antigen stimulation and inflammation. It is defined by poor effector function, sustained expression of inhibitory receptors, and a transcriptional state distinct from that of functional effector or memory T cells. In this state, cells remain in the local environment but lack effector functions necessary to combat the tumor or infection. In the current study, we developed an in vitro human antigen-specific CD8 T cell exhaustion model to evaluate the ability of immune checkpoint inhibitors to restore functionality to exhausted T cells. Using the fully human, autologous MIMIC (Modular IMmune In vitro Construct) effector CD8 T cell assay as a framework, we assessed the effect of antigen dose, timing, and frequency of repeated antigen stimulation with antiviral HLA Class I-restricted peptides to drive the development of Ag-specific CD8 T cells toward an exhausted state. Epitope-specific CD8 T cell responses were monitored by HLA class I-restricted pentamers and establishment of an exhausted profile was evaluated by increased expression of inhibitory co-stimulatory receptors and decreased intracellular expression of antiviral effector cytokine via flow cytometry relative to functional Ag-specific CD8 T cells from the same donor. Repeated antigen exposure led to decreased production of IFN-γ and TNF-α and increased expression of inhibitory co-stimulation markers on antigen-specific CD8 T cells. After establishment of an exhausted phenotype, treatment with various immune checkpoint inhibitor molecules restored functionality to Ag-specific CD8 T cells upon an additional antigen re-stimulation. Moreover, here using this model we characterized distinct transcriptomic signatures of functional and exhausted MIMIC CD8 T cells. Development of an in vitro human viral antigen-specific CD8 T cell exhaustion model with characteristic features of dysfunctional CD8 T cells as observed in vivo and the ability to restore effector function by treatment with immune checkpoint inhibitors, provides a platform to assess the effectiveness of therapeutic mono-specific or bi-specific “checkpoint blockade” antibody candidates and, in general, the potential to evaluate a myriad of immunotherapeutic approaches for cancer treatment. Citation Format: Roberto Carrio, Margot Cucchetti, Mikielia Devonish, Louis Poisson, Mihaela Babiceanu, Andrew Kettring, Yingchun Liu, Donald Jackson, Evan Gomes, Jeremy Baudhuin, Donald R. Drake, Valeria Fantin, Anthony Byers, Ingrid Sassoon. An in vitro human CD8 T cell exhaustion model for the functional screening of immune checkpoint inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6378.

Cell-mediated immunity is an important defense mechanism against pathogens and developing tumor cells. The thymus is the main lymphoid organ involved in the formation of the cell-mediated immune response by the maturation and differentiation of lymphocytes that travel from the bone marrow, through the lymphatic ducts, to become T lymphocytes. Thymic involution has been associated with aging; however, other factors such as obesity, viral infection and tumor development have been shown to increase the rate of shrinkage of this organ. The heavy infiltration of adipocyte fat cells has been reported in the involuted thymuses of aged mice. In the present study, the possible accumulation of such cells in the thymus during tumorigenesis was examined by immunohistochemistry. A significant number of adipocytes around and infiltrating the thymuses of tumor-bearing mice was observed. Leptin is a pro-inflammatory adipocytokine that enhances thymopoiesis and modulates T cell immune responses. The levels of leptin and adiponectin, another adipocytokine that has anti-inflammatory properties, were examined by western blot analysis. While no changes were observed in the amounts of adiponectin present in the thymuses of the normal and tumor-bearing mice, significantly higher levels of leptin were detected in the thymocytes of the tumor-bearing mice. This correlated with an increase in the expression of certain cytokines, such as interleukin (IL)-2, interferon (IFN)-γ and granulocyte-macrophage colony-stimulating factor (GM-CSF). The co-culture of thymocytes isolated from normal mice with ex vivo isolated adipocytes from tumor-bearing mice yielded similar results. Our findings suggest that the infiltration and accumulation of adipocytes in the thymuses of tumor-bearing mice play an important role in their altered morphology and functions.

The relationship between obesity and breast cancer (BC) has focused on serum factors. However, the mammary gland contains adipose tissue (AT) which may enable the crosstalk between adipocytes and tumor cells contributing to tumor macrophage recruitment. We hypothesize that the breast AT (bAT) is inflamed in obese females and plays a major role in breast cancer development. The effects of this interplay on macrophage chemotaxis were examined in vitro, using co-cultures of mouse macrophages, mammary tumor cells and adipocytes. Macrophages were exposed to the adipocyte and tumor paracrine factors leptin, CCL2 and lauric acid (alone or in combinations). In cell supernatants Luminex identified additional molecules with chemotactic and other pro-tumor functions. Focus on the adipokine leptin, which has been shown to have a central role in breast cancer pathogenesis, indicated it modulates macrophage phenotypes and functions. In vivo experiments demonstrate that mammary tumors from obese mice are larger and that bAT from obese tumor-bearers contains higher numbers of macrophages/CLS and hypertrophic adipocytes than bAT from lean tumor-bearers, thus confirming it is more inflamed. Also, bAT distal from the tumor is more inflamed in obese than in lean mice. Our results reveal that bAT plays a role in breast cancer development in obesity.

Mucin 1 (MUC1) is a polymorphic type 1 transmembrane protein found on the apical surface of normal cells lining the lumen of ducts and glands. Mucins are thought to provide mucosal protection from environmental exposures and carcinogens. An altered form of the MUC1 glycoprotein, which is hypoglycosylated, is expressed in several types of human cancers. In our laboratory, we have found that transfection of a murine mammary tumor cell line with a human secreted isoform of MUC1 rendered these DA-3 cells (DA-3/sec) incapable of growing in intact BALB/c mice. In contrast, implantation of DA-3 cells transfected with the human transmembrane isoform of MUC1 (DA-3/TM), resulted in tumor formation and ultimately death of the animals, similar to the DA-3 parental line. Importantly, inoculation of the DA-3/sec cells in immunodeficient nude mice resulted in tumor formation, indicating that the MUC1/sec molecule's antitumor activity is immunologically controlled. In this review, we summarize the studies we have performed to elucidate possible mechanisms for the immune-mediated antitumor effect of MUC1/sec and/or a unique peptide present in this mucin. Understanding these mechanisms may provide new immunotherapeutic approaches that could be used to target different types of cancer.

Disseminated metastasis accounts for over 90% of breast cancer deaths. Recently, elevated serum levels of a glycoprotein known as chitinase-3 like-protein-1 (CHI3L1) has been correlated with poor prognosis and shorter survival of patients with metastatic breast cancer. In this study, we show that there are increased levels of CHI3L1 in plasma of tumor-bearing mice and that both tumor cells and immune cells express and secrete CHI3L1. However, the biological and physiological functions of CHI3L1 are still unclear. We demonstrate that while CHI3L1 has an inhibitory role in the expression of interferon-gamma (IFN-γ), CHI3L1 up-regulates pro-inflammatory mediators, C-chemokine ligand 2 (CCL2), chemokine CX motif ligand 2 (CXCL2) and matrix metalloproteinase-9 (MMP-9) all of which contribute to tumor growth and metastasis. We found that in vitro inhibition of CHI3L1 by siRNA suppressed the production of CCL2, CXCL2 and MMP-9 by macrophages. In vivo treatment of mammary tumor-bearing mice with chitin (β-(1-4)-poly-N-acetyl D-glucosamine), a TH(1) adjuvant and a ligand for CHI3L1, promoted immune effector functions with increased production of IFN-γ and decreased CCL2, CXCL2 and MMP-9 expression. In vivo administration of chitin to mammary tumor-bearing mice significantly decreased lung metastasis. These studies show that CHI3L1 plays a role in tumor progression and that chitin can inhibit the pleiotropic effects of CHI3L1 giving support to the idea that CHI3L1 is a useful therapeutic target for treatment of breast cancer.

Although much is known concerning the immunobiology of CD8+ T memory cells, the initial events favoring the generation of CD8+ T memory cells remain poorly defined. Using a culture system that yields memory-like CD8+ T cells, we show that 1 day after Ag encounter, Ag-activated T cells developed into memory-like T cells, but this optimally occurred 3 days after Ag encounter. Key phenotypic, functional, and molecular properties that typify central memory T cells were expressed within 48 h when the activated CD8+ T cells were cultured with IL-7 or IL-15 in the absence of Ag or following transfer into normal mice. These data support a model whereby Ag activation of naive CD8+ T cells not only programs effector cell expansion and contraction but the potential to develop into a memory cell which ensues in an Ag-free environment containing IL-7 or IL-15.

UEV proteins are enzymatically inactive variants of the E2 ubiquitin-conjugating enzymes that regulate noncanonical elongation of ubiquitin chains. In Saccharomyces cerevisiae, UEV is part of the RAD6-mediated error-free DNA repair pathway. In mammalian cells, UEV proteins can modulate c-FOS transcription and the G2-M transition of the cell cycle. Here we show that the UEV genes from phylogenetically distant organisms present a remarkable conservation in their exon–intron structure. We also show that the human UEV1 gene is fused with the previously unknown gene Kua. In Caenorhabditis elegans and Drosophila melanogaster, Kua and UEV are in separated loci, and are expressed as independent transcripts and proteins. In humans, Kua and UEV1 are adjacent genes, expressed either as separate transcripts encoding independent Kua and UEV1 proteins, or as a hybrid Kua–UEV transcript, encoding a two-domain protein. Kua proteins represent a novel class of conserved proteins with juxtamembrane histidine-rich motifs. Experiments with epitope-tagged proteins show that UEV1A is a nuclear protein, whereas both Kua and Kua–UEV localize to cytoplasmic structures, indicating that the Kua domain determines the cytoplasmic localization of Kua–UEV. Therefore, the addition of a Kua domain to UEV in the fused Kua–UEV protein confers new biological properties to this regulator of variant polyubiquitination./n/n[Kua cDNAs isolated by RT-PCR and described in this paper have been deposited in the GenBank data library under accession nos. AF1155120 (H. sapiens) and AF152361 (D. melanogaster). Genomic clones containing UEV genes: S. cerevisiae, YGL087c (accession no. Z72609); S. pombe, c338 (accession no. AL023781); P. falciparum, MAL3P2 (accession no. AL034558); A. thaliana, F26F24 (accession no. AC005292); C. elegans, F39B2 (accession no. Z92834); D. melanogaster, AC014908; and H. sapiens, 1185N5 (accession no. AL034423). Accession numbers for Kua cDNAs in GenBank dbEST: M. musculus, AA7853; T. cruzi, AI612534. Other Kua-containing sequences: A. thaliana genomic clones F10M23 (accession no. AL035440), F19K23 (accession no. AC000375), and T20K9 (accession no. AC004786).

SHIP2 is a new member of the inositol polyphosphate 5-phosphatase family showing homology to SHIP1. The structure of both enzymes is characterized by the presence of a 5' SH2 domain, a central catalytic domain, and a 3' proline-rich region. Recent results suggest that SHIP2 and SHIP1 act downstream of various receptors by removing a phosphate from the 5' position of the phosphatidylinositol 3'-kinase phosphatidylinositol 3,4, 5-triphosphate product and of inositol 1,3,4,5-tetrakisphosphate. Human SHIP2 is highly expressed in adult heart, skeletal muscle, and placenta, whereas SHIP1 expression is limited to the hematopoietic system. We report here the molecular analysis of the mouse SHIP2 cDNA and the corresponding protein, the structure of the gene, and the identification of its promoter. SHIP2 mRNA expression was analyzed in embryonic and adult mouse tissues by reverse transcription-polymerase chain reaction and in situ hybridization. In embryonic day 15.5 mice, SHIP2 was strongly expressed in the liver, specific regions of the central nervous system, the thymus, the lung, and the cartilage perichondrium. In adult mice, SHIP2 mRNA was markedly present in the brain and the thymus and at different stages of spermatozoa maturation in the seminiferous tubules. The subtle differences in the protein structure of SHIP2 and SHIP1 as well as their different patterns of expression are discussed.

We have identified and characterized Diva, which is a novel regulator of apoptosis. Sequence analysis revealed that Diva is a member of the Bcl-2 family of proteins containing Bcl-2 homology domain 1, 2, 3, and 4 (BH1, BH2, BH3, and BH4) regions and a carboxyl-terminal hydrophobic domain. The expression of Diva mRNA was detected in multiple embryonic tissues but was restricted to the ovary and testis in adult mice. The expression of Diva promoted the death of 293T, Ramsey, and T47D cells as well as that of primary sensory neurons, indicating that Diva is a proapoptotic protein. Significantly, Diva lacks critical residues in the conserved BH3 region that mediate the interaction between BH3-containing proapoptotic Bcl-2 homologues and their prosurvival binding partners. Consistent with this, Diva did not bind to cellular Bcl-2 family members including Bcl-2, Bcl-XL, Bcl-w, Mcl-1, and A1/Bfl-1. Furthermore, mutants of Diva lacking the BH3 region fully retained their proapoptotic activity, confirming that Diva promotes apoptosis in a BH3-independent manner. Significantly, Diva interacted with a viral Bcl-2 homologue (vBcl-2) encoded by the Kaposi's sarcoma-associated herpesvirus. Consistent with these associations, apoptosis induced by Diva was inhibited by vBcl-2 but not by Bcl-XL. Importantly, Diva interacted with Apaf-1, an adapter molecule that activates caspase-9, a central death protease of the apoptotic pathway. The expression of Diva inhibited the binding of Bcl-XL to Apaf-1, as determined by immunoprecipitation assays. Thus, Diva represents a novel type of proapoptotic Bcl-2 homologue that promotes apoptosis independently of the BH3 region through direct binding to Apaf-1, thus preventing Bcl-XL from binding to the caspase-9 regulator Apaf-1.

The thymus is a central lymphoid organ critical for the development and maintenance of an effective peripheral T-cell repertoire. Most important, it provides a specialized environment for the selection of rearranged clones that will function appropriately in the adaptive immune response. Thymic involution has been observed in several model systems; including graft-versus-host disease, aging, viral infection, and tumor development, however, the precise mechanisms involved in this phenomenon remain poorly defined. Here, we review some of our results related to the studies of the cell-mediated immunity in a mammary tumor model; more specifically, those related to the tumor-induced impaired T-cell development and thymic involution. Collectively, the understanding of the mechanisms and pathways associated with the tumor-induced thymic involution is essential for the development of innovative and safe therapies to fight against the immune suppression caused by the tumor development.

Semaphorins, a large family of molecules involved in the axonal guidance and development of the nervous system, have been recently shown to have both angiogenic and anti-angiogenic properties. Specifically, semaphorin 7A (SEMA7A) has been reported to have a chemotactic activity in neurogenesis, and to be an immune modulator via it binding to α1β1integrins. Additionally, SEMA7A has been shown to promote chemotaxis of monocytes, inducing them to produce proinflammatory mediators. In this study we explored the role of SEMA7A in the tumoral context. We show that SEMA7A is highly expressed by DA-3 murine mammary tumor cells in comparison to normal mammary cells (EpH4), and that peritoneal macrophages from mammary tumor-bearing mice also express SEMA7A at higher levels compared to peritoneal macrophages derived from normal control mice. We also show that murine macrophages treated with recombinant murine SEMA7A significantly increased their expression of proangiogenic molecules, such as CXCL2/MIP-2. Gene silencing of SEMA7A in peritoneal elicited macrophages from DA-3 tumor-bearing mice resulted in decreased CXCL2 expression. Mice implanted with SEMA7A silenced tumor cells showed decreased angiogenesis in the tumors compared to the wild type tumors. Furthermore, peritoneal elicited macrophages from mice bearing SEMA7A-silenced tumors produce significantly (p< 0.01) lower levels of angiogenic proteins, such as MIP-2, CXCL1 and MMP-9, compared to macrophages from control DA-3 mammary tumors. We postulate that SEMA7A derived from mammary carcinomas may serve as a monocyte chemoattractant and skew monocytes into a pro-tumorigenic phenotype. A putative relationship between tumor-derived SEMA7A and monocytes could prove valuable in establishing new research avenues towards unraveling important tumor-host immune interactions in breast cancer patients.

The bcl-2 protooncogene has been shown to provide a survival signal to self-reactive B cells, but it fails to override their developmental arrest after encounter with antigen. Furthermore, constitutive expression of bcl-2 in B cells does not promote the development of autoimmune disease in most strains of mice, indicating that signals other than those conferred by bcl-2 are required for long-term survival and differentiation of self-reactive B cells in vivo. To further examine the factors that are required for the pathogenesis of autoimmune disease, we have assessed the effect of bcl-2 overexpression on the development of host-versus-graft disease, a self-limited model of systemic autoimmune disease. In this model, injection of spleen cells from (C57BL/6 x BALB/c)F1 hybrid mice into BALB/c newborn parental mice induces immunological tolerance to donor tissues and activation of autoreactive F1 donor B cells through interactions provided by allogeneic host CD4+ T cells. BALB/c newborns injected with spleen cells from (C57BL/6 x BALB/c)F1 mice expressing a bcl-2 transgene in B cells developed high levels of anti-single-stranded DNA and a wide range of pathogenic autoantibodies that were not or barely detectable in mice injected with nontransgenic spleen cells. In mice injected with transgenic B cells, the levels of pathogenic autoantibodies remained high during the course of the study and were associated with long-term persistence of donor B cells, development of a severe autoimmune disease, and accelerated mortality. These results demonstrate that bcl-2 can provide survival signals for the maintenance and differentiation of autoreactive B cells, and suggest that both increased B cell survival and T cell help play critical roles in the development of certain forms of systemic autoimmune disease.

Elevated levels of chitinase-3-like-1 (CHI3L1) are associated with poor prognosis, shorter recurrence-free intervals and low survival in breast cancer patients. Breast cancer often metastasizes to the lung. We hypothesized that molecules expressed in the pre-metastatic lung microenvironment could support the newly immigrant tumor cells by providing growth and angiogenic factors. Macrophages are known to play an important role in tumor growth by releasing pro-angiogenic molecules. Using mouse mammary tumor models, we have previously shown that during neoplastic progression both the mammary tumor cells and splenic macrophages from tumor-bearing mice express higher levels of CHI3L1 compared to normal control mice. However, the role of CHI3L1 in inducing angiogenesis by macrophages at the pulmonary microenvironment to support newly arriving breast cancer cells is not yet known. In this study, we determined the expression of CHI3L1 in bronchoalveolar lavage macrophages and interstitial macrophages in regulating angiogenesis that could support the growth of newly immigrant mammary tumor cells into the lung. Here we show that in vitro treatment of pulmonary macrophages with recombinant murine CHI3L1 resulted in enhanced expression of pro-angiogenic molecules including CCL2, CXCL2 and MMP-9. We and others have previously shown that inhibition of CHI3L1 decreases the production of angiogenic molecules. In this study, we explored if in vivo administration of chitin microparticles has an effect on the expression of CHI3L1 and pro-angiogenic molecules in the lungs of mammary tumor-bearing mice. We show that treatment with chitin microparticles decreases the expression of CHI3L1 and pro-angiogenic molecules in the metastatic lung. These studies suggest that targeting CHI3L1 may serve as a potential therapeutic agent to inhibit angiogenesis and thus possibly tumor growth and metastasis.

Myeloid-derived suppressor cells (MDSC) have been shown to play a critical role in tumor-induced immunosuppression, in many mouse and human cancers. The aim of this study was to show that MDSC accumulation is tumor burden-dependent, and to investigate the role of the tumor-derived urokinase plasminogen activator (uPA) and its receptor (uPAR) on MDSC recruitment.Levels of MDSC were assessed in tumor-bearers, and the ability to recruit MDSC by uPA was investigated in normal, tumor-bearers, uPAR(-/-), and CD11b(-/-) mice. uPAR expression in MDSC was also explored.MDSC accumulate to dramatic levels in tumor-bearers, and tumor-derived factors such as uPA also increase to great levels in circulation. MDSC can be recruited by uPA, and uPAR but not CD11b are required for such recruitment.MDSC accumulation is tumor burden-dependent, and tumor-derived factors such as uPA and its receptor uPAR play a role in their recruitment.

Breast cancer is the second leading cause of death by cancer in women in the United States. The occurrence of high numbers of macrophages in the tumor stroma has been associated with tumor progression and poor prognosis in breast and other solid malignancies. However, macrophage numbers in tumors have not been validated as a prognostic factor in clinical practice. The present analysis was designed as a pilot study aimed at determining whether the presence of CD68+ macrophages is an independent prognostic factor in small T1 estrogen receptor (ER)+ breast cancers across three different ethnic groups, i.e. African-American, Latina and Caucasian women. A retrospective pilot analysis of 30 T1 breast cancer cases encompassing these three ethnic groups was carried out. African-American and Latina women present with less incidence but more aggressive breast cancer disease and, therefore, proportionally higher death rates. Using immuno-histochemistry, we sought to identify whether there was any association between the presence and density of CD68+ macrophages and standard prognostic markers with overall survival in these groups. Our data revealed that overall survival did not differ significantly for the occurrence or density of CD68+ macrophages in T1 ER+ tumors. There were also no significant differences in overall survival for the occurrence of CD68+ macrophages across ethnicities, although macrophage numbers were significantly higher in tumors from African-American and Latina than in Caucasian patients. Importantly, but not surprisingly, the absence of the progesterone receptor was associated very strongly with decreased overall survival. This pilot project shows that CD68+ macrophages are not pivotal in determining tumor prognosis in early T1 breast cancers. New studies are presently being conducted to assess the value of different macrophage markers and macrophage activation profiles as prognostic factors in breast cancers of different clinical stages, using a larger number of patients among these three different ethnicities.

We have previously shown that peritoneal macrophages from mice bearing advanced D1-DMBA3 mammary tumors are impaired in their inflammatory functions but are not alternatively activated either and are less differentiated than the ones from normal mice. However, little is known about whether similar defects exist in their precursor stages as blood monocytes. We examined if blood monocytes from mammary tumor-bearing mice are already altered in their activation profiles before becoming macrophages and whether they correspond to inflammatory or resident monocyte subtypes. Much effort is currently devoted to reversing macrophage adverse traits in tumor hosts; as these cells reside within tissues, access is limited. Blood monocytes could be better targeted and manipulated by less invasive means. In the present study, mononuclear cells were isolated from whole blood of D1-DMBA-3 mammary tumor-bearing and normal BALB/c mice and CD115(+) monocytes were analyzed. Our results show that there is an increase in circulating monocytes in tumor hosts; these monocytes exhibit a reduced expression of several myeloid differentiation markers such as CD115, F4/80, CD68 and CD11b. Moreover, downregulation of MHC II, CD62L and the proangiogenic marker Tie-2 are observed in these cells, whereas Gr-1 and Ly6C are upregulated. Furthermore, gene microarray analysis performed for the first time in blood monocytes from tumor hosts indicates that they express a mixture of pro-inflammatory and anti-inflammatory cytokines and chemokines. Interestingly, CCR2 and CX3CR1, which are crucial in monocyte definition as inflammatory or resident, respectively, are both upregulated. Importantly, complement proteins are enhanced whereas nitric oxide production is decreased and there is no measurable arginase activity detected in these cells. Collectively, our study represents the first comprehensive analysis of blood monocytes from tumor-bearing mice; we conclude that these cells are neither completely inflammatory nor suppressive and are less differentiated, similar to the macrophages they later become.

The thymus is a central lymphoid organ in which T lymphocytes undergo differentiation and maturation without the need for antigenic stimulation. Apoptosis (programmed cell death), plays a critical role in shaping the T cell repertoire, deleting unproductive as well as potentially autoreactive T cells. Thymic atrophy has been observed in several model systems, including aging, graft-vs-host-disease and tumor development. However, the mechanisms involved in this phenomenon remain to be completely elucidated. We have previously shown that the progressive growth of D1-DMBA-3 mammary tumor leads to extreme thymic atrophy in the host. This thymic involution is associated with an early block in T cell maturation at the triple negative stage of differentiation. In the present study we have used our murine mammary tumor model to further analyze the specific T cell subpopulations present in the thymus of tumor-bearing animals as well as to characterize the alterations of the apoptotic process present during the impaired thymopoiesis associated to this thymic involution. Flow cytometric analysis revealed a moderate increase in the percentages of single positive CD4+ and CD8+ cells within the CD3 negative population in the thymuses of tumor-bearing mice. Moreover, we observed a prolonged increase in apoptosis among thymocytes from tumor-bearing mice compared with thymocytes from normal mice during tumor development. Lastly, we found a major decrease of Bcl-XL and A1, two crucial anti-apoptotic Bcl-2 family members that are developmentally regulated in T cells. Together, our data suggest that the severe thymic involution seen in mammary tumor bearers is due to an arrest in at least two steps of T cell differentiation and a down-regulation of important molecules that control programmed cell death.

During mammary tumorigenesis, there is a profound thymic involution associated with severe depletion of the most abundant subset of thymocytes, CD4(+)CD8(+) immature cells, and an early arrest in at least two steps of T cell differentiation. Thymic atrophy that is normally related with aging has been observed in other model systems, including graft-vs-host disease (GVHD) and tumor development. However, the mechanisms involved in this phenomenon remain to be elucidated. Vascular endothelial growth factor (VEGF) has been associated with thymic involution, when expressed at high levels systemically. In thymuses of D1-DMBA-3 tumor-bearing mice, this growth factor is diminished relative to the level of normal thymuses. Interestingly, the expression of hepatocyte growth factor (HGF), which has been associated with proliferation, cell survival, angiogenesis and B-cell differentiation, is profoundly down-regulated in thymuses of tumor bearers. In parallel, IL-7 and IL-15 mRNA, crucial cytokines involved in thymocytes development and cellular homeostasis, respectively, are also down-regulated in the thymuses of tumor hosts as compared to those of normal mice. Injection of HGF into mice implanted with mammary tumors resulted in normalization of thymic volume and levels of VEGF, IL-7 and IL-15. While, injections of IL-7 partially restored the thymic involution observed in the thymuses of tumor-bearing mice, injection of IL-15 did not have any significant effects. Our data suggest that the downregulation of HGF and IL-7 may play an important role in the thymic involution observed in tumor-bearing hosts.

Adoptive T-cell therapy with CD8+ CTLs is often characterized by poor persistence of the transferred T cells and limited effector responses. Improved persistence and therapeutic efficacy have been noted when antigen-activated CD8+ T cells express properties of memory cells. The current study was undertaken to more precisely characterize the development of memory-like CD8+ T cells from short-term CTLs in vitro and upon transfer in vivo, including their antitumor activity. Ovalbumin (OVA)–specific OT-I CTLs acquired phenotypic and functional properties of memory cells 2 to 3 days later either by lowering the concentration of antigen to a level that does not support primary responses and providing a survival signal through transgenic Bcl-2 in vitro or simply by transferring early day 3 CTLs to antigen-free lymphoid-replete mice. In lymphoid-replete mice, established OVA-expressing E.G7 tumor was rejected by short-term CTLs that simultaneously acquired memory-like properties in secondary lymphoid tissues, where tumor antigen level remained low. Collectively, these data indicate that CTLs readily converted to memory-like cells upon lowering antigen to a concentration that selectively supports memory responses and suggest that such conversion predicts successful adoptive immunotherapy. [Cancer Res 2008;68(8):2984–92]

IL-7 and IL-15 are important cytokines for CD8 memory T cells. However, the extent that IL-7 is essential for CD8 T cell memory remains unclear because blocking IL-7 in vivo results in near complete inhibition of T cell development with the few mature T cells exhibiting functional abnormalities. To bypass this complication, CD8 memory development was examined utilizing a mouse model where transgenic IL-7Ralpha was selectively expressed in the thymus of IL-7Ralpha(-/-) mice. T cell development was corrected but the resulting peripheral T cells were essentially IL-7 non-responsive. Activation of IL-7R-defective OT-I CD8(+) T cells with OVA(257-264) and IL-2 readily yielded CTL. Upon further culture with IL-15, these CTL expressed phenotypic and functional properties of central memory-like cells. Thus, IL-7R-defective CD8(+) T cells do not exhibit intrinsic defects in effector or memory development. When IL-7R-defective OT-I CTL were adoptively transferred into normal or IL-15(-/-) recipient mice in a non-inflammatory setting, they converted into memory-like cells, but did not persist, which was even more striking in IL-15(-/-) recipients. This poor persistence was rescued after expression of transgenic Bcl-2 in IL-7R-defective OT-I T cells. Collectively, these data indicate that IL-7 is non-redundantly required for the survival of CD8 memory T cells.

IL-21 costimulates B cell proliferation and cooperatively with IL-4 promotes T cell-dependent Ab responses. Somewhat paradoxically, IL-21 also induces apoptosis of B cells. The present study was undertaken to more precisely define the expression of the IL-21R, using a novel mAb, and the circumstances by which IL-21 promotes B cell growth vs death. The IL-21R was first detected during T and B cell development, such that this receptor is expressed by all mature lymphocytes. The IL-21R was further up-regulated after B and T activation, with the highest expression by activated B cells. Functional studies demonstrated that IL-21 substantially inhibited proliferation and induced Bim-dependent apoptosis for LPS or CpG DNA-activated B cells. In contrast, IL-21 induced both costimulation and apoptosis for anti-CD40-stimulated B cells, whereas IL-21 primarily costimulated B cells activated by anti-IgM or anti-IgM plus anti-CD40. Upon blocking apoptosis using C57BL/6 Bim-deficient or Bcl-2 transgenic B cells, IL-21 readily costimulated responses to anti-CD40 while proliferation to LPS was still inhibited. Engagement of CD40 or the BCR plus CD40 prevented the inhibitory effect by IL-21 for LPS-activated B cells. Collectively, these data indicate that there are three separable outcomes for IL-21-stimulated B cells: apoptosis, growth arrest, or costimulation. We favor a model in which IL-21 promotes B cell maturation during a productive T cell-dependent B cell response, while favoring growth arrest and apoptosis for nonspecifically or inappropriately activated B cells.

Ced-4 and Apaf-1 belong to a major class of apoptosis regulators that contain caspase-recruitment (CARD) and nucleotide-binding oligomerization domains. Nod1, a protein with an NH2-terminal CARD-linked to a nucleotide-binding domain and a COOH-terminal segment with multiple leucine-rich repeats, was identified. Nod-1 was found to bind to multiple caspases with long prodomains, but specifically activated caspase-9 and promoted caspase-9-induced apoptosis. As reported for Apaf-1, Nod1 required both the CARD and P-loop for function. Unlike Apaf-1, Nod1 induced activation of nuclear factor-kappa-B (NF-kappaB) and bound RICK, a CARD-containing kinase that also induces NF-kappaB activation. Nod1 mutants inhibited NF-kappaB activity induced by RICK, but not that resulting from tumor necrosis factor-alpha stimulation. Thus, Nod1 is a leucine-rich repeat-containing Apaf-1-like molecule that can regulate both apoptosis and NF-kappaB activation pathways.

We have identified and characterized CIPER, a novel protein containing a caspase recruitment domain (CARD) in its N terminus and a C-terminal region rich in serine and threonine residues. The CARD of CIPER showed striking similarity to E10, a product of the equine herpesvirus-2. CIPER formed homodimers via its CARD and interacted with viral E10 but not with several apoptosis regulators containing CARDs including ARC, RAIDD, RICK, caspase-2, caspase-9, or Apaf-1. Expression of CIPER induced NF-kappaB activation, which was inhibited by dominant-negative NIK and a nonphosphorylable IkappaB-alpha mutant but not by dominant-negative RIP. Mutational analysis revealed that the N-terminal region of CIPER containing the CARD was sufficient and necessary for NF-kappaB-inducing activity. Point mutations in highly conserved residues in the CARD of CIPER disrupted the ability of CIPER to activate NF-kappaB and to form homodimers, indicating that the CARD is essential for NF-kappaB activation and dimerization. We propose that CIPER acts in a NIK-dependent pathway of NF-kappaB activation.

We have identified and characterized Mtd, a novel regulator of apoptosis. Sequence analysis revealed that Mtd is a member of the Bcl-2 family of proteins containing conserved BH1, BH2, BH3, and BH4 regions and a carboxyl-terminal hydrophobic domain. In adult tissues, Mtd mRNA was predominantly detected in the brain, liver, and lymphoid tissues, while in the embryo Mtd mRNA was detected in the liver, thymus, lung, and intestinal epithelium. Expression of Mtd promoted the death of primary sensory neurons, 293T cells and HeLa cells, indicating that Mtd is a proapoptotic protein. Unlike all other known death agonists of the Bcl-2 family, Mtd did not bind significantly to the survival-promoting proteins Bcl-2 or Bcl-XL. Furthermore, apoptosis induced by Mtd was not inhibited by Bcl-2 or Bcl-XL. A Mtd mutant with glutamine substitutions of highly conserved amino acids in the BH3 domain retained its ability to promote apoptosis, further indicating that Mtd does not promote apoptosis by heterodimerizing with Bcl-2 or Bcl-XL. Mtd-induced apoptosis was not blocked by broad range synthetic caspase inhibitors z-VAD-fmk or a viral protein CrmA. Mtd is the first example of a naturally occurring Bcl-2 family member that can activate apoptosis independently of heterodimerization with survival-promoting Bcl-2 and Bcl-XL.

The thymus is a central lymphoid organ in which T lymphocytes undergo differentiation and maturation without the need for antigenic stimulation. Apoptosis (programmed cell death), plays a critical role in shaping the T cell repertoire, deleting unproductive as well as potentially autoreactive T cells. Thymic atrophy has been observed in several model systems, including aging, graft-vs-host-disease and tumor development. However, the mechanisms involved in this phenomenon remain to be completely elucidated. We have previously shown that the progressive growth of D1-DMBA-3 mammary tumor leads to extreme thymic atrophy in the host. This thymic involution is associated with an early block in T cell maturation at the triple negative stage of differentiation. In the present study we have used our murine mammary tumor model to further analyze the specific T cell subpopulations present in the thymus of tumor-bearing animals as well as to characterize the alterations of the apoptotic process present during the impaired thymopoiesis associated to this thymic involution. Flow cytometric analysis revealed a moderate increase in the percentages of single positive CD4+ and CD8+ cells within the CD3 negative population in the thymuses of tumor-bearing mice. Moreover, we observed a prolonged increase in apoptosis among thymocytes from tumor-bearing mice compared with thymocytes from normal mice during tumor development. Lastly, we found a major decrease of Bcl-XL and A1, two crucial anti-apoptotic Bcl-2 family members that are developmentally regulated in T cells. Together, our data suggest that the severe thymic involution seen in mammary tumor bearers is due to an arrest in at least two steps of T cell differentiation and a down-regulation of important molecules that control programmed cell death.

Metastasis of a primary tumor to distant organs is the principal cause of mortality in patients with breast cancer. Recently, it was reported that asthmatic patients have a greater propensity to develop distant metastasis to the lung. Using a ragweed pulmonary inflammation model, we found that asthmatic mice implanted with 4T1 mammary tumors have a 5-fold increase in formation of metastatic foci in their lungs compared to non-asthmatic 4T1 mammary tumor-bearing mice. Further, asthmatic tumor-bearing mice showed accelerated tumor growth and shorter disease-free survival. We have previously reported that Chitinase-3 like-1 protein (CHI3L1) expression is increased in mammary tumor-bearing mice and that it induces production of prometastatic mediators, CCL2, CXCL2 and MMP-9 by macrophages. Asthmatic patients have been reported to exhibit elevated levels of CHI3L1 in their lungs and circulation while in breast cancer patients these levels are further elevated. We found that the levels of CHI3L1 are higher in circulation and lungs of asthmatic mammary tumor-bearers compared to mice with either asthma or tumor alone. It is unknown if exposure to high levels of CHI3L1 previous to tumorigenesis accelerates metastasis. We hypothesize that CHI3L1-induced pulmonary inflammation generates the proper environment for recruiting circulating breast cancer cells as well as proinflammatory leukocytes (M2 macrophages and myeloid derived suppressors), resulting in increased rate of metastasis to the lung. Treatment of 4T1 asthmatic mammary tumor-bearing mice with chitin microparticles, the ligand of CHI3L1, resulted in decreased levels of metastasis to the lung. These studies provide an understanding of the role of CHI3L1 and existing inflammation in accelerating metastasis, the major cause of death in breast cancer patients. Citation Format: Stephania Libreros, Ramon Garcia-Areas, Roberto Carrio, Vijaya Iragavarapu-Charyulu. Pulmonary inflammation associated with Chitinase-3-like-1 protein (CHI3L1) expression accelerates breast cancer metastasis to the lung. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2710. doi:10.1158/1538-7445.AM2013-2710

The thymus is a central lymphoid organ critical for the development and maintenance of an effective peripheral T cell repertoire. Most important, it provides a specialized environment for the selection of rearranged clones that will function appropriately in the adaptive immune response. T cell maturation progresses through well-defined stages in which proliferation, differentiation, and apoptosis are central to the selection of a functional TCR repertoire. During mammary tumorigenesis, there is a profound thymus involution associated with a severe depletion of the most abundant subset of thymocytes, CD4+CD8+ double positive (DP) immature cells. Thymic involution has been observed in several model systems; including graft-vs-host disease, aging, and tumor development, however, the precise mechanisms involved in this phenomenon remain poorly defined. Previous results from our laboratory have reported that the severe thymic atrophy and impaired T cell development seen in mammary tumor bearers are associated with a profound decrease in thymus size accompanied by a disrupture of the normal thymic architecture, an arrest in at least two steps of T cell differentiation, and an increase in thymic apoptosis in tumor-bearers. In our studies we have used the murine D1-DMBA-3 mammary tumor model to elucidate the exact mechanisms associated to the tumor-induced impaired T cell development and thymic involution. We have found that the disruption in the thymic architecture of tumor bearers appears to be related to a downregulated expression of hepatocyte growth factor in the medullar zone of the thymus. Moreover, the progressive increase of apoptosis in thymocytes during the tumor development is associated to a downregulation of Bcl-xL and A1, two important molecules that control programmed cell death. Additionally, the impaired T cell development observed during the tumor-induced thymic involution is associated to a profound decrease of IL-7 and IL-15, two crucial cytokines involved in T cell development; a downregulation in the expression of most of the Jak/Stat signaling proteins; and an increased expression of several suppressor of cytokine signaling (SOCS) members. Our data provides the bases for understanding the mechanisms associated to the impaired T cell development and thymic involution present in the thymuses of tumor bearers. Citation Format: Roberto Carrio-Jardines, Vijaya Iragavarapu-Charyulu, Stephania Libreros, Ramón A. García-Areas, Marta Torroella-Kouri, Diana M. Lopez. Mechanisms involved in the tumor-induced thymic involution. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 448. doi:10.1158/1538-7445.AM2013-448

Breast cancer is the second leading cause of death by cancer in women in the United States. The occurrence of high numbers of macrophages in the tumor stroma has been associated with tumor progression and poor prognosis in breast and other solid malignances. However, macrophage numbers in tumors have not been validated as a prognostic factor in clinical practice. The present analysis was designed as a pilot study aimed at determining whether the presence of CD68+ macrophages is an independent prognostic factor in small T1 ER+ breast cancers across three different ethnic groups, i.e. African American, Latinas and Caucasian women. A retrospective pilot analysis of 30 T1 breast cancers cases encompassing these three ethnic groups was carried out. African American and Latina women present with less incidence but more aggressive breast cancer disease and therefore proportionally higher death rates. Using immunohistochemistry, we sought to find out whether there was any association between the presence and density of CD68+ macrophages and standard prognostic markers with overall survival in these groups. Our data showed that overall survival did not differ significantly for the occurrence or density of CD68+ macrophages in T1 ER+ tumors. There were also no significant differences in overall survival for the occurrence of CD68+ macrophages across ethnicities, although macrophage numbers were significantly higher in tumors from African American and Latinas than in Caucasian patients. Interestingly but not surprisingly, the absence of PR associated very strongly with decreased overall survival. This pilot project shows that CD68+ macrophages are not pivotal in determining tumor prognosis in early T1 breast cancers. New studies are presently being conducted to assess the value of different macrophage markers and macrophage activation profiles as prognostic factors in breast cancers of different clinical stages, using a larger number of patients among these three different ethnicities. Citation Format: Roberto Carrio, Tulay Koru-Sengul, Feng Miao, Stefan Gluck, Omar Lopez, Yamil Selman, Consuelo Alvarez, Clara Milikowski, Carmen Gomez, Merce Jorda, Mehrad Nadji, Marta Torroella-Kouri. Macrophages as independent prognostic factors in small T1 breast cancers. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3456. doi:10.1158/1538-7445.AM2013-3456

Macrophages are key players in the inflammatory response and exhibit significant roles in the different stages of tumor progression. We have previously reported deficient functions of peritoneal macrophages of D1-DMBA3 mammary tumors bearers (T-PEMs). We showed that T-PEMs are impaired in inflammatory activity due to diminished expression of transcription factors NFκB and C/EBP. We have also demonstrated that T-PEMs display neither M1 nor M2 phenotypes, exhibit deficiencies in the production of several inflammatory cytokines, are less differentiated and show increased apoptosis. Importantly, we showed for the first time that their apoptosis in periphery contributes to increased myelopoiesis. We examined the blood monocytes from these tumor mice and demonstrated that these cells are neither inflammatory nor suppressive and are less differentiated, similar to the T-PEMs they later become. In the present study we investigate tumor-associated macrophages (TAMs) from the same tumor model and compare them with T-PEMs and with peritoneal macrophages from normal mice (N-PEMs). Our results show that TAMs downregulate IL-12p70, but upregulate IL-12p40, IL-23, IL-6 and IL-10 and chemokines and their receptors are very differently expressed in these two macrophages subpopulations. NFκB and C/EBP family members are decreased in TAMs as compared with T-PEMs, however NFκBp50 homodimers, STAT1/pSTAT1 and STAT3/pSTAT3 are all overexpressed. Moreover TAMs block T-cell proliferation and are more prone to apoptosis than T-PEMs due to a higher expression of activated caspase-3 and downregulation of Bcl-X. Our results show that T-PEMs and TAMs have equally impaired phagocytic capacity compared with fully-phagocytic N-PEMs. Moreover, TAMs constitutively express iNOS, produce nitric oxide but no arginase and are Gr-1high and CD11blow, thus are not classic myeloid-derived suppressor cells. Collectively, our results show that the exposure to different locations and tumor factor gradients determine macrophage phenotypes and functions. The tumor microenvironment, as the setting in most intimate contact with tumor cells is the one that most alters macrophage activity. Targeting tumor factors and other cells in the tumor microenvironment may allow reversion of macrophage dysfunction. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 398. doi:1538-7445.AM2012-398

The thymus is the major site of T cell differentiation and a key organ of the immune system. Most important, it provides a specialized environment for the selection of rearranged clones that will function appropriately in the adaptive immune response. Thymic involution has been observed in several model systems; including graft-vs-host disease, aging, and tumor development, however, the mechanisms involved in this phenomenon remain to be elucidated. Previous results from our laboratory have reported that the severe thymic atrophy and impaired T cell development seen in mammary tumor bearers are associated with an arrest in at least two steps of T cell differentiation, changes in the levels of crucial cytokines expressed in the thymus microenvironment, and a progressive increase in apoptosis during the tumor development mainly due to downregulation of important molecules that control programmed cell death. Cytokines regulate numerous aspects of hematopoiesis via activation of the Jak/Stat pathways. In the present study we have used our mammary tumor model to investigate whether changes in the levels of cytokines in the thymus could affect the normal expression of the aforementioned pathways. RNA and protein analysis revealed an overexpression of the different interferons, a downregulation of most of the Jak/Stat pathways, and an increased expression of several suppressors of cytokine signaling (SOCS) in the thymuses of tumor bearers. Collectively, our data suggest a mechanism by which the impaired Jak/Stat signaling pathways observed in the whole thymus of tumor-bearing mice could be contributing to the abnormal T cell development and apoptosis observed during the tumor-induced thymic atrophy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 792. doi:10.1158/1538-7445.AM2011-792

Macrophages are key players in the inflammatory response and exhibit significant roles in the different stages of tumor progression. We have previously reported the deficient functions of elicited macrophages recruited to the peritoneal cavity of mice bearing advanced D1-DMBA3 mammary tumors (T-PEMs). We showed that these T-PEMs are impaired in inflammatory activity due to diminished expression of transcription factors NFκB and C/EBP. We have also demonstrated that T-PEMs display neither M1 nor M2 phenotypes, exhibit deficiencies in the production of several inflammatory cytokines and proinflammatory signaling pathways intermediates and are less differentiated. Moreover, due in part to NFκB downregulation, increased apoptosis is observed in T-PEMs, a phenomenon which we reported for the first time that may contribute to increased myelopoiesis in tumor hosts. We have also recently examined the characteristics of blood monocytes from mice bearing the same mammary tumors and have demonstrated that these cells are neither inflammatory nor suppressive and are less differentiated, similar to the T-PEMs they later become. In the present study we investigate tumor-associated macrophages (TAMs) from the same animal tumor model and compare them with T-PEMs and with peritoneal macrophages from normal mice (N-PEMs). Our results show that TAMs downregulate IL-12p70, yet upregulate IL-12p40, IL-23 and IL-10. NFκB and C/EBP family members are decreased in TAMs as compared with T-PEMs, however NFκBp50 homodimers, STAT1/pSTAT1 and STAT3/pSTAT3 are all overexpressed. Interestingly, macrophages from tumor-bearing mice block T-cell proliferation, with TAMs exerting a more powerful inhibitory effect than T-PEMs. Also, TAMs are more prone to apoptosis than T-PEMs due to a higher expression of activated caspase 3 and downregulation of Bclx. TAMs also exhibit lower levels of differentiation than T-PEMs. In addition, our results show that T-PEMs and TAMs have equally impaired phagocytic capacity compared with fully-phagocytic N-PEMs. Moreover, TAMs constitutively express iNOS and produce nitric oxide as compared with T-PEMs, and they have constitutively lower arginase activity than T-PEMs. Furthermore, TAMs are Gr-1high and CD11blow, thus they are not classic myeloid-derived suppressor cells. Our results show that different locations in tumor hosts determine macrophage phenotypes and functions. The tumor microenvironment, as the location in most intimate contact with tumor cells, is the one that most alters macrophage activity. This is not only due to the occurrence of higher levels of tumor factors secreted by tumor cells, but also to the presence of other cell types that may interact with macrophages and modulate their activity. Targeting these tumor factors and cells in the tumor microenvironment will allow reversion of macrophage dysfunction. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 449. doi:10.1158/1538-7445.AM2011-449

The thymus is a central lymphoid organ critical for the development and maintenance of an effective peripheral T cell repertoire. Most important, it provides a specialized environment for the selection of rearranged clones that will function appropriately in the adaptive immune response. The tumor-induced immunosuppression observed during murine mammary tumorigenesis has been associated with a profound thymus involution accompanied with a severe depletion of the most abundant subset of thymocytes; CD4+CD8+ double positive (DP) immature cells. Thymic involution has been observed in several model systems; including graft-vs-host disease, aging, and tumor development, however, the mechanisms involved in this phenomenon remain to be elucidated. Previous results from our laboratory have reported that the severe thymic atrophy and impaired T cell development seen in mammary tumor bearers are associated with an arrest in at least two steps of T cell differentiation, changes in the levels of crucial cytokines expressed in the thymus microenvironment, and a progressive increase in apoptosis during the tumor development mainly due to downregulation of important molecules that control programmed cell death. Moreover, we have shown that mice bearing the murine parental D1-DMBA-3 mammary tumor and tumors derived from the parental tumor, the DA-3, develop many changes in their cytokine production. For example, in mice bearing these tumors there is a decrease in the IFN-γ in the peripheral circulation and production of this crucial cytokine is greatly diminished in the T cells. In the present study we have used our DA-3 mammary tumor model to investigate whether the levels of IFN-γ have an important role in anti-tumor activity, in the pathogenesis of thymic atrophy as well as the tumor-induced immunosuppression in these mice. Interestingly, our results show that the overexpression of IFN-γ in DA-3 tumor cells results in a marked delay of tumor growth and a blockage in the tumor-associated thymus atrophy. Importantly, peripheral T cells from IFN-γ-transfected DA-3 tumor-bearing mice, show markedly high levels of this cytokine. Moreover, when thymuses from tumor-bearing mice that received IFN-γ were analyzed, thymic populations were very similar to those observed in the thymuses of normal mice. Collectively, our data suggest that the replacement of the faulty levels of IFN-γ in tumor bearers results in a delayed tumor growth and thymic involution leading to a decrease of tumor-induced immune suppression caused by the mammary tumor development. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1904.

During mammary tumorigenesis, there is a profound thymus involution associated with a severe depletion of the most abundant subset of thymocytes, CD4+CD8+ immature cells, however, the mechanisms involved in this phenomenon remain to be elucidated. We have previously reported that the thymic involution observed in tumor bearing mice is associated with an early block in T cell maturation. This alteration in thymocyte differentiation might be due to an impaired function of stromal cell microenvironment in this organ. Using the D1-DMBA-3 mammary tumor model we found that IL-7 and IL-15 mRNA, crucial cytokines involved in thymic development and cellular homeostasis respectively, are profoundly down-regulated in the thymuses of tumor hosts. Importantly, the expression of the gene for hepatocyte growth factor (HGF), which has been associated with proliferation, cell survival, angiogenesisand differentiation, is down-regulated in thymuses of tumor bearers. Injection of HGF into mice implanted with the mammary tumor resulted in a partial restoration of the thymus volume and of the levels of IL-7 and IL-15 in this organ. Collectively, our data suggest that HGF may play an important role in the thymic involution in tumor bearing hosts and that the cytokines expressed in the thymus microenvironment may be modulated by this growth factor.

It is difficult to study the time frame and requirements for antigen removal as CD8 T effector cells transit to memory cells during an immune response because memory cells only readily appear after contraction of the effector response and clearance of antigen. To overcome these limitations, we have modeled the effector to memory transition in vitro and by the adoptive transfer of effector CTL to normal mice. When OVA-specific OT-I CTL were cultured in IL-15 without antigen, they acquired phenotypic and functional properties of memory cells 48 hr later. Such memory conversion occurred in the presence of 0.01 nM OVA peptide and APC, a dose that only induces a strong recall response, but not at a higher dose (0.1 nM) that readily activates naïve OT-I T cells. Following adoptive transfer of OT-I CTL to antigen-free normal mice, OT-I effector cells developed into central memory-like cells by 3 days post-transfer. Upon adoptive transfer to mice bearing the OVA-expressing E.G7 tumor, the OT-I CTL effector cells also readily converted to memory-like cells by day 3 post-transfer while the effector cells rejected the tumor. However, under conditions where the tumor was not cleared, memory production was impaired. Collectively, these data suggest that some CTL rapidly convert to memory cells concurrent with an effector response, without complete clearance of antigen, provided that antigen level is not too high. (Supported by the NIH)

Tumor progression is associated with the development of a state of immunosuppression in the host. Macrophages from mice bearing advanced mammary tumors are profoundly dysfunctional, exhibiting decreased levels of several pro-inflammatory cytokines and of nitric oxide, which are critical in the anti-tumor immune response. We have found that the impaired function of these macrophages is associated with reduced expression and nuclear translocation of transcription factors NFkB and C/EBP. The diminished expression of these transcription factors is observed both at the protein and mRNA levels, and interestingly, there is evidence that proteasomal degradation might also be involved in their proteolysis. We have shown that several factors produced by the mammary tumor are associated with this phenomenon. Our results provide evidence that NFkB and C/EBP are targets of the tumor evasion mechanisms observed in advanced cancers.

Members of the bcl-2 gene family are essential regulators of cell survival in a wide range of biological processes. A1, a member of the family, is known to be expressed in certain adult tissues. However, the precise tissue distribution and function of A1 remains poorly understood. We show here that A1 is expressed in multiple tissues during murine embryonic development. In the embryo, A1 was detected first at embryonic day 11.5 in liver, brain, and limbs. At day 13.5 of gestation, A1 expression was observed in the central nervous system, liver, perichondrium, and digital zones of developing limbs in a pattern different from that of bcl-X. In the central nervous system of 15.5-day embryos, A1 was expressed at high levels in the ventricular zone and cortical plate of brain cortex. Significantly, the interdigital zones of limbs and the intermediate region of the developing brain cortex, two sites associated with extensive cell death, were devoid of A1 and bcl-X. The expression of A1 was retained in many adult tissues. To assess the ability of A1 to modulate cell death, stable transfectants expressing different amounts of A1 protein were generated in K562 cells. Expression of A1 was associated with retardation of apoptotic cell death induced by actinomycin D and cycloheximide as well as by okadaic acid. Confocal microscopy showed that the A1 protein was localized to the cytoplasm in a pattern similar to that of Bcl-2. These results demonstrate that the expression of A1 is wider than previously reported in adult tissues. Furthermore, its distribution in multiple tissues of the embryo suggests that A1 plays a role in the regulation of physiological cell death during embryonic development.