Cutaneous solitary fibrous tumor: Report of three cases with review of histopathological mimics

Solitary fibrous tumor (SFT) is a relatively uncommon spindle cell mesenchymal neoplasm that is most often based on the pleura but may rarely arise in extrapleural locations, including the skin. Herein, we describe three cases of cutaneous SFTs. SFT is characterized by epithelioid and spindle cells arranged in random patterns with focal prominent stromal collagen and pericytomatous vessels. Immunohistochemical evaluation is required for definitive distinction of SFT from other benign and malignant cutaneous spindle cell neoplasms. Although aggressive biologic behavior is uncommon, accurate diagnosis of it is required for prognostication and counseling. CD34, bcl-2, and CD99 stains are positive in SFT, but not specific. STAT6 is the most sensitive and specific immunohistochemical marker to confirm diagnosis of SFT.

Myeloid-derived suppressor cells are elevated in patients with psoriasis and produce various molecules

Psoriasis is a debilitating chronic inflammatory disease. In addition to the characteristic effects on the skin, chronic inflammation associated with the disease is recognized to contribute to cardiovascular, hepatic and renal comorbidities. Immature myeloid regulatory cells, known as myeloid‑derived suppressor cells (MDSCs), have been demonstrated to accumulate in various diseases and chronic inflammatory states, including inflammatory bowel disease and various types of cancer. The results of the present study, obtained using flow cytometry and cell culture analysis of peripheral blood mononuclear cells from psoriasis and healthy patients, revealed that MDSC levels are significantly increased in the blood of patients with psoriasis compared with healthy controls. Furthermore, these cells are capable of producing various molecules, including matrix metalloproteinase‑9 and‑1, interleukin‑8, growth‑related oncogene, and monocyte chemoattractant protein 1. These molecules may recruit additional immune cells involved in the pathogenesis of the disease, and contribute to the chronic inflammatory state in these patients. Therefore, MDSCs, which have various immune regulatory functions, may contribute to the pathogenesis of psoriasis as a systemic inflammatory disease.

uPA and uPA-receptor are involved in cancer-associated myeloid-derived suppressor cell accumulation

BACKGROUND

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.

MATERIALS AND METHODS

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.

RESULTS

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.

CONCLUSION

MDSC accumulation is tumor burden-dependent, and tumor-derived factors such as uPA and its receptor uPAR play a role in their recruitment.

Role of immune-regulatory cells in skin pathology

The skin harbors a complex and unique immune system that protects against various pathologies, such as infection and cancer. Although many of the mechanisms of immune activation in the skin have been investigated, it is likewise important to uncover the immune-regulatory components that limit effective immunity or prevent autoimmunity. Several cell populations are involved in this immune-regulatory function, including CD4+ T cells that coexpress the transcription factor Foxp3, known as Tregs, and cells with immune-regulatory function known as myeloid-derived suppressor cells (MDSCs). This review focuses on the role that immune-regulatory cells, such as MDSCs and Tregs, play in cutaneous pathology, such as malignancy, psoriasis, dermatitis, burn wounds, and transplantation. Although their depletion may serve to augment immunity, expansion of these cells may be used to suppress excessive immune reactions. These cells are attractive, therapeutic targets for various conditions and thus, deserve further exploration.

Myeloid-derived suppressor cells down-regulate L-selectin expression on CD4+ and CD8+ T cells

Effective cell-mediated antitumor immunity requires the activation of tumor-reactive T cells and the trafficking of activated T cells to tumor sites. These processes involve the extravasation of lymphocytes from the blood and lymphatics, and their homing to lymph nodes and tumors. L-selectin (CD62L) is an important molecule in these processes. It directs naive lymphocytes to peripheral lymph nodes where they become activated and it traffics naive lymphocytes to inflammatory environments, such as tumors. Individuals with advanced cancer are immune suppressed due to myeloid-derived suppressor cells (MDSC), a population of immature myeloid cells that accumulate to high levels in response to tumor-secreted and proinflammatory factors. We now demonstrate that the reduction in T cell levels of L-selectin that is commonly seen in individuals with cancer inversely correlates with MDSC levels. Three lines of evidence demonstrate that MDSC directly down-regulate L-selectin on naive T cells: 1) naive T cells cocultured with tumor-induced MDSC have reduced L-selectin; 2) T cells in tumor-free aged mice with elevated levels of MDSC have reduced L-selectin, and 3) peritoneal exudate T cells of tumor-free mice treated with plasminogen activator urokinase to elevate MDSC have reduced levels of L-selectin. MDSC are likely to down-regulate L-selectin through their plasma membrane expression of ADAM17 (a disintegrin and metalloproteinase domain 17), an enzyme that cleaves the ectodomain of L-selectin. Therefore, MDSC down-regulate L-selectin levels on naive T cells, decreasing their ability to home to sites where they would be activated. This is another mechanism by which MDSC inhibit antitumor immunity.

The liver is a site for tumor-induced myeloid-derived suppressor cell accumulation and immunosuppression

Tumor-induced immunosuppression plays a key role in tumor evasion of the immune system. A key cell population recognized as myeloid-derived suppressor cells (MDSC) contributes and helps orchestrate this immunosuppression. MDSC can interact with T cells, macrophages, and natural killer cells to create an environment favorable for tumor progression. In various tumor models, their presence at high levels has been reported in the bone marrow, blood, spleen, and tumor. We report for the first time that MDSC accumulate and home to the liver in addition to the other organs. Liver MDSC suppress T cells and accumulate to levels comparable with splenic MDSC. Additionally, hematopoiesis in the liver contributes to the dramatic expansion of MDSC in this organ. Furthermore, MDSC in the liver interact with macrophages, also known as Kupffer cells, and cause their up-regulation of PD-L1, a negative T-cell costimulatory molecule. The liver is thus an organ in which MDSC accumulate and can contribute to immunosuppression directly and indirectly. MDSC play a role in various pathologic states in addition to cancer, and these results contribute to our understanding of their biology and interactions with immune-related cells.

Decreased levels of both Stat1 and Stat3 in T lymphocytes from mice bearing mammary tumors

BACKGROUND

Lymphocytes from tumor-bearing animals have been shown to lack antitumor function. The objective of this study was to investigate the status of the signal transducers, Stat1 and Stat3, in T lymphocytes of animals bearing D1-DMBA-3 mammary tumors and to elucidate if any alterations in these signal transducers can be explained by the presence of tumor-derived factors and correlated with the lack of antitumor function in these cells.

MATERIALS AND METHODS

T Lymphocytes from spleens of normal and tumor-bearing mice were purified and assayed for the presence of Stat1 and Stat3 by Western blot analysis.

RESULTS

It was found that levels of both Stat1 and Stat3 were reduced in T lymphocytes of tumor-bearers not only in their active, phosphorylated form but in total protein levels.

CONCLUSION

These findings indicate that during mammary tumor progression, alteration of various transcription factors may contribute to the down-regulation of immune function.

Immune modulation by melanoma-derived factors

Melanomas, while the less common of skin cancers, are highly aggressive and once they metastasize usually indicate a poor prognosis. Melanomas are in many cases immunogenic and thus have been a prime target for immunotherapy, which has resulted in objective responses in some patients. To understand why antitumor immunity fails, and for the purpose of discovering new targets to improve therapy, there has been great interest to analyse the antitumor immune responses which exist in these patients, and uncover mechanisms which block tumor-specific immune responses. It is now evident that immunosuppressive cell networks and factors play a major role in the failure of the antitumor immune responses and therapies to eradicate the tumor. In this review, the factors produced by melanomas which can modulate and enhance these suppressive mechanisms are discussed. The roles of immature dendritic cells, neutrophils, T-regulatory cells, myeloid-derived suppressor cells and M2 macrophages or tumor-associated macrophages are described. Furthermore, taking into consideration of the cross-talk which exists among these different cell types and the cycle of immunosuppression which is evident in melanoma cancer patients and animal models, will be important for future therapeutic approaches.

Reduction of the number and/or suppressive mechanisms of myeloid cells by mammary tumor cells expressing a secreted isoform of MUC1 (50.10)

Expression of the transmembrane isoform of MUC1 (MUC1/TM) in an aggressive murine mammary tumor line, DA-3, results in tumor development leading to metastasis and death of the host, as does the untransfected parental tumor line. However, tumor cells expressing a secreted isoform of MUC1 (MUC1/sec) fail to develop tumors in vivo. The rejection of tumors was found to be immunologically mediated, as initially innate cells and ultimately T cells are required. Previous work to determine which lymphoreticular cells may be involved in the immune rejection revealed that MUC1/sec expressing cells recruited four times the amount of F4/80+ cells, while recruiting significantly lower numbers of GR-1+ cells, relative to MUC1/TM expressing tumor cells. Gr-1+CD11b+ cells known as immature Myeloid Derived Suppressor Cells (MDSC) have been correlated with immune suppression in many models of cancer and chronic infections. MDSC accumulate in response to MUC1/TM expressing tumor cells, but remaine at normal levels in animals exposed to MUC1/sec expressing tumor cells. Futhermore, supernatants from MUC1/sec expressing tumor cells blocked induction of arginase in MDSC, a mechanism of suppression. This block in induction of arginase could also be demonstrated by use of a unique peptide, Immuno Enhancing Peptide, only found in the MUC1/sec protein. NIH, NCI R01CA25583.

MHC class II and CD80 tumor cell-based vaccines are potent activators of type 1 CD4+ T lymphocytes provided they do not coexpress invariant chain

We are developing vaccines that activate tumor-specific CD4+ T cells. The cell-based vaccines consist of MHC class I+ tumor cells that are genetically modified to express syngeneic MHC class II and costimulatory molecules. Previous studies demonstrated that treatment of mice with established tumors with these vaccines resulted in regression of solid tumors, reduction of metastatic disease, and increased survival time. Optimal vaccines will prime naïve T cells and activate T cells to tumor peptides derived from diverse subcellular compartments, since potential tumor antigens may reside in unique cellular locales. To determine if the MHC class II/costimulatory molecule vaccines fulfill these conditions, the vaccines have been tested for their ability to activate antigen-specific, naïve, transgenic CD4+ T lymphocytes. MHC class II(+)CD80+ vaccine cells were transfected with hen eggwhite lysozyme targeted to the cytosol, nuclei, mitochondria, or endoplasmic reticulum, and used as antigen-presenting cells to activate I-Ak-restricted, lysozyme-specific CD4+ 3A9 transgenic T cells. Regardless of the cellular location of lysozyme, the vaccines stimulated release of high levels of IFN-gamma and IL-2. If the vaccines coexpressed the MHC class II accessory molecule invariant chain, then IFN-gamma and IL-2 release was significantly reduced. These studies demonstrate that in the absence of invariant chain the MHC class II and CD80 tumor cell vaccines (1) function as antigen-presenting cells to activate naïve, tumor-specific CD4+ cells to endogenously synthesized tumor antigens; (2) polarize the activated CD4+ T cells toward a type 1 response; and (3) present epitopes derived from varied subcellular locales.

Invariant Chain and the MHC Class II Cytoplasmic Domains Regulate Localization of MHC Class II Molecules to Lipid Rafts in Tumor Cell-Based Vaccines

Cell-based tumor vaccines, consisting of MHC class I+ tumor cells engineered to express MHC class II molecules, stimulate tumor-specific CD4+ T cells to mediate rejection of established, poorly immunogenic tumors. Previous experiments have demonstrated that these vaccines induce immunity by functioning as APCs for endogenously synthesized, tumor-encoded Ags. However, coexpression of the MHC class II accessory molecule invariant chain (Ii), or deletion of the MHC class II cytoplasmic domain abrogates vaccine immunogenicity. Recent reports have highlighted the role of lipid microdomains in Ag presentation. To determine whether Ii expression and/or truncation of MHC class II molecules impact vaccine efficacy by altering MHC class II localization to lipid microdomains, we examined the lipid raft affinity of MHC class II molecules in mouse M12.C3 B cell lymphomas and SaI/A(k) sarcoma vaccine cells. Functional MHC class II heterodimers were detected in lipid rafts of both cell types. Interestingly, expression of Ii in M12.C3 cells or SaI/A(k) cells blocked the MHC class II interactions with cell surface lipid rafts. In both cell types, truncation of either the alpha- or beta-chain decreased the affinity of class II molecules for lipid rafts. Simultaneous deletion of both cytoplasmic domains further reduced localization of class II molecules to lipid rafts. Collectively, these data suggest that coexpression of Ii or deletion of the cytoplasmic domains of MHC class II molecules may reduce vaccine efficacy by blocking the constitutive association of MHC class II molecules with plasma membrane lipid rafts.