Regulation gone wrong: a subset of Sézary patients have malignant regulatory T cells

Combined High-Throughput Approaches Reveal the Signals Driven by Skin and Blood Environments and Define the Tumor Heterogeneity in Sézary Syndrome

Simple Summary

Sézary syndrome (SS) is a leukemic and incurable variant of cutaneous T-cell lymphoma characterized by the accumulation of neoplastic CD4+ lymphocytes in the blood, lymph nodes, and skin. With the exception of allogenic transplantation, no curative chance is available to treat SS, and it is a priority to find new therapies that target SS cells within all disease compartments. This review aims to summarize the more recent analyses conducted on skin- and blood-derived SS cells concurrently obtained from the same SS patients. The results highlighted that skin-SS cells were more active/proliferating with respect to matched blood SS cells that instead appeared quiescent. These data shed the light on the possibility to treat blood and skin SS cells with different compounds, respectively. Moreover, this review recaps the more recent findings on the heterogeneity of circulating SS cells that presented a series of novel markers that could improve diagnosis, prognosis and therapy of this lymphoma.

Abstract

Sézary syndrome (SS) is an aggressive variant of cutaneous t-cell lymphoma characterized by the accumulation of neoplastic CD4+ lymphocytes—the SS cells—mainly in blood, lymph nodes, and skin. The tumor spread pattern of SS makes this lymphoma a unique model of disease that allows a concurrent blood and skin sampling for analysis. This review summarizes the recent studies highlighting the transcriptional programs triggered by the crosstalk between SS cells and blood–skin microenvironments. Emerging data proved that skin-derived SS cells show consistently higher activation/proliferation rates, mainly driven by T-cell receptor signaling with respect to matched blood SS cells that instead appear quiescent. Biochemical analyses also demonstrated an hyperactivation of PI3K/AKT/mTOR, a targetable pathway by multiple inhibitors currently in clinical trials, in skin SS cells compared with a paired blood counterpart. These results indicated that active and quiescent SS cells coexist in this lymphoma, and that they could be respectively treated with different therapeutics. Finally, this review underlines the more recent discoveries into the heterogeneity of circulating SS cells, highlighting a series of novel markers that could improve the diagnosis and that represent novel therapeutic targets (GPR15, PTPN13, KLRB1, and ITGB1) as well as new genetic markers (PD-1 and CD39) able to stratify SS patients for disease aggressiveness.

Phenotypical Markers, Molecular Mutations, and Immune Microenvironment as Targets for New Treatments in Patients with Mycosis Fungoides and/or Sézary Syndrome

Primary cutaneous lymphomas encompass a wide spectrum of rare lymphoproliferative disorders originating in the skin, among which, mycosis fungoides (MF) is the most common subtype. The treatment of this disease is based on skin-directed therapies eventually in association with biologic response modifiers in the early phases, whereas in patients with the advanced stages, several therapeutic strategies can be used including mono and/or polychemotherapy and bone marrow transplantation. In recent years, the identification of specific markers (phenotypical, immunological, and molecular) has led to the development of several studies (including two randomized phase III trials). The results of these studies are modifying our therapeutic strategy toward a personalized treatment approach in which the clinical characteristics of the patients and tumor-node-metastasis-blood stage are considered together with the expression of specific markers (i.e., a CD30-positive expression for the use of brentuximab vedotin). This review will provide a comprehensive scenario of the main phenotypical, molecular, and immunological markers related to MF pathogenesis and disease evolution, which could represent the target for the development of innovative effective treatments in this disease.

MKL1/miR34a/FOXP3 axis regulates cell proliferation in gastric cancer

Megakaryoblastic leukemia 1 (MKL1) was closely related to the pathogenesis of various human malignant cancers. MiR34a was reported to be closely related to cancer cell proliferation. Forkhead box protein 3 (FOXP3) was a transcription factor that played a different role in different cancer types. CDK6 was involved in cell cycle progression and was upregulated in several types of cancers. The present study investigated the effects of MKL1/miR34a/FOXP3 axis on cell proliferation in MGC803 gastric cancer cells. Our results demonstrated that overexpression of MKL1 promoted proliferation of MGC80-3 cells, MKL1 directly binding to the promoter of CDK6 to increase its expression. Knockdown of FOXP3 promoted proliferation of MGC80-3 cells and MKL1 inhibited the expression of FOXP3 via miR-34a. The finding can contribute to elucidating the regulatory mechanism involved in the cell cycle progression of gastric cancer cells and may aid in screening potential gene targets for the biological therapy of gastric cancer.

The role of regulatory T cells and genes involved in their differentiation in pathogenesis of selected inflammatory and neoplastic skin diseases. Part II: The Treg role in skin diseases pathogenesis

Regulatory FOXP3+ T cells (Tregs) constitute 5% to 10% of T cells in the normal human skin. They play an important role in the induction and maintenance of immunological tolerance. The suppressive effects of these cells are exerted by various mechanisms including the direct cytotoxic effect, anti-inflammatory cytokines, metabolic disruption, and modulation of the dendritic cells function. The deficiency of Treg cells number or function are one of the basic elements of the pathogenesis of many skin diseases, such as psoriasis, atopic dermatitis, bacterial and viral infections. They also play a role in the pathogenesis of T cell lymphomas of the skin (cutaneous T cell lymphomas - CTCL), skin tumors and mastocytosis. Here, in the second part of the cycle, we describe dysfunctions of Tregs in selected skin diseases.

Expression of Granulysin and FOXP3 in Cutaneous T Cell Lymphoma and Sézary Syndrome

BACKGROUND

Multiple complex pathways are operable in the evolution of cutaneous T cell lymphomas (CTCLs). These pathways involve interaction between neoplastic T cells and cells of the immune system (especially dendritic cells and the non-malignant T cells). Granulysin is a proinflammatory antimicrobial peptide which has an immune alarmin function, activating dendritic cells, as well as an active role in tumor immunology and prognosis. FOXP3+ regulatory T cells Tregs are an important player in the immune system. Much controversy is found in the literature about the role of Tregs in CTCL.

AIM

The present study aimed to investigate the expression of granulysin and FOXP3 in mycosis fungoides (MF), its precursor lesion large plaque parapsoriasis and its leukemic form Sezary syndrome (SS).

MATERIALS AND METHODS

Immunohistochemical expression of granulysin and FOXP3 were assessed in lesional skin biopsies taken from 58 patients (4 large plaque parapsoriasis, 48 MF and 6 SS).

RESULTS

Granulysin positivity was cytoplasmic and higher in MF than in parapsoriasis en plaque and higher in the more advanced stages of MF (p<0.001). All groups showed significant differences between each other except between MF tumor stage and SS. FOXP3 positivity was nuclear and higher in early stage MF (plaque and patch stages) than in tumor stages and SS (p<0.001). However the FOXP3 count was lower in parapsoriasis en plaque than in other stages of MF. All the groups showed significant differences between each other except between parapsoriasis and SS and between patch and plaque stages of MF.

CONCLUSIONS

The present study supports a role for granulysin in MF progression and proposes a novel hypothesis about the effect of FOXP3 +veTregs in the suppression of the activity of the neoplastic cells in MF.

FoxP3-Positive T-Regulatory Cells in Lymph Nodes with Mycosis Fungoides and Sézary Syndrome

Mycosis fungoides and Sézary syndrome are indolent cutaneous T-cell lymphomas, with skin-associated peripheral lymph nodes being the most frequent extracutaneous site of involvement. Acquisition of functional properties of regulatory T-cells by malignant T-cells in advanced disease may contribute to immunosuppression. Whereas previous studies examining FoxP3 protein expression in mycosis fungoides and Sézary syndrome have focused on skin specimens, little data are available on lymph nodes from patients with these conditions. In this study we examined FoxP3+ regulatory T-cells in lymph nodes from 26 patients with mycosis fungoides and Sézary syndrome and correlated the findings with clinical data, molecular assays for T-cell clonality, and flow cytometry. Except for one case of Sézary syndrome in which malignant T-cells expressed FoxP3 protein, a significantly lower number of FoxP3-expressing cells occurred in lymph nodes that were clearly involved with lymphoma as compared to uninvolved nodes. Cox proportional hazards model showed that lymph node rating and histological evidence of transformation, but not number of FoxP3+ cells, were factors significantly associated with adverse prognosis. We speculate that modulation of FoxP3+ cells in lymph nodes involved with lymphoma might play a role in disease progression. Attainment of a regulatory T-cell phenotype by a subset of lymphoma cells might signal a poor prognosis.

The four types of Tregs in malignant lymphomas

Regulatory T cells (Tregs) are a specialized subpopulation of CD4⁺ T cells, which act to suppress the activation of other immune cells. Tregs represent important modulators for the interaction between lymphomas and host microenvironment. Lymphomas are a group of serious and frequently fatal malignant diseases of lymphocytes. Recent studies revealed that some lymphoma T cells might adopt a Treg profile. Assessment of Treg phenotypes and genotypes in patients may offer prediction of outcome in many types of lymphomas including diffuse large B-cell lymphoma, follicular lymphoma, cutaneous T cell lymphoma, and Hodgkin's lymphoma. Based on characterized roles of Tregs in lymphomas, we can categorize the various roles into four groups: (a) suppressor Tregs; (b) malignant Tregs; (c) direct tumor-killing Tregs; and (d) incompetent Tregs. The classification into four groups is significant in predicting prognosis and designing Tregs-based immunotherapies for treating lymphomas. In patients with lymphomas where Tregs serve either as suppressor Tregs or malignant Tregs, anti-tumor cytotoxicity is suppressed thus decreased numbers of Tregs are associated with a good prognosis. In contrast, in patients with lymphomas where Tregs serve as tumor-killing Tregs and incompetent Tregs, anti-tumor cytotoxicity is enhanced or anti-autoimmune Tregs activities are weakened thus increased numbers of Tregs are associated with a good prognosis and reduced numbers of Tregs are associated with a poor prognosis. However, the mechanisms underlying the various roles of Tregs in patients with lymphomas remain unknown. Therefore, further research is needed in this regard as well as the utility of Tregs as prognostic factors and therapy strategies in different lymphomas.

Regulatory T cells and immunodeficiency in mycosis fungoides and Sézary syndrome

Cutaneous T-cell lymphoma (CTCL) is the term for diseases characterized by primary accumulation of malignant T cells in the skin. Patients with the two predominant clinical forms of CTCL called mycosis fungoides (MF) and Sézary syndrome (SS) characteristically develop severe immunodeficiency during disease progression and consequently patients with advanced disease frequently die of infections and not from the tumor burden. For decades, it has been suspected that the malignant T cells actively drive the evolving immunodeficiency to avoid antitumor immunity, yet, the underlying mechanisms remain unclear. The identification of a subset of highly immunosuppressive regulatory T cells (Tregs) triggered a variety of studies investigating if MF and SS are malignant proliferations of Tregs but seemingly discordant findings have been reported. Here, we review the literature to clarify the role of Tregs in MF and SS and discuss the potential mechanisms driving the immunodeficiency.