Mac attack: macrophages as key drivers of cutaneous T-cell lymphoma pathogenesis

Preclinical in vitro and in vivo evidence for targeting CD74 as an effective treatment strategy for cutaneous T-cell lymphomas

BACKGROUND

Prognosis and quality of life in patients with advanced cutaneous T-cell lymphoma (CTCL), particularly in those with Sézary syndrome (SS) or advanced-stage mycosis fungoides (MF), are poor. Monoclonal antibodies or antibody-drug conjugates (ADCs) have been added into CTCL treatment algorithms, but the spectrum of antibody-targetable cell surface antigens in T-cell non-Hodgkin lymphomas (T-NHLs) is limited.

OBJECTIVES

To evaluate the expression of the major histocompatibility complex class II chaperone CD74 in common subtypes of CTCL by various methods, and to explore the efficacy of targeting CD74 in CTCL cells with an anti-CD74 ADC in vitro and in vivo.

METHODS

We comprehensively investigated the expression of CD74 in well-defined CTCL cell lines by polymerase chain reaction, immunoblotting and flow cytometry. More than 140 primary CTCL samples of all common subtypes were analysed by immunohistochemistry, flow cytometry, immunofluorescence and 'co-detection by indexing' (CODEX) multiplexed tissue imaging, as well as by single-cell RNA sequencing (scRNAseq) analyses. DNA methylation of CTCL cell lines was interrogated by the generation of genome-wide methylation profiling. The effect of a maytansinoid-conjugated humanized ADC against CD74 was investigated in CTCL cell lines in vitro, alone or in combination with gemcitabine, and in vivo after xenotransplantation of CTCL cell lines in NOD-scid Il2rgnull mice.

RESULTS

We demonstrated that CD74 is widely and robustly expressed in CTCL cells. In addition, CD74 expression in SS and MF was confirmed by scRNAseq data analysis and was correlated in CTCL cell lines with CD74 DNA hypomethylation. CD74 was rapidly internalized in CTCL cells and CD74 targeting by the ADC STRO-001 efficiently killed CTCL-derived cell lines. Finally, targeting of CD74 synergized with conventional chemotherapy in vitro and eradicated murine xenotransplants of CTCL cell lines in vivo.

CONCLUSIONS

CD74 is expressed in common CTCL subtypes. Targeting CD74 efficiently killed CTCL cells in vitro and in vivo. We therefore suggest the targeting of CD74 to be a highly promising treatment strategy for CTCL.

Reprogramming of PD-1+ M2-like tumor-associated macrophages with anti-PD-L1 and lenalidomide in cutaneous T cell lymphoma

Cutaneous T cell lymphoma (CTCL) is a disfiguring and incurable disease characterized by skin-homing malignant T cells surrounded by immune cells that promote CTCL growth through an immunosuppressive tumor microenvironment (TME). Preliminary data from our phase I clinical trial of anti-programmed cell death ligand 1 (anti-PD-L1) combined with lenalidomide in patients with relapsed/refractory CTCL demonstrated promising clinical efficacy. In the current study, we analyzed the CTCL TME, which revealed a predominant PD-1+ M2-like tumor-associated macrophage (TAM) subtype with upregulated NF-κB and JAK/STAT signaling pathways and an aberrant cytokine and chemokine profile. Our in vitro studies investigated the effects of anti-PD-L1 and lenalidomide on PD-1+ M2-like TAMs. The combinatorial treatment synergistically induced functional transformation of PD-1+ M2-like TAMs toward a proinflammatory M1-like phenotype that gained phagocytic activity upon NF-κB and JAK/STAT inhibition, altered their migration through chemokine receptor alterations, and stimulated effector T cell proliferation. Lenalidomide was more effective than anti-PD-L1 in downregulation of the immunosuppressive IL-10, leading to decreased expression of both PD-1 and PD-L1. Overall, PD-1+ M2-like TAMs play an immunosuppressive role in CTCL. Anti-PD-L1 combined with lenalidomide provides a therapeutic strategy to enhance antitumor immunity by targeting PD-1+ M2-like TAMs in the CTCL TME.

Mycosis Fungoides and Sézary Syndrome: Microenvironment and Cancer Progression

Mycosis fungoides and Sézary syndrome are epidermotropic cutaneous lymphomas, and both of them are rare diseases. Mycosis fungoides is the most frequent primary cutaneous lymphoma. In about 25% of patients with mycosis fungoides, the disease may progress to higher stages. The pathogenesis and risk factors of progression in mycosis fungoides and Sézary syndrome are not yet fully understood. Previous works have investigated inter- and intrapatient tumor cell heterogeneity. Here, we overview the role of the tumor microenvironment of mycosis fungoides and Sézary syndrome by describing its key components and functions. Emphasis is put on the role of the microenvironment in promoting tumor growth or antitumor immune response, as well as possible therapeutic targets. We focus on recent advances in the field and point out treatment-related alterations of the microenvironment. Deciphering the tumor microenvironment may help to develop strategies that lead to long-term disease control and cure.

Single-cell transcriptomics links malignant T cells to the tumor immune landscape in cutaneous T cell lymphoma

Cutaneous T cell lymphoma (CTCL) represents a heterogeneous group of non-Hodgkin lymphoma distinguished by the presence of clonal malignant T cells. The heterogeneity of malignant T cells and the complex tumor microenvironment remain poorly characterized. With single-cell RNA analysis and bulk whole-exome sequencing on 19 skin lesions from 15 CTCL patients, we decipher the intra-tumor and inter-lesion diversity of CTCL patients and propose a multi-step tumor evolution model. We further establish a subtyping scheme based on the molecular features of malignant T cells and their pro-tumorigenic microenvironments: the T_CyEM group, demonstrating a cytotoxic effector memory T cell phenotype, shows more M2 macrophages infiltration, while the T_CM group, featured by a central memory T cell phenotype and adverse patient outcome, is infiltrated by highly exhausted CD8⁺ reactive T cells, B cells and Tregs with suppressive activities. Our results establish a solid basis for understanding the nature of CTCL and pave the way for future precision medicine for CTCL patients.

Challenging Cutaneous T-Cell Lymphoma: What Animal Models Tell us So Far

Cutaneous T-cell lymphomas are characterized by heterogeneity of clinical variants, further complicated by genomic and microenvironmental variables. Furthermore, in vitro experiments are hampered by the low culture efficiency of these malignant cells. Animal models are essential for understanding the pathogenetic mechanisms underlying malignancy and for discovering new anticancer treatments. They are divided into two main categories: those in which tumors arise in the host owing to genetic modifications and those that use tumor cell transplantation. In this review, we summarize the attempts to decipher the complexity of the pathogenesis of cutaneous T-cell lymphoma by exploiting genetically modified and xenograft models.

The Role of Tumor Microenvironment in Mycosis Fungoides and Sézary Syndrome

Mycosis fungoides (MF) and Sézary syndrome (SS) are the most common subtypes of cutaneous T-cell lymphomas (CTCLs). Most cases of MF display an indolent course during its early stage. However, in some patients, it can progress to the tumor stage with potential systematic involvement and a poor prognosis. SS is defined as an erythrodermic CTCL with leukemic involvements. The pathogenesis of MF and SS is still not fully understood, but recent data have found that the development of MF and SS is related to genetic alterations and possibly to environmental influences. In CTCL, many components interacting with tumor cells, such as tumor-associated macrophages, fibroblasts, dendritic cells, mast cells, and myeloid-derived suppressor cells, as well as with chemokines, cytokines and other key players, establish the tumor microenvironment (TME). In turn, the TME regulates tumor cell migration and proliferation directly and indirectly and may play a critical role in the progression of MF and SS. The TME of MF and SS appear to show features of a Th2 phenotype, thus dampening tumor-related immune responses. Recently, several studies have been published on the immunological characteristics of MF and SS, but a full understanding of the CTCL-related TME remains to be determined. This review focuses on the role of the TME in MF and SS, aiming to further demonstrate the pathogenesis of the disease and to provide new ideas for potential treatments targeted at the microenvironment components of the tumor.

Genome-wide transcriptome analysis of the STAT6-regulated genes in advanced-stage cutaneous T-cell lymphoma

The signal transducer and activator of transcription 6 (STAT6) is a critical up-stream mediator of interleukin-13 (IL-13) and IL-4 signaling and is constitutively activated in malignant lymphocytes from Sezary syndrome (SS) and mycosis fungoides (MF), the most common subtypes of cutaneous T-cell lymphomas. By combining genome-wide expression profiling with pharmacological STAT6 inhibition, we have identified the genes regulated by STAT6 in MF/SS tumors. We found that STAT6 regulates several common pathways in MF/SS malignant lymphocytes that are associated with control of cell-cycle progression and genomic stability as well as production of Th2 cytokines. Using ex vivo skin explants from cutaneous MF tumors as well as Sezary cells derived from the blood of SS patients, we demonstrated that inhibition of STAT6 activation downregulates cytokine production and induces cell-cycle arrest in MF/SS malignant lymphocytes, inhibiting their proliferation but not their survival. Furthermore, we show that STAT6 promotes the protumoral M2-like phenotype of tumor-associated macrophages in the tumor microenvironment of advanced stage MF by upregulating the expression of genes associated with immunosuppression, chemotaxis, and tumor matrix remodeling. Thus, we show STAT6 to be a major factor in the pathogenesis and progression of MF/SS, promoting proliferation and invasion of the malignant lymphocytes while inducing a progressive depression of the antitumor immune response. Together, our results provide new insights into disease pathogenesis and offer new prospective targets for therapeutic intervention.

Cancer-Associated Fibroblasts Play an Important Role in Early-Stage Mycosis Fungoides

Research in cutaneous T-cell lymphoma has widened from the malignant T cell itself to the tumor microenvironment. In this issue of the Journal of Investigative Dermatology, Aronovich et al. (2020) report the presence of cancer-associated fibroblasts (CAFs) in mycosis fungoides (MFs). They show that CAFs are abundant in early-stage MF and that they differ from normal fibroblasts. Moreover, CAFs are described to promote MF by increasing the motility and chemoresistance of malignant T cells. Thus, targeting CAFs in MF may be of therapeutic value.

Enhancing antitumor immunity through checkpoint blockade as a therapeutic strategy in T-cell lymphomas

The majority of historical therapies for managing T-cell lymphomas (TCLs) have consisted of T-cell-depleting strategies. Unfortunately, these forms of therapies can hamper the ability to mount effective antitumor immune responses. Recently, the use of checkpoint inhibitors has revolutionized the therapy of solid and hematologic malignancies. The development of immunotherapies for the management of TCL has lagged behind other malignancies given 2 central reasons: (1) the competing balance of depleting malignant T cells while simultaneously enhancing an antitumor T-cell response and (2) concern for tumor hyperprogression by blocking inhibitory signals on the surface of the malignant T cell, thereby leading to further proliferation of the malignant cells. These challenges were highlighted with the discovery that programmed cell death protein 1 (PD-1) functions paradoxically as a haploinsufficient tumor suppressor in preclinical TCL models. In contrast, some preclinical and clinical evidence suggests that PD-1/programmed death ligand 1 may become an important therapeutic tool in the management of patients with TCL. Improved understanding of the immune landscape of TCL is necessary in order to identify subsets of patients most likely to benefit from checkpoint-inhibitor therapy. With increased preclinical research focus on the tumor microenvironment, substantial strides are being made in understanding how to harness the power of the immune system to treat TCLs. In this review, designed to be a "call to action," we discuss the challenges and opportunities of using immune-modulating therapies, with a focus on checkpoint inhibitors, for the treatment of patients with TCL.

Platform independent protein-based cell-of-origin subtyping of diffuse large B-cell lymphoma in formalin-fixed paraffin-embedded tissue

Diffuse large B-cell lymphoma (DLBCL) is commonly classified by gene expression profiling according to its cell of origin (COO) into activated B-cell (ABC)-like and germinal center B-cell (GCB)-like subgroups. Here we report the application of label-free nano-liquid chromatography - Sequential Window Acquisition of all THeoretical fragment-ion spectra - mass spectrometry (nanoLC-SWATH-MS) to the COO classification of DLBCL in formalin-fixed paraffin-embedded (FFPE) tissue. To generate a protein signature capable of predicting Affymetrix-based GCB scores, the summed log₂-transformed fragment ion intensities of 780 proteins quantified in a training set of 42 DLBCL cases were used as independent variables in a penalized zero-sum elastic net regression model with variable selection. The eight-protein signature obtained showed an excellent correlation (r = 0.873) between predicted and true GCB scores and yielded only 9 (21.4%) minor discrepancies between the three classifications: ABC, GCB, and unclassified. The robustness of the model was validated successfully in two independent cohorts of 42 and 31 DLBCL cases, the latter cohort comprising only patients aged >75 years, with Pearson correlation coefficients of 0.846 and 0.815, respectively, between predicted and NanoString nCounter based GCB scores. We further show that the 8-protein signature is directly transferable to both a triple quadrupole and a Q Exactive quadrupole-Orbitrap mass spectrometer, thus obviating the need for proprietary instrumentation and reagents. This method may therefore be used for robust and competitive classification of DLBCLs on the protein level.

Novel Immunotherapies for T Cell Lymphoma and Leukemia

PURPOSE OF REVIEW

Novel immunotherapies such as checkpoint inhibitors, bispecific antibodies, and chimeric antigen receptor T cells are leading to promising responses when treating solid tumors and hematological malignancies. T cell neoplasms include leukemia and lymphomas that are derived from T cells and overall are characterized by poor clinical outcomes. This review describes the rational and preliminary results of immunotherapy for patients with T cell lymphoma and leukemia.

RECENT FINDINGS

For T cell neoplasms, despite significant research effort, only few agents, such as monoclonal antibodies and allogeneic stem cell transplantation, showed some clinical activity. One of the major hurdles to targeting T cell neoplasms is that activation or elimination of T cells, either normal or neoplastic, can cause significant toxicity. A need to develop novel safe and effective immunotherapies for T cell neoplasms exists. In this review, we will discuss the rationale for immunotherapy of T cell leukemia and lymphoma and present the most recent therapeutic approaches.

New Therapies and Immunological Findings in Cutaneous T-Cell Lymphoma

Primary cutaneous lymphomas comprise a group of lymphatic malignancies that occur primarily in the skin. They represent the second most common form of extranodal non-Hodgkin’s lymphoma and are characterized by heterogeneous clinical, histological, immunological, and molecular features. The most common type is mycosis fungoides and its leukemic variant, Sézary syndrome. Both diseases are considered T-helper cell type 2 (Th2) diseases. Not only the tumor cells but also the tumor microenvironment can promote Th2 differentiation, which is beneficial for the tumor cells because a Th1 environment enhances antitumor immune responses. This Th2-dominant milieu also underlies the infectious susceptibility of the patients. Many components, such as tumor-associated macrophages, cancer-associated fibroblasts, and dendritic cells, as well as humoral factors, such as chemokines and cytokines, establish the tumor microenvironment and can modify tumor cell migration and proliferation. Multiagent chemotherapy often induces immunosuppression, resulting in an increased risk of serious infection and poor tolerance. Therefore, overtreatment should be avoided for these types of lymphomas. Interferons have been shown to increase the time to next treatment to a greater degree than has chemotherapy. The pathogenesis and prognosis of cutaneous T-cell lymphoma (CTCL) differ markedly among the subtypes. In some aggressive subtypes of CTCLs, such as primary cutaneous gamma/delta T-cell lymphoma and primary cutaneous CD8⁺ aggressive epidermotropic cytotoxic T-cell lymphoma, hematopoietic stem cell transplantation should be considered, whereas overtreatment should be avoided with other, favorable subtypes. Therefore, a solid understanding of the pathogenesis and immunological background of cutaneous lymphoma is required to better treat patients who are inflicted with this disease. This review summarizes the current knowledge in the field to attempt to achieve this objective.

Novel B7-H4-mediated crosstalk between human non-Hodgkin lymphoma cells and tumor-associated macrophages leads to immune evasion via secretion of IL-6 and IL-10

Non-Hodgkin lymphoma (NHL) is an incurable lymphoproliferative cancer, and patients with NHL have a poor prognosis. The present study explored the regulatory mechanism of expression and possible roles of the immunosuppressive B7-H4 molecule in human NHL. For functional studies, NHL-reactive T cell lines were generated via the isolation of allogeneic CD3+ T cells from healthy donors and repeated in vitro stimulation with irradiated NHL cells isolated from patients. B7-H4 was found to be distributed in NHL cells and tissues, and its surface protein expression levels were further upregulated by the incubation of NHL cells with interleukin (IL)-6, IL-10, or interferon-γ. Additionally, the supernatants of tumor-associated macrophages (tMφs) upregulated B7-H4 surface expression by producing IL-6 and IL-10. B7-H4 expressed in NHL cells inhibited the cytotoxic activity of NHL-reactive T cells. Conversely, the inhibition of B7-H4 in NHL cells promoted T cell immunity and sensitized NHL cells to cytolysis. Furthermore, tMφs induced B7-H4 promoted NHL cell evasion of the T cell immune response. In conclusion, this study shows that NHL-expressed B7-H4 is an important immunosuppressive factor that inhibits host anti-tumor immunity to NHL. Targeting tumor-expressed B7-H4 may thus provide a new treatment strategy for NHL patients.

T-cell lymphomas, a challenging disease: types, treatments, and future

T-cell lymphomas are rare and aggressive malignancies associated with poor outcome, often because of the development of resistance in the lymphoma against chemotherapy as well as intolerance in patients to the established and toxic chemotherapy regimens. In this review article, we discuss the epidemiology, pathophysiology, current standard of care, and future treatments of common types of T-cell lymphomas, including adult T-cell leukemia/lymphoma, angioimmunoblastic T-cell lymphoma, anaplastic large-cell lymphoma, aggressive NK/T-cell lymphoma, and cutaneous T-cell lymphoma.