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Mogamulizumab is a humanized monoclonal antibody that targets C-C chemokine receptor 4 (CCR4) present on certain T cells in lymphomas and leukemias. This antibody-based therapy has demonstrated efficacy in treating various cutaneous T cell lymphomas (CTCLs), including mycosis fungoides and Sézary syndrome, through the depletion of CCR4-expressing T cells by antibody-dependent cellular cytotoxicity (ADCC). However, the precise epitope and binding mode of mogamulizumab responsible for its augmented ADCC activity remain undisclosed. Here, X-ray crystallographic studies of mogamulizumab in complex with a 28-residue N-terminal peptide indicated that SIYSNYYLYES (residues 14–24) would constitute the antibody epitope. Another high-resolution structure, using a short core peptide of these 11 residues, has elucidated unambiguous electron density for the bound peptide, confirming consistent binding for both peptides. This linear epitope is located in the membrane-proximal region of CCR4, facilitating the Fc-mediated effector functions, including ADCC. The structures also provide insights into the molecular basis for the resistance of the CCR4 L21V variant to mogamulizumab, which is due to a lack of structural complementarity with mogamulizumab binding. Understanding the structural basis for the mechanism of action of mogamulizumab is crucial for optimizing anti-CCR4 therapeutics to improve treatment outcomes for patients with these challenging diseases.

Elevated expression of the chemokine receptor CCR4 in tumors is associated with poor prognosis in several cancers. Here, we have determined that CCR4 was highly expressed in human renal cell carcinoma (RCC) biopsies and observed abnormal levels of CCR4 ligands in RCC patient plasma. An antagonistic anti-CCR4 antibody had antitumor activity in the RENCA mouse model of RCC. CCR4 inhibition did not reduce the proportion of infiltrating leukocytes in the tumor microenvironment but altered the phenotype of myeloid cells, increased NK cell and Th1 cytokine levels, and reduced immature myeloid cell infiltrate and blood chemokine levels. In spite of prominent changes in the myeloid compartment, the anti-CCR4 antibody did not affect RENCA tumors in T cell-deficient mice, and treatment with an anti-class II MHC antibody abrogated its antitumor activity. We concluded that the effects of the anti-CCR4 antibody required the adaptive immune system and CD4+ T cells. Moreover, CCL17-induced IFN-γ production was reduced when Th1-polarized normal CD4+ T cells were exposed to the CCR4 ligand, evidencing the involvement of CCR4 in Th1/Th2 regulation. The anti-CCR4 antibody, alone or in combination with other immune modulators, is a potential treatment approach to human solid cancers with high levels of CCR4-expressing tumor-infiltrating leukocytes and abnormal plasma CCR4 ligand levels.

Infiltrating T-regulatory cells in the tumor microenvironment is a key impediment to immunotherapy and is linked to a poor prognosis. We found that tumor-infiltrating Tregs express a higher expression of the chemokine receptor CCR4 than peripheral Tregs in breast cancer patients. CCL22 and CCL17 are released by tumor cells and tumor-associated macrophages, attracting CCR4 + Tregs to the tumor site. The Treg lineage-specific transcription factor FOXP3 changes the CCR4 promoter epigenetically in conjunction with HAT1 to provide a space for FOXP3 binding and activation of the CCR4 gene. To increase CCR4 expression in Tregs, the FOXP3/HAT1 axis is required for permissive (K23 and K27) or repressive (K14 and K18) acetylation of histone-3. In murine breast and melanoma tumor models, genetic ablation of FOXP3 reduced CCR4 + Treg infiltration and tumor size while also restoring anti-tumor immunity. Overexpression of FOXP3, on the other hand, increased CCR4 + Treg infiltration, resulting in a decreased anti-tumor immune response and tumor progression. These findings point to FOXP3 playing a new role in the tumor microenvironment as a transcriptional activator of CCR4 and a regulator of Treg infiltration.

ObjectiveDendritic cells (DC) mediate intestinal immune tolerance. Despite striking differences between the colon and the ileum both in function and bacterial load, few studies distinguish between properties of immune cells in these compartments. Furthermore, information of gut DC in humans is scarce. We aimed to characterise human colonic versus ileal DC.DesignHuman DC from paired colonic and ileal samples were characterised by flow cytometry, electron microscopy or used to stimulate T cell responses in a mixed leucocyte reaction.ResultsA lower proportion of colonic DC produced pro-inflammatory cytokines (tumour necrosis factor-α and interleukin (IL)-1β) compared with their ileal counterparts and exhibited an enhanced ability to generate CD4+FoxP3+IL-10+ (regulatory) T cells. There were enhanced proportions of CD103+Sirpα− DC in the colon, with increased proportions of CD103+Sirpα+ DC in the ileum. A greater proportion of colonic DC subsets analysed expressed the lymph-node-homing marker CCR7, alongside enhanced endocytic capacity, which was most striking in CD103+Sirpα+ DC. Expression of the inhibitory receptor ILT3 was enhanced on colonic DC. Interestingly, endocytic capacity was associated with CD103+ DC, in particular CD103+Sirpα+ DC. However, expression of ILT3 was associated with CD103− DC. Colonic and ileal DC differentially expressed skin-homing marker CCR4 and small-bowel-homing marker CCR9, respectively, and this corresponded to their ability to imprint these homing markers on T cells.ConclusionsThe regulatory properties of colonic DC may represent an evolutionary adaptation to the greater bacterial load in the colon. The colon and the ileum should be regarded as separate entities, each comprising DC with distinct roles in mucosal immunity and imprinting.

Objectives Interleukin (IL)-21 is mainly produced by CD4 T helper (Th) cells including Th2, Th17 and follicular helper T (Tfh) cells. Recent studies have reported that IL-21 is involved in the formation of germinal centres (GCs) and class switching of IgG4. It has been suggested that IgG4-related dacryoadenitis and sialoadenitis (IgG4-DS), so-called Mikulicz's disease (MD), is distinct from Sjögren's syndrome (SS) and shows a high frequency of GC formation in salivary glands. In this study the expression of IL-21 in IgG4-DS and SS patients was examined. Methods Twelve patients with IgG4-DS, 15 with SS and 15 healthy subjects were screened for (1) ectopic GC formation in formalin-fixed labial salivary gland (LSG) biopsy samples; (2) expression of IL-21, Th2-, Th17- and Tfh-related molecules (cytokines, chemokine receptors and transcription factors) in LSGs; (3) relationship between IgG4/IgG ratio and mRNA expression of IL-21 in LSGs. Results mRNA expression of IL-21 and Bcl-6 in LSGs from patients with IgG4-DS was significantly higher than in patients with SS and controls. IL-21 and CXCR5 were detected by immunohistochemistry in or around GC in patients with SS and those with IgG4-DS. IL-21 was detected in infiltrating lymphocytes outside GC only in patients with IgG4-DS. Expression of IL-21 was consistent with that of Th2-related molecules while IL-17 was rarely seen in IgG4-DS. Furthermore, the expression of IL-21 in LSGs was correlated with the number of GC formations and the IgG4/IgG ratio in patients with IgG4-DS. Conclusions These results suggest that overexpression of IL-21 by Th2 cells might play a key role in GC formation and IgG4 production in IgG4-DS.

CCR4 is expressed on tumor cells of most patients with adult T-cell leukemia/lymphoma (ATL). Gain-of-function mutations of the CCR4 gene in ATL patients may be associated with alterations at the carboxyl terminus, a finding which led to a high efficacy anti-CCR4 antibody, mogamulizumab. Only a few studies have reported CCR4 protein expression and genomic CCR4 mutations in non-ATL T/NK-cell lymphomas. Furthermore, an association between CCR4 protein expression, genomic CCR4 mutations, and transcript CCR4 mutations has not been well analyzed. The T/NK-cell lymphomas (n = 226) enrolled in this study were examined for CCR4 expression by immunohistochemistry. CCR4 mutations in the codons 322–348 were detected by direct sequencing and a SNaPshot Multiplex assay. CCR4 protein expression was positive in 48/52 (92%) and 58/174 (33%) of ATL and non-ATL cases, respectively, and genomic CCR4 mutations were detected in 17/52 (33%) and 6/174 (3.4%), respectively. While all 17 ATL cases with genomic CCR4 mutations were positive for CCR4 protein expression, five of six mutated non-ATL cases were negative for CCR4 protein expression and transcript CCR4 mutations. This study suggests that frequencies of CCR4 expression and genomic CCR4 mutations and an association between the two may be considerably different between ATL cases and non-ATL T/NK-cell lymphomas.

CD4 ⁺ Treg cells expressing the transcription factor FOXP3 (forkhead box P3) are abundant in tumor tissues and appear to hinder the induction of effective antitumor immunity. A substantial number of T cells, including Treg cells, in tumor tissues and peripheral blood express C-C chemokine receptor 4 (CCR4). Here we show that CCR4 was specifically expressed by a subset of terminally differentiated and most suppressive CD45RA ⁻FOXP3 ʰⁱCD4 ⁺ Treg cells [designated effector Treg (eTreg) cells], but not by CD45RA ⁺FOXP3 ˡᵒCD4 ⁺ naive Treg cells, in peripheral blood of healthy individuals and cancer patients. In melanoma tissues, CCR4 ⁺ eTreg cells were predominant among tumor-infiltrating FOXP3 ⁺ T cells and much higher in frequency compared with those in peripheral blood. With peripheral blood lymphocytes from healthy individuals and melanoma patients, ex vivo depletion of CCR4 ⁺ T cells and subsequent in vitro stimulation of the depleted cell population with the cancer/testis antigen NY-ESO-1 efficiently induced NY-ESO-1–specific CD4 ⁺ T cells. Nondepletion failed in the induction. The magnitude of the responses was comparable with total removal of FOXP3 ⁺ Treg cells by CD25 ⁺ T-cell depletion. CCR4 ⁺ T-cell depletion also augmented in vitro induction of NY-ESO-1–specific CD8 ⁺ T cells in melanoma patients. Furthermore, in vivo administration of anti-CCR4 mAb markedly reduced the eTreg-cell fraction and augmented NY-ESO-1–specific CD8 ⁺ T-cell responses in an adult T-cell leukemia-lymphoma patient whose leukemic cells expressed NY-ESO-1. Collectively, these findings indicate that anti-CCR4 mAb treatment is instrumental for evoking and augmenting antitumor immunity in cancer patients by selectively depleting eTreg cells.

Human T-lymphotropic virus type 1 (HTLV-1) is linked to multiple diseases, including the neuroinflammatory disease HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and adult T cell leukemia/lymphoma. Evidence suggests that HTLV-1, via the viral protein Tax, exploits CD4+ T cell plasticity and induces transcriptional changes in infected T cells that cause suppressive CD4+CD25+CCR4+ Tregs to lose expression of the transcription factor FOXP3 and produce IFN-γ, thus promoting inflammation. We hypothesized that transformation of HTLV-1-infected CCR4+ T cells into Th1-like cells plays a key role in the pathogenesis of HAM/TSP. Here, using patient cells and cell lines, we demonstrated that Tax, in cooperation with specificity protein 1 (Sp1), boosts expression of the Th1 master regulator T box transcription factor (T-bet) and consequently promotes production of IFN-γ. Evaluation of CSF and spinal cord lesions of HAM/TSP patients revealed the presence of abundant CD4+CCR4+ T cells that coexpressed the Th1 marker CXCR3 and produced T-bet and IFN-γ. Finally, treatment of isolated PBMCs and CNS cells from HAM/TSP patients with an antibody that targets CCR4+ T cells and induces cytotoxicity in these cells reduced both viral load and IFN-γ production, which suggests that targeting CCR4+ T cells may be a viable treatment option for HAM/TSP.

CC chemokine receptor 4 (CCR4) has attracted much attention as a promising therapeutic drug target for CCR4+ tumor cells and Tregs. CCR4 is expressed on some tumor cells such as T-cell acute lymphoblastic leukemia (ALL), adult T-cell leukemia/lymphoma (ATLL), adult peripheral T cell lymphoma (PTCL) and cutaneous T cell lymphoma (CTCL). CCR4 is also expressed on majority of Tregs, mainly effector Tregs. In this study we have successfully developed three versions of diphtheria-toxin based anti-human CCR4 immunotoxins (monovalent, bivalent and single-chain fold-back diabody). Binding analysis by flow cytometry showed that all three versions of the anti-human CCR4 immunotoxins bound to the human CCR4+ tumor cell line as well as CCR4+ human PBMC. The bivalent isoform bound stronger than its monovalent counterpart and the single-chain foldback diabody isoform was the strongest among the three versions. In vitro efficacy analysis demonstrated that the bivalent isoform was 20 fold more potent in inhibiting cellular proliferation and protein synthesis in human CCR4+ tumor cells compared to the monovalent anti-human CCR4 immunotoxin. The single-chain fold-back diabody isoform was 10 fold more potent than its bivalent counterpart and 200 fold more potent than its monovalent counterpart. The in vivo efficacy was assessed using a human CCR4+ tumor-bearing mouse model. The immunotoxin significantly prolonged the survival of tumor-bearing NOD/SCID IL-2 receptor γ−/− (NSG) mice injected with human CCR4+ acute lymphoblastic leukemia cells compared with the control group. This novel anti-human CCR4 immunotoxin is a promising drug candidate for targeting human CCR4+ tumor cells and Tregs in vivo. •An anti-human CCR4 immunotoxin was expressed and purified in Pichia Pastoris.•In vitro binding affinity was characterized by flow cytometry.•In vitro efficacy was characterized using protein synthesis inhibition assay.•In vivo efficacy was assessed using CCR4+ tumor-bearing NSG mouse model.•This immunotoxin is a promising drug candidate for targeting CCR4+ tumors and Tregs.

Triple-negative breast cancer (TNBC) is particularly aggressive, with enhanced incidence of tumor relapse, resistance to chemotherapy, and metastases. As the mechanistic basis for this aggressive phenotype is unclear, treatment options are limited. Here, we showed an increased population of myeloid-derived immunosuppressor cells (MDSCs) in TNBC patients compared with non-TNBC patients. We found that high levels of the transcription factor ΔNp63 correlate with an increased number of MDSCs in basal TNBC patients, and that ΔNp63 promotes tumor growth, progression, and metastasis in human and mouse TNBC cells. Furthermore, we showed that MDSC recruitment to the primary tumor and metastatic sites occurs via direct ΔNp63-dependent activation of the chemokines CXCL2 and CCL22. CXCR2/CCR4 inhibitors reduced MDSC recruitment, angiogenesis, and metastasis, highlighting a novel treatment option for this subset of TNBC patients. Finally, we found that MDSCs secrete prometastatic factors such as MMP9 and chitinase 3-like 1 to promote TNBC cancer stem cell function, thereby identifying a nonimmunologic role for MDSCs in promoting TNBC progression. These findings identify a unique crosstalk between ΔNp63+ TNBC cells and MDSCs that promotes tumor progression and metastasis, which could be exploited in future combined immunotherapy/chemotherapy strategies for TNBC patients.