Foxp3-expressing CD25+CD4+ regulatory T cells (Tregs) are abundant in tumor tissues. Here, hypothesizing that tumor Tregs would clonally expand after they are activated by tumor-associated antigens to suppress antitumor immune responses, we performed single-cell analysis on tumor Tregs to characterize them by T cell receptor clonotype and gene-expression profiles. We found that multiclonal Tregs present in tumor tissues predominantly expressed the chemokine receptor CCR8. In mice and humans, CCR8+ Tregs constituted 30 to 80% of tumor Tregs in various cancers and less than 10% of Tregs in other tissues, whereas most tumor-infiltrating conventional T cells (Tconvs) were CCR8–. CCR8+ tumor Tregs were highly differentiated and functionally stable. Administration of cell-depleting anti-CCR8 monoclonal antibodies (mAbs) indeed selectively eliminated multiclonal tumor Tregs, leading to cure of established tumors in mice. The treatment resulted in the expansion of CD8+ effector Tconvs, including tumor antigen-specific ones, that were more activated and less exhausted than those induced by PD-1 immune checkpoint blockade. Anti-CCR8 mAb treatment also evoked strong secondary immune responses against the same tumor cell line inoculated several months after tumor eradication, indicating that elimination of tumor-reactive multiclonal Tregs was sufficient to induce memory-type tumor-specific effector Tconvs. Despite induction of such potent tumor immunity, anti-CCR8 mAb treatment elicited minimal autoimmunity in mice, contrasting with systemic Treg depletion, which eradicated tumors but induced severe autoimmune disease. Thus, specific removal of clonally expanding Tregs in tumor tissues for a limited period by cell-depleting anti-CCR8 mAb treatment can generate potent tumor immunity with long-lasting memory and without deleterious autoimmunity.

BackgroundThrombocytopenia is a common problem in the management of patients with cancer and other conditions that affect hematopoietic cells. In previous clinical trials, the polyethylene-glycolconjugated recombinant human megakaryocyte growth and development factor increased platelet counts in patients with idiopathic thrombocytopenic purpura and solid tumors undergoing chemotherapy. However, antibodies to polyethylene-glycol-conjugated recombinant human megakaryocyte growth and development factor develop in healthy volunteers and patients undergoing chemotherapy and cross-react with endogenous thrombopoietin. As a result, clinical development of polyethylene-glycol-conjugated recombinant human megakaryocyte growth and development factor was discontinued in 1998. The aim of this study was to identify an orally bioavailable human Mpl activator that does not develop autoantibodies against endogenous thrombopoietin.

Mannan-binding protein (MBP) is a C-type mammalian lectin specific for mannose and N-acetylglucosamine. MBP is mainly synthesized in the liver and occurs naturally in two forms, serum MBP (S-MBP) and intracellular MBP (I-MBP). S-MBP activates Mannan-binding protein (MBP),4 also known as mannanbinding lectin, is a Ca 2ϩ -dependent (C-type) mammalian lectin exhibiting primary specificity for mannose, fucose, and N-acetylglucosamine (1). Because its discovery as a vital serum component associated with innate immunity, this lectin has been regarded as a multifunctional protein. MBP occurs naturally in two forms, secretory serum MBP (S-MBP) and intracellular MBP, which is termed I-MBP in this study and was called liver MBP (L-MBP) in our previous studies (2-4). Human S-MBP and I-MBP are mainly synthesized in the liver and translated from a single form of mRNA. Both S-MBP and I-MBP are homooligomers composed of 32-kDa subunits. Each subunit has an NH 2 -terminal region containing cysteines involved in interchain disulfide bond formation, a collagen-like domain containing hydroxyproline and hydroxylysine residues, and a carbohydrate-recognition domain (CRD) with an amino acid sequence highly homologous to those of other C-type lectins (5). The CRD is specific for high-mannose oligosaccharide structures on exogenous and endogenous ligands, whereas the collagen-like domain is believed to be responsible for interactions with other effector proteins involved in host defense. S-MBP activates complement through interaction with three novel MBP-associated serine proteases, which is called the lectin pathway (6). Furthermore, S-MBP was shown to exhibit novel cytotoxic activity toward some in vivo colorectal carcinoma cell experiments, which we proposed to term MBP-dependent cell-mediated cytotoxicity (4, 7). However, little is known about the subcellular localization and physiological significance of I-MBP. Recently, the functions of glycoprotein glycan chains in protein quality control have been attracting more attention, highmannose-type oligosaccharides especially having been shown to play important roles in this process (8,9). Glycosylation with an asparagine-linked (N-linked) oligosaccharides is a co-translational process that occurs in the ER. High-mannose-type oligosaccharides, presumably representing nascent core-glycosylated proteins, are subsequently transferred to the Golgi

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