The use of therapeutic monoclonal antibody (mAb) for the treatment of cancer has evolved into a promising approach over the last several years [
1‐
6]. Antibodies of the human IgG1 isotype are commonly used for therapeutic applications as they can mediate multiple effector functions including antibody-dependent cellular cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and direct apoptosis induction [
7‐
9]. Of these, ADCC is an especially important mechanism of action of therapeutic mAb against tumor cells [
10‐
13]; therefore, a better understanding of ADCC will allow the development of novel, more effective treatment strategies using therapeutic mAbs. ADCC depends on the cytotoxic activity of immune effector cells, so to evaluate antitumor effects of therapeutic mAb in a small animal model in vivo, the species incompatibility of the immune system between humans and animals is a critical issue. Indeed, we have previously reported that the mouse effector system mediating the antitumor action of therapeutic mAb does differ from the human [
14,
15]. Thus, a current crucial problem in the field of human ADCC research is the lack of suitable small animal models. To overcome this, we attempted to establish “humanized mice”, in which human immune cells could mediate the antitumor action of the therapeutic mAb. In order to construct such “humanized mice”, here we tested NOD/Shi-
scid, IL-2Rγ
null (NOG) mice as recipients of human immune cells, because it has been reported that these mice have multiple immune dysfunctions, and that human immune cells can be engrafted in NOG mice and retain almost the same functions as in humans [
16,
17].
In the clinical field of hematological malignancies, the development of the therapeutic mAb rituximab has changed the standard therapy in patients with B-cell lymphomas [
1,
2], and has markedly improved their prognosis. In contrast, T-cell lymphomas have very poor prognoses, and no standard treatment strategies for these diseases have been developed so far [
18]. Because we previously found that CC chemokine receptor 4 (CCR4) is expressed on certain types of these tumors [
19,
20], we postulated that this molecule might represent a novel molecular target for immunotherapy against refractory T-cell lymphoma. Accordingly, we have developed a next-generation chimeric anti-CCR4 mAb, KM2760, the Fc region of which is defucosylated [
21], resulting in highly enhanced ADCC due to increased binding affinity to the Fcγ receptor (FcγR) on effector cells [
10,
15]. Importantly, based on our laboratory work on CCR4 [
10,
14,
15,
19,
20,
22‐
25], and as an outcome of the success of this translational research, we have conducted a phase I clinical trial of defucosylated humanized anti-CCR4 mAb in patients with CCR4-positive T-cell leukemia/lymphoma in Japan (clinical trials gov. identifier: NCT00355472). The KM2760 antibody can induce potent ADCC activity, whereas it does not mediate CDC, and has no anti-proliferative or direct apoptosis induction effect itself [
22]. Accordingly, here we use KM2760 as a therapeutic mAb to evaluate ADCC in our humanized NOG mouse model. We selected two different types of CCR4-expressing tumor cell lines as targets in our system. One, L-428, is a Hodgkin lymphoma (HL) cell line, characterized by high production of TARC/CCL17, a ligand of CCR4 [
23]. We have previously reported that KM2760 induced robust ADCC against L-428 by peripheral blood mononuclear cells (PBMC) from healthy individuals in vitro, and demonstrated a promising antitumor activity in the L-428-bearing non-humanized SCID mouse model [
14]. We also demonstrated that, in HL, specific ligands for CCR4 are produced by tumor cells, and then attract CCR4-expressing regulatory T (Treg) cells [
10,
26‐
29] to the tumor, where they create a favorable environment for HL tumor cells to survive despite host immune recognition [
23]. In addition, KM2760 could deplete CCR4-positive T-cells and inhibit CD4-positiveCD25-positive T-cell migration induced by interaction between CCR4 and its ligands, in vitro [
23]. Therefore, we here test KM2760-induced effects, using HL-bearing humanized NOG mice, against not only tumor cells but also HL tumor-infiltrating lymphocytes (TIL), in vivo. The other tumor cell line selected for study in this model is a cutaneous T-cell lymphoma (CTCL) cell line, HH. We have also previously reported that KM2760 induced robust ADCC by healthy donor PBMC against HH in vitro, and a promising antitumor activity in the HH-bearing non-humanized SCID mouse model as well [
30]. In the present study, we also tested KM2760-induced antitumor effects, using CTCL-bearing humanized NOG mice.