Extranodal natural killer (NK)/T-cell lymphoma, nasal type (NNKTL) has very unique epidemiological, etiologic, histologic, and clinical characteristics. It is commonly observed in Eastern Asia, but quite rare in the United States and Europe. The progressive necrotic lesions mainly in the nasal cavity, poor prognosis caused by rapid local progression with distant metastases, and angiocentric and polymorphous lymphoreticular infiltrates are the main clinical and histologic features. Phenotypic and genotypic studies revealed that the lymphoma is originated from either NK- or γδ T-cell, both of which express CD56. In 1990, the authors first reported the presence of Epstein-Barr virus (EBV)-DNA and EBV-oncogenic proteins, and EBV has now been recognized to play an etiological role in NNKTL. in vitro studies revealed that a wide variety of cytokines, chemokines, and micro RNAs, which may be produced by EBV-oncogenic proteins in the lymphoma cells, play important roles for tumor progression in NNKTL, and could be therapeutic targets. In addition, it was revealed that the interaction between NNKTL cells and immune cells such as monocytes and macrophages in NNKTL tissues contribute to lymphoma progression. For diagnosis, monitoring the clinical course and predicting prognosis, the measurements of EBV-DNAs and EBV-micro RNAs in sera are very useful. For treatment with early stage, novel concomitant chemoradiotherapy such as DeVIC regimen with local radiotherapy and MPVIC-P regimen using intra-arterial infusion developed with concomitant radiotherapy and the prognosis became noticeably better. However, the prognosis of patients with advanced stage was still poor. Establishment of novel treatments such as the usage of immune checkpoint inhibitor or peptide vaccine with molecular targeting therapy will be necessary. This review addresses recent advances in the molecular understanding of NNKTL to establish novel treatments, in addition to the epidemiologic, clinical, pathological, and EBV features.

Stimulator of IFN genes (STING) spontaneously contributes to anti-tumor immunity by inducing type I interferons (IFNs) following sensing of tumor-derived genomic DNAs in the tumor-bearing host. Although direct injection of STING ligands such as cyclic diguanylate monophosphate (c-di-GMP) and cyclic [G(2',5')pA(3',5')p] (cGAMP) into the tumor microenvironment exerts anti-tumor effects through strong induction of type I IFNs and activation of innate and adaptive immunity, the precise events caused by STING in the tumor microenvironment remain to be elucidated. We describe here our finding that a CD45 CD11b Ly6C cell subset transiently accumulated in mouse tumor microenvironment of 4T1 breast cancer, squamous cell carcinomas, CT26 colon cancer, or B16F10 melanoma tissue after intratumoral injection of cGAMP. The accumulated cells displayed a macrophage (M ) phenotype since the cells were positive for F4/80 and MHC class II and negative for Ly6G. Intratumoral cGAMP treatment did not induce Mφ accumulation in STING-deficient mice. Depletion of CD8 T cell using anti-CD8 mAb impaired the anti-tumor effects of cGAMP treatment. Depletion of the Mφ using clodronate liposomes impaired the anti-tumor effects of cGAMP treatment. Functional analysis indicated that the STING-triggered tumor-migrating Mφ exhibited phagocytic activity, production of tumor necrosis factor alpha TNFα), and high expression levels of T cell-recruiting chemokines, Cxcl10 and Cxcl11, IFN-induced molecules, MX dynamin-like GTPase 1 (Mx1) and 2'-5' oligoadenylate synthetase-like 1 (Oasl1), nitric oxide synthase 2 (Nos2), and interferon beta 1 (Ifnb1). These results indicate that the STING-triggered tumor-migrating Mφ participate in the anti-tumor effects of STING-activating compounds.

Nasal natural killer/T-cell lymphoma (NNKTL) is an aggressive neoplasm with poor therapeutic responses and prognosis. The programmed death-1/programmed death-ligand 1 (PD-1/PD-L1) pathway plays an important role in immune evasion of tumor cells through T-cell exhaustion. The aim of the present study was to examine the expression of PD-L1 and PD-1 molecules in NNKTL. We detected the expression of PD-L1 in biopsy samples from all of the NNKTL patients studied. PD-L1 was found on both malignant cells and tumor-infiltrating macrophages, while PD-1-positive mononuclear cells infiltrated the tumor tissues in 36% of patients. Most significantly, soluble PD-L1 (sPD-L1) was present in sera of NNKTL patients at higher levels as compared to healthy individuals and the levels of serum sPD-L1 in patients positively correlated with the expression of PD-L1 in lymphoma cells of tumor tissues. In addition, the high-sPD-L1 group of patients showed significantly worse prognosis than the low-sPD-L1 group. Furthermore, we confirmed that membrane and soluble PD-L1 was expressed on the surface and in the culture supernatant, respectively, of NNKTL cell lines. The expression of PD-L1 was observed in tumor tissues and sera from a murine xenograft model inoculated with an NNKTL cell line. Our results suggest that sPD-L1 could be a prognostic predictor for NNKTL and open up the possibility of immunotherapy of this lymphoma using PD-1/PD-L1 axis inhibitors.

Synthetic peptide vaccines aim to elicit and expand tumor-specific T cells capable of controlling or eradicating the tumor. Despite the high expectations based on preclinical studies, the results of clinical trials using peptide vaccines have been disappointing. Thus, many researchers in the field have considered peptide vaccines as outdated and no longer viable for cancer therapy. However, recent progress in understanding the critical roles of immune adjuvants, modes of vaccine administration and T cell dynamics has lead to a rebirth of this approach and reconsidering the use of peptide vaccines for treating malignant disorders.