As a novel toll-like receptor 9 (TLR9) agonist, synthetic unmethylated cytosine-phosphate-guanine (CpG) oligodeoxynucleotides can stimulate a Th1 immune response and potentially be used as therapeutic agents or vaccine adjuvants for the treatment of cancer. However, some drawbacks of CpG limit their applications, such as rapid elimination by nuclease-mediated degradation and poor cellular uptake. Therefore, repeat high-dose drug administration is required for treatment. In this work, a CpG delivery system based on 3-aminopropyltriethoxysilane (APTES)-modified Fe3O4 nanoparticles (FeNPs) was designed and studied for the first time to achieve better bioactivity of CpG. In our results, we designed FeNP-delivered CpG particles (FeNP/CpG) with a small average size of approximately 50 nm by loading CpG into FeNPs. The FeNP/CpG particle delivery system, with enhanced cell uptake of CpG in bone marrow-derived dendritic cells (BMDCs) in vitro and through intratumoral injection, showed significant antitumor ability by stimulating better humoral and cellular immune responses in C26 colon cancer and 4T1 breast cancer xenograft models in vivo over those of free CpG. Moreover, mice treated by FeNP/CpG particles had delayed tumor growth with an inhibitory rate as high as 94.4%. In addition, approximately 50% of the tumors in the C26 model appeared to regress completely. Similarly, there were lower pulmonary metastases and a 69% tumor inhibitory rate in the 4T1 breast cancer tumor model than those in the untreated controls. In addition to their effectiveness, the easy preparation, safety, and high stability of FeNP/CpG particles also make them an attractive antitumor immunotherapy.

Granzyme B is a renowned effector molecule primarily utilized by CTLs and NK cells against ill-defined and/or transformed cells during immunosurveillance. The overall expression of granzyme B within tumor microenvironment has been well-established as a prognostic marker indicative of priming immunity for a long time. Until recent years, increasing immunosuppressive effects of granzyme B are unveiled in the setting of different immunological context. The accumulative evidence confounded the roles of granzyme B in immune responses, thereby arousing great interests in characterizing detailed feature of granzyme B-positive niche. In this paper, the granzyme B-related regulatory effects of major suppressor cells as well as the tumor microenvironment that defines such functionalities were longitudinally summarized and discussed. Multiplex networks were built upon the interactions among different transcriptional factors, cytokines, and chemokines that regarded to the initiation and regulation of granzyme B-mediated immunosuppression. The conclusions and prospect may facilitate better interpretations of the clinical significance of granzyme B, guiding the rational development of therapeutic regimen and diagnostic probes for anti-tumor purposes.