Date Published: March 25, 2018
Publisher: John Wiley and Sons Inc.
Author(s): Yan Li, Lianghua He, Haiqing Dong, Yiqiong Liu, Kun Wang, Ang Li, Tianbin Ren, Donglu Shi, Yongyong Li.
Although there have been more than 100 clinical trials, CpG‐based immunotherapy has been seriously hindered by complications in the immunosuppressive microenvironment of established tumors. Inspired by the decisive role of fever upon systemic immunity, a photothermal CpG nanotherapeutics (PCN) method with the capability to induce an immunofavorable tumor microenvironment by casting a fever‐relevant heat (43 °C) in the tumor region is developed. High‐throughput gene profile analysis identifies nine differentially expressed genes that are closely immune‐related upon mild heat, accompanied by IL‐6 upregulation, a pyrogenic cytokine usually found during fever. When treated with intratumor PCN injection enabling mild heating in the tumor region, the 4T1 tumor‐bearing mice exhibit significantly improved antitumor immune effects compared with the control group. Superb efficacy is evident from pronounced apoptotic cell death, activated innate immune cells, enhanced tumor perfusion, and intensified innate and adaptive immune responses. This work highlights the crucial role of mild heat in modulating the microenvironment in optimum for improved immunotherapy, by converting the tumor into an in situ vaccine.
Despite some technical breakthroughs in cancer treatment, reliable cure is still limited within the conventional methods such as surgery, chemotherapy, and radiotherapy. Among several novel cancer therapeutics, immunotherapy has recently been the center of attention in both basic medical science and clinical research communities, for its effectiveness, specificity, and adaptation to highly variant disease conditions.1, 2 The major immunotherapeutic approaches include checkpoint molecules programmed cell death 1 (PD‐1), programmed cell death ligand 1 (PD‐L1), and cytotoxic T‐lymphocyte antigen 4 (CTLA4). Immunotherapy adjuvant with CpG as Toll‐like receptor (TLR) agonists is capable of activating an innate immune response to potentiate vaccine‐specific immunity.3, 4 More than 100 clinical trials have been carried out involving CpG oligodeoxynucleotides (CpG ODN) as adjuvants and shown to be clinically effective.3 However, the drawback of CpG ODN‐based immunotherapy is the short‐termed benefits in patients, therefore not particularly viable and useful in a clinic setting.4 The inadequate efficacy is likely associated with the tumor microenvironment being detrimental to the immune system.3 The key to address this critical issue is, therefore, to modify the microenvironment toward immune activation that effectively enhances immunotherapy.
CpG has been shown to induce a Th1‐biased immune response and support CD8+ T cell responses, enabling them to be the promising adjuvants for cancer vaccines.33, 34, 35 However, the tumor elimination efficiency of CpG‐based vaccines is usually counteracted by the immunosuppressive microenvironment of the established tumors. It is, therefore, critical to develop a new approach that offsets the original balance and establishes a microenvironment favorable to the tumoricidal activity. An immunofavorable tumor microenvironment can be established via fever‐like immunoresponse induced by the photothermal effect of PCN (Figure6).
A highly versatile, integrative PCN nanosystem was developed by a convenient approach to coordinate with tumor microenvironment and reverse the tumor suppressive condition. This study highlighted the critical role of fever‐like heat in an immunofavorable microenvironment that significantly improved the efficiency of CpG‐based immunotherapies. Analysis of genetic profile demonstrated immune‐related DEGs that closely correlated with tumor microenvironment including immune cell recruitment (CCL8) and trafficking (ICAM‐1). The fever‐inspired strategy has been shown successful to enhance the innate and adaptive immune response, a critical bioprocess in tumor immunotherapy. This unique approach is therefore directly converting the tumor into an in situ vaccine by creating a microenvironment favorable for the vaccine to exert its immune effect.
Materials: Unless otherwise indicated, all chemicals were purchased from Sigma‐Aldrich. The thiol–CpG 1826(5′‐TCC ATG ACG TTC CTG ACG TT‐3′) was purchased from Sangon Biotech Ltd. (Shanghai, China). APC‐conjugated anti‐mouse CD11c, PE‐conjugated anti‐mouse CD86, PE‐conjugated anti‐mouse CD40, FITC‐conjugated anti‐mouse CD80, FITC‐conjugated anti‐mouse I‐A/I‐E, APC‐conjugated CD3, FITC/Percp Cy5.5‐conjugated anti‐mouse CD8a, efluor 450‐conjugated anti‐mouse CD4, and purified anti‐mouse CD16/CD32 antibodies against cell surface markers for flow cytometry assay and ELISA kits were purchased from eBioscience (San Diego, CA). Fetal bovine serum (FBS), Dulbecco’s modified Eagle’s medium (DMEM), penicillin‐streptomycin, trypsin, and Dulbecco’s phosphate‐buffered saline (DPBS) were supplied by Gibco Invitrogen Corp. Co. Ltd. Annexin V‐FITC Apoptosis Detection Kit was obtained from Beyotime Institute of Biotechnology. Paraformaldehyde (4%) was obtained from DingGuo Chang Sheng Biotech.
The authors declare no conflict of interest.