Macrophages play an important role in cancer development and metastasis. Proinflammatory M1 macrophages can phagocytose tumor cells, while anti-inflammatory M2 macrophages such as tumor-associated macrophages (TAMs) promote tumor growth and invasion. Modulating the tumor immune microenvironment through engineering macrophages is efficacious in tumor therapy. M1 macrophages target cancerous cells and, therefore, can be used as drug carriers for tumor therapy. Herein, the strategies to engineer macrophages for cancer immunotherapy, such as inhibition of macrophage recruitment, depletion of TAMs, reprograming of TAMs, and blocking of the CD47-SIRPα pathway, are discussed. Further, the recent advances in drug delivery using M1 macrophages, macrophage-derived exosomes, and macrophage-membrane-coated nanoparticles are elaborated. Overall, there is still significant room for development in macrophage-mediated immune modulation and macrophage-mediated drug delivery, which will further enhance current tumor therapies against various malignant solid tumors, including drug-resistant tumors and metastatic tumors.

Engineering Macrophages for Cancer Immunotherapy and Drug Delivery.

Adoptive cell therapy (ACT) with antigen-specific T cells has shown remarkable clinical success; however, approaches to safely and effectively augment T cell function, especially in solid tumors, remain of great interest. Here we describe a strategy to 'backpack' large quantities of supporting protein drugs on T cells by using protein nanogels (NGs) that selectively release these cargos in response to T cell receptor activation. We designed cell surface-conjugated NGs that responded to an increase in T cell surface reduction potential after antigen recognition and limited drug release to sites of antigen encounter, such as the tumor microenvironment. By using NGs that carried an interleukin-15 super-agonist complex, we demonstrated that, relative to systemic administration of free cytokines, NG delivery selectively expanded T cells 16-fold in tumors and allowed at least eightfold higher doses of cytokine to be administered without toxicity. The improved therapeutic window enabled substantially increased tumor clearance by mouse T cell and human chimeric antigen receptor (CAR)-T cell therapy in vivo.

Enhancing T cell therapy through TCR-signaling-responsive nanoparticle drug delivery

In recent years, conventional treatments including surgery, chemotherapy and radiotherapy have been the main approaches in tumour therapy. Cancer immunotherapy is a new therapeutic modality to fight cancer by harnessing the power of patients’ own immune system. Ongoing research related to these therapies has demonstrated their advantages and intrinsic limitations. Nanomaterial-based platforms are utilized in these emerging fields. In particular, a combination of other treatment methods with cancer immunotherapy to achieve precision medicine and prevent recurrence and metastasis, could improve patients’ outcome. The combined multiple treatments have superior efficacy to any monotherapy alone in producing improved anti-cancer activity. Therefore, it's necessary to summarise research advances in nanomaterial-based combination cancer immunotherapy contributing to clinical transformation. This review is based on the principles of cancer immunotherapy and the combined treatment design reflected by advances in materials science, including the structures of nanoplatforms and their underlying mechanisms towards cancer. The ultimate goals are to stimulate the design of better strategies for versatile use in the future based on biomaterial engineering methods to enhance the efficacy of combined cancer treatments, and to provide new ideas for the prospects of a synergistic cancer combination immunotherapy for clinical application transformation.

Recent advances in nanomaterial-based synergistic combination cancer immunotherapy.

Synthetic biology based on bacteria has been displayed in antitumor therapy and shown good performance. In this study, an engineered bacterium Escherichia coli MG1655 is designed with NDH-2 enzyme (respiratory chain enzyme II) overexpression (Ec-pE), which can colonize in tumor regions and increase localized H2 O2 generation. Following from this, magnetic Fe3 O4 nanoparticles are covalently linked to bacteria to act as a catalyst for a Fenton-like reaction, which converts H2 O2 to toxic hydroxyl radicals (•OH) for tumor therapy. In this constructed bioreactor, the Fenton-like reaction occurs with sustainably synthesized H2 O2 produced by engineered bacteria, and severe tumor apoptosis is induced via the produced toxic •OH. These results show that this bioreactor can achieve effective tumor colonization, and realize a self-supplied therapeutic Fenton-like reaction without additional H2 O2 provision.

Engineered Bacterial Bioreactor for Tumor Therapy via Fenton‐Like Reaction with Localized H 2 O 2 Generation

Colorectal cancer (CRC) is a heterogeneous disease of the intestinal epithelium that is characterized by the accumulation of mutations and a dysregulated immune response. Up to 90% of disease risk is thought to be due to environmental factors such as diet, which is consistent with a growing body of literature that describes an 'oncogenic' CRC-associated microbiota. Whether this dysbiosis contributes to disease or merely represents a bystander effect remains unclear. To prove causation, it will be necessary to decipher which specific taxa or metabolites drive CRC biology and to fully characterize the underlying mechanisms. Here we discuss the host-microbiota interactions in CRC that have been reported so far, with particular focus on mechanisms that are linked to intestinal barrier disruption, genotoxicity and deleterious inflammation. We further comment on unknowns and on the outstanding challenges in the field, and how cutting-edge technological advances might help to overcome these. More detailed mechanistic insights into the complex CRC-associated microbiota would potentially reveal avenues that can be exploited for clinical benefit.

Host-microbiota maladaptation in colorectal cancer.

The microbiota in the human gut is strongly correlated with the progression of colorectal cancer (CRC) and with therapeutic responses to CRC. Here, by leveraging the higher concentration of the pro-tumoural Fusobacterium nucleatum and the absence of antineoplastic butyrate-producing bacteria in the faecal microbiota of patients with CRC, we show that—in mice with orthotopic colorectal tumours or with spontaneously formed colorectal tumours—oral or intravenous administration of irinotecan-loaded dextran nanoparticles covalently linked to azide-modified phages that inhibit the growth of F. nucleatum significantly augments the efficiency of first-line chemotherapy treatments of CRC. We also show that oral administration of the phage-guided irinotecan-loaded nanoparticles in piglets led to negligible changes in haemocyte counts, immunoglobulin and histamine levels, and liver and renal functions. Phage-guided nanotechnology for the modulation of the gut microbiota might inspire new approaches for the treatment of CRC. Dextran nanoparticles loaded with a chemotherapeutic agent and bound to phages that eliminate a pro-tumoural gut bacterium and promote the growth of anticancer-compound-producing bacteria boost chemotherapy responses in mouse models of colorectal cancer.

Phage-guided modulation of the gut microbiota of mouse models of colorectal cancer augments their responses to chemotherapy.

To engineer patient-derived cells into therapy-purposed biologics is a promising solution to realize personalized treatments. Without using gene-editing technology, a live cell-typed therapeutic is engineered for tumor treatment by artificially reprogramming macrophages with hyaluronic acid-decorated superparamagnetic iron oxide nanoparticles (HIONs). This nanoparticle-assisted cell-reprogramming strategy demonstrates profound advantages, due to the combined contributions from the biological regulation of HIONs and the intrinsic nature of macrophages. Firstly, the reprogrammed macrophages present a substantial improvement in their innate capabilities, such as more effective tumor targeting and more efficient generation of bioactive components (e.g., reactive oxygen species, bioactive cytokines) to suppress tumor growth. Furthermore, this cell therapeutic exhibits cytostatic/proapoptotic effects specific to cancer cells. Secondly, HIONs enable macrophages more resistant to the intratumoral immunosuppressive environment. Thirdly, the macrophages are endowed with a strong ability to prime in situ protumoral M2 macrophages into antitumor M1 phenotype in a paracrine-like manner. Consequently, a synergistic tumor-inhibition effect is achieved. This study shows that engineering nanomaterial-reprogrammed live cells as therapeutic biologics may be a more preferable option to the commonly used approaches where nanomaterials are administrated to induce bioresponse of certain cells in vivo.

Artificially Reprogrammed Macrophages as Tumor-Tropic Immunosuppression-Resistant Biologics to Realize Therapeutics Production and Immune Activation.

Mounting evidence suggests that the gut microbiota contribute to colorectal cancer (CRC) tumorigenesis, in which the symbiotic Fusobacterium nucleatum (Fn) selectively increases immunosuppressive myeloid-derived suppressor cells (MDSCs) to hamper the host’s anticancer immune response. Here, a specifically Fn-binding M13 phage was screened by phage display technology. Then, silver nanoparticles (AgNP) were assembled electrostatically on its surface capsid protein (M13@Ag) to achieve specific clearance of Fn and remodel the tumor-immune microenvironment. Both in vitro and in vivo studies showed that of M13@Ag treatment could scavenge Fn in gut and lead to reduction in MDSC amplification in the tumor site. In addition, antigen-presenting cells (APCs) were activated by M13 phages to further awaken the host immune system for CRC suppression. M13@Ag combined with immune checkpoint inhibitors (α-PD1) or chemotherapeutics (FOLFIRI) significantly prolonged overall mouse survival in the orthotopic CRC model.

Bioinorganic hybrid bacteriophage for modulation of intestinal microbiota to remodel tumor-immune microenvironment against colorectal cancer

Chemotherapy is well recognized to induce immune responses during some chemotherapeutic drugs-mediated tumor eradication. Here, a strategy involving blocking programmed cell death protein 1 (PD-1) to enhance the chemotherapeutic effect of a doxorubicin nanoprodrug HA-Psi-DOX is proposed and the synergetic mechanism between them is further studied. The nanoprodrugs are fabricated by conjugating doxorubicin (DOX) to an anionic polymer hyaluronic acid (HA) via a tumor overexpressed matrix metalloproteinase sensitive peptide (CPLGLAGG) for tumor targeting and enzyme-activated drug release. Once accumulated at the tumor site, the nanoprodrug can be activated to release antitumor drug by tumor overexpressed MMP-2. It is found that HA-Psi-DOX nanoparticles can kill tumor cells effectively and initiate an antitumor immune response, leading to the upregulation of interferon-γ. This cytokine promotes the expression of programmed cell death protein-ligand 1 (PD-L1) on tumor cells, which will cause immunosuppression after interacting with PD-1 on the surface of lymphocytes. The results suggest that the therapeutic efficiency of HA-Psi-DOX nanoparticles is significantly improved when combined with checkpoint inhibitors anti-PD-1 antibody (α-PD1) due to the neutralization of immunosuppression by blocking the interaction between PD-L1 and PD-1. This therapeutic system by combining chemotherapy and immunotherapy further increases the link between conventional tumor therapies and immunotherapy.

PD-1 Blockade for Improving the Antitumor Efficiency of Polymer-Doxorubicin Nanoprodrug.

The unsatisfactory response rate of immune checkpoint blockade (ICB) immunotherapy severely limits its clinical application as a tumor therapy. Here, we generate a vaccine-based nanosystem by integrating siRNA for Cd274 into the commercial human papillomavirus (HPV) L1 (HPV16 L1) protein. This nanosystem has good biosafety and enhances the therapeutic response rate of anti-tumor immunotherapy. The HPV16 L1 protein activates innate immunity through the type I interferon pathway and exhibits an efficient anti-cancer effect when cooperating with ICB therapy. For both resectable and unresectable breast tumors, the nanosystem decreases 71% tumor recurrence and extends progression-free survival by 67%. Most importantly, the nanosystem successfully induces high response rates in various genetically modified breast cancer models with different antigen loads. The strong immune stimulation elicited by this vaccine-based nanosystem might constitute an approach to significantly improve current ICB immunotherapy. Immune checkpoint blockade (ICB) immunotherapy efficacy has still limitations. Here, the authors generate a vaccine that integrates CD274 siRNA into the L1 protein of human papillomavirus, which cooperates with ICB by activating innate immunity in breast cancer models.

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Xue Dong

Papers

Phage-guided modulation of the gut microbiota of mouse models of colorectal cancer augments their responses to chemotherapy.

Artificially Reprogrammed Macrophages as Tumor-Tropic Immunosuppression-Resistant Biologics to Realize Therapeutics Production and Immune Activation.

Bioinorganic hybrid bacteriophage for modulation of intestinal microbiota to remodel tumor-immune microenvironment against colorectal cancer

PD-1 Blockade for Improving the Antitumor Efficiency of Polymer-Doxorubicin Nanoprodrug.

A vaccine-based nanosystem for initiating innate immunity and improving tumor immunotherapy.