Combining Nanomedicine and Immunotherapy

Abstract

Nanomedicine holds significant potential to improve the efficacy of cancer immunotherapy. Thus far, nanomedicines, i.e., 1-100(0) nm sized drug delivery systems, have been primarily used to improve the balance between the efficacy and toxicity of conjugated or entrapped chemotherapeutic drugs. The clinical performance of cancer nanomedicines has been somewhat disappointing, which is arguably mostly due to the lack of tools and technologies for patient stratification. Conversely, the clinical progress made with immunotherapy has been spectacular, achieving complete cures and inducing long-term survival in advanced-stage patients. Unfortunately, however, immunotherapy only works well in relatively small subsets of patients. Increasing amounts of preclinical and clinical data demonstrate that combining nanomedicine with immunotherapy can boost therapeutic outcomes, by turning "cold" nonimmunoresponsive tumors and metastases into "hot" immunoresponsive lesions. Nano-immunotherapy can be realized via three different approaches, in which nanomedicines are used (1) to target cancer cells, (2) to target the tumor immune microenvironment, and (3) to target the peripheral immune system. When targeting cancer cells, nanomedicines typically aim to induce immunogenic cell death, thereby triggering the release of tumor antigens and danger-associated molecular patterns, such as calreticulin translocation, high mobility group box 1 protein and adenosine triphosphate. The latter serve as adjuvants to alert antigen-presenting cells to take up, process and present the former, thereby promoting the generation of CD8⁺ cytotoxic T cells. Nanomedicines targeting the tumor immune microenvironment potentiate cancer immunotherapy by inhibiting immunosuppressive cells, such as M2-like tumor-associated macrophages, as well as by reducing the expression of immunosuppressive molecules, such as transforming growth factor beta. In addition, nanomedicines can be employed to promote the activity of antigen-presenting cells and cytotoxic T cells in the tumor immune microenvironment. Nanomedicines targeting the peripheral immune system aim to enhance antigen presentation and cytotoxic T cell production in secondary lymphoid organs, such as lymph nodes and spleen, as well as to engineer and strengthen peripheral effector immune cell populations, thereby promoting anticancer immunity. While the majority of immunomodulatory nanomedicines are in preclinical development, exciting results have already been reported in initial clinical trials. To ensure efficient translation of nano-immunotherapy constructs and concepts, we have to consider biomarkers in their clinical development, to make sure that the right nanomedicine formulation is combined with the right immunotherapy in the right patient. In this context, we have to learn from currently ongoing efforts in nano-biomarker identification as well as from partially already established immuno-biomarker initiatives, such as the Immunoscore and the cancer immunogram. Together, these protocols will help to capture the nano-immuno status in individual patients, enabling the identification and use of individualized and improved nanomedicine-based treatments to boost the performance of cancer immunotherapy.

Figure 1. Schematic illustration of the cancer-immunity cycle.

The anticancer immune reaction starts with the release of cancer cell antigens (1), which are taken up, processed and presented by antigen-presenting cells (APCs) to naive T cells in secondary lymphoid organs, such as lymph nodes and spleen (2+3). Subsequently, cytotoxic T lymphocytes (CTLs) are generated, which migrate to and infiltrate tumors and metastases (4+5). In tumors and metastases, CTLs can then recognize (6) and kill (7) cancer cells. Reproduced with permission from ref. . Copyright 2013 Elsevier.

Figure 2. Publications on nanomedicine, immunotherapy and nano-immunotherapy.

Searches were performed in Pubmed using [(nanoparticle) AND (drug delivery) in all fields, a], [(immunotherapy) in all fields, b], and [(immunotherapy) AND (nanoparticle) in all fields, c].

Figure 3. Nano-immunotherapy based on targeting cancer cells.

a: The cancer-immunity cycle is often impaired in tumors (depicted by grey arrows). Upon nanomedicine-based targeting of immunogenic cell death (ICD) inducing drugs to cancer cells, tumor antigens and damage-associated molecular patterns (i.e. calreticulin, adenosine triphosphate and high mobility group box 1 protein) are released. Together, these components promote antigen uptake, processing and presentation by antigen-presenting cells, which contributes to the generation of cytotoxic T cells. b: Immunopotentiation exerted by ICD-inducing nanomedicines, such as PEGylated liposomal doxorubicin (Doxil), can be exemplified by the notion that Doxil is significantly more effective in inhibiting CT26 tumor growth in immunocompetent Balb/C mice than in immunodeficient nude mice. The benefit of nanomedicine-based drug targeting to cancer cells was demonstrated by the higher efficacy and lower toxicity of Doxil as compared to free doxorubicin. Adapted with permission from ref. . Copyright 2015 Elsevier. c: Nanoparticle-based delivery of ICD-inducing oxaliplatin resulted in stronger immunopotentiation that oxaliplatin in free form, as exemplified by higher levels of CD8⁺ T cells infiltration into Pan02 tumors. In case of non-ICD-inducing gemcitabine treatment, no enhanced T cell infiltration into tumors was observed. Adapted with permission from ref. . Copyright 2016 Elsevier. d: Pyrolipid-loaded nanomedicines induced ICD and potentiated cancer immunity in distant tumors via the abscopal effect, which synergized with anti-PD-L1 antibodies to efficiently eradicate the tumors. Adapted with permission from ref. . Copyright 2013 American Chemical Society.

Figure 4. Nano-immunotherapy based on targeting the tumor immune microenvironment (TIME).

a: Nanomedicines can inhibit immunosuppressive cells and molecules, and they can potentiate effector immune cells (such as APCs and cytotoxic T cells). Both approaches enhance the cancer-immunity cycle. b: Immunosuppressive M2-like macrophages (left) can be decreased by CaCO₃ nanoparticles, via modulating tumor acidity. At the same time, the level of immunopotentiating M1-like macrophages (right) was increased. Adapted with permission from ref. . Copyright 2019 Springer Nature. c: Downregulation of TGF-β levels in tumors was induced by siRNA-loaded nanoparticles, when used alone and when combined with vaccination at early or late stages of tumor development. Adapted with permission from ref. . Copyright 2014 American Chemical Society. d: Multivalent bi-specific nanobioconjugate engager (mBiNE) modified with calreticulin (CRT) and with antibodies targeting the human epidermal growth factor receptor (HER) trigger macrophage-mediated phagocytosis of HER2-expressing tumor cells (i.e. SK-BR-3 and TUBO). Adapted with permission from ref. . Copyright 2017 Springer Nature.

Figure 5. Nano-immunotherapy based on targeting the peripheral immune system.

a: Nanomedicines can improve cytotoxic T cell generation in peripheral immune organs, such as lymph nodes, by modulating antigen presentation or by mimicking APCs. Furthermore, nanomedicines can potentiate or engineer peripheral T cells for more efficient killing of cancer cells. b: CpG motifs modified with lipid tails (Lipo-G2-CpG) efficiently targeted lymph nodes to activate APCs following intravenous injection. Adapted with permission from ref. . Copyright 2014. Springer Nature. c: In vivo T cell maturation and activation were more effectively achieved by artificial APCs (aAPC) with optimized surface chemistry compared to fixed aAPC and soluble activating antibodies. Adapted with permission from ref. . Copyright 2017 American Chemical Society. d: Peripheral T cells were engineered using intravenously injected gene delivery nanoparticles to express chimeric antigen receptors (CAR) in mice bearing B-cell acute lymphoblastic leukemia. High numbers of effector and memory T cells could be detected in peripheral blood for up to one month. Adapted with permission from ref. . Copyright 2017 Springer Nature.

Figure 6. The cancer immunogram and Immunoscore.

a: The cancer immunogram is a scoring tool based on seven parameters related to cancer-immune system interactions. MHC: major histocompatibility complex; LDH: lactate dehydrogenase; CRP: C-reactive protein. Adapted with permission from ref. . Copyright 2016 The American Association for the Advancement of Science. b: The Immunoscore aims to analyze the location, type, density and function of T cells in tumors. In the most recent version, tumors are categorized in four types: absent (“cold” tumors), altered-immunosuppressed, altered-excluded and optimal (“hot” tumors). The latter have an increased likelihood to respond to immunotherapeutic interventions, such as checkpoint inhibition. CT-Lo: low T cells in the core of tumors. Hi-IM: high T cells in the invasive margin. CD3⁺ T cells are stained in brown and background tissue is stained in blue. Adapted with permission from ref. . Copyright 2019 Springer Nature.