Positron emission tomography allows in vivo tracking of EVs and reveals changes in their biodistribution after glycosylation modification.

Riboflavin acts as bioorthogonal photocatalyst to activate a PtIV anticancer prodrug in the biological environment.

Development of vaccines to prevent and treat emerging new pathogens and re-emerging infections and cancer remains a major challenge. An attractive approach is to build the vaccine upon a biocompatible NP that simultaneously acts as accurate delivery vehicle and radiotracer for PET/SPECT imaging for ultrasensitive and quantitative in vivo imaging of NP delivery to target tissues/organs. Success in developing these nanovaccines will depend in part on having a "correct" NP size and accommodating and suitably displaying antigen and/or adjuvants (e.g., TLR agonists). Here we develop and evaluate a NP vaccine based on iron oxide-selective radio-gallium labeling suitable for SPECT((67)Ga)/PET((68)Ga) imaging and efficient delivery of antigen (OVA) and TLR 9 agonists (CpGs) using lipid-coated magnetite micelles. OVA, CpGs and rhodamine are easily accommodated in the hybrid micelles, and the average size of the construct can be controlled to be ca. 40 nm in diameter to target direct lymphatic delivery of the vaccine cargo to antigen presenting cells (APCs) in the lymph nodes (LNs). While the OVA/CpG-loaded construct showed effective delivery to endosomal TLR 9 in APCs, SPECT imaging demonstrated migration from the injection site to regional and nonregional LNs. In correlation with the imaging results, a range of in vitro and in vivo studies demonstrate that by using this microdosed nanosystem the cellular and humoral immune responses are greatly enhanced and provide protection against tumor challenge. These results suggest that these nanosystems have considerable potential for image-guided development of targeted vaccines that are more effective and limit toxicity.

Encouraging results are emerging from systems that exploit Toll like receptor (TLR) signaling, nanotechnology, checkpoint inhibition and molecular imaging for cancer immunotherapy. A major remaining challenge is developing effective, durable and tumour-specific immune responses without systemic toxicity. Here, we report a simple and versatile system based on synergistic activation of immune responses and direct cancer cell killing by combined TLR ligation using polyIC as TLR3 and imiquimod (R837) as TLR7 agonist, in combination with the model antigen ovalbumin (OVA) and phospholipid micelles loaded with zinc-doped iron oxide magnetic nanoparticles (MNPs). The combination of TLR agonists triggered a strong innate immune response in the lymph nodes (LNs) without systemic release of pro-inflammatory cytokines. The vaccines showed excellent efficacy against aggressive B16-F10 melanoma cells expressing OVA, which was improved with immune checkpoint abrogation of the immunosuppressive programmed death-ligand 1 (PD-L1) at the level of the cancer cells. By magnetic resonance (MR) and nuclear imaging we could track the vaccine migration from the site of injection to LNs and tumour. Overall, we show this synergistic TLR agonists and their combination with MNPs and immune checkpoint blockade to have considerable potential for preclinical and clinical development of vaccines for cancer immunotherapy.

Therapeutic vaccination offers great promise as an intervention for a diversity of infectious and non‐infectious conditions. Given that most chronic health conditions are thought to have an immune component, vaccination can at least in principle be proposed as a therapeutic strategy. Understanding the nature of protective immunity is of vital importance, and the progress made in recent years in defining the nature of pathological and protective immunity for a range of diseases has provided an impetus to devise strategies to promote such responses in a targeted manner. However, in many cases, limited progress has been made in clinical adoption of such approaches. This in part results from a lack of safe and effective vaccine adjuvants that can be used to promote protective immunity and/or reduce deleterious immune responses. Although somewhat simplistic, it is possible to divide therapeutic vaccine approaches into those targeting conditions where antibody responses can mediate protection and those where the principal focus is the promotion of effector and memory cellular immunity or the reduction of damaging cellular immune responses as in the case of autoimmune diseases. Clearly, in all cases of antigen‐specific immunotherapy, the identification of protective antigens is a vital first step. There are many challenges to developing therapeutic vaccines beyond those associated with prophylactic diseases including the ongoing immune responses in patients, patient heterogeneity, and diversity in the type and stage of disease. If reproducible biomarkers can be defined, these could allow earlier diagnosis and intervention and likely increase therapeutic vaccine efficacy. Current immunomodulatory approaches related to adoptive cell transfers or passive antibody therapy are showing great promise, but these are outside the scope of this review which will focus on the potential for adjuvanted therapeutic active vaccination strategies.

Despite the tremendous potential of Toll‐like receptor 4 (TLR4) agonists in vaccines, their efficacy as monotherapy to treat cancer has been limited. Only some lipopolysaccharides (LPS) isolated from particular bacterial strains or structures like monophosphoryl lipid A (MPLA) derived from lipooligosaccharide (LOS), avoid toxic overactivation of innate immune responses while retaining adequate immunogenicity to act as adjuvants. Here, different LOS structures are incorporated into nanoparticle‐filled phospholipid micelles for efficient vaccine delivery and more potent cancer immunotherapy. The structurally unique LOS of the plant pathogen Xcc is incorporated into phospholipid micelles encapsulating iron oxide nanoparticles, producing stable pathogen‐mimicking nanostructures suitable for targeting antigen presenting cells in the lymph nodes. The antigen is conjugated via a hydrazone bond, enabling rapid, easy‐to‐monitor and high‐yield antigen ligation at low concentrations. The protective effect of these constructs is investigated against a highly aggressive model for tumor immunotherapy. The results show that the nanovaccines lead to a higher‐level antigen‐specific cytotoxic T lymphocyte (CTL) effector and memory responses, which when combined with abrogation of the immunosuppressive programmed death‐ligand 1 (PD‐L1), provide 100% long‐term protection against repeated tumor challenge. This nanovaccine platform in combination with checkpoint inhibition of PD‐L1 represents a promising approach to improve the cancer immunotherapy of TLR4 agonists.

The success of nanoparticle-based therapies will depend in part on accurate delivery to target receptors and organs. There is, therefore, considerable potential in nanoparticles which achieve delivery of the right drug(s) using the right route of administration to the right location at the right time, monitoring the process by non-invasive molecular imaging. A challenge is harnessing immunotherapy via activation of Toll-like receptors (TLRs) for the development of vaccines against major infectious diseases and cancer. In immunotherapy, delivery of the vaccine components to lymph nodes (LNs) is essential for effective stimulation of the immune response. Although some promising advances have been made, delivering therapeutics to LNs remains challenging. It is here shown that iron-oxide nanoparticles can be engineered to combine in a single and small (<50 nm) nanocarrier complementary multimodal imaging features with the immunostimulatory activity of polyinosinic-polycytidylic acid (poly (I:C)). Whilst the fluorescence properties of the nanocarrier show effective delivery to endosomes and TLR3 in antigen presenting cells, MRI/SPECT imaging reveals effective delivery to LNs. Importantly, in vitro and in vivo studies show that, using this nanocarrier, the immunostimulatory activity of poly (I:C) is greatly enhanced. These nanocarriers have considerable potential for cancer diagnosis and the development of new targeted and programmable immunotherapies.

The incidence and mortality of cancer demand more innovative approaches and combination therapies to increase treatment efficacy and decrease off-target side effects. We describe a boron-rich nanoparticle composite with potential applications in both boron neutron capture therapy (BNCT) and photothermal therapy (PTT). Our strategy is based on gold nanorods (AuNRs) stabilized with polyethylene glycol and functionalized with the water-soluble complex cobalt bis(dicarbollide) ([3,3′-Co­(1,2-C2B9H11)2]−), commonly known as COSAN. Radiolabeling with the positron emitter copper-64 (64Cu) enabled in vivo tracking using positron emission tomography imaging. 64Cu-labeled multifunctionalized AuNRs proved to be radiochemically stable and capable of being accumulated in the tumor after intravenous administration in a mouse xenograft model of gastrointestinal cancer. The resulting multifunctional AuNRs showed high biocompatibility and the capacity to induce local heating under external stimulation and trigger cell death in heterogeneous cancer spheroids as well as the capacity to decrease cell viability under neutron irradiation in cancer cells. These results position our nanoconjugates as suitable candidates for combined BNCT/PTT therapies.