Non-viral siRNA delivery to T cells: Challenges and opportunities in cancer immunotherapy.

T lymphocytes are the major drivers of antitumor immunity. The recent clinical success of adoptive T cell therapies and immune checkpoint inhibitors has demonstrated the strength of modulating T cell function in fighting cancer. Nonetheless, a significant fraction of patients remain unresponsive largely due to the immunosuppressive tumor environment that blunts T cell activity. Small interfering RNAs (siRNAs) offer the potential to sequence-specifically silence the expression of negative regulator genes in T cells in a transient manner, thereby releasing the block on anti-tumor responses. Despite the current focus on small molecule- and antibody-based immune checkpoint inhibitors as well as T cell-directed delivery of mRNA and genome editing machinery, the application of siRNA involves important clinical advantages. The recent surge of adoptive cell therapies and development of new and potent delivery approaches has enabled efficient siRNA delivery to T cells both ex vivo and in vivo. As such, siRNA molecules have a newfound potential to improve the proliferation, survival, tumor infiltration and potency of T cells in cancer immunotherapy. In this review, we briefly discuss the extracellular and intracellular delivery hurdles associated with siRNA therapy, in particular with regard to T cell targeting. We provide a timely and comprehensive overview of current and emerging delivery technologies used for siRNA transfection, discussing their strengths and weaknesses from a clinical as well as a manufacturing point-of-view. Finally, we critically review the current status and new potential avenues for modulating T cell function in cancer immunotherapy using siRNA.

Non-invasive cell-tracking methods for adoptive T cell therapies.

Adoptive T cell therapies (ACT) have demonstrated groundbreaking results in blood cancers and melanoma. Nevertheless, their significant cost, the occurrence of severe adverse events, and their poor performance in solid tumors are important hurdles hampering more widespread applicability. In vivo cell-tracking allows instantaneous and non-invasive monitoring of the distribution, tumor homing, persistence, and redistribution to other organs of infused T cells in patients. Furthermore, cell-tracking could aid in the clinical management of patients, allowing the detection of non-responders or severe adverse events at an early stage. This review provides a concise overview of the main principles and potential of cell-tracking, followed by a discussion of the clinically relevant labeling strategies and their application in ACT.

Photothermal nanofibres enable safe engineering of therapeutic cells.

Nanoparticle-sensitized photoporation is an upcoming approach for the intracellular delivery of biologics, combining high efficiency and throughput with excellent cell viability. However, as it relies on close contact between nanoparticles and cells, its translation towards clinical applications is hampered by safety and regulatory concerns. Here we show that light-sensitive iron oxide nanoparticles embedded in biocompatible electrospun nanofibres induce membrane permeabilization by photothermal effects without direct cellular contact with the nanoparticles. The photothermal nanofibres have been successfully used to deliver effector molecules, including CRISPR-Cas9 ribonucleoprotein complexes and short interfering RNA, to adherent and suspension cells, including embryonic stem cells and hard-to-transfect T cells, without affecting cell proliferation or phenotype. In vivo experiments furthermore demonstrated successful tumour regression in mice treated with chimeric antibody receptor T cells in which the expression of programmed cell death protein 1 (PD1) is downregulated after nanofibre photoporation with short interfering RNA to PD1. In conclusion, cell membrane permeabilization with photothermal nanofibres is a promising concept towards the safe and more efficient production of engineered cells for therapeutic applications, including stem cell or adoptive T cell therapy.

Hydrogel-Induced Cell Membrane Disruptions Enable Direct Cytosolic Delivery of Membrane-Impermeable Cargo.

Intracellular delivery of membrane-impermeable cargo offers unique opportunities for biological research and the development of cell-based therapies. Despite the breadth of available intracellular delivery tools, existing protocols are often suboptimal and alternative approaches that merge delivery efficiency with both biocompatibility, as well as applicability, remain highly sought after. Here, a comprehensive platform is presented that exploits the unique property of cationic hydrogel nanoparticles to transiently disrupt the plasma membrane of cells, allowing direct cytosolic delivery of uncomplexed membrane-impermeable cargo. Using this platform, which is termed Hydrogel-enabled nanoPoration or HyPore, the delivery of fluorescein isothiocyanate (FITC)-dextran macromolecules in various cancer cell lines and primary bovine corneal epithelial cells is convincingly demonstrated. Of note, HyPore demonstrates efficient FITC-dextran delivery in primary human T cells, outperforming state-of-the-art electroporation-mediated delivery. Moreover, the HyPore platform enables cytosolic delivery of functional proteins, including a histone-binding nanobody as well as the enzymes granzyme A and Cre-recombinase. Finally, HyPore-mediated delivery of the MRI contrast agent gadobutrol in primary human T cells significantly improves their T1 -weighted MRI signal intensities compared to electroporation. Taken together, HyPore is proposed as a straightforward, highly versatile, and cost-effective technique for high-throughput, ex vivo manipulation of primary cells and cell lines.

Cationic Amphiphilic Drugs Boost the Lysosomal Escape of Small Nucleic Acid Therapeutics in a Nanocarrier-Dependent Manner.

Small nucleic acid (NA) therapeutics, such as small interfering RNA (siRNA), are generally formulated in nanoparticles (NPs) to overcome the multiple extra- and intracellular barriers upon in vivo administration. Interaction with target cells typically triggers endocytosis and sequesters the NPs in endosomes, thus hampering the pharmacological activity of the encapsulated siRNAs that occurs in the cytosol. Unfortunately, for most state-of-the-art NPs, endosomal escape is largely inefficient. As a result, the bulk of the endocytosed NA drug is rapidly trafficked toward the degradative lysosomes that are considered as a dead end for siRNA nanomedicines. In contrast to this paradigm, we recently reported that cationic amphiphilic drugs (CADs) could strongly promote functional siRNA delivery from the endolysosomal compartment via transient induction of lysosomal membrane permeabilization. However, many questions still remain regarding the broader applicability of such a CAD adjuvant effect on NA delivery. Here, we report a drug repurposing screen (National Institutes of Health Clinical Collection) that allowed identification of 56 CAD adjuvants. We furthermore demonstrate that the CAD adjuvant effect is dependent on the type of nanocarrier, with NPs that generate an appropriate pool of decomplexed siRNA in the endolysosomal compartment being most susceptible to CAD-promoted gene silencing. Finally, the CAD adjuvant effect was verified on human ovarian cancer cells and for antisense oligonucleotides. In conclusion, this study strongly expands our current knowledge on how CADs increase the cytosolic release of small NAs, providing relevant insights to more rationally combine CAD adjuvants with NA-loaded NPs for future therapeutic applications.

MIF inhibition interferes with the inflammatory and T cell-stimulatory capacity of NOD macrophages and delays autoimmune diabetes onset.

Macrophages contribute in the initiation and progression of insulitis during type 1 diabetes (T1D). However, the mechanisms governing their recruitment into the islets as well as the manner of retention and activation are incompletely understood. Here, we investigated a role for macrophage migration inhibitory factor (MIF) and its transmembrane receptor, CD74, in the progression of T1D. Our data indicated elevated MIF concentrations especially in long-standing T1D patients and mice. Additionally, NOD mice featured increased MIF gene expression and CD74+ leukocyte frequencies in the pancreas. We identified F4/80+ macrophages as the main immune cells in the pancreas expressing CD74 and showed that MIF antagonism of NOD macrophages prevented their activation-induced cytokine production. The physiological importance was highlighted by the fact that inhibition of MIF delayed the onset of autoimmune diabetes in two different diabetogenic T cell transfer models. Mechanistically, macrophages pre-conditioned with the MIF inhibitor featured a refractory capacity to trigger T cell activation by keeping them in a naïve state. This study underlines a possible role for MIF/CD74 signaling pathways in promoting macrophage-mediated inflammation in T1D. As therapies directed at the MIF/CD74 pathway are in clinical development, new opportunities may be proposed for arresting T1D progression.