The act of influencing the immune system to elicit a robust antitumor immune response without the need for administration of drugs in solution is called immunoengineering. It is based in knowledge from diverse disciplines such as bioengineering, materials science, nanotechnology, drug delivery and immunology to influence the behavior of the immune system . The recent developed (and still in development) cancer immunotherapy demonstrated that these diseases can be effectively treated without directly targeting tumor cells , as it confers superior outcomes relative to molecular targeted therapies or cytotoxic chemotherapy.
Even though certain tumors are moderately responsive to immunotherapy (like melanoma), response rates for the majority of indications remain low , as tumors exhibit primary, adaptive and acquired mechanisms of resistance . This effect is, in part, due to the induction of autoimmune-type pathologies induced by immunotherapy drugs, as only a small percentage of the administered dose specifically acts on target leukocytes at target sites. Immune-related adverse events (irAEs) comprise a commonly observed in clinic set of self directed inflammatory processes associated with cancer immunotherapy due to the administration of immunomodulatory compounds that can disrupt the homeostatic functions of immune cells at non-target sites. In this regard, being able to break the tumor immune tolerance without breaking the systemic immune tolerance would meaningfully change disease progression. Immunoengineering, based on recent nanotechnology and bioengineering developments , can improve not only the safety but also the efficacy of cancer immunotherapy by designing new drug delivery solutions that targets specific cells within particular anatomical locations .
A general view of some immunoengineering strategies to combat cancer. Abdou P, et al. Advances in engineering local drug delivery systems for cancer immunotherapy. Wiley Interdiscip Rev Nanomed Nanobiotechnol. 2020 Sep;12(5):e1632. doi: 10.1002/wnan.1632.
It has been demonstrated that extended release of immunotherapy from particles or matrices confers vastly superior safety and efficacy relative to its administration in solution. Furthermore, local retention is very important for immunotherapies that modulate adaptive immunity. For example, antibodies that mediate immune checkpoint blockade (ICB) can be retained at the site of infection by conjugating to them super affinity peptides that bind to components of the extracellular matrix (ECM), thus reducing antibody levels within the circulation and preventing systemic side effects. Engineering a liposome nanocarrier with an anti CD137 and IL-2-Fc domain fusion protein restricted its distribution to the tumor parenchyma and tumor-draining lymph nodes where T cells are primed by antigen presenting cells (APCs), preventing leakage into circulation . Even if administered systemically, anchored liposomes could provide antitumor efficacy in the absence of systemic toxicity.
It is worth noting that whereas nanoparticles containing cancer cell-intrinsic drugs must deliver their cargo to the vast majority of targets within a tumor to be effective, even a modest accrual of immunotherapy loaded particles can elicit robust antitumoral responses because immune cells can proliferate as well as propagate the response by activating complementary immune cells.
Improving effector responses through vaccine formulation. Goldberg MS. Improving cancer immunotherapy through nanotechnology. Nat Rev Cancer. 2019 Oct;19(10):587-602. doi: 10.1038/s41568-019-0186-9.
Immunoengineering can also be applied ex vivo, especially for the activation and expansion of T cells prior to their adoptive transfer. The standard protocol for manufacturing autologous T cells for adoptive transfer involves the use of spherical superparamagnetic polymer particles coated with anti-CD3 and anti-CD28 antibodies, that constituted the first generation of artificial APCs (aAPCs). Promoting the aggregation of aAPCs will lead to the clustering of activated T cell receptors (TCRs), thus increasing T cell activation . Alternatively, these particles can be used to enrich and expand rare tumor-specific T cells from bulk leukocyte populations . Engineering the shape, size, concentration, stimuli and ligand choice and density of aAPCs impacts the quality of T cells for adoptive cell transfer, and tuning the spatial arrangement and diffusivity of surface factors can promote the formation of immunological synapses and receptor clustering. Carbon nanotubes and polymer-based aAPCs have been also used to great effect due to the high surface area of these materials [10, 11].
The main advantage of nanotechnology formulations is that it allows to load multiple components into the same formulation, whether these be small molecules, nucleic acids, polypeptides or cells. In the context of vaccines, co-encapsulation of an antigen and an adjuvant ensures that both are delivered at the same time to the same APCs. When the antigen and the adjuvant are delivered in solution, they will not properly reach the APCs at the same time and those APCs that take up the antigen in the absence of the adjuvant become tolerogenic, counteracting the benefits of the intended vaccinal effect. It has been described that nanoparticles loaded or conjugated with toll like receptor (TLR) agonists and peptides increase the number of primed T cells in mice more than an order of magnitude, relative to the administration of the same components in solution. Another advantage is that the biomaterial carrier can itself act as an adjuvant, obviating the need to incorporate a separate agonist of innate immunity and therefore simplifying its production.
An approach that increases both T cell priming and antitumor efficacy in mice, while substantially decreasing systemic toxicity consist of targeting the lymph nodes (LNs) by appending lipophilic albumin-binding tails to the antigen and adjuvant, allowing vaccine delivery to the lymphatic system by circulating albumin. Alternatively, the use of nanodiscs (a mixture of high-density lipoproteins) with a cysteine-modified antigen and a cholesterol modified CpG adjuvant that prolongs antigen presentation for improved cross priming of T cells also showed and enhanced co-delivery to LNs and promoted robust and sustained antigen presentation. Nanodiscs have been combined with ICB to eliminate stablished mouse colorectal and melanoma tumors . Some researchers are also working on the inclusion of dense arrays of glycans on the surface of nanoparticles, thus facilitating its recognition by mannose-binding lectin in LNs and promoting particle transport to the B cell zone, thereby enhancing the quality and quantity of resultant humoral immunity.
Delivery of immunomodulatory payloads using polymeric nanoparticles. Goldberg MS. Improving cancer immunotherapy through nanotechnology. Nat Rev Cancer. 2019 Oct;19(10):587-602. doi: 10.1038/s41568-019-0186-9.
Nanovaccines can improve the effectiveness of messenger RNA (mRNA)-based vaccines considerably, as nucleic acids are susceptible to nuclease-mediated hydrolysis and carriers greatly enhance their stability. The advantage of mRNA is that it contains both specificity (in the form of an encoded antigen) and function (adjuvanticity due to its nature) in a single molecule, as it is a natural ligand for TLR-7 and -8. Therefore, every cell that takes up the mRNA is poised to induce productive immunity rather than tolerance. Traditionally, lipids have been used to package nucleic acids and increase the efficiency of their delivery . Following endocytosis, lipid nanoparticles facilitate payload release from membrane-bound compartments into the cytosol, where mRNA will be transcribed.
With this technology researchers can also use polymeric nanoparticles to transfect primary human T cells or hematopoietic stem cells following in vitro incubation to induce a transient expression of therapeutically relevant proteins that can generate permanent alterations in the absence of transgene integration. In a recent study , these particles were used to modify T cells present in a mixed population of immune cells isolated from peripheral blood by knocking out the native TCR among T cells to which a chimeric antigen receptor (CAR) was subsequently introduced. T cells were also transfected with an mRNA encoding a transcription factor that promotes central memory T cell formation, and the resultant improved antitumor functionality of these CAR T cells in a mouse model of lymphoma led to enhanced survival.
One main advantage of lipid nanoparticles is that they do not involve neither the costly and elaborate protocols required by viral vectors, nor physical disruption of the cell membrane that results in the cytotoxicity observed upon electroporation.
Some immunoengineering approaches are now entering the clinic, although the manufacturing of clinical-grade materials represents a key factor that cannot be overlooked. Particles, devices and cells require reproducibility and scalable chemistry, manufacturing and a translation towards good manufacturing practice-grade production. Despite all these difficulties, immunoengineering is maturing fast and soon will positively impact the patient lives.
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