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Rare monogenic disorders are a group of single-gene-mutated diseases that have a low incidence rate (less than 0.5‰) and eventually lead to patient disability and even death. Due to the relatively low number of people affected, these diseases typically fail to attract a great deal of commercial investment and research interest, and the affected patients thus have unmet medical needs. Advances in genomics biology, gene editing, and gene delivery can now offer potentially effective options for treating rare monogenic diseases. Herein, we review the application of gene therapy strategies (traditional gene therapy and gene editing) against various rare monogenic diseases with nuclear or mitochondrial gene mutations , including eye, central nervous system, pulmonary, systemic, and blood cell diseases. We summarize their pathologic features, address the barriers to gene delivery for these diseases, discuss available therapies in the clinic and in clinical trials, and sum up in-development gene delivery systems for various rare monogenic disorders. Finally, we elaborate the possible directions and outlook of gene therapy for rare monogenic disorders.

As hepatic stellate cells (HSCs) are essential for hepatic fibrogenesis, HSCs targeted nano-drug delivery system is a research hotspot in liver fibrosis therapy. However, the excessive deposition of fibrosis collagen (mainly collagen I) in the space of Disse associated with hepatic fibrogenesis would significantly hinder nano-formulation delivery to HSCs. Here, we have prepared a collagenase I and retinol co-decorated polymeric micelle that possess nanodrill-like and HSCs-target function based on poly-(lactic-co-glycolic)-b-poly (ethylene glycol)-maleimide (PLGA-PEG-Mal) (named CRM) for liver fibrosis therapy. Upon encountering collagen I barrier, CRM exerted a nanodrill-like function, efficiently degrading pericellular collagen I and showing greater uptake by human HSCs than other micelle formulations. Besides, CRM could realize excellent accumulation in the fibrotic liver and accurate targeting to activated HSCs in mouse hepatic fibrosis model. Moreover, CRM loaded with nilotinib (CRM/NIL), a second-generation tyrosine kinase inhibitor used in the treatment of liver fibrosis, showed optimal antifibrotic activity. This work suggests that CRM with dual function is an efficient carrier for liver fibrosis drug delivery and collagenase I decorating could be a new strategy for building more efficient HSCs targeted nano-drug delivery system.

A novel biomimetic drug delivery system (BDDS) inspired by the pH-dependent ferric ion-transport and release manner of transferrin (Tf) was developed for combating multidrug-resistant breast cancer. Tf-inspired carrier was synthesized by modifying bovine serum albumin (BSA) with histamine (HA) through amide reaction to provide superior specific coordination sites for ferric ion-drug complexes, and self-assembled into nanoparticles (NPs) induced by coordination bond. Tf-inspired NPs were prepared via environment-friendly method, and well redispersed in saline after lyophilization. When internalized into tumor cells by SPARC (secreted protein acidic and rich in cysteine) mediated endocytosis, Tf-inspired NPs bypassed and decreased the P-glycoprotein-mediated drug efflux and led to more effective treatment of multidrug-resistant breast cancer compared with free drugs both in vitro and in vivo due to the enhanced cellular uptake and rapid pH-responsive drug release. Moreover, Tf-inspired NPs exhibited good biocompatibility and low systemic toxicity. Thus, our results demonstrate that Tf-inspired NPs based on coordination bond represent as a smart drug delivery strategy to combat multidrug-resistant cancer and have great potential for clinical applications in cancer therapy.

Here we report an accelerated gene transfer through a polysorbitol-based osmotically active transporter (PSOAT) that shows several surprising results through interesting mechanisms. The nano-sized and well-complexed PSOAT/DNA particles are less toxic, stable at serum and show no aggregation after lyophilization due to their polysorbitol backbone. The transfection is remarkably accelerated both in vitro and in vivo, presumably due to a transporter mechanism of PSOAT in spite of possibility of reduction of transfection by many hydroxyl groups in the transporter. PSOAT possesses a transporter mechanism owing to its polysorbitol backbone, which enhances cellular uptake by exerting polysorbitol transporter activity, thus accelerates gene transfer to cells because transfection ability of PSOAT is drastically reduced in the presence of a cyclooxygenase (COX)-2-specific inhibitor, which we have reported as an inhibitor of the transporter to cells. Moreover, the gene expression is found to be enhanced by hyperosmotic activity and buffering capacity due to polysorbitol and polyethylenimine backbone of PSOAT, respectively. The polysorbitol in PSOAT having polyvalency showed more efficiency in accelerating gene transfer capability than monovalent sorbitol. The above interesting mechanisms display PSOAT as a remarkably potential system to deliver therapeutic (small interfering RNA) and diagnostic agents for effective treatment of cancer.

To circumvent carrier related obstacles, we developed a biodegradable, folate conjugated poly (ester amine) (FP-PEA) that mediates high level folate receptor (FR) mediated endocytosis in vitro as well as in vivo. We report the efficacy of a therapeutic strategy that combines the potency of FP-PEA based on polycaprolactone (PCL) and low molecular weight polyethylenimine (LMW-PEI) with the tumor targeting potential of receptor mediated endocytosis. When tested on cells in culture, FP-PEA was found to retain high affinity for FR-positive cells compared with PEA without folate moiety (P-PEA). The FR specific activity of FP-PEA was drastically decreased in the presence of an excess free folic acid and very less significant transfection was detected against FR-negative cells. FP-PEA showed marked anti-tumor activity against FR-positive human KB tumors in nude mice with no evidence of toxicity during and after therapy using TAM67 gene. Furthermore, the therapeutic effect occurred in the apparent absence of weight loss or noticeable tumor apoptosis. In contrast, no significant anti-tumor activity was observed in P-PEA treated mice which were co dosed with an excess of FR, thus demonstrating the target specific gene delivery. Furthermore, anti-tumor activity with PEA without folic acid moiety (P-PEA) proved not to be effective against xenograft mice model with KB cells when administered at the same dose to that of FP-PEA. Taken together, these results indicate that FP-PEA is highly effective gene carrier capable of producing therapeutic benefit in xenograft mice model without any sign of toxicity.

A vaccine delivery system based on mannosylated chitosan microspheres (MCMs) was studied in vitro and in vivo. Bordetella bronchiseptica antigens containing dermonecrotoxin (BBD) were loaded in MCMs or chitosan microspheres (CMs). Fluorescence confocal microscopy indicated that BBD-loaded MCMs (BBD-MCMs) bound with mannose receptors on murine macrophages (RAW264.7 cells). In vitro experiments using macrophages demonstrated that BBD-MCMs had more effective immune-stimulating activity than BBD-loaded CMs (BBD-CMs). Mice intranasally immunized with BBD-MCMs showed significantly higher BBD-specific IgA antibody responses in saliva and serum than mice immunized with BBD-CMs (p