Scientists tested whether the natural peptide LL‑37 can act like a tiny carrier to shove a piece of HIV‑1 DNA into human cells. They found it can bundle the DNA into small particles that protect it from being broken down, and the bundles can get into cells without killing them, although the peptide by itself is toxic. The overall gene‑delivery success was modest – about one‑quarter to one‑third of the cells took up the DNA.

DNA-based therapeutic vaccines have been proposed as a promising strategy for the treatment of established HIV infections. However, these vaccines are often associated with certain shortcomings, such as poor immunogenicity and low transfection efficiency. In this study, we investigated the ability of LL-37 to deliver a potential immunogenic fusion construct comprising HIV-1 nef and vpr genes into a mammalian cell line. First, the pEGFP-N1 eukaryotic expression vector harboring the HIV-1 nef-vpr fusion was produced free of endotoxin on a large scale. Then, DNA/LL-37 complexes were prepared by coincubation of pEGFP-nef-vpr with LL-37 for 45 minutes at different nitrogen to phosphate (N/P) ratios. The formation of DNA/peptide complexes was investigated by gel retardation assay. Next, the stability and morphological characteristics of the nanoparticles were evaluated. The toxicity of LL-37 and the nanoparticles in HEK-293T cells were assessed by MTT assay. The transfection efficiency of the DNA/LL-37 complexes was studied by fluorescence microscopy, flow cytometry, and western blot analysis. LL-37 formed stable complexes with pEGFP-nef-vpr (diameter of 150-200 nm) while providing good protection against nucleolytic and proteolytic degradation. The peptide significantly affected cell viability even at low concentrations. However, the LL-37/DNA complexes had no significant cytotoxic effect. Treatment of cells with pEGFP-N1/LL-37 and pEGFP-nef-vpr/LL-37 resulted in transfection of 36.32% ± 1.13 and 25.55% ± 2.07 of cells, respectively. Given these findings and the important immunomodulatory and antiviral activities of LL- 37, the use of this peptide can be further exploited in the development of novel gene delivery strategies and vaccine design.