2.1. Cells and culture conditions
Mononuclear cells were isolated from human peripheral blood (PBMCs) of a healthy donor in a Ficoll density gradient (1.077 g/cm3, PanEco, Russia) in accordance with approved ethical standards and current legislation (the protocol was approved by the Committee on Biomedical Ethics of Kazan Federal University (No. 3, 03/23/2017). An informed consent was obtained from the healthy donor. M-14 melanoma cell line was received from John Wayne Cancer Institute Specimen Repository (JWCI). Cells were maintained at 37°C and 5% CO2 in a humidified incubator in RPMI 1640 medium (PanEco, Russia), supplemented with 10% fetal bovine serum (Invitrogen, USA), 2mM L-glutamine (PanEco, Russia), and 5000 µg/ml mixed penicillin-streptomycin (Rosmedbio, Russia). All cell lines were tested for mycoplasma routinely.
2.2. Lentivirus production
Lentiviral vector plasmid encoding human IL-2 gene (pLX304-IL-2) was obtained from the Harvard Plasmid Database (#HsCD00421565-4). The production of lentiviruses encoding IL-2 genes was carried out by calcium phosphate co-transfection of a packaging HEK293T cell line with three plasmids: an expression plasmid (pLX304-IL2); packaging plasmid (psPAX2, AddGene #12260); and enveloping plasmid (pCMV-VSV-G, AddGene #8454). The concentration of lentiviral particles was carried out by ultracentrifugation for 2 h at 26,000 rpm at 4°C.
2.3. Genetic Modification and Selection
M-14 cell line was transduced by lentivirus encoded IL-2 gene (vector plasmid pLX304-IL-2 #HSCD 00421565-4, Harvard University, USA) in serum-free medium using 10 µg/ml protamine sulfate (#P4020, Sigma, USA). Antibiotic selection was performed with 7.5 µg/ml Blasticidin S HCl (#R21001, Gibco, USA) for 7 days. Cell culture was tested and resulted negative for Mycoplasma.
2.4. Isolation of cytochalasin B-induced membrane vesicles
Cells were washed from medium with Dulbecco’s Phosphate Buffer Saline (PanEco, Russia) and supplemented with serum-free medium. After counting 2 ⋅ 106 cells were suspended with 10 ml serum-free medium containing Cytochalasin B from Drechslera dematioidea (#C6762-5mg, Sigma-Aldrich, USA) in concentration 10 µg/ml. Cells were incubated for 30 min in a humidified incubator at 37°C and 5% CO2 with gentle shaking every 10 minutes. After incubation cells were mixed by vortex during 1 min and then centrifuged for 10 min at 100 g (Biosan Laboratory centrifuge LMC-3000), supernatant was collected in the new tube and centrifuged for 10 min at 350 g, supernatant was collected into the clean tube and filtered through polyvinylidene difluoride (PVDF) membrane filter (GVS filter technology, UK) with pore size 1µm. After filtration supernatant was centrifuged for 30 min at 8064 g. The precipitate containing CIMVs was collected. The determination of protein concentration was carried out using Pierce BCA Protein Assay Kit (#23225, Thermo Scientific™, USA) according to manufacturer’s manual.
2.5. Western blot analysis
Cell samples were lysed by RIPA buffer (Thermo Fisher Scientific, USA) with addition of protease and phosphatase inhibitor cocktail (#78444, Thermo Fisher Scientific, USA), after which the protein concentration was quantified. Equal amounts of protein were loaded and separated on 12% SDS-PAGE gels and then transferred onto PVDF membranes. The membranes were incubated with primary antibodies at 4°C overnight and then washed in PBS-T and incubated with secondary antibody at room temperature for 2 h. Then membranes were washed in PBS-T and targeted band of proteins were visualized using HRP (BioRad, USA) and analyzed using ChemiDoc XRS + system (BioRad Laboratories, USA). The primary rabbit polyclonal antibodies to IL-2 (1:500) were purchased from Abcam, UK (ab180780). The secondary goat anti-rabbit IgG H&L antibodies (Alkaline Phosphatase) (1:2000) were purchased from Abcam, UK (ab97048).
2.6. Confocal microscopy
To avoiding losing CIMVs in staining process, M-14 cells were previously stained by CellTracker™ Green CMFDA Dye (#C7025, Invitrogen, USA) according to manufacturer’s instructions. After staining CIMVs were isolated using previously described protocol. PBMCs were stained by Vybrant™ Multicolor Cell-Labeling Kit (#V-22889, Thermo Fisher Scientific, USA) by DiD spectrum according to manufacturer’s instruction and seeded on 12-well culture plate. PBMCs were incubated with CIMVs for 3 h incubation in a humidified incubator at 37°C and 5% CO2.
PBMCs were pelleted by centrifugation at 250 g for 5 min. After that, cells were washed from the growth culture medium using PBS and pelleted onto the bottom of the culture plate wells on the coverslip. At this moment it is important to ensure that coverslip remains on the well. This procedure followed by incubation for 30 min at room temperature for sedimentation and adherence of PBMCs onto the coverslips. After PBMCs have been adherent the PBS was gently removed and cells were fixed with 500 µl 10% formalin for 10 min at room temperature. Fixed cells were, firstly, washed once with 500 µl PBS for 5 minutes and then permeabilized with 500 µl 0.5% Triton X-100 for 10 min. Permeabilized cells were washed once again with 500 µl PBS for 5 min. Nuclei were stained with Dapi (dilution 1:10,000) for 10 min and were then washed twice with PBS for 5 min to remove excessive dye. In order to prepare samples coverslips were gently carefully mounted onto glass microscope slides using aqueous mounting medium (ab128982, Abcam, UK). Samples were analyzed by confocal microscopy using LSM 780 confocal microscope and Zen black 2012 software (Carl Zeiss, Germany) at the KFU Interdisciplinary Center for Analytical Microscopy.
2.7. PBMC activation
Isolated PBMCs were seeded on 6-well culture plate (2.5 ⋅ 106 cells per well). CIMVs from native or IL-2 modified M-14 cells were added to the immune cells in concentration 145 µg/ml. Native PBMCs were used as a control. The flow cytometry assay was performed after 72 h of incubation. Also, part of these PBMCs was used for apoptosis analysis after 72 h of cultivation.
2.8. Flow cytometry assay of activated PBMCs
For identification of activated immune cell populations conjugated antibodies staining was performed. Cells were separated by panels and stained with the next conjugated antibodies: FITC anti-human CD8a Antibody (#300906, Biolegend, USA), APC anti-human CD4 Antibody (#357408, Biolegend, USA), PE/Cy7 anti-human CD38 Antibody (#356608, Biolegend, USA), PE anti-human HLA-DR Antibody (#307605, Biolegend, USA), Brilliant Violet 421™ anti-human CD107a (LAMP-1) Antibody (#328626, Biolegend, USA), FITC anti-human CD3 Antibody (#300306, Biolegend, USA), Pacific Blue™ anti-human CD4 Antibody (#317429, Biolegend, USA), PE anti-human CD127 (IL-7Rα) Antibody (#351304, Biolegend, USA), PE/Cyanine7 anti-human CD25 Antibody (#356108, Biolegend, USA), PE anti-human CD196/CCR6 Antibody (#353410, Biolegend, USA), APC anti-human CD183/CXCR3 Antibody (#353708, Biolegend, USA), PerCP/Cyanine5.5 anti-human CD56/NCAM Antibody (#362506, Biolegend, USA) according with manufacture’s instruction. Data was analyzed using FACS Aria III (BD Biosciences, USA) and BD FACSDiva™ software version 7.0.
2.9. Apoptosis analysis
Native M-14 melanoma cells were seeded on cultural 12-well plate (2 ⋅ 105 cells per well) previously before 48 h for performing apoptosis analysis. Then, CIMV-activated PBMCs were added to M-14 melanoma cells (2 ⋅ 105 cells per well). After 24 h of cultivation M-14 cells were collected and washed by DPBS. For performing apoptotic analysis FITC Annexin V Apoptosis Detection Kit with PI (#640914, Biolegend, USA) was used according to manufacturer’s instruction. Data was analyzed using FACS Aria III (BD Biosciences, USA) and BD FACSDiva™ software version 7.0.
2.10. Statistical analysis
Statistica 10.0 version software was used for statistical analysis. One-way ANOVA analysis was used to compare independent groups by quantitative trait. Differences between groups were considered statistically significant at p < 0.05.