Non-Viral Transfection of Human T Lymphocytes

Component: Transfection Agent; Description: 24-armed PDMAEMA nanostar — synthesized via ATRP from silsesquioxane initiator core; Mn: 755 kDa, PDI <1.21; each arm ~200 monomeric units

Component: Comparison Agent; Description: Linear PEI (l-PEI, 25 kDa) — Polysciences; "gold standard" for non-viral transfection

Component: Nucleic Acid; Description: pEGFP-N1 (4.7 kb) — encodes enhanced GFP driven by CMV promoter; purified (EndoFree, >80% supercoiled)

Component: Jurkat Cell Model; Description: Human T-cell leukemia cell line (ATCC TIB-152); suspension cells; model for primary T lymphocytes

Component: Primary Cells; Description: Human peripheral blood mononuclear cells (PBMCs) from healthy donors (Bavarian Red Cross); cultured in LymphoGrow medium (PHA-stimulated)

Component: Polyplex Properties; Description: • Size (hydrodynamic radius): 70.4 ± 4.5 nm (N/P 20)<br>• Zeta potential: +10 mV (N/P 20); neutral at N/P 5; negative at N/P 3

Component: Protocols Tested; Description: • Standard 6-well: Polyplex pre-formation; addition to cells; 4 h incubation; polymer density 10-50 μg/10⁶ cells<br>• HCD: Cells + pDNA mixed (20×10⁶ cells/mL); polymer added directly; 4 h incubation; dilution factor 20-80<br>• Eppendorf tube: Cells directly suspended in polyplex solution (0.25-0.5 mL); 15-90 min incubation; higher local concentration

Parameter: Standard Protocol Optimization; Details: Jurkat cells seeded at 0.05×10⁶ cells/mL (12 h pre-transfection); N/P 10; polymer density 10-50 μg/10⁶ cells; 4 h incubation in 6-well plates; transfection volume 1.2-2.2 mL; assessed at 48 h

Parameter: HCD Protocol; Details: Jurkat cells (20×10⁶ cells/mL in Opti-MEM); pDNA added; polymer added; 4 h incubation with rotation (20 rpm, 37°C); diluted to 1×10⁶ cells/mL; small scale (5×10⁶ cells, 0.25 mL) to large scale (2×10⁹ cells, 50 mL spinner flask)

Parameter: Eppendorf Tube Protocol; Details: Jurkat cells (0.2×10⁶ cells; 0.5 mL transfection volume); polyplexes prepared; cells suspended directly in polyplex solution; 15-90 min incubation; 48 h post-transfection analysis

Parameter: Primary T Cell Transfection; Details: PBMCs cultured 48 h in LymphoGrow; CD3⁺/CD25⁺ activated T cells (~86-98%); Eppendorf or HCD protocols; post-transfection culture with rhIL-2 (11 ng/mL)

Parameter: Controls; Details: l-PEI transfections; untransfected cells; N/P=0 (no polymer)

Parameter: Readouts; Details: • Flow cytometry: % GFP+ cells (low/mid/high producers), viability (PI exclusion)<br>• Polyplex characterization: DLS (Zetasizer Nano ZS), zeta potential, gel retardation assay

Parameter: Replicates; Details: n≥2 independent experiments; mean ± SD

Parameter: Statistical Tests; Details: One-way ANOVA with Bonferroni post-test (Sigma Plot); p < 0.05 significant

Analysis Category: Polyplex Characterization; Methods: Zetasizer Nano ZS — hydrodynamic radius (DLS) and zeta potential; Gel retardation assay (1% agarose, TAE, EtBr) — N/P ratio for charge neutralization

Analysis Category: Transfection Efficiency; Methods: Flow cytometry (Beckman Coulter FC500): GFP fluorescence (em 510 nm); % GFP+ cells categorized as low (1-10 a.u.), mid (10-100 a.u.), high (>100 a.u.)

Analysis Category: Cell Viability; Methods: PI staining (1 μg/mL); flow cytometry; Trypan blue exclusion; automated cell counter (Luna) for primary cells

Analysis Category: Primary Cell Phenotyping; Methods: Flow cytometry: CD3-PE (clone UCHT1), CD25-PE-Cy5; % CD3⁺CD25⁺ activated T cells

Analysis Category: Large-Scale Transfection; Methods: 50 mL spinner flask (100 mL volume); 70 rpm stirring; 2×10⁹ cells; 50 mL transfection volume

Analysis Category: Statistical Analysis; Methods: One-way ANOVA with Bonferroni post-test; Sigma Plot 11.0

Parameter: Size (N/P 20, in HBG); PDMAEMA Nanostar Polyplexes: 70.4 ± 4.5 nm (stable over time)

Parameter: Zeta potential (N/P 3); PDMAEMA Nanostar Polyplexes: -30.7 ± 2.1 mV (negatively charged)

Parameter: Zeta potential (N/P 5); PDMAEMA Nanostar Polyplexes: -0.4 ± 4.0 mV (neutral)

Parameter: Zeta potential (N/P 10); PDMAEMA Nanostar Polyplexes: +7.4 ± 1.8 mV

Parameter: Zeta potential (N/P 20); PDMAEMA Nanostar Polyplexes: +10.1 ± 1.2 mV

Parameter: DNA retardation (gel shift); PDMAEMA Nanostar Polyplexes: Complete at N/P ≥3 (vs. N/P ≥2 for l-PEI)

Polymer Density (μg/10⁶ cells): 50 (l-PEI); Viability (%): 83.1 ± 3.8; Transfection Efficiency (%): 7.9 ± 0.7

Polymer Density (μg/10⁶ cells): 50 (nanostar); Viability (%): 31.3 ± 11.2; Transfection Efficiency (%): 57.7 ± 8.9

Polymer Density (μg/10⁶ cells): 25 (nanostar); Viability (%): 39.1 ± 1.9; Transfection Efficiency (%): 51.0 ± 0.3

Polymer Density (μg/10⁶ cells): 20 (nanostar); Viability (%): ~42; Transfection Efficiency (%): ~60 (viability-optimized)

Polymer Density (μg/10⁶ cells): 10 (nanostar); Viability (%): 94.8 ± 0.8; Transfection Efficiency (%): 8.9 ± 5.7

Polymer Density (μg/10⁶ cells): 3; N/P Ratio: 10; Viability (%): 72.9 ± 9.4; Transfection Efficiency (%): 58.2 ± 10.9

Polymer Density (μg/10⁶ cells): 3 (1×10⁸ cells scale); N/P Ratio: 10; Viability (%): 72.9; Transfection Efficiency (%): 58.2 (maintained)

Polymer Density (μg/10⁶ cells): 3 (2×10⁹ cells scale); N/P Ratio: 10; Viability (%): 58.2 ± 2.1; Transfection Efficiency (%): 70.0 ± 1.9

Polymer Density (μg/10⁶ cells): 2; N/P Ratio: 10; Viability (%): >80; Transfection Efficiency (%): 40-50

Polymer Density (μg/10⁶ cells): 4; N/P Ratio: 10; Viability (%): ~60; Transfection Efficiency (%): ~65

Polymer Density (μg/10⁶ cells): 10; Viability (%): ~60; Transfection Efficiency (%): ~75; High Producers (%): ~30

Polymer Density (μg/10⁶ cells): 5; Viability (%): >80; Transfection Efficiency (%): ~85; High Producers (%): ~35

Polymer Density (μg/10⁶ cells): 4; Viability (%): >80; Transfection Efficiency (%): >80; High Producers (%): ~30

Polymer Density (μg/10⁶ cells): 3; Viability (%): ~80; Transfection Efficiency (%): ~60; High Producers (%): ~25

Polymer Density (μg/10⁶ cells): Optimal conditions; Viability (%): >80%; Transfection Efficiency (%): >80%; High Producers (%): >30% high producers

Parameter: Transfection volume; 6-Well (optimized): 2.2 mL; Eppendorf (optimized): 0.5 mL

Parameter: Cell density; 6-Well (optimized): 0.09×10⁶ cells/mL; Eppendorf (optimized): 0.4×10⁶ cells/mL

Parameter: Polymer concentration; 6-Well (optimized): ~2.4 μg/mL; Eppendorf (optimized): 20-30 μg/mL (higher local concentration)

Parameter: Incubation time; 6-Well (optimized): 4 h; Eppendorf (optimized): 90 min (reduced)

Parameter: Transfection efficiency; 6-Well (optimized): ~60%; Eppendorf (optimized): >80%

Parameter: Viability; 6-Well (optimized): ~42%; Eppendorf (optimized): >80%

Protocol: Eppendorf (90 min); Polymer Density (μg/10⁶ cells): 6; Transfection Efficiency (Donor 1/2): 19.4% / 13.6%; Viability (Donor 1/2): 75.8% / 78.2%

Protocol: Eppendorf; Polymer Density (μg/10⁶ cells): 3; Transfection Efficiency (Donor 1/2): 7.8% / 15.0%; Viability (Donor 1/2): 41.6% / 44.7%

Protocol: Eppendorf; Polymer Density (μg/10⁶ cells): 2; Transfection Efficiency (Donor 1/2): 56.8% / 44.7% (viability compromised); Viability (Donor 1/2): 18.0% / 23.0%

Protocol: HCD (4 h); Polymer Density (μg/10⁶ cells): 3; Transfection Efficiency (Donor 1/2): 37.5% / not shown; Viability (Donor 1/2): 68.9% / not shown

Protocol: Control (no polymer); Polymer Density (μg/10⁶ cells): 0; Transfection Efficiency (Donor 1/2): 0.8% / 0.9%; Viability (Donor 1/2): 75.8% / 78.2%

1. Primary T cell transfection much lower than Jurkat: Transfection efficiencies for primary T cells (up to 56.8% in one donor, but with poor viability; ~37.5% with HCD) were substantially lower than Jurkat cells (>80%). The authors state that "further research into the response of individual T cells to the transfection agent will be necessary, before either method can be used to routinely transfect primary T lymphocytes."

2. Donor-to-donor variability: Cells from two donors showed "distinct differences in their reaction to the conditions of the protocols," with donor 1 performing better in Eppendorf protocol and donor 2 in HCD protocol. The authors note that "the level of activation of the T lymphocytes might be responsible for the observed results."

3. Preliminary primary cell data: The authors explicitly describe these as "preliminary experiments" and "proof-of-concept" for primary T cells; optimization is ongoing.

4. Polymer synthesis complexity: The 24-armed PDMAEMA nanostar is synthesized via ATRP from a silsesquioxane initiator core, which may limit accessibility for many laboratories compared to commercially available PEI.

5. No functional cargo demonstrated: The study used only EGFP reporter plasmid; delivery of therapeutic genes (e.g., CAR constructs) was not tested.

6. CMV promoter may be stress-activated: The authors note that "the transcriptional activity of the CMV promoter... is sensitive to a variety of environmental stresses... and can be upregulated via an intracellular stress-activated MAP kinase pathway." This may overestimate transfection efficiency relative to other promoters.

7. Episomal expression only: The study assessed transient expression at 48 h; no data on expression duration or plasmid integration (which was not intended for this approach).

8. No in vivo data: All experiments were performed in vitro; no demonstration of in vivo efficacy, biodistribution, or therapeutic benefit.

9. Limited mechanistic insight: The authors speculate about different uptake mechanisms for PDMAEMA vs. PEI but do not provide mechanistic evidence (e.g., endocytosis pathway inhibitors, intracellular trafficking).

10. Polymer concentration vs. N/P ratio confounding: The authors found that "the cytotoxicity of the transfection cocktail depends strongly on the absolute amount of polymer added," but the relationship between N/P ratio and polymer density is complex and not fully resolved.

11. No comparison to viral transduction: The study does not benchmark PDMAEMA nanostars against the gold standard for T cell genetic modification (lentiviral or retroviral transduction).

12. Primary cell activation method: Cells were activated with PHA-containing LymphoGrow medium, which may not reflect clinically relevant T cell activation methods.

Report prepared based on the published International Journal of Molecular Sciences article. For full experimental details, supplementary data, and complete references, please refer to the original publication.