Delivery Vehicles, Not Payloads, Will Decide CGT Success, USP Scientist Argues

A principal scientist at USP argues that the next phase of innovation in cell and gene therapy will be driven less by payload design and more by the delivery vehicle itself. In a viewpoint published in GEN, Anthony Blaszczyk, PhD, of USP's Global Biologics Department, writes that therapeutic efficacy, safety and manufacturability in CGT are directly influenced by delivery performance, and that safely and repeatedly delivering the correct genetic cargo to the right cell remains one of the most critical determinants of clinical success.

What separates the three leading platforms?

Blaszczyk frames AAV vectors, lentiviral vectors (LVVs) and lipid nanoparticles (LNPs) as complementary rather than competing systems, each with measured structural constraints.

• AAV: a small, non-enveloped vector of roughly 20–25 nm carrying a single-stranded DNA genome, with a packaging capacity limited to about 4.7 kb. Serotypes differ in receptor and surface proteins, which shape tissue tropism and immune recognition.
• LVV: a lipid-enveloped vector with an RNA genome and viral enzymes for integration, accommodating approximately 8–10 kb — roughly double AAV's capacity. It is the only one of the three platforms that integrates permanently into the host genome, supporting durable expression in dividing cells.
• LNP: a synthetic, non-viral particle of 50–150 nm built from ionizable lipids, phospholipids, cholesterol and PEG-lipids. It offers the greatest payload flexibility — large mRNAs, combinations of nucleic acids and gene-editing cargoes that exceed viral packaging limits — and translates its RNA cargo directly in the cytoplasm without nuclear delivery.

How do the platforms compare on targeting and safety?

AAV offers the highest target specificity in vivo and is described as the most mature platform for targeted in vivo gene delivery, aided by natural serotype tropisms and capsid engineering. LVVs show moderate in vivo specificity but have excelled ex vivo — the CAR T workflow of isolating, modifying and reinfusing cells — while in vivo LVV success will likely require custom envelope engineering beyond the commonly used VSV-G glycoprotein. LNPs carry the lowest intrinsic specificity and accumulate in the liver after systemic administration, though advances in lipid chemistry and targeting strategies show promise.

On safety, the author links delivery efficiency directly to dose reduction: high-dose requirements raise off-target risk, toxicity and unintended immune responses. Citing a 2023 review in Drugs, he notes that high AAV dosing has been linked to hepatotoxicity, thrombotic microangiopathy, cytokine-mediated toxicity and sensory neuron toxicity, increasing regulatory focus on dose optimization and immune monitoring. Pre-existing immunity to natural AAV serotypes further complicates re-dosing.

LVV integration carries insertional mutagenesis risk; Blaszczyk notes that modern self-inactivating designs have substantially reduced this concern but that long-term monitoring remains important. LNPs avoid genomic integration and yield only transient expression, yet both lipid components and RNA payloads can trigger innate immune responses, and uncommon risks include PEG-associated immunogenicity and lipid-associated toxicity — risks amplified in repeat dosing, which is increasingly common for RNA therapies.

Where is each platform heading?

Future AAV work centers on engineered capsids with better transduction, tissue specificity and reduced susceptibility to pre-existing immunity, supporting lower doses and manufacturing demand. Dual-AAV systems that split large transgenes across two vectors, and smaller engineered machinery proteins, are being pursued to carry CRISPR payloads past the 4.7 kb ceiling. LVVs are expected to keep dominating ex vivo applications while expanding in vivo, contingent on new envelope designs. For LNPs, better lipid chemistry, surface engineering and improved endosomal escape could unlock extrahepatic delivery and position them for future RNA and genome-editing therapies.

Blaszczyk closes on analytical infrastructure: USP has already developed a portfolio of AAV reference materials, has recently expanded into LVV reference materials, and has additional LVV- and LNP-related standards under development. He argues the next generation of transformative medicines will be defined not by payloads alone but by the ability to deliver them to the right cells at the right dose.