New Cytometry Technique for Characterizing Viral Vectors

Kite Pharma, a Gilead Company, has developed a technique for analyzing individual lentiviral vector particles, which it hopes will allow better characterization of future in vivo CAR T therapy products than traditional Western blotting.

“The virus is going to be our product, and we want to have the deepest understanding we can have of that,” explains Kristen Kellar, a scientist working in analytical development at Kite.

“Given how new and nascent the in vivo lentiviral vector delivery space is, we’re trying to understand what the methods are by which we can more robustly characterize our products,” adds Priti Hegde, PhD, senior vice president of research and development, also at Kite.

According to Kellar, the new technique will be of interest to everyone in gene and cell therapies based on enveloped viruses like lentiviruses. “As reagents are developed,” she says, “more people will be on board with how powerful this technology can be.”

The new technique is based on flow virometry and involves individual particles passing a detector where attributes, such as their size and proteins on the surface, can be characterized, she says.

This allows for, as an example, the mapping of protein distribution as differences in protein abundance between particles are not lost during averaging. As Kellar explains, if one vector particle has, for example, 10 times more of a specific protein than another, a Western blot would characterize both particles as the average of five times for both particles.

According to Kellar, while flow virometrry has been used in the past, new instruments focused on analysis of nanoparticles allow for deeper characterization.

“They’ve brought the technology to a place where we feel very confident that we’re seeing all the particles and they seem the right size,” she says. “What’s relatively new is we’re able to stain the protein on the surface, and there’s one abundant protein we can see.”

Going forward, Kite Pharma hopes to use the technology throughout the development process, including during the final stages to assess the consistency from batch-to-batch. They’re also investigating some quantitation bead sets, which will allow them to quantify viral proteins on the vector surface, she says.

Hegde adds, “Given how nascent the field [of in vivo cell therapy] is, what’s exciting for us is we’re already seeing clinical proof of concept and, so, the next challenge at Kite is knowing how to scale robustly.”

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