We built a codon optimizer that boosts expression of clinically-relevant transgenes up to 7x. We’ve compared our algorithm to five other codon optimizers available on the market, and results suggest that our algorithm is consistently superior across genes of interest.
But what is a codon optimizer? And why does any of this matter?
Generally, a codon optimizer is a software tool that alters the DNA or RNA sequence of a gene by adjusting its codons — the three-nucleotide units encoding amino acids — to match the preferred codon usage in a specific organism. Consider, for example, the amino acid leucine. This amino acid can be encoded by several different codons (including CTT, CTC, and TTA), so codon optimization tools begin by swapping out unpopular codons and replacing them with more widely-used variants.
If scientists want to take a gene from, say, a plant, and insert it into a human cell, then they’d use codon optimization to adjust the plant gene’s codons to match the human cell’s preferences, thus enhancing protein translation and boosting expression. In other words, codon optimization makes it easier for a cell to ‘read’ a gene and convert it into proteins.
But this is, admittedly, a simplistic explanation. Modern codon optimizers do a lot more than just swap out “unpopular” codons. Some algorithms also check mRNA folding patterns to make sure the gene, once transcribed, won’t fold into weird structures that impede translation.
Our codon optimizer does all of these things and more. Our algorithm accounts for the entire lifecycle of a gene. When designing an AAV vector, for example, it considers not only “unpopular” codons, but also ensures the gene will be faithfully packaged into the vector, its mRNA is not prone to rapid degradation, and that it will effectively utilize the host cell’s gene expression machinery. It’s not easy to select sequences that are compatible with all these bottlenecks, so we augment our optimizer with in-house knowledge of AAV biology.
To test out our codon optimizer, we did an experiment. Briefly, we took two clinically-relevant payloads — Luxturna and Zolgensma — and tagged of them with a fluorescent reporter protein. These sequences were either altered using our codon optimizer, or left intact. We packaged these payloads into AAVs and then transduced HEK293T cells with them. Finally, we studied protein expression levels using both microscopy and flow cytometry. The data are shown below (cells “glowing green” is a good thing, as is shifting purple peaks to the right.)
We are still validating this tool across more conditions, but all of our data so far suggests that these results are transferable across different cell lines and different cell types (HEK293, HEK293T, T-cells).
This codon optimizer is part of our AAV Edge platform.