Is There a CRISPR Future for Allergy?

Christine B. Franzese, MD, Chair, on behalf of the Allergy, Asthma, and Immunology Committee

Avoidance is one of the three mainstays for treating allergic disorders such as allergic rhinitis or food allergy. If you are allergic to certain foods, until recently, the main treatment option was avoiding the trigger foods. Similarly, with allergic rhinitis, avoidance of triggers such as dust or pet dander is a potential treatment option albeit not an easy one. It can be very difficult to avoid common triggers such as dust or pollen, and many patients would rather get a new allergy doctor than get rid of their pet.

But what if there was another way to avoid our allergens? What if we could engineer foods to eliminate the triggering epitopes that would lead to your severe allergic reaction? What if we could engineer pets—without harming them—that did not produce proteins that would elicit allergy symptoms, such as sneezing, itchy eyes, and nasal congestion? While this may sound like science fiction, the reality is closer than we may think, thanks to a technique known as CRISPR.

What exactly is CRISPR? CRISPR stands for clustered regularly interspaced short palindromic repeats and it is a gene-editing technique that allows for the precise editing of DNA within a targeted organism. CRISPR technology is derived from a bacterial defense mechanism that involves slicing viral DNA using CRISPR-associated proteins (Cas) to prevent or protect against infection. The most commonly used protein is Cas9, which is derived from Streptococcus pyogenes. This defense system has been adapted to produce site-specific double-stranded DNA breaks to edit the genome such that a targeted gene of interest can be disabled, repaired, or completely replaced.

Gene-editing technologies, like CRISPR, are currently being evaluated for a wide variety of applications, including their ability to alter immune cells and their responses. On the flip side—rather than engineering our immune cells to not respond to allergens and triggers—others are evaluating “avoidance” measures by potentially engineering hypoallergic foods and pets.

Food allergies to eggs, peanuts, and milk account for a significant proportion of food-induced anaphylaxis. So, engineering foods that are commonly associated with childhood or adult food allergies has gained attention. Ara h 2, one of the major peanut epitopes, was recently targeted using RNA interference, a predecessor of CRISPR that reduces gene expression at the mRNA level. The resulting stable transgenic plant produced ~25% less Ara h 2.¹ By transitioning to using CRISPR technology, it may be possible to completely remove Ara h2 and other major peanut allergens rather than reduce gene expression.

CRISPR was used in a proof of principle study producing homozygous second-generation Gal d1 (ovomucoid, a major egg allergen) knockout chickens that had no evidence of off-target mutations.² Beta-lactoglobulin (BLG) has been identified as the primary component of milk whey protein and a BLG gene knockout cow produced BLG-free milk that resulted in significantly less Immunoglobulin (Ig) E binding in cow’s milk allergic patients.³ Additional studies are looking at other common allergenic foods such as, wheat and soy.

For domestic pets, the most attention has been dedicated to cats, as cat allergy is very common and causes a wide range of symptoms. Current research is in-vitro and is focusing on the major cat allergen Fel d1. The actual function of Fel d1 is still unknown, but it is a protein that consists of two different chains encoded by the genes CH1 and CH2. Using DNA extracted from tissue samples from 50 cats, CH1 and CH2 were sequenced and then targeted using CRISPR technology to essentially delete Fel d1 from cat cells with no evidence of off-target CRISPR editing found.⁴

Certainly, there are still many questions, including ethical ones, that need to be addressed prior to the widespread utilization of such technology. And there is a long road ahead before CRISPR technology truly reaches mainstream applications. Still, there has already been some progress down this road. The application of this technology in the allergy space is still in its infancy, but there are already positive Phase II trial results evaluating NTLA-2002, a one-time in vivo CRISPR-based therapy targeting KLKB1, for hereditary angioedema.⁵ Maybe the future will arrive sooner than we think.

References

1. Dodo HW, Konan KN, Chen FC, Egnin M, and Viquez OM. 2008. "Alleviating Peanut Allergy Using Genetic Engineering: The Silencing of the Immunodominant Allergen Ara h 2 Leads to Its Significant Reduction and a Decrease in Peanut Allergenicity." Plant Biotechnology Journal 6: 135–45.
2. Oishi I, Yoshii K, Miyahara D, Kagami H, and Tagami T. 2016. "Targeted Mutagenesis in Chicken Using CRISPR/Cas9 System." Scientific Reports 6: 23980.
3. Sun, Z, Wang M, Han S, Ma S, Zou Z, Ding F, et al. 2018. "Production of Hypoallergenic Milk from DNA-Free Beta-Lactoglobulin (BLG) Gene Knockout Cow Using Zinc-Finger Nucleases mRNA." Scientific Reports 8: 15430.
4. Brackett, N, Pomés A, and Chapman M. 2021. "The Major Cat Allergen, Fel d 1, Is a Viable Target for CRISPR Gene Editing." Journal of Allergy and Clinical Immunology 147: AB175.
5. Cohn, D, Gurugama P, Magerl M, et al. 2021. "Results from a Phase 2, Randomized, Placebo-Controlled Trial of CRISPR-Based Therapy NTLA-2002 for Hereditary Angioedema." Annals of Allergy, Asthma & Immunology 133 (6): S6–S7.