Precision engineering for localization, validation, and modification of allergenic epitopes

The allergen-IgE interaction is essential for the genesis of allergic responses, yet investigation of the molecular basis of these interactions is in its infancy. Precision engineering has unveiled the molecular features of allergen-antibody interactions at the atomic level. High-resolution technologies, including x-ray crystallography, nuclear magnetic resonance spectroscopy, and cryo-electron microscopy, determine allergen-antibody structures. X-ray crystallography of an allergen-antibody complex localizes in detail amino acid residues and interactions that define the epitope-paratope interface. Multiple structures involving murine IgG mAbs have recently been resolved. The number of amino acids forming the epitope broadly correlates with the epitope area. The production of human IgE mAbs from B cells of allergic subjects is an exciting recent development that has for the first time enabled an actual IgE epitope to be defined. The biologic activity of defined IgE epitopes can be validated in vivo in animal models or by measuring mediator release from engineered basophilic cell lines. Finally, gene-editing approaches using the Clustered Regularly Interspaced Short Palindromic Repeats technology to either remove allergen genes or make targeted epitope engineering at the source are on the horizon. This review presents an overview of the identification and validation of allergenic epitopes by precision engineering.

Longitudinal T Cell Responses against Ancestral, Delta, and Omicron SARS-CoV-2 Variants Determined by Rapid Cytokine Release Assay in Whole Blood

T cell immunity to natural SARS-CoV-2 infection may be more robust and longer lived than Ab responses. Accurate assessment of T cell responses is critical for understanding the magnitude and longevity of immunity across patient cohorts, and against emerging variants. By establishing a simple, accurate, and rapid whole blood test, natural and vaccine-induced SARS-CoV-2 immunity was determined. Cytokine release in whole blood stimulated with peptides specific for SARS-CoV-2 was measured in donors with previous PCR-confirmed infection, suspected infection, or with no exposure history (n = 128), as well as in donors before and after vaccination (n = 32). Longitudinal assessment of T cell responses following initial vaccination and booster vaccination was also conducted (n = 50 and n = 62, respectively). Cytokines were measured by ELISA and multiplex array. IL-2 and IFN-γ were highly elevated in PCR-confirmed donors compared with history-negative controls, with median levels ∼33-fold and ∼48-fold higher, respectively. Receiver operating curves showed IL-2 as the superior biomarker (area under the curve = 0.9950). Following vaccination, all donors demonstrated a positive IL-2 response. Median IL-2 levels increased ∼32-fold from prevaccination to postvaccination in uninfected individuals. Longitudinal assessment revealed that T cell responses were stable up to 6 mo postvaccination. No significant differences in cytokine production were observed between stimulations with Wuhan, Delta, or Omicron peptides. This rapid, whole blood-based test can be used to make comparable longitudinal assessments of vaccine-induced T cell immunity across multiple cohorts and against variants of concern, thus aiding decisions on public health policies.

Evolutionary Biology and Gene Editing of Cat Allergen, Fel d 1

Allergy to domestic cat affects up to 15% of the population, and sensitization to cat allergen is associated with asthma. Despite the pervasiveness of cat allergic disease, current treatments have limited impact. Here, we present a bioinformatics analysis of the major cat allergen, Fel d 1, and demonstrate proof of principle for CRISPR gene editing of the allergen. Sequence and structural analyses of Fel d 1 from 50 domestic cats identified conserved coding regions in genes CH1 and CH2 suitable for CRISPR editing. Comparative analyses of Fel d 1 and orthologous sequences from eight exotic felid species determined relatively low-sequence identities for CH1 and CH2, and implied that the allergen may be nonessential for cats, given the apparent lack of evolutionary conservation. In vitro knockouts of domestic cat Fel d 1 using CRISPR-Cas9 yielded editing efficiencies of up to 55% and found no evidence of editing at predicted potential off-target sites. Taken together, our data indicate that Fel d 1 is both a rational and viable candidate for gene deletion, which may profoundly benefit cat allergy sufferers by removing the major allergen at the source.

New Frontiers: Precise Editing of Allergen Genes Using CRISPR

Genome engineering with clustered regularly interspaced short palindromic repeats (CRISPR) technology offers the unique potential for unequivocally deleting allergen genes at the source. Compared to prior gene editing approaches, CRISPR boasts substantial improvements in editing efficiency, throughput, and precision. CRISPR has demonstrated success in several clinical applications such as sickle cell disease and β-thalassemia, and preliminary knockout studies of allergenic proteins using CRISPR editing show promise. Given the advantages of CRISPR, as well as specific DNA targets in the allergen genes, CRISPR gene editing is a viable approach for tackling allergy, which may lead to significant disease improvement. This review will highlight recent applications of CRISPR editing of allergens, particularly cat allergen Fel d 1, and will discuss the advantages and limitations of this approach compared to existing treatment options.