Table 3.

Approaches used for decreasing immunogenic potential of wheat gluten proteins

Approach	Gluten proteins targeted	Main finding	References
RNA interference of gliadin genes	γ-Gliadins	Reduced expression of γ-gliadins in nine transgenic lines, accompanied by increased levels of α- and ω-gliadins; higher SDS-sedimentation values observed in six transgenic lines.	Gil-Humanes et al. (2008) and Pistón et al. (2011)
	α-, ω- and/or γ-gliadins	Gliadin expression strongly down-regulated (by 85.6% on average); transgenic wheat lines with very low levels of toxicity for CD patients obtained; many of the transgenic lines exhibiting improved end-use quality and nutritional value	Gil-Humanes et al. (2010, 2012, 2014a, b)
	ω-5 gliadins	Content of ω-5 gliadin decreased by 80% in one line and eliminated in another line; reactivity to the IgE antibody of WDEIA patients greatly reduced; dough functionality parameters improved	Altenbach and Allen (2011) and Altenbach et al. (2014a, b, 2015)
	α-Gliadins	Content of α-gliadin strongly reduced in two transgenic lines, compensated by increased levels of γ- and ω-gliadins, HMW-GSs and other seed proteins; no significant effect on flour functionality observed	Becker et al. 2012
	α-, γ- and ω-gliadins, LMW-GSs	Strong silencing of different types of gliadins and LMW-GSs achieved; several lines devoid of CD epitopes from the highly immunogenic α- and ω-gliadins; total protein and starch contents unaffected in the grains of the transgenic lines	Barro et al. (2016)
	Secalins in 1BL/1RS wheat line	Significant decreases in multiple secalins and closely related ω-gliadins; increased levels of α-gliadins and HMW-GSs; improved dough functionality for two transgenic lines	Blechl et al. (2016)
	ω-1,2 gliadins	Effective silencing of ω-1,2 gliadins achieved; immunoreactivity of flour protein to the antibodies of CD patients decreased; dough functionality improved in one transgenic line	Altenbach et al. (2019a, b)
Deletion of gluten chromosomal loci	α-, γ- and ω-gliadins	Three deletion lines with null allele at Gli-D1, Gli-B1 or Gli-B2 developed; immunoreactivity of flour proteins reduced by 6–18% in the deletion lines	Waga et al. (2013)
	ω-1,2 and ω-5 gliadins	Wheat genotypes lacking both ω-1,2 and ω-5 gliadins developed, with approximately 30% reduction of gliadin immunoreactivity but improved gluten functionality	Waga and Skoczowski (2014)
	α-Gliadins	Three deletion lines lacking Gli-A2, Gli-D2 or Gli-A2/Gli-D2 prepared; large decreases in α-gliadin expression observed in the three lines; the 33-mer peptide bearing gliadins not detected in the lines missing Gli-D2 or Gli-A2/Gli-D2	Camerlengo et al. (2017)
	α-Gliadins	Six deletion lines lacking gliadin chromosome loci developed; the line missing Gli-D2 showed improved dough functionality and breadmaking quality, with the level of CD epitopes significantly decreased	Wang et al. (2017) and Li et al. (2018)
Expression of engineered glutenases	α-Gliadins	Transgenic wheat expressing engineered glutenases developed, which could degrade the CD epitopes carried by α-gliadins under simulated gastrointestinal conditions	Osorio et al. (2019)
Manipulation of regulators	LMW-GSs and gliadins	Expression of gliadins and LMW-GSs in wheat grains significantly decreased by suppressing the function of 5-methylcytosine DNA glycosylase or the WPBF TF	Wen et al. (2012) and Moehs et al. (2019)
Genome editing of gliadin genes	α-Gliadins	Effective mutation of multiple α-gliadin genes accomplished using CRISPR/Cas9 mediated genome editing, with the immunoreactivity of gluten proteins reduced by up to 85%	Sánchez-León et al. (2018) and Jouanin et al. (2019a)