Allergenicity assessment of genetically modified organisms (GMOs)

Some important definitions:

Allergy: ”Overwhelming pathological reactions of the body due to intercurrent contact with antigens” Clemens von Pirquet 1906

IgE-mediated allergy is the most frequent form of allergy, but many other forms exist (e.g., celiac disease, immune complex diseases-Type III, cell-mediated forms of allergy-Type IV)

Allergenic activity: Induction of an allergic reaction in allergic individual

Allergenicity: Induction of allergy in a not yet allergic individual (i.e., sensitization and induction of allergic reactions)

Source of gene allergenic

Yes

YesYes

Yes

Noo

Sequence Homology

Sequence Homology

Target SerumScreen

Specific Serum Screen

NoNo

Pepsin Resistance &

Animal Models

No

+/+ +/- -/-High Low

Probability of Allergenicity

LikelyAllergenic

Yes Yes

No

Yes Yes

Assessment of the allergenic potential of foods derived from biotechnology FAO/WHO decision tree

Current practice in the assessment of the allergenicity of GMOs

Mainly arguments but rarely experiments

Arguments against the allergenic potential of a GMO

· Lack of sequence homology with known allergens · Inserted gene is expressed only at low levels · Easily digestable protein · Protein source is not an allergen source · Lack of glycolsylation

Sequence comparisons are not suitable for predicting or excluding allergenicity with certainty

Human IgE and T cell reactivity patterns of Bet v 1

isoforms a, e, b, d, and l

T cell reactivity(rel. %)

IgE binding(rel. %)

Skin prick testwheal areas(mm2)

nBet v 1 100 100 ND

rBet v 1a 41 100 70

rBet v 1e 67 83 50

rBet v 1l 87 3 10

rBet v 1d 100 5 7

rBet v 1b 92 60 19

Isoforms of the major birch pollen allergen, Bet v 1 without allergic activity

T1, a Bet v 1-homologous plant protein without allergenic activity

T1, a Bet v 1-homologous plant protein without allergenic activity

The level of expression is not associated with allergenicity

Example: Profilin, a potent cross-reactive plant allergen is expressed at low levels

Resistance to proteolytic digestion does not predict allergenicity

Example: Pollen contains trypsin-labile as well as trypsin-resistant allergens

Glycosylation does not predict allergenicityExample: Phl p 7, a potent allergen from timothy grass pollen is not glycosylated

Pleiotropic effects affecting the overall allergenicity of the GMO must be considered

Example: Upregulation of profilin expression during pollen maturation

The expression of PR-proteins, which represent important allergens, is regulated by various factors

Allergenic activity and allergenicity need to be assessed: Induction of allergic responses in

experimental animal models

Suggestion:

Evaluation of allergenicity by standardized experimental procedures

Develop procedures for allergenicity assessment which can be applied for GMOs as well as for any other new organism

Investigation of the allergenic activity in allergic patients: IgE reactivity of extracts from GMOs and

from the wildtype

Assessment of allergenicity: Induction of IgE responses in animals with

extracts from GMOs and from the wildtype

Allergenic activity

Investigation of whole GMOs

NoYes

Allergenicity

Thanks to:

Armin Spök, Inter-University Research Center for Technology, Work and Culture, Graz, Austria.

Helmut Gaugitsch, Federal Environment Agency, Vienna, Austria.

Sylvia Laffer, Dept. of Pathophysiology, University of Vienna, Austria.