Managing Allergenic Proteins
A potential consequence of the genetic modification of crop plants is introduction or creation of allergens. This could occur in several possible ways, including introduction of unknown allergens with the transgenic protein itself, modification by the host transgenic plant of the immunogenic properties of the transgenic protein, modification of the immunogenicity of endogenous proteins in the transgenic plant, and dissemination of an allergen through pollen that induces respiratory sensitization (Moneret-Vautrin, 2002). Such risks need to be evaluated prior to widespread use of a transgenic crop plant. Unfortunately, the possibility of allergen induction can be exaggerated to the general public and used to fuel the idea that genetic modification is an unpredictable and irresponsible science. It is true that the allergenicity of proteins, such as BNA, may not be widely known before their introduction into a crop plant. However, the scientific community quickly becomes aware of such potential problems (Nordlee et al., 1996) and acts appropriately. For example, the transgenic soybean plants expressing BNA were never commercially developed. As we gain a better understanding of the identity and epitopic composition of common allergenic proteins, their selective modification or elimination becomes feasible, and this could lead to the development of hypoallergenic versions.
Rice induces allergic reactions in some people and this is a growing problem in some countries, like Japan (Watanabe, 1993). One of the major rice allergens was identified as a 16-kDa albumin (Matsuda et al., 1988; Urisu et al., 1991). This protein is encoded by a multigene family composed of at least ten members (Tada et al., 2003), each of which has allergenic properties (Matsuda et al., 1991). An antisense strategy was used to reduce the abundance of the 16-kDa albumin as well as other gene family members (Tada et al., 1996). An 80% reduction in abundance of the 16-kDa rice allergen was achieved (Tada et al., 1996), and the reduction in protein levels of other family members was proportional to their degree of nucleotide sequence identity with the transgene. Highly homologous proteins were markedly lowered, and proteins with less identity were hardly reduced at all (Tada et al., 2003). Highly immunogenic proteins need only be present in minute quantities in order to elicit an immune response. Thus, these results suggest that the antisense strategy may not be suitable for complete removal of allergenic proteins, especially if they are encoded by divergent multigene families. In this regard, gene silencing strategies (Waterhouse et al., 1998) that require smaller regions of DNA sequence identity may prove to be more suitable.