advances-in-protein-chemistry

allergen induces IgG response which eventually overrides the allergic IgE response [39,40]. It is an interesting approach although it is not
effective all the time. Peanut allergy has attracted a lot of attention, since very severe reactions can occur with it, which makes accidental
ingestions more worrisome. One study reports a 38-year-old woman with peanut allergy who underwent oral desensitization. At the end
of desensitization and maintenance phase of 6 months she can eat 40 g of peanuts three-times a week daily for an indefinite period of
time; moreover, she was able to tolerate peanut-containing products without issues.
Figure 8: Immuno therapy for food allergy.
Administration of heat-denatured proteins: This approach of immunotherapy revolves around the fact the allergic antibody binds
to both sequential and conformational epitopes on allergic proteins. Heat denaturation destroys conformational epitopes and makes
allergic protein tolerable [41]. Studies on cow’s milk have shown that, children that were allergic to milk, 73% tolerated extensively heated
milk products. Similarly another group saw similar results in children with hen’s egg allergy being challenged with baked egg products.
This may represent another avenue to explore with regard to therapy of food allergy.
Peptide immunotherapy: One of the major drawbacks of protein based immunotherapy is the potential for severe systemic reactions,
since whole allergens( which are usually large molecules) are associated with the risk of inducing allergic reaction owing to the presence
of B-cell epitopes on the allergen that can crosslink IgE [36,37]. Peptide-based immunotherapy uses short peptides instead of large
proteins. It can prevent the crosslinking of IgE and hence triggering mast cells and basophils which mediate allergic reaction. This was
studied regarding cat hyper-sensitivity, with significant clinical improvement in symptoms. Studies have yet to reach the clinical trial
stage in peptide immunotherapy, but this may be a future direction.
Use of recombinant allergens: This concept involves engineering antigenic epitope-free proteins through PCR mutagenesis and as
in peptide immunotherapy, allows an antigen to influences specific T cells without crosslinking IgE. This has been investigated in the
case of peanut allergy, where mutated Ara h 1, 2 and 3 (HKE-MP123) have been engineered to be expressed by Escherichia coli and then
administered in murine model [42]. The outcome demonstrated a decrease in food challenge reactivity compared with the native allergen.
Anti-IgE therapy: Anti-IgE is a humanized mouse monoclonal IgG antibody directed against the human IgE molecule which binds
to freely circulating IgE, thereby rendering it unable to bind to its specific high-affinity receptor (FcεRI) on mast cells and basophils. This
works through an ‘allergen nonspecific’ approach, whereby it can be effective against multiple different allergens. AntiIgE has already
been studied and administered successfully in asthma and allergic rhinitis. Given the success of these studies, humanized monoclonal
anti-IgE [43] has recently been used in animal studies and preliminary clinical studies in human with considerable success.
Treatment type Key features Clinical trials on Human
Desensitization
Incrementally increased swallowed allergen Dose resulting in
desensitization, Tolerance
Heat-denatured protein Extensively heated foods may be less Allergenic Yes
Peptide immunotherapy Prevents IgE crosslinking, mast cells not activated No
Anti-IgE immunotherapy Decreases IgE available for allergen binding Yes
Table 2: Immune therapies for food allergy.
In the past decade, new expression systems have emerged as a serious competitive force in the large-scale production of recombinant
proteins and peptides.Some products of these expression systems have reached market and is likely to become Gen-next in production
in the proteins and peptides. Very briefly, we discuss two important ones.
Molecular Pharming
Yes
Pharming is derived from two words- farming and pharmaceuticals. It refers to large scale production of recombinant pharmaceutical
proteins in which living cells or organisms (such as plants) are used as expression hosts. In simple words, pharming or molecular
farming as it is often called, involves the use of genetically enhanced plants to produce varied array of pharmaceutical proteins (Figure
9). Growing recombinant proteins in plants is relatively new concept and it has evolved as a method that is simple, inexpensive and allow
large scale production of safe recombinant proteins [44,45]. Until recently, most plant derived proteins have been produced in transgenic
tobacco plants and extracted directly from leaves. These proteins were produced in low levels typically less than 0.1 % of the total soluble
proteins. As an alternative to transgenic plants, transplastomic plants are now being used to achieve higher yields. Transplastomic plant
is a transgenic plant in which the desired transgene is introduced into the plastid genome rather than nuclear genome by the process
of particle bombardment. Transplastomic plants provide higher yield of expressed transgene which in some cases can be as high as
25% of the total soluble protein [45]. Other plants that nowadays used in molecular farming include maize (for producing antibodies,
enzymes such as trypsin, laccase, proteins such as avidin),vegetables such as potatoes (for antibodies,human milk protein), tomatoes (for
producing rabies vaccine) as well as other fruit plants such as banana which can be consumed raw by adult and children. As can be seen a
large number of proteins ranging from enzymes to complex proteins such as antibodies have been expressed in plants but we shall focus
on only those proteins that come under our purview and have diagnostic, therapeutic and prophylactic applications.
Proteins currently being produced in plants for molecular farming purposes can be categorized into two main categories areas: (1)
Therapeutic proteins (antibodies,vaccine peptides etc) (2) industrial proteins (e.g., enzymes). Industrial proteins are out of the scope of
this chapter and will not be discussed.
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