Risk of an immediate allergic reaction during immunotherapy can be decreased by modifying the IgE antibody binding sites (epitopes) with point mutations introduced by site-directed mutagenesis or with protein polymerization.
61 () Modified food allergens may be combined with bacterial adjuvants (such as heat-killed Listeria moncytogenes, HKLM, or heat-killed E coli, HKE) to enhance the Th1-skewing effect and decrease the Th2-skewing effect. Peanut-allergic C3H/HeJ mice were treated subcutaneously 10 weeks following sensitization with a mixture of the recombinant, modified major peanut allergens and HKLM (m Ara h 1-3 plus HKLM).
62 All mice in the sham-treated group developed anaphylactic symptoms, whereas only 31% of mice in the m Ara h 1-3 plus HKLM group developed mild anaphylaxis during a post-treatment oral peanut challenge. In subsequent studies, a non-pathogenic strain of
Escherichia coli containing the modified peanut proteins was used as an adjuvant and the vaccine was administered via the oral, nasal, subcutaneous and rectal route. Oral delivery was not effective, presumably due to breakdown of the peanut-containing
E coli. Although nasal and subcutaneous routes were effective, the rectal delivery was selected for further study because of safety concerns, since non-pathogenic
E. coli bacteria reside in the colon. Peanut-allergic C3H/HeJ mice received 0.9 (low dose), 9 (medium dose), or 90 (high dose) μg of heat-killed
E. coli expressing modified proteins Ara h 1-3 (HKE-MP123) per rectum, HKE-containing vector (HKE-V) alone, or vehicle alone (sham) weekly for 3 weeks.
63 Mice were challenged with peanut 2 weeks following the final vaccine dose, and then at monthly intervals for two more months. After the first peanut challenge, all 3 doses of HKE-MP123 and the HKE-V-treated groups had reduced severity of anaphylaxis (
P<0.01, 0.01, 0.05, 0.05, respectively) compared with the sham-treated group. However, only the medium- and high-dose HKE-MP123-treated mice remained protected for up to 10 weeks following treatment. Peanut specific-IgE levels were significantly lower in all HKE-MP123-treated groups (P<0.001); they were most reduced in the high-dose HKE-MP123-treated group at the time of each challenge.
In vitro, peanut-stimulated splenocytes from the high-dose HKE-MP123-treated mice produced significantly less IL-4, IL-13, IL-5 and IL-10 (
P<0.01, 0.001, 0.001, and 0.001, respectively). IFN-γ and TGF-β synthesis were significantly increased (
P<.00001 and 0.01, respectively) compared with sham-treated mice at the time of the last challenge. A Phase I clinical safety study is currently enrolling adult subjects with peanut allergy. In the future studies, probiotic bacteria may also be used as bacterial adjuvants to avoid the concerns of excessive Th1 stimulation by killed pathogenic bacteria.
64 | TABLE IIIModified recombinant allergen immunotherapy for food allergy |
Other approaches
Several additional approaches to peanut allergy have been evaluated in animal studies, as outlined in . In peptide immunotherapy, the antigen presenting cells are provided with T-cell epitopes in the absence of a second signal and mast cells are not activated because the short peptides are unable to cross-link two IgE molecules.
65 66Immunization with bacterial plasmid DNA (pDNA) that encodes specific antigens can induce prolonged humoral and cellular immune Th1 responses. The Th1 effect is mediated by immunostimulatory sequences (ISSs) consisting of un-methylated cytosine and guanine motifs (CpG motifs) in the bacterial pDNA backbone. Intramuscular immunization of naïve AKR/J (H-2
K) and C3H/HeJ (H-2
K) mice with pDNA encoding Ara h 2 prior to intra-peritoneal peanut sensitization had a protective effect in AKR/J mice, but induced anaphylactic reactions in C3H/HeJ mice following peanut challenge.
67 In another study, oral chitosan-embedded Ara h 2 had a protective effect in AKR mice.
68 These studies raise concern that the effect of pDNA-based immunotherapy may be strain-dependent and not universally effective in reversing IgE-mediated food hypersensitivity in man.
Synthetic immunostimulatory oligodeoxynucleotides containing unmethylated CpG motifs (ISS) linked to allergenic proteins represent an alternative approach to DNA-based immunotherapy. ISS-linked Ara h 2 administration was effective in the suppression of anaphylactic symptoms compared to shame controls.
69 Similarly, intradermal immunization with a mixture of ISS and β-galactosidase (β-gal) provided protection against fatal anaphylaxis induced by intraperitoneal β-gal sensitization and challenge that was comparable to protection provided by immunization with the pDNA-encoding β-gal.
70 Protection was associated with an increase in IgG
2a/IFN-γ and a decrease in IgE, IL-4, and IL-5. ISS-linked allergen immunization may have a prophylactic effect against food allergy, however, the ability to reverse established food allergy remains to be determined.
Other novel therapeutic approaches that may be utilized to treat food allergy include human immunoglobulin Fc-Fc fusion proteins that cross-link the high affinity FcεRI and low affinity FcγRIIb on mast cells and basophils leading to inhibition of degranulation.
71, 72 73 Since many major food allergens have been identified, this approach might be applied to food allergy therapy. C-type lectin receptors on dendritic cells, SIGNR-1 (also called CD209b) may play a role in promoting oral tolerance development and thus preventing food-induced anaphylaxis.
74 Mice sensitized with mannoside-conjugated BSA (Man
51-BSA) were protected from anaphylaxis during an oral challenge with BSA and Man
51-BSA whereas mice sensitized with BSA alone developed significant allergic symptoms during oral challenge with BSA. Man
51-BSA selectively targeted lamina propria dendritic cells that expressed SIGNR-1 and induced the expression of IL-10, but not IL-6 or IL-12p70, promoting the generation of CD4+ type 1 regulatory T. These findings suggest that sugar-modified food antigens might be used to induce oral tolerance by targeting SIGNR-1 and lamina propria dendritic cells.