Sublingual immunotherapy with recombinant Mal d 1 downregulates the allergen‐specific Th2 response

1. Muraro A, Roberts G, Halken S, et al. EAACI guidelines on allergen immunotherapy: executive statement. Allergy. 2018;73(4):739‐743. 2. Marsh DG, Lichtenstein LM, Campbell DH. Studies on “allergoids” prepared from naturally occurring allergens. I. Assay of allerge‐ nicity and antigenicity of formalinized rye group I component. Immunology. 1970;18(5):705‐722. 3. Hoiby AS, Strand V, Robinson DS, Sager A, Rak S. Efficacy, safety, and immunological effects of a 2‐year immunotherapy with Depigoid birch pollen extract: a randomized, double‐blind, placebo‐ controlled study. Clin Exp Allergy. 2010;40(7):1062‐1070. 4. Pfaar O, Biedermann T, Klimek L, Sager A, Robinson DS. Depigmented‐ polymerized mixed grass/birch pollen extract immunotherapy is ef‐ fective in polysensitized patients. Allergy. 2013;68(10):1306‐1313. 5. Shamji MH, Ljorring C, Francis JN, et al. Functional rather than im‐ munoreactive levels of IgG4 correlate closely with clinical response to grass pollen immunotherapy. Allergy. 2011;67(2):217‐226. 6. Shamji MH, Wilcock LK, Wachholz PA, et al. The IgE‐facilitated al‐ lergen binding (FAB) assay: validation of a novel flow‐cytometric based method for the detection of inhibitory antibody responses. J Immunol Methods. 2006;317(1–2):71‐79. 7. Reithofer M, Böll SL, Kitzmüller C, et al. Alum‐adjuvanted aller‐ goids induce functional IgE‐blocking antibodies. Clin Exp Allergy. 2018;48(6):741‐744. 8. Möbs C, Ipsen H, Mayer L, et al. Birch pollen immunotherapy results in long‐term loss of Bet v 1‐specific TH2 responses, transient TR1 activation, and synthesis of IgE‐blocking antibodies. J Allergy Clin Immunol. 2012;130(5):1108‐1116. 9. Zissler UM, Jakwerth CA, Guerth FM, et al. Early IL‐10 producing B‐cells and coinciding Th/Tr17 shifts during three year grass‐pollen AIT. EBioMedicine. 2018;36:475‐488. 10. Wambre E. Effect of allergen‐specific immunotherapy on CD4 + T cells. Curr Opin Allergy Clin Immunol. 2015;15(6):581‐587.


S U PP O RTI N G I N FO R M ATI O N
Additional supporting information may be found online in the Supporting Information section at the end of the article.

Sublingual immunotherapy with recombinant Mal d 1 downregulates the allergen-specific Th2 response
To the Editor, Birch pollen-related food allergy (BPRFA) is the most prevalent food allergy in adolescents/adults and affects more than 70% of birch pollen-allergic patients. Following sensitization to the major birch pollen allergen Bet v 1, allergic symptoms to food occur due to immunological cross-reactivity to homologous proteins. Mal d 1, the Bet v 1-homologue in apple, is among the most frequent triggers of BPRFA. Allergenspecific immunotherapy (AIT) with birch pollen extract is established as effective treatment for birch pollinosis. However, its benefit for the concomitant food allergy is controversial. In search of alternative and more efficient treatment options for BPRFA, we conducted a rand-

CCR4+ cells among CD4+ T cells
It has been suggested that successful AIT induces the selective deletion of so-called pro-allergic Th2 effector cells, probably because they are prone to activation-induced cell death. 5 These CD27 − CRTh2 + CCR4 + CD4 + T cells represent the dominant allergenspecific T-cell subset associated with Th2 cytokine production in allergic patients. 5 In PBMC from rMal d 1-treated patients, we found a significant decrease in CD27 − CRTh2 + CCR4 + CD3 + CD4 + CD45RA − T cells after 4 weeks of treatment, which was even more pronounced after 16 weeks (Figure 2). No changes of pro-allergic Th2 cells were detected in the placebo group. In parallel, we analysed other T-cell subsets within CD3 + CD4 + CD45RA − memory T cells, that is CCR4 + (Th2), CXCR3 + and CCR5 + (Th1) and CD25 + CD127 − (Treg). 6 Additionally, we assessed the number of circulating T follicular helper (Tfh)-like cells (CXCR5 + ), which have been shown to induce Ig production in naive and memory B cells, 7 and further characterized them as Tfh1 However, no significant alterations in the relative numbers of any of these subpopulations were observed ( Figure S1). We speculate that the proportion of allergen-specific Th2 cells was sufficient to be detected within the CD27 − CRTh2 + CCR4 + CD4 + subset and declined promptly after the onset of SLIT. However, the number of allergen-specific T cells within the other subsets was too small to result in detectable changes.
Still, we cannot exclude that SLIT may have altered the function of Treg vious studies performed with allergen extracts and strengthen the concept that the reconstitution of peripheral tolerance by suppression of allergen-specific Th2 cells represents an early step in successful SLIT. 2,8,9 Finally, this study again provides evidence that a switch from Th2 to Th1 responses happens during a later phase of AIT. 6,10

ACK N OWLED G M ENTS
This work was supported by the Österreichischer Jubiläumsfonds, project ÖNB 16620, by the Austrian Science Fund, projects KLI96 and SFBF4610, by the Christian Doppler Research Association, and Biomay AG, Austria. We thank Birgit Nagl and Sandra Heizer for excellent technical support.

CO N FLI C T S O F I NTE R E S T
The authors declare that they have no conflicts of interest.