LETTER TO THE EDITORNo apparent impact of incremental dosing on eliciting dose at double-blind, placebo-controlled peanut challengeOlaya Álvarez García,1,2 Joan Bartra,1,3 Monica Ruiz-Garcia,1Isabel J. Skypala,1,4 Stephen R. Durham,1,4 Robert J. Boyle,1 E.N. Clare Mills,5 Paul J. Turner1

Background: There is increasing interest in the use of eliciting doses (EDs) to inform allergen risk management. EDs can be estimated from the distribution of threshold doses for allergic subjects undergoing food challenges within a specified population. Estimated ED05 values for cow’s milk (the dose expected to cause objective allergic symptoms in 5% of the milk-allergic population) range from 0.5mg to 13.9mg cow’s milk protein. We undertook a single-dose challenge study to validate a predicted ED05 for cow’s milk of 0.5mg protein. Methods: Participants were recruited from 4 clinical centres. Predetermined criteria were used to identify patients reacting to 0.5mg cow’s milk protein (approximately 0.015ml of fresh cow’s milk). Children over 1 year underwent formal challenge to cow’s milk to confirm clinical reactivity. Results: 172 children (median age 6 (IQR 0.7-11) years, 57% male) were included in this analysis. Twelve (7.0%, 95% CI 3.7-11.9%) children experienced objective symptoms that met the predetermined criteria. One participant had mild anaphylaxis which responded to a single dose of adrenaline, the remainder experienced only mild symptoms with no treatment required. We did not identify any baseline predictors of sensitisation which were associated with objective reactivity to the single-dose challenge using 0.5mg cow’s milk protein. Conclusions: These data support an estimated ED05 for cow’s milk of 0.5mg protein. Values for ED05 above 0.5mg for cow’s milk protein proposed for allergen risk management need to be reviewed.

Background: Effector cells assays provide an overall measure of responsiveness to allergen, but the lack of reliable, high-throughput assays limits the clinical utility of this approach. The aim of this study was to develop a high-throughput Basophil Activation Test (BAT), based on human progenitor cell-derived basophils (PCB), and to investigate the role of PCB activation test (PCBAT) in allergy diagnosis. Methods: PCBs were differentiated from CD34+ progenitor cells, and sensitized with sera from subjects sensitized to cat (n=35, 17 subjects clinical reactivity validated), peanut-allergic (n=30, 15 subjects clinical reactivity validated), peanut-sensitized but tolerant subjects (n=13). Sensitized PCBs were then stimulated with a range of concentrations of the corresponding allergens and degranulation was measured using CD63 expression on flow cytometry. Results: Following passive sensitisation of the mature PCB (2D7+/FcεRI+/CD117-/HLADR-) with serum and stimulation with allergen, we saw a dose-dependent increase in CD63 expression which was allergen specific. In subjects sensititsed to cat there was a positive correlation between PCBAT area under curve (AUC) versus specific IgE (sIgE) to cat (p=0.001) and versus airway responsiveness to inhaled cat allergen (p=0.026). There was a significant negative correlation between PCBAT AUC for peanut allergen and response to oral food challenge test to peanut - subjects with higher PCBAT AUC reacted to a lower dose on the oral food challenge to peanut (p=0.001), and had higher sIgE to Ara h 1 (p=0.007). All peanut tolerant subjects showed no reaction to peanut on PCBAT. Conclusion: PCBAT may confer a powerful alternative tool in allergy testing.