Hereby, we describe the case of a 15-year-old boy, diagnosed with severe egg allergy, who was referred to our Clinic because he had never received MMR vaccination, despite the fact that it was mandatory. Therefore, he could not be admitted to school, further. Indeed, his parents considered MMR vaccination highly risky because of his underlying egg allergy.
A thorough allergological workup was carried out.
As for the clinical history, a single adverse reaction to egg was reported, which had occurred in early infancy (9 months), following the first ingestion of cooked egg. Typically, symptoms included wheezing, dyspnea, change in voice pitch, cough, cry, and pallor. The rapid involvement of the respiratory tract indicated that the reaction was severe4 (the child was hospitalized and treated with corticosteroids and antihistamines). After this event, eggs were completely excluded from the child diet. Moreover, when the child was 9, he suffered from anaphylactic shock, after pine nuts ingestion.
Quantitative SPT were performed with an array of 36 commercially available food allergens (Lofarma, Milan, Italy), reflecting the spectrum of food allergy in Southern Italy (where people consume a typical Mediterranean Diet). Multiple sensitizations were detected, including peanuts, almonds, hazelnuts, wheat, and, particularly, egg white (Fig. 1A). We also performed prick-by-prick, also testing a baked cake (sponge cake; well cooked eggs) and cooked egg (hard boiled; Fig. 1B). Results were expressed in terms of ratio between the area of the allergen wheal and the area of the exogenous histamine wheal (referred to as Skin Index). Moreover, the wheals obtained with egg white, hard-boiled egg white, and baked egg were all greater than 5 mm (average diameter), regarded as associated with a high specificity in childhood.5 These tests indicated that the boy was sensitized to multiple food allergens and that egg allergy was still present.
Furthermore, we evaluated specific IgE level in serum for egg white, OVM, OVA, and OVT. These last results confirmed the skin test results (Fig. 1C). Total IgE levels were particularly high (Fig. 1C).
Having assessed egg allergy, we performed SPT with pure MMR vaccine, which proved negative. Then, we performed intradermal tests with two increasing dilutions of MMR vaccine (viz. 1/100, 1/10). As expected, also this procedure proved negative (Fig. 1D). Moreover, 100 µl of 1/10 dilution of MMR vaccine were injected subcutaneously (injection test). No immediate reaction was observed, either local or systemic.
Finally, in order to confirm the absence of vaccine-specific B-cell clones, which would corroborate the results obtained in vivo, we also performed an ex-vivo B-lymphocyte proliferation assay (Fig. 2 A-D).6 By this approach, also a possible delayed allergic response towards MMR vaccine components was investigated (proliferation of vaccine-specific T-cells). Thus, peripheral blood mononuclear cells (PBMC) were isolated as described 6 and stained with carboxyfluorescein succinimidyl ester (CFSE; 5µM) for 5 minutes, washed, and cultured in Dulbecco’s modified Eagle’s medium (DMEM), supplemented with 10% of the patient’s serum. These PBMC were exposed to 3 different dilutions of the vaccine (1/4000, 1/400, and 1/40, respectively), in triplicate micro cultures (2x105 PBMC in 200 µl), maintained at 37 ºC in a 5% CO2, vapour-saturated atmosphere. Cultures with no vaccine were used as negative control. After 48 hours, the PBMC were harvested, washed, and stained with fluorochrome-coupled anti-CD19 and anti-CD3 antibodies, for 20 minutes. After further washing, the cells were analyzed by flow cytometry (Navios 3L 10C, Beckman Coulter, Milan), for the detection of proliferating B- and T-lymphocytes. Importantly, no B-lymphocyte proliferation (CD19+ cells) was observed in the presence of MMR vaccine (Fig. 2 A-E). CD3+ cell proliferation was not observed, also (data not shown).
Based on this further evidence, we administered the MMR vaccine to the boy, in two 50% doses, 250 µl each, with an interval of one hour between the two injections. The patient remained under observation for one hour (after the second injection). As expected, no immediate nor delayed adverse reactions were observed. Therefore, he could be readmitted to school.
Nine months later, the B-lymphocyte proliferation assay was repeated with similar results (Fig. 2 E). A second MMR vaccine administration was then carried out, according to the inoculation schedule specified.