Background mRNA‐based COVID‐19 vaccines have been reported to induce hypersensitivity reactions (HSR) in a small number of individuals. We aimed to evaluate the real‐world incidence of the BNT162b2 mRNA COVID‐19 vaccine HSR and to determine the value of the basophil activation test (BAT) in the allergological workup of patients reporting these reactions. Methods We prospectively enrolled patients with a clinical history indicative of HSR to the BNT162b2 mRNA COVID‐19 vaccine. The allergological workup included skin testing (STs) and BAT with polyethylene glycol (PEG) and the vaccine. In those with negative allergy assessments, the administration of the second dose of the BNT162b2 mRNA COVID‐19 vaccine was offered. Results Seventeen adults were included. Eleven cases (64.7%) tested negative in the allergological workup and tolerated the re‐administration of the second dose of the vaccine and considered non‐allergic. Six cases (35.3%) were considered allergic and classified into three groups: 2 subjects displayed positive STs and/or BAT to PEG (Group A), two individuals displayed positive BAT to the vaccine (Group B), and in 2 patients with moderate or severe reactions, the culprit was not identified, tested negative to STs and BAT to both PEG and vaccine (Group C). We further evaluated the value of BAT when the results were positive to the vaccine and negative to PEG by performing BAT in controls groups, finding positive BAT results in 50% of controls, all of them recovered from COVID‐19 infection. In contrast, BAT was negative in patients who had not suffered from COVID‐19 disease. Conclusions BAT can be used as a potential diagnostic tool for confirming allergy to PEG excipient but not to the vaccine as a positive result in BAT may indicate a past COVID‐19 infection instead of an allergy.

The immunological mechanisms involved in drug hypersensitivity reactions (DHRs) are complex, and despite important advances, multiple aspects remain poorly understood. These not fully known aspects are mainly related to the factors that drive towards either a tolerant or a hypersensitivity response and specifically regarding the role of B and T cells. In this review, we focus on recent findings on this knowledge area within the last 2 years. We highlight new evidences of covalent and non‐covalent interactions of drug antigen with proteins, as well as the very first characterization of naturally processed flucloxacillin‐haptenated human leukocyte antigen (HLA) ligands. Moreover, we have analysed new insights into the identification of risk factors associated with the development of DHRs, such as the role of oxidative metabolism of drugs in the activation of the immune system and the discovery of new associations between DHRs and HLA variants. Finally, evidence of IgG‐mediated anaphylaxis in humans and the involvement of specific subpopulations of effector cells associated with different clinical entities are also topics explored in this review. All these recent findings are relevant for the underlying pathology mechanisms and advance the field towards a more precise diagnosis, management and treatment approach for DHRs.

BackgroundAmoxicillin (AX) combined or not with clavulanic acid (CLV) is frequently involved in IgE‐mediated reactions. Drug provocation test (DPT) is considered as the gold standard for diagnosis, although contraindicated in high‐risk patients. Basophil activation test (BAT) can help diagnose immediate reactions to beta‐lactams, although controversy exists regarding the best activation marker. We have performed a real‐life study in a prospective cohort to analyze the real value of BAT as diagnostic tool and the best activation marker, CD63 and CD203c, for the evaluation of immediate reactions to these drugs.MethodsWe prospectively evaluated patients with a clinical suspicion of immediate reactions after AX or AX‐CLV administration during a 6‐year period. The allergological work‐up was done following the EAACI recommendations. BAT was performed in all patients using CD63 and CD203c as activation markers.ResultsIn AX‐allergic patients, both activation markers, CD63 and CD203c, showed similar SE values (48.6% and 46.7%, respectively); however, specificity was of 81.1% and 94.6%, respectively, with CD203c showing good positive predictive value and like‐hood ratio. In CLV‐allergic patients, CD203c showed higher SE (50%) than CD63 (42.9%), maintaining the same value of SP (80%). Combining the results of both markers can slightly increase the sensitivity (51.4% for AX and 54.8% for CLV), although decreasing the specificity (79.7% and 73%, respectively). Interestingly, all patients with an anaphylactic shock showed a positive BAT to CLV using CD203c.ConclusionsBAT using CD203c showed a good confirmatory power, especially for AX allergy. Placing BAT as a first step in the diagnostic procedure can help reduce the need of performing a complete allergological work‐up in 46.6% of patients, diminishing the risk of reinducing allergic reactions.

β-lactam antibiotics (BLs) are the drugs most frequently involved in drug hypersensitivity reactions. However, current in vitro diagnostic tests have limited sensitivity, partly due to a poor understanding of in vivo drug–protein conjugates that both induce the reactions and are immunologically recognized. Dendrimeric Antigen-Silica particle composites (DeAn@SiO2), consisting on nanoparticles decorated with BL-DeAns are promising candidates for improving the in vitro clinical diagnostic practice. In this nano-inspired system biology, the synthetic dendrimer plays the role of the natural carrier protein, emulating its haptenation by drugs and amplifying the multivalence. Herein, we present the design and synthesis of new multivalent mono- and bi-epitope DeAn@SiO2, using amoxicillin and/or benzylpenicillin allergenic determinants as ligands. The homogeneous composition of nanoparticles provides high reproducibility and quality, which is critical for in vitro applications. The suitable functionalization of nanoparticles allows the anchoring of DeAn, minimizing the nonspecific interactions and facilitating the effective exposure to specific IgE; while the larger interaction area increments the likelihood of capturing specific IgE. This achievement is particularly important for improving sensitivity of current immunoassays since IgE levels in BL allergic patients are very low. Our data suggest that these new nano-based platforms provide a suitable tool for testing IgE recognition to more than one BL simultaneously. Immunochemical studies evidence that mono and bi-epitope DeAn@SiO2 composites could potentially allow the diagnosis of patients allergic to any of these drugs with a single test. These organic–inorganic hybrid materials represent the basis for the development of a single screening for BL-allergies.

Background Immediate drug hypersensitivity reactions (IDHRs) to clavulanic acid (CLV) have increased in the last decades due to a higher consumption alongside amoxicillin (AX). Due to its chemical instability, diagnostic procedures to evaluate IDHRs to CLV are difficult, and current in vitro assays do not have an optimal sensitivity. The inclusion of the specific metabolites after CLV degradation, which are efficiently recognised by the immune system, could help to improve sensitivity of in vitro tests. Methods Recognition by dendritic cells (DCs) of CLV and the synthetic analogues of two of its hypothesised antigenic determinants (ADs) was evaluated by flow cytometry in 27 allergic patients (AP) and healthy controls (HC). Their ability to trigger the proliferation of T cells was also analysed by flow cytometry. Results The inclusion of synthetic analogues of CLV ADs, significantly increased the expression of maturation markers on DCs from AP compared to HC. A different recognition pattern could be observed with each AD, and, therefore, the inclusion of both ADs achieves an improved sensitivity. The addition of synthetic ADs analogues increased the proliferative response of CD4+Th2 compared to the addition of native CLV. The combination of results from both ADs increased the sensitivity of proliferative assays from 19% to 65% with a specificity higher than 90%. Conclusions Synthetic ADs from CLV are efficiently recognised by DCs with ability to activate CD4+Th2 cells from AP. The combination of analogues from both ADs, significantly increased the sensitivity of DC maturation and T‐cell proliferation compared to native CLV.