A Murine Model of Asparaginase Allergy

In order to study interventions that influence the severity of symptoms and serum asparaginase activity following asparaginase-induced hypersensitivity reactions, we developed a murine model of asparaginase allergy that recapitulates key features of clinical hypersensitivity to native E. coli asparaginase. BALB/c mice received 10 μg ip doses of E. coli asparaginase formulated with aluminum hydroxide adjuvant on day 0 and 14 of treatment in order to sensitize mice to asparaginase. Asparaginase allergies were induced in sensitized mice by challenging with a 100 μg iv dose of E. coli asparaginase on day 24 of treatment. The severity of hypersensitivity was reflected by the decrease in rectal temperature following the asparaginase challenge. Pre-challenge plasma samples were collected for anti-asparaginase antibody levels before inducing asparaginase allergies, and post-challenge samples were collected at the end of the experiment for measuring anti-asparaginase antibody levels, asparaginase activity, and mouse mast cell protease 1 (mMCP-1) levels.

Sensitized mice developed high levels of anti-asparaginase IgG antibodies (P = 1.1 x 10^-7) and had immediate hypersensitivity reactions (P = 3.3 x 10^-10) to asparaginase upon challenge compared to non-sensitized mice. Furthermore, sensitized mice had profoundly lower plasma asparaginase activity (P = 4.2 x 10^-13) and elevated levels of mouse mast cell protease 1 (mMCP-1, P = 6.1 x 10^-3) after the asparaginase challenge compared to non-sensitized mice.

We investigated the influence of pretreatment with the H1 receptor antagonist triprolidine, the H2 receptor antagonist cimetidine, the PAF receptor antagonist CV-6209, or dexamethasone on the severity of asparaginase-induced allergies. Our studies showed that the combination of triprolidine and CV-6209 was best for mitigating asparaginase-induced hypersensitivity symptoms (i.e., temperature drop) compared to non-pretreated, sensitized mice (P = 1.2 x 10^-5). However, pretreatment with oral dexamethasone (4 mg/L in drinking water starting 7 days before asparaginase sensitization) was the only agent capable of mitigating the severity of the hypersensitivity symptoms (P = 0.03) and also partially restoring asparaginase activity (P = 8.3 x 10^-4) compared to sensitized mice.

Dose adjustment strategies were investigated for rescuing asparaginase activity in sensitized mice without requiring pretreatment with dexamethasone, and a 5-fold greater dose of asparaginase was required to restore enzyme activity to a similar concentration as in non-sensitized mice. In the absence of pretreatment, we found that the severity of asparaginase-induced reactions increased in a dose-dependent manner and that mMCP-1 levels correlated to the severity of the reactions (R² = 0.577, P = 3.0 x 10^-16).

Our results suggest a role of histamine and PAF in asparaginase-induced allergies and demonstrate possible strategies for mitigating the severity of asparaginase-induced reactions and maintaining targeted concentrations of asparaginase. Furthermore, our results indicate that mast cell-derived proteases released during allergic reactions to asparaginase may be a useful marker of hypersensitivity, as elevated levels of mMCP-1 were detected in all sensitized mice and correlated with the severity of the reaction.