P31: Severe systemic allergic reactions to Jack Jumper Ant Venom Immunotherapy: basophil response during treatment with Omalizumab

Background

Recurrent severe systemic reactions to Jack Jumper Ant (JJA) Venom Immunotherapy (VIT) although rare, hinder a patient's ability to achieve protective maintenance doses. Patients who discontinue treatment remain at high risk of potentially life threatening reactions. The administration of concurrent Omalizumab has been reported to reduce the rate of such reactions. We sought to evaluate the basophil response during treatment with Omalizumab in this setting.

Case History

We describe the case of a 50 year old female who has suffered multiple episodes of severe anaphylaxis following JJA stings. She commenced JJA VIT by conventional semirush protocol complicated by a severe (Brown grade III) anaphylaxis following a 10 mcg JJA venom (JJAV) dose. She suffered a further moderate (Brown grade II) severity anaphylaxis three weeks later. Geographic considerations were significant and treatment proceeded with a modified ultrarush protocol. A cumulative total of 45mcg of JJAV was achieved before she experienced another severe (Brown grade III) anaphylaxis. A subsequent basophil activation test (BAT) demonstrated 44.4%, reactive, CD63 positive basophils at a dilution of 0.1 mcg/ml JJAV.

Immunotherapy was recommenced with the addition of Omalizumab 150 mcg 30 minutes before JJA VIT every fortnight. She achieved a maintenance dose of 50mcg JJAV 10 weeks later. A BAT was repeated 4 weeks following her first maintenance dose demonstrating no JJA venom basophil reactivity. Omalizumab was continued for 6 months. Three months after discontinuing Omalizumab our patient experienced a mild (Brown grade I) systemic reaction. Repeat BAT demonstrated reduction of CD63 positive, reactive, basophils from 44.4% to 18.9% at a dilution of 0.1mcg/ml JJAV.

Conclusion

Recurrent systemic VIT allergic reactions may occur after Omalizumab has been discontinued or reduced. The potential role of BAT for therapeutic monitoring in this setting is promising and requires further investigation.