EVOLUTION OF LYMPHOCYTE-TRANSFORMATION TO WASP VENOM ANTIGEN DURING IMMUNOTHERAPY FOR WASP VENOM ANAPHYLAXIS

Background Venom immunotherapy (VIT) has proven to be safe and effecti ve in wasp venom anaphylaxis. However, there are no good parameters to indicate when to stop venom immunotherapy. Objective To evaluate the relationship of the lymphocyte transformation test (LTT) to history an d specific IgE determination, and to address the time course of lympho cyte transformation responses to wasp (Vespula) venom during VIT and t he possible utility of LTT to determine the duration of therapy. Metho ds Peripheral blood mononuclear cells (PBMCs) of 18 individuals with a history of wasp sting anaphylaxis and a positive serum-venom-specific IgE, were stimulated with wasp venom before immunotherapy, at the end of a 5-day semi-rush immunotherapy and at 24 months during venom immu notherapy. Results, expressed as stimulation index (SI), were compared with the SI in seven asymptomatic stung controls. Results In controls the median (minimum-maximum) of the SI were 2.39 (0.52-3.39) before t herapy and 2.39 (1.12-6.02) when repeated after 24 months. For patient s the median (minimum-maximum) of the SI were 10.13 (1.19-44.88) befor e immunotherapy (d0), 2.73 (0.67-12.03) at the end of the build-up imm unotherapy (d5) and 4.21 (0.88-14.66) at the end of 24 months of maint enance therapy (m24). The proliferation responses in vespid-allergic p atients were significantly higher than in stung controls (P = 0.006) b ut only 13/18 patients showed a positive LTT result before the start o f immunotherapy (sensitivity of the LTT 72%). When the LTT was repeate d after a 5 day build-up hyposensitization course the SI significantly dropped as compared to the pre-treatment levels (P = 0.002). The SI o f the LTT was negative in eight out of 18 patients at 24 months and th e median values were significantly lower than before therapy (P = 0.03 ). Conclusions Although, in the absence of sting challenge data it is not possible to draw conclusions about the predictive value of the LTT , our data may suggest that abolition of the LTT during VIT might indi cate clinical insensitivity. Further studies, comparing the results of sting challenges, with the results of lymphocyte transformation will be necessary in order to evaluate the role of LTT in stopping immunoth erapy.