Supplementary Material for: Impact of Processing Delays and Cryopreservation on Sensitivity and Specificity of the Lymphocyte Transformation Test

Introduction In the lymphocyte transformation test (LTT) peripheral blood mononuclear cells (PBMCs) from patients with presumed drug allergy are cultured with the implicated drug. No systematic study has investigated how delayed processing or cryopreservation of PBMCs affects the sensitivity and specificity of the LTT to detect a drug sensitization. We evaluated the impact of delayed processing or cryopreservation of PBMCs on the sensitivity and specificity of the LTT focusing on interferon-y (IFN-γ) secretion as read-out. Additionally, we investigated the impact of the respective processing method on non-stimulated reference and TT-stimulated PBMCs. Methods Blood from 30 patients and 30 gender-matched controls was split for paired processing: one aliquot was processed immediately as internal reference of the patient/control, the other subjected to either a 24 h delay (n=15) or immediate processing followed by cryopreservation of the PBMCs (n=15). Thereby, each patient and control in the respective cohort served as its own reference for the assessment of the methodical processing impact. IFN-γ concentrations in PBMC culture supernatants were measured by ELISA. Results Cryopreservation of PBMCs resulted in a statistically non-significant trend towards higher sensitivity and specificity for detecting drug sensitization compared to delayed processing (45% vs. 31% and 81% vs 79%, respectively). 80% of the LTT results using cryopreserved PBMCs were consistent with those obtained from the immediately processed reference group. Conclusion When blood samples cannot be processed within 4 hours, cryopreservation of PBMCs appears preferable to delayed processing, as it better preserves LTT performance for detecting drug sensitization.