Performance characteristics of common immunologic biomarkers used in clinical trials
620 Background: Standardization of cell-based immunologic monitoring is becoming increasingly important as methods for measuring cellular immunity become more complex. We assessed the ability of 2 cell-based assays widely used in immune monitoring, the ELISPOT assay and a modified limiting dilution assay based on titrated thymidine incorporation, to predict T cell responses to a HER-2/neu protein vaccine in breast cancer patients. We also assessed the ability of these assays to predict T cell response to tetanus toxoid and CMV, and analyzed the correlation between results from the ELISPOT and modified limiting dilution assays. Methods: 27 Stage II, II, and IV HER-2/neu positive breast cancer patients were vaccinated against the HER-2/neu protein and tt. PBMC were collected before and after vaccination. Samples were analyzed by mLDA and ELISPOT for T cell response to HER-2/neu (a low level response), response to tt (moderate level) and T cell response to CMV (high level). Results: Correlation analysis indicates that there is a strong, significant association between results from the ELISPOT assay and the mLDA for HER-2/neu specific T cell response (Rs=0.547, p=0.02). ROC curves plotted to assess the diagnostic performance of the mLDA and ELISPOT assay indicate that T cell proliferation measurements are a significant indicator of T cell response to the HER-2/neu vaccine (p=0.05), as well as responses to tt (p=0.01) and CMV (p=0.016), respectively. Precursor frequency, as measured by ELISPOT, is a significant indicator of high level T cell response to CMV (p=0.03), but not of a moderate tt response (p=0.09), or HER-2/neu (p=0.09) T cell responses. Conclusion: The mLDA achieves greater assay accuracy in measuring low level T cell responses to HER-2/neu and moderate responses to tt than the ELISPOT assay. No significant financial relationships to disclose.