Figure 6. Role of the CEA splice variant in MEDI-565 mediated T cell activation and target cell killing.

A, expression of full-length CEA and CEA splice variant proteins in CHO cells as determined by flow cytometry. Mouse IgG1, mouse IgG1 control antibody. B, CHO DHFR-, CHO FL, CHO SV and CHO FL+SV cells were tested for their susceptibility to be killed by CD3+ T cells from 3 individual donors in the presence of MEDI-565 at the indicated concentrations. EC₅₀ values listed indicate the mean value among 3 donors±standard error of the mean. p = 0.79 comparing cytotoxicity EC₅₀ values between CHO FL CEA and CHO FL+SV CEA cells. C, activation (increased cell surface CD25/IL-2R levels) of CD8+ T cells and D, activation of CD4+ T cells isolated from each of the 3 healthy donors was investigated concurrently with the cytotoxicity assays shown in panel B. p = 0.60 comparing CD8+ T cell activation EC₅₀ values between CHO FL CEA and CHO FL+SV CEA; p = 0.15 comparing CD4+ T cell activation EC₅₀ values between CHO FL CEA and CHO FL+SV CEA. MFI CD25-APC = mean fluorescence intensity of bound APC labeled, anti-human CD25 mAb. Experiment was repeated once with similar results.