Analysis of the endogenous antibody response against tumor cells and passive immunity transfer in vivo. (A) IgM, IgG, and IgG2a binding to EL4-huCD20 cells was analyzed by indirect immunofluorescence assay with sera from CAT-13–treated and naive animals. Mean fluorescence intensities (MFI) are shown. Black arrows indicate the time of tumor challenge (day 70). (B) Naive recipient mice were intravenously injected on day −1 with either pooled sera from untreated mice (sera from day 20 after intravenous injection of EL4-huCD20 cells; ◇, n = 6) or pooled sera from surviving CAT-13–treated mice (sera from day 90, 20 days after intravenous tumor challenge; ♦ n = 6). Recipient mice subsequently had intravenous injections on day 0 of 5 × 105 EL4-huCD20 cells. Untreated mice (□, n = 6) were used as controls (log-rank analysis, not significant).
