The CpG-adjuvanted PS3 vaccine generates long-lived BM plasma cells. (A-E) Ten-week-old mice were immunized with PS3 and injected 2 days later with CpG1668 before being irradiated at 7.5 Gy (750 rad) to deplete naive and memory B lymphocytes 45 days later. (A) Numbers of B-1a and B-1b cells in peritoneal washings determined by numeration and flow cytometry at the indicated time points, in control and irradiated mice. (B) Numbers of B-1 and B-2 cells in the spleen remaining 60 days after irradiation, determined as in panel A. (C) Numbers of B cells responsive to in vitro PS3 stimulation in peritoneal washings of mice immunized with the CpG-adjuvanted PS3 vaccine 180 days after irradiation. (D-E) The numbers of PS3-specific IgM (D) and IgG (E) ASCs in the BM of control and irradiated mice were determined by ELISPOT assay at the indicated time points. (F) Adoptive transfer of PS3-specific plasma cells results in prolonged PS3-specific Ab production in B cell–deficient mice. Donor C57BL/6 mice received a single injection of the CpG-adjuvanted PS3 vaccine or 2 sequential injections of PS3TT with a 28-days interval. Forty days after the last injection, total femoral BM cells or CD138-depleted BM cells were adoptively transferred into naive B cell–deficient (μMT) mice. Each recipient mice received 3.5 × 10⁴ PS3-specific ASCs (from donors immunized with the CpG-adjuvanted PS3 vaccine) or 2.25 × 10⁴ PS3-specific ASCs (from donors immunized with the PS3-TT vaccine). Sera were collected at the indicated time points after transfer, and PS3-specific IgM titers were determined by ELISA. Results are expressed as means ± SEM of the values collected in 5 individual mice.