Priming CD8⁺T-cell responses in HSC-transplanted RAG1^−/−hosts by DNA vaccination. (A) Schematic representation of the experimental set-up: 12 weeks after transplantation, recipient mice were immunized with pCI/C DNA encoding the hepatitis B virus Core antigen. Thirteen days after immunization, splenic K^b/C_93-100 dimer⁺ CD8⁺ T-cell frequencies were determined by flow cytometry. Representative graphs of individual stains as well as quantification of the K^bC_93-100 dimer staining are shown in (B) and (C), respectively (DY, n = 9; DO, n = 8). (D) Schematic representation of the experimental set-up. HSCs were isolated from old B6.SJL mice and cultured for 16 hours ± 5 µM CASIN. Subsequently, 600 HSCs were transplanted in subleathally irradiated young RAG1^−/− mice. Twelve weeks after transplantation, recipient mice were immunized with the mammalian expression vector pCI/C. Thirteen days after immunization, transplanted mice were sacrificed and the percentage of K^b/C_93-100 dimer⁺ cells was determined within the CD3⁺CD8⁺ population by flow cytometry. Quantification as well as representative graphs of the K^b/C_93-100 dimer staining for spleen (DO, n = 11; DO+C, n = 9) and liver (DO, n = 8; DO+C, n = 6) are shown in (E) and (F), respectively. *P < .05; **P < .01, 2-tailed unpaired Student's t-test, mean + SEM.