Immunization and challenge with c-MYC over-expressing lymphomas.

<p>Immunized recipient mice were challenged with human c-MYC over-expressing B-cell lymphoma cells subcutaneously 7 days past boost immunization. When tumors reached a diameter of more than 10 mm, mice were sacrificed and survival was plotted. Combined data from 3 independent experiments are shown. A: Mice were immunized with a vaccine containing c-MYC protein (solid line, n=45) or OVA protein (dashed line, n=30). Lymphomas grew out simultaneously in both groups and no significant difference in survival was observed (p=0.16). B: Vaccine comprised NHP-A (dotted line, n=10), NHP-E (solid line, n=15) or NHP-B (dashed line, n=24). NHP-B immunization resulted in delayed lymphoma outgrowth and significantly improved survival compared to NHP-A (p=0.006) and NHP-E (p=0.001) vaccination. Depletion of CD25⁺ cells prior to immunization with NHP-B further delayed lymphoma outgrowth and improved survival (CD25depl+NHP-B). C: <i>In </i><i>vivo</i> killing assay: lymphoma surviving animals (LS) were challenged with NHP-B2-pulsed splenocytes and percentage of specific killing was assessed 18 hours after injection. Lymphoma surviving animals display a significantly higher <i>in </i><i>vivo</i> killing activity compared to naïve animals (p=0.016, Mann-Whitney test). D: IFNγ secretion after stimulation of splenocytes from lymphoma-rejecting mice using c-MYC over-expressing 291PC stimulator cells with (+IFNγ) or without (-IFNγ) prior IFNγ treatment (100U/ml), c-MYC or OVA protein, MCA205MYC-tet with (+tet) and without (-tet) prior tetracycline treatment (1µg/ml) or untransfected MCA205 cells (C and D, n=4 animals per group).