Generation of protective memory responses. (A) Survival after rechallenge with 289-GFP ALL. Previously, CpG ODN-treated mice in remission were rechallenged with 10⁵ GFP⁺ ALL cells, along with a leukemia-naive cohort. The survival curve for mice given GFP⁺ 289 is shown (P < .001). (B) Survival after rechallenge with wild-type t309 ALL. To demonstrate that the observed protection from ALL was not limited to a single cell line or to the presence of GFP as an antigen, we repeated the rechallenge experiment in mice who had been cured of wild-type t309, as in panel A. The survival curve for mice followed for 4 months is shown (P < .001). (C) Adoptive transfer of T cells into NSG mice. BALB/cJ mice were given CpG ODN 100 μg every 4 days for 3 doses, as in panels A and B, beginning on day 7 after injection with 10⁶ GFP⁺ ALL cells. A group of nonleukemic mice were also injected with CpG ODN. One month after injection, mice in both groups were killed, and T cells were magnetically selected from their splenocytes to be injected into NSG mice along with 10⁵ GFP⁺ ALL cells. Mice were followed for development of peripheral blasts by FACS, with mice receiving ALL-targeted T cells showing lower percentages than stimulated but naive T cells (*P < .02).