CYCLOPHOSPHAMIDE PLUS TUMOR-NECROSIS-FACTOR-ALPHA CHEMOIMMUNOTHERAPY CURED MICE - LIFELONG IMMUNITY AND REJECTION OF RE-IMPLANTED PRIMARY LYMPHOMA

Changes in functionally and phenotypically definable splenocyte subsets in aging mice which had been rendered tumor-free in early life by immunochemotherapy (cyclophosphamide plus tumor necrosis factor-alpha) were studied in the syngeneic EL4 lymphoma-C57BL/6 murine model. Treatment-induced longterm survivors (LTS) surviving rechallenge are termed ''immune-LTS''. On day 120 (day 0, initial tumor inoculation), splenocytes from day 60 rechallenged immune-LTS developed significantly greater specific anti-EL4 cytolytic activity in an ex vitro assay than those from non-rechallenged LTS. Splenocytes from combination-treated groups developed significantly higher activity than those from cyclophosphamide-induced immune-LTS. The splenic effector precursor was a CD8(+) T cell. The specific anti-EL4 effector cell from the cyclophosphamide-induced immune-LTS was CD4(-) CD8(+); however, approximately 50% of those from combination-treated immune-LTS appeared to be CD4(+)CD8(+). On day 520 immune-LTS were randomized into 2 groups. One group was re-implanted with EL4 tumor; all mice survived. The other group was killed and, even though their splenocytes developed considerable anti-EL4 activity, their allogeneic responsiveness was as reduced as that of age-matched controls. Phenotypic analysis, compared with splenocytes from young and age-matched controls, revealed changes in the makeup of each T-cell subset, except the CD4(+)CD8(+), and all subsets, except the CD4(-)CD8(-), had increases in CD44 positivity. On day 625, the age of these mice was equivalent to the median life-span of C57BL/6 mice; nevertheless, their splenocytes developed high anti-EL4 activity. Phenotypic analysis indicated that, compared to day 520, there was a major decrease in CD4(-)CD8(+) splenocytes; we suggest that these cells had migrated to the site of tumor eradication. (C) 1995 Wiley-Liss, Inc.