EFFECT ON LEUKEMIA-CELL NUMBERS OF IN-VIVO ADMINISTRATION OF IMMUNOTHERAPEUTIC AGENTS IS AGE-DEPENDENT

On the basis of our previous findings that erythroleukemia-bearing mic e of different ages responded positively to immunotherapy [indomethaci n +/- recombinant interleukin (rIL-2)] in vivo [stimulated natural kil ler (NK) cells and increased life span], we aimed, in the present stud y, to determine if changes in these parameters could be correlated to change in erythroleukemia cell numbers. Infant (<3 weeks old), young a dult (5-8 weeks) and aged (>10 months) DBA/2 mice were injected with e rythroleukemia cells. Some mice remained untreated for the 10-day dura tion of the tumor-bearing period, while others were treated with eithe r indomethacin alone for the 10 days from tumor inoculation, rIL-2 alo ne for the last 4 days of the 10-day tumor-bearing period, or with bot h indomethacin and rIL-2 as above. In all cases, both treated and untr eated mice were killed at 10 days after tumor inoculation. Cytospot pr eparations from single cell suspensions of spleen and bone marrow, in all cases, were stained with MacNeal's tetrachrome hematologic stain a nd the :relative, and absolute number of erythroleukemia cells in thes e organs were determined using light microscopy. The results show that indomethacin-and/or rIL-2-treated leukemic infant and young adult mic e have significantly lower numbers of erythroleukemia cells in both th e spleen and bone marrow relative to untreated, leukemic mice of corre sponding age. Leukemic aged mice, however, show no change in erythrole ukemia cell numbers in either organ, regardless of treatment, parallel ing our observations of a lack of immunotherapeutic value of these age nts on NK cell production/function in aged mice.