LYMPHOKINE-ACTIVATED KILLER (LAK) PRECURSOR CELL-ACTIVITY IS PRESENT IN INFUSED PERIPHERAL-BLOOD STEM-CELLS AND IN THE BLOOD AFTER AUTOLOGOUS PERIPHERAL-BLOOD STEM-CELL TRANSPLANTATION

Immunotherapy with interleukin-2 (IL-2) early after peripheral blood s tem cell transplantation (PBSCT) is being considered as a potential wa y to eradicate minimal residual disease. The aim of this study was to determine whether lymphocytes which can acquire lymphokine-activated k iller (LAK) cell activity are present in PBSC and in the blood of pati ents after PBSCT. Fresh and cryopreserved G-CSF-mobilized PBSC from ei ght patients were incubated with IL-2 (1000 U/ml) for 3-6 days and the n tested for LAK activity as measured by lysis of the Daudi cell line. LAK activity was present in both fresh and cryopreserved PBSC, with m ean lysis of 32% and 36%, respectively, at an effector:target (E:T) ra tio of 50:1. To assess the reconstitution of LAK precursor activity af ter PBSCT, peripheral blood (PB) obtained from eight other patients 15 -60 days after PBSCT was similarly tested. LAK activity was detected i n PB from every patient (mean lysis of 38% at an E:T ratio of 12.5:1). PB from patients after PBSCT contained a higher percentage of CD8(+) cells and CD56(+) cells than did PB from 9 normal controls (47.2% vs. 21.4% CD8(+) cells, P<0.005 and 28.6% vs. 8.6% CD56(+) cells, P < 0.00 05). Moreover, PB from 4 of 5 patients tested after PBSCT exhibited a high percentage of cells expressing p75, the intermediate affinity IL- 2R. Thus, precursor cells capable of acquiring IL-2-inducible LAK acti vity are present in PBSC and are rapidly reconstituted after PBSCT. Th e findings provide a rationale for testing IL-2 as a way of decreasing relapses after PBSCT.