EXPRESSION OF P75 CHAIN OF IL-2 RECEPTOR IN THE EARLY IMMUNOLOGICAL RECONSTITUTION AFTER ALLOGENEIC BONE-MARROW TRANSPLANTATION

Expression of p55 and p75 chains of IL-2 receptor (IL-2R) on the surfa ce of both T and natural killer (NK) circulating lymphocytes was inves tigated in 14 paediatric patients given allogeneic bone marrow transpl antation (BMT) from HLA-identical sibling or partially matched family donors. IL-2-induced proliferative and cytotoxic responses were also s tudied and all analysis was performed within 45 days from transplant. We found that, early after transplant, the percentage of p55(+) and of p75(+) peripheral blood lymphocytes (PBL) was not significantly diffe rent in patients who had received HLA-identical BMT (p55(+) 8.04 +/- 4 .87%; p75(+) 28.27 +/- 18.85%) compared with healthy controls (p55(+) 7.26 +/- 6.17%; p75(+) 19.42 +/- 10.49%), while recipients of T cell-d epleted marrow included a remarkably high percentage (76-90%) of p75() PBL, which were mostly CD3(-) and co-expressed CD56 molecule. Compar able values of p55(+) lymphocytes were observed in all patients and co ntrols. However, in contrast to the other two groups, in recipients of T cell-depleted BMT the majority of these cells co-expressed p75 chai n and CD56 antigen. IL-2-induced proliferation and lymphokine-activate d killer (LAK) activity were detectable in all patients, and their val ues did not correlate with expression of p55 or p75 chains. Our data s uggest that expansion of NK subsets expressing IL-2R chains after T ce ll-depleted BMT may be related to early reconstitution of natural immu nity in the presence of allogeneic stimuli.