Haematologica 2004;89: supplement no. 6 - Supplements ...

16Oral Communicationsexpression. TRAILR expression was explored at proteinlevel using specific monoclonal antibodies. Wefound that TRAIL R3 and TRAIL R4 are expressed inthe majority of cases, TRAIL R1 on about 30% of cases,while TRAIL R2 only in two cases out 44 analyzed.In spite the heterogeneity of the cases analyzed,pertaining to all FAB subtypes, it is possible tocorrelate TRAILR expression pattern with differentAML subgroups. Interestingly the expression ofTRAIL-R1 is limited to AMLs with monocytic features,as supported by the presence of CD14 andCD11b antigens. AML M3 express TRAIL-R3 andTRAIL-R4 in the majority of cases, while TRAIL-R1and TRAIL-R2 were usually undetectable. MembraneTRAIL-bound was observed in the majority of APLpatients (4/5), while it was observed only in a lowpercentage of the other AML subtypes. Given theresults we explored the effect of fusion proteinPML/RAR-α on TRAIL/TRAILRs expression and on themodulation of TRAIL sensitivity. Using U937 as a cellularsystem we showed that induction of thePML/RAR-α protein in these cells was associatedwith a downmodulation of both TRAIL-R1 expressionand TRAIL-mediated cytotoxicity (i. e. , U937cells expressing PML/RAR-α became resistant toTRAIL). Treatment of APL blast with retinoic acid wasassociated with a marked downmodulation of TRAILexpression and with no modification of the sensitivityto TRAIL (i. e. , the cells remained resistant toTRAIL-mediated cytotoxicity). According to the theseresults we suggest that AMLs are resistant to TRAILdue to the expression of TRAIL decoy receptors andto the down modulation of TRAIL-R1. Furthermore,the expression of TRAIL membrane bound on the surfaceof APL blasts may confer a condition ofimmunologic privilege to these cells.BEST-03BONE MARROW STROMAL CELLS (BMSC) FROM ACUTEMYELOID LEUKEMIA PATIENTS: INTERACTION WITH NATURALKILLER CELLSPoggi A,* Negrini S,°* Massaro AM, § * Pierri I, #Balocco M, # Urbani S, & Saccardi R, & Gobbi M, #Zocchi MR §#*Laboratory of Immunology, National CancerResearch Institute, Genoa; # Clinical Hemathology,and °Laboratory of Clinical Immunology, Departmentof Internal Medicine, University of Genoa,Genoa. § Laboratory of Tumor Immunology, Departmentof Internal Medicine, IRCCS San Raffaele,Milan. & Laboratory of Bone Marrow Transplantation,Careggi Hospital, Florence; ItalyNormal blood cell differentiation needs the interactionbetween hematopoietic precursors and bonemarrow stromal cells (BMSC). It is thought thatabnormalities occurring during such interactionsmay contribute to the oncogenesis in acuteleukemias, making of interest the definition of thefunctional role of BMSC in normal hemopoiesis andneoplastic transformation. In this study, BMSC wereobtained from 10 patients suffering from acutemyeloid leukemia (AML), six M0/1 two M2, and twoM5 (according to the FAB classification), 8 out of 10in post-chemotherapy complete remission. BMSCwere obtained from all of these patients and maintainedin culture for two months. These cells wereanalysed for the expression of a panel of surfacemarkers at different culture passages (from 1 to 4).BMSC were CD44+, CD73a+ CD73b+ CD105+, β1integrin+, ICAM1+, HLA-I+, HLA-II+ (variable proportions),CD34- CD14- CD45-, CD31-, and theycould express the stress-inducible MHC-related moleculesMIC-A and the UL16 (induced at the surfaceof cells infected by cytomegalovirus) binding proteinULBP3.These molecules are reported ligands for theNKG2D receptor expressed by Natural Killer (NK) andCD8+ T lymphocytes, effector cells that are thoughtto play a role in host defence against tumors. NKcells have also been shown to regulate normal differentiationof hemopoietic precursor into themyeloid or lymphoid cell lineage. Moreover, it hasbeen stated that NK cells are not able to damageautologous cells, as they receive negative signalsthrough inhibitory receptors, including killer Ig-likereceptors (KIR) or C-type lectin inhibitory receptors(CLIR), which bind to HLA-I discrete alleles. Surprisingly,we found that autologous IL2-activated, butnot freshly isolated, NK cells lysed BMSC, while Tlymphocytes did not kill self or non-self BMSC. Bindingof ICAM-1 expressed by BMSC to its receptor,the integrin LFA-1, expressed by NK cells plays a keyrole in BMSC/NK interaction. More importantly,NKG2D/MICA and/or NKG2D/ULBP3 engagement isresponsible for the delivery of lethal hit. Conversely,it appears that HLA-I molecules do not protect BMSCfrom NK cell-mediated injury. Taken together, thesedata suggest that NK cells, when activated as it mayoccur during the first response to viral infections, areable to eliminate BMSC, thus altering the normalinteractions with hemopoietic precursors and possiblyaffecting their differentiation. This mechanismmight also contribute to the development of aberrantprecursors as observed in acute leukaemias.haematologica vol. 89[suppl. n. 6]:september 2004