ANALYSIS OF A “NOVEL” SUBSET OF CD34+ HAEMATOPOIETIC PRECURSORS IN PERIPHERAL BLOOD OF PATIENTS WITH CHRONIC INFLAMMATORY DISEASES

Background: in chronic inflammatory disorders, both infectious and non infectious, a novel population of CD34+ hemopoietic precursors is detectable in high proportions in peripheral blood (PB). These precursors display peculiar phenotypic characteristics, namely the expression of DNAM-1 (bright), an activating receptor expressed by natural killer (NK) cells and CXCR4, a chemokine receptor that suggests their recent exit from bone marrow (BM). In healthy donors (HD), these precursors are virtually undetectable in PB while they represent 10-15% of BM CD34+ cells. It is conceivable that, in chronic inflammatory processes, pro-inflammatory cytokines may favor the exit of this CD34+ subset. While their presence in PB during chronic inflammation may represent a homeostatic event to compensate an accelerated cell death, a major interest in these cells is related to their differentiating capacity, which has been analyzed in the present study. Methods: we evaluated by cytofluorimetric analysis the presence of CD34+ DNAM1bright CXCR4+ cells in different pathological conditions characterized by chronic inflammation including selected viral infections and autoimmune diseases and defined the phenotypic and functional characteristics of both NK and T cells generated in vitro from purified CD34+ DNAM1bright CXCR4+ progenitors. Results: first, we confirmed in our cohorts that patients with autoimmune diseases or with chronic viral infections display high proportions of CD34+DNAM-1brightCXCR4+ precursors, which could even outnumber the conventional CD34+DNAM-1-CXCR4- precursors. Analysis of the progenies of these cells cultured in the presence of appropriate cytokines, showed that both CD56+CD3- (NK) and CD56-CD3+ (T) cells can be generated. Comparison of the lymphoid progenies derived from precursors isolated from patients with viral infections versus patients with autoimmunity revealed a high prevalence of NK cells in the former, while, in autoimmunity, T cell progenies largely prevailed. In the first set of experiments, we focused on NK cell progenies, mostly from HIV and HCV infected patients. CD34+DNAM-1brightCXCR4+ cells gave rise, in approximately 20 days of colture, to sizeable populations of fully mature NK cells expressing KIRs, CD57, DNAM-1, NKG2D and NKG2C (a HLA-E specific activating receptor correlated with infection/sieropositivity for cytomegalovirus, CMV). This rapid differentiation towards mature NK cells was never occurring in conventional CD34+ precursors. Notably, the NKG2C+ progenies could undergo selective expansion upon NK cell colture with HLA-E-transfected 221 cell line. Further analysis of T cell progenies derived from highly purified (>99%) CD34+DNAM-1brightCXCR4+ precursors isolated from patients with autoimmune diseases, revealed the presence of both CD4+ and CD8+ T cells. Importantly, the large majority of cells expressed CXCR4 and the activating receptors DNAM-1 and NKG2D and 2B4 co-receptor. Analysis of CD4+ T cell progenies showed the presence of both Th1 star (Th1*) and Th17 subsets. Conclusions: the generation of T cells in the absence of thymic selection together with the expression of activating NK receptors capable of inducing a HLA-independent T-cell activation (or to amplify low affinity TCR responses) and the presence of Th1* and Th17 may suggest the possible involvement of these cells in the pathogenesis of self-damage in autoimmunity.