Differential expression of lymphoid and myeloid markers on differentiating hematopoietic stem cells in normal and tumor-bearing adult human liver.

The presence and phenotype of lineage-committed hematopoietic progenitors in the normal adult human liver (AHL) were investigated and compared with the profiles of differentiating hematopoietic precursor populations detected in liver bearing metastases of colonic origin. Levels of hematopoietic stem cells (HSCs) (CD34(+)CD45(+)) detected in hepatic mononuclear cell (HMNC) populations were increased 6-fold when compared with matched peripheral blood samples. In normal liver, less than 5% of HSCs expressed the myeloid-associated antigen, CD33, whereas considerable proportions expressed lymphoid-associated markers (T cell, 33.39%; B cell, 17.39%; and natural killer [NK] cell, 37.17%). Significant increases were observed in the relative proportions of hepatic HSCs coexpressing CD33 (20.53%; P =.001), and the T-cell marker (CD7, 58. 13%; P =.02) in tumor-bearing liver compared with normal liver. HSCs with B-cell progenitor phenotype (CD19(+)) were significantly decreased in tumor-bearing liver (0.06%; P =.02). Despite these differences, the activation status of hematopoiesis, as measured by the coexpression of the differentiation and activation markers, CD38 and CD45RA, did not differ significantly between normal and tumor-bearing liver. These results indicate that the normal AHL harbors lineage-committed hematopoietic progenitors, and the vast majority of these progenitors express lymphoid-associated antigens with changes occurring in both the myeloid and lymphoid compartments of the hepatic hematopoietic pathway on tumor challenge. While tumor-bearing livers are enriched for intrahepatic myeloid precursors and T-cell progenitor cells, further studies are required to establish the origin and in situ development potential of hepatic HSCs in the adult human and their role in tumor immunity.