LAUSR

6 Introduction Although it is known that fetal hematopoiesis and development of lymphocyte subsets, such as natural killer (NK) cells occur in distinct waves, resulting in a restricted set of hematopoietic functions, it remains unclear how these physiological transitions can be translated in transplantation settings. Cord blood (CB) contains a higher percentage of immature or immunologically naive lymphocytes than adult blood (AB) and studies have established that NK cells/T cells have a major impact on the outcome of umbilical cord blood transplantation. Objective Analyses comparing individual blood populations derived from AB compared with neonatal CB with respect to their developmental age are limited. Because HOX genes are known to be mandatory in hematopoietic development and, moreover, are suitable to reflect the developmental age, the individual HOX code was analyzed. Methods The expression patterns of 39 HOX genes were determined in neonatal CD34 isolated hematopoietic stem cells, as well as the expanded counterpart. The mononuclear cell fraction was stained with specific antibodies against CD34, B-cells (CD19), T cells (CD3), T helper cells (CD4), cytotoxic T cells (CD8), NK cells (CD56), and monocytes (CD14). The individual populations were sorted, applying the respective individual antibodies using a MoFlo XDP cell sorter (Beckman Coulter, Brea, CA, USA) with a purity of >99.5%. Total RNA was isolated using Tri Reagent (Invitrogen, Karlsruhe, Deutschland) followed by DNA digestion with DNase I (Invitrogen). Reverse transcription was performed with SuperScriptIII (Invitrogen). Complementary DNA that approximated 50 ng of RNA was used for subsequent RT-PCR and qPCR analyses of all 39 HOX genes. Results The expansion/differentiation of hematopoietic stem cells from CB results in a differentiation-dependent downregulation of HOX genes. Developmental age-dependent specific expression level of HOX genes in blood populations derived from CB, especially in the NK-cell subset, reveal a higher expression of HOXA5, HOXA9, HOXD1 and HOXD11, compared with AB. Generally the younger developmental age of cord blood subpopulations is reflected by expression of more HOX genes. Discussion The individual HOX code reflects not only the developmental age of blood populations and differentiation status but might also reflect the functional differences of the individual cells. STEM CELLS TRANSLATIONAL MEDICINE | StemCellsTM.com © AlphaMed Press 2019 PRECLINICAL STUDIES