NK Receptor (NKR)-Mediated Signaling Pathways in Cord Blood (CB) CD56dim Versus Peripheral Blood (PB) CD56dim NK Cells: Implication for Immaturity in Cord Blood NK CD56dim Innate Immunity

Abstract

Background: NK cells are characterized by absent CD3 but expression of CD56dim (90%, cytotoxic) and CD56bright (10%, mediator). NK cells may contribute to the immaturity in cord blood innate and adaptive immunity, and play an important role in the GVL effect post CBT. However, little is known regarding the NKR signaling pathways in CB vs PB CD56dim NK cells and its relationship to the cytotoxic activity. We previously demonstrated the ability to ex-vivo expand CB into NK subsets with profound NK in-vitro and in-vivo cytotoxic activity (Ayello/Cairo BBMT 2006). We further observed that there were 33 and 37 proteins over and under expressed by proteomic expression profiling studies of CB vs PB CD56dim (Shereck/Cairo, ASH 2007; ASPHO 2007; AACR 2007). The differential protein expressions included NKG2A, IP3R type 3, NCR3, MAPKAPK5, Notch 2, PLEK, and NF-X1 using both immunophenotype and proteomic profiling studies.Objectives: To understand the importance of NKR signaling pathways in mediating the differential protein expression and thus in regulating the NK cytotoxic activities in CB vs PB CD56dim, we compared the genomic expression pattern in CB vs PB CD56dim.Methods: For CD56dim isolation, first, NK cells were isolated indirectly by magnetic separation from non-NK cells. Second, the pre-enriched NK cells (CD56+/CD3−) from CB and PB were directly labeled with CD16 (FCGR3) MicroBeads, and the CD56+ CD16+ NK cells (CD56dim) were eluted after removing the column from the magnetic field (Miltenyi). Purity of CD56dim NK cells were then examined by flow cytometry (BD FACScan). For genomic studies, total RNA was isolated and reverse transcribed to cDNA using T7-Oligo (dT) primer. cRNA was Biotin-labeled by in vitro transcription. Fragmented biotin-labeled cRNA was hybridized to GeneChip U133A_2 in GCOS-operated Fluidics Station 450, and then scanned by GeneChip Scanner 3000 (Affymetrix). Data were analyzed using Agilent GeneSpring. Signal intensities were compared using one way ANOVA and Welch Test for statistical analysis.Results: There were 193 and 222 genes over and under expressed at the genomic level between CB vs PB CD56dim NK cells, respectively. CB vs PB CD56dim significantly overexpressed NKG2A (2.14F), CD16b (2.46F), KIR2D (2.13F), NKp44 (NCR2; 2.62F), PBX1 (4.29F), ENPEP (3.93F). There was no significant difference in NKR gene expression of CD16a, CD161, NKG2C, and NKp46 in CB vs PB CD56dim. CB vs PB CD56dim underexpressed the following NK genes: IP3R (1.32F), MAPKAPK5 (1.77F), NCR3 (1.24F), ACACB (3.23F), BBS1 (2.00F).Conclusion: CB vs PB CD56dim overexpressed NKG2A, CD16b, KIR2D, and NKp44 genes compared to only NKG2A was overexpressed at the protein level. These results suggest that NKR protein product levels in CB CD56dim may be directly regulated at the translation level, but not the transcription level. The discrepancy of IP3R, ENPEP, PBX1, and MAPKAPK5 gene expression suggest the involvements of IP3 and calcium ions in NKR signaling pathways. Since the Notch2, PLEK, and NF-X1 gene expression patterns were not increased, the augmented protein levels may result from the regulation of protein translation. The potential regulators of this process may include PBX1, ENPEP, ACACB, and BBS1 though the roles of these regulators need to be defined. We conclude that genomic differences between CB vs PB CD56dim may play an important role in regulating NKR signaling pathway, and thus contribute to disparate cytotoxic activity between CB vs PB and suggest a possible explanation for immaturity of cord blood innate and adaptive immunity.