1. ¹Department of Medicine, Case Comprehensive Cancer Center, Case Western Reserve University, Cleveland, OH, USA
2. ²Department of Biology, University of Konstanz, Konstanz, Germany
3. ³Biochemistry, Case Comprehensive Cancer Center, Cleveland, OH, USA
4. ⁴Department of Medicine, James Graham Brown Cancer Center, University of Louisville, Louisville, KY, USA
5. ⁵Abraham J and Phyllis Katz Cord Blood Foundation, Cleveland Cord Blood Center, Cleveland, OH, USA
6. ⁶Department of Hematologic Oncology and Blood Disorders, Cleveland Clinic Foundation Taussig Cancer Center, Cleveland, OH, USA

Correspondence: Dr MJ Laughlin, Department of Medicine, Case Comprehensive Cancer Center, Case Western Reserve University, 10900 Euclid Avenue Wolstein Research Building 2-129, Cleveland, OH 44106-7284, USA. E-mail: mary.laughlin@case.edu

Received 26 February 2008; Revised 11 June 2008; Accepted 17 July 2008; Published online 4 September 2008.

Abstract

On activation, umbilical cord blood (UCB) CD4⁺ T cells demonstrate reduced expression of tumor necrosis factor- (TNF-) and interferon- (IFN-), whereas maintaining equivalent interleukin-2 (IL-2) levels, as compared with adult peripheral blood (PB) CD4⁺ T cells. Nuclear factor of activated T cells (NFAT1) protein, a transcription factor known to regulate the expression of IL-2, TNF- and IFN-, is reduced in resting and activated UCB CD4⁺ T cells. In contrast, expression of Broad-complex-Tramtrack-Bric-a-Brac and Cap'n'collar homology 1 bZip transcription factor 2 (BACH2) was shown by gene array analyses to be increased in UCB CD4⁺ T cells and was validated by qRT-PCR. Using chromatin immunoprecipitation, BACH2 was shown binding to the human IL-2 proximal promoter. Knockdown experiments of BACH2 by transient transfection of UCB CD4⁺ T cells with BACH2 siRNA resulted in significant reductions in stimulated IL-2 production. Decreased IL-2 gene transcription in UCB CD4⁺ T cells transfected with BACH2 siRNA was confirmed by a human IL-2 luciferase assay. In summary, BACH2 maintains IL-2 expression in UCB CD4⁺ T cells at levels equivalent to adult PB CD4⁺ T cells despite reduced NFAT1 protein expression. Thus, BACH2 expression is necessary to maintain IL-2 production when NFAT1 protein is reduced, potentially impacting UCB graft CD4⁺ T-cell allogeneic responses.