DNA sequence encoding Flt3L (696 bp) was amplified from the C57BL/6 mouse spleen cDNA using the following oligonucleotides: 59-CGG GAT CCA TGA CAG TGC TGG CGC C-39 and 59-CGG AAT TCA TCC TAG GGA TGG GAG-39. The resulting products were subsequently cloned into a pGEX-4T3 vector with a glutathione S-transferase tag. The plasmid was transformed into Escherichia coli strain BL21. Recombinant Flt3L expression was induced by addition of 1 mM IPTG and then purified using the glutathione sepharose 4B resin columns as instructed by the manufacturer. A GST vector protein was also expressed and purified to homogeneity. The proteins were passed over polymyxin B columns (PIERCE) to remove any contaminated LPS and further concentrated by 3KD Micropore Filters. The purified recombinant Flt3L and rGST were stored in aliquots at 280uC until use. 