A truncated human CD4-IRES-cre sequence with a stop codon was inserted into exon 1 of Ccl19 at the ATG translational start codon in a BAC (RP23446D10). Ccl21b, which is located very close to Ccl19 in the BAC, was disrupted by inserting the human CD8 gene into the first exon. Seven founders were generated and screened by crossing to R26-EYFP reporter mice. 2 of 7 lines had identical stromal-cell specific transgene expression, and founder line 1 was used for all subsequent studies.