IL7 and neoplasm: We next crossed Il7-Cre mice with Cxcl12fl/fl mice and found that cell type-specific genetic ablation of Cxcl12 expression substantially reduced the frequency of tumor-initiating cells (1 in 4,809 control vs. 1 in 44,814 Il7-Cre Cxcl12fl/fl) without affecting the time to engraftment (Fig.6C).