Adipocyte progenitors are derived from mesenchymal stem cells and express the transmembrane marker PREF1 (also known as DLK1). Imaging of embryonic lymph nodes and their associated fat pads revealed the presence of PREF1+ cells co-expressing lymphoid stromal markers in lymph node anlagen. Moreover, embryonic adipocyte progenitors responded to lymphotoxin-β receptor (LTβR) stimulation, which has a key role in lymph node development, by downregulating their adipogenic transcriptional programme. LTβR-dependent reprogramming of adipocyte progenitors involved the non-canonical NF-κB pathway, and after LTβR stimulation both embryonic and adult adipocyte progenitors migrated from fat pads to lymph node anlagen and expressed lymphocyte pro-survival factors. So, adult adipocyte progenitors may also drive the formation of tertiary lymphoid structures in the presence of lymphotoxin.