Human IL-7 Recombinant Protein. Interleukin 7 (IL-7) is a hematopoietic cytokine that is constitutively produced by stromal cells from the bone marrow and thymus. IL-7 signals through the IL-7R to promote the differentiation of hematopoietic stem cells to lymphoid precursor cells, which give rise to T cells, B cells, and natural killer cells.