Where have all the T cells gone?

In this issue of Blood, Beq and colleagues describe the massive yet transient exodus of T cells from peripheral blood to lymph nodes, skin, and gut lymphoid tissue after in vivo IL-7 administration to healthy Rhesus macaques. This dramatic brief T-cell lymphopenia has previously been described in both cancer and HIV clinical trials of rhIL-7. Tissue redistribution of T lymphocytes had been invoked to explain this unusual occurrence but there was no data supporting this hypothesis until now.