Moreover, although IL-7 was demonstrated to induce viral evolution of X4 viruses in vitro[30], no association between current IL-7 levels and the presence of archived X4 variants in vivo was observed in the present study; however, it cannot be excluded that lymphopenia-induced IL-7 production might have previously favored the R5 to X4 switch at previous timepoints during the patient’s history, but this association was not apparent at time of analysis. Here, IL7 is linked to lymphopenia.