The uncommitted Thpp cells are likely not equivalent to two other precursor populations that have been described: A CXCR5+ subset of Tcm could differentiate to Th1 or Th2 cells depending on the culture conditions [45], however, most of the 2+γ- cells in human PBMC responses to influenza or tetanus are CXCR5- [24]. This evidence concerns the gene CXCR5 and tetanus.