A researcher is comparing the cellular tropism of Human T-cell leukemia virus 1 (HTLV-1) and Human T-cell leukemia virus 2 (HTLV-2) by analyzing infected peripheral blood mononuclear cells. The analysis is most likely to confirm that HTLV-1 has a known preference for infecting CD4+ T-cells, while HTLV-2 preferentially infects which cell type?