a, b Representative flow cytometry staining for CD4 and CD8 in CD3+ T cells (a) and summaries for the absolute number of CD4+ T cells (***p < 0.0001) and CD8+ T cells (***p < 0.0001) at pre- and post-mogamulizumab treatment (b) are shown. PBMCs (n = 25) obtained from pre- and post-mogamulizumab treatment. Pre-treatment samples were collected within two weeks before the initial mogamulizumab administration, and post-treatment samples were collected at 9-16 weeks after mogamulizumab administration and were subjected to flow cytometry. c Representative flow cytometry staining for CD45RA and FoxP3 in CD4+ T cells. Red dots, CCR4+ cells; black dots, CD4+ T cells. d Summaries for the absolute number of each CD4+ T cell fraction (Fr. I, ***p < 0.0001; Fr. II, ***p < 0.0001; Fr. III, ***p < 0.0001; Fr. IV, ***p < 0.0001 and Fr. V, ***p < 0.0001) as depicted in (c) at pre- and post-mogamulizumab treatment are shown (n = 25). e. Longitudinal changes in the absolute number of Treg cells (Fr. II) in CD4+ T cells at pre- and post-mogamulizumab treatment are shown. Red lines, long survivors; blue lines, short survivors. f, g. Representative flow cytometry staining for CD45RA and CCR7 in CD8+ T cells (f) and summaries for the absolute number of each CD8+ T cell fraction (Central memory, **p = 0.0005; Naive, ***p < 0.0001; Effector memory, *p = 0.0021 and TEMRA, **p = 0.0006) as depicted in (f) at pre- and post-mogamulizumab treatment (g) are shown (n = 14). Red dots, CCR4+ cells; black dots, CCR4- cells. In (b, d and g), black dots, patients who received 1.0 mg/kg mogamulizumab; blue dots, patients who received 0.1 mg/kg mogamulizumab and two-sided Mann–Whitney test was used. In (b, d and g), the center line indicates the median, and the box limits indicate the 1st and 3rd quartiles. The whiskers go down to the smallest value and up to the largest. week: wk, naive CD8+ T cells: Naive, central memory CD8+ T cells: Central memory, effector-memory CD8+ T cells: Effector memory, TEMRA CD8+ T cells: TEMRA, *p < 0.01, **p < 0.001, ***p < 0.0001. Source data are provided as a Source Data file.