The frequency of TERT-specific CD4+ T cells in age-matched HD was 45% (10/22) in accordance with recent observation reporting high precursor frequencies of tumour antigen-specific CD4+ T cells in healthy subjects (Supplementary Fig. 1).21 No change of anti-TERT CD4+ T-cell response was observed according to patients’ main clinical characteristics, such as age, smoking status, histology and mutational status (Supplementary Table 2). Here, CD4 is linked to Huntington disease.