Recently, two Phase I clinical trials of melanoma neoantigen-vaccines in the form of peptide or mRNA [43,44], resulted in both CD4+ and CD8+ vaccine-specific T-cell immunity, with a bias towards CD4+ T-cell responses, and clinical efficacy ranging from no recurrence in ~2 out of three of patients, to two (n = 5) relapsed patients favourably responding to post-vaccination anti-PD-1 treatment by the end of the study. The gene discussed is CD4; the disease is melanoma.