CD4 and neoplasm: Despite also inducing retinoic acid receptor-related orphan receptor-γt (RORγt) [123], a transcription factor that regulates the pro-tumour Th17 phenotype in CD4+ T cells, IV bolus injections of IL-21 have shown favourable outcomes against solid tumours in early phase clinical trials [124,125], indicating the potential benefit of this cytokine as an anti-tumour agent.