Observations that 1,25(OH)2D3 or VDR deficiency is associated with increased susceptibility to tumours and autoimmune disease, both due to the action of Th1 based cellular immunity, suggests that 1,25(OH)2D3 acts to reset T-cell responses to an immunological baseline, limiting hyper-activated T-cell responses in autoimmunity whilst preventing the exhaustion or skewing of anti-tumour T-cell responses in the setting of cancer. This evidence concerns the gene VDR and neoplasm.