Vhl∆/∆Trp53∆/∆Rb1∆/∆Hif1a∆/∆ but not Vhl∆/∆Trp53∆/∆Rb1∆/∆Hif2a∆/∆ tumours showed increased densities of CD4 positive cells compared to Vhl∆/∆Trp53∆/∆Rb1∆/∆ tumours. This evidence concerns the gene CD4 and neoplasm.