The pathway by which lymphocytes, or specific subpopulations of lymphocytes, trigger the expression of TP is not clear, although there are reports implicating CD4 positive cells in tumour angiogenesis (Blotnick et al, 1994) and natural killer (NK) cells in complex interactions with angiogenic factors (Melder et al, 1996). This evidence concerns the gene TYMP and neoplasm.