CTLA4 and neoplasm: T regulatory lymphocytes can be divided into three groups according to their immunophenotype: (1) Treg lymphocytes with a pro-tumour phenotype (CTLA-4++, FoxP3+, CD25+), (2) Treg lymphocytes with an incomplete differentiation phenotype (CTLA-4+, FoxP3++, CD25++), and (3) undifferentiated and depleted Treg lymphocytes (CTLA-4−, FoxP3+/−, CD25++).