CCR5 and colorectal carcinoma: Therefore, based on the fact that all three CT26 tumor types (subcutaneous, liver and lung) expressed both CCL5 and CCR5 in vivo, whereas HT29 xenografts exhibited levels of CCR5 below the threshold of detection of the PCR technique, we have found more appropriate to work with the CT26 models to assess the role played by CCL5/CCR5 interaction in colorectal carcinoma.