Exploiting the lacZ reporter gene for quantitative analysis of disseminated tumor growth within the brain: use of the lacZ gene product as a tumor antigen, for evaluation of antigenic modulation, and to facilitate image analysis of tumor growth in situ.

We extend use of the lacZ reporter gene for tumor biology. Intracerebral growth of 9L/lacZ, a gliosarcoma cell line that stably expresses lacZ, was evaluated in syngeneic rats. The reporter gene product, Escherichia coli-derived beta-galactosidase (beta-gal), was detected histochemically on tissue sections. This permits visualization of disseminated tumor and, as shown here, facilitates image analysis. We show that the beta-gal marker protein itself can serve as a tumor antigen in appropriate contexts. Quantitative image analysis of tumor areas is used to show that immunization with beta-gal protects against tumor growth. Abnormal beta-gal- areas are easily detected, facilitating study of antigenic modulation. The tumor studied did not escape through this mechanism. All abnormal beta-gal- areas examined were shown to reflect accumulation of inflammatory or reactive cells, not tumor. Taken together, these findings show several ways in which the lacZ reporter gene can be exploited to facilitate quantitative analysis of disseminated tumor growth within the brain. They draw attention to the growing appreciation that tumor antigens need not be cell surface molecules.