A method was developed to compare the lymphocytic infiltrates in regressing vs. progressing experimental mouse tumors using a model for human papillomavirus-16 (HPV-16) oncoprotein-linked cancer. Tumor cells mixed with matrigel, composed of natural matrix substances that provide a basement membrane structure for adherent cells, were inoculated into mice vaccinated with an efficacious vaccine to the E7 oncoprotein or a vaccine to a control antigen. The tumor cells remained within the solidified gel and recruited a cellular infiltrate that could readily be analyzed upon removal of the gelatinous mass containing progressing or regressing tumors. The results show that tumors recruit activated CD8(+) T cells regardless of their antigen specificity. In regressing tumors expressing an appropriate target antigen for the vaccine-induced CD8(+) T cells, a strong increase of the tumor antigen-specific T cell population was observed over time. Progressing tumors that lacked the target antigen for the activated CD8(+) T cell population did not show this selective enrichment.