Tumor antigens are constitutively presented in the draining lymph nodes

Tumor growth is rarely associated with a strong specific CTL response, sugg esting that the immune system is ignorant of the presence of tumor because the Ags are not readily available to or are sequestered from potential effe ctor cells, We studied the in vivo activation of naive TCR transgenic hemag glutinin (HA)-specific CD8(+) T cells adoptively transferred into mice bear ing HA-expressing tumor using 5,6-carboxy-succinimidyl-fluorescein-ester la beling, which allows the identification of proliferating HA-specific T cell s. We demonstrate that tumor Ags are constitutively presented in the lymph nodes draining tumors and are powerfully mitogenic for responding T cells d espite the absence of anti-tumor CTL responses. Importantly, this prolifera tive signal occurs throughout tumor growth and is still detectable 6 mo aft er tumor inoculation when tumor is not palpable. These results provide the first evidence that there is constitutive presentation of tumor Ags in drai ning lymph nodes.