Studies of in vivo recruitment and activation of cytotoxic lymphocytes using a gelatin-sponge model of concomitant tumor immunity.

We have earlier described a sponge model of concomitant tumor immunity that permits the capture and isolation of effector T lymphocytes that mediate the rejection of a secondary EMT6 tumor implant. In this study, we have employed the sponge model to study lymphocyte homing and in situ activation during the development of concomitant tumor immunity. Our results demonstrate that EMT6-specific CTL in animals bearing primary EMT6 tumors home preferentially to sponges implanted with EMT6 tumor cells, as compared with contralateral sponges lacking tumor cells or sponges injected with antigenically distinct 168 tumor cells. We further show that recruitment is selective and is not in response to a foreign-body reaction to the sponge. In addition, we show that EMT6-specific CTL were recovered from sponges injected either with intact EMT6 tumor cells or with a mixture of EMT6-derived membranes and supernatant. In contrast, cells accumulating in sponges injected with membranes or supernatant alone were not cytolytic. Thus, maximal recruitment, retention, and activation of CTL precursors require putative chemo-attractive factors secreted by tumor cells as well as interaction with tumor antigen.