Recruitment and activation of tumor‐specific immune t cells in situ : Functional studies using a sponge matrix model

The activation of tumor‐specific precursor cytotoxic T lymphocytes (CTLP) into cytotoxic T cells (CTL) was demonstrated in situ using the well‐defined, highly metastatic ESb tumor as murine model system. Ten days after optimal immunization of syngeneic mice with a sublethal dose of live ESb tumor cells in the pinna, tumor‐sensitized non‐cytotoxic CTLP were recovered from the spleen and lymph nodes. These cells mature into tumor‐specific CTL upon restimulation in vitro . Using a confined sponge matrix compartment, in combination with a specific tumor vaccine (autologous inactivated tumor cells), we induced a CD8 + (Lyt 2 + ) T‐cell‐mediated, highly cytotoxic anti‐tumor immune response in situ in immunized mice. It was not possible to activate a similar response directly in lymphoid organs such as the spleen. The cytotoxic CD8 + T cells, recovered by simple mechanical pressing of the sponge, were active against the specific tumor cells in a 51 Cr‐release assay in vitro and also in a Winn neutralization assay in vivo . CTL activity was increased and remained in the non‐adherent fraction when the cell mixture, squeezed out of the sponges, was passed over nylon wool. In a cell recruitment assay, the delayed‐type hypersensitivity (DTH) potential of the activated sponge‐infiltrating T cells was demonstrated by their capacity to recruit circulating host lymphocytes to sites of tumor‐cell location in situ .