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Tumor Sponge Implantation: An in Vivo Method for Studying Syngeneic, Primary Antitumor Lymphocyte Responses¹

Department of Therapeutic Radiology, University of Minnesota, Minneapolis, Minnesota 55455

Sponge matrices surgically implanted in the s.c. space of the back of normal BALB/c mice were injected with a "regressor" dose of Moloney virus-induced BALB/c tumor cells. The kinetics of the generation of cytotoxic cells within the sponge was studied over a 22-day period in a short-term ⁵¹Cr release assay. Cytotoxic activity peaked on Day 16 and then declined to negligible levels by Day 22. No cytotoxicity was detectable when nontransformed BALB/c blast cells, Moloney leukemia virus-induced tumor (LSTRA) cells, or unrelated chemically induced tumor (EL4) cells were used as targets. When the cellular composition of implanted tumor sponges was examined on Day 16, it was found to be 30 to 40% myeloperoxidasepositive cells, 15 to 25% surface immunoglobulin-positive cells, and 40 to 50% -positive cells. Treatment with anti-Thy 1.2 plus complement eliminated the cytotoxic response on Day 16.

The ratio of T-cells to tumor cells within the sponge was determined by immunofluorescence. Kinetic studies showed that the number of -positive cells increased well before cytolytic activity was detected, possibly reflecting increasing numbers of amplifier T-cells or cytotoxic cell precursors. A later decline in -positive cells correlated directly with decreased cytotoxicity. Furthermore, onset of cytotoxic activity also correlated with a decline in the percentage of Moloney murine sarcoma virus tumor cells within the sponge. Sponge cells isolated on Day 16 (peak cytotoxicity), mixed with lethal dosages of Moloney murine sarcoma virus tumor cells, successfully neutralized the lethal challenge demonstrating the in vivo antitumor efficacy of these effector cells.

Sponges were also implanted in mice which had been immunized with a single injection of Moloney murine sarcoma virus cells. Inoculation of the sponge with tumor cells resulted in a second set response in which cytotoxic cells appeared much earlier than in unsensitized animals. Cells from spleen, lymph node, or peritoneal cavity of normal or presensitized animals with tumor sponge implants were not cytotoxic, suggesting a highly localized response.

¹ This work was supported in part by the Hubert Humphrey Cancer Fund; West Side Citizens' Band Club, Delano, Minn.; and the Minnesota Medical Foundation's Zagaria Fellowship and Grant CRF-36-79.

² To whom requests for reprints should be addressed, at Department of Therapeutic Radiology, Box 367, Mayo Memorial Building, University of Minnesota, Minneapolis, Minn. 55455.

Received 5/ 4/81. Accepted 10/27/81.