The multicellular spheroid as a model tumor allograft. II. Characterization of spheroid-infiltrating cytotoxic cells.

Alloimmune lymphoid cells infiltrating multicellular spheroids of EMT6 mammary sarcoma cells (a solid tumor allograft model) have been characterized according to their morphological and functional properties. Both lymphocytes and macrophages were found within spheroids at the time of peak tumor cell damage. Cytotoxic cells specific for allograft antigens were also present. Using a short-term 51-Cr release assay, the cells responsible for cytotoxicity were characterized as a nonadherent, nonphagocytic T cell population. Velocity sedimentation cell separation further demonstrated that these cytotoxic cells had the physical properties of small lymphocytes. Some evidence for selective spheroid infiltration by specifically alloimmune cells was also obtained. The possible relationship of this cellular infiltrate to graft damage is discussed.