Tumor neutralization by immune in vitro ‐sensitized splenocytes depends on an interaction with bone‐marrow‐derived cells

In a Winn assay, the inhibition of methylcholanthrene‐induced sarcoma growth by tumor‐immune, secondarily in vitro ‐sensitized splenocytes was augmented by normal unsensitized bone‐marrow cells. Bone‐marrow cells augmented the effect of a fixed number of sensitized splenocytes in a dose‐dependent manner, yet had no tumor‐neutralizing capacity by themselves. The marrow's capacity to enhance tumor neutralization was not shared by normal splenocytes, thymocytes or lymph‐node cells. When two non‐cross‐reacting tumors were used, marrow cells were capable of augmenting tumor neutralization only if admixed with sensitized splenocytes and the sensitizing neoplasm. Equal numbers of bone‐marrow cells administered intravenously to recipients of an admixture of sensitized splenocytes and tumor were unable to augment neutralization, suggesting a direct interaction between sensitized lymphocytes and normal bone‐marrow cells in the inhibition of tumor growth.