Specific depression of the antitumor cellular immune response with autologous tumor homogenate

A momogenate of an SV40-transformed firbosarcoma of BALB/c mice (E4 tumor) injected i.p. into E4, tumor-immune syngeneic mice specifically depressed their cell-mediated immune responses to autologous tumor cells, as measured by a radioisotopic foot pad assay. The fraction of the tumor homogenate that brought about this depression was present in the high-speed supernatant and pellet of a 3 M KCl extract of the tumor. The specificity of the depression was shown in three ways: (a) the serum of E4 tumor-immune mice, but not of normal mice, given injections of E4 tumor homogenate 24 hr previously, suppressed antitumor immunity in vitro, as measured by the release of 51Cr from labeled E4 tumor cells incubated with spleen cells from tumor-immune animals; (b) the i.p. inoculation of E4 tumor homogenate did not alter the cellular immune response of tuberculin-sensitized mice to tuberculin; and (c) the i.p. injection of a homogenate of antigenically unrelated tumor did not depress the cellular immune response of E4 tumor-immune mice to E4 tumor cells.