In Vivo Effects and Parallel in Vitro Cytotoxicity of Splenocytes Harvestedfrom Treated or ControlC57BL/6J Mice after Adjuvant Immunotherapy of Pulmonary Metastases Using Xenogeneic RNA Specific to Bi 6 MurineMelanom&

Following excision of Bi 6 melanoma isografts from C57BL/ 6J mice, 80 to i 00% of untreated animals develop progressive pulmonary metastases after 4 to 6 weeks and die within 100 days. Immune RNA (1-ANA)extracted from the lymphoid tissues of guinea pigs immunized with Bi 6 melanoma or antigenically distinct syngeneic Lewis lung carcinoma was incubated in vitro with splenocytes harvested from normal C57BL/6J mice. After Bi 6 isograft excision, animals receiving five separate i.p. injec tions (every other day) of 75 x 106 Bi 6 1-ANA-treated synge neic splenocytes showed significantly improved long-term sur vival as summarized from three successive experiments (52%) compared to animals receiving Lewis lung carcinoma i-RNA treated splenocytes (p < 0.0001 ). The effect of 1-ANAtreat ment was RNase sensitive. Splenocytes were harvested from selected animals in each group 1 to 5 weeks after adjuvant therapy and tested for in vitro cytotoxicity against Bi 6 murine melanoma targets. [†̃251]lododeoxyuridmne assays, “long-term― 51Crassays, and microcytotoxicity assays with visual counting of remaining target cells were performed in parallel. Spleno cytes harvested from Bi 6 i-RNA-treated animals were consist ently and significantly cytotoxic to Bi 6 melanoma target cells when compared to spienocytes harvested from Lewis lung carcinoma I-RNA-treated animals. This in vitro cytotoxic effect was demonstrated from the second through the fifth week after in vivo treatment when animals in the control groups began to die from progressive pulmonary metastases.