High‐grade tumor‐specific immunity induced by L1210 leukemia variants obtained from the culture of L1210 cells fused with Lesch‐Nyhan fibroblasts

A highly immunogenic variant of the murine L1210 leukemia cell (L1210/LN‐1) for generation of tumor immunity has been obtained from culture of L1210 cells originally fused with human Lesch‐Nyhan fibroblasts. In L1210/LN‐1 cells, no human chromosomes were identified and chromosomes Ml and No. I carried by the parent L1210 cells were missing. L1210/LN‐1 cells displayed an intermediate morphology between L1210 cells and Lesch‐Nyhan fibroblasts. Most of the CDF 1 mice that were inoculated with less than 2 × 10 6 L1210/LN‐1 cells survived over 60 days without evidence of tumor, whereas the original L1210 cells killed all the mice tested in about 2 weeks. When inoculated with more than 5 × 10 6 L1210/LN‐1 cells, CDF 1 mice developed tumor. The CDF 1 mice which rejeted 2 × 10 6 L1210/LN‐1 cells were protected very effectively against challenge of otherwise highly aggressive 1–5 × 10 5 L1210 leukemia cells; 40 out of 43 primed mice tested survived for 60 days or longer after the tumor challenge. Even the CDF 1 mice primed with irradiated or mitomycin‐treated L1210/LN‐1 cells survived against a challenge of 10 s L1210 leukemia cells. They were, however, not protected against P388 leukemia or Meth A sarcoma, indicating that the immunity was specific to L1210 leukemia. The immunity induced by L1210/LN‐1 cells was transplantable by immune spleen cells into syngeneic recipients. Thus, the L1210/LN‐1 cells we obtained seem to be very useful as an immunogen for generation of high‐grade tumor‐specific immunity against highly malignant L1210 leukemia.