Suppression of Burkitt's lymphoma tumorigenicity in nude mice by co-inoculation of EBV-immortalized lymphoblastoid cells

EBV-immortalized B-lymphoblastoid cell lines (LCL) inoculated s.c. into T-cell-deficient nude mice regress completely after a short initial growth period. We tested whether the putative host response underlying this phenomenon might also be directed against progressively growing Burkitt's lymphoma (BL) tumors in nude mice. Outgrowth of BL tumors was suppressed when cells of the highly tumorigenic BL cell line BL 60 were mixed with cells of the autologous LCL IARC 277 before s.c. inoculation into nude mice. Even when the cells were inoculated separately and simultaneously into contralateral flanks of the mice, regression of initially growing BL tumors could be observed, albeit with reduced frequency and dependent on the dose of LCL cells. Tumor growth of BL 60 cells could also be suppressed by co-inoculation with the non-autologous LCL IARC 174 and IARC 277 cells could suppress growth of the non-autologous BL cell line Eli. Pronounced infiltration with murine (m)CD-11b-positive mouse macrophages and mCD-8a-positive mouse lymphoid cells, most probably natural killer cells, was seen in histological tissue sections of regressing BL 60 tumors when LCL cells were inoculated contralaterally. In regressing BL tumors, these mouse cells were present not only in necrotic areas but also in vital BL tissue, indicating that infiltration of mouse cells had taken place before the development of necrosis. Since tumor-infiltrating mouse cells can be activated at least by some human cytokines, we measured cytokine production of BL 60 and IARC 277. High amounts of IL 6 and IL 10 were produced by the LCL cells, whereas IL-6 and IL-10 production by the BL 60 cells was beyond or close to the detection threshold. In addition, IL 8 was secreted up to 5-fold more by the LCL than by the BL cells. The results presented here thus suggest a host response of the nude mouse, which is triggered by cytokines released from the LCL but, once induced, is directed also against BL cells.