Soluble tumor necrosis factor receptor type I enhances tumor development and persistence in vivo.

Secretion of human soluble tumor necrosis factor receptor type I (sTNFRI) by the mouse fibrosarcoma cell line, L929, previously has been demonstrated to confer resistance to in vitro lysis by TNF and to LAK- and CTL-mediated cytolysis. These findings suggest that, in vivo, sTNFRI contributes to tumor survival by inhibiting these immunologic mechanisms. To evaluate this hypothesis, we compared the growth of sTNFRI-secreting L929 cells with that of the unmodified parental fibrosarcoma in an in vivo mouse transplantation model. Secretion of sTNFRI by L929 cells markedly enhanced their tumorigenicity and persistence in syngeneic recipients. This benefit was abrogated by sTNFRI-neutralizing antibodies induced by immunization prior to tumor challenge. These data demonstrate that sTNFRI directly influences tumor formation and persistence in vivo and suggest the selective removal and/or inactivation of sTNFRI as a promising new avenue for cancer immunotherapy.