Interleukin-2 gene transfer into murine neuroblastoma decreases tumorigenicity and enhances systemic immunity causing regression of preestablished retroperitoneal tumors

Murine neuroblastoma, neuro-2a, was transduced with the retroviral vector LIL-2SN in order to examine the influence of localized interleukin (IL)-2 production on the immune response against a low major histocompatibility complex (MHC) class I, class II-negative, and intercellular adhesion molecule (ICAM)-l-negative tumor. Two neomycin-resistant (neo R) clones, N-2a/IL-2/L (2.5 ± 0.4 U/ml/10⁶cells/24 h) and N-2a/IL-2/H (44.6 ± 8.8 U/ml), were studied as representative low and high IL-2 producers, respectively. Using a recently developed retroperitoneal (r.p.) model for implantation of neuroblastoma in its natural site, we demonstrated that production of IL-2 by neuro-2a reduces its tumorigenicity in a dose-dependent fashion. T-cell, but not natural killer (NK) cell, depletion significantly increased tumor induced mortality in syngeneic A/J mice. Mice genetically devoid of T-cells (C.B-17 scidlscid) also experienced a significant increase in mortality rates. This indicates that the antitumor effect of locally secreted IL-2 is mediated primarily through activation of T-cells. Immunization of mice with irradiated N-2a/IL- 2/H cells resulted in protection when challenged at a later date with unmodified neuro-2a cells. Depletion of CD8⁺, but not CD4⁺, T-cells prior to vaccination abrogated the protective effect, indicating that the priming phase of the immune response is CD8⁺T-cell dependent. Mice with established r.p. tumors were vaccinated with N-2a/IL-2/H, which significantly prolonged their survival compared to unimmunized controls and to mice immunized with non-IL-2- producing neuro-2a cells. Because of the similarities of this model with the human tumor, our studies indicate that IL-2-transduced neuroblastoma cells may be effective in generating systemic immunity leading to eradication of minimal residual disease.