Neuroblastoma cells expressing mature IL-18, but not proIL-18, induce a strong and immediate antitumor immune response.

Retroviral constructs were designed to express the novel cytokine interleukin 18 (IL-18), also known as interferon-gamma-inducing factor, in a murine neuroblastoma cell line [neuro-2a (N-2a)] to examine the effects of IL-18 expression on tumorigenicity. N-2a cells expressing proIL-18 (N-2a/IL-18p) were as tumorigenic as parental N-2a cells, whereas N-2a cells engineered to secrete mature IL-18 (N-2a/IL-18m) were nontumorigenic. Inoculation of mice with N-2a/IL-18m generated immediate immunity to parental N-2a. N-2a/IL-18m formed tumors in mice depleted of CD4+ and CD8+ T cells, suggesting that the antitumor immune response was T cell mediated. The resulting T-helper (Th) immune response was also characterized in vitro and had a large Th1 component based on in vitro production of the cytokines IFN-gamma and granulocyte macrophage colony-stimulating factor in response to tumor cells and IL-18.

Retrovirus-mediated gene transfer of B7-1 and MHC class II converts a poorly immunogenic neuroblastoma into a highly immunogenic one.

The T cell co-stimulatory molecule B7-1 was transduced into a poorly immunogenic murine neuroblastoma cell line (Neuro-2a, N-2a) alone or in combination with MHC class II genes to test the ability of these genes to stimulate antitumor immunity. N-2a cells transduced with B7-1 exhibited reduced tumorigenicity, whereas N-2a cells overexpressing both MHC class II (syngeneic, I-Ak) and B7-1 totally abrogated tumorigenicity. Rejection of I-Ak/B7-1 cells was dependent on both CD4+ and CD8+ T cells. The ability of both vaccines to induce protection against parental N-2a was temporally dependent on the time of secondary N-2a challenge. To investigate the immunity generated by N-2a/B7-1 and N-2a/I-Ak/B7-1 vaccines, we tested the ability of these modified cells to stimulate in vitro the proliferation of syngeneic splenocytes from naive mice. A significant increase in splenocyte proliferation was observed with N-2a/I-Ak/B7-1 cells compared to N-2a cells. We also determined that vaccination with N-2a/I-Ak/B7-1 cells was able to generate cytotoxic T cell responses to unmodified N-2a cells. The introduction of B7-1 and I-Ak into N-2a was able to convert a poorly immunogenic tumor to a highly immunogenic one; however, mice bearing large established unmodified tumors had little response to vaccination with N-2a/I-Ak/B7-1 cells. Our results emphasize the importance of tumor immunogenicity in the treatment of established tumors with MHC class II/B7-1 tumor cell vaccines.

Murine neuroblastoma vaccines produced by retroviral transfer of MHC class II genes.

Malignant tumors express tumor-related antigens, but effective antitumor immunity does not occur in the primary host. One hypothesis is that there is insufficient stimulation of T-cell responses due to ineffective antigen presentation. An approach to overcome these deficiencies is to modify tumor cells to express major histocompatibility complex (MHC) class II genes and thus facilitate the presentation of antigens directly by tumor cells. Our experiments with a murine neuroblastoma cell line (neuro-2a) transduced with DR (xenogeneic), 1-Ab (allogeneic), or 1-Ak (syngeneic) MHC class II genes support this notion. The relative potencies of the modified neuro-2a to induce immunity to unmodified neuro-2a were neuro-2a/DR > neuro-2a/1-Ab > neuro-2a/1-Ak. Modified neuro-2a also could stimulate naive splenocyte proliferation in vitro. The relative magnitude of the proliferative responses seen after stimulation with modified tumor cells was neuro-2a/DR > neuro-2a/1-Ab > neuro-2a/1-Ak > unmodified neuro-2a. Hence, the tumor cell-induced splenocyte proliferative responses observed in vitro correlate with the effectiveness of the tumor cell vaccines to induce antitumor immunity in vivo. These data show that the expression of exogenous MHC class II on tumor cells is a potent stimulus for specific antitumor immunity. Because of the correlation of the in vivo and in vitro immune responses to modified tumor cells, the tumor-induced lymphocyte proliferation assay may be useful in evaluating tumor cell vaccines produced by additional genetic modifications of tumor cells.

Human class II major histocompatibility complex gene transfer into murine neuroblastoma leads to loss of tumorigenicity, immunity against subsequent tumor challenge, and elimination of microscopic preestablished tumors.

Immunological recognition of transformed cells is critically important to limit tumor development and proliferation. Because established tumors have escaped immune recognition and elimination, novel strategies to enhance antitumor immunity have been developed. A unique approach has used the introduction of genes encoding major histocompatibility complex (MHC) antigens into tumor cells. Experiments in mice have shown that the expression of syngeneic class II MHC antigens in tumor cells completely abrogates tumorigenicity and induces tumor-specific immunity. In this study we sought to determine whether a more effective antitumor immune response would be generated by introducing xenogeneic class II MHC genes into tumor cells. To address this question we used recombinant retroviruses to express human class II MHC genes in a highly malignant murine neuroblastoma cell line, Neuro-2a. We found that normal mice inoculated with Neuro-2a expressing the human class II MHC antigen did not develop tumors and were immune to subsequent challenge with unmodified Neuro-2a cells. In addition, mice bearing small established Neuro-2a tumors were cured by vaccination with Neuro-2a expressing human class II MHC. We hypothesize that a similar approach using retroviral-mediated transduction of class II MHC genes into human tumor cells may be an effective alternative to current cancer treatment.