Interleukin-21 gene transfection into mouse bladder cancer cells results in tumor rejection through the cytotoxic T lymphocyte response.

PURPOSE

We developed the genetically modified mouse bladder carcinoma MBT2 (American Type Culture Collection, Manassas, Virginia), which secretes interleukin-21, to investigate the functional activities of interleukin-21 in tumor immunity.

MATERIALS AND METHODS

The IL-21 gene was cloned from activated T cells by reverse transcriptase-polymerase chain reaction, inserted into an expression vector and then introduced into MBT2 using Lipofectamine. Exogenous interleukin-21 was assayed in culture supernatants from transfectants using sandwich enzyme-linked immunoassay. Direct antitumor and tumor vaccine effects were investigated in syngeneic mice rendered immunodeficient by administration of the corresponding antibody.

RESULTS

MBT2 cells secreting interleukin-21 (MBT2/IL-21) were completely rejected when subcutaneously injected into syngeneic mice. MBT2/IL-21 proliferated only when CD8+ T cells were depleted, whereas MBT2/IL-21 proliferation was totally abrogated in mice depleted of CD4+ T cells, natural killer cells or interferon-gamma. Subcutaneous injection of MBT2/IL-21 treated with mitomycin C remarkably inhibited parental MBT2 tumor growth at the contralateral site. Cytotoxicity assays using splenocytes from mice that rejected MBT2/IL-21 and the immunohistochemical features of MBT2/IL-21 tumors confirmed that in situ production of interleukin-21 can elicit powerful antitumor activity through CD8+ T-cell activation.

CONCLUSIONS

Interleukin-21 production in situ elicits antitumor activity through the activation of CD8+ T cells in vivo.