Tumor-specific CD8+ T cells expressing IL-12 eradicate established cancers in lymphodepleted hosts

T-cell based immunotherapies can be effective in the treatment of large vascularized tumors, but they rely on adoptive transfer of substantial numbers (~ 20 million) of tumor-specific T cells administered together with vaccination and high-dose IL-2. In this study, we report that ~10,000 T cells gene-engineered to express a single-chain IL-12 molecule can be therapeutically effective against established tumors in the absence of exogenous IL-2 and vaccine. Although IL-12 engineered cells did not persist long-term in hosts, they exhibited enhanced functionality and were detected in higher numbers intra-tumorally along with increased numbers of endogenous NK and CD8 + T cells just prior to regression. Importantly, transferred T cells isolated from tumors stably overproduced supra-physiological amounts of IL-12 and the therapeutic impact of IL-12 produced within the tumor microenvironment could not be mimicked with high doses of exogenously provided IL-12. Furthermore, anti-tumor effects could be recapitulated by engineering wild-type open-repertoire splenocytes to express both the single-chain IL-12 and a recombinant tumor-specific T-cell receptor (TCR), but only when individual cells expressed both the TCR and IL-12, indicating that arrested migration of T cells at the tumor site was required for their activities. Successful tumor eradication was dependent on a lymphodepleting pre-conditioning regimen that reduced the number of intratumoral CD4 + Foxp3 + T regulatory cells. Our findings reveal an approach to genetically modify T cells to reduce the cell number needed, eliminate the need for vaccines or systemic IL-2, and improve immunotherapy efficacy based on adoptive transfer of gene-engineered T cells.