Self-sufficient primary natural killer cells engineered to express T cell receptors and interleukin-15 exhibit improved effector function and persistence.

ABSTRACT

Background: NK cells can be genetically engineered to express a transgenic T-cell receptor (TCR). This approach offers an alternative strategy to target heterogenous tumors, as NKTCR cells can eradicate both tumor cells with high expression of HLA class I and antigen of interest or HLA class I negative tumors. Expansion and survival of NK cells relies on the presence of IL-15. Therefore, autonomous production of IL-15 by NKTCR cells might improve functional persistence of NK cells. Here we present an optimized NKTCR product harnessed with a construct encoding for soluble IL-15 (NKTCR/IL-15), to support their proliferation, persistence and cytotoxic capabilities. Methods: Expression of tumor-specific TCRs in peripheral blood derived NK-cells was achieved following retroviral transduction. NKTCR/IL-15 cells were compared with NKTCR cells for autonomous cytokine production, proliferation and survival. NKBOB1-TCR/IL-15 cells, expressing a HLA-B*0702-restricted TCR against BOB1, a B-cell lineage specific transcription factor highly expressed in all B-cell malignancies, were compared with control NKBOB1-TCR and NKCMV-TCR/IL-15 cells for effector function against TCR antigen positive malignant B-cell lines in vitro and in vivo. Results: Viral incorporation of the interleukin-15 gene into engineered NKTCR cells was feasible and high expression of the TCR was maintained, resulting in pure NKTCR/IL-15 cell products generated from peripheral blood of multiple donors. Self-sufficient secretion of IL-15 by NKTCR cells enables engineered NK cells to proliferate in vitro without addition of extra cytokines. NKTCR/IL-15 demonstrated a marked enhancement of TCR-mediated cytotoxicity as well as enhanced NK-mediated cytotoxicity resulting in improved persistence and performance of NKBOB1-TCR/IL-15 cells in an orthotopic multiple myeloma mouse model. However, in contrast to prolonged anti-tumor reactivity by NKBOB1-TCR/IL-15, we observed in one of the experiments an accumulation of NKBOB1-TCR/IL-15 cells in several organs of treated mice, leading to unexpected death 30 days post-NK infusion. Conclusion: This study showed that NKTCR/IL-15 cells secrete low levels of IL-15 and can proliferate in an environment lacking cytokines. Repeated in vitro and in vivo experiments confirmed the effectiveness and target specificity of our product, in which addition of IL-15 supports TCR- and NK-mediated cytotoxicity.