Autologous chimeric antigen receptor-modified (CAR) T cells with specificity for CD19 showed potent antitumor efficacy in clinical trials against relapsed and refractory B-cell acute lymphoblastic leukemia (B-ALL). Contrary to T cells, natural killer (NK) cells kill their targets in a non-antigen-specific manner and do not carry the risk of inducing graft vs. host disease (GvHD), allowing application of donor-derived cells in an allogenic setting. Hence, unlike autologous CART cells, therapeutic CD19-CAR-NK cells can be generated as an off-the-shelf product from healthy donors. Nevertheless, genetic engineering of peripheral blood (PB) derived NK cells remains challenging and optimized protocols are needed. In our study, we aimed to optimize the generation of CD19-CAR-NK cells by retroviral transduction to improve the high antileukemic capacity of NK cells. We compared two different retroviral vector platforms, the lentiviral and alpharetroviral, both in combination with two different transduction enhancers (Retronectin and Vectofusin-1). We further explored different NK cell isolation techniques (NK cell enrichment and CD3/CD19 depletion) to identify the most efficacious methods for genetic engineering of NK cells. Our results demonstrated that transduction of NK cells with RD114-TR pseudotyped retroviral vectors, in combination with Vectofusin-1 was the most efficient method to generate CD19-CAR-NK cells. Retronectin was potent in enhancing lentiviral/VSV-G gene delivery to NK cells but not alpharetroviral/RD114-TR. Furthermore, the Vectofusin-based transduction of NK cells with CD19-CARs Müller et al.
Cellular therapy has entered the daily clinical life with the approval of CAR T cell therapeutics and dendritic cell (DCs) vaccines in the US and the EU. In addition, numerous other adoptive cellular products, including natural killer (NK) cells, are currently evaluated in early phase I/ II clinical trials for the treatment of cancer patients. Despite these promising accomplishments, various challenges remain to be mastered in order to ensure sustained therapeutic success. These include the identification of strategies by which tumor cells escape the immune system or establish an immunosuppressive tumor microenvironment (TME). As part of the innate immune system, DCs and NK cells are both present within the TME of various tumor entities. While NK cells are well known for their intrinsic anti-tumor activity by their cytotoxicity capacities and the secretion of pro-inflammatory cytokines, the role of DCs within the TME is a double-edged sword as different DC subsets have been described with either tumor-promoting or -inhibiting characteristics. In this review, we will discuss recent findings on the interaction of DCs and NK cells under physiological conditions and within the TME. One focus is the crosstalk of various DC subsets with NK cells and their impact on the progression or inhibition of tumor growth. In addition, we will provide suggestions to overcome the immunosuppressive outcome of the interaction of DCs and NK cells within the TME.
Background: Natural Killer (NK) cells are known for their high intrinsic cytotoxic capacity. Recently, we and others showed that virally transduced NK cells equipped with a synthetic chimeric antigen receptor (CAR) targeting CD19 induced enhanced killing of acute lymphoblastic leukemia (ALL) cells. Here, we demonstrate for the first time that primary NK cells can be engineered using the non-viral Sleeping Beauty (SB) transposon/transposase system to stably express a CD19-CAR with a safe genomic integration profile and high anti-leukemic efficiency in vitro and in vivo. Methods: Primary NK cells were isolated from PBMCs from healthy donors. SB transposons vectorized as minicircles (MC), which encode either a Venus fluorescent protein or a CD19-CAR together with truncated EGFR (tEGFR) as a marker, were introduced in combination with the hyperactive SB100X transposase into primary NK cells via nucleofection. The genetically engineered NK cells were expanded using IL-15 cytokine stimulation under feeder-cell free conditions. Vector integration sites were mapped by analyzing the genomic region around each insertion site in genomic DNA from long-term cultivated gene-modified NK cells, engineered ether by lentiviral (LV) or SB-based technology. Stable gene delivery and biological activity were monitored by flow cytometry and cytotoxicity of CD19-CAR NK cells against CD19-positive ALL and CD19-negative cell lines. Results: Applying a protocol optimized with respect to nucleofection pulses, time points and plasmid ratios, primary NK cells showed long-lasting Venus expression (up to 50%) upon SB-mediated gene delivery with similar viability as non-treated (NT) NK cells during feeder-cell free ex-vivo expansion using IL-15. Likewise, SB transposon-engineered CD19-CAR NK cells displayed high viability, durable transgene expression (Fig 1 A), and no significant change in the NK cell phenotype profile. Next, we assessed vector integration into genomic safe harbors (GSH). GSH are defined as regions of human chromosomes that fulfill the following five criteria: not ultraconserved, >300 kb away from miRNA genes, >50 kb away from transcriptional start sites (TSS), >300 kb away from genes involved in cancer and outside transcription units. CD19-CAR NK cells generated using SB100X showed a significantly higher frequency of vector integration into GSH compared to LV-transduced CAR-NK cells and a significantly more-close to random nucleotide frequency (computer-generated random positions in the genome map to GSHs; random 43.68%; LV 14.78%, SB100X 23.99%; p<0.05) (Fig 1 B). MC.CD19-CAR NK cells generated with the SB platform demonstrated significantly higher cytotoxicity compared to NT NK cells against CD19-positive Sup-B15 ALL cells after long-term cultivation for two to three weeks and no loss of natural intrinsic cytotoxicity. After 4-hour co-culture, significantly enhanced specific tumor cell lysis was found for MC.CD19-CAR NK cells vs NT NK cells at all effector to target cell ratios (E:T) tested (E:T 20:1 83.88% vs 43.13%; E:T 10:1 75.18% vs 31.32%; E:T 5:1 67.38 vs 32.22%; E:T 1:1 42.54 vs 10.19%; p<0.05) (Fig 1 C). With regard to intrinsic natural cytotoxicity of NK cells, no significant decrease in cell killing was overserved for SB-gene-modified CD19-CAR NK cells compared to NT NK cells against CD19-negative K562 cells (E:T 5:1 83%; p<0.05) (Fig 1 D). Significantly enhanced antitumor potential of SB-generated CD19-CAR NK cells was confirmed in a systemic CD19-positive lymphoma xenograft model (NSG-Nalm-6/Luc) in vivo. After injection of 0.5x10 6 tumor cells per mouse and lymphoma engraftment, animals were treated with a single dose of 10x10 6 SB-modified CD19-CAR NK cells pooled from three different donors with a mean tEGFR/CAR expression of 34%. MC.CD19-CAR NK cell therapy resulted in rapid lymphoma eradication in all treated mice (n=4; p<0.05), whereas mice receiving similar amounts of NT NK cells showed progressive lymphoma growth comparable to untreated control mice (Fig 1 E-F). Conclusion: Taken together, the Sleeping Beauty transposon system represents an innovative gene therapy approach for non-viral engineering of safe, highly functional and relatively cost-efficient CAR-NK cells that may not only be suitable for ALL therapy but also for a broad range of other applications in cancer therapy. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.
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