Expression of IL-15 in NK cells results in rapid enrichment and selective cytotoxicity of gene-modified effectors that carry a tumor-specific antigen receptor

Natural killer (NK) cells hold promise for adoptive cancer immunotherapy but are dependent on cytokines such as interleukin (IL)-2 for growth and cytotoxicity. Here, we investigated the consequences of ectopic expression of IL-15 in human NK cells. IL-2 and IL-15 belong to the common γ chain family of cytokines and have overlapping activities. Transduction of clinically applicable NK-92 cells with lentiviral vectors encoding human IL-15 resulted in predominantly intracellular expression of the cytokine, and STAT5 activation, proliferation and cytotoxicity of the producer cells in the absence of IL-2. Growth of non-transduced bystander cells was not supported, allowing rapid enrichment of gene-modified cells solely by IL-2 withdrawal. This was also the case upon transduction of NK-92 and NKL cells with a bicistronic lentiviral vector encoding IL-15 and a chimeric antigen receptor (CAR) targeting the pancarcinoma antigen EpCAM. Effector cells co-expressing CAR and IL-15 continued to proliferate in the absence of exogenous cytokines and displayed high and selective cell-killing activity against EpCAM-expressing breast carcinoma cells that were resistant to the natural cytotoxicity of unmodified NK cells. This strategy facilitates rapid isolation and continuous expansion of retargeted NK cells and may extend their potential clinical utility.

Expression of a CD20-specific chimeric antigen receptor enhances cytotoxic activity of NK cells and overcomes NK-resistance of lymphoma and leukemia cells

Despite the clinical success of CD20-specific antibody rituximab, malignancies of B-cell origin continue to present a major clinical challenge, in part due to an inability of the antibody to activate antibody-dependent cell-mediated cytotoxicity (ADCC) in some patients, and development of resistance in others. Expression of chimeric antigen receptors in effector cells operative in ADCC might allow to bypass insufficient activation via FcgammaRIII and other resistance mechanisms that limit natural killer (NK)-cell activity. Here we have generated genetically modified NK cells carrying a chimeric antigen receptor that consists of a CD20-specific scFv antibody fragment, via a flexible hinge region connected to the CD3zeta chain as a signaling moiety. As effector cells we employed continuously growing, clinically applicable human NK-92 cells. While activity of the retargeted NK-92 against CD20-negative targets remained unchanged, the gene modified NK cells displayed markedly enhanced cytotoxicity toward NK-sensitive CD20 expressing cells. Importantly, in contrast to parental NK-92, CD20-specific NK cells efficiently lysed CD20 expressing but otherwise NK-resistant established and primary lymphoma and leukemia cells, demonstrating that this strategy can overcome NK-cell resistance and might be suitable for the development of effective cell-based therapeutics for the treatment of B-cell malignancies.

Cytotoxic targeting of F9 teratocarcinoma tumours with anti-ED-B fibronectin scFv antibody modified liposomes

We prepared small unilamellar liposomes derivatised with single chain antibody fragments specific for the ED-B domain of B-fibronectin. This extracellular matrix associated protein is expressed around newly forming blood vessels in the vicinity of many types of tumours. The single chain antibody fragments were functionalised by introduction of C-terminal cysteines and linked to liposomes via maleimide groups located at the terminal ends of poly(ethylene glycol) modified phospholipids. The properties of these anti-ED-B single chain antibody fragments-liposomes were analysed in vitro on ED-B fibronectin expressing Caco-2 cells and in vivo by studying their biodistribution and their therapeutic potential in mice bearing subcutanous F9 teratocarcinoma tumours. Radioactively labelled ((114m)Indium) single chain antibody fragments-liposomes accumulated in the tumours at 2-3-fold higher concentrations during the first 2 h after i.v. injection compared to unmodified liposomes. After 6-24 h both liposome types were found in similar amounts (8-10% injected dose g(-1)) in the tumours. Animals treated i.v. with single chain antibody fragments-liposomes containing the new cytotoxic agent 2'-deoxy-5-fluorouridylyl-N(4)-octadecyl-1-beta-D-arabinofuranosylcytosine (30 mg kg(-1) per dose, five times every 24 h) showed a reduction of tumour growth by 62-90% determined on days 5 and 8, respectively, compared to animals receiving control liposomes. Histological analysis revealed a marked reduction of F9 tumour cells and excessive deposition of fibronectin in the extracellular matrix after treatment with single chain antibody fragments-2-dioxy-5-fluorouridylyl-N(4)-octadecyl-1-beta-D-arabinofuranosylcytosine-liposomes. Single chain antibody fragments-liposomes targeted to ED-B fibronectin positive tumours therefore represent a promising and versatile novel drug delivery system for the treatment of tumours.