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NK-92 is a continuously growing cell line that has features and characteristics of natural killer (NK) cells that every person has circulating in the blood. Blood NK cells and NK-92 recognize "invaders" such as viruses and fungus. Most importantly, NK-92, like blood NK cells, can attack cancer cells as long as the tumor has not grown out of control. NK-92 cells were isolated and characterized by the laboratory of Dr. H. Klingemann - at that time at the British Columbia Cancer Control Agency in Vancouver, Canada. The cells came from a patient who had a NK cell lymphoma, a rare lymphoma type. Although several other NK cell lines have been cloned, only NK-92 can be expanded to larger numbers and consistently kill tumor cells vigorously. When NK-92 cells bind to a cancer or infected cell, they secrete perforin which punches holes in target cells followed by release of granzymes which induce apoptosis in the target cells. NK-92 cells also attack cancer cells through the Fas-Fas Ligand system and are capable of producing cytokines that by themselves can kill cancer cells (such as TNF-alpha) or stimulate and expand other immune cells such as interferon.
Over the past 2 decades (the cell line was established in 1992) researchers worldwide have used NK-92 cells to test their anti-cancer activity in mouse models. and also use it as a model to learn more about the biology of NK cells. NK-92 cells are a very close match with blood NK cells: they express on their surface the characteristic CD56 antigen and are negative for CD3 which is typical for T-lymphocytes. In addition they express a number of adhesion molecules such as ICAM and LFA that facilitates binding to infected and cancer cells. Blood NK cells, unlike NK-92 cells, recognize "invaders" or foreign cells only if those cells do not express self MHC molecules. This means if cancer cells maintain their MHC phenotype they may go unnoticed by NK cells but not of NK-92 cells. The reason for this difference in target cell recognition relates to the fact that NK-92 cells do not express killer cell immunoglobulin‑like receptors (KIR) that are negative regulators of NK cell activity through interaction with self-MHC.
NK-92 in clinical trials
Three phase I clinical trials, led by experts in adoptive immunotherapy of cancer, have so far yielded excellent results. Hans Klingemann, MD, PhD and Sally Arai, MD completed the US trial at Rush University Medical Center (Chicago) in renal cell and melanoma patients, and Torsten Tonn, MD and Oliver Ottmann, MD completed the European trial at the University of Frankfurt in patients with various solid and hematological malignancies. Armand Keating, MD is completing the last cohort of patients in the Canadian trial at Princess Margaret Hospital in Toronto in lymphoma patients after autologous bone marrow transplants. In all three programs, NK-92 cells were administered as a simple intravenous infusion, dosed two or three times per treatment course and given in the outpatient setting.
Most importantly, there were no grade ≥ 2 side-effects during or after the short infusion of NK-92 cells. The maximum dose given in the Frankfurt trial was 10e10 cells/me2 x 2 infusions, each 48 hours apart. The Chicago study infused NK-92 at a maximum of 5 x 10e cells/me2 x 3 infusions, each 48 hours apart. This was not the MTD but rather the number of cells that could be expanded in culture bags over a three-week culture period. Alternative cell expansion technologies (bioreactors) will make it possible to further expand the numbers of NK-92 on a smaller 'footprint'. Anecdotal reports of antitumor activity in the two completed phase I studies have been observed in 6/11 patients with renal cancer, 3/4 patients with lung cancer, and 1/1 patient with melanoma, all with very advanced disease. In addition to disease stabilization and regression of metastases in lung and lymph nodes, the severe pain associated with tumor metastases in several patients, which had been refractory to standard chemotherapy, was remarkably lessened. The ongoing trial in Toronto treats patients with lymphoma who have relapsed after an autologous stem cell transplant. Preliminary results suggest a significant benefit in several patients.
NK-92 cells can be genetically engineered to recognize and kill human cancer cells. Chimeric Antigen Receptor (CAR) engineered T-lymphocytes are currently the buzz in Immuno-Oncology, having shown that infusion of those engineered cells can achieve remissions in some patients with acute and chronic leukemia. In contrast, NK cells (either from peripheral blood or cord blood) have not generated sufficient interest as CAR‑engineered cytotoxic effector cells, largely for two reasons: the extent of NK cell expansion can be dependent on the donor; secondly, transfection efficiency, even with lentiviral or retroviral vectors is only moderately efficient. NK-92 cells on the other hand, have predictable expansion kinetics and can be grown in bioreactors to billions of cells within a couple of weeks. They can easily be transfected either with viral supernatant or physical methods. Even mRNA can be shuttled into the cells with high efficiency. Since no integration of mRNA into the genome occurs, this transfection is less risky and the regulatory burden is equally reduced.
NK-92 have also been transfected with a high affinity Fc Receptor (NK-92Fc) which is the main receptor for monoclonal antibodies to execute antibody dependent cellular cytotoxicty (ADCC) - examples: rituximab, ofatumumab. Based on this variant, an assay has developed an assay that allows to quantify the ADCC component of monoclonal antibodies (Neukopanel), a technology that has caught the attention of a number of Biotech and Pharmaceutical companies that use Neukopanel to determine the contribution of ADCC of their monoclonal antibodies.
The cell line has been licensed to Conkwest and is currently being developed under Neukoplast:
- for intravenous therapy in hematological malignancies and lung cancer
- for local intra-tumor injection
- as effector cells for chimeric antigen receptor (CAR) specific killing
- for an assay that quantifies the contribution of ADCC in the therapeutic effect of monoclonal antibodies (Neukopanel)
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