Posted on Jun 15, 2020, 3 p.m.
As it turns out natural killer cells don't have to be natural born natural killer cells, and mass produced natural killer cells derived from induced pluripotent stems cells may even be more persistent and effective killers according to recent research from scientists at the University of California published in Cell Stem Cell.
The scientists suggest that one way to turn human iPSCs derived into NKCs into uninhibited killing machines is by depriving them of a gene that encodes a crucial cytokine regulator. The gene is called CISH and it encodes cytokine inducible SH2-containing protein which is a braking mechanism that is typically expressed by NKCs that are stimulated by cytokines such as IL-15; without this mechanism NKCs are able to go on a killing spree.
The experimental evidence suggests that the human iPSC derived NKCs have a greater cytotoxic activity level in vitro, they are also better at inhibiting tumor progression in vivo, and they display greater metabolic fitness which is what they need to keep a killing spree going.
“We found that CISH-deleted iPSC-derived NK cells were able to effectively cure mice that harbor human leukemia cells, whereas mice treated with the unmodified NK cells died from the leukemia,” said Dan Kaufman, MD, PhD, who is a professor of medicine in the division of regenerative medicine and director of cell therapy at UCSD School of Medicine.who is also a faculty member of both the Sanford Consortium for Regenerative Medicine and the Sanford Stem Cell Clinical Center at UCSD Health. “These studies demonstrate that we can now edit iPSC-derived NK cells to remove an inhibitory gene inside the cell to improve activation of NK cells.
“We demonstrate that the CISH deletion improves NK cell function in at least two different ways. First, it removes a brake on IL-15 signaling, which improves NK cell activation and function, even at low IL-15 concentrations. Second, it leads to metabolic reprogramming of the NK cells. They become more efficient at energy utilization, which improves their function in vivo.”
Natural killer cells are lymphocytes in the same family as T and B cells, and they are a part of the innate immune system circulating throughout the body that are among the first to respond to the presence of foreign cells or invaders, but most notably viruses and the early signs of cancer. NKCs hold great promise as the basis for anticancer therapies as they are able to identify and target malignant cells, but their efficacy has thus far proven to be limited.
Skin or blood cells were reprogrammed to become iPSCs which were directed to become NKCs to produce a standardized cell population rather than needing to isolate cells on a patient specific basis. Then the CISH gene was deleted in the iPSC derived NKCs, lacking this gene the cells demonstrated increased IL-15 mediated JAK-STAT signaling, which is a mechanism that alerts immune cells to the sites of inflammation, infection, and trauma.
“Consequently, CISH−/− iPSC-NK cells exhibit improved expansion and increased cytotoxic activity against multiple tumor cell lines when maintained at low cytokine concentrations,” the authors wrote. “CISH−/− iPSC-NK cells display significantly increased in vivo persistence and inhibition of tumor progression in a leukemia xenograft model.”
“Mechanistically, CISH−/− iPSC-NK cells display improved metabolic fitness characterized by increased basal glycolysis, glycolytic capacity, maximal mitochondrial respiration, ATP-linked respiration, and spare respiration capacity mediated by mammalian target of rapamycin (mTOR) signaling that directly contributes to enhanced NK cell function.”
“As iPSC-derived NK cells are now in clinical trials to treat both hematologic (blood) malignancies and solid tumors, we expect that CISH-deleted iPSC-NK cells can provide an even more effective treatment,” Kaufman stated. “Importantly, iPSCs provide a stable platform for gene modification, and since NK cells can be used as allogeneic cells that do not need to be matched to individual patients, we can create a line of appropriately modified iPSC-derived NK cells suitable for treating hundreds or thousands of patients as a standardized, off-the-shelf therapy.”
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