NK cell therapy holds the promise of new therapeutics for underserved cancer indications. A recent publication in Nature Communications uses Excellos sourced cellular starting materials for research on the mechanisms behind NK cell cytotoxicity. 
The capacity for cancer cells to avoid immune detection is notorious. Normally, cells that are faulty, diseased, or reaching the end of their useful lives are quickly and efficiently cleared away by the immune system. Not so for cancer cells, which use various mechanisms to essentially hide in plain sight by co-opting immune tolerance mechanisms and “tricking” immune cells into passing them by.
Improving the Efficacy of NK Cell Therapy
The good news is that scientists are discovering new strategies to combat cancer cells, for example by reprogramming cytotoxic immune cells to effectively identify their target. In this latest publication, researchers in San Diego uncovered mechanisms that allow tumor cells to develop resistance to NK cell mediated killing. Their goal is to discover key genetic regulators of tumor sensitivity and resistance to NK cell activity in order to improve the efficacy of NK cell therapy.
To begin their study, the researchers obtained healthy donor apheresis material from Excellos (formerly based at the San Diego Blood Bank). Peripheral Blood Mononuclear Cells (PBMC) were isolated from this cellular starting material through density gradient centrifugation. NK cells were then purified from the PBMCs via CD3+ and CD19+ cell depletion, then expanded in tissue culture prior to further experimentation.
The San Diego researchers used a whole genome CRISPR-Cas9 screening system to identify key regulators of tumor sensitivity and resistance in 4 different glioblastoma stem cell (GSC) lines.
Whole Genome Screening System
Glioblastoma is a type of brain tumor that is known to develop resistance mechanisms to escape NK cell-mediated killing. Researchers used a “two cell type” whole genome screening system. This means that by comparing co-cultures of GSCs and NK cells with GSC monocultures, they were able to screen for genes that induce either resistance or sensitivity to NK cell killing. This method was successful in identifying a set of 25 genes that induced either sensitivity or resistance. These genes were involved in functions such as antigen presentation, cellular localization, and regulation of the innate immune response. The screening further revealed CHMP2A to be a key gene regulating sensitivity of GSCs to NK cell-mediated cytotoxicity.
Extracellular Vesicle Pathway
CHMP2A is part of the cellular machinery critical to the secretion of extracellular vesicles from GSCs. GSC vesicle secretion supports tumor progression by mediating tumor cell migration, invasion, and persistence. This extracellular vesicle pathway is also known to be used by tumor cells to secrete two proteins that impair NK cell function: tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), and MHC Class I Polypeptide-Related Sequence A/B (MICA/B). MICA/B binds to NK cell activating receptors; the down-regulation of this ligand in various tumor cell types has been shown to reduce NK cell recognition and killing. TRAIL acts more directly and can induce apoptosis of both NK cells and cytotoxic T cells.
Promising Strategy for NK Cell Therapy
Targeting CHMP2A-related extracellular vesicle secretion is thus a promising method for turning the tables on cancer cells, potentially blocking their ability to evade NK cell recognition and cytotoxic activity. To confirm the results of their in-vitro studies, the research team elected to carry out a series of experiments examining NK-cell mediated cytotoxicity in a xenograft immunodeficient mouse model. They demonstrated that deletion of CHMP2A in head and neck cancer cell xenografts leads to increased NK cell-mediated killing compared to wild-type cancer cells.
This work represents a promising new strategy for increasing the efficiency of NK cell therapy.
This work represents a promising new strategy for increasing the efficiency of NK cell mediated cancer immunotherapy. The authors hope to continue their work and believe that further characterization of tumor cell secreted extracellular vesicles in cancer patients will lead to a deeper understanding of immune evasion and, ultimately, better cancer treatments.
- Bernareggi, D., Xie, Q., Prager, B.C. et al. (2022) CHMP2A regulates tumor sensitivity to natural killer cell-mediated cytotoxicity. Nat Commun 13, 1899. https://doi.org/10.1038/s41467-022-29469-0