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Pharma Tech Outlook | Friday, July 08, 2022
Immune checkpoint inhibitors exhibit limited response rates in patients with triple-negative breast cancer (TNBC), suggesting that additional immune escape mechanisms may exist.
FREMONT, CA: One heterogeneous subtype of breast cancer called triple-negative breast cancer (TNBC) lacks the expression of the human epidermal growth factor receptor as well as the oestrogen and progesterone receptors. TNBC has a worse prognosis than other subtypes of breast cancer because it exhibits more aggressive biological behaviour, relapses more frequently, and has fewer treatment options. Recently, the development of immune checkpoint inhibitors for cancer immunotherapy has changed the paradigm for treating numerous cancers. Immune checkpoint inhibitors combined with adjuvant chemotherapy may have a therapeutic impact on some TNBC patients. Immune checkpoint inhibitors have undesirable side effects, and a significant portion of patients do not experience a sustained clinical response, highlighting the significance of identifying previously unidentified genes that encourage immune evasion by tumour cells and developing additional immunotherapeutic approaches. The components and interactions between immune cells and tumour cells in the tumour microenvironment (TME) have been the subject of numerous research. CRISPR screens have significantly improved genome editing and allowed for the discovery of previously unidentified genes linked to immunotherapy responses. In vivo models might be a more pertinent setting to screen for tumour-immune interactions than in vitro CRISPR screenings. Furthermore, to find therapeutically significant targets in high-throughput in vivo CRISPR screens, it is preferable to use a variety of immune-selection pressures on tumours given the complexity of immune systems.
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A mouse single-guide RNA (sgRNA) library was created corresponding to all human disease-related immune genes to identify the immune-related genes in the antitumor or protumor process that may offer possible treatment approaches. 12,000 sgRNAs were targeting 2796 genes in the DrIM library. The DrIM library was used to create the mouse TNBC cell line 4T1 and transduce it with steady Cas9 expression. To compare the various immune-selection pressures on tumour cells, DrIM-transduced 4T1-Cas9 cells were transplanted under the skin of immunocompetent BALB/c mice and immunodeficient nonobese diabetic (NOD)-PrkdcscidII2rgnull (NPG) mice, which lack T cells, B cells, and natural killer (NK) cells. Mice were put to sleep after 14 days, and tumours were collected for high-throughput sgRNA library sequencing. Due to poor next-generation sequence quality, two samples were discarded to reduce bias and improve the accuracy of our screens. While primary plasmid and pretransplant tumour cells (day 0) had a library representation that followed a log-normal distribution, post transplanted cells were taken from tumour masses on BALB/c and NPG mice had sgRNA representation that displayed a shift.
All four types of mice (n = 10) developed tumours containing the mini-DrIM library. Pretransplant tumour cells, post transplanted tumour cells, plasmid representation in the library and the distribution of sgRNA were all consistent with the results of the initial screen. It was discovered that under various selection conditions, the dynamics of the sgRNA abundance altered significantly. The mini-DrIM library of genes was sorted according to the score derived from comparisons between various immune-selection pressure settings. In the analyses of different immunological deficits, a total of 60 genes were congruously connected with immune evasion (score 0), while 5 genes were identified as possible regulators of immune surveillance in all screening scenarios.
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