Assessing the effect of CRISPR/Cas9-mediated PD-1 knock-out in cord blood-derived TCR-engineered CD8+ T cells using a short-term in vitro exhaustion system
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Cancer immunotherapy, whereby the patient’s own immune system is boosted in its fight against cancer, is one of the most promising cancer treatment options of recent years. Within this emerging field, adoptive T cell therapies aim to improve, replace, or restore the patient’s cancer-specific T cells by extracting T cells from the blood of healthy individuals or cancer patients, multiplying and modifying them in the lab, and afterwards (re)infusing them in the patient. Importantly, the need for T cell-based therapies stems from the dysfunction of most cancer-specific T cells – the so-called T cell exhaustion phenomenon – which renders the key players of the immune system (i.e. T cells) ineffective in their fight against cancer cells. Interestingly, both adoptive T cells and the patient’s own T cells are equally prone to become exhausted due to the suppressive environment they encounter while engaging tumor cells. Thus, T cell-based therapies under development can be significantly hindered by the phenomenon of T cell exhaustion, which, in turn, could strongly determine whether the patient receiving the adoptive T cells survives, is cured, or possibly relapses. In my project, we aimed to prevent the onset of T cell exhaustion altogether in a T cell-based therapy product developed in my research group. Starting with healthy T cells, we used novel gene-editing techniques – the so-called CRISPR/Cas9 system – to stop the expression of certain inhibitory markers on the surface of the T cells. Importantly, inhibitory markers expressed on T cells can be bound by their targets which are highly expressed on tumor cells, thereby leading to a state of T cell inhibition, and ultimately a lack of killing of tumor cells. Thus, we hypothesized that the gene-engineered T cells would better resist the onset of exhaustion once infused into the patients, since they are genetically uncapable of expressing the given inhibitory markers. However, prior to infusion in patients, T cell therapy products need to be extensively tested both in vitro (i.e. in the lab), as well as in animal models (such as mouse studies), so my project focused on extensively characterizing the function of gene-edited T cells in vitro. Indeed, we found that in the healthy lab setting (so without the suppressive influence of tumor cells), the deletion of a key inhibitory receptor did not affect (neither positively nor negatively) the function of the gene-edited T cells with respect to growth, killing capacity, nor ability to produce molecules that help other immune cells (i.e. cytokines). However, it is likely that the testing of the gene-engineered T cells in a more ‘realistic’ lab setting – one that closely mimics the suppressive tumor environment in the patients’ bodies – would more accurately show the contribution of the genetic modification for protection against exhaustion. Ultimately, we hope that this strategy would soon allow cancer patients to receive T cell-based immunotherapies that are highly functional for a long(er) period of time, so that they have a higher chance of beating cancer.