CD133, a pentaspan glycoprotein, has long been known to represent aggressive, stem-like populations across various human malignancies. While its expression correlates with numerous clinical outcomes including disease progression, metastasis, recurrence, and poor overall survival in numerous cancers, little is currently known about its function. In the brain cancer glioblastoma (GBM), CD133-expressing cells have previously been shown to initiate tumours, evade therapy and interestingly, self-renew, a key property of cancer stem cells. With an implied signalling role in driving self-renewal, we aim to elucidate the role of CD133 in glioblastoma. To understand the role of CD133, we aim to study its protein-protein interactions using the proximity-dependent labelling technique known as miniTurboID. By tagging proteins of interest with a promiscuous biotin ligase at both protein termini, potential interactors can be biotinylated and identified by subsequent mass spectrometry. While miniTurboID has traditionally been performed by synthetic transgenes expressing the tagged proteins of interest in commercial cell lines, overexpression may not recapitulate its native function. Thus, using CRISPR technology, we aim to insert the miniTurboID ligase at both the N- and C-terminus of CD133 in patient-derived human GBM lines. Although little is currently known about CD133 function, development of targeted therapies has presented a promising strategy in pre-clinical studies. In the Singh Lab, we previously developed a chimeric antigen receptor T-cell, or CAR-T, comprised of a T-cell expressing a synthetic receptor capable of recognizing a tumor-associated antigen and activating cytolytic-killing directed towards the target cell. Currently, CAR-T therapies are autologous, or patient-derived, in nature which may host a myriad of concerns including patient-specific qualitative and quantitative T-cell dysfunction, inconsistent generation of CAR products, and availability to rapidly progressing patients. To circumvent this concern, “off-the-shelf”, donor-derived or allogeneic CAR-T products may be generated for use in GBM patients. However, in addition to CAR integration, allogeneic products must be additionally modified to eradicate expression of the endogenous TCR, as this would induce a phenomenon known as graft versus host disease, in which healthy tissues are targeted. Thus, in this thesis, we show gene editing potential in human GBMs to perform an endogenous genomic knock-in of miniTurboID. With the identification of interacting proteins, defining the subsequent functionality of CD133 may elucidate oncogenic cellular programs, and highlight common nodes of interaction within divergent cell signaling pathways. To develop an allogeneic CAR-T product, we designed a two-step approach in which the CAR sequence was integrated into the TCR gene for simultaneous knock-out. We later show early pre-clinical efficacy in comparison to traditional autologous CAR-T in our patient-derived models of human GBM. Thus, by using CD133 as a centralizing concept in this thesis, we ultimately hope to develop our biological understanding of CD133, while testing the therapeutic development of a donor-derived CAR-T therapy. / Thesis / Master of Science (MSc) / Glioblastoma (GBM) is one of the most common malignant brain tumors in adults. Despite an aggressive therapy regimen, almost all patients relapse 7-9 months post-diagnosis. Therapy failure and poor patient outcome may be attributed to a small population of cells known as glioblastoma stem cells, or GSCs, that are able to escape therapy and seed disease recurrence. GSCs are most notably identified by the cell surface protein CD133, which has previously been shown to associate with pro-tumor properties including treatment resistance, tumor growth, maintenance, progression and metastasis. While expression of CD133 in cancer has been heavily characterized, little is currently known about its function. One such avenue to understand its mechanism of action in cancer, and more particularly GBM, is to define its interactions with other proteins. Protein-protein interactions play a pivotal part as the backbone of signalling pathways that drive tumor development and growth. Therefore, defining and mapping the CD133 interaction network may help us understand how this protein governs regulation of GSCs, and ultimately, GBM progression. While the biology of CD133 has yet to be elucidated, targeting CD133 on GSCs has presented a promising therapeutic strategy for patients with GBM. Previously in the Singh Lab, we developed an engineered T-cell therapy, known as a CAR-T, that can recognize CD133 to induce tumor cell death. While this showed success in our animal models of human GBM, other considerations must be addressed on its path to clinical development. As of current, CAR-T therapies are generated from T-cells taken from cancer patients. This hosts a myriad of concerns including the quality of patient T-cells, the time and cost to manufacture, and its availability for patients with rapidly progressing disease. To circumvent this issue, donor-derived CAR-T cells can be genetically engineered for safe usage in GBM patients as a readily available, “off-the-shelf” therapy. To define the function of CD133, we have attempted to use a technique known as BioID, which tags the protein of interest with a smaller biotin ligase. This biotin ligase can subsequently tag proteins that come within the vicinity of CD133, that may later be identified by sequencing as potential interactors. As current use of BioID may not reliably mimic the interaction of CD133, we sought to genetically engineer human GBM lines with the BioID protein to more closely resemble tumor-relevant behaviours of CD133. To develop a donor-derived CAR-T therapy, we similarly used genetic engineering of T-cells to ensure specific targeting of tumor cells with CD133, while sparing healthy tissues. By using CD133 as a centralizing concept in this thesis, we ultimately hope to develop our biological understanding of CD133, while testing the therapeutic development of a donor-derived CAR-T therapy.

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