CAR- T therapy heralds a new and innovative approach to cancer immunotherapy. The core concept is to reprogram a patient’s T cells externally with chimeric antigen receptors (CARs) that are then transfused back into the patient. The modified T cells can recognize the tumor cells expressing these antigens, and trigger a defense reaction. So far, only six CAR-T therapies have been FDA approved, all autologous (patient’s own T cells are modified) and primarily liquid cancers ( B cell malignancies). For solid tumors, the promise of the therapy is a hot and challenging area of research, and the first therapy has been approved for treating multiple myeloma.
Despite the progress, the state of the art processes in generating autologous CAR-T cells have several limitations.
- Generating personalized T cells for every patient is prohibitively expensive ( $$ average cost)
- Not all patients have adequate number of T cells at an advanced stage of cancer
- Despite the CAR modifications, it is hard to predict the baseline state of exhaustion of their T cells and their ability to proliferate in vivo
- Solid tumors present the additional challenge for the T cells to travel through a toxic and resistant microenvironment of the stroma, to cell the tumor.
- Preventing the emergence of a “cytokine release syndrome” during the CAR-T treatment, an inevitable collateral damage that can lead to organ failure.
The major roles of CRISPR being investigated in CAR-T production are in
- Preventing onset of graft vs host disease (GvHD): In allogeneic T cells, this phenomenon will cause a rejection of infused T cells. CRISPR directed editing can remove endogenous T cell receptor (TCR), MHC proteins and self-antigens.
- Knocking out immune checkpoint inhibitors: PD-1, CTLA-4 and LAG3 that that in cancer cells are inhibited thereby reducing the release of interleukins, part of the defense strategy..
- Moderating the Cytokine release syndrome: Knock out of certain toxic interleukins and simultaneous knock-in of certain desirable cytokines can boost cytokine production. Several of these strategies are in the preclinical models. Eg: Silencing of the TGF-beta signaling
Major challenges that are in optimization for CRISPR edited CAR-T are reduction of off-target effects in CRISPR editing and simultaneous knocking off/ in of multiple loci to reduce the GvHD, and cytokine release syndrome and release the inhibition on immune checkpoint inhibitors.