Perspective and future direction
Here, we reviewed studies highlighting the promising impact of new
technologies in cancer immunotherapy (Figure 3 ). Editing CAR-T
cells with CRISPR/Cas9 can overcome many challenges such as allogeneic
reaction, tonic signaling, exhaustion, low performance in TME and
toxicity. In addition, the large-scale genetic screens using the
CRISPR/Cas9 system provides scalable methods to interrogate thousands of
genes in T cells with high efficiency and specificity.
TCR and HLA knocked out T cells present great potential for developing
allogeneic third-party T cell products. However, there is controversy
over benefits of TCR deletion. In a recent study, TCRβ knocked-out CD19
CAR-T cells were compared to TCR intact CD19 CAR-T cells (Stenger,
Stief, Kaeuferle, et al., 2020). Although knocking out the endogenous
TCR in CAR-T cells strongly eliminated alloreactivity compared to
TCR-expressing CAR-T cells; co-expression of endogenous TCR plus CAR led
to superior persistence of T cells and significantly extended the
control of leukemia in vivo. This data highlights that despite the
benefits of TCR knocked out T cells in developing off-the-shelf cell
therapies, presence of endogenous TCR might be better for long-term
survival of T cells. Hence, a deeper understanding of T cell biology and
TCR signaling provides useful insights for designing and engineering
more effective CAR-T cells.
CRISPR/Cas9 technology can also indirectly assist in developing more
effective CAR-T cell therapies. Using large scale CRISPR screening
libraries, we can discover novel antigens to be targeted by CAR-T cells.
Moreover, we can identify factors in T cells, tumor cells or TME which
induce resistance to CAR-T cells (Dufva et al., 2020). By genome-wide
genetic perturbation/CRISPR screen, Dufva et al. investigated
genes which their loss in cancer cells impaired the effector function of
CAR-T cells and revealed the essentiality of death receptor signaling
for CAR-T cell cytotoxicity. Similar studies provide a better
understanding of mechanisms influencing CAR-T cell function and the
potential for modulation using combination therapy or genetic
engineering strategies.
Although recently emerged, CRISPR/Cas9 nowadays is a “go to” method
for gene editing in many research labs in academic and pharmaceutical
industry. With this fast advancement in the CRISPR/Cas9 application and
emergence of new gene-editing technologies, we hope to soon witness the
success of CAR-T cells in treating many refractory cancers including
solid tumors.