Cancer Cell: Wang Haoyi's team reported that BATF deletion can improve the anti-tumor activity of CAR-T cells

T cells will gradually lose their ability to kill tumor cells under the continuous stimulation of antigens, accompanied by the upregulation of a variety of inhibitory receptors, the decline of proliferative differentiation ability, the remodeling of transcriptome and epigenetic group, etc.
, this phenomenon is called T cell depletion
.

T cell depletion was first discovered in the context of chronic viral infection and later in tumor patients
.
T cell depletion is one of the main obstacles for T cell immunotherapy such as CAR-T to overcome solid tumors, and further understanding and regulation of this process is the key to
improving the clinical effect of T cell-based immunotherapy.

Recently, the team of Wang Haoyi, Institute of Zoology, Chinese Academy of Sciences, State Key Laboratory of Stem Cell and Reproductive Biology, and Beijing Institute of Stem Cell and Regenerative Medicine published in the journal Cancer Cell entitled : Research paper on Depletion of BATF in CAR-T cells enhances antitumor activity by inducing resistance against exhaustion and formation of central memory cells.

Firstly, in order to better study the process and mechanism of T cell depletion, this study obtained a human primary CAR-T cell depletion model
with typical depletion characteristics in vitro by reducing the ratio of CAR-T cells to tumor cells and prolonging co-culture.
In order to discover new regulators of T cell depletion, the study screened candidate genes based on this model and found that knocking out the transcription factor BATF can significantly increase the in vivo and in vitro anti-tumor activity
of CAR-T cells.
Subsequent mechanistic studies found that BATF directly targets and upregulates the expression of multiple key genes related to depletion, while BATF targets and regulates the expression
of effector and memory T cell-related genes.
Therefore, knocking out BATF improves the ability of CAR-T cells to resist depletion while making CAR-T cells produce more central memory cell subsets, thereby improving the effect of CAR-T cells in the treatment of
solid tumors.

In recent years, a number of studies have shown that a variety of transcription factors are involved in regulating the process of T cell depletion, such as TOX, NR4A, c-jun, etc
.
The role of the transcription factor BATF in T cell depletion is controversial, and different conclusions
have been reported in previous studies.
On the one hand, some studies say that PD-1 causes T cell depletion by upregulating the expression of BATF, and some studies have shown that CAR-T cell knockout BATF improves the secretion of effector factors IL-2 and IFNγ; On the other hand, studies have found that the loss of BATF reduces the ability of T cells to
secrete IFNγ and proliferate.
At the same time, some studies believe that BATF can block the depletion of CAR-T cells, and overexpression of BATF makes CAR-T cells have stronger value-added ability and tumor killing ability, and produces long-term tumor suppression effect
.
These seemingly opposing conclusions made the team more interested in understanding how BATF regulates T cell depletion
.

In order to further verify the function of BATF, Wang Haoyi's team conducted more in-depth and detailed research
.
Through the knockout and overexpression of BATF in 6 different kinds of human CAR-T cells and OT-1 T cells in mice, it was found that BATF knockout could improve the anti-tumor activity of CAR-T/OT-1 T cells under different depletion-induced conditions, while BATF overexpression reduced the killing ability
of CAR-T/OT-1 T cells.

Further analysis found that BATF plays different roles in different CAR-T cell depletion situations, and with the deepening of depletion (decrease of the target ratio or increase of tumor stimulation rounds), the effect of BATF on CAR-T cell function becomes more and more significant
.
At the same time, the study also found that BATF directly binds to and upregulates a series of genes related to cell proliferation, so under non-depleting experimental conditions, the overexpression of BATF can promote T cell proliferation, thus enhancing its function
as a whole.
However, under experimental conditions that cause severe depletion of T cells, BATF's function of promoting depletion plays a leading role
.
Therefore, the data from this study are a good illustration of why previous studies have come to the opposite conclusion
about the function of BATF.

As a transcriptional regulator, this study shows that BATF-specific binding regulates the expression of genes related to T cell depletion, proliferation, and subtype differentiation, reflecting a multifaceted function
.

Genes always function in their environment, so when studying and elucidating the function of a gene, choosing different experimental conditions is likely to lead to different conclusions
.
The study believes that in most cases, CAR-T cells infiltrated into tumors will be in a state of depletion, so the in vitro depletion model of human primary CAR-T cells established by this study is an ideal tool
to study the function and mechanism of depletion-related genes.

Function of BATF under CAR-T cell depletion-induced conditions

In summary, the study found that the transcription factor BATF plays an important role in the depletion of CAR-T cells, and knocking out BATF can improve the anti-depletion ability of CAR-T cells and the ability to form central memory cells, thereby producing a lasting and effective anti-tumor effect
.
BATF-deficient CAR-T cells have the advantage
of persistence and efficacy in future clinical applications.

Zhang Xingying, Zhang Chenze, doctoral students of the Institute of Zoology, Chinese Academy of Sciences, and Miaomiao Qiao, a master student, are the co-first authors
of the paper.
Researcher Wang Haoyi, Institute of Zoology, Chinese Academy of Sciences, State Key Laboratory of Stem Cell and Reproductive Biology, and Beijing Institute of Stem Cell and Regenerative Medicine is the corresponding author
of this paper.

Original source:

XingyingZhang， et al.
Depletion of BATF in CAR-T cells enhances antitumor activity by inducing resistance against exhaustion and formation of central memory cells.
Cancer Cell， 2022.