Pre-depletion of TRBC1+ T cells promotes the therapeutic efficacy of anti-TRBC1 CAR-T for T-cell malignancies
Molecular Cancer volume 19, Article number: 162 (2020)
Targeting T cell receptor β-chain constant region 1 (TRBC1) CAR-T could specifically kill TRBC1+ T-cell malignancies. However, over-expressed CARs on anti-TRBC1 CAR transduced TRBC1+ T cells (CAR-C1) bound to autologous TRBC1, masking TRBC1 from identification by other anti-TRBC1 CAR-T, and moreover only the remaining unoccupied CARs recognized TRBC1+ cells, considerably reducing therapeutic potency of CAR-C1. In addition, co-culture of anti-TRBC1 CAR-T and TRBC1+ cells could promote exhaustion and terminal differentiation of CAR-T. These findings provide a rationale for pre-depleting TRBC1+ T cells before anti-TRBC1 CAR-T manufacturing.
Chimeric antigen receptor (CAR) T cells showed remarkable efficacy for the treatment of B-cell malignancies and have been approved by the US Food and Drug Administration for the treatment of relapsed/refractory B-cell acute lymphoblastic leukemia (B-ALL) and diffuse large B-cell lymphoma (DLBCL) [1, 2]. However, the development of CAR-T cells against T-cell malignancies seems more challenging due to the similarities between the normal, malignant and therapeutic T cells, which could result into CAR-T cell fratricide, T cell aplasia, and contamination of CAR-T cell products with malignant T cells [3, 4].
An innovative treatment option for T-cell malignancy was proposed that targeting T cell receptor β-chain constant region 1 (TRBC1) CAR-T could specifically identify and kill TRBC1+ T-cell malignancies, since either TRBC1 or TRBC2 is mutually exclusively expressed in T cells and moreover proportion of TRBC1+ T cells varies between 25 and 47% in healthy individuals, but malignant T cells are clonally TRBC1 positive or negative [5, 6]. Thus, anti-TRBC1 CAR-T cells could specifically kill TRBC1+ malignant T cells while sparing TRBC2+ normal T cells. However, anti-TRBC1 CAR gene could probably be inadvertently transferred into TRBC1+ malignant T cells during CAR-T cell manufacturing, and its product could in cis bind to autologous TRBC1 on the surface of malignant T cells, which could result into masking TRBC1 from identification by and mediating resistance to anti-TRBC1 CAR-T and meanwhile weaken effector function of anti-TRBC1 CAR transduced TRBC1+ cells. Following transduction of T cells with lentivirus encoding anti-TRBC1 CAR, all T cells could be categorized into TRBC1+ cells (C1), TRBC2+ cells (C2), anti-TRBC1 CAR transduced C1 cells (CAR-C1) and anti-TRBC1 CAR transduced C2 cells (CAR-C2) (Fig. 1a). Thus, it is interesting to evaluate whether both C1 and CAR-C1 could be identified and killed by CAR-C1 and CAR-C2 (Fig. 1a).
Results and discussions
To evaluate whether C1 and CAR-C1 could be identified and killed by CAR-C1 and CAR-C2, we first sorted donor T cells into TRBC1+ and TRBC1− (designated as C2) fractions using magnetic beads. A portion of C1 or C2 were used as target cells and other C1 and C2 from the same donor were genetically engineered with anti-TRBC1 CAR to obtain CAR-C1 and CAR-C2 as effect cells. We confirmed that transduction efficacy of anti-TRBC1 CAR was similar on C1 and C2, and moreover TRBC1 was not detected on CAR-C1 through flow cytometry (Fig. 1b). Since primed T cells could increase CD137 expression and IFN-γ secretion, and moreover cytotoxic T cells could express CD107 and mediated killing of target cells, these markers could be used to detect activation and cytolytic activity of T cells. We found that CAR-C2 than CAR-C1 showed higher level of IFN-γ production and CD137 expression when co-cultured with C1 but not CAR-C1 or C2 (Fig. 1c and d). In flow cytometry–based cytotoxicity assays, CAR-C2 and CAR-C1 both specifically killed C1 but not CAR-C1 or C2, more so in CAR-C2 than CAR-C1 (Fig. 1e and f).
We next evaluated the anti-tumour activity of CAR-C1 and CAR-C2 in vivo using Luc-expressing Jurkat T-ALL cells. NOG mice were transplanted with 3 × 106 Luc-expressing Jurkat cells 3 days before IV infusion of 5 × 105 CAR-C1, CAR-C2 or MOCK T cells (Fig. 1g). Consistent with the in vitro observation, CAR-C1 induced transient tumour regression, but tumours re-progressed rapidly. In contrast, mice treated with an equal number of CAR-C2 exhibited significantly higher ani-tumour ability with significantly prolonged survival (P < 0.001) (Fig. 1h-j).
To investigate why CAR-C1 than CAR-C2 demonstrated lesser killing ability against C1 and moreover neither of them could identify and kill CAR-C1, we hypothesize that since expression abundance of anti-TRBC1 CAR is significantly higher than TRBC1 on CAR-C1, a proportion of CARs in cis bind to autologous TRBC1 on CAR-C1, masking TRBC1 from identification by other anti-TRBC1 CAR-T, and meanwhile only the remaining unoccupied CARs identify C1, weakening effector function of CAR-C1 (Fig. 2a).
We first found that TRBC1 mRNA expression was preserved in CAR-C1 as compared to C1 determined by qRT-PCR analysis (Fig. 2b). We further confirmed via flow cytometry that TRBC1 on CAR-C1 was detectable by anti-TRBC monoclonal antibody (mAb) 8A3 targeting not the same epitope recognized by mAb JOVI-1 from which the anti-TRBC1 CAR was derived (Fig. 2c), and moreover expression level of TRBC1 protein was similar on CAR-C1 and C1 (Fig. 2d). Meanwhile, qRT-PCR analysis demonstrated that expression level of CAR was significantly higher than TRBC1 in CAR-C1 and moreover confocal microscopy further confirmed that colocalization of anti-TRBC1 CAR and TRBC1 on the cell surface of CAR-C1 (Fig. 2e and f). These findings supported that TRBC1 molecules were still expressed on the surface of CAR-C1 but in cis bound by a proportion of anti-TRBC1 CARs, masking TRBC1 from identification by other anti-TRBC1 CAR-T, and meanwhile only the remaining unoccupied CARs identified C1, weakening effector function of CAR-C1.
In addition, contaminating TRBC1+ malignant cells during anti-TRBC1 CAR-T manufacturing not only produced CAR-C1 which was resistant to anti-TRBC1 CAR-T and had lesser killing ability, but were expected to accelerate exhaustion and terminal differentiation of anti-TRBC1 CAR-T with limited in vivo persistence due to continuous (tonic) ligand-driven CAR stimulation [7, 8]. Co-culture of CAR-C2 with C1 in a 2:1 ratio (physiological condition) for 6 days revealed lower and higher percent of naïve and effect CAR-C2 cells, respectively, compared to solo culture of CAR-C2 (Fig. 2g). In addition, the co-culture of CAR-C2 and C1 exhibited increasing expression of PD-1, TIM-3 and LAG-3 in CAR-C2 (Fig. 2h-j). These findings suggested that compared with unfractionated T cells, TRBC1-depleted T cells genetically engineered with anti-TRBC1 CAR not only avoided resistance to anti-TRBC1 CAR-T, but reduced exhaustion and terminal differentiation.
Although anti-TRBC1 CAR-T appeared a promising approach for T-cell malignancy, unfractioned T cells transduced to express anti-TRBC1 CAR could not only produce CAR-C1 cells which had lesser killing ability against TRBC1+ malignant T cells and moreover were resistant to anti-TRBC1 CAR-T, but contaminate TRBC1+ cells which promoted exhaustion and terminal differentiation of anti-TRBC1 CAR-T. Therefore, it was necessary to pre-deplete TRBC1+ T cells, even if allogeneic T cells were used for anti-TRBC1 CAR-T manufacturing for patients without sufficient autologous T cells.
Availability of data and materials
The datasets used and analysed during the current study are available from the corresponding author on reasonable request.
Chimeric antigen receptor
B-cell acute lymphoblastic leukemia
diffuse large B-cell lymphoma
T cell receptor β-chain constant region 1
anti-TRBC1 CAR transduced C1 cells
anti-TRBC1 CAR transduced C2 cells
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We thank Dr. Huirong Ding at the Department of Central Laboratory, Key laboratory of Carcinogenesis and Translational Research (Ministry of Education/Beijing) for her assistance of flow cytometry experiments.
This work was supported by National Key R&D Program of China (Grant No 2018YFC0910700); Natural Science Foundation of China [Grant No 81972880, Grant No 82003246, Grant No 81760525]; Beijing Natural Science Foundation (Grant No 7171001, Grant No 7182029); Beijing Municipal Science & Technology Commission (Grant No Z171100001017136); Capital’s Funds for Health Improvement and Research (Grant No 2020–4-1028); Open Project funded by Key laboratory of Carcinogenesis and Translational Research, Ministry of Education/Beijing (Grant No 2019 Open Project-4).
Ethics approval and consent to participate
This study was approved by the Institutional Review Board of the Peking University School of Oncology, China.
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Zhang, C., Palashati, H., Rong, Z. et al. Pre-depletion of TRBC1+ T cells promotes the therapeutic efficacy of anti-TRBC1 CAR-T for T-cell malignancies. Mol Cancer 19, 162 (2020). https://doi.org/10.1186/s12943-020-01282-7