Cancers: Research status of dual-target CAR-T cell therapy

Chimeric antigen receptor (CAR) T cells have achieved remarkable success in the treatment of recurrent hematologic malignancies, such as acute lymphoblastic leukemia (ALL), non-Hodgkin lymphoma (NHL), and multiple myeloma (MM).

CD19 and B cell maturation antigen (BCMA) are two of the most successful CAR targets with good response rates
.
The total effective rate (ORR) of approved CAR-T drugs targeting CD19 reached more than 70%, while the idecabtagene vicleucel and ciltacabtagene autoleucel targeting BCMA reached 73% and 97%,
respectively.
However, at least 50% of patients treated with CAR-T cells still experience relapse or progression
.

The main mechanism of recurrence after CAR-T cell therapy is the limited persistence of CAR-T cells, inhibition of CAR-T cell function and antigen escape
.
In order to minimize the risk of recurrence due to target escape, dual-target CAR-T is actively exploring strategies
for dual-target CAR-T to identify more than one tumor-associated antigen in clinical trials.
This strategy can be achieved
by using two mixed CAR-T cells with different antigen binding specificities or a single CAR-T cell capable of targeting two different antigens.

Currently, in preclinical models and clinical trials of hematological malignancies, there are at least three combinations of antigens for dual-target CAR-T cell therapy: CD19/CD20, CD19/CD22, and BCMA/CD38
.
Recently, dual-target CAR-T has been used more and more in clinical practice, and from the disclosed comprehensive clinical data, dual-target CAR-T has shown promising application value
.

Common dual CAR strategy

The main CAR structures for dual-target CAR-T cell therapy include: single-target CAR mix, bivalent tandem CAR, bivalent ring CAR, and bicistron CAR
.

Two separate CAR-T cell products
can be generated by transducing T cells with two different vectors separately.
Then, two separate CAR-T cells are mixed together in a 1:1 ratio and infused simultaneously or sequentially
.

Another method can be generated by co-transduction of T cells with two separate vectors, each encoding a separate CAR structure
.
Two separate single-target CAR-T cells and one dual-target CAR-T cell
are included in the final mix.

Dicistron CAR-T cells are the introduction of a double cistronic vector into T cells to produce two different CARs in the same T cell, where each CAR targets a different antigen-binding domain
.

Divalent tandem CAR-T cells are the introduction of a divalent vector into T cells to generate bidomains
.
By arranging the light chain variable domain (VL) and heavy chain variable domain (VH) of the single-chain antibody fragment (scFv) in different orders, two different structures can be formed: tandem and ring.

The tandem structure is formed by the VL-VH of one single-chain antibody directly attached to the VL-VH of another single-chain antibody, while the circular structure is formed by the VL-VH of one single-chain antibody sandwiched between the VH-VL of another single-chain antibody, as distinguished from the bivalent tandem CAR
.

Clinical efficacy of dual-target CAR-T

Compared with single-target CAR-T cell therapy, the advantage of dual-target CAR-T cell therapy is that it can reduce antigen escape
of tumor cells.
Clinical studies of single-target CAR-T cell therapy have shown a complete response (CR) of more than 90%, with little room for
improvement in the initial response to dual-target CAR-T cell therapy.
Therefore, the expectation of dual-target CAR-T cell therapy is not only to improve the persistence of the response, but also to regenerate the response
in patients who relapse or refractory after single-target CAR-T cell therapy.

In a small number of studies, dual-target CAR-T cell therapy appears to have demonstrated that DOR and OS are superior to single-target CAR-T cells
.
For example, patients receiving CD19 single-target CAR-T cell therapy had similar OS to those receiving CD22 single-target CAR-T cell therapy, but shorter
than those of patients receiving CD19/CD22 dual-target CAR-T cell therapy.
In non-Hodgkin lymphoma, the percentage of PFS and OS treated with CD19/CD20 dual-target CAR-T cells was higher than that of CD19 single-target CAR-T cells
.

The design strategy for CD19/CD20 or CD19/CD22 dual-target CAR-T is based on the assumption that targeting CD20 or CD22 will be beneficial in reducing antigen escape
of CD19.
Disclosed data suggest that single-target CAR-T cell therapy or dual-targeted CAR-T cell therapy targeting CD22 or CD20 can enable patients with CD19 escape to obtain CR.

In particular, seven patients who had previously received CD19 single-target CAR-T cell therapy, five of whom received CR
after receiving dual-target CAR-T cell therapy.
Therefore, clinical data support CD19/CD20 or CD19/CD22 dual-targeted CAR-T cell therapy for relapsed patients
who are resistant to CD19-CAR-T cell therapy.

In addition, in multiple myeloma, the combination of BCMA-CAR and second CAR is still being explored
.
Dual-target CAR-T cell therapy for BCMA/CD19 and BCMA/CD38 has entered the clinic, while BCMA/CS1 (SLAMF7) and BCMA/GPRC5D dual-target CAR-T cell therapy are about to enter the clinic
.
BCMA/CD19 dual-target CAR-T cell therapy showed exciting efficacy in a small subset of patients, with an ORR of 100% in five patients, with only one grade 3 cytokine release syndrome (CRS) occurring and no neurotoxicity (NT) occurring
.
In addition, BCMA/CD38 dual-target CAR-T cells also showed good results
.
After treatment with BCMA/CD38 dual-target CAR-T cells, 5 of the 8 patients with sCR maintained sCR at a median follow-up of 9 months, and the PFS at 9 months was 75%.

Safety of dual-target CAR-T cells

Theoretically, dual-target CAR-T cell therapy is stimulated by two antigens, which raises the question of whether the patient's CAR-T cell activation is stronger than that of single-target CAR-T cells, resulting in a higher incidence of adverse events than single-target CAR-T cells.

Available data suggest that the incidence of grade 1-2 CRS is similar
between single-target CAR-T cell and dual-target CAR-T cell therapy.
Of the available reported studies, two (22.
2%) of the nine clinical trials of single-target CAR-T cell therapy did not report grade 3-4 CRS, while dual-target CAR-T cells did not report grade 3-4 CRS
in three (37.
5%) of eight clinical trials.
In addition, 42.
9% (3/7) of single-target CAR-T cell clinical trials did not report grade 3-4 NT, while 50% (4/8) of dual-target CAR-T cells did not report grade 3-4 NT.

Through a simple numerical comparison, it can be found that compared with single-target CAR-T cell therapy, dual-target CAR-T cell therapy does not produce more severe CRS and NT, but is lower
.
Of course, given the sample size, different clinical indications, and the management of CRS and NT in the early stages of CAR-T cell therapy, it seems that more research is needed to confirm this conclusion
.

brief summary

Although CAR-T cell therapy has achieved excellent results in hematological malignancies, the problem of recurrence is still serious
.
In order to overcome tumor immune evasion of CAR-T cell therapy, multi-target CAR-T cell therapy has become a hot spot
in current research.
The efficacy of dual-target CAR-T cell therapy has been verified in some clinical trials, and the safety of dual-target CAR-T cells seems to be better than that of single-target CAR-T cells, and the incidence of severe CRS and NT is lower
.

However, in dual-target CAR-T cell therapy, how to achieve 1+1>2 still needs to be further optimized
for the selection of CAR targets and the structure of CAR.
In short, dual-target CAR-T cell therapy is still in the early stage of development, which needs more preclinical and clinical trial data to support, and it is believed that it will play a unique and critical role
in tumor immunotherapy in the future.

References:

1.
Current Status and Perspectives of Dual-Targeting Chimeric Antigen Receptor T-Cell Therapy for the Treatment of Hematological Malignancies.
Cancers (Basel).
2022 Jul; 14(13): 3230