What is the recent progress of Multi-target CAR-T cell therapy?

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What is the recent progress of Multi-target CAR-T cell therapy?

Compared with the breakthroughs of immune checkpoint inhibitors in the field of solid tumors, CAR-T has only made breakthroughs in the field of hematological tumors. In the field of solid tumors with more patients, there are few progress and breakthroughs.

What is expected is that CAR-T therapy has not only begun to try to engineer other types of immune cells such as CAR-NK, CAR-NKT, and CAR-Treg. In addition, due to the heterogeneity of tumor antigens, single-target CAR-T has gradually begun to transform to multi-target CAR-T cell therapy, and has achieved good anti-tumor therapeutic effects. This article will review the recent progress in multi-target CAR-T cell therapy for readers.

Mechanism of Multi-target CAR-T

First of all, let us briefly review the mechanism of CAR-T therapy. CAR (Chimeric Antigen Receptor) is an artificial receptor molecule manufactured by genetic engineering technology, which can give immune effector cells (such as T lymphocytes) to a certain The specificity of each target epitope can enhance the function of T lymphocytes to recognize antigen signal and activation, and then return lymphocytes to achieve anti-tumor effect.

What is the recent progress of Multi-target CAR-T cell therapy?
Figure 2 CAR structure [1]

The so-called multi-target CAR-T cells are mainly designed to target different tumor antigens, including dual CAR-T cells with two CARs or tandem CAR-T cells with multiple single-chain antibodies (scFv) . This multi-target CAR-T can theoretically overcome tumor antigen heterogeneity and tumor antigen escape

What is the recent progress of Multi-target CAR-T cell therapy?
Figure 3 Multi-target CAR-T, overcoming tumor antigen escape [2]

CD19/CD22 CAR-T

CAR-T also has drug resistance in clinical applications.

Taking B-cell acute lymphoblastic leukemia (B-ALL) as an example, as many as 25% of patients receiving CD19-targeted CAR-T cell therapy relapse, showing CD19 negative or low CD19. This phenomenon is called antigen escape. The main reason is that the single target is down-regulated or lost, and the therapeutic effect is not as expected. If a dual-redirect CAR-T that can target CD19 and CD22 is designed, theoretically, it can effectively solve the shortcomings of single target resistance. This idea has been verified clinically.

On October 12, 2021, Nature Medicine published a report on anti-CD19 and anti-CD22 CAR autotransduced T cells (AUTO3) in children and young adult patients with relapsed or refractory B-ALL (n=15) Phase I trial to evaluate the efficacy of AUTO3.

The results of the study show that AUTO3 has good safety, and there is no case report of dose-limiting toxicity or serious cytokine release syndrome or neurotoxicity related to AUTO3. At 1 month after treatment, the remission rate (ie, complete remission or complete remission but incomplete bone marrow recovery) was 86% (13 out of 15 patients). The 1-year overall survival rate and event-free survival rate were 60% and 32%, respectively.

What is the recent progress of Multi-target CAR-T cell therapy? Figure 4 The structure of AUTO3 and the results of flow cytometry [3]

In fact, as early as 2019, AUTO3 obtained the orphan drug qualification for the treatment of ALL. The good curative effect and prospects come from AUTO3 is a kind of self-enriched T cells, modified by a single retroviral vector to express two independent chimeric antigen receptors (CAR), respectively targeting the B lymphocyte antigens CD19 and CD22, and Each CAR is independently optimized for the activity of a single target. By targeting two B-cell antigens at the same time, AUTO3 aims to reduce the recurrence of patients with B-cell malignancies due to the loss of a single antigen.

By addressing antigen escape (a common cause of relapse in such patients), AUTO3 has the opportunity to become the best-in-class therapy for pediatric ALL. Compared with the currently marketed CAR-T therapy, AUTO3 can also provide better safety, and low levels of severe cytokine release syndrome (CRS) and neurotoxicity have been observed in clinical studies.

Multi-targeted CAR-T and solid tumors

Compared with the drug resistance caused by single target antigen escape, the problem of drug resistance or drug non-response caused by physical barrier and/or immunosuppressive tumor microenvironment (TME) is a more difficult clinical bottleneck. Therefore, CAR-T cells successfully treat solid tumors at least to determine the appropriate target antigen, so that CAR-T cells can enter all parts of the tumor and overcome the immunosuppressive effect of the tumor microenvironment (TME).

Among solid tumors, glioblastoma (GBM) is the most difficult one. Due to the high heterogeneity of tumor cells and the low permeability of the blood-brain barrier, there have been few advances in therapeutic drugs. What is worth looking forward to is that a September 2021 study from the University of North Carolina at Chapel Hill, the United States, has exciting results.

Researchers have discovered a newly developed CAR-T cell immunotherapy that uses genetically modified T cells to target and attack two antigens on cancer cells (CD28 and 4-1BB), which can be used to implant human neuroblastoma tissue The mice are very effective. This dual targeting limits the re-growth of tumors and prevents neuroblastoma cells from evading these aggressive T cells.

What is the recent progress of Multi-target CAR-T cell therapy? Figure 5 Schematic diagram of confocal microscope imaging [4]

Confocal microscopy imaging showed that CARs aggregated in T cells expressing GFP-labeled GD2.28ζ (green) and B7-H3.BB (red), which can target neuroblastoma cells and observe the killing effect. In mice implanted with neuroblastoma, the excellent anti-tumor results of dual-targeting CAR-T cell therapy were also verified.

Figure 6 Three design strategies for multi-targeting CAR [5]

But we also know that the human tumor microenvironment and heterogeneity are much higher than that of mice. It is possible that even dual-targeting CAR-T cannot cover enough target antigens.

Therefore, CAR-T cell therapy that combines multiple target antigens may have a breakthrough in glioblastoma (GBM). A research team has developed trivalent CAR-T cells (targeting HER2, IL13Rα2 and EphA2 at the same time) for GBM patients, and the final clearance rate of cancer cells is close to 100%.

The reason why Trivalent CAR has such a strong anti-tumor activity is that it can cover multiple target antigens and has three signal transduction pathways to activate T cells with high intensity, and the trivalent immune synapse formed when Trivalent CAR binds to target antigens improves Anti-tumor activity.

Summary

Although a number of research data show that the efficacy of multi-targeted CAR-T in the treatment of a variety of malignant tumors is positive and has become an effective means to prevent antigen evasion, this type of CAR-T cell can be recognized by multiple target antigens and has a high intensity. Activating T cells can easily cause a cytokine storm and over-kill normal cells with low expression of the target antigen.

Therefore, it is necessary to further optimize the structure design and function to effectively exert the tumor killing effect while ensuring safety. We sincerely hope that CAR-T therapy can achieve new breakthroughs in the field of solid tumors.

references

[1]Gill, S., M.V.Maus, and D.L. Porter, Chimeric antigen receptor T cell therapy: 25years in themaking. Blood Reviews, 2016. 30(3): p. 157-167.

[2] Abreu, T.R., et al., Currentchallenges and emerging opportunities of CAR-T cell therapies. Journal ofControlled Release, 2020. 319: p. 246-261.

[3] Nature Medicine | VOL 27 | Octob er2021 | 1797–1805 |.

[4] Koichi Hirabayashi et al. NatureCancer, 2021, doi:10.1038/s43018-021-00244-2.

[5] Han X, Wang Y, Wei J, Han W. Multi-antigen-targeted chimeric antigen receptor T cells for cancer therapy. JHematol Oncol. 2019;12(1):128.