Immunotherapy is one of the most popular and rapidly developing cancer therapies in clinical trials. Researchers at Uppsala University have recently developed a novel immunotherapy that enhances the immune defense of CAR T cells against cancer, and is very promising for treating a variety of solid tumors.
In recent years, various immunotherapies have been introduced into clinical practice. Among them, the cutting-edge genetic engineering of CAR T cells has been a remarkable success in the treatment of hematological tumors. However, conventional CAR T-cell therapies have some inherent limitations as well. For example, in treating solid tumors, CAR T cells tend to fail due to a highly immunosuppressive tumor microenvironment. Aditionally, the high heterogeneity of antigens in solid tumors also allows tumors to effectively escape CAR T cells. These factors greatly reduced efficacy of CAR T cells in solid tumors.
To overcome such limitations, researchers at Uppsala University armed CAR T cells with a gene from the bacteria Helicobacter pylori that encodes an immune-stimulating protein (neutrophil activating protein, NAP). This protein attracts innate immune cells, induces the maturation of dendritic cells, and forms a local pro-inflammatory environment that increases the production of the cytokine interleukin-12. When NAP is released from CAR T cells, it fights the immunosuppressive microenvironment in solid tumors and enhances the function of CAR T cells.
To study the overall role of murine CAR (NAP) T cells in cancer treatment, the researchers conducted experiments in mice with different tumor types. In order to explore the effect of CAR (NAP) T cells on the tumor microenvironment, the researchers conducted gene collection enrichment analysis. On the other hand, a mouse model of the heterogeneous tumor was established by subcutaneous injection of wild-type (antigen-negative) NXS2 cells and antigen-positive NXS2-mCD19 cells in a 1:1 ratio to reflect the effect of antigen heterogeneity on CAR (NAP) cell activities. The NXS2-mCD19 cell line was established by transducing NXS2 cells with lentiviral vectors. The gene sequences used to construct lentiviral vectors were provided by GenScript.
In vitro, proof-of-concept experiments were also performed with human CAR (NAP) T cells to show the translational potential of this novel immunotherapy for patients.
In two different mouse cancer models, mice treated with CAR (NAP) T cells had tumor growth inhibited. The survival rate of mice in the experimental groups was improved compared to those treated with conventional CAR T cells. In one of the experiments, 75% of the mice in the CAR (NAP) T-cell treated group became tumor-free, compared with 30% of the cure rate of mice treated with conventional CAR T cells.
Heterogeneous tumor-treatment experiments revealed that CAR (NAP) T-cell therapy significantly reduced tumor growth and increased survival in mice with tumors expressing heterogeneous CAR target antigens. In contrast, conventional CAR T-cell therapy failed to yield any significant results.
Moreover, the mice treated with CAR (NAP) T cells resisted re-attack by wild-type NXS2 cells, suggesting that a protective immune memory was established in the mice. Subsequent studies have found that splenocytes isolated from CAR (NAP) T-cell treated mice respond to wild-type NXS2 tumor cell lysate, and their endogenous bystander T-cell response is systematically activated, allowing mice to be effectively protected when attacked again by wild-type NXS2 cells.
A key feature of the bystander T cell response is epitope diffusion, in which endogenous CD8+ T cells activate against multiple antigens, not just CAR-targeted ones, which is critical for eradicating antigen-heterogeneous solid tumors.
Gene collection enrichment analysis revealed that in the CAR (NAP) T-cell therapy group, the upregulated expression of genes associated with monocyte migration, proliferation, inflammatory response, and regulation of response to external stimuli was more than twice that of the conventional CAR T-cell treatment group. In addition, CAR T cell tumor infiltration in mice receiving CAR (NAP) T-cell treatment was also much higher than that in the conventional CAR-T treatment group.
Combined with other experimental data, the researchers concluded that CAR (NAP) T cells could induce a more pronounced pro-inflammatory tumor microenvironment, achieving a superior therapeutic effect than conventional CAR-T treatment.
Similar reinforcement of the immune defense was observed in human CAR (NAP) T-cell experiments as in murine CAR (NAP) T-cell ones.
 Jin, C., Ma, J., Ramachandran, M. et al. CAR T cells expressing a bacterial virulence factor trigger potent bystander antitumour responses in solid cancers. Nat. Biomed. Eng (2022). https://doi.org/10.1038/s41551-022-00875-5