Chimeric antigen receptor T cells (CAR-T) and T cell antigen receptor chimeric T cells (TCR-T) are currently the “top stream” in adoptive T cell tumor immunotherapy. In particular, CAR-T therapy, which has been approved by the FDA, is rewriting the treatment paradigm of some hematological tumors.
However, adoptive T cell therapy remains of little success in solid tumors. The main reason is that these T cells, which are reinfused into the patient, need to reach the tumor parenchyma with the peripheral blood circulation “wading” before they can exert a killing effect. In the road of “killing enemies”, the immunosuppressive microenvironment of the body gradually depletes reinfused T cells and cannot proliferate and survive for a long time.
In order to improve the outcome of adoptive T cell therapy, patients often require prior radiotherapy or chemotherapy-induced myeloablative therapy. This conditioning regimen may improve the proliferation and durable viability of adoptive T cells in vivo by balancing cytokine production in vivo and removing some immunosuppressive cells (such as regulatory T cells and myeloid-derived suppressor cells) in vivo. However, high-dose chemoradiotherapy also brings serious side effects to the body, making many patients unable to tolerate myeloablative regimens and lose the chance of benefit.
Recently, the research team led by K. Christopher Garcia of Stanford University, Carl H. June of the University of Pennsylvania, and Antoni Ribas and Anusha Kalbasi of the University of California, Los Angeles, published important research results in Nature.
They designed for the first time a chimeric receptor fused with orthogonal IL-2 receptor (oIL-2R) and IL-9 receptor (IL-9R) that activates adoptive T cells without the need for prior chemoradiotherapy for myeloablative treatment and confers a dual phenotype of their stem-like memory T cells and effector T cells to effectively exert anti-tumor function.
More importantly, this new therapy has been validated in mouse solid tumor models of melanoma and pancreatic cancer, providing new strategies for the study and application of adoptive T cells in the treatment of solid tumors.
IL-2 is a cytokine required for proliferation, survival, and functional maintenance of effector T cells and is an important therapeutic adjunct to adoptive T cells. However, the pleiotropic effects of IL-2 and the widespread expression of IL-2R also amplify the inhibitory immune response and systemic toxic side effects, limiting its therapeutic use.
Christopher Garcia’s research team has published some pioneering work in Science in 2018. By genetically modifying IL-2 as well as the extracellular domain (ECD) of the IL-2Rβ chain, they designed a mouse IL-2/IL-2Rβ orthogonal pair. This T cell expressing orthogonal IL-2Rβ (o2R) can only be activated by orthogonal IL-2 (oIL-2), thus avoiding the toxicity of activating other immunosuppressive cells.
In this latest study, the investigators hope to investigate the therapeutic potential of other members of the γc cytokine receptor family (6) using the oIL-2 system. They replaced the intracellular domain (ICD) of o2R with ICD of the γc cytokines IL-4, IL-7, IL-9, and IL-21 receptors to construct chimeric orthogonal receptors, respectively.
After analysis and screening, it was found that o9R was similar to the known signaling characteristics of wild-type IL-9 receptor and was able to lead to STAT1, STAT3 and STAT5 phosphorylation.
According to previous studies, IL-9R is mainly expressed in mast cells, memory B cells, innate lymphocytes and hematopoietic progenitor cells. There are also Th9 isoforms characterized by IL-9 secretion in T cells. But mouse T cells do not express IL-9R, so IL-9 naturally fails to activate mouse T cells. When the researchers artificially transduced T cells from mice with IL-9R, treatment of T cells with IL-9 also caused phosphorylation of STAT1, STAT3, and STAT5.
At the same time, they found that when o9R was activated with MSA-oIL-2, cells expressed CD62L, Sca-1, and Fas (CD95) more highly, trending toward a stem-like memory T cell phenotype (Tscm), an important cell type that can survive continuously and exert antitumor activity in adoptive cell therapy.
Given the unique signal transduction of o9R and the phenotypic characteristics conferring importance to cells, researchers want to use this newly designed adoptive T cell to treat solid tumors.
First, they used a B16-F10 mouse melanoma model expressing gp100 antigen using pmel mouse T cells as a source of modification (the TCR of pmel T cells itself recognizes gp100) and found that o9R pmel T cells were able to exert significant antitumor effects in combination with systemic delivery of oIL-2 without prior lymphodepleting radiotherapy.
At the same time, o9R pmel T cells not only infiltrated more in tumors, but also had higher in vitro cytolytic ability and IFNγ production. Using transcriptome sequencing, the researchers identified and validated genes involved in determining o9R pmel T cell infiltration, effector function, and in vivo activity.
They found that o9R, in addition to being able to induce the Tscm phenotype, observed enrichment of genes associated with T cell activation (Pdcd1, Icos, Entpd1, Lag3, and Havcr2) and effector function (Ifng, Gzma, and Prf1). In addition, Jun/Fos expression ratio was increased, suggesting resistance to tumor-induced failure. In the meantime, o9R signaling downregulates genes associated with T-cell dysfunction (Nr4a1 and Tox). This suggests that o9R or native IL-9R signaling pathways may induce heterogeneous mixed subsets.
Next, to investigate the role of o9R signaling in CAR-T, the researchers used a model of immunotherapy resistance, mesothelin-expressing pancreatic cancer mice, and constructed CARs. Meanwhile, in order to investigate the effect of o9R signaling pathway on CAR-T cell dysfunction in the tumor microenvironment, they designed to deliver oIL-2 (Ad-oIL-2) with adenoviral vectors only intratumorally.
The results showed that the combination of Ad-oIL-2 plus CAR-o9R achieved a higher proportion of complete responses (5/12) and longer survival without prior lymphodepleting chemotherapy. Although CAR-o9R infiltrated fewer tumors than CAR-o2R T cells compared to the pmel model, the transcriptome changes of CAR-o9R T cells remained similar to o9R pmel T cells.
So, does this new method have potential for clinical application? The authors designed human-derived orthogonal IL-2Rβ (ho2R) and chimeric IL-2Rβ-IL-9R (ho9R) and constructed TCR T cells and CAR-T cells that recognize tumor antigens NY-ESO-1 and mesothelin, respectively, on this basis. The results showed that, similar to mice, ho9R activated consistent phosphorylation signaling, stem cell-like functional phenotypes, and stronger multifunctional effector molecule expression and killing ability.
Overall, this study designed a novel chimeric receptor o9R to engineer T cells, allowing them to acquire a unique dual identity of stem cell memory T cells and effector T cells that can survive and proliferate and kill tumors for a long time in vivo.
Whether the cytokine oIL-2 was administered systemically or locally to tumor-bearing mice, this modified T cell was able to exert a significant antitumor effect in vivo without chemoradiotherapy myeloablative treatment.
This new approach is undoubtedly important for adoptive T cells in the treatment of solid tumors. At the same time, this study constructs and validates human-derived o9R T cells in vitro and also provides attractive data for subsequent clinical translation.