Chimeric Antigen Receptor (CAR) T-Cell Therapy in solid tumor, challenge and solution
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Overview:
Introduction of immunotherapy
History of immunotherapy
Classification of immunotherapy
CAR-T Cell
Structure of CAR-T cell
Generations of CAR-T cell
CAR-T cell therapy in solid tumor
Side effect of CAR-T cell
Clinical trial in solid tumor
Conclusion
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Cancer Treatment
Recently, cancer immunotherapies received a high degree of attention.
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Immunothrapy(History)
In 1891 Coley injected streptococcal organisms into a patient with inoperable cancer. He and other doctors who used them reported excellent results, especially in bone and soft-tissue sarcomas. many doctors did not believe his results. However, the modern science of immunology has shown that Coley's principles were correct and that some cancers are sensitive to an enhanced immune system. Coley known as the “Father of Immunotherapy”.
In 1989 Zelig Eshhar published the first study in which a T cell’s targeting receptor was replaced, and noted that this could be used to direct T cells to attack any kind of cell; this is the essential biotechnology underlying CAR-T therapy.
In 2006 administration of normal circulating lymphocytes transduced with a retrovirus encoding a T-cell receptor (TCR) that recognized the MART-1 melanoma-melanocyte antigen, mediated tumor regression.
In 2010 administration of lymphocytes genetically engineered to express a chimeric antibody receptor (CAR) against B cell antigen CD19 was shown to mediate regression of an advanced B cell lymphoma.
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Classification of immunothrapy:
Cell immunotherapy(DC,NK,T)
Monoclonal antibodies
Cytokine therapy
DNA vaccine
Mediate immunotherapy viruses and bacteria
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Adoptive Immunotherapy (Adoptive cell transfer –ACT)
ACT:
1.tumour-infiltrating lymphocytes(TILs)
2.TCR engineered T cells (TCRT)
3.CAR T-cell therapy
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Immune Response to tumor
Antigen recognition
Tumor Ags.
T cell activation & T cell proliferation
Requires signals by accessory molecules
Effector phase & antigen elimination (tumor cell destruction)
Cytotoxicity, cytokine production, ADCC,…….
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CAR-T Cell
CAR was a synthesized transmembrane protein, redirecting the target antigens
expressed in tumour cells through genetic reprogramming.The CARs endow T cells
with antigen-specific recognition, activation and proliferation in a major
histocompatibility complex(MHC) independent manner.
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Structure of CAR-T cell
The classic CARs consist of:
an extracellular antigen recognition domain
a hinge domain
a transmembrane (TM) domain
and an intracellular domain
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The extracellular antigen-binding moiety in CARs, typically derived
from a single chain variable fragment (scFv) that isolated from an
antigen-specific monoclonal antibody, renders T cells the ability to
bind antigens with retained specificity and affinity. The hinge region
mediates CAR flexibility, transduces essential signals, and exerts
profound impacts on ensuring the suitable positioning of the binding
domain during scFv-antigen interactions . The transmembrane domains
are derived from CD3-ζ. The intracellular domain is responsible for
signal delivery within CARs.
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The first generation CARs provided the proof for the concept of the targeting and activation of CAR-T cells, but had very modest clinical activity and poor persistence in vivo , to overcome these limitations, the second and third generation CARs have incorporated co-stimulatory molecules, including CD27, CD28, CD134, CD137 and ICOS. CAR-T cells with multiple signaling receptors have been demonstrated with sustained proliferation, enhanced cytokine production, improved tumor lytic activity, and reduced AICD both in vitro and in vivo. Nowadays, the second-generation CAR-T cells have been more exclusively and ubiquitously applied in clinical trials than the third generation CAR-T cells, because the reduced activation threshold of the third generation CAR-T cells may cause on-target/off-tumor side effects to normal tissues.
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The fourth-generation CAR T cells with additional genetic modification were able
to express proliferative T-cell–co-stimulatory ligands or pro-inflammatory cytokines
(IL-12)Once recognizing the TSAs/TAAs on the tumour cells, the fourth-generation CAR T cells released a large number of perforins, granzymes and tumour necrosis factors (TNFs), which eventually led to apoptosis of tumour cells. Compared with the first three generations, the ‘TRUCK’ T cells had more advantages on affecting local suppressive cells and were enable to cause more anti-tumour destruction.
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treating solid tumors with CAR-T cells has been limited by tumor because of:
1-histopathological structure
2-strong immunosuppressive environment,
3-lack of ideal target
Poor infiltration of T lymphocytes into solid tumors:
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high concentration of blood vessel, wide gap of vessel wall
clearance,extensive vascular leakage, poor integrity of issue structure
cause selectively enhanced permeability and retention of lipid
particles and macromolecular substances within solid tumors
EPR effect(enhanced permeability and retention Effect)
suppressive nature of the tumor microenvironment
mismatching of chemokine-chemokine receptor pairs, down
regulation of adhesion molecules may also
contribute to the poor trafficking of T cells(rolling,adhesion,
extravasation, and chemotaxis)
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Over-expression of endothelin B receptor (ETBR) in tumor blood vessel impeding the adhesion of lymphocyte to vascular endothelium ETBR blocker BQ-788
tumor angiogenesis down-regulating endothelial cell-adhesion molecules such as ICAM-1 ICAM-1 up-regulation TNF-а
solution
Enhance CAR-T cells trafficking to tumor sites:
unfavorable chemokine gradients, which means that tumor-specific T cells may lack the appropriate chemokine receptors for chemokines secreted by tumor cells poor infiltration
Tumor-derived chemokines have immune-modulatory effects decrease the immunogenicity of tumors and the desensitization of chemokine receptors on T cells.tumor cells can utilize chemokines to provide autocrine growth signals and signals to enhance angiogenesis poor infiltration
SO: arming CAR-T cells with the expression of CXCR2 (CXCL1 receptor), CCR4 (CCL17 receptor), Gro-a, CCL17, and CCL2
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In addition, the difference of T cell administration also exerts an
important impact on CAR-T cells expansion and effector
differentiation. Studies have evaluated two different routes of CAR-T
cells delivery, regional intra-pleural administration and conventional
systemic intravenous of mesothelin-targeted M28z CAR-T cells, the
Former route presented robust T cells persistence and enhanced anti
tumor efficacy compared to the latter by circumventing obligate
circulation and transient pulmonary sequestration. Similarly, the
intra-cerebral injection method of CAR-T cells has also been applied
to treat glioblastoma with CAR-T cells to avoid the traffic blocking
blood brain barrier. The remarkable ability of regional delivery of CAR-T
cells provides another approach to enhance functional T cell
persistence and improve therapeutic efficacy through choosing
favorable traffic route for CAR-T cells.
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Cytokines released by engineered CAR-T cells promote tumor elimination:
defect of CAR-T cell that can’t eliminate inaccessible tumor lesions
fourth generation CARs TRUCKs the process of T
cells redirected for universal cytokine-mediated killing The
mechanism is that once activated by the CAR vector, T cells secrete
IL12 further activate innate immune cells response toward
tumor cells that are invisible to CAR-T cells and subsequent inaccessible
to antigen-directed immunotherapy.
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Optimizing culture condition for CAR-T cells:
Cytokine and stimulation conditions are indispensable ingredients in
the process of CAR-T cells manufacturing IL-7 and
IL-15 or IL-2 are mostly used IL-7 and IL-15 are superior to IL-2 for
preserving CAR-T cell expansion in vitro and in vivo, survival
when exposed to antigens stimulation, and exhibited enhanced
persistence and antitumor activity.
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Scarcity of specific antigen within solid tumors
shortage of tumor specific antigens (TSA) The solid tumor heterogeneity differences in cell origin, patient ethnicity, genetic and epigenetic changes, different distribution of an individual tumor, cancer stem cells or the direction of evolution.
tumor associated antigens (TAA) that relatively over expressed on the tumor cell surface, but CAR-T cells targeting TAAs may cause collateral damage to normal tissues.
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solution
Engineered CARs targeting mutation phenotype(neoantigen) of tumor cells:
Epidermal growth factor receptor (EGFR) is a member of HER2 family,
which frequently overexpressed in cancers. Researchers have found
that 40–70% of brain tumors express mutant EGFR variant III (EGFRvIII)
with a deletion of exons 2-7 of EGFR, which causes a defect in
The extracellular ligand-binding domain and constitutive activation in
a ligand-independent manner. Its specific expression on tumor cells.
EGFRvIII a novel promising target.So the EGFRvIII targeting CAR
system was utilized in the treatment of EGFRvIII expressing gliomas.
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Modify CARs to better target tumor associated antigens
WT1 was overexpressed in many cancers, including haematologic
malignancies, like acute and chronic leukaemias and numerous solid tumours.
A study designed WT1 28z CAR T cell, the first one against a human
Intracellular protein, WT1.outcome provided the proof-of-concept that CAR T
cells could not only target the protein expressed on the cell surface of the
tumour, but also target at intracellular antigens.
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Tuning affinity of CARs to selectively target tumor cells
Applying suicide gene to enhance the safety of CAR-T cell therapy
herpes-simplex-thymidine-kinase (HSV-TK) and inducible-caspase-9 (iCasp9) to enhance the safety of CAR-T cell therapy agains the matologic malignancies.
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Immunosuppressive environment within solid tumor
The limiting factors that hinder T cells efficiency within solid tumor
microenvironment are:
microenvironment characteristics such as hypoxia and low pH, the
lack of arginine or tryptophan, inhibitory effects of tumor-derived
cytokines, inhibitory pathways mediated by up-regulation of inhibitory
receptors .
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Solution:
Engineer CARs to target stroma cells:
the tumor-associated stroma, occupying up to 90% of the tumor
volume, has gained increasing attention for its role in initiating and
sustaining tumor growth.
Cancer associated fibroblasts (CAFs)
CAR-T cells targeting TAAs combine with CAR-T cells targeting CAFs
fibroblast activation protein-α (FAP)
SO:When combined with CAR-T cells targeting TAAs, FAP-specific CAR-T
cells presented ever more attractive anti-tumor effects . This novel
combination provides another direction for solid tumor immunotherapy.
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Combine with immune checkpoint inhibitors:
immune checkpoint inhibitors are efficacious for just few patients with high mutation loaded melanoma and lung cancer, the efficacy in treating solid tumors with CAR-T cells is limited due to the unfavorable microenvironment . Thus, combination therapy of CAR-T cells with immune checkpoint inhibitors may be a solution.
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Clinical trial:
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Side effect:
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Conclusion:
Manufacture of CAR-T Cell is a teamwork.
It is especially efficiency for hematologic malignant.
Escape mechanisms of tumor is one cause of failure in CAR-T.
combination therapy of CAR-T cells with other treatments holds great potential for treating solid tumors.
the application of CAR T-cell therapy still requires efforts and multiple exploratory studies to limit or contain the side effects.
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