Enhancing CAR-T Cell Therapy for Glioblastoma
Surgery, chemotherapy and radiation have formed the mainstay of cancer therapy for many years. However, in addition to destroying tumor cells, these treatments are detrimental to healthy cells giving rise to side effects, which can be severe. During the last two decades, more targeted therapies that specifically destroy cancer cells have been developed to minimize unwanted side effects.
These are among others immunotherapies that direct cells of the immune system, which have high specificity for their targets, to attack tumors by recognizing tumor-specific antigens. A rapidly growing immunotherapy approach is the use of chimeric antigen receptor (CAR) T cells. However, the application of this technology to solid tumors, such as glioblastoma, has been challenging.
The T-cell is a type of lymphocyte able to detect and remove abnormal cells and cells infected by a virus. Cancer cells, however, acquire the ability to evade the body’s immune system during the course of the disease , so tumors continue to grow uncontrolled. In CAR T-cell therapy the patient’s T-cells are harvested, modified to give them specificity for antigens found on the cell surface of the target tumor, and reintroduced to the patient. This primes the immune system to find and kill the target cancer cells. Since the T-cells recognize an antigen unique to the specific tumor, only cancer cells are targeted, leaving healthy cells unharmed.
The T cells are made specific for the tumor cell antigen by the introduction of a chimeric antigen receptor (CAR) that recognizes the target tumor antigen. This CAR protein comprises one protein that binds to the antigen on the cancer cell surface and two further proteins that signal the T cell to activate when that first protein attaches to the target antigen on the cancer cell.
Once activated by binding to the tumor antigen, the CAR T-cell multiplies and recruits additional cells of the immune system to the site of the cancer cells. The cytokines and activated T cells cause significant activation of the anti-tumor immune response.
CAR-T therapy has shown great success in the treatment of hematological cancers1. In contrast, the effectiveness of CAR T cells therapy in solid tumors has been limited by the lack of ideal target antigens that are both absolutely tumor-specific and homogeneously expressed.
Glioblastoma is an aggressive solid tumor that forms from astrocytes in the brain, typically in the cerebrum. It accounts for around a third of all brain tumors and is the most aggressive. Since the tumor grows very rapidly it soon impacts healthy areas of the brain, interfering with normal function. Symptoms include headache, loss of balance, personality changes, and problems with memory. The survival rate for patients with glioblastoma is 40% after 1 year, and decreases drastically to 6% by 5 years.
It is also difficult to treat; treatments are available that may slow the growth of the tumor, but there is currently no cure for glioblastoma. Glioblastoma has not been successfully treated with immunotherapy due to the complexity of the tumor and the lack of unique antigens2. Recent research at the University of California, San Francisco, has provided hope that this may soon change. Using novel technologies, smart immune cells have been designed that demonstrated efficacy against solid tumors, previously resistant to immunotherapy3.
Enabling CAR T-cell Therapy for Glioblastoma
The researchers enhanced the recognition of glioblastoma antigens by engineering combinatorial recognition T cells. The novel system utilizes multiple existing CAR targets that proved ineffective when used previously in traditional single-antigen systems. The innovative new synNotch-CAR circuits synergistically combine recognition of several complementary antigens that were imperfect as single-antigen targets.
Furthermore, such circuits can be primed by a variety of antigens that need not be homogeneously expressed on all tumor cells. The flexibility and precision afforded by these multi-antigen prime-and-kill recognition circuits were shown to overcome the challenges of immunotherapy in the treatment of glioblastoma3.
T cells transduced with a synNotch-CAR circuit primed by the CNS-specific antigen MOG (myelin oligodendrocyte glycoprotein) exhibited precise and potent control of intracerebral patient-derived xenografts without evidence of priming outside of the brain. The use of circuits that integrated recognition of multiple imperfect but complementary antigens improved the specificity, completeness, and persistence of T cells directed against glioblastoma.
The Role of TissueFAXS and StrataQuest in CAR-T Cell Research
In this research, immunofluorescence was detected through TissueFAXS PLUS and StrataQuest software (TissueGnostics)4.
TissueFAXS PLUS is an upright fluorescence and brightfileld system for the scanning and analysis of slides, cytospins, smears and Tissue Microarrays. The system is equipped with the contextual image analysis software StrataQuest.
References and Further Reading
1. June CH and Sadelain M. Chimeric Antigen Receptor Therapy. N Engl J Med. 2018;379(1):64-73.
2. O'Rourke DM, et al. A single dose of peripherally infused EGFRvIII-directed CAR T cells mediates antigen loss and induces adaptive resistance in patients with recurrent glioblastoma.Sci Transl Med. 2017 Jul 19; 9(399):
3. Choe JH, et al. SynNotch-CAR T cells overcome challenges of specificity, heterogeneity, and persistence in treating glioblastoma. Sci Transl Med. 2021;13(591):eabe7378. doi:10.1126/scitranslmed.abe7378
4. TissueGnostics. https://tissuegnostics.com/products/fluorescence-brightfield-cytometer/tissuefaxs-plus