Recently, it has been reported that tumor-infiltrating regulatory T (Treg) cells mediate pre-mRNA splicing of cytotoxic T-cell-associated protein-4 (CTLA-4) through massive uptake of lactic acid, which promotes the expression of CTLA-4, and thus improves the efficacy of CTLA-4 monoclonal antibody. Revealing this delicate network could have significant ramifications for the development of innovative immune checkpoint therapeutic approaches, particularly in cancer medicine.
With our world-leading technology platforms and professional experts at antibody development, Creative Biolabs has perfected our technical pipelines in immune checkpoint antibody development. Our comprehensive service portfolio includes polyclonal antibody discovery and development, monoclonal antibody (mAb) discovery and development, antibody fragment discovery and development, antibody characterization, antibody engineering and optimization, antibody production, and manufacture.
In solid tumors, not only the presence of tumor cells alone, but also blood vessels, various immune cells, fibroblasts, bone marrow-derived inflammatory cells, various signaling molecules, and extracellular matrix, etc., which together form the tumor microenvironment (TME). Tumor-infiltrating Treg cells are a member of this group, which is a unique subpopulation of immune T cells with immunosuppressive effects that inhibit or down-regulate the proliferation and differentiation of effector T cells. Treg cells constitutively express a very important molecule, CTLA-4, which is on par with PD-1 and PD-L1 as immune checkpoints. When CTLA-4 binds to CD80/CD86 on the surface of antigen-presenting cells, it acts as an "off" switch, which contributes to the suppressive function of Treg cells.
According to the Warburg effect, tumor cells rely on aerobic glycolysis to support their survival, which often leads to excessive lactate accumulation in the TME. It has been reported that Treg cells utilize lactate to maintain their immunosuppressive function. However, the regulation of the expression of CTLA-4, an important molecule in Treg cells, by lactate is not known.
The researchers found that tumor-infiltrating Treg cells must promote CTLA-4 expression through lactate uptake to maintain their high suppressive properties.
Fig. 1 Lactate modulates RNA splicing to promote CTLA-4 expression in tumor-infiltrating regulatory T cells.1
Lactate uptake by Treg cells promoted not only the expression of CTLA-4 but also the expression of the important transcription factor Foxp3. In turn, Foxp3 induced high expression of ubiquitin-specific peptidase 39 (USP39). Although USP39 is an inactive deubiquitinating enzyme that lacks key catalytic cysteine residues, it is involved in RNA spliceosome assembly and will directly affect RNA splicing after transcription. Therefore, when researchers deleted USP39 in Treg cells, it not only disrupted the effective splicing of CTLA-4 pre-mRNA, but also impaired Treg cell-mediated immunosuppression.
In conclusion, lactate modulates RNA splicing to increase CTLA-4 expression and enhance immunosuppressive function of Treg cells, which contributes to the efficacy of CTLA-4 blockade therapy.
Lactate acts as a signaling molecule that affects the expression of immune checkpoint molecules on tumor cells and immune cells.
New evidence that lactate regulates immune checkpoint expression certainly provides a potential therapeutic target.
Table 1 Lactate dehydrogenase (LDH) and MCT inhibitors.2
Inhibitors | Targets | Cancer types |
Oxamate | LDHA | Gastric cancer cells; cervical cancer cells; leukemia cells; lung cancer cells |
Gossypol | LDHA | Melanoma cells; lung cancer cells; breast cancer cells; cervical cancer cells; leukemia cells; glioma cells; adrenal cancer cells |
FX11 | LDHA | B‐lymphoma cells; pancreatic cancer cells; papillary thyroid carcinoma cells |
Quinoline 3-sulfonamides | LDHA/LDHB | Hepatocellular carcinoma cells |
NHI | LDHA/LDHB | Pancreatic ductal adenocarcinoma cells; cervical cancer cells; mesothelioma cells |
Galloflavin | LDHA | Breast cancer cells; hepatocellular carcinoma cells |
GNE‐140 | LDHA | Pancreatic cancer cells |
7ACC2 | MCT1 | Cervix cancer cells; pharynx squamous cell carcinoma cells; breast cancer cells; pancreatic adenocarcinoma cells |
AR-C155858 | MCT1/2 | Breast cancer cells; cervix cancer cells; leukemic cells |
AZD3965 | MCT1/2 | Breast cancer cells; small cell lung cancer cells; colorectal cancer cells |
BAY-8002 | MCT1/2 | Colorectal cancer cells |
CHC | MCT1/4 | Cervix cancer cells; pharynx squamous cell carcinoma cells; breast cancer cells; colorectal cancer cells; prostate cancer cells; osteosarcoma cells; renal cell carcinoma cells |
DIDS | MCT1/4 | Colorectal cancer cells; lung cancer cells |
Lonidamine | MCT1/4 | DB-1 melanoma cells |
Phloretin | MCT1/4 | Breast cancer cells; lung cancer cells |
pCMBS | MCT1/4 | Colorectal cancer cells |
Quercetin | MCT1/4 | Colorectal cancer cells; glioma cells; lung cancer cells |
Simvastatin | MCT1/4 | Lung cancer cells; breast cancer cells; prostate cancer cells; ovarian cancer cells; cervix cancer cells |
By unraveling the intricate crosstalk between metabolism and immunity, Creative Biolabs researchers are pioneering new approaches in cancer immunotherapy and beyond.
References
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