To repeat the success of CAR-T therapies in blood cancers, a key direction for solid tumor research focuses on enabling the engineered immune cells to better target those tumors. Now, a group of scientists in Italy has proposed a method to do just that.
Sugar-based structures called N-glycans, which are expressed on the surface of pancreatic tumor cells, could protect the cancer from CAR-T cells, scientists at the IRCCS San Raffaele Scientific Institute have found. Disruption of the coating with a sugar analog dubbed 2DG enhanced CAR-T killing in different mouse models of pancreatic tumors and showed promising efficacy against other cancers in lab dishes.
The findings, published in Science Translational Medicine, could pave the way to designing improved CAR-T cell therapy strategies against pancreatic cancer and other solid tumors, the researchers said.
Glycosylation, the process by which sugar-based molecules attach to and modify a protein, plays an important role in cellular processes. Cancer cells display abnormal glycosylation, with the expression of a more diverse glycan coat compared with healthy cells. Among them, an increase in N-glycans is among the most frequent alterations found in cancer.
For their study, the San Raffaele researchers hampered branched N-glycan in pancreatic tumor cells by crippling the MGAT5 gene, which encodes for an enzyme key to the synthesis of the sugar-based coat. They treated the cancer cells with CAR-T cells directed at CD44v6, a heavily glycosylated protein. The CAR-T cells showed markedly enhanced antitumor activity with increased cancer-killing and the production of the proimmune cytokines interferon-gamma and TNF-alpha.
By digging deeper into the mechanism behind the improved efficacy, the researchers found that N-glycans interfered with the formation of immunological synapses. CARs rely on such synapses with tumor cells to activate the T cells and exert their functions.
The team then tried blocking N-glycan with the glucose analog 2DG. In two xenograft mouse models of pancreatic cancer, a combination of 2DG and the CAR-T cells showed the best tumor control, significantly prolonging the survival of mice compared with either single treatment alone, the team reported.
What’s more, in mice that also received 2DG, T cells that entered the tumors showed a reduced exhaustion profile with lower expression of several immune inhibitory markers such as TIM-3 and PD-1. Exhaustion of T cells, which could be caused by sustained antigen stimulation and the expression of inhibitory receptors, is a major obstacle to CAR-T cell efficacy against solid tumors.
“These findings suggest that combination with 2DG not only improves tumor clearance but might also enable CAR-T cells to evade immune checkpoint inhibition,” the researchers wrote in the study.
Beyond pancreatic cancer, the addition of 2DG also helped increase the killing of other highly glycosylated tumors that CD44v6 CAR-T alone failed to tackle, including in mice with bladder cancer and ovarian cancer.
CAR-T therapies such as Gilead Sciences’ Yescarta have demonstrated impressive results in blood cancers, and scientists are in hot pursuit of effective solutions to overcome the many barriers that stop the immunotherapy from working in solid tumors.
To tackle the problem of there being a lack of appropriate tumor-specific antigens that a CAR can target, a team at the University of Pennsylvania's Children’s Hospital of Philadelphia designed “peptide-centric” CAR-T cells to hunt down fragments of cancer-related proteins that are revealed to immune cells through antigen-presenting MHC proteins.
Canadian biotech Oncolytics Biotech is working on an oncolytic virus called pelareorep to alter the hostile tumor microenvironment that could suppress T-cell activity. Working with Mayo Clinic, the company previously showed CAR-T cells armed with the virus enhanced antitumor activity in mice with solid tumors.
The San Raffaele team now believes breaking down the sugar barrier around tumor cells represents a promising strategy to overcome solid tumors' resistance to CAR-T therapy by improving CAR-T cell activation and alleviating CAR-T cell exhaustion.
“Our findings point to the therapeutic potential of combining CAR-T cells with 2DG to counteract multiple layers of tumor resistance including the inadequate tumor engagement and the damaging effects of inhibitory pathways,” the researchers said in the study.