Tandem Meetings 2026 | Investigating the integration of low-dose TBI into lymphodepletion to enhance CAR-T efficacy in LBCL

The CD19 CAR T-cells are very effective in treating large B-cell lymphoma and provide a cure to a significant portion of patients. However, unfortunately, about 50%, close to 50%, of our patients do experience relapse. It usually happens within the first year after the CAR T infusion. Approaches and strategies to improve the outcomes of CAR T-cells are an unmet need, and the one that we presented in this study is exploring the impact of low-dose radiation shaped by a low-dose TBI at one gray on the behavior and the outcomes of CD19 CAR T-cells in the mouse model. 

And in this syngeneic mouse model, in which the mice were immunocompetent, the mice were given a lymphoma, mouse lymphoma, and then treated with mouse-generated CAR T-cells as well. And then that’s the control group. And then the intervention group received additional low-dose total body radiation just prior to the CAR-T infusion to study the impact of the radiation addition. And the outcomes of this experiment were striking in a sense of the mice who received the combination of low-dose TBI and CAR T-cells demonstrated better disease control and went into remission and then lived longer. While the mice that received only CAR T-cells succumbed to the disease and died pretty quickly after. 

And to further understand the impact of this, we performed additional experimentations that include first examining or testing the CAR-T level in the blood of the mice who received radiation and CAR-T cells. And we established that the mice that received radiation and CAR-T cells demonstrated two to three-fold higher of the CAR-T presence in peripheral blood compared to mice that did not receive radiation. And the other thing was testing the cytokines profile of these mice and seeing if there is any specific signal. And what we saw in this experiment is a significant increase in interferon gamma and CCL2, both cytokines and chemokines that are known for their inflammatory characteristics and also for intratumoral trafficking and intratumoral migration of the CAR T-cells. 

Additionally, in this experiment, particularly, we examined the intratumoral trafficking or the migration of the CAR T-cells to inside the tumor tissue following radiation. And that’s an additional experiment with the same syngeneic model. And we found that the mice that receive radiation, a combination of radiation and CAR T-cells, CD19 CAR T-cells, demonstrated better intratumoral trafficking and migration of the CAR T-cells inside the tumor tissue. And one additional experiment is looking at the CAR-T persistence, and that was demonstrated by a basal aplasia since the CD19 CAR-T does not differentiate between lymphoma cells and indigenous B-cells. So B-cell aplasia is a good surrogate marker to follow in these mice. And the long surviving mice demonstrated B-cell aplasia all along, suggestive CAR-T presence. And after sacrificing these animals, the CAR T-cells were still present in the liver and the spleen, demonstrated by flow cytometry and additional testing suggested that the combination of radiation CAR-T contributed to longevity of the CAR T-cells. 

And lastly, in a group of these mice we were also interested in understanding the impact on the T-cell subset and if there’s any preferential expansion of a certain subset that could explain the benefit of adding radiation. And in this group of mice, the spleens were harvested after radiation and CAR T-cells compared to mice that received only CAR T-cells. And then the T-cells was collected and we performed a single cell RNA sequencing in these cohorts. And what we found is that the T-cells were more enriched in the group that received radiation. And additionally, there was a preferential expansion of a specific T-cell subset called effector cytotoxic T-cell subset, which is now known over the last couple of years that this particular CD4 subset is associated with superior antitumor characteristics. And additionally, we found that among the CAR-positive, through the single-cell sequencing, among the CAR-positive T-cells, there was a decrease in the CAR-positive regulatory T-cells in the group that received radiation compared to the mice that received only CAR T-cells. 

So there are potentially many mechanisms that could explain the improvement in the outcomes of the CAR T-cells when radiation is used in this platform. I think this preclinical study suggests that this approach can be used prospectively in humans, in phase one, two trials and open the door to a new strategy to hopefully improve the outcomes of CAR T-cells in lymphoma for our lymphoma patients and reduce the chances of relapse by the first year.

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