Oligoclonal T Cells Transiently Expand And Express Tim3 And Lag3 Following Cd19 Car T Cell Therapy.

e19017 Background: CAR T therapies targeted towards the CD19 antigen have shown tremendous promise in the treatment of multiple B cell malignancies. However, not all B cell malignancies show the same degree of response; B cell lymphomas such as DLBCL have been more resistant to CAR T-mediated lysis. The reasons for the higher treatment failures and relapse rates in this setting are poorly understood which prompts investigation into the dynamics of T cell responses following CAR T infusion. Methods: Peripheral blood was collected from a single DLBCL patient enrolled on a single-patient compassion-use CAR T cell protocol utilizing a single chain CD19 with 4-1BB co-stimulatory signaling domain (NCT02445248 IND 16130). Blood samples were obtained prior to and on day 1, 8, 17, 24, 31, and 58 post-CAR T infusion. A bone marrow aspirate was collected on day 58. Mononuclear cells were collected by ficoll gradient and cryopreserved. Flow cytometry was performed on thawed samples to identify CAR T cells and surface markers. TCR sequencing was performed using the ImmunoSeq platform on an additional sample from each time point. Results: TCR sequencing revealed distinct waves of oligoclonal T cells within the first two months following CAR T therapy. A population of T cells expressing Vβ 20 appeared early following CAR T infusion and contracted by day 17. Additionally, a population of cells expressing Vβ 27.1 also expanded at the peak of the response (D8), but remained at a high frequency up to two months post-treatment. A third wave of T cells expressing Vβ 7.3 expanded in the blood and marrow on day 58. The expression of TIM3 and LAG3 also changed over time. TIM3 was expressed predominantly in the CD8 compartment while LAG3 expression was limited to the CD4 compartment. Expression of both increased at peak and decreased over time. Low levels of PD-1 expression were detected in contrast to the much higher levels of TIM3. Conclusions: The waves of oligoclonal T cell expansion and dynamic expression of TIM3 and LAG3 provide further insight into the CAR T response and may provide new possible targets for supportive therapies that can enhance the overall response. Clinical trial information: NCT02445248.