Cox, Michelle J.

Background:The expression of the receptor tyrosine kinase (RTK) Axl on cancer cells has been associated with poor prognosis and implicated in disease progression. Inhibition of Axl‐RTK with TP‐0903, a high affinity Axl‐RTK inhibitor induces robust apoptosis of several tumors, including chronic lymphocytic leukemia (CLL). Axl‐RTK inhibition has also been found to induce nonspecific immunomodulatory effects in syngeneic tumor models.Aims:We aimed to investigate the impact and downstream effects of Axl‐RTK inhibition on naïve T cells and chimeric antigen receptor T cells (CART), using CD19 directed CART cells (CART19) as a model.Methods:We utilized either PMA/Ionomycin or the CD19+ mantle cell lymphoma cell line, JeKo as a stimulant for naïve T cells and CART19, respectively. Cells were analyzed for cytokine profile, T cell phenotype, and kinetics after the stimulation in the presence or the absence of the Axl‐RTK inhibitor TP‐0903. Regarding in vivo experiment, a relapse JeKo xenograft model was used. Mice were treated with vehicle alone, TP‐0903 alone, CART19 alone, or TP‐0903 + CART19. Three weeks after the treatment, mice were re‐challenged with JeKo as a CART19 relapse model.Results:Stimulation of naïve T cells in the presence of the Axl‐RTK inhibitor TP‐0903 resulted in a significant reduction of Th2 cytokines and downregulation of inhibitory receptors. The differential expansion of either effector T cells or Tregs in the presence of TP‐0903 resulted in a preferential reduction of Tregs (Fig 1A). Axl‐RTK inhibition of CART19 led to Th1 polarization upon stimulation with the JeKo, as evident by the selective reduction of Th2 cytokine. Additionally, this resulted in a reduction of myeloid attracting cytokines, such as CXCL1, IL‐8, IL‐6, and IL‐10, cytokines implicated in the development cytokine release syndrome and neurotoxicity after CART cell therapy and in adaptive resistance to immunotherapy (Fig 1B). TP‐0903 also significantly downregulated inhibitory receptors on activated CARTs (Fig 1C). In our relapsed in vivo model, mice treated with CART19 + TP‐0903 rejected the JeKo challenge while mice received CART19 alone redeveloped disease, suggesting that Axl‐RTK inhibition enhanced CART cell persistence. Peripheral blood analysis of mice after the rechallenge showed a higher number of circulating T cells and lower level of MCP‐1. Western blotting was performed to investigate the downstream effect of Axl‐RTK inhibition on CART19 and it revealed a relatively selective inhibition of LCK on stimulated CART19. Transcriptome analysis of activated CARTs treated with TP‐0903 revealed >100 genes that were differentially expressed compared to untreated cells. Among these, Th cell and Treg polarization genes were significantly altered in activated CARTs treated with TP‐0903.imageFinally, we validated our findings in phase I clinical trial of TP‐0903 (NCT02729298). T cells isolated from 3 cancer patients showed a significant reduction of Tregs and Th1 polarization. This will be further investigated in a planned phase I clinical trial of TP‐0903 in relapsed/refractory CLL (NCT03572634).Summary/Conclusion:We showed for the first time that Axl‐RTK inhibition polarizes T cells into a Th1 functional phenotype, downregulates inhibitory receptors, and reduces myeloid associated cytokine production by CART19. The combination therapy yielded synergistic cytotoxicity against JeKo in vitro and in a CART19 relapse model. These findings encourage further study of Axl‐RTK inhibition with TP‐0903 as an enhancer of T cell immunotherapies.

Despite the remarkable outcomes of CD19-directed chimeric antigen receptor T (CART19) cell therapy in B-cell malignancies, the durable responses in diffuse large B-cell lymphoma are less than 40%, and strategies to enhance this response are desperately needed. Inhibition of AXL RTK with TP0903, a high-affinity AXL inhibitor has been found to induce robust apoptosis of malignant B cells. Here, we aimed to examine the role of AXL RTK inhibition with TP0903 on T-cell function in B-cell malignancies. First, we investigated the influence of TP0903 on CART19 cell phenotype and functions. Here, we used 41BB costimulated, lentiviral-transduced CART cells. AXL inhibition led to polarization of CART cells into a Th1 phenotype when T cells were stimulated with the CD19+ mantle cell lymphoma (MCL) cell line Jeko or with leukemic B cells isolated from patients with chronic lymphocytic leukemia (CLL), in the presence of TP0903 (Fig 1A). Exposure of activated CART cells to TP0903 also resulted in significant downregulation of inhibitory receptors on activated CART cells (Fig 1B), a reduction of conical cytokines known to be associated with the development of cytokine release syndrome (CRS) (Fig 1C). To investigate the effect of AXL RTK inhibition of CART cells with TP0903 in vivo, we established MCL xenografts through the injection of 1.0x106 of Jeko into NSG mice. A week later, mice were treated with either vehicle alone, TP0903 (20 mg/kg/day) alone, 0.5x106 of CART19 alone, or TP0903 (20mg/kg/day)+0.5x106 of CART19. Three weeks after the treatment, mice were rechallenged with 1.0x106 of Jeko. Mice treated with CART19 and TP0903 rejected the tumor challenge while mice previously treated with CART19 alone redeveloped MCL, suggesting that AXL inhibition enhanced CART cell persistence (Fig 1D). Finally, we validated our preclinical findings in correlative analyses of phase 1 clinical trial of TP0903 in patients with solid tumors (NCT02729298). Similar to our findings, there was a significant reduction in Tregs, reduction of inhibitory receptors and polarization to a Th1 phenotype. These findings will be further investigated in a planned phase 1 clinical trial of TP0903 in relapsed/refractory CLL (NCT03572634) In summary, we demonstrated for the first time that AXL inhibition polarizes T cells into a Th1 phenotype, downregulates inhibitory receptors, and synergizes with CART cells in B-cell malignancies. These findings encourage further study of TP0903 as an enhancer of T-cell immunotherapies.

Background: Unprecedented clinical outcomes were reported after CD19 chimeric antigen receptor T-cell (CART19) therapy. However, the complete response rate in chronic lymphocytic leukemia (CLL) is much lower, at approximately 20%–30%. Several immune defects have been identified in CLL that result from the complex interaction between CLL cells and the microenvironment. This leukemic microenvironment is rich with extracellular vesicles (EVs) secreted by B-CLL cells. Here, we aimed to investigate the role of EVs play in the diminished CART response seen in some CLL patients. Methods: EVs were isolated from peripheral blood of 16 patients with untreated CLL at different Rai stages and risk profile by FISH. Cytometry was used to determine size, number of particles per μl, and CD19 expression. To investigate the impact of EVs on CAR T-cell functions, CART19 cells were stimulated with either CLL B cells or the CD19-positive cell line JEKO and different effector functions were analyzed. Results: Two patterns of EVs in CLL patients were identified; a single versus 2 distinct EV populations, characterized by size (small [EVssmall] and large [EVslarge], Fig 1A). In 25% of patients, EVs were CD19 positive (EVCD19+). CD19 positivity was detected only in patients with the EVslarge (Fig 1B). The EVs concentration, CD19 expression (EVsCD19+ vs EVsCD19-), or the size (EVssmall vs EVslarge) did not correlate with disease stage (early vs advanced Rai stage) or risk profile of CLL (low vs high risk). To investigate our hypothesis that EVs could modulate CART19 function, CART19 cell effector functions were examined in the presence of EVsCD19+, EVsCD19-, EVssmall, or EVslarge. EVs alone were insufficient to stimulate CART19 cells. However when CART19 cells were stimulated with the CD19-positive cell line JEKO, their effector functions were reduced only in the presence of EVsCD19+ but not EVsCD19-. This included a significant reduction in CART-specific killing (Fig 1C) and a reduction in cytokine production. The impairment of CART cell functions was independent of the size of EVs, ie, there was no impairment of CART functions with large or small size EVCD19- in co-culture. Conclusion: We identify CD19-positive large size EVs from patients with CLL and demonstrate that these EVs play a role in the leukemic microenvironment by reducing CAR T-cell activity. Studies are ongoing to define the mechanism(s).

Abstract Chimeric antigen receptor T (CAR-T) cell therapy is a new pillar in cancer therapeutics; however, its application is limited by the associated toxicities. These include cytokine release syndrome (CRS) and neurotoxicity. Although the IL-6R antagonist tocilizumab is approved for treatment of CRS, there is no approved treatment of neurotoxicity associated with CD19-targeted CAR-T (CART19) cell therapy. Recent data suggest that monocytes and macrophages contribute to the development of CRS and neurotoxicity after CAR-T cell therapy. Therefore, we investigated neutralizing granulocyte-macrophage colony-stimulating factor (GM-CSF) as a potential strategy to manage CART19 cell–associated toxicities. In this study, we show that GM-CSF neutralization with lenzilumab does not inhibit CART19 cell function in vitro or in vivo. Moreover, CART19 cell proliferation was enhanced and durable control of leukemic disease was maintained better in patient-derived xenografts after GM-CSF neutralization with lenzilumab. In a patient acute lymphoblastic leukemia xenograft model of CRS and neuroinflammation (NI), GM-CSF neutralization resulted in a reduction of myeloid and T cell infiltration in the central nervous system and a significant reduction in NI and prevention of CRS. Finally, we generated GM-CSF–deficient CART19 cells through CRISPR/Cas9 disruption of GM-CSF during CAR-T cell manufacturing. These GM-CSFk/o CAR-T cells maintained normal functions and had enhanced antitumor activity in vivo, as well as improved overall survival, compared with CART19 cells. Together, these studies illuminate a novel approach to abrogate NI and CRS through GM-CSF neutralization, which may potentially enhance CAR-T cell function. Phase 2 studies with lenzilumab in combination with CART19 cell therapy are planned.