T helper 17 (Th17) cells have a prominent role in autoimmune diseases. In contrast, the nature of these cells in cancer is controversial, with either pro- or antitumorigenic activities depending on various cancer settings. Chronic lymphocytic leukemia (CLL), a B-cell malignancy, is characterized by an imbalance in T-cell immune responses that contributes to disease progression and increased mortality. Many clinical reports indicate an increase in Th17 cells and/or interleukin 17 serum cytokine levels in patients with CLL compared with healthy individuals, which correlates with various prognostic markers and significant changes in the tumor microenvironment. The exact mechanisms by which Th17 cells might contribute to CLL progression remain poorly investigated. In this review, we provide an updated presentation of the clinical information related to the significance of Th17 cells in CLL and their interaction with the complex leukemic microenvironment, including various mediators, immune cells, and nonimmune cells. We also address the available data regarding the effects of CLL-targeted therapies on Th17 cells and the potential of using these cells in adoptive cell therapies. Having a sound understanding of the role played by Th17 cells in CLL is crucial for designing novel therapies that can achieve immune homeostasis and maximize clinical benefits.

An unmet clinical need in chronic lymphocytic leukemia (CLL) is emerging due to the rapidly expanding group of patients with double refractory (Bruton's tyrosine kinase- and B-cell lymphoma 2-inhibitor) disease. So far, autologous T-cell–based therapies, including chimeric antigen receptor (CAR) T cells, have limited success in CLL, which has been attributed to an acquired CLL-mediated T-cell dysfunction and subset skewing toward effector cells at the expense of memory formation. T-cell responses rely on dynamic metabolic processes, particularly mitochondrial fitness. Although mitochondrial disruptions have been observed in solid tumor–infiltrating lymphocytes, their impact on T-cell immunity in lymphoproliferative disorders is unknown. Recent findings indicate that mitochondrial mass in CAR T cells correlates with CLL clinical outcomes. This prompted our investigation into the mitochondrial fitness in CLL T cells. Integrated metabolic and functional analyses revealed impaired, depolarized mitochondria across all T-cell subsets in untreated patients with CLL, leading to further ex vivo and in vivo mouse studies on the underlying signaling alterations. Multiomics profiling of transcriptome and epigenome revealed significant alterations in mitochondrial signaling, diminished adenosine monophosphate-activated protein kinase and autophagy activity, and upregulated glycolysis coupled with hyperactivation of Akt. Inhibition of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway during CLL T-cell culture induced metabolic reprogramming, enhancing mitochondrial activity, expression of peroxisome proliferator-activated receptor-gamma coactivator 1-alpha, and memory differentiation. Underscoring clinical relevance, supplementation with the PI3Kδ inhibitor idelalisib during CAR T-cell manufacturing improved persistence and long-term leukemia-free remissions in an immunocompetent murine model. Our study suggests that modulating the abnormal CLL T-cell metabolism can enhance the efficacy of autologous T-cell therapies.

Chronic lymphocytic leukemia (CLL) presents challenges in treatment despite advancements in targeted therapies, often facing resistance or relapse. Chronic inflammation plays a significant role in CLL biology, with heightened inflammatory responses and immune dysfunction. Elevated levels of inflammatory cytokines support this notion. Activating signaling pathways such as NF-κB, Phosphoinositide 3-kinase delta (PI3Kδ), and MAPK via B-cell receptors and CD40 confers advantages to leukemic lymphocytes. Our research focuses on the proinflammatory protein S100A9 in CLL progression. We previously described that patients with CLL release exosomes containing S100A9 during disease progression, correlating with NF-κB activation. S100A9, known for its role in autoimmune diseases and cancers, modulates the antitumor immune response by influencing myeloid-derived suppressor cells. Receptors for S100A9 include Toll-like receptor 4, receptor for advanced glycation end products, and extracellular matrix metalloproteinase inducer (EMMPRIN). We identified a novel molecular mechanism involving the S100A9-EMMPRIN interaction in CLL using primary cells and an in vivo CLL mouse model (Eμ-TCL1). Additionally, we developed an Eμ-TCL1/S100A9–/– mouse model and explored pharmacological targeting of S100A9 in a patient-derived xenograft model, highlighting S100A9 as a promising therapeutic target in CLL with potential clinical applications.

Although preclinical investigations have shown notable efficacy in solid tumor models utilizing in vitro-differentiated Th17 cells for adoptive cell therapy (ACT), the potential benefits of this strategy in enhancing ACT efficacy in hematological malignancies, such as chronic lymphocytic leukemia (CLL), remain unexplored. CLL is a B-cell malignancy with a clinical challenge of increased resistance to targeted therapies. T-cell therapies, including chimeric antigen receptor (CAR) T cells, have demonstrated limited success in CLL, which is attributed to CLL-mediated T-cell dysfunction and skewing toward immunosuppressive phenotypes. Herein, we illustrate the feasibility of polarizing CD4⁺ T cells from the Eμ-TCL1 murine model, the most representative model for human CLL, into Th17 phenotype, employing a protocol of T-cell activation through the inducible co-stimulator (ICOS) alongside a polarizing cytokine mixture. We demonstrate augmented memory properties of in vitro-polarized IL-17-producing T cells, and preliminary in vivo persistence in leukemia-bearing mice. Our findings gain translational relevance through successful viral transduction of Eμ-TCL1 CD4⁺ T cells with a CD19-targeted CAR construct during in vitro Th17 polarization. Th17 CAR T cells exhibited remarkable persistence upon encountering antigen-expressing target cells. This study represents the first demonstration of the potential of in vitro-differentiated Th17 cells to enhance ACT efficacy in CLL.

Phosphatidylinositol-3 kinase (PI3K) delta signaling is essential for CLL B cell survival and proliferation. Several PI3K inhibitors are approved for treatment of CLL, but PI3K inhibitor-induced alterations in T cell function have been correlated with immune-related adverse events (irAEs). Zandelisib is a novel selective PI3Kδ inhibitor in clinical development with an intermittent dosing schedule for treatment of B cell malignancies. Here, we investigated the dynamic immunomodulatory properties of zandelisib alone or in combination with BTK inhibitor ibrutinib in normal human T cells, as well as the impact of continuous dosing of zandelisib on effector and regulatory immune cells, irAEs, and survival in a preclinical CLL murine model. Normal human T cells treated ex vivo with zandelisib, ibrutinib, or both were assessed for phenotype and function. A CLL model was initiated by transferring leukemic EμTCL1 splenocytes into syngeneic wildtype recipients. CLL-bearing mice were treated with vehicle or zandelisib (50 mpk bid or 100 mpk qd) for 3 weeks (n=5 per group). Antitumor efficacy, T cell and myeloid subsets in blood, bone marrow and spleen were analyzed. Survival was also observed in a separate cohort of mice treated with zandelisib (100 mpk qd). T cell proliferation was impaired by zandelisib (250nM) and ibrutinib (100 nM) alone, with the combination further reducing T cell proliferation. Zandelisib decreased expression of suppressive markers PD-1, CTLA-4, GITR and CD39 on iTregs; however, no further decrease was observed when zandelisib was combined with ibrutinib. Zandelisib also reduced normal T cell activation and expression of immune checkpoints PD-1 and CTLA-4 on CD4+ T cells and dose dependently inhibited T cell memory differentiation ex vivo, increasing the naïve/central to effector memory ratio. Combination with ibrutinib did not further affect T cell activation, checkpoint expression or memory differentiation. In the CLL murine model, no meaningful difference was seen between bid or qd administration of zandelisib in the reduction of tumor burden (CD19+ CD5+ CLL cells). Zandelisib treatment reduced activated T cells, antigen-experienced T cells, and Tregs. Increased naïve/central to effector memory ratio was observed in treated mice, and PD-1 was downregulated on memory T cells, indicating less T cell exhaustion. Zandelisib decreased macrophages in the spleen but did not impact myeloid-derived suppressor cells. Zandelisib treatment improved survival of CLL-bearing mice significantly when compared to vehicle group (median survival of zandelisib group 140 days vs. 105 days vehicle). In conclusion, zandelisib treatment reduced Tregs, prevented terminal memory differentiation, and T-cell exhaustion—features that have been shown to permit CLL immune evasion—demonstrated antitumor efficacy, and improved overall survival in a preclinical CLL model. Citation Format: Kamira Maharaj, Melanie Mediavilla-Varela, John J. Powers, Sandra Wiley, Angimar Uriepero, Wael Gamal, Kun Jiang, Eva Sahakian, Javier Pinilla-Ibarz. Efficacy and immune profiling of PI3K delta inhibitor zandelisib (ME-401) in a preclinical chronic lymphocytic leukemia (CLL) model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5496.