Chimeric antigen receptor (CAR)-T cell therapy is a revolutionary new pillar in cancer treatment. Although treatment with CAR-T cells has produced remarkable clinical responses with certain subsets of B cell leukemia or lymphoma, many challenges limit the therapeutic efficacy of CAR-T cells in solid tumors and hematological malignancies. Barriers to effective CAR-T cell therapy include severe life-threatening toxicities, modest anti-tumor activity, antigen escape, restricted trafficking, and limited tumor infiltration. In addition, the host and tumor microenvironment interactions with CAR-T cells critically alter CAR-T cell function. Furthermore, a complex workforce is required to develop and implement these treatments. In order to overcome these significant challenges, innovative strategies and approaches to engineer more powerful CAR-T cells with improved anti-tumor activity and decreased toxicity are necessary. In this review, we discuss recent innovations in CAR-T cell engineering to improve clinical efficacy in both hematological malignancy and solid tumors and strategies to overcome limitations of CAR-T cell therapy in both hematological malignancy and solid tumors.

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.

As with many immunopathologically driven diseases, the malignant T cells of cutaneous T-cell lymphomas (CTCLs), such as Sézary syndrome, display aberrant cytokine secretion patterns that contribute to pathology and disease progression. Targeting this disordered release of cytokines is complicated by the changing cytokine milieu that drives the phenotypic changes of CTCLs. Here, we characterize a novel signaling pathway that can be targeted to inhibit the secretion of cytokines by modulating either CXCR4 or CXCR4-mediated signaling. We demonstrate that upon ligation of the T-cell antigen receptor (TCR), the TCR associates with and transactivates CXCR4 via phosphorylation of S339-CXCR4 in order to activate a PREX1-Rac1-signaling pathway that stabilizes ,, and messenger RNA (mRNA) transcripts. Pharmacologic inhibition of either TCR-CXCR4 complex formation or PREX1-Rac1 signaling in primary human T cells decreased mRNA stability and inhibited secretion of IL-2, IL-4, and IL-10. Applying this knowledge to Sézary syndrome, we demonstrate that targeting various aspects of this signaling pathway blocks both TCR-dependent and TCR-independent cytokine secretion from a Sézary syndrome-derived cell line and patient isolates. Together, these results identify multiple aspects of a novel TCR-CXCR4-signaling pathway that could be targeted to inhibit the aberrant cytokine secretion that drives the immunopathogenesis of Sézary syndrome and other immunopathological diseases.

Purpose of review Chimeric antigen receptor (CAR)-T-cell therapy is a revolutionary tool in the treatment of cancer. CAR-T cells exhibit their effector functions through the recognition of their specific antigens on tumor cells and recruitment of other immune cells. However, this therapy is limited by the development of severe toxicities and modest antitumor activity in solid tumors. The host and tumor microenvironment interactions with CAR-T cells play an important role in orchestrating CAR-T-cell functions. Specifically, myeloid lineage cells and their cytokines critically influence the behavior of CAR-T cells. Here, we review the specific effects of myeloid cell interactions with CAR-T cells, their impact on CAR-T-cell response and toxicities, and potential efforts to modulate myeloid cell effects to enhance CAR-T-cell therapy efficacy and reduce toxicities. Recent findings Independent studies and correlative science from clinical trials indicate that inhibitory myeloid cells and cytokines contribute to the development of CAR-T-cell-associated toxicities and impairment of their effector functions. Summary These findings illuminate a novel way to reduce CAR-T-cell-associated toxicities and enhance their efficacy through the modulation of myeloid lineage cells and inhibitory cytokines.

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The bone marrow microenvironment harbors and protects leukemic cells from apoptosis-inducing agents via mechanisms that are incompletely understood. We previously showed SDF-1 (CXCL-12), a chemokine readily abundant within the bone marrow microenvironment, induces apoptosis in acute myeloid leukemia (AML) cells that express high levels of the SDF-1 receptor CXCR4. However, differentiating osteoblasts found within this niche protect cocultured AML cells from apoptosis. Additionally, this protection was abrogated upon treatment of the differentiating osteoblasts with histone deacetylase inhibitors (HDACi). In this study, we begin to characterize and target the molecular mechanisms that mediate this osteoblast protection. Quantitative RT-PCR revealed that HDACi treatment of differentiating osteoblasts (mouse MC3T3 osteoblast cell line) reduced expression of multiple genes required for osteoblast differentiation, including genes important for producing mineralized bone matrix. Interestingly, pretreating differentiating osteoblasts with cyclosporine A, a drug known to inhibit osteoblast differentiation, similarly impaired osteoblast-mediated protection of cocultured AML cells (KG1a and U937 human AML cell lines). Both HDACi and cyclosporine A reduced osteoblast expression of the key mineralization enzyme tissue-nonspecific alkaline phosphatase (TNAP; encoded by ). Moreover, specifically reducing TNAP expression or activity in differentiating osteoblasts significantly impaired the ability of the osteoblasts to protect cocultured AML cells. Together, our results indicate that inhibiting osteoblast matrix mineralization by specifically targeting TNAP is sufficient to significantly impair osteoblast-mediated protection of AML cells. Therefore, designing combination therapies that additionally target the osteoblast-produced mineralized bone matrix may improve treatment of AML by reducing the protection of leukemic cells within the bone marrow microenvironment.

Chimeric antigen receptor (CAR)-T cell therapy is an emerging staple in the treatment of certain hematological malignancies. While CAR-T cells have produced robust responses in certain hematological malignancies, toxicities associated with the therapy have limited their use. Immune Effector Cell Associated Neurotoxicity Syndrome (ICANS) is a potentially life-threatening neurotoxicity that commonly occurs with CAR-T cell therapy. Here we will discuss ICANS, its treatment, possible mechanisms, and potential solutions to this critical limitation of CAR-T cell therapy. As the field of CAR-T cell therapy evolves, improved treatments and methods to circumvent or overcome ICANS are necessary to improve morbidity, mortality, and decrease the cost of CAR-T cell therapy. This serious, life-threatening side effect needs to be studied to better understand its mechanisms and develop treatments and alternative strategies.