INSPIRED Symposium Part 5: Expanding the Use of CAR T Cells in Children and Young Adults

Chimeric antigen receptor (CAR) T cell therapy has demonstrated remarkable efficacy in relapsed/refractory (r/r) B cell malignancies, including in pediatric patients with acute lymphoblastic leukemia (ALL). Expanding this success to other hematologic and solid malignancies is an area of active research and, although challenges remain, novel solutions have led to significant progress over the past decade. Ongoing clinical trials for CAR T cell therapy for T cell malignancies and acute myeloid leukemia (AML) have highlighted challenges, including antigen specificity with off-tumor toxicity and persistence concerns. In T cell malignancies, notable challenges include CAR T cell fratricide and prolonged T cell aplasia, which are being addressed with strategies such as gene editing and suicide switch technologies. In AML, antigen identification remains a significant barrier, due to shared antigens across healthy hematopoietic progenitor cells and myeloid blasts. Strategies to limit persistence and circumvent the immunosuppressive tumor microenvironment (TME) created by AML are also being explored. CAR T cell therapies for central nervous system and solid tumors have several challenges, including tumor antigen heterogeneity, immunosuppressive and hypoxic TME, and potential for off-target toxicity. Numerous CAR T cell products have been designed to overcome these challenges, including "armored" CARs and CAR/T cell receptor (TCR) hybrids. Strategies to enhance CAR T cell delivery, augment CAR T cell performance in the TME, and ensure the safety of these products have shown promising results. In this manuscript, we will review the available evidence for CAR T cell use in T cell malignancies, AML, central nervous system (CNS), and non-CNS solid tumor malignancies, and recommend areas for future research.

Chimeric antigen receptor T cells march into T cell malignancies

T cell malignancies represent a diverse collection of leukemia/lymphoma conditions in humans arising from aberrant T cells. Such malignancies are often associated with poor clinical prognoses, cancer relapse, as well as progressive resistance to anti-cancer treatments. While chimeric antigen receptor (CAR) T cell immunotherapy has emerged as a revolutionary treatment strategy that is highly effective for treating B cell malignancies, its application as a treatment for T cell malignancies remains to be better explored. Furthermore, the effectiveness of CAR-T treatment in T cell malignancies is significantly influenced by the quality of contamination-free CAR-T cells during the manufacturing process, as well as by multiple characteristics of such malignancies, including the sharing of antigens across normal and malignant T cells, fratricide, and T cell aplasia. In this review, we provide a detailed account of the current developments in the clinical application of CAR-T therapy to treat T cell malignancies, offer strategies for addressing current challenges, and outline a roadmap toward its effective implementation as a broad treatment option for this condition.

Orchestral role of lipid metabolic reprogramming in T-cell malignancy

The immune function of normal T cells partially depends on the maneuvering of lipid metabolism through various stages and subsets. Interestingly, T-cell malignancies also reprogram their lipid metabolism to fulfill bioenergetic demand for rapid division. The rewiring of lipid metabolism in T-cell malignancies not only provides survival benefits but also contributes to their stemness, invasion, metastasis, and angiogenesis. Owing to distinctive lipid metabolic programming in T-cell cancer, quantitative, qualitative, and spatial enrichment of specific lipid molecules occur. The formation of lipid rafts rich in cholesterol confers physical strength and sustains survival signals. The accumulation of lipids through de novo synthesis and uptake of free lipids contribute to the bioenergetic reserve required for robust demand during migration and metastasis. Lipid storage in cells leads to the formation of specialized structures known as lipid droplets. The inimitable changes in fatty acid synthesis (FAS) and fatty acid oxidation (FAO) are in dynamic balance in T-cell malignancies. FAO fuels the molecular pumps causing chemoresistance, while FAS offers structural and signaling lipids for rapid division. Lipid metabolism in T-cell cancer provides molecules having immunosuppressive abilities. Moreover, the distinctive composition of membrane lipids has implications for immune evasion by malignant cells of T-cell origin. Lipid droplets and lipid rafts are contributors to maintaining hallmarks of cancer in malignancies of T cells. In preclinical settings, molecular targeting of lipid metabolism in T-cell cancer potentiates the antitumor immunity and chemotherapeutic response. Thus, the direct and adjunct benefit of lipid metabolic targeting is expected to improve the clinical management of T-cell malignancies.

Targeting lysosomal HSP70 induces acid sphingomyelinase-mediated disturbance of lipid metabolism and leads to cell death in T cell malignancies

BACKGROUND

T cell malignancies proliferate vigorously, are highly dependent on lysosomal function, with limited therapeutic options. Deregulation of lysosomal structure and function has been confirmed to be a key role in the treatment of hematologic malignant disease.

METHODS

Cell counting kit 8 and Annexin V/PI staining were used to assess the cell viability and apoptosis rate. Flow cytometry, liquid chromatography mass spectrometry, immunofluorescence and western blot were performed to detect the effect on lysosomes. Drug affinity responsive target stability, molecular docking and cellular thermal shift assay were employed to confirm the target protein of V8 on lysosomes. A xenograft model was constructed in NOD/SCID mice to assess the effect and mechanism.

RESULTS

V8, a new lysosomotropic compound, could be rapidly trapped by lysosomes and accumulation in lysosomes, contributing to lysosomal-dependent cell death by evoking lysosomal membrane permeabilization (LMP), accompanied with disrupted lysosome and autophagic flux. Mechanistically, heat shock protein 70 (HSP70) was identified as the binding target of V8 in lysosome. As a downstream effect of targeting HSP70, enzymatic activity of acid sphingomyelinase (ASM) was inhibited, which induced disturbance of lipid metabolism, instability of lysosomal membrane, and leakage of cathepsin B and D, leading to LMP-mediated cell death. In vivo study showed V8 well controlled the growth of the tumour and confirmed lysosomal cell death induced by V8.

CONCLUSIONS

Collectively, this study suggests targeting lysosomal HSP70-ASM axis by V8 illustrates the great value of drug therapy for T cell malignancies and the unlimited potential of lysosomal targeting for cancer therapy.

Feasibility and preclinical efficacy of CD7-unedited CD7 CAR T cells for T cell malignancies

Chimeric antigen receptor (CAR)-mediated targeting of T lineage antigens for the therapy of blood malignancies is frequently complicated by self-targeting of CAR T cells or their excessive differentiation driven by constant CAR signaling. Expression of CARs targeting CD7, a pan-T cell antigen highly expressed in T cell malignancies and some myeloid leukemias, produces robust fratricide and often requires additional mitigation strategies, such as CD7 gene editing. In this study, we show fratricide of CD7 CAR T cells can be fully prevented using ibrutinib and dasatinib, the pharmacologic inhibitors of key CAR/CD3ζ signaling kinases. Supplementation with ibrutinib and dasatinib rescued the ex vivo expansion of unedited CD7 CAR T cells and allowed regaining full CAR-mediated cytotoxicity in vitro and in vivo on withdrawal of the inhibitors. The unedited CD7 CAR T cells persisted long term and mediated sustained anti-leukemic activity in two mouse xenograft models of human T cell acute lymphoblastic leukemia (T-ALL) by self-selecting for CD7-, fratricide-resistant CD7 CAR T cells that were transcriptionally similar to control CD7-edited CD7 CAR T cells. Finally, we showed feasibility of cGMP manufacturing of unedited autologous CD7 CAR T cells for patients with CD7+ malignancies and initiated a phase I clinical trial (ClinicalTrials.gov: NCT03690011) using this approach. These results indicate pharmacologic inhibition of CAR signaling enables generating functional CD7 CAR T cells without additional engineering.

The rational development of CD5-targeting biepitopic CARs with fully human heavy-chain-only antigen recognition domains

T cell malignancies are a group of hematologic cancers with high recurrence and mortality rates. CD5 is highly expressed in ∼85% of T cell malignancies, although normal expression of CD5 is restricted to thymocytes, T cells, and B1 cells. However, CD5 expression on chimeric antigen receptor (CAR)-T cells leads to CAR-T cell fratricide. Once this limitation is overcome, CD5-targeting CAR-T therapy could be an attractive strategy to treat T cell malignancies. Here, we report the selection of novel CD5-targeting fully human heavy-chain variable (FHV_H) domains for the development of a biepitopic CAR, termed FHV_H3/V_H1, containing FHV_H1 and FHV_H3, which were validated to bind different epitopes of the CD5 antigen. To prevent fratricide in CD5 CAR-T cells, we optimized the manufacturing procedures of a CRISPR-Cas9-based CD5 knockout (CD5KO) and lentiviral transduction of anti-CD5 CAR. In vitro and in vivo functional comparisons demonstrated that biepitopic CD5KO FHV_H3/V_H1 CAR-T cells exhibited enhanced and longer lasting efficacy; produced moderate levels of cytokine secretion; showed similar specificity profiles as either FHV_H1, FHV_H3, or the clinically tested H65; and is therefore suitable for further development.

Characterization of an Anti-CD5 Directed CAR T-Cell against T-Cell Malignancies

T-cell malignancies often result in poor prognosis and outcome for patients. Immunotherapy has recently emerged as a revolutionary treatment against cancer, and the success seen in CD19 CAR clinical trials may extend to T cell diseases. However, a shared antigen pool coupled with the impact of T-cell depletion incurred by targeting T cell disease remain concepts to be clinically explored with caution. Here we report on the ability of T cells transduced with a CD5CAR to specifically and potently lyse malignant T-cell lines and primary tumors in vitro in addition to significantly improving in vivo control and survival of xenograft models of T-ALL. To extensively explore and investigate the biological properties of a CD5 CAR, we evaluated multiple CD5 CAR constructs and constructed 3 murine models to characterize the properties of CD5 down-regulation, the efficacy and specificity produced by different CD5 CAR construct designs, and the impact of incorporating a CD52 safety switch using CAMPATH to modulate the persistency and function of CAR cells. These data support the potential use of CD5CAR T cells in the treatment of T cell malignancies or refractory disease in clinical settings.

Single-Cell RNA-seq Reveals Characteristics of Malignant Cells and Immune Microenvironment in Subcutaneous Panniculitis-Like T-Cell Lymphoma

Background

Subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is a malignant primary T-cell lymphoma that is challenging to distinguish from autoimmune disorders and reactive panniculitides. Delay in diagnosis and a high misdiagnosis rate affect the prognosis and survival of patients. The difficulty of diagnosis is mainly due to an incomplete understanding of disease pathogenesis.

Methods

We performed single-cell RNA sequencing of matched subcutaneous lesion tissue, peripheral blood, and bone marrow from a patient with SPTCL, as well as peripheral blood, bone marrow, lymph node, and lung tissue samples from healthy donors as normal controls. We conducted cell clustering, gene expression program identification, gene differential expression analysis, and cell-cell interaction analysis to investigate the ecosystem of SPTCL.

Results

Based on gene expression profiles in a single-cell resolution, we identified and characterized the malignant cells and immune subsets from a patient with SPTCL. Our analysis showed that SPTCL malignant cells expressed a distinct gene signature, including chemokines families, cytotoxic proteins, T cell immune checkpoint molecules, and the immunoglobulin family. By comparing with normal T cells, we identified potential novel markers for SPTCL (e.g., CYTOR, CXCL13, VCAM1, and TIMD4) specifically differentially expressed in the malignant cells. We also found that macrophages and fibroblasts dominated the cell-cell communication landscape with the SPTCL malignant cells.

Conclusions

This work offers insight into the heterogeneity of subcutaneous panniculitis-like T-cell lymphoma, providing a better understanding of the transcription characteristics and immune microenvironment of this rare tumor.

Targeting T Cell Malignancies Using CD4CAR T-Cells and Implementing a Natural Safety Switch

T cell malignancies are aggressive diseases with no standard treatment available, often resulting in poor patient outcomes. Lately, the recent FDA approval of a CD19 CAR T cell therapy for B cell acute lymphoblastic leukemia has earned nationwide attention, leading to the possibility that success of CD19 CAR therapy can be extended to T cell malignancies. However, the impact of T cell depletion due to a shared antigen pool remains an issue to be resolved. Here, we describe a CD4CAR capable of eliminating CD4-positive T cell acute lymphoblastic leukemia in a systemic mouse model, with CAMPATH (alemtuzumab) as a natural safety switch to deplete the infused CD4CAR T cells to prevent toxicities associated with CD4 cell aplasia. Our data support the potential use of CD4CAR T cells for the treatment of CD4-postive T-cell acute lymphoblastic leukemia malignancies or refractory disease in clinical settings.

2B4 costimulatory domain enhancing cytotoxic ability of anti-CD5 chimeric antigen receptor engineered natural killer cells against T cell malignancies

BACKGROUND

Chimeric antigen receptor engineered T cells (CAR-T) have demonstrated extraordinary efficacy in B cell malignancy therapy and have been approved by the US Food and Drug Administration for diffuse large B cell lymphoma and acute B lymphocytic leukemia treatment. However, treatment of T cell malignancies using CAR-T cells remains limited due to the shared antigens between malignant T cells and normal T cells. CD5 is considered one of the important characteristic markers of malignant T cells and is expressed on almost all normal T cells but not on NK-92 cells. Recently, NK-92 cells have been utilized as CAR-modified immune cells. However, in preclinical models, CAR-T cells seem to be superior to CAR-NK-92 cells. Therefore, we speculate that in addition to the short lifespan of NK-92 cells in mice, the costimulatory domain used in CAR constructs might not be suitable for CAR-NK-92 cell engineering.

METHODS

Two second-generation anti-CD5 CAR plasmids with different costimulatory domains were constructed, one using the T-cell-associated activating receptor-4-1BB (BB.z) and the other using a NK-cell-associated activating receptor-2B4 (2B4.z). Subsequently, BB.z-NK and 2B4.z-NK were generated. Specific cytotoxicity against CD5⁺ malignant cell lines, primary CD5⁺ malignant cells, and normal T cells was evaluated in vitro. Moreover, a CD5⁺ T cell acute lymphoblastic leukemia (T-ALL) mouse model was established and used to assess the efficacy of CD5-CAR NK immunotherapy in vivo.

RESULTS

Both BB.z-NK and 2B4.z-NK exhibited specific cytotoxicity against CD5⁺ malignant cells in vitro and prolonged the survival of T-ALL xenograft mice. Encouragingly, 2B4.z-NK cells displayed greater anti-CD5⁺ malignancy capacity than that of BB.z-NK, accompanied by a greater direct lytic side effect versus BB.z-NK.

CONCLUSIONS

Anti-CD5 CAR-NK cells, particularly those constructed with the intracellular domain of NK-cell-associated activating receptor 2B4, may be a promising strategy for T cell malignancy treatment.

2B4 costimulatory domain enhancing cytotoxic ability of anti-CD5 chimeric antigen receptor engineered natural killer cells against T cell malignancies

BACKGROUND

Chimeric antigen receptor engineered T cells (CAR-T) have demonstrated extraordinary efficacy in B cell malignancy therapy and have been approved by the US Food and Drug Administration for diffuse large B cell lymphoma and acute B lymphocytic leukemia treatment. However, treatment of T cell malignancies using CAR-T cells remains limited due to the shared antigens between malignant T cells and normal T cells. CD5 is considered one of the important characteristic markers of malignant T cells and is expressed on almost all normal T cells but not on NK-92 cells. Recently, NK-92 cells have been utilized as CAR-modified immune cells. However, in preclinical models, CAR-T cells seem to be superior to CAR-NK-92 cells. Therefore, we speculate that in addition to the short lifespan of NK-92 cells in mice, the costimulatory domain used in CAR constructs might not be suitable for CAR-NK-92 cell engineering.

METHODS

Two second-generation anti-CD5 CAR plasmids with different costimulatory domains were constructed, one using the T-cell-associated activating receptor-4-1BB (BB.z) and the other using a NK-cell-associated activating receptor-2B4 (2B4.z). Subsequently, BB.z-NK and 2B4.z-NK were generated. Specific cytotoxicity against CD5⁺ malignant cell lines, primary CD5⁺ malignant cells, and normal T cells was evaluated in vitro. Moreover, a CD5⁺ T cell acute lymphoblastic leukemia (T-ALL) mouse model was established and used to assess the efficacy of CD5-CAR NK immunotherapy in vivo.

RESULTS

Both BB.z-NK and 2B4.z-NK exhibited specific cytotoxicity against CD5⁺ malignant cells in vitro and prolonged the survival of T-ALL xenograft mice. Encouragingly, 2B4.z-NK cells displayed greater anti-CD5⁺ malignancy capacity than that of BB.z-NK, accompanied by a greater direct lytic side effect versus BB.z-NK.

CONCLUSIONS

Anti-CD5 CAR-NK cells, particularly those constructed with the intracellular domain of NK-cell-associated activating receptor 2B4, may be a promising strategy for T cell malignancy treatment.

Novel anti-CD3 chimeric antigen receptor targeting of aggressive T cell malignancies

Peripheral T-cell lymphomas (PTCLS) comprise a diverse group of difficult to treat, very aggressive non-Hodgkin's lymphomas (NHLS) with poor prognoses and dismal patient outlook. Despite the fact that PTCLs comprise the majority of T-cell malignancies, the standard of care is poorly established. Chimeric antigen receptor (CAR) immunotherapy has shown in B-cell malignancies to be an effective curative option and this extends promise into treating T-cell malignancies. Because PTCLS frequently develop from mature T-cells, CD3 is similarly strongly and uniformly expressed in many PTCL malignancies, with expression specific to the hematological compartment thus making it an attractive target for CAR design. We engineered a robust 3^rd generation anti-CD3 CAR construct (CD3CAR) into an NK cell line (NK-92). We found that CD3CAR NK-92 cells specifically and potently lysed diverse CD3⁺ human PTCL primary samples as well as T-cell leukemia cells lines ex vivo. Furthermore, CD3CAR NK-92 cells effectively controlled and suppressed Jurkat tumor cell growth in vivo and significantly prolonged survival. In this study, we present the CAR directed targeting of a novel target - CD3 using CAR modified NK-92 cells with an emphasis on efficacy, specificity, and potential for new therapeutic approaches that could improve the current standard of care for PTCLs.

Illegitimate V(D)J recombination-mediated deletions in Notch1 and Bcl11b are not sufficient for extensive clonal expansion and show minimal age or sex bias in frequency or junctional processing

Illegitimate V(D)J recombination at oncogenes and tumor suppressor genes is implicated in formation of several T cell malignancies. Notch1 and Bcl11b, genes involved in developing T cell specification, selection, proliferation, and survival, were previously shown to contain hotspots for deletional illegitimate V(D)J recombination associated with radiation-induced thymic lymphoma. Interestingly, these deletions were also observed in wild-type animals. In this study, we conducted frequency, clonality, and junctional processing analyses of Notch1 and Bcl11b deletions during mouse development and compared results to published analyses of authentic V(D)J rearrangements at the T cell receptor beta (TCRβ) locus and illegitimate V(D)J deletions observed at the human, nonimmune HPRT1 locus not involved in T cell malignancies. We detect deletions in Notch1 and Bcl11b in thymic and splenic T cell populations, consistent with cells bearing deletions in the circulating lymphocyte pool. Deletions in thymus can occur in utero, increase in frequency between fetal and postnatal stages, are detected at all ages examined between fetal and 7 months, exhibit only limited clonality (contrasting with previous results in radiation-sensitive mouse strains), and consistent with previous reports are more frequent in Bcl11b, partially explained by relatively high Recombination Signal Information Content (RIC) scores. Deletion junctions in Bcl11b exhibit greater germline nucleotide loss, while in Notch1 palindromic (P) nucleotides are more abundant, although average P nucleotide length is similar for both genes and consistent with results at the TCRβ locus. Non-templated (N) nucleotide insertions appear to increase between fetal and postnatal stages for Notch1, consistent with normal terminal deoxynucleotidyl transferase (TdT) activity; however, neonatal Bcl11b junctions contain elevated levels of N insertions. Finally, contrasting with results at the HPRT1 locus, we find no obvious age or gender bias in junctional processing, and inverted repeats at recessed coding ends (Pr nucleotides) correspond mostly to single-base additions consistent with normal TdT activity.