Inducible T-cell receptor expression in precursor T cells for leukemia control

The role of the thymus in allogeneic bone marrow transplantation and the recovery of the peripheral T-cell compartment

As the thymus represents the primary site of T-cell development, optimal thymic function is of paramount importance for the successful reconstitution of the adaptive immunity after allogeneic hematopoietic stem cell transplantation. Thymus involutes as part of the aging process and several factors, including previous chemotherapy treatments, conditioning regimen used in preparation to the allograft, occurrence of graft-versus-host disease, and steroid therapy that impair the integrity of the thymus, thus affecting its role in supporting T-cell neogenesis. Although the pathways governing its regeneration are still poorly understood, the thymus has a remarkable capacity to recover its function after damage. Measurement of both recent thymic emigrants and T-cell receptor excision circles is valuable tools to assess thymic output and gain insights on its function. In this review, we will extensively discuss available data on factors regulating thymic function after allogeneic hematopoietic stem cell transplantation, as well as the strategies and therapeutic approaches under investigation to promote thymic reconstitution and accelerate immune recovery in transplanted patients, including the use of cytokines, sex-steroid ablation, precursor T-cells, and thymus bioengineering. Although none of them is routinely used in the clinic, these approaches have the potential to enhance thymic function and immune recovery, not only in patients given an allograft but also in other conditions characterized by immune deficiencies related to a defective function of the thymus.

Therapeutic Zfra4-10 or WWOX7-21 Peptide Induces Complex Formation of WWOX with Selective Protein Targets in Organs that Leads to Cancer Suppression and Spleen Cytotoxic Memory Z Cell Activation In Vivo

Synthetic Zfra4-10 and WWOX7-21 peptides strongly suppress cancer growth in vivo. Hypothetically, Zfra4-10 binds to the membrane Hyal-2 of spleen Z cells and activates the Hyal-2/WWOX/SMAD4 signaling for cytotoxic Z cell activation to kill cancer cells. Stimulation of membrane WWOX in the signaling complex by a WWOX epitope peptide, WWOX7-21, is likely to activate the signaling. Here, mice receiving Zfra4-10 or WWOX7-21 peptide alone exhibited an increased binding of endogenous tumor suppressor WWOX with ERK, C1qBP, NF-κB, Iba1, p21, CD133, JNK1, COX2, Oct4, and GFAP in the spleen, brain, and/or lung which led to cancer suppression. However, when in combination, Zfra4-10 and WWOX7-21 reduced the binding of WWOX with target proteins and allowed tumor growth in vivo. In addition to Zfra4-10 and WWOX7-21 peptides, stimulating the membrane Hyal-2/WWOX complex with Hyal-2 antibody and sonicated hyaluronan (HAson) induced Z cell activation for killing cancer cells in vivo and in vitro. Mechanistically, Zfra4-10 binds to membrane Hyal-2, induces dephosphorylation of WWOX at pY33 and pY61, and drives Z cell activation for the anticancer response. Thus, Zfra4-10 and WWOX7-21 peptides, HAson, and the Hyal-2 antibody are of therapeutic potential for cancer suppression.

Chimeric antigen receptor-induced BCL11B suppression propagates NK-like cell development

The transcription factor B cell CLL/lymphoma 11B (BCL11B) is indispensable for T lineage development of lymphoid progenitors. Here, we show that chimeric antigen receptor (CAR) expression during early phases of ex vivo generation of lymphoid progenitors suppressed BCL11B, leading to suppression of T cell-associated gene expression and acquisition of NK cell-like properties. Upon adoptive transfer into hematopoietic stem cell transplant recipients, CAR-expressing lymphoid progenitors differentiated into CAR-induced killer (CARiK) cells that mediated potent antigen-directed antileukemic activity even across MHC barriers. CD28 and active immunoreceptor tyrosine-based activation motifs were critical for a functional CARiK phenotype. These results give important insights into differentiation of murine and human lymphoid progenitors driven by synthetic CAR transgene expression and encourage further evaluation of ex vivo-generated CARiK cells for targeted immunotherapy.

Conditional Immortalization of Lymphoid Progenitors via Tetracycline-Regulated LMO2 Expression

Conditional immortalization of hematopoietic progenitors through lentiviral expression of selected transcription factors in hematopoietic stem and progenitor cells provides a promising tool to study stem cell and leukemia biology. In this study, to generate conditionally immortalized lymphoid progenitor (ciLP) cell lines, murine hematopoietic progenitor cells were transduced with an inducible lentiviral "all-in-one" vector expressing LMO2 under doxycycline (DOX) stimulation and the reverse tetracycline-regulated transactivator (rtTA3). For selection of LMO2-expressing ciLPs (LMO2-ciLPs) and longitudinal manipulation in T cell differentiation lymphoid conditions, we developed a robust approach based on coculture with OP9-DL1 stromal cells and improved cytokine conditions allowing a controlled balance between cell proliferation and differentiation in vitro. LMO2-ciLP cell lines with the highest proliferation, vector copy number, and similar insertion pattern were selected for LMO2 "on/off" in vitro study. LMO2 expression under DOX induction resulted in a double negative (DN) 2 differentiation arrest and a propagation of CD44⁺CD25^- myeloid cell population characterized by lymphoid and myeloid phenotypes, respectively. Both DN2 and CD44⁺CD25^- myeloid cell subpopulations expressed c-KIT, suggesting that LMO2-ciLPs were similar to uncommitted progenitors under DOX supplementation. DOX removal resulted in cessation of ectopic LMO2 expression and LMO2-ciLPs continued T cell lymphoid differentiation accompanied by c-KIT downregulation and interleukin 7 receptor expression. Switching off LMO2 expression was accompanied by increased Notch signaling and significant reduction of the CD44⁺CD25^- myeloid cell population under T cell differentiation lymphoid conditions. Although vector insertions in cooperation with LMO2 expression could influence the fate of LMO2-ciLPs and additional experiments are required to evaluate it, our approach provides a promising tool to investigate mechanisms underlying stem cell, leukemia, and lymphocyte biology, leading to novel approaches for disease modeling and therapy evaluation.

Obstacles Posed by the Tumor Microenvironment to T cell Activity: A Case for Synergistic Therapies

T cell dysfunction in solid tumors results from multiple mechanisms. Altered signaling pathways in tumor cells help produce a suppressive tumor microenvironment enriched for inhibitory cells, posing a major obstacle for cancer immunity. Metabolic constraints to cell function and survival shape tumor progression and immune cell function. In the face of persistent antigen, chronic T cell receptor signaling drives T lymphocytes to a functionally exhausted state. Here we discuss how the tumor and its microenvironment influences T cell trafficking and function with a focus on melanoma, and pancreatic and ovarian cancer, and discuss how scientific advances may help overcome these hurdles.

Generation of Genetically Engineered Precursor T-Cells From Human Umbilical Cord Blood Using an Optimized Alpharetroviral Vector Platform

Retroviral engineering of hematopoietic stem cell-derived precursor T-cells (preTs) opens the possibility of targeted T-cell transfer across human leukocyte antigen (HLA)-barriers. Alpharetroviral vectors exhibit a more neutral integration pattern thereby reducing the risk of insertional mutagenesis. Cord blood-derived CD34+ cells were transduced and differentiated into preTs in vitro. Two promoters, elongation-factor-1-short-form, and a myeloproliferative sarcoma virus variant in combination with two commonly used envelopes were comparatively assessed choosing enhanced green fluorescent protein or a third-generation chimeric antigen receptor (CAR) against CD123 as gene of interest. Furthermore, the inducible suicide gene iCaspase 9 has been validated. Combining the sarcoma virus-derived promoter with a modified feline endogenous retrovirus envelope glycoprotein yielded in superior transgene expression and transduction rates. Fresh and previously frozen CD34+ cells showed similar transduction and expansion rates. Transgene-positive cells did neither show proliferative impairment nor alteration in their lymphoid differentiation profile. The sarcoma virus-derived promoter only could express sufficient levels of iCaspase 9 to mediate dimerizer-induced apoptosis. Finally, the CD123 CAR was efficiently expressed in CD34+ cells and proved to be functional when expressed on differentiated T-cells. Therefore, the transduction of CD34+ cells with alpharetroviral vectors represents a feasible and potentially safer approach for stem cell-based immunotherapies for cancer.

Retroviral Vectors for Cancer Gene Therapy

Advances in molecular technologies have led to the discovery of many disease-related genetic mutations as well as elucidation of aberrant gene and protein expression patterns in several human diseases, including cancer. This information has driven the development of novel therapeutic strategies, such as the utilization of small molecules to target specific cellular pathways and the use of retroviral vectors to retarget immune cells to recognize and eliminate tumor cells. Retroviral-mediated gene transfer has allowed efficient production of T cells engineered with chimeric antigen receptors (CARs), which have demonstrated marked success in the treatment of hematological malignancies. As a safety point, these modified cells can be outfitted with suicide genes. Customized gene editing tools, such as clustered regularly interspaced short palindromic repeats-CRISPR-associated nucleases (CRISPR-Cas9), zinc-finger nucleases (ZFNs), or TAL-effector nucleases (TALENs), may also be combined with retroviral delivery to specifically delete oncogenes, inactivate oncogenic signaling pathways, or deliver wild-type genes. Additionally, the feasibility of retroviral gene transfer strategies to protect the hematopoietic stem cells (HSC) from the dose-limiting toxic effects of chemotherapy and radiotherapy was demonstrated. While some of these approaches have yet to be translated into clinical application, the potential implications for improved cellular replacement therapies to enhance and/or support the current treatment modalities are enormous.