Mireya Paulina Velasquez

Engager T Cells: A New Class of Antigen-specific T Cells That Redirect Bystander T Cells

Adoptive immunotherapy with antigen-specific T cells has shown promise for the treatment of malignancies. However, infused T cells are unable to redirect resident T cells, limiting potential benefit. While the infusion of bispecific T-cell engagers can redirect resident T cells to tumors, these molecules have a short half-life, and do not self amplify. To overcome these limitations, we generated T cells expressing a secretable T-cell engager specific for CD3 and EphA2, an antigen expressed on a broad range of human tumors (EphA2-ENG T cells). EphA2-ENG T cells were activated and recognized tumor cells in an antigen-dependent manner, redirected bystander T cells to tumor cells, and had potent antitumor activity in glioma and lung cancer severe combined immunodeficiency (SCID) xenograft models associated with a significant survival benefit. This new class of tumor-specific T cells, with the unique ability to redirect bystander T cells, may be a promising alternative to current immunotherapies for cancer.

Improving Care for Children With Sickle Cell Disease/Acute Chest Syndrome

BACKGROUND: Acute chest syndrome (ACS) is a leading cause of hospitalization and death of children with sickle cell disease (SCD). An evidence-based ACS/SCD guideline was established to standardize care throughout the institution in February 2008. However, by the summer of 2009 use of the guideline was inconsistent, and did not seem to have an impact on length of stay. As a result, an implementation program was developed. OBJECTIVE: This quality-improvement project evaluated the influence of the development and implementation of a clinical practice guideline for children with SCD with ACS or at risk for ACS on clinical outcomes. METHODS: Clinical outcomes of 139 patients with SCD were evaluated before and after the development of the implementation program. Outcomes included average length of stay, number of exchange transfusions, average cost per SCD admission, and documentation of the clinical respiratory score and pulmonary interventions. RESULTS: Average length of stay decreased from 5.8 days before implementation of the guideline to 4.1 days after implementation (P = .033). No patients required an exchange transfusion. Average cost per SCD admission decreased from

CD123-Engager T Cells as a Novel Immunotherapeutic for Acute Myeloid Leukemia

30 359 before guideline implementation to

T cells expressing CD19-specific Engager Molecules for the Immunotherapy of CD19-positive Malignancies.

22 368. Documentation of the clinical respiratory score increased from 31.0% before implementation to 75.5%, which is an improvement of 44.5% (P < .001). Documentation of incentive spirometry and positive expiratory pressure increased from 23.3% before implementation to 50.4%, which is an improvement of 27.1% (P < .001). CONCLUSIONS: Implementation of a guideline for children with SCD with ACS or at risk for ACS improved outcomes for patients with SCD.

T Cell-Activating Mesenchymal Stem Cells as a Biotherapeutic for HCC

Immunotherapy with CD123-specific T-cell engager proteins or with T cells expressing CD123-specific chimeric antigen receptors is actively being pursued for acute myeloid leukemia. T cells secreting bispecific engager molecules (ENG-T cells) may present a promising alternative to these approaches. To evaluate therapeutic potential, we generated T cells to secrete CD123/CD3-bispecific engager molecules. CD123-ENG T cells recognized primary acute myeloid leukemia (AML) cells and cell lines in an antigen-dependent manner as judged by cytokine production and/or tumor killing, and redirected bystander T cells to AML cells. Infusion of CD123-ENG T cells resulted in regression of AML in xenograft models conferring a significant survival advantage of treated mice in comparison to mice that received control T cells. At high effector to target ratios, CD123-ENG T cells recognized normal hematopoietic stem and progenitor cells (HSPCs) with preferential recognition of HSPCs from cord blood compared to bone marrow. We therefore introduced the CD20 suicide gene that can be targeted in vivo with rituximab into CD123-ENG T cells. The expression of CD20 did not diminish the anti-AML activity of CD123-ENG T cells, but allowed for rituximab-mediated ENG-T cell elimination. Thus, ENG-T cells coexpressing CD20 suicide and CD123 engager molecules may present a promising immunotherapeutic approach for AML.

Targeting CD19: the good, the bad, and CD81

T cells expressing chimeric antigen receptors (CARs) or the infusion of bispecific T-cell engagers (BITEs) have shown antitumor activity in humans for CD19-positive malignancies. While BITEs redirect the large reservoir of resident T cells to tumors, CAR T cells rely on significant in vivo expansion to exert antitumor activity. We have shown that it is feasible to modify T cells to secrete solid tumor antigen-specific BITEs, enabling T cells to redirect resident T cells to tumor cells. To adapt this approach to CD19-positive malignancies we now generated T cells expressing secretable, CD19-specific BITEs (CD19-ENG T cells). CD19-ENG T cells recognized tumor cells in an antigen-dependent manner as judged by cytokine production and tumor killing, and redirected bystander T cells to tumor cells. Infusion of CD19-ENG T cells resulted in regression of leukemia or lymphoma in xenograft models and a survival advantage in comparison to control mice. Genetically modified T cells expressing engager molecules may present a promising addition to current CD19-targeted immunotherapies.

CD28 and 41BB Costimulation Enhances the Effector Function of CD19-Specific Engager T Cells

The outcome for advanced stage hepatocellular carcinoma (HCC) remains poor, highlighting the need for novel therapies. Genetically modified mesenchymal stem cells (MSCs) are actively being explored as cancer therapeutics due to their inherent ability to migrate to tumor sites. We reasoned that MSCs can be genetically modified to redirect T cells to Glypican-3 (GPC3)+ HCC, and genetically modified these with viral vectors encoding a GPC3/CD3 bispecific T cell engager (GPC3-ENG), a bispecifc T cell engager specific for an irrelevant antigen (EGFRvIII), and/or costimulatory molecules (CD80 and 41BBL). Coculture of GPC3+ cells, GPC3-ENG MSCs, and T cells resulted in T cell activation, as judged by interferon γ (IFNγ) production and killing of tumor cells by T cells. Modification of GPC3-ENG MSCs with CD80 and 41BBL was required for antigen-dependent interleukin-2 (IL-2) production by T cells and resulted in faster tumor cell killing by redirected T cells. In vivo, GPC3-ENG MSCs ± costimulatory molecules had antitumor activity in the HUH7 HCC xenograft model, resulting in a survival advantage. In conclusion, MSCs genetically modified to express GPC3-ENG ± costimulatory molecules redirect T cells to GPC3+ tumor cells and have potent antitumor activity. Thus, further preclinical exploration of our modified approach to GPC3-targeted immunotherapy for HCC is warranted.

ENGAGER CELLS FOR IMMUNOTHERAPY

In this issue of Blood, Braig et al have identified a novel mechanism of CD19-targeted immune escape.1

CD123-Engager T Cells As a Novel Immunotherapeutic for AML

T cells expressing a bispecific linker coupling tumor-expressed CD19 to CD3 were more effective when also expressing CD80 and 41BBL costimulatory molecules. Such T cells had increased IFNγ and IL2 production and enhanced antitumor activity in mouse models. T cells expressing CD19-specific chimeric antigen receptors (CARs) with endodomains that encode a signaling domain derived from CD3ζ and CD28 or 41BB have potent antitumor activity in early-phase clinical studies for B-cell malignancies. Besides CD19-specific CARs, other approaches are actively being pursued to redirect T cells to CD19, including recombinant bispecific T-cell engager (BiTE) proteins or T cells genetically modified to express BiTEs [engager (ENG) T cells]. As BiTEs provide no costimulation, we investigated here if provision of costimulation through CD28 and 41BB enhances the effector function of CD19-ENG T cells. CD19-ENG T cells expressing CD80 and 41BBL on their cell surface (CD19-ENG.41BBL/CD80 T cells) were generated by retroviral transduction. CD19-ENG.41BBL/CD80 T cells retained their antigen specificity and had superior effector function compared with both unmodified T cells and CD19-ENG T cells expressing either CD80, 41BBL, or no costimulatory molecule, as judged by cytokine (IFNγ and IL2) production, T-cell proliferation, and their ability to sequentially kill target cells. In vivo, CD19-ENG.41BBL/CD80 T cells had superior antileukemia activity in the BV173 xenograft model, resulting in a survival advantage in comparison to CD19-ENG T cells. Thus, provision of costimulation is critical for the effector function of ENG T cells. Cancer Immunol Res; 5(10); 860–70. ©2017 AACR.