Receptor affinity and extracellular domain modifications affect tumor recognition by ROR1-specific chimeric antigen receptor T cells

Antigen-Specific T-Cell Activation Independently of the MHC: Chimeric Antigen Receptor-Redirected T Cells

Adoptive T-cell therapy has recently shown promise in initiating a lasting anti-tumor response with spectacular therapeutic success in some cases. Specific T-cell therapy, however, is limited since a number of cancer cells are not recognized by T cells due to various mechanisms including the limited availability of tumor-specific T cells and deficiencies in antigen processing or major histocompatibility complex (MHC) expression of cancer cells. To make adoptive cell therapy applicable for the broad variety of cancer entities, patient's T cells are engineered ex vivo with pre-defined specificity by a recombinant chimeric antigen receptor (CAR) which consists in the extracellular part of an antibody-derived domain for binding with a "tumor-associated antigen" and in the intracellular part of a T-cell receptor (TCR)-derived signaling moiety for T-cell activation. The specificity of CAR-mediated T-cell recognition is defined by the antibody domain, is independent of MHC presentation and can be extended to any target for which an antibody is available. We discuss the advantages and limitations of MHC-independent T-cell targeting by an engineered CAR in comparison to TCR modified T cells and the impact of the CAR activation threshold on redirected T-cell activation. Finally we review most significant progress recently made in early stage clinical trials to treat cancer.

T lymphocytes expressing a CD16 signaling receptor exert antibody-dependent cancer cell killing

To expand applications for T-cell-based immunotherapy in cancer, we designed a receptor that binds the Fc portion of human immunoglobulins and delivers activation signals. The construct included the high-affinity CD16 (FCGR3A) V158 variant, CD8α hinge, and transmembrane domains, along with signaling domains from CD3ζ and 4-1BB (TNFRSF9), forming a chimeric receptor termed CD16V-BB-ζ. After retrovirus-mediated expression in human T cells, CD16V-BB-ζ bound humanized antibodies with higher affinity than a control receptor containing the more common F158 variant. Engagement of CD16V-BB-ζ provoked T-cell activation, exocytosis of lytic granules, and sustained proliferation, with a mean cell recovery after 4-week coculture with Daudi lymphoma cells and rituximab of nearly 70-fold relative to input cells. In contrast, unbound antibody alone produced no effect. CD16V-BB-ζ T cells specifically killed lymphoma cells and primary chronic lymphocytic leukemia cells in combination with rituximab at a low effector:target ratio, even when assayed on mesenchymal cells. Trastuzumab triggered CD16V-BB-ζ-mediated killing of HER2 (ERBB2)(+) breast and gastric cancer cells; similar results were obtained with an anti-GD2 antibody in neuroblastoma and osteosarcoma cells. Furthermore, coadministration of CD16V-BB-ζ T cells with immunotherapeutic antibodies exerted considerable antitumor activity in vivo. Signaling mediated by 4-1BB-CD3ζ induced higher T-cell activation, proliferation, and cytotoxicity than CD3ζ or FcεRIγ, and the receptor was expressed effectively after mRNA electroporation without viral vectors, facilitating clinical translation. Our results offer preclinical proof of concept for CD16V-BB-ζ as a universal, next-generation chimeric receptor with the potential to augment the efficacy of antibody therapies for cancer.

Cytokine release syndrome in cancer immunotherapy with chimeric antigen receptor engineered T cells

Adoptive transfer of chimeric antigen receptor (CAR)-engineered T cells is a promising therapy for cancers. However, the safety of this approach is concerned. Cytokine release syndrome (CRS) is a common but lethal complication of CAR-T cell therapy. The development of CRS correlates with CAR structures, tumor type and burden, and patients' genetic polymorphisms. CRS related adverse events may be reduced by designing safer CARs and CAR-T cells and following strict dose-escalation scheme. Timely and effective cytokine-directed treatment with corticosteroid and various cytokine antagonists is important to avoid CRS associated death.

T cells expressing CD123-specific chimeric antigen receptors exhibit specific cytolytic effector functions and antitumor effects against human acute myeloid leukemia

Induction treatments for acute myeloid leukemia (AML) have remained largely unchanged for nearly 50 years, and AML remains a disease of poor prognosis. Allogeneic hematopoietic cell transplantation can achieve cures in select patients and highlights the susceptibility of AML to donor-derived immunotherapy. The interleukin-3 receptor α chain (CD123) has been identified as a potential immunotherapeutic target because it is overexpressed in AML compared with normal hematopoietic stem cells. Therefore, we developed 2 chimeric antigen receptors (CARs) containing a CD123-specific single-chain variable fragment, in combination with a CD28 costimulatory domain and CD3-ζ signaling domain, targeting different epitopes on CD123. CD123-CAR-redirected T cells mediated potent effector activity against CD123+ cell lines as well as primary AML patient samples. CD123 CAR T cells did not eliminate granulocyte/macrophage and erythroid colony formation in vitro. Additionally, T cells obtained from patients with active AML can be modified to express CD123 CARs and are able to lyse autologous AML blasts in vitro. Finally, CD123 CAR T cells exhibited antileukemic activity in vivo against a xenogeneic model of disseminated AML. These results suggest that CD123 CAR T cells are a promising immunotherapy for the treatment of high-risk AML.

Chimeric antigen receptor-engineered T cells for cancer immunotherapy: progress and challenges

Recent years have witnessed much progress in both basic research and clinical trials regarding cancer immunotherapy with chimeric antigen receptor (CAR)-engineered T cells. The unique structure of CAR endows T cell tumor specific cytotoxicity and resistance to immunosuppressive microenvironment in cancers, which helps patients to better tackle the issue of immunological tolerance. Adoptive immunotherapy (AIT) using this supernatural T cell have gained momentum after decades of intense debates because of the promising results obtained from preclinical models and clinical trials. However, it is very important for us to evaluate thoroughly the challenges/obstacles before widespread clinical application, which clearly warrants more studies to improve our understanding of the mechanism underlying AIT. In this review, we focus on the critical issues related to the clinical outcomes of CAR-based adoptive immunotherapy and discuss the rationales to refine this new cancer therapeutic modality.

Immunotherapeutic strategies including transplantation: eradication of disease

Although there have been recent advances with targeted therapies in chronic lymphocytic leukemia (CLL), chemoimmunotherapy remains the treatment of choice; however, this approach is not curative. A key feature of CLL is that it induces a state of immunosuppression, causing increased susceptibility to infections and failure of an antitumor immune response, often worsened by the immunosuppressive effect of treatment. Because of its improved specificity, immunotherapy potentially offers a way out of this dilemma. Allogeneic stem cell transplantation remains the only curative option, but is hampered by the toxicity of GVHD. After many years of promise but little reward, many other immunotherapeutic approaches are now in transition to the clinical setting. Clinical trials including CLL vaccines, CXCR4 antagonists, and adoptive cellular immunotherapies such as chimeric antigen receptor-modified T cells, CD40 ligand gene therapy, and the immunomodulatory drug lenalidomide are ongoing. Results to date suggest that immunotherapeutic approaches for the treatment of CLL might finally be fulfilling their promise.