Allogeneic CAR T Cells: An Alternative to Overcome Challenges of CAR T Cell Therapy in Glioblastoma

Abstract

Chimeric antigen receptor (CAR) T cell therapy has emerged as one of the major breakthroughs in cancer immunotherapy in the last decade. Outstanding results in hematological malignancies and encouraging pre-clinical anti-tumor activity against a wide range of solid tumors have made CAR T cells one of the most promising fields for cancer therapies. CAR T cell therapy is currently being investigated in solid tumors including glioblastoma (GBM), a tumor for which survival has only modestly improved over the past decades. CAR T cells targeting EGFRvIII, Her2, or IL-13Rα2 have been tested in GBM, but the first clinical trials have shown modest results, potentially due to GBM heterogeneity and to the presence of an immunosuppressive microenvironment. Until now, the use of autologous T cells to manufacture CAR products has been the norm, but this approach has several disadvantages regarding production time, cost, manufacturing delay and dependence on functional fitness of patient T cells, often reduced by the disease or previous therapies. Universal "off-the-shelf," or allogeneic, CAR T cells is an alternative that can potentially overcome these issues, and allow for multiple modifications and CAR combinations to target multiple tumor antigens and avoid tumor escape. Advances in genome editing tools, especially via CRISPR/Cas9, might allow overcoming the two main limitations of allogeneic CAR T cells product, i.e., graft-vs.-host disease and host allorejection. Here, we will discuss how allogeneic CAR T cells could allow for multivalent approaches and alteration of the tumor microenvironment, potentially allowing the development of next generation therapies for the treatment of patients with GBM.

Keywords: CAR T cells; allogeneic; allorejection; glioblastoma; graft-vs.-host disease; tumor microenvironment.

Figure 1

Allogeneic (“off-the-shelf”) CAR T cells generation and sources of T cells. Allogeneic T cells can be obtained from peripheral blood mononuclear cells from healthy donors, umbilical cord blood or derived from induced pluripotent stem cells (iPSCs). CAR T cells are generated by virus transduction and in vitro expansion before patient administration.

Figure 2

Allogeneic CAR T cells must avoid host immune rejection and GVHD. Allogeneic CAR T cells can evade the patient immune response by genetic disruption of HLA class I and II molecules, resist lymphodepleting regimens using anti-CD52 antibodies by elimination of the CD52 molecule and inhibit NK elimination by increasing expression of Siglec ligands of HLA-E and G variants. To protect patients from GVHD, allogeneic CAR T cells can be engineered to lose TCR expression.

Figure 3

Allogeneic CAR T cells provide a versatile platform to attack GBM and its environment. GBM heterogeneity require a multitarget approach that can be achieved using allogeneic CAR T cells using multiple CAR T cell mixes, multivalent CAR T cells or by modular CAR T combined with several adaptors. To overcome the immunosuppressive TME of GBM several strategies to engineer allogeneic CAR T cells can be used: secretion of pro-inflammatory cytokines (such as IL-7, IL-12, IL-15, IL-21, or IL-23), expression of decoy or switch receptors (to change immunosuppressive signals into activating ones), expression of chemokine receptors (to direct CAR T cells to the tumor site) and generation of locally activated CAR T cells (such as hypoxia-inducible CAR T cells).

Figure 4

To develop new and effective anti-GBM therapies better experimental models are required. Experimental in vitro and in vivo models need to move to more realistic settings. Patient derived primary cell lines and xenograft models, orthotopic tumor growth and mice with humanized immune system must become the standard to evaluate allogeneic CAR T cells against GBM.