CAR T-cell therapy has emerged as a transformative cancer treatment, with recent reports showing two patients remaining in remission 12 years after treatment. Carl June and David Porter of the University of Pennsylvania reported these remarkable outcomes in Nature, with June asserting that CAR T-cell therapy can actually cure some patients with leukemia.
The therapy works by genetically modifying a patient's T cells to express chimeric antigen receptors (CARs) that specifically target cancer cells. According to the National Cancer Institute, the process involves extracting T cells from patient blood, adding genes for special receptors that bind to cancer cell proteins, expanding these modified cells in the laboratory, and reinfusing them into the patient.
Manufacturing and Production Challenges
Despite its success in blood cancers, CAR T-cell therapy faces significant manufacturing limitations. The current autologous process is extremely expensive and can take 2 to 8 weeks, with treatment available only at limited institutions. The complexity involves multiple steps including T cell extraction, CAR engineering, laboratory expansion, and patient reinfusion.
Allogeneic Approaches
Researchers are developing off-the-shelf allogeneic CAR T-cell therapies using healthy donor T cells instead of patient-derived cells. This approach could enable manufacturing for dozens of patients simultaneously, potentially reducing costs and allowing hospitals to maintain frozen cell inventories for immediate treatment availability.
Several biotechnology companies are exploring induced pluripotent stem cells (iPSCs) as T cell precursors that can be edited to add CARs and developed into T cell banks for broader distribution.
Accelerated Manufacturing
Penn Medicine researchers have demonstrated that functional CAR T cells can be produced within 24 hours from peripheral blood T cells without requiring traditional T cell activation or ex vivo expansion. The process efficiency depends on medium formulation and vessel surface-area-to-volume ratios.
In Vivo Generation
Innovative in vivo approaches are being developed to bypass traditional manufacturing entirely. Researchers at NC State and UNC Chapel Hill created the Multifunctional Alginate Scaffold for T Cell Engineering and Release (MASTER), an implantable device seeded with human blood cells and CD19-encoding retroviral particles that produces and releases functional CAR T cells directly in mice.
Other in vivo strategies include gene therapy via fusogen delivery vehicles targeting T cell surface proteins and platforms using small-molecule bispecific adapters to tag tumors.
Solid Tumor Limitations
While six CAR T-cell therapies have received FDA approval for blood cancers, solid tumor applications remain experimental. The tumor microenvironment presents significant barriers including T cell exhaustion, hostile signaling, and poor penetration of stroma and vasculature.
Combination Therapies
BioNTech is developing a combination approach pairing CAR T-cell therapy with mRNA vaccines encoding the same target protein. This strategy aims to enhance CAR T cell expansion and persistence, potentially improving solid tumor treatment efficacy. Early Phase I results presented at AACR2022 showed encouraging safety and tumor-killing efficacy.
Mayo Clinic researchers have combined CAR T-cell therapy with oncolytic viruses, creating virus-loaded CAR T cells that demonstrated superior solid tumor targeting compared to either therapy alone in preclinical models.
Armored CAR Designs
Researchers are engineering "armored" CAR T cells resistant to immunosuppressive factors in the tumor microenvironment. One approach involves creating CAR cells resistant to TGF-beta, a protein that can shut down T cells and help cancer cells evade immune detection.
Microenvironment Reconditioning
Scientists have identified PAK4, a protein kinase regulating aberrant vascularization, as a target for improving CAR T cell infiltration. Preclinical studies showed PAK4 inhibition reduces vascular abnormalities, improves T cell infiltration, and inhibits glioblastoma growth in mice.
Clinical Applications and Outcomes
CAR T-cell therapies have shown remarkable success in hematologic malignancies. Clinical trials have demonstrated high overall response rates and complete response rates in non-Hodgkin lymphoma, with some studies reporting 82% overall response rates and 54% complete response rates in refractory cases.
In multiple myeloma, anti-BCMA CAR T-cell therapies have achieved partial or complete responses in 18 of 19 treated patients in phase I trials. However, immune escape through antigen loss remains a challenge, with some patients developing CD19-negative or BCMA-negative cells.
Safety Considerations
CAR T-cell therapies can cause severe side effects including cytokine release syndrome (CRS), immune effector cell-associated neurotoxicity syndrome (ICANS), and tumor lysis syndrome. CRS results from massive cytokine release following T cell activation and can cause fever, hypotension, and organ dysfunction. One recent CAR T-cell therapy trial was paused after two patient deaths were reported.
Tocilizumab, an anti-IL6 receptor antibody, has shown efficacy in rapidly eliminating CRS symptoms. Researchers are developing safety switches including biodegradable CAR T-cells and suicide gene incorporation to eliminate CAR T-cells once desired responses are achieved.
The field continues advancing with multiple phase III clinical trials ongoing to determine CAR T-cell therapy efficacy across various malignancies, while new approaches address manufacturing complexity, cost barriers, and solid tumor penetration challenges.
