6.6.3 Clinical development of CAR T Cells
As of the end of 2016, 220 CAR T cell trials are documented of which 188 are ongoing including nine long-term follow-up studies.Most of the clinical trials conducted are phase 1 (128) primarily evaluating safety and dose finding, but phase 1/2 and phase 2 trials assessing efficacy are catching up especially with CD19 as the CAR antigen [172].
The first CAR T cell trials initiated about 20 years ago included patients with advanced epithelial ovarian cancer or metastatic renal cell carcinoma and targeted the folate receptor or carbonic anhydrase IX (CAIX), respectively.The next two registered clinical trials with published results reported on single patients suffering from neuroblastoma or follicular lymphoma reaching complete response.However, the breakthrough was achieved over the following years with CD19-specific CAR T cells targeting B-cell malignancies.Complete or partial response was reported not only for single individuals but also for the majority of patients in some trials (Dataset EV4).From then on,the number of CAR T cell trials substantially increased and now grows exponentially.In 2016 alone,62 new CAR T cell clinical trials have been entered into ClinicalTrials.gov [165].
CAR T cell therapy was initially introduced in the USA, then spreading to the rest of the world.Currently, 89 CAR T cell clinical trials are in progress outside the USA, with highest numbers in China and Europe.Compared to the USA and China, Europe is clearly lagging behind.The majority of trials in Europe are performed in UK, followed by Germany and France [165].
Of the current trials, 133 target hematological malignancies and 78 solid tumors.For tumors of the hematopoietic and lymphoid system, 17 different CAR antigens are under investigation.The most frequently targeted antigen is CD19 with 56 ongoing and eight non-active trials.Even more antigens are investigated for the treatment of solid tumors.Previous trials focused on CEA as antigen-targeting colorectal cancer, breast cancer, gastric cancer, adenocarcinoma as well as liver metastases.Ongoing trials target mesothelin, ErbB2/Her2, GD2 (neuroblastoma or sarcoma), or GPC3 (hepatocellular carcinoma) [165].(https://www.daowen.com)
Most clinical trials have used autologous, unselected peripheral blood mononuclear cells (PBMC)as the starting material and IL-2 for stimulation resulting in a CAR T cell product consisting of CD4 and CD8 T cells with an activated effector T-cell phenotype.Methods to isolate defined T cell subsets or to drive T cells into a certain phenotype have been developed.In addition, automated manufacturing might be an option to simplify the process and enhance the robustness of CAR T cell production.CD19-CAR T cells generated using a closed automated GMP cell processing system have been shown to be comparable to CD19-CAR T cells produced by the conventional processes in terms of transduction efficiency, phenotype, function, and overall yield [166-168].
Typically, CAR T cells are infused intravenously.However, intra-tumoral, intracranial or intra-peritoneal injection, hepatic artery, pleural, or transcatheter arterial infusion are being investigated as well.To increase the tolerability of the treatment and to lower the risk of side effects,the given CAR T cell dose is often split over multiple injections.The total treatment dose is in the range of 7.5 × 107-3.4 × 108 CAR T cells if a fixed dose is applied.However, the majority of trials use an inter- or intra-patient dose escalation regime.Dose escalation usually covers 2-log steps starting somewhere between 1 × 106 and 1 × 109 CAR T cells.Notably, the total number of infused cells depends on the percentage of CAR-positive T cells within the product, which is highly variable, not only between different studies but also within single trials [165].
For the generation of CAR T cells, a slight preference for the use of gamma-retroviral vectors(RVs), directly followed by lentiviral vectors (LVs), can be observed.Only very few clinical studies used electroporation for the transfer of the CAR construct.In the majority of all trials,second-generation CARs were transferred.Third- or fourth-generation CARs are being tested especially when targeted to CD19 [165].