Author(s): Yarne Klaver aff1 , Andre Kunert aff1 , Stefan Sleijfer aff1 , Reno Debets aff1 , Cor HJ Lamers [*] aff1
CAR T cell; flow cytometry; IFN-[gamma] production; immune monitoring; pMHC multimers; qPCR; T-cell markers; T-cell therapy; TCR T cell; TIL
Immunotherapy is becoming part of the systemic treatment options for cancer patients. In particular immunomodulating agents, like the checkpoint blocking antibodies that block the negative regulators of T-cell immunity. Recently, ipilimumab, that blocks CTLA-4 and nivolumab and lambrolizumab, that block PD-1, have drawn a lot of attention [1-8 ]. These agents applied as monotherapy have shown promising clinical results, in particular in patients with metastatic melanoma. The combination of ipilimumab and nivolumab resulted even in a higher objective response rate up to 53%, whereas adverse effects were comparable to those experienced with monotherapy [9 ]. Investigations in clinical application of these agents for other cancer types is rapidly expanding.
In addition to immunomodulating drugs, another promising immunotherapeutic approach is adoptive T-cell therapy, an immunotherapeutic treatment that is based on the principle of transferring autologous and ex vivo expanded tumor-specific T cells to patients. In recent years, T-cell therapy has yielded impressive clinical results in patients who had previously failed to standard treatments. Adoptively transferred T cells have the capacity to kill antigen-expressing tumor cells and thereby provide a direct cytolytic effector function. Therapy with tumor-infiltrating lymphocytes (TILs) has shown initial objective responses in about 50% of the metastatic melanoma patients, and complete responses that ranged between 10 and 20%, including durable complete responses beyond 3 years [10-13 ]. Although these results are promising, the majority of patients are not eligible for TIL therapy, as not all patients have pre-existing tumor reactive T cells and in many cancers it is still difficult to identify and obtain tumor reactive lymphocytes. To overcome this limitation, the genetic introduction of chimeric antigen receptors (CARs) and T-cell receptors (TCRs) into autologous T cells is considered an alternative, rendering T-cell therapy available for a larger group of patients. CARs are single-chain variable fragments (scFv) derived from monoclonal antibodies that are fused to a transmembrane and a signaling domain. When introduced in T cells binding of the CAR with its antigen leads to T-cell activation. Trials with first-generation CARs showed limited success, but trials with second-generation CARs have shown more promising results. Second-generation CARs harbor an extra intracellular cosignaling domain derived from CD28 or 4-1BB (CD137). Recently in two clinical trials with second-generation CAR T cells, patients with B-cell acute lymphocytic leukemia (B-ALL) were treated with a CAR targeting CD19, and remarkable high complete response percentages of 90% were reported [14-16 ]. Also, several TCR gene-modified T-cell trials have shown successes, although with variable response rates. T cells endowed with a TCR against NY-ESO1/HLA-A2 showed an objective response in about 50% of patients with metastatic melanoma, and in about 70% of patients with metastatic synovial cell sarcoma with no detectable toxicities [17 ]. Other TCR trials have shown antitumor responses that in some cases were accompanied by toxicities...