An allogeneic NK cell line engineered to express chimeric antigen receptors: A novel strategy of cellular immunotherapy against cancer

Potential Cancer Prevention and Treatment by Silencing the Killer Cell Immunoglobulin-like Receptor Gene in Natural Killer Cells Derived from Induced Pluripotent Stem Cells

Cancer immunosurveillance is an important host protection process, monitoring the presence of irregular cells that could potentially transform into tumor cells, effectively clearing the body of transformed tumor cells at their earliest stages, and thus maintaining regular cellular homeostasis. Natural killer (NK) cells are effector lymphocytes of the innate immune system, playing a critical role in surveillance for tumor cells, while also eliminating virally infected cells. The significance of the anti-tumor role of NK cells was recently further verified by findings that immunosuppression in most cancer patients is not perceptible until late stages. NK cells express the low-affinity Fc-activating receptor, CD16, and the inhibitory receptor, killer cell immunoglobulin-like receptor (KIR). Consequently, activation of NK cells is determined by the balance of inhibitory and activating receptor stimulation. Here, we propose establishing an induced pluripotent stem cell (iPSC)-derived NK cell line with KIR gene knockout or knockdown as a possible regimen to treat and prevent cancer. We further postulate that an optimal mixture of NK iPSCs with and without KIR gene knockout, would reach a maximum antitumor activity, with minimal side effects. We also discuss the possible advantages of KIR-knockout NK iPSCs for adoptive immunotherapy in patients with cancer.

Trial Watch: Adoptive cell transfer for oncological indications

One particular paradigm of anticancer immunotherapy relies on the administration of (potentially) tumor-reactive immune effector cells. Generally, these cells are obtained from autologous peripheral blood lymphocytes (PBLs) ex vivo (in the context of appropriate expansion, activation and targeting protocols), and re-infused into lymphodepleted patients along with immunostimulatory agents. In spite of the consistent progress achieved throughout the past two decades in this field, no adoptive cell transfer (ACT)-based immunotherapeutic regimen is currently approved by regulatory agencies for use in cancer patients. Nonetheless, the interest of oncologists in ACT-based immunotherapy continues to increase. Accumulating clinical evidence indicates indeed that specific paradigms of ACT, such as the infusion of chimeric antigen receptor (CAR)-expressing autologous T cells, are associated with elevated rates of durable responses in patients affected by various neoplasms. In line with this notion, clinical trials investigating the safety and therapeutic activity of ACT in cancer patients are being initiated at an ever increasing pace. Here, we review recent preclinical and clinical advances in the development of ACT-based immunotherapy for oncological indications.

Classification of current anticancer immunotherapies

During the past decades, anticancer immunotherapy has evolved from a promising therapeutic option to a robust clinical reality. Many immunotherapeutic regimens are now approved by the US Food and Drug Administration and the European Medicines Agency for use in cancer patients, and many others are being investigated as standalone therapeutic interventions or combined with conventional treatments in clinical studies. Immunotherapies may be subdivided into "passive" and "active" based on their ability to engage the host immune system against cancer. Since the anticancer activity of most passive immunotherapeutics (including tumor-targeting monoclonal antibodies) also relies on the host immune system, this classification does not properly reflect the complexity of the drug-host-tumor interaction. Alternatively, anticancer immunotherapeutics can be classified according to their antigen specificity. While some immunotherapies specifically target one (or a few) defined tumor-associated antigen(s), others operate in a relatively non-specific manner and boost natural or therapy-elicited anticancer immune responses of unknown and often broad specificity. Here, we propose a critical, integrated classification of anticancer immunotherapies and discuss the clinical relevance of these approaches.

Trial Watch: Adoptive cell transfer for anticancer immunotherapy

The expression "adoptive cell transfer" (ACT) is commonly employed to indicate an immunotherapeutic regimen involving the isolation of autologous blood-borne or tumor-infiltrating lymphocytes, their selection/expansion/activation ex vivo, and their reinfusion into the patient, most often in the context of lymphodepleting pre-conditioning and in combination with immunostimulatory treatments. Optionally, the cellular material for ACT is genetically manipulated before expansion to (1) target specific tumor-associated antigens; (2) endogenously express immunostimulatory molecules; and/or (3) persist for long periods upon reinfusion. Consistent efforts have been dedicated at the amelioration of this immunotherapeutic regimen throughout the past decade, resulting in the establishment of ever more efficient and safer ACT protocols. Accordingly, the number of clinical trials testing ACT in oncological indications does not cease to increase. In this Trial Watch, we summarize recent developments in this exciting area of research, covering both high-impact studies that have been published during the last 12 months and clinical trials that have been launched in the same period to evaluate the safety and therapeutic potential of ACT in cancer patients.