NK Cell–Targeting Strategies Come Into Their Own

Although anticancer therapies that leverage T cells have commanded the most attention in the immuno-oncology era of the past decade, strategies based on natural killer cells have recently emerged as attractive approaches.

Although anticancer therapies that leverage T cells have commanded the most attention in the immuno-oncology era of the past decade, strategies based on natural killer (NK) cells have recently emerged as attractive approaches.1,2

NK cell–based adoptive cell therapies (ACTs), including genetically modified chimeric antigen receptor (CAR)-NK cells, are safer than their T cell–based counterparts and have the potential for “off-the-shelf” use.1,2 NK cellbased strategies in clinical development also include NK cells that express activating cytokines, as well as antibodies targeting receptors on the NK cell surface.

Most excitingly, the first FDA approval for an NK cell-based therapy may be on the horizon. The QUILT-3.032 trial (NCT03022825) of interleukin 15 (IL-15) superagonist N-803 (Anktiva; formerly ALT-803) recently met its primary end point. ImmunityBio, the company developing the therapy, expects to file a biologics license application for FDA approval of N-803 in combination with BCG vaccine for the treatment of patients with non–muscle-invasive bladder cancer (NMIBC) in 2021.3

Nature's Weapons of Mass Destruction

Named for their innate ability to kill target cells, NK cells are sentinels of the antitumor response, rapidly recognizing and killing transformed cells without the need for prior sensitization. Cancer cells often downregulate the expression of major histocompatibility complex class I molecules on their surface as a way to evade cytotoxic T cells, but this makes them susceptible to NK cells, which are activated in part by this lack of “self” molecules.1,2,4

A greater abundance of NK cells in the tumor microenvironment has been associated with improved survival in a number of cancer types, including liver, gastric, and breast cancers, as well as melanoma.2 Therefore, a leading approach to NK cell–targeted therapy has been the adoptive transfer of NK cells to boost NK cell numbers.

Typically, ACT involves harvesting NK cells from the blood of the patient (autologous) or a healthy donor (allogeneic), whereupon the cells are expanded and then infused into the patient. Although autologous NK cells have proved to be safe, studies to date have demonstrated limited clinical benefit, particularly in patients with solid tumors; obstacles have included difficulties in expanding NK cells and in attaining adequate functionality of infused cells.2,5-7

Clinical trials of autologous NK cells are ongoing, however. California-based NKMax America is developing SNK01, which the company describes as highly pure autologous NK cells that have been activated to enhance cytotoxicity, although there is no publicly available information about how this is achieved.8,9

Several clinical trials testing the agent are ongoing. According to data from a phase 2 trial, SNK01 in combination with pembrolizumab (Keytruda) in patients with stage IV non–small cell lung cancer (NSCLC) who progressed on frontline platinum-based chemotherapy demonstrated an overall response rate (ORR) of 44.4% in 9 evaluable patients treated with the combination. The findings were presented at the 2020 American Society of Clinical Oncology (ASCO) Virtual Scientific Program.10

Off the Shelf

Investigators in the field have largely shifted their attention to allogeneic NK cells, which have potential for highly sought after “off-the-shelf” utility because they can be collected from donors and stored as readily available banks of NK cells, reducing production time and cost.5 Allogeneic T-cell therapy is limited by the potential for graft-vs-host disease, wherein the infused T cells also attack healthy tissue, causing severe toxicity, but allogeneic NK cells are safer in this regard.5,7

A plethora of clinical trials are ongoing, with a focus on strategies to boost the activity of the adoptively transferred NK cells, according to a search of the website (Table). In addition to growing the NK cells in the presence of activating substances, other strategies being explored include combination therapy and genetic modification.1,7

Table. Select NK-Targeting Therapies in Clinical Development

Gamida Cell is developing GDA-201, allogeneic NK cells expanded in the presence of the activating cytokine IL-15 and nicotinamide, which has been shown to boost NK-cell expansion, survival, and cytotoxicity.5,11 In a phase 1 clinical trial (NCT03019666), investigators are evaluating GDA-201 in combination with the monoclonal antibodies rituximab (Rituxan) in patients with relapsed or refractory B-cell non-Hodgkin lymphoma (NHL), or elotuzumab (Empliciti), in participants with multiple myeloma. Preliminary results for 19 patients with NHL demonstrated an ORR of 74%, with all responses but 1 being complete response (CR).12 Recruitment of patients into the trial has been suspended pending a study amendment, according to an update posted on in February 2021.

In addition to being collected from blood, mature NK cells can be differentiated from stem cells isolated from umbilical cord blood or from induced pluripotent stem cells (iPSCs), as well as from clonal cell lines derived from immortalized tumor cells. Each source of NK cells has unique advantages.4,7

NK cells derived from cord blood are a source of functional allogeneic NK cells in contrast to the often dysfunctional state of autologous NK cells, according to investigators from The University of Texas MD Anderson Cancer Center.

They presented findings from a phase 2 trial (NCT03019640) during the 2021 Transplant & Cellular Therapy Meetings showing that NK cells derived from cord blood could be safely and effectively expanded and administered to patients with B-cell NHL after high-dose chemotherapy and in advance of autologous stem cell trans-plant. At a median follow-up of 18 months, the relapse-free survival rate was 68% and the overall survival rate was 84% among 19 patients who received the regimen.13

Fate Therapeutics is developing several iPSC-derived allogeneic cell lines. FT516 and FT596 are engineered to express the high- affinity variant of the CD16 receptor, to boost the antibody-dependent cellular cytotoxicity capability of NK cells, and an IL-15 receptor fusion, which promotes NK cell cytotoxicity. FT596 also can express a CD19-targeted CAR.14

NantKwest has developed “t-haNK” cells, which are CAR-NK cells targeting either PD-L1 or CD19. They are based on high- affinity NK (haNK) cells derived from NK-92, a tumor cell line engineered to express the high-affinity CD16 receptor.4 Non-CAR haNK cells are being evaluated in numerous ongoing clinical trials and form part of NantKwest’s NANT Cancer Vaccines. These are combinations of metronomic low-dose chemotherapy, low-dose radiation therapy, adenoviral tumor-associated antigen vaccines, immune checkpoint inhibitors (ICIs), N-803, and haNK cells.15

Data from 12 patients with advanced pancreatic cancer enrolled across the QUILT-3.039, -3.060, -3.070, and -3.080 trials of this vaccine were presented at 2020 ASCO; 11 patients (92%) achieved stable disease lasting longer than 8 weeks. The 12th patient, who received PD-L1–targeted t-haNK instead of haNK, achieved a CR.16 The ongoing QUILT-88 trial (NCT04390399) is evaluating PD-L1 t-haNK as part of combination immunotherapy in pancreatic cancer. The original 2 cohorts included patients treated in the first- and second-line settings, respectively. A third cohort was recently added for third-line and beyond treatment of patients who have progressed on all approved standards of care.17

NK Cell-Activating Cytokines

N-803 was developed by Altor BioScience Corporation, which was acquired by ImmunityBio in 201718; it is an IL-15 superagonist complex consisting of an IL-15 mutant bound to a high-affinity IL-15 receptor (IL-15Rα) fused to the fragment crystallizable (Fc) domain of immunoglobulin (Ig) G1.19 N-803, which strongly activates NK cells, is being evaluated in combination with a number of different anticancer therapies.

In 2019, ImmunityBio received a break-through therapy designation for N-803 in combination with BCG for the treatment of NMIBC.17 Two clinical trials of this combination are ongoing: the phase 1/2 QUILT-2.005 trial (NCT02138734) in BCG-naïve patients and the phase 2/3 QUILT-3.032 (NCT03022825) in BCG-unresponsive patients.

ImmunityBio recently announced that QUILT-3.032 had met its primary end point.3 The combination induced CRs in 71% (95% CI, 59%-81%) of 72 evaluable patients for a median duration of 19.2 months, with a 56% probability (95% CI, 38.8%-70.3%) that the CRs would be maintained for at least 12 months, according to findings presented at the 2021 Genitourinary Cancers Symposium.20

Meanwhile, N-803 also is being evaluated in the phase 3 QUILT 2.023 trial (NCT03520686) in combination regimens as a first-line therapy for patients with stage III or IV advanced or metastatic NSCLC. The trial aims to randomize 1538 participants to experimental cohorts of N-803 with pembrolizumab or with pembrolizumab plus carboplatin and nab-paclitaxel (Abraxane) with or without pemetrexed; or control arms comprising pembrolizumab monotherapy, pembrolizumab plus carboplatin with either nab-paclitaxel or paclitaxel, or pembrolizumab plus pemetrexed with either cisplatin or carboplatin.

Other cytokine-based therapies include M9241, an immunocytokine that uses a naked DNA–detecting antibody to target delivery of IL-12 to regions of tumor necrosis and apoptosis, such as the tumor microenvironment; and bempegaldesleukin (NKTR-214), a CD122preferential IL-2 pathway agonist designed to stimulate CD8-positive effector T cells and NK cells.21,22

Nektar Therapeutics has an extensive development program underway for bempegaldesleukin in combinations that include nivolumab (Opdivo), with phase 3 trials in metastatic and adjuvant melanoma (NCT03635983; NCT04410445), renal cell carcinoma (NCT03729245), and muscle- invasive bladder cancer (NCT04209114).

Targeting NK Cell Receptors

In an alternative approach, the power of NK cells can be harnessed for cancer therapy using antibodies that target cell-surface receptors. Affimed is developing several bispecific antibodies that target CD16 on the NK cell surface and a tumor-associated antigen. These antibodies are designed to bring NK cells and tumor cells into close proximity to facilitate more targeted killing by NK cells.5

Results from a phase 1 trial (NCT02665650) of AFM13, which targets CD16 on NK cells and CD30 on tumor cells, were recently published. In 30 heavily pretreated patients with relapsed or refractory Hodgkin lymphoma, a combination of AFM13 and pembrolizumab elicited an ORR of 83%.23 Affimed is also collaborating with NKMax America on a planned study of EGFR/CD16-bispecific antibody AFM24 in combination with SNK01.24

Meanwhile, GTB-3550 (GT Biopharma) is a trispecific killer engager (TriKE) composed of 2 single-chain variable fragments—1 binding CD16 on NK cells and 1 binding CD33 on myeloid cancer cells—joined by an IL-15 linker. In a phase 1 trial (NCT03214666), GTB-3550 produced NK cell proliferation without significant toxicity. Investigators hope to see clinical efficacy at higher doses.25

Similar to ICIs, therapeutic monoclonal antibodies designed to target inhibitory receptors on the surface of NK cells are also of great interest. To date, most efforts have focused on the killer-cell Ig-like receptors (KIRs). Lirilumab (IPH2102/BMS-986015), which targets several inhibitory KIRs, had demonstrated promise in several cancer types in a phase 1 trial, but results of a phase 2 trial were disappointing. The drug is no longer in development by Innate Pharma or Bristol Myers Squibb, which had acquired licensing rights.4,26,27

Similar to ICIs, therapeutic monoclonal antibodies designed to target inhibitory receptors on the surface of NK cells are also of great interest. To date, most efforts have focused on the killer-cell Ig-like receptors (KIRs). Lirilumab (IPH2102/BMS-986015), which targets several inhibitory KIRs, had demonstrated promise in several cancer types in a phase 1 trial, but results of a phase 2 trial were disappointing. The drug is no longer in development by Innate Pharma or Bristol Myers Squibb, which had acquired licensing rights.4,26,27

Lacutamab (IPH4102) is a first-in-class specific inhibitor of KIR3DL2 that showed promise in a phase 1 clinical trial (NCT02593045) in patients with relapsed or refractory cutaneous T-cell lymphoma, especially those with Sézary syndrome, a particularly aggressive form of this cancer.28

The phase 2 TELLOMAK trial (NCT03902184) is underway to evaluate the activity of lacutamab as monotherapy and in combination with chemotherapy in patients with Sézary syndrome and other types of T-cell lymphoma. The FDA had placed this trial on a partial hold due to deficiencies in a subcontractor’s manufacturing procedures, but the hold was lifted in June 2020.29

Monalizumab (IPH2201), a first-in-class antibody targeting NKG2A, an inhibitory receptor on NK cells, was developed by Innate Pharma; AstraZeneca acquired the rights in 2018.30 Several clinical trials are ongoing, and the agent has advanced into phase 3 testing (INTERLINK-1;NCT04590963) in combination with cetuximab (Erbitux) in patients with head and neck cancer previously treated with platinum-based chemotherapy and a PD-1/L1 inhibitor. This follows a phase 1/2 trial (NCT02643550) in which the combination elicited an ORR of 20% among 40 patients with platinum- and PD-1/PD-L1 inhibitor–refractory disease.31

Jane de Lartigue, PhD, is a freelance medical writer and editor based in Gainesville, Florida.


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