Allogeneic natural killer cell therapy

Abstract

Interest in adoptive cell therapy for treating cancer is exploding owing to early clinical successes of autologous chimeric antigen receptor (CAR) T lymphocyte therapy. However, limitations using T cells and autologous cell products are apparent as they (1) take weeks to generate, (2) utilize a 1:1 donor-to-patient model, (3) are expensive, and (4) are prone to heterogeneity and manufacturing failures. CAR T cells are also associated with significant toxicities, including cytokine release syndrome, immune effector cell-associated neurotoxicity syndrome, and prolonged cytopenias. To overcome these issues, natural killer (NK) cells are being explored as an alternative cell source for allogeneic cell therapies. NK cells have an inherent ability to recognize cancers, mediate immune functions of killing and communication, and do not induce graft-versus-host disease, cytokine release syndrome, or immune effector cell-associated neurotoxicity syndrome. NK cells can be obtained from blood or cord blood or be derived from hematopoietic stem and progenitor cells or induced pluripotent stem cells, and can be expanded and cryopreserved for off-the-shelf availability. The first wave of point-of-care NK cell therapies led to the current allogeneic NK cell products being investigated in clinical trials with promising preliminary results. Basic advances in NK cell biology and cellular engineering have led to new translational strategies to block inhibition, enhance and broaden target cell recognition, optimize functional persistence, and provide stealth from patients' immunity. This review details NK cell biology, as well as NK cell product manufacturing, engineering, and combination therapies explored in the clinic leading to the next generation of potent, off-the-shelf cellular therapies for blood cancers.

Graphical abstract

Figure 1.

NK cell responses are determined by the balance of signals received through activating and inhibitory receptors. (A) NK cells sense healthy self-tissues through interactions between KIR and MHC-I molecules, which inhibit NK cell killing. (B) Malignant or virally infected cells upregulate stress ligands recognized through NK activating receptors, which can trigger killing. In the event that infected or transformed cells downregulate MHC-I, NK cells kill via missing-self response. (C) NK cells can induce apoptosis by releasing perforin and granzyme-containing granules or engaging death receptors on target cells; in addition, NK cells produce immune modulating cytokines and chemokines upon activation. (Inset) main activating and inhibitory receptors expressed by NK cells and their ligands, present on target cells. KIR-Long contain intracellular immunoreceptor tyrosine-based inhibitory motifs whereas KIR-Short lack intracellular immunoreceptor tyrosine-based inhibitory motifs and instead associate with membrane adapters with activating motifs.

Figure 2.

Constitutively expressed cytokine receptors on NK cells. Common gamma chain (γ_c) receptors constitutively expressed by NK cells include intermediate affinity IL-2/IL-15 (βγ_c) receptor. High-affinity IL-15Rα is presented in trans by other cell types. CD56^bright NK cell subsets constitutively express high-affinity IL-2Rα and IL-7R, CD56^dim NK cells upregulate these receptors upon activation. IL-12R is constitutively expressed and required for adaptive memory responses. TGFβR inhibits IL-15R signal transduction and significantly alters NK cell phenotype and effector functions.

Figure 3.

Adaptive and cytokine-induced memory-like NK cells. Adaptive and cytokine-induced memory-like NK cells are distinct memory NK cell types. Adaptive NK cells are induced after viral infection and demonstrate enhanced responses to antibody-mediated activation, and they proliferate robustly after subsequent virus exposure. Memory-like NK cells are induced through IL-12, IL-15, IL-18 and with the addition of CD16 engagement. Memory-like NK cells demonstrate enhanced cytokine production and killing in response to multiple stimuli, including Fc-receptor ligation, activating receptor ligation, and cytokine receptor activation.

Figure 4.

Strategies for improving NK cell–based therapy. NK cells used in therapy can be improved by increasing effector responses, enhancing targeting, decreasing suppression, and improving in vivo functional persistence. ECD, extracellular domain; HCW9201, IL-12/IL-15/IL-18 receptor agonist; HCW9206, IL-7/IL-15/IL-21 receptor agonist; N-803, IL-15 receptor super agonist; mbIL-15-Rα, membrane-bound IL-15 receptor associated with high-affinity IL-15 receptor alpha subunit; HCW9218, IL-15 receptor agonist fused with TGF-β trap; BiKE/TriKE, bi- or tri-specific killer engagers, respectively; TM/ICS, transmembrane/intracellular signaling domain.

Figure 5.

Multiple sources for NK cells used in allogeneic NK cell therapy. Source of NK cells for therapy include iPSCs, HSPCs, and CB-derived and PB- or blood-derived NK cells.

Figure 6.

Strategies for stealth NK cell products. Approaches that limit T-cell responses to donor allo-antigens, specifically MHC-I, make NK cell products susceptible to recipient NK cell killing via missing-self responses. Current strategies include knocking out MHC-I and overexpressing nonclassical MHC-I molecules to protect donor NK cells from recipient lymphocyte-mediated rejection.