Table 1.

Comparing two common feeder cells for NK expansion.

Feeder Cells	EBV-Lymphoblastoid Cell Lines	mbIL21-4-1BBL expressing K562
Source	Infection and transformation of B-lymphocytes with EBV in vitro	Viral/non-viral transduction of parental K562 erythroleukemia cell line.
Ligand (receptor) candidates favoring NK expansion	Soluble Cytokines: rhIL-2 ± IL-21 Primary Candidates: 4-1BB Ligand (4-1BB), CD48 (2B4) (24, 29)	Soluble Cytokines: rhIL-2 Primary Candidates: Low HLA-A and HLA-B expression (iKIR), 4-1BB Ligand (4-1BB), mbIL-21 (IL-21R) (13)
	Additional Candidates: CD58 (CD2), OX40L (OX40), CD155 (DNAM-1) (25, 37, 38)	Additional Candidates: NKG2D ligands (NKG2D), natural cytotoxicity receptor ligands (NKp30, NKp44, NKp46) (39)
Selected Fold Expansion	Purified PB NK cell, 2-weeks: 815-3267 fold (12), 2900-fold (with IL-21) (29)	Purified PB NK cells, 2-weeks: ~2,000-fold (13)
Characteristics of Expanded NK Cells	Increased Receptor Expression: NKG2D, NKG2C, NKp30, NKp44, DNAM-1, NKG2A, KIR2DL2/3, TIGIT. Effector Molecule Production: TRAIL, FasL, Granzymes	Increased Receptor Expression: NKG2D, NKp30, NKp44, NKp46, DNAM-1, CD16, NKG2A Effector Molecule Production: Granzyme B, Perforin
Examples of Genome Editing Combinations	Lentiviral Transduction (40) TcBuster DNA Transposon (41)	Retroviral Transduction (3, 42) TcBuster DNA Transposon (43)
Clinical Trial Examples	NCT00720785 (multiple malignancies, with Bortezomib)	NCT01904136 (haploidental donor blood, AML) (44), NCT03056339 (CD19 CAR-IL-5-iCas9 NK cells, cord blood, CD19+ malignancies) (3), NCT01729091 (cord blood, multiple myeloma)