Table 1.

Different sources of NK cells for CAR NK cell production

Source	Specifications	Advantages	Disadvantages	Reference
PBMC	Peripheral blood collected and NK cells isolated by apheresis and NK cell-isolation kit	1. Potent anti-tumor efficacy 2. Higher expression of activatory receptors 3. Includes CD56dimCD16+ cells up to 90% 4. Appropriate ex-vivo expansion potential 5. No need for HLA-matching	1. Donor-dependent 2. Heterogeneous cell population 3. Various in-vivo expansion potential 4. Short in-vivo lifespan 5. Limited NK cell therapeutic dose 6. Expensive isolation and storage 7. High risk of GVHD	[40, 193, 194]
UCB	NK cells are isolated from the cord blood of the neonates	1. Higher in-vivo proliferation 2. Superior cytotoxicity against tumor cell 3. High NK cell concentration (15–30%) 4. Lower GVHD risk 5. Easy to collect 6. Lower immunogenicity 7. Higher purity of CAR NK cell product (92.3%) 8. Faster recovery of NK cell after transplantation 9. Higher in-vivo stimulation using ILs 10.Safe for mother and child 11. Resistant to cryopreservation 12. The option to choose a specific NK receptor profile and HLA from the donor bank 13. Suitable to produce an off-the-shelf product	7. Heterogeneous cell population 8. Specific donors with certain NK-receptor profile and HLA typing required 9. Immature NK cells with weak immunotoxicity 10. Limited volume and cell count 11. Lower cytotoxicity and less mature phenotype 12. Higher expression of inhibitory mediators	[39, 67, 193, 195–198]
hPSC iPSC	CD34+ hPSCs are isolated from embryonic, bone marrow, and peripheral blood stem cells and are differentiated to NK cells using a specific cytokine cocktail iPSCs are cultured in media using VEGF, BMP4, and SCF and are differentiated to CD34+ stem cells and then NK cells	1. High purity and concentration of NK cell (> 90%) 2. More stable expression of CAR 3. Homogeneous population 4. No need for eradiation before injection 5. No HLA-typing and donor selection required 6. Easier genetic manipulation of NK cells 7. Higher in-vivo tumor-killing potency 8. Potent proliferative capacity 9. Multiple doses can be produced and injected 10. Potency to produce “off-the-shelf” CAR NK cell production	1. Complicated production process 2. Immature phenotype and high inhibitory receptor expression by iPSC-derived CAR NK cells	[50, 194, 199, 200]
NK cell line	NK-92, NKG, YT, NK-YS, HANK-I, YTS, and NKL cell lines	1. Lesser GVHD risk 2. Easily expanded and transduced 3. Cheaper and easier standardization 4. Unlimited proliferation potential 5. Possibility of “off-the-shelf” CAR NK cell production	1. Need for irradiation before injection to prevent uncontrolled proliferation 2. Homogenous population 3. More stable expression of CAR 4. Limited in-vivo expansion 5. Higher expression of specific inhibitory KIRs, NKp44, and 6. NKp46 6. Lack most inhibitory KIRs 7. Lack multiple activatory receptors such as CD16 and NKp44 8. Possible carrier of abnormal genes and EBV	[17, 38, 40, 67, 201, 202]

PBMC, Peripheral blood mononuclear cell; UCB, Umbilical cord blood; hPSC, Human pluripotent stem cell; iPSC, Induced pluripotent stem cell; NK, Natural killer cell; SCF, Stem cell factor; VEGF, Vascular endothelial growth factor; HLA, Human leukocyte antigen; GVHD, Graft-versus host disease; CAR, Chimeric antigen receptor; BMP4, Bone morphogenic protein 4