Optimal Ex-Vivo Expansion (EvE) of Cord Blood (CB) Natural Killer (NK) Cells, NK Cytotoxicity and NK Receptor (NKR) Expression: Potential for CB Adoptive Cellular Immunotherapy (ACI).

CD56⁺ NK subsets exhibit differential receptor profiles including killer-Ig-like receptors (KIR), C-lectin (NKG2) and natural cytotoxicity receptors (NCR) involved with tumor target recognition which may play a role in ACI for malignancies (Farag et al Blood, 2002). NK cell activation and NK mediated cytolysis is induced by several triggering receptors such as NCR (i.e. NKp44, NKp46) and NKG2 surface receptors like NKG2D (Moretta, et al, Curr Opinion in Immunol, 2004; Marcenaro et al, Eur J Immunol, 2003). UCB is limited by the absence of available donor effector cells (NK, CTL, LAK and NKT cells) for infusion after transplantation for the treatment of minimal residual resistant hematological relapse and/or PTLD (Barker et al, Blood, 2001; Locatelli, et al Blood,1999). We demonstrated the ability to EvE CB in short term culture (48 hrs) with IL-2, IL-7, IL-12 and anti-CD3 (ABCY) cryopreserved, thawed, recryopreserved, rethawed and ex vivo expanded (CTCTE) with significant increase in CD3⁻/16⁺/56^{+ bright/dim} subsets expressing KIR3DL1, KIR2DL1/S1, KIR2DL2 and CD94/NKG2A (Ayello/Cairo et al, BBMT, 25a, 2004). In this study, we compared short-term cultures (48 hrs) with prolonged cultures (4 to 10 days) on expansion, maturation and expression of NCR, NKG2, KIR and cytolytic mechanisms in previously cryopreserved CB that were TCTE. CB was cryopreserved and thawed by the NHLBI/COBLT method. (Kurtzberg/Cairo, Transfuison, 2005). Rethawed nonadherent CB cells were cultured (2–10 days) in serum-free medium alone or with anti-CD3 (50 ng/ml, IL-2 (5 ng/ml), IL-7 (10 ng/ml) and IL-12 (10 ng/ml) (ABCY). NK receptor expression (CD94, NKG2C, NKG2D, NKp44, NKp46, KIR2DS4) and intracellular perforin and granzyme B activity were determined by flow cytometry. NK and LAK cytotoxicity was measured by europium release assay. Significant increases were seen in NK activating KIR2DS4 at day 10 vs 2 in ABCY both in CD3⁻/16⁺/56^{+ dim and bright} subsets (16.9±0.4 vs 2.1±0.2% and 22.3±0.3 vs 0.9±0.2%, p<0.001, respectively). C-lectin activating receptor CD94/NKG2D was increased at day 7 vs 2 following ABCY EvE (41.4 ±0.43 vs 23.7±2.0 %, p<0.001). A significant increase was seen in NK (CD3⁻/16⁺/56^+dim) KIR3DL1 subset at day 10 vs 2 (38.3±2.8 vs 18.9±6.3 7%, p<0.05). In contrast, NCR expression in CD3⁻/16⁺/56^{+ dim} NKp44 subset was significantly decreasedat day 10 vs 2 of EvE with ABCY (15.2±0.7 vs 27.2±0.7%, p<0.001). A significant decrease was seen in CD3⁻/16⁺/56^{+ dim} NKp46 expression following day 10 vs 2 (8.5±0.2 vs 23.5±1.2 %, p<0.001). Perforin expression demonstrated a significant decrease in ABCY at day 10 vs 2 (55.7±1.8 vs 84.3±1.3%, p<0.001) yet increasing levels of granzyme B from day 2 to 10 (25.8±1.8 vs 45.1±1.7%, p<0.0001). A significant increase in CB NK and LAK cytotoxicity was seen in ABCY on day 10 vs 2 (NK: 71.5 ±1.6 vs 53.8±10.3%, p<0.001; LAK: 63.2±0.24 vs 31.8±1.8%, p<0.001). In summary, CB MNC may be thawed at time of CB transplantation, recryopreserved, rethawed and at a later date EvE and activated for 7–10 days to yield viable NK subsets. EvE in ABCY at 10 days yielded increased expression of NK KAR (CD56^{+dim and bright}) and granzyme B expression but decreased NK C-lectin CD94/NKG2D, NCR NKp46 and NKp48 and perforin expression.