Monica Betancur

Essential role for Stat5a/b in myeloproliferative neoplasms induced by BCR-ABL1 and JAK2(V617F) in mice.

STAT5 proteins are constitutively activated in malignant cells from many patients with leukemia, including the myeloproliferative neoplasms (MPNs) chronic myeloid leukemia (CML) and polycythemia vera (PV), but whether STAT5 is essential for the pathogenesis of these diseases is not known. In the present study, we used mice with a conditional null mutation in the Stat5a/b gene locus to determine the requirement for STAT5 in MPNs induced by BCR-ABL1 and JAK2(V617F) in retroviral transplantation models of CML and PV. Loss of one Stat5a/b allele resulted in a decrease in BCR-ABL1-induced CML-like MPN and the appearance of B-cell acute lymphoblastic leukemia, whereas complete deletion of Stat5a/b prevented the development of leukemia in primary recipients. However, BCR-ABL1 was expressed and active in Stat5-null leukemic stem cells, and Stat5 deletion did not prevent progression to lymphoid blast crisis or abolish established B-cell acute lymphoblastic leukemia. JAK2(V617F) failed to induce polycythemia in recipients after deletion of Stat5a/b, although the loss of STAT5 did not prevent the development of myelofibrosis. These results demonstrate that STAT5a/b is essential for the induction of CML-like leukemia by BCR-ABL1 and of polycythemia by JAK2(V617F), and validate STAT5a/b and the genes they regulate as targets for therapy in these MPNs.

Transfection with mRNA for CD19 specific chimeric antigen receptor restores NK cell mediated killing of CLL cells

An emerging treatment option for chronic lymphocytic leukemia (CLL) is to make cytotoxic immune cells express a chimeric antigen receptor (CAR) that recognizes specific surface molecules on CLL cells. Here an mRNA coding for an anti-CD19 CAR was transfected into the NK-92 cell line by electroporation. In contrast to cDNA, mRNA resulted in high transfection efficiency (47.2 +/- 8% versus <5% for cDNA) with minimal effect on cell viability. NK-92 cells expressing anti-CD19 CAR killed previously resistant CD19+ B-ALL cell lines, as well as primary CLL cells and therefore may present a safe, cell-based, targeted treatment for patients with CLL.

Umbilical Cord Mesenchymal Stem Cells Increase Expansion of Cord Blood Natural Killer Cells

Natural killer (NK) cell-mediated cytotoxicity can control leukemia relapse while protecting patients from graft-versus-host disease (GVHD) after allogeneic stem cell transplant. Cord blood (CB) is rich in NK cell progenitors with similar properties of proliferation and cytotoxicity as adult blood NK cells. Hence, it is attractive to expand and potentially utilize these cells for adoptive immunotherapy. In this study, CB mononuclear cells were CD3-depleted by immunomagnetic microbead selection to remove T cells. This CD3(dep) CB-MNC fraction was then plated for ex vivo expansion, with or without a feeder layer of irradiated umbilical cord mesenchymal stem cells (UC-MSC), with or without cytokines that have been shown to be critical for NK expansion: IL-2, IL-15, IL-3, and FLT-3L. At an average of 2 weeks of culture, there was significantly higher expansion (64.7 +/- 8.4-fold) of CD56(+)/CD3(-) NK cells in the presence of the UC-MSC feeder layer and cytokines compared to controls (no increase with feeder layer only and 6.4 +/- 1.5-fold increase with cytokines only, P < .05). Contact between CD3(dep) CB-MNC cells and UC-MSC augmented NK expansion. The combination of all 4 cytokines was superior to IL-2 alone or 2 cytokines combinations: mean 64.7 +/- 8.4-fold expansion with 4 cytokines combination versus IL-2 alone, IL-2 + FLT-3L, IL-2 + IL-15 or IL-2 + IL-3 (12.2 +/- 2.0, 14.4 +/- 2.4, 10.4 +/- 4.1, 25.2 +/- 8.1 respectively). We also observed that only fresh CD3(dep) CB-MNC preparations could be expanded reliably, whereas frozen and thawed CD3(dep) CB-MNC cells did not expand consistently (mean fold increase 6.5 +/- 3.2). Cytotoxicity of expanded NK cells was compared with NK cells from fresh and overnight IL-2 activated CD3(dep) CB-MNC. Whereas fresh cells displayed no discernible killing, strong cytotoxicity against K562, Raji, REH, and SUP-B15 cells lines was noted after overnight activation in IL-2. Cytotoxicity of expanded NK cells against Raji, REH, and SUP-B15 was lower, which, however, correlated with a predominant expansion of CD56(+)/CD16(-) cells known to have less cytolytic activity than CD56(+)/CD16(+). To test the transfection efficiency in NK cells, fresh or expanded CD3(dep) CB-MNC cells were electroporated with either DNA or mRNA constructs for GFP. DNA had a low transfection efficiency (<10%), whereas the one for mRNA reached 52%, but at the cost of significant cell death. Our results suggest that CB NK cell progenitors can be expanded to obtain large numbers by using an irradiated feeder of UC-MSC. They maintain an elevated cytotoxic profile, and may be genetically manipulated-all characteristics that make them suitable for cellular therapies.

Comparison of mRNA and lentiviral based transfection of natural killer cells with chimeric antigen receptors recognizing lymphoid antigens

Abstract Natural killer (NK) cells can be engineered to kill resistant B-lymphoid cell lines and primary B-cell chronic lymphocytic leukemia (B-CLL) cells after transfection with chimeric antigen receptors (CARs) recognizing CD19 or CD20. Here we compared mRNA electroporation with lentiviral vector (LV) transduction for both CARs. Transfection efficiency and cytotoxicity of previously NK-92 resistant CLL cells were significantly higher after mRNA electroporation than after LV transduction. Further cell sorting of LV-transduced NK-92 cells resulted in a highly enriched population of transduced cells with significant target cell lysis. Compared to NK-92 cells, peripheral blood and cord blood cells consistently showed < 10% transfection efficiency with mRNA, while LV transduction varied between 8 and 16% for peripheral blood and 12 and 73% for cord blood. These results suggest that LV should be used to achieve sufficient transgene expression if blood NK cells are considered for CAR transduction. Transfection with mRNA results in clinically relevant levels of transfection only in NK-92 cells.

Variable contribution of monoclonal antibodies to ADCC in patients with chronic lymphocytic leukemia.

Monoclonal antibodies (mAbs) are increasingly used in treatment protocols for chronic lymphocytic leukemia (CLL). Here we determined (i) the extent of antibody-dependent cellular cytotoxicity (ADCC) of four different mAbs against primary CLL cells, (ii) whether ADCC correlates with antigen density on CLL cells, and (iii) whether allogeneic natural killer (NK) cells display superior ADCC than autologous. Effector cells for ADCC were (i) NK-92 cells not expressing FcR, (ii) NK-92 cells transfected with a high-affinity Fc receptor, (iii) autologous NK cells from patients with CLL, (iv) allogeneic NK cells. Results suggest that ADCC contributes to killing of CLL cells by anti-CD20 antibodies (rituximab and veltuzumab), whereas mAbs against CD22 (epratuzumab) and CD23 (lumiliximab) showed minimal ADCC. The magnitude of anti-CD20 mediated ADCC did not correlate with antigen density of CD20. ADCC was not influenced by the FcR genotype expressed by autologous NK cells. Allogeneic NK cells were superior to autologous NK cells in killing primary CLL cells.

Distinct graft-versus-leukemic stem cell effects of early or delayed donor leukocyte infusions in a mouse chronic myeloid leukemia model

Among hematologic neoplasms, chronic myeloid leukemia (CML) is exquisitely sensitive to graft-versus-leukemia (GVL) because patients relapsing after allogeneic hematopoietic stem-cell transplantation (alloHSCT) can be cured by donor leukocyte infusion (DLI); however, the cellular mechanisms and strategies to separate GVL from GVHD are unclear. We used a BCR-ABL1 transduction/transplantation mouse model to study the mechanisms of DLI in MHC-matched, minor histocompatibility antigen-mismatched allogeneic chimeras with CML-like leukemia, in which DLI can be administered at the time of transplantation (early) or after recovery of hematopoiesis (delayed). After early DLI, CML-like leukemia cannot be transferred into immunocompetent secondary recipients as soon as 4 days after primary transplantation, demonstrating that cotransplantation of T lymphocytes blocks the engraftment of BCR-ABL1-transduced stem cells. In contrast, in allogeneic chimeras with established CML-like leukemia, combined treatment with delayed DLI and the kinase inhibitor imatinib eradicates leukemia with minimal GVHD. The GVL effect is directed against minor histocompatibility antigens shared by normal and leukemic stem cells, and is mediated predominantly by CD8+ T cells, with minor contributions from CD5- splenocytes, including natural killer cells. These results define a physiologic model of adoptive immunotherapy of CML that will be useful for investigating the cellular and molecular mechanisms of GVL.