Natural killer cells in graftversus-host disease and graft-versus-leukemia - Immune Biology of Allogeneic Hematopoietic Stem Cell Transplantation - page 342

increased NK cell killing of CD20-positive lymphoma and breast cancer
cells [109] . Pegram and colleagues [110] genetically engineered mouse NK
cells with a CAR consisting of erbB2 (Her-2/neu) and CD28 fused to CD3ζ.
These NK cells were adoptively transferred into Rag-1 −/− mice and inhib-
ited growth of erbB2 + lymphoma by directly lysing the tumors. Altvater and
colleagues [111] genetically modified in vitro -stimulated NK cells from
healthy donors and pediatric leukemia patients with CARs consisting of
either CD19 or Gd2. They also tested 2B4 as the endodomain or a combi-
nation of CD3ζ and 2B4. NK cells expressing CD19-2B4 failed to produce
IFN-γ and TNF-α when stimulated but did express CD107a. They also did
not upregulate expression of CD25. When combined with CD3ζ, NK cells
were significantly more potent against CD19 + leukemia cells, suggesting
that 2B4 can act as a costimulatory receptor to increase NK cell activity.
Similarly, NK cells expressing Gd2-CD3ζ-2B4 were able to lyse resistant
neuroblastoma cell lines.

Enhancing NK cell function to eliminate tumors

Several tumor-targeted monoclonal antibodies have been developed and
have been used clinically to treat various malignancies ( Figure 15.2 ). Since
inhibitory KIRs bind to self-HLA class I and inhibit NK cell function, mono-
clonal antibodies directed against the inhibitory KIRs have been developed.
Romagne and colleagues [112] generated a human monoclonal antibody
called 1-7F9 that recognizes the inhibitory KIRs KIR2DL1, KIR2DL2, and
KIR2DL3. It does not cross-react with KIR3DL1. During preclinical char-
acterization, it was demonstrated that 1-7F9 did not stimulate peripheral
blood NK cells to degranulate or produce IFN-γ, and blocking KIR with 1-7F9
increased lysis of primary AML blasts. In transgenic mice engineered to
express KIR2DL3, HLA-Cw3 + splenocytes were rejected after adding 1-7F9,
and furthermore, in NOD-SCID mice, NK cells lysed autologous tumors
when 1-7F9 was added. Current clinical trials are under way to investigate
the efficacy of this monoclonal antibody in humans.

346

CD137 or 4-1BB is a costimulatory molecule of the TNF receptor family. It is
expressed on activated NK cells, T cells, B cells, dendritic cells, monocytes,
and neutrophils. On resting NK cells its expression is low and CD16 activa-
tion can induce its expression [113] . CD137 can be activated by binding to
its natural ligand or triggered with a monoclonal antibody against it. Anti-
CD137 antibodies have been used in combination with other monoclonal
antibodies to increase NK cell activation, which is discussed below. Artifi-
cial APCs have also been engineered to express CD137L, which has been
shown to increase expansion of NK cells as discussed above.

NK cells recognize antibody-coated targets through CD16 and medi-
ate ADCC. Rituximab, a monoclonal antibody directed against CD20 on
mature B cells, has been used to treat non-Hodgkin's lymphoma [114] .
Allelic polymorphisms within the CD16 gene have been shown to influ-
ence NK-cell-mediated ADCC. One such polymorphism is at position 158,
a region of the receptor that interacts with the hinge region of IgG antibod-
ies, has either a phenylalanine or a valine (V) at this position, and alters
NK cell binding [115] . The 158V polymorphism results in higher CD16
binding to IgG. Cartron and colleagues [116] demonstrated that the 158V