NK cells from an AML patient have recovered in remission and reached comparable cytolytic activity to that of a healthy monozygotic twin mediated by the single-chain triplebody SPM-2

Background: The capacity of patient's Natural Killer cells (NKs) to
be activated for cytolysis is an important prerequisite for the
success of antibody-derived agents such as single-chain
triplebodies (triplebodies) in cancer therapy. NKs recovered from
AML patients at diagnosis are often found to be reduced in
peripheral blood titers and cytolytic activity. Here, we had the
unique opportunity to compare blood titers and cytolytic function
of NKs from an AML patient with those of a healthy monozygotic
twin. The sibling's NKs were compared with the patient's drawn
either at diagnosis or in remission after chemotherapy. The
cytolytic activities of NKs from these different sources for the
patient's autologous AML blasts and other leukemic target cells in
conjunction with triplebody SPM-2, targeting the surface antigens
CD33 and CD123 on the AML cells, were compared. Methods: Patient
NKs drawn at diagnosis were compared to NKs drawn in remission
after chemotherapy and a sibling's NKs, all prepared from PBMCs by
immunomagnetic beads (MACS). Redirected lysis (RDL) assays using
SPM-2 and antibody-dependent cellular cytotoxicity (ADCC) assays
using the therapeutic antibody Rituximab (TM) were performed with
the enriched NKs. In addition, MACS-sorted NKs were analyzed for NK
cell activating receptors (NCRs) by flow cytometry, and the release
of TNF-alpha and IFN-gamma from blood samples of both siblings
after the addition of the triplebody were measured in ELISA-assays.
Results: Patient NKs isolated from peripheral blood drawn in
remission produced comparable lysis as NKs from the healthy twin
against the patient's autologous bone marrow (BM) blasts, mediated
by SPM-2. The NCR receptor expression profiles on NKs from patient
and twin were similar, but NK cell titers in peripheral blood were
lower for samples drawn at diagnosis than in remission.
Conclusions: Peripheral blood NK titers and ex vivo cytolytic
activities mediated by triplebody SPM-2 were comparable for cells
drawn from an AML patient in remission and a healthy twin. If these
results can be generalized, then NKs from AML patients in remission
are sufficient in numbers and cytolytic activity to make
triplebodies promising new agents for the treatment of AML.