The CD3-depletion process did not affect the NKLR expression profiles of unactivated NK cells (Figure 7B). performed tests over two months, indicates that NKLR-guided selection of donors is feasible. As a proof of concept, we show that melanoma cells are dominantly recognized by three NKLRs: NKG2D, NKp30 and NKp44. Notably, the expression of NKp30 on circulating NK cells among metastatic melanoma patients was significantly decreased, which diminishes their ability to kill melanoma cells. expansion of NK cells results not only in increased amount of cells but also in a Rabbit Polyclonal to eNOS consistently superior and predictable expression of NKG2D, NKp30 and NKp44. Moreover, expanded NK cultures with high expression of NKG2D or NKp30 were mostly derived from the corresponding NKG2Dhigh or NK30high donors. These NK cultures subsequently displayed an improved cytotoxic activity against melanoma in a HLA/KIR-ligand mismatched setup, which was NKLR-dependent, as demonstrated with blocking anti-NKG2D antibodies. Conclusions/Significance NKLR/NKLR-ligand matching reproducibly elicits enhanced NK anti-tumor response. Common NKLR recognition patterns of tumors, as demonstrated here in melanoma, would allow implementation of this approach in solid malignancies and potentially in hematological malignancies, either independently or in adjunction to other modalities. Introduction Natural Killer (NK) cells are lymphocytes that belong to the innate immune branch, comprise 5C15% of the peripheral blood lymphocytes and are able to eliminate without Ruzadolane prior antigenic stimulation virus-infected and malignantly transformed cells, but to spare normal healthy cells C. NK cells eliminate tumor cells through perforin/granzyme dependent mechanisms, apoptotic mechanism and through secretion of various inflammatory and Th1-promoting cytokines [reviewed in 3]C. NK cells respond to a variety of bioactive agents, including cytokines such as interleukin-2 (IL-2), IL-12, or interferons, by up-regulation of cytolytic, secretory, and/or proliferative functions . Triggering of effector NK cell functions depends on a balance between inhibitory and stimulating signals [reviewed in 1], . Ruzadolane Most inhibitory signals are mediated through Killer Ig-like Receptors (KIR) that recognize various alleles of major histocompatibility complex (MHC) class I molecules , and it was postulated that all NK cells express at least one receptor that recognizes a self MHC allele, probably to avoid autoreactivity . However, recent evidence show that Ruzadolane up to 20% of the peripheral blood NK cells may be KIR-negative, yet self-tolerant, as these cells probably reflect an immature stage C. In addition, MHC class I independent NK inhibitory mechanisms have already been reported C. NK Lysis Receptors (NKLR) are collectively comprised from the family of natural cytotoxicity receptors (NCR) that includes NKp46 , NKp44  and NKp30 , and from other main killing receptors such as NKG2D Ruzadolane  and CD16 . Ligands for some NKLRs are found on abnormal cells, such as virus-infected, transformed or stressed cells . Ligands for other NKLRs, such as NKG2D, are not restricted to abnormal cells, but are usually overexpressed under various conditions . Notably, while the cellular ligands for the NCRs are still undefined, several ligands for NKG2D have been identified and include MICA, MICB, ULBP1, ULBP2, ULBP3 and ULBP4 . CD16 is the high affinity FcRIII receptor , but a cellular ligand is yet to be described. So far, the tumor ligands for the NKLRs are still elusive, as only two viral ligands were identified: hemagglutinins of paramyxoviridae viruses are recognized by NKp46  and NKp44 , and the CMV tegument protein pp65 that is recognized by NKp30 . The suppression of NK cells by self MHC class I might be a mechanism that enables malignantly transformed cells to evade NK-mediated elimination. Since KIR-ligands on tumors always match the self NK cell KIR repertoire, autolgous NK cells are constantly susceptible to inhibition. This may at least partially explain the past clinical failure of adoptively transferred autologous NK or lymphokine activated killer (LAK) cells to mediate objective rejection of metastatic solid malignancies C. These notions led to the development of the KIR/KIR-ligand mismatch concept to augment anticancer NK-mediated activity C. This concept can be employed only in an allogeneic setting. The use of allogeneic NK cells has shown substantial clinical benefit against acute myeloid leukemia (AML) after haploidentical and partially mismatched unrelated hematopoietic cell transplantation when KIR/KIR-ligand incompatibility existed in the graft-versus-host (GVH) direction . Surprisingly, in contrast to allogeneic T cells, NK cells seem to have an anti GVH effect . A similar approach based on KIR/KIR-ligand mismatching was pre-clinically developed for allogeneic NK adoptive cell transfer (ACT) in solid malignancies . So far, there is still.