Natural killer (NK) cells are a sub-population of lymphocytes, involved in non-conventional immunity. NK cells can be obtained by various techniques known in the art, such as from blood samples, cytapheresis, collections, etc.
Characteristics and biological properties of NK cells include the expression of surface antigens including CD16, CD56, and/or CD57; the absence of the alpha/beta or gamma/delta TCR complex on the cell surface; the ability to bind to and kill cells that fail to express “self” MHC/HLA antigens by the activation of specific cytolytic enzymes; the ability to kill tumor cells or other diseased cells that express a NK activating receptor-ligand; the ability to release cytokines that stimulate or inhibit the immune response; and the ability to undergo multiple rounds of cell division and produce daughter cells with similar biologic properties as the parent cell. Within the context of this invention “active” NK cells designate biologically active NK cells, more particularly NK cells having the capacity of lysing target cells. For instance, an “active” NK cell is able to kill cells that express an NK activating receptor-ligand and fail to express “self” MHC/HLA antigens (KIR-incompatible cells).
Based on their biological properties, various therapeutic and vaccine strategies have been proposed in the art that rely on a modulation of NK cells. However, NK cell activity is regulated by a complex mechanism that involves both stimulating and inhibitory signals. Accordingly, effective NK cell-mediated therapy may require both a stimulation of these cells and a neutralization of inhibitory signals.
NK cells are negatively regulated by major histocompatibility complex (MHC) class I-specific inhibitory receptors (Kärre et al., 1986; Öhlén et al, 1989). These specific receptors bind to polymorphic determinants of MHC class I molecules or HLA present on other cells and inhibit NK cell lysis. In humans, certain members of a family of receptors termed killer Ig-like receptors (KIRs) recognize groups of HLA class I alleles.
KIRs are a large family of receptors present on certain subsets of lymphocytes, including NK cells. The nomenclature for KIRs is based upon the number of extracellular domains (KIR2D or KIR3D) and whether the cytoplasmic tail is either long (KIR2DL or KIR3DL) or short (KIR2DS or KIR3DS). Within humans, the presence or absence of a given KIR is variable from one NK cell to another within the NK population present in a single individual. Within the human population there is also a relatively high level of polymorphism of the KIR molecules, with certain KIR molecules being present in some, but not all individuals. Certain KIR gene products cause stimulation of lymphocyte activity when bound to an appropriate ligand. The confirmed stimulatory KIRs all have a short cytoplasmic tail with a charged transmembrane residue that associates with an adapter molecule having an immunostimulatory motif (ITAM). Other KIR gene products are inhibitory in nature. All confirmed inhibitory KIRs have a long cytoplasmic tail and appear to interact with different subsets of HLA antigens depending upon the KIR subtype. Inhibitory KIRs display in their intracytoplasmic portion one or several inhibitory motifs that recruit phosphatases. The known inhibitory KIR receptors include members of the KIR2DL and KIR3DL subfamilies. KIR receptors having two Ig domains (KIR2D) identify HLA-C allotypes: KIR2DL2 (formerly designated p58.2) or the closely related gene product KIR2DL3 recognizes an epitope shared by group 2 HLA-C allotypes (Cw1, 3, 7, and 8), whereas KIR2DL1 (p58.1) recognizes an epitope shared by the reciprocal group 1 HLA-C allotypes (Cw2, 4, 5, and 6). The recognition by KIR2DL1 is dictated by the presence of a Lys residue at position 80 of HLA-C alleles. KIR2DL2 and KIR2DL3 recognition is dictated by the presence of an Asn residue at position 80. Importantly the great majority of HLA-C alleles have either an Asn or a Lys residue at position 80. One KIR with three Ig domains, KIR3DL1 (p70), recognizes an epitope shared by HLA-Bw4 alleles. Finally, a homodimer of molecules with three Ig domains KIR3DL2 (p140) recognizes HLA-A3 and -A11.
Although inhibitory KIRs and other class-I inhibitory receptors (Moretta et al, 1997; Valiante et al, 1997a; Lanier, 1998) may be co-expressed by NK cells, in any given individual's NK repertoire there are cells that express a single KIR and thus, the corresponding NK cells are blocked only by cells expressing a specific class I allele group.
NK cell population or clones that are KIR mismatched, i.e., population of NK cells that express KIR that are not compatible with a HLA molecules of a host, have been shown to be the most likely mediators of the graft anti-leukemia effect seen in allogeneic transplantation (Ruggeri et al., 2002). One way of reproducing this effect in a given individual would be to use reagents that block the KIR/HLA interaction.
Monoclonal antibodies specific for KIR2DL1 have been shown to block the interaction of KIR2DL1 with Cw4 (or the like) alleles (Moretta et al., 1993). Monoclonal antibodies against KIR2DL2/3 have also been described that block the interaction of KIR2DL2/3 with HLACw3 (or the like) alleles (Moretta et al., 1993). However, the use of such reagents in clinical situations would require the development of two therapeutic mAbs to treat all patients, regardless of whether any given patient was expressing class 1 or class 2 HLA-C alleles. Moreover, one would have to pre-determine which HLA type each patient was expressing before deciding which therapeutic antibody to use, thus resulting in much higher cost of treatment.
Watzl et al., Tissue Antigens, 56, p. 240 (2000) produced cross-reacting antibodies recognizing multiple isotypes of KIRs, but those antibodies did not exhibit potentiation of NK cell activity. G. M. Spaggiara et al., Blood, 100, pp. 4098-4107 (2002) carried out experiments utilizing numerous monoclonal antibodies against various KIRs. One of those antibodies, NKVSF1, was said to recognize a common epitope of CD158a (KIR2DL1), CD158b (KIR2DL2) and p50.3 (KIR2DS4). It is not suggested that NKVSF1 can potentiate NK cell activity and there is no suggestion that it could be used as a therapeutic. Accordingly, practical and effective approaches in the modulation of NK cell activity have not been made available so far in the art and still require HLA allele-specific intervention using specific reagents.