Development of allogeneic NK cell adoptive transfer therapy in metastatic melanoma patients: in vitro preclinical optimization studies

Natural killer (NK) cells have long been considered as potential agents for adoptive cell therapy for solid cancer patients. Until today most studies utilized autologous NK cells and yielded disappointing results. Here we analyze various modular strategies to employ allogeneic NK cells for adoptive cell transfer, including donor-recipient HLA-C mismatching, selective activation and induction of melanoma-recognizing lysis receptors, and co-administration of antibodies to elicit antibody-dependent cell cytotoxicity (ADCC). We show that NK cell activation and induction of the relevant lysis receptors, as well as co-administration of antibodies yield substantial anti-cancer effects, which are functionally superior to HLA-C mismatching. Combination of the various strategies yielded improved effects. In addition, we developed various clinically-compatible ex vivo expansion protocols that were optimized according to fold expansion, purity and expression of lysis receptors. The main advantages of employing allogeneic NK cells are accessibility, the ability to use a single donor for many patients, combination with various strategies associated with the mechanism of action, e.g. antibodies and specific activation, as well as donor selection according to HLA or CD16 genotypes. This study rationalizes a clinical trial that combines adoptive transfer of highly potent allogeneic NK cells and antibody therapy.

Antibodies targeting the catalytic zinc complex of activated matrix metalloproteinases show therapeutic potential

Endogenous tissue inhibitors of metalloproteinases (TIMPs) have key roles in regulating physiological and pathological cellular processes. Imitating the inhibitory molecular mechanisms of TIMPs while increasing selectivity has been a challenging but desired approach for antibody-based therapy. TIMPs use hybrid protein-protein interactions to form an energetic bond with the catalytic metal ion, as well as with enzyme surface residues. We used an innovative immunization strategy that exploits aspects of molecular mimicry to produce inhibitory antibodies that show TIMP-like binding mechanisms toward the activated forms of gelatinases (matrix metalloproteinases 2 and 9). Specifically, we immunized mice with a synthetic molecule that mimics the conserved structure of the metalloenzyme catalytic zinc-histidine complex residing within the enzyme active site. This immunization procedure yielded selective function-blocking monoclonal antibodies directed against the catalytic zinc-protein complex and enzyme surface conformational epitopes of endogenous gelatinases. The therapeutic potential of these antibodies has been demonstrated with relevant mouse models of inflammatory bowel disease. Here we propose a general experimental strategy for generating inhibitory antibodies that effectively target the in vivo activity of dysregulated metalloproteinases by mimicking the mechanism employed by TIMPs.

Structural and functional bases for allosteric control of MMP activities: can it pave the path for selective inhibition?

The zinc-dependent matrix metalloproteinases (MMPs) belong to a large family of structurally homologous enzymes. These enzymes are involved in a wide variety of biological processes ranging from physiological cell proliferation and differentiation to pathological states associated with tumor metastasis, inflammation, tissue degeneration, and cell death. Controlling the enzymatic activity of specific individual MMPs by antagonist molecules is highly desirable, first, for studying their individual roles, and second as potential therapeutic agents. However, blocking the enzymatic activity with synthetic small inhibitors appears to be an extremely difficult task. Thus, this is an unmet need presumably due to the high structural homology between MMP catalytic domains. Recent reports have recognized a potential role for exosite or allosteric protein regions, distinct from the extended catalytic pocket, in mediating MMP activation and substrate hydrolysis. This raises the possibility that MMP enzymatic and non-enzymatic activities may be modified via antagonist molecules targeted to such allosteric sites or to alternative enzyme domains. In this review, we discuss the structural and functional bases for potential allosteric control of MMPs and highlight potential alternative enzyme domains as targets for designing highly selective MMP inhibitors.

Building of the tetraspanin web: distinct structural domains of CD81 function in different cellular compartments

The tetraspanin web is composed of a network of tetraspanins and their partner proteins that facilitate cellular interactions and fusion events by an unknown mechanism. Our aim was to unravel the web partnership between the tetraspanin CD81 and CD19, a cell surface signaling molecule in B lymphocytes. We found that CD81 plays multiple roles in the processing, intracellular trafficking, and membrane functions of CD19. Surprisingly, these different roles are embodied in distinct CD81 domains, which function in the different cellular compartments: the N-terminal tail of CD81 has an effect on the glycosylation of CD19; the first transmembrane domain of CD81 is sufficient to support the exit of CD19 from the endoplasmic reticulum, although the large extracellular loop (LEL) of CD81 associates physically with CD19 early during biosynthesis; and finally, the TM2 and TM3 domains of CD81 play a role in the transmission of signals initiated upon engagement of the LEL. The participation of distinct CD81 domains in varied functions may explain the pleiotropic effects of CD81 within the tetraspanin web.

Protein-protein interactions in the tetraspanin web

Tetraspanins are evolutionarily conserved membrane proteins that tend to associate laterally with one another and to cluster dynamically with numerous partner proteins in membrane microdomains. Consequently, members of this family are involved in the coordination of intracellular and intercellular processes, including signal transduction; cell proliferation, adhesion, and migration; cell fusion; and host-parasite interactions.

The CD9 Tetraspanin Is Not Required for the Development of Peripheral B Cells or for Humoral Immunity

The CD9 tetraspanin is known to be expressed at high levels on marginal zone (MZ) B cells, B-1 B cells, and plasma cells, and its expression is believed to be dependent on signals derived via Btk. In CD9 null mice, however, the development and survival of MZ B cells, B-1 B cells, and plasma cells all appear to be unaffected, and humoral immune responses to T-dependent and T-independent Ags are similar to those seen in wild-type littermate controls. In wild-type mice, CD9 levels may serve to distinguish between the presumed MZ precursor B cell population in the spleen and other IgD-expressing transitional B cells that express lower levels of CD21 and CD1d. These results suggest that CD9 is dispensable for B cell development and humoral immunity, but that this protein may serve as an additional marker for the presumed MZ precursor population of splenic B cells.

The tetraspanin web modulates immune-signalling complexes

The tetraspanin web represents a new concept of molecular interactions in the immune system. Whereas most surface immune-modulating molecules involve receptor-ligand interactions, tetraspanins associate with partner proteins and facilitate their lateral positioning in the membrane. Moreover, the same tetraspanin molecule can associate with different proteins depending on the cell type. Most importantly, members of this family tend to associate with each other, together with their partners, in membrane microdomains that provide a scaffold for the transmission of external stimuli to intracellular-signalling components.

The tetraspanin CD81 is necessary for partitioning of coligated CD19/CD21-B cell antigen receptor complexes into signaling-active lipid rafts

Tetraspanins have been hypothesized to facilitate the organization of functional multimolecular membrane complexes. In B cells the tetraspanin CD81 is a component of the CD19/CD21 complex. When coligated to the B cell Ag receptor (BCR), the CD19/CD21 complex significantly enhances BCR signaling in part by prolonging the association of the BCR with signaling-active lipid rafts. In this study CD81 is shown to associate with lipid rafts upon coligation of the BCR and the CD19/CD21 complex. Using B cells from CD81-deficient mice we demonstrate that in the absence of CD81, coligated BCR and CD19/CD21 complexes fail to partition into lipid rafts and enhance BCR signaling from rafts. Furthermore, a chimeric CD19 protein that associates only weakly if at all with CD81 fails to promote the association of coligated BCR with lipid rafts. The requirement for CD81 to promote lipid raft association may define a novel mechanism by which tetraspanins function as molecular facilitators of signaling receptors.

The Tetraspanin CD81 Regulates the Expression of CD19 During B Cell Development in a Postendoplasmic Reticulum Compartment

CD81 is a widely expressed tetraspanin that associates in B cells with CD19 in the CD19-CD21-CD81 signaling complex. CD81 is necessary for normal CD19 expression; cd81(-/-) B cells express lower levels of CD19, especially cd81(-/-) small pre-BII cells, which are almost devoid of surface CD19. The dependence of CD19 expression on CD81 is specific to this particular tetraspanin since cd9(-/-) B cells express normal levels of CD19. Furthermore, expression of human CD81 in mouse cd81(-/-) B cells restored surface CD19 to normal levels. Quantitative analysis of CD19 mRNA demonstrated normal levels, even in cd81(-/-) pre-BII cells. Analysis of CD19 at the protein level identified two CD19 glycoforms in both wild-type and cd81(-/-) B cells. The higher M(r) glycoform is significantly reduced in cd81(-/-) B cells and is endoglycosidase H (endo-H) resistant. In contrast, the low M(r) glycoform is comparably expressed in cd81(-/-) and in wild-type B cells and is endo-H sensitive. Because endo-H sensitivity is tightly correlated with endoplasmic reticulum localization, we suggest that the dependency of CD19 expression on CD81 occurs in a postendoplasmic reticulum compartment where CD81 is necessary for normal trafficking or for surface membrane stability of CD19.

The mesenchymal stroma negatively regulates B cell lymphopoiesis through the expression of activin A

The negative control of B cell generation is only partially resolved. We assessed the role of activin A in regulation of B lymphopoiesis in view of its specific inhibitory effects on tumor B lineage cells. Activin A is constitutively expressed in mouse hemopoietic organs and in cultured mesenchymal cell lines. We observed an inverse relationship between activin A titer and B lineage cell production. In the spleen, the red pulp exhibited a relatively higher abundance of the protein as compared with the lymphoid follicles, wherein B cell accumulation occurs. Furthermore, a specific shut off in activin A expression was observed in bone marrow and spleen following in vivo induction of B lymphocyte polyclonal activation. We further substantiated these in vivo observations by in vitro studies of primary bone marrow cultures, in which the expression of functional activin A was found to be diminished prior to the onset of B lymphopoiesis. The reduction in functional activin A is shown to concomitantly occur with spontaneous induction of the expression of activin A specific inhibitors. We therefore propose that the mesenchymal organ stroma expresses activin A that negatively controls B cell lymphopoiesis.

Reduced expression of activin A in focal lymphoid agglomerates within nasal polyps

It has been previously reported that activin A, a homodimer of the betaA inhibin subunit, is secreted by stromal cells from mouse bone marrow and causes apoptotic death of mouse plasmacytoma tumor cells. Recent in vitro studies have also implicated this cytokine in the suppression of normal B-cell lymphopoiesis. In this study we examined the occurrence of activin A in nasal polyp tissues that present a combination of epithelium, mesenchyme, and vascular endothelium, with frequent massive hemopoietic infiltration. Anti-betaA-chain antibodies strongly stained epithelial mucous glands and some endothelial cells, and diffusely stained the polyp stroma. Normal adult conchae were similarly stained, whereas activin A was not detected prenatally by immunostaining of nasal tissues. Staining specificity was substantiated by ligand competition assays. Detailed examination of the inflammatory polyp infiltrate showed that activin A staining was reduced in sites of focal infiltration of B-lymphoid cells. It is therefore implied that local accumulation of a large number of B-cells is associated with relatively low activin A expression.

The promotion of plasmacytoma tumor growth by mesenchymal stroma is antagonized by basic fibroblast growth factor induced activin A

The mesenchymal stroma has been shown to play a crucial role in the development of multiple myeloma, partly by secretion of interleukin (IL)-6, that serves as a growth factor for myeloma cells. However, it is still unclear which other stromal molecules are involved in the pathogenesis of this disease. We chose, as a model system, a mouse plasmacytoma cell line, which does not respond to IL-6. We found that the formation of mouse plasmacytoma tumors, in an in vivo skin transplantation model, is facilitated by co-injection of these tumor cells along with a mesenchymal stromal cell. The tumor promoting effect of the stroma was reproduced in an in vitro model; stromal cells induced the proliferation of plasmacytoma cells under serum-free conditions. This growth promotion could not be mimicked by a series of cytokines including IL-6 and insulin-like growth factor (IGF)-I implying a role for yet unidentified stromal factors. The in vivo formation of plasmacytoma tumors was reduced following administration of activin A, a cytokine member of the transforming growth factor (TGF)beta superfamily. Furthermore, the in vitro growth promoting effect of the stroma was abrogated by basic fibroblast growth factor (bFGF) which induced a higher stromal expression of activin A. Our results thus show that mesenchymal stroma expresses plasmacytoma growth stimulating activities that overcome the low constitutive level of the plasmacytoma inhibitor, activin A. The expression of activin A is upregulated by bFGF rendering the stroma suppressive for plasmacytoma growth. The balance between the expression of these regulators may contribute to mesenchymal stroma activity and influence the progression of multiple myeloma.