Grabbing the Bull by Both Horns: Bovine Ultralong CDR-H3 Paratopes Enable Engineering of 'Almost Natural' Common Light Chain Bispecific Antibodies Suitable For Effector Cell Redirection.

A subset of antibodies found in cattle comprises ultralong CDR-H3 regions of up to 70 amino acids. Interestingly, this type of immunoglobulin usually pairs with the single germline VL gene, V30 that is typically very conserved in sequence. In this work, we have engineered ultralong CDR-H3 common light chain bispecific antibodies targeting Epidermal Growth Factor Receptor (EGFR) on tumor cells as well as Natural Cytotoxicity Receptor NKp30 on Natural Killer (NK) cells. Antigen-specific common light chain antibodies were isolated by yeast surface display by means of pairing CDR-H3 diversities following immunization with a single V30 light chain. After selection, EGFR-targeting paratopes as well as NKp30-specific binders were combined into common light chain bispecific antibodies by exploiting the strand-exchange engineered domain (SEED) technology for heavy chain heterodimerization. Biochemical characterization of resulting bispecifics revealed highly specific binding to the respective antigens as well as simultaneous binding to both targets. Most importantly, engineered cattle-derived bispecific common light chain molecules elicited potent NK cell redirection and consequently tumor cell lysis of EGFR-overexpressing cells as well as robust release of proinflammatory cytokine interferon-γ. Taken together, this data is giving clear evidence that bovine bispecific ultralong CDR-H3 common light chain antibodies are versatile for biotechnological applications.

Functional capacity of natural killer cells in HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP) patients.

BACKGROUND: Natural killer (NK) cells are part of the innate immune system and provide surveillance against viruses and cancers. The ability of NK cells to kill virus-infected cells depends on the balance between the effects of inhibitory and activating NK cell receptors. This study aimed to investigate the phenotypic profile and the functional capacity of NK cells in the context of HTLV-1 infection. METHODS: This cross-sectional study sequentially recruited HTLV-1 infected individuals with HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP) and asymptomatic HTLV-1 (AS) from the Integrated and Multidisciplinary HTLV Center in Salvador, Brazil. Blood samples from healthy blood donors served as controls. NK cell surface receptors (NKG2D, KIR2DL2/KIR2DL3, NKp30, NKG2A, NKp46, TIM-3 and PD-1), intracellular cytolytic (Granzyme B, perforin) and functional markers (CD107a for degranulation, IFN-γ) were assayed by flow cytometry in the presence or absence of standard K562 target cells. In addition, cytotoxicity assays were performed in the presence or absence of anti-NKp30. RESULTS: The frequency of NKp30+ NK cells was significantly decreased in HAM/TSP patients [58%, Interquartile Range (IQR) 30-61] compared to controls (73%, IQR 54-79, p = 0.04). The production of cytolytic (perforin, granzyme B) and functional markers (CD107a and IFN-γ) was higher in unstimulated NK cells from HAM/TSP and AS patients compared to controls. By contrast, stimulation with K562 target cells did not alter the frequency of CD107a+ NK cells in HAM/TSP subjects compared to the other groups. Blockage of the NKp30 receptor was shown to decrease cytotoxic activity (CD107a) and IFN-γ expression only in asymptomatic HTLV-1-infected individuals. CONCLUSIONS: NK cells from individuals with a diagnosis of HAM/TSP present decreased expression of the activating receptor NKp30, in addition to elevated degranulation activity that remained unaffected after blocking the NKp30 receptor.

NK cells kill mycobacteria directly by releasing perforin and granulysin.

Although the mechanisms underlying the cytotoxic effect of NK cells on tumor cells and intracellular bacteria have been studied extensively, it remains unclear how these cells kill extracellular bacterial pathogens. In this study, we examine how human NK cells kill Mycobacterium kansasii and M.tb. The underlying mechanism is contact dependent and requires two cytolytic proteins: perforin and granulysin. Mycobacteria induce enhanced expression of the cytolytic proteins via activation of the NKG2D/NCR cell-surface receptors and intracellular signaling pathways involving ERK, JNK, and p38 MAPKs. These results suggest that NK cells use similar cellular mechanisms to kill both bacterial pathogens and target host cells. This report reveals a novel role for NK cells, perforin, and granulysin in killing mycobacteria and highlights a potential alternative defense mechanism that the immune system can use against mycobacterial infection.

Important role for NKp30 in synapse formation and activation of NK cells.

Natural killer (NK) cells play an important role in host defense against viral infections and tumor cells. NK cells require contact with target cells and must subsequently form an NK cell immunological synapse (NKIS). The NKIS represents the interface formed between NK cells and their target cells via receptor recognition and adhesion molecule binding, and it is essential for NK cell cytotoxicity, which is mediated through degranulation and release of cytolytic enzymes. In this study, NKp30-mediated signaling and the role of NKp30 in the formation of the NKIS were investigated. The results from confocal microscopy studies showed that the activating receptor, NKp30, and the adhesion molecule, LFA-1 (CD11a), accumulated at the interface between NK92 cells, which are a human NK cell line, and HeLa cells, which are a human tumor cell line (NK92-HeLa). Blockade of NKp30 inhibited NK cell degranulation, cytotoxicity and cytokine secretion but did not affect the conjugation between NK and target cells. Additionally, ligation with HeLa cells activated the Erk1/2 signaling pathway in NK92 cells, and blockade of NKp30 decreased the phosphorylation of Erk1/2. Therefore, NKp30 is a triggering receptor downstream of adhesion and plays an important role in NK cell activation, degranulation and cytotoxicity.

Preparation and functional identification of a monoclonal antibody against the recombinant soluble human NKp30 receptor.

NKp30 is an important activating receptor of human natural killer (NK) cells that participates in NK cell activation and cytotoxicity against tumor and infected cells. To study the function of NKp30, anti-human NKp30 monoclonal antibody was prepared. The human NKp30 ectodomain (rhNKp30) was expressed in Escherichia coli as inclusion bodies and refolded using the dilution method. The refolded rhNKp30 was purified by immobilized metal affinity chromatography. The activity of soluble rhNKp30 was confirmed by flow cytometry and NK cytotoxicity assays. Four hybridoma cell lines producing monoclonal antibodies against rhNKp30 were obtained. One of the monoclonal antibodies, designated as "3G5", was highly specific and could be used in western blotting, immunoprecipitation, ELISA, and flow cytometry assays. The preparation of soluble rhNKp30 and a monoclonal antibody against NKp30 may provide useful tools for further functional studies of human NKp30.