A functional mammalian display screen identifies rare antibodies that stimulate NK cell-mediated cytotoxicity

An engineered NKp46 antibody for construction of multi-specific NK cell engagers

Recent developments in cancer immunotherapy have highlighted the potential of harnessing natural killer (NK) cells in the treatment of neoplastic malignancies. Of these, bispecific antibodies, and NK cell engager (NKCE) protein therapeutics in particular, have been of interest. Here, we used phage display and yeast surface display to engineer RLN131, a unique cross-reactive antibody that binds to human, mouse, and cynomolgus NKp46, an activating receptor found on NK cells. RLN131 induced proliferation and activation of primary NK cells, and was used to create bispecific NKCE constructs of varying configurations and valency. All NKCEs were able to promote greater NK cell cytotoxicity against tumor cells than an unmodified anti-CD20 monoclonal antibody, and activity was observed irrespective of whether the constructs contained a functional Fc domain. Competition binding and fine epitope mapping studies were used to demonstrate that RLN131 binds to a conserved epitope on NKp46, underlying its species cross-reactivity.

Altered NCR3 Splice Variants May Result in Deficient NK Cell Function in Renal Cell Carcinoma Patients

BACKGROUND/AIM

The natural killer (NK) cell function of patients with malignant tumours may be suppressed by deficiency, and the poor prognosis of renal cell carcinoma (RCC) patients may be due to escape from NK cell cytotoxicity, especially with respect to natural cytotoxicity receptors (NCRs) on the NK cell surface. However, the specific mechanism remains unclear. Therefore, in this study, we sought to explore the role of NCR, especially NCR3 splice variants, in the process of NK cell deficiency in RCC patients.

MATERIALS AND METHODS

We used flow cytometry to analyse the phenotype of NK cells from the peripheral blood and kidney tumour tissue of RCC patients. The NKp30-mediated NK cell killing function was measured by antibody-dependent cell-mediated cytotoxicity (ADCC) in NK and RCC cell coincubation. We extracted RNA from the peripheral blood mononuclear cells (PBMCs) of RCC patients and renal carcinoma tissue and carried out real-time quantitative PCR to detect the mRNA levels of NKp30a, NKp30b and NKp30c. mRNA expression levels of cytokines (IL-6, IL-8, IL-10, IL-18 and TGF-β) based on RNA extracted from renal carcinoma tissue and adjacent normal kidney tissues were also measured by real-time quantitative PCR.

RESULTS

Regarding the phenotype of NK cells in RCC patients, the proportion of NK cells in tumour tissue was significantly reduced, with changes in the NK cell proportion being most obvious in NKp30+ NK cells. Furthermore, the results of the ADCC function assay showed limited NKp30+ NK cell-mediated cytotoxicity in RCC patients. Through real-time quantitative PCR, we found lower expression of NKp30a and NKp30b, the immunostimulatory splice variants of NCR3 encoding NKp30, in RCC patients. Moreover, expression of activating cytokines (IL-6 and IL-8) in renal cancer tissue was decreased, though inhibitory cytokine (TGF-β) expression remained unchanged, which may result in an immunosuppressive cytokine microenvironment.

CONCLUSION

Decreased expression of immunostimulatory NCR3 splice variants and the inhibitory cytokine microenvironment in RCC patients may contribute to deficient NK cell cytotoxicity and renal carcinoma cell immune escape from NK cell killing, which may provide a theoretical basis for finding new immunotherapeutic targets for RCC.

High-fidelity large-diversity monoclonal mammalian cell libraries by cell cycle arrested recombinase-mediated cassette exchange

Mammalian cells carrying defined genetic variations have shown great potentials in both fundamental research and therapeutic development. However, their full use was limited by lack of a robust method to construct large monoclonal high-quality combinatorial libraries. This study developed cell cycle arrested recombinase-mediated cassette exchange (aRMCE), able to provide monoclonality, precise genomic integration and uniform transgene expression. Via optimized nocodazole-mediated mitotic arrest, 20% target gene replacement efficiency was achieved without antibiotic selection, and the improved aRMCE efficiency was applicable to a variety of tested cell clones, transgene targets and transfection methods. As a demonstration of this versatile method, we performed directed evolution of fragment crystallizable (Fc), for which error-prone libraries of over 107 variants were constructed and displayed as IgG on surface of CHO cells. Diversities of constructed libraries were validated by deep sequencing, and panels of novel Fc mutants were identified showing improved binding towards specific Fc gamma receptors and enhanced effector functions. Due to its large cargo capacity and compatibility with different mutagenesis approaches, we expect this mammalian cell platform technology has broad applications for directed evolution, multiplex genetic assays, cell line development and stem cell engineering.