Cell immunocapture microfluidic chip based on high-affinity recombinant protein binders

Engineering PD-1-targeted small protein variants for in vitro diagnostics and in vivo PET imaging

BACKGROUND

Programmed cell death 1 (PD-1) belongs to immune checkpoint proteins ensuring negative regulation of the immune response. In non-small cell lung cancer (NSCLC), the sensitivity to treatment with anti-PD-1 therapeutics, and its efficacy, mostly correlated with the increase of tumor infiltrating PD-1+ lymphocytes. Due to solid tumor heterogeneity of PD-1+ populations, novel low molecular weight anti-PD-1 high-affinity diagnostic probes can increase the reliability of expression profiling of PD-1+ tumor infiltrating lymphocytes (TILs) in tumor tissue biopsies and in vivo mapping efficiency using immune-PET imaging.

METHODS

We designed a 13 kDa β-sheet Myomedin scaffold combinatorial library by randomization of 12 mutable residues, and in combination with ribosome display, we identified anti-PD-1 Myomedin variants (MBA ligands) that specifically bound to human and murine PD-1-transfected HEK293T cells and human SUP-T1 cells spontaneously overexpressing cell surface PD-1.

RESULTS

Binding affinity to cell-surface expressed human and murine PD-1 on transfected HEK293T cells was measured by fluorescence with LigandTracer and resulted in the selection of most promising variants MBA066 (hPD-1 KD = 6.9 nM; mPD-1 KD = 40.5 nM), MBA197 (hPD-1 KD = 29.7 nM; mPD-1 KD = 21.4 nM) and MBA414 (hPD-1 KD = 8.6 nM; mPD-1 KD = 2.4 nM). The potential of MBA proteins for imaging of PD-1+ populations in vivo was demonstrated using deferoxamine-conjugated MBA labeled with 68Galium isotope. Radiochemical purity of 68Ga-MBA proteins reached values 94.7-99.3% and in vitro stability in human serum after 120 min was in the range 94.6-98.2%. The distribution of 68Ga-MBA proteins in mice was monitored using whole-body positron emission tomography combined with computerized tomography (PET/CT) imaging up to 90 min post-injection and post mortem examined in 12 mouse organs. The specificity of MBA proteins was proven by co-staining frozen sections of human tonsils and NSCLC tissue biopsies with anti-PD-1 antibody, and demonstrated their potential for mapping PD-1+ populations in solid tumors.

CONCLUSIONS

Using directed evolution, we developed a unique set of small binding proteins that can improve PD-1 diagnostics in vitro as well as in vivo using PET/CT imaging.

Secretion and surface display of binders of IL-23/IL-17 cytokines and their receptors in Lactococcus lactis as a therapeutic approach against inflammation

The cytokine IL-23 activates the IL-23 receptor (IL-23R) and stimulates the differentiation of naïve T helper (Th) cells into a Th17 cell population that secretes inflammatory cytokines and chemokines. This IL-23/Th17 proinflammatory axis drives inflammation in Crohn's disease and ulcerative colitis and represents a therapeutic target of monoclonal antibodies. Non-immunoglobulin binding proteins based on the Streptococcus albumin-binding domain (ABD) provide a small protein alternative to monoclonal antibodies. They can be readily expressed in bacteria. Lactococcus lactis is a safe lactic acid bacterium that has previously been engineered as a vector for the delivery of recombinant therapeutic proteins to mucosal surfaces. Here, L. lactis was engineered to display or secrete ABD-variants against the IL-17 receptor (IL-17R). Its expression and functionality were confirmed with flow cytometry using specific antibody and recombinant IL-17R, respectively. In addition, L. lactis were engineered into multifunctional bacteria that simultaneously express two binders from pNBBX plasmid. First, binders of IL-17R were combined with binder of IL-17. Second, binders of IL-23R were combined with binders of IL-23. The dual functionality of the bacteria was confirmed by flow cytometry using corresponding targets, namely the recombinant receptors IL-17R and IL-23R or the p19 subunit of IL-23. Binding of IL-17 was confirmed by ELISA. With the latter, 97% of IL-17 was removed from solution by 2 × 109 recombinant bacteria. Moreover, multifunctional bacteria targeting IL-17/IL-17R prevented IL-17A-mediated activation of downstream signaling pathways in HEK-Blue IL-17 cell model. Thus, we have developed several multifunctional L. lactis capable of targeting multiple factors of the IL-23/Th17 proinflammatory axis. This represents a novel therapeutic strategy with synergistic potential for the treatment of intestinal inflammations.

Immunocapturing rare cells from blood: A simple and robust microsystem approach

Cell immunocapture microsystems are a fast-emerging field with several potential medical diagnostic applications. Isolation and quantification of circulating rare cells (CRCs) show great importance in the early stages of disease diagnostics and prognostics. Here, we present a simple and robust stop-flow microsystem (fabricated by a combination of glass microblasting and 3D printing) based on a planar antibody-coated surface that is effective in the immunocapture of the model as well as naturally occurring rare cells. A chip with a planar immunocapture channel working in the so-called stop-flow dynamic regime was designed to enable monitoring the efficiency of the cell capture by fluorescence microscopy. Up to 90% immunocapture efficiency of MCF-7 cells spiked into whole blood on CD326 antibody-coated planar surfaces was achieved. We discuss the role of the planar surface modifications, the influence of the set stop-flow dynamic conditions, and medium complexity on the efficiency of cell immunocapture. The presented results could be further employed in the design of microsystems for cell-size-independent isolation and identification of rare cells from blood.

Simplifying the complex: accessible microfluidic solutions for contemporary processes within in vitro diagnostics

In vitro diagnostics (IVDs) form the cornerstone of modern medicine. They are routinely employed throughout the entire treatment pathway, from initial diagnosis through to prognosis, treatment planning, and post-treatment surveillance. Given the proven links between high quality diagnostic testing and overall health, ensuring broad access to IVDs has long been a focus of both researchers and medical professionals. Unfortunately, the current diagnostic paradigm relies heavily on centralized laboratories, complex and expensive equipment, and highly trained personnel. It is commonly assumed that this level of complexity is required to achieve the performance necessary for sensitive and specific disease diagnosis, and that making something affordable and accessible entails significant compromises in test performance. However, recent work in the field of microfluidics is challenging this notion. By exploiting the unique features of microfluidic systems, researchers have been able to create progressively simple devices that can perform increasingly complex diagnostic assays. This review details how microfluidic technologies are disrupting the status quo, and facilitating the development of simple, affordable, and accessible integrated IVDs. Importantly, we discuss the advantages and limitations of various approaches, and highlight the remaining challenges within the field.