The art of blocking ADP-ribosyltransferases (ARTs): nanobodies as experimental and therapeutic tools to block mammalian and toxin ARTs

Identification of Follicular T Cells in the Gut

Humoral adaptive immune responses trigger the establishment of plasma B cells secreting antibodies of various isotypes that bind antigen specifically and with high affinity. Moreover, memory B cells will be generated. To accomplish this, B cells need assistance from a special subset of CD4 T cells, the so called follicular T cells that differentiate from naïve T cells in the course of the immune response. Therefore, the study of follicular T cells is of primordial interest when investigating the molecular and cellular determinants of adaptive immune responses. This is done by direct analysis of the cells isolated from mice following an immunological challenge but in many instances such analyses must involve follow-up studies in cell culture requiring living cells. Especially, in vitro experimentation necessitates isolation and sorting of follicular T cells. However, follicular T cells are generally difficult to handle because they are prone to apoptosis and cell death. This is particularly evident when dealing with follicular T cells residing in the gut since we observed that isolation and processing from murine gut notoriously results in very high loss rates when compared for example to cells obtained from immunized peripheral lymph nodes. To bypass these limitations, we developed a protocol that allows for efficient isolation of intact follicular T cells. The protocol introduced here illustrates isolation and handling of follicular T cells using murine Peyer's Patches as an example because they constantly harbor significant amounts of these cells.

CD4+ T cell immunity to Salmonella is transient in the circulation

While Salmonella enterica is seen as an archetypal facultative intracellular bacterial pathogen where protection is mediated by CD4⁺ T cells, identifying circulating protective cells has proved very difficult, inhibiting steps to identify key antigen specificities. Exploiting a mouse model of vaccination, we show that the spleens of C57BL/6 mice vaccinated with live-attenuated Salmonella serovar Typhimurium (S. Typhimurium) strains carried a pool of IFN-γ⁺ CD4⁺ T cells that could adoptively transfer protection, but only transiently. Circulating Salmonella-reactive CD4⁺ T cells expressed the liver-homing chemokine receptor CXCR6, accumulated over time in the liver and assumed phenotypic characteristics associated with tissue-associated T cells. Liver memory CD4⁺ T cells showed TCR selection bias and their accumulation in the liver could be inhibited by blocking CXCL16. These data showed that the circulation of CD4⁺ T cells mediating immunity to Salmonella is limited to a brief window after which Salmonella-specific CD4⁺ T cells migrate to peripheral tissues. Our observations highlight the importance of triggering tissue-specific immunity against systemic infections.

Helper T cells are essential for controlling infections by bacterial pathogens, such as Salmonella enterica var Typhimurium (S. Typhimurium). While it is well-established that this role is related to their provision of IFN-γ, when and where helper T cells elicit their protective function in vivo remains unresolved. We identified a protective helper T cell population in the circulation of mice early after inoculation with growth-attenuated S. Typhimurium strains; this population waned overtime. We observed that circulating helper T cell immunity can adoptively protect naïve recipient mice against lethal S. Typhimurium infection when harvested from a short time-window. In comparing helper T cell responses between spleen and liver in Salmonella-infected mice, we have observed a previously uncharacterized trafficking of helper T cells to the liver followed by the residence of S. Typhimurium-specific T cell memory in the organ. Taken together these findings identify that protective immunity to Salmonella infections is transient in the circulation and the liver as a preferential site of helper T memory cells.

Nanobodies targeting immune checkpoint molecules for tumor immunotherapy and immunoimaging (Review)

The immune checkpoint blockade is an effective strategy to enhance the anti-tumor T cell effector activity, thus becoming one of the most promising immunotherapeutic strategies in the history of cancer treatment. Several immune checkpoint inhibitor have been approved by the FDA, such as anti-CTLA-4, anti-PD-1, anti-PD-L1 monoclonal antibodies. Most tumor patients benefitted from these antibodies, but some of the patients did not respond to them. To increase the effectiveness of immunotherapy, including immune checkpoint blockade therapies, miniaturization of antibodies has been introduced. A single-domain antibody, also known as nanobody, is an attractive reagent for immunotherapy and immunoimaging thanks to its unique structural characteristic consisting of a variable region of a single heavy chain antibody. This structure confers to the nanobody a light molecular weight, making it smaller than conventional antibodies, although remaining able to bind to a specific antigen. Therefore, this review summarizes the production of nanobodies targeting immune checkpoint molecules and the application of nanobodies targeting immune checkpoint molecules in immunotherapy and immunoimaging.

Nanobody-based binding assay for the discovery of potent inhibitors of CFTR inhibitory factor (Cif)

Lead identification and optimization are essential steps in the development of a new drug. It requires cost-effective, selective and sensitive chemical tools. Here, we report a novel method using nanobodies that allows the efficient screening for potent ligands. The method is illustrated with the cystic fibrosis transmembrane conductance regulator inhibitory factor (Cif), a virulence factor secreted by the opportunistic pathogen Pseudomonas aeruginosa. 18 nanobodies selective to Cif were isolated by bio-panning from nanobody-phage library constructed from immunized llama. 8 out of 18 nanobodies were identified as potent inhibitors of Cif enzymatic activity with IC₅₀s in the range of 0.3-6.4 μM. A nanobody VHH219 showed high affinity (K_D = 0.08 nM) to Cif and the highest inhibitory potency, IC₅₀ = 0.3 μM. A displacement sandwich ELISA (dsELISA) with VHH219 was then developed for classification of synthetic small molecule inhibitors according their inhibitory potency. The developed assay allowed identification of new inhibitor with highest potency reported so far (0.16 ± 0.02 μM). The results from dsELISA assay correlates strongly with a conventional fluorogenic assay (R = 0.9998) in predicting the inhibitory potency of the tested compounds. However, the novel dsELISA is an order of magnitude more sensitive and allows the identification and ranking of potent inhibitors missed by the classic fluorogenic assay method. These data were supported with Octet biolayer interferometry measurements. The novel method described herein relies solely on the binding properties of the specific neutralizing nanobody, and thus is applicable to any pharmacological target for which such a nanobody can be found, independent of any requirement for catalytic activity.

Monoclonal Antibodies and Antibody Like Fragments Derived from Immunised Phage Display Libraries

Morbidity and mortality associated with infectious diseases are always on the rise, especially in poorer countries and in the aging population. The inevitable, but unpredictable emergence of new infectious diseases has become a global threat. HIV/AIDS, severe acute respiratory syndrome (SARS), and the more recent H1N1 influenza are only a few of the numerous examples of emerging infectious diseases in the modern era. However despite advances in diagnostics, therapeutics and vaccines, there is need for more specific, efficacious, cost-effective and less toxic treatment and preventive drugs. In this chapter, we discuss a powerful combinatorial technology in association with animal immunisation that is capable of generating biologic drugs with high affinity, efficacy and limited off-site toxicity, and diagnostic tools with great precision. Although time consuming, immunisation still remains the preferred route for the isolation of high-affinity antibodies and antibody-like fragments. Phage display is a molecular diversity technology that allows the presentation of large peptide and protein libraries on the surface of filamentous phage. The selection of binding fragments from phage display libraries has proven significant for routine isolation of invaluable peptides, antibodies, and antibody-like domains for diagnostic and therapeutic applications. Here we highlight the many benefits of combining immunisation with phage display in combating infectious diseases, and how our knowledge of antibody engineering has played a crucial role in fully exploiting these platforms in generating therapeutic and diagnostic biologics towards antigenic targets of infectious organisms.

Construction of a camelid VHH yeast two-hybrid library and the selection of VHH against haemagglutinin-neuraminidase protein of the Newcastle disease virus

BACKGROUND

Newcastle disease (ND), which is caused by the Newcastle disease virus (NDV), is one of the most important avian diseases in poultry. Since its discovery in 1926, ND has caused great economic losses to the world poultry industry and remains a threat to chickens and wild birds. Although a stringent vaccination policy is widely adopted to control ND, ND outbreaks still occur, and virulent NDV is sporadically isolated from chickens and wild birds. To study the pathogenesis of ND and provide tools to prevent its prevalence, novel antibody fragments should be developed. The variable domains of the heavy chain of the heavy-chain antibodies (VHH) are the smallest naturally occurring antibodies derived from camelid heavy-chain antibodies. The comparatively small size, high affinity, high solubility, low immunogenicity and ability to bind epitopes inaccessible to conventional antibodies of VHH make them ideal candidates for a considerable number of therapeutic and biotechnological applications. However, an anti-NDV VHH has not been reported to date.

RESULTS

In this study, a VHH yeast two-hybrid library was constructed from NDV vaccine immunized C. bactrianus, and seven VHH fragments to the haemagglutinin-neuraminidase (HN) protein of NDV were successfully screened and characterized for the first time. These selected VHH clones were all expressed as soluble protein in E. coli. ELISA, dot blot, immunocytochemistry and pull down results showed that the screened VHHs could interact with NDV virion, among which five had neutralizing activity. In addition, the seven VHHs could inhibit the haemagglutination activity of different NDV strains.

CONCLUSIONS

We constructed an NDV-immunized VHH yeast two-hybrid library and screened and characterized seven VHHs targeting NDV HN protein for the first time. The seven VHHs may have great potential for NDV diagnosis, pathogenesis and therapeutics.

Nanobodies as modulators of inflammation: potential applications for acute brain injury

Nanobodies are single domain antibodies derived from llama heavy-chain only antibodies (HCAbs). They represent a new generation of biologicals with unique properties: nanobodies show excellent tissue distribution, high temperature and pH stability, are easy to produce recombinantly and can readily be converted into different formats such as Fc-fusion proteins or hetero-dimers. Moreover, nanobodies have the unique ability to bind molecular clefts, such as the active site of enzymes, thereby interfering with the function of the target protein. Over the last decade, numerous nanobodies have been developed against proteins involved in inflammation with the aim to modulate their immune functions. Here, we give an overview about recently developed nanobodies that target immunological pathways linked to neuroinflammation. Furthermore, we highlight strategies to modify nanobodies so that they can overcome the blood brain barrier and serve as highly specific therapeutics for acute inflammatory brain injury.