Using Reference Reagents to Confirm Robustness of Cytokine Release Assays for the Prediction of Monoclonal Antibody Safety.

New immunostimulatory antibody drugs designed to either directly stimulate specific immune cells or indirectly enhance the immune response by blocking or activating an endogenous regulator of the immune system have the potential to cause serious immune-related adverse events such as cytokine release syndrome (CRS). It is, therefore crucial to assess the safety profile of such drugs with a combination of in vivo and in vitro experiments before first-in-human dose administration. Cytokine release assays (CRAs), where the proposed antibody therapeutic is co-cultured with human immune cells (such as peripheral blood mononuclear cells (PBMCs), whole blood, or otherwise) and the amount of inflammatory cytokine produced is measured, are critical for hazard identification. However, different labs using different control antibodies can threaten the harmonization of CRAs, and clinically relevant controls (such as TGN1412) can be difficult to source, which can lead to less accurate or reliable results or data which are difficult to compare between laboratories. The inclusion of positive and negative controls in a CRA can ensure the accuracy and reliability of the results. The National Institute for Biological Standards and Control (NIBSC) has produced a panel of lyophilized antibody controls intended for use in various CRA platforms to harmonize results across various laboratories and assay methods. A set of three different positive control antibodies include anti-CD52, anti-CD3, and anti-CD28 superagonist (SA), which are known to induce dose-dependent CRS in patients. Each antibody is provided with an isotype-matched negative control antibody. This panel of reference reagents has previously been shown to have good inter-lab reproducibility and are suitable controls to increase the confidence and robustness of safety data from a variety of CRA platforms.

Simultaneous evaluation of treatment efficacy and toxicity for bispecific T-cell engager therapeutics in a humanized mouse model.

Immuno-oncology (IO)-based therapies such as checkpoint inhibitors, bi-specific antibodies, and CAR-T-cell therapies have shown significant success in the treatment of several cancer indications. However, these therapies can result in the development of severe adverse events, including cytokine release syndrome (CRS). Currently, there is a paucity of in vivo models that can evaluate dose-response relationships for both tumor control and CRS-related safety issues. We tested an in vivo PBMC humanized mouse model to assess both treatment efficacy against specific tumors and the concurrent cytokine release profiles for individual human donors after treatment with a CD19xCD3 bispecific T-cell engager (BiTE). Using this model, we evaluated tumor burden, T-cell activation, and cytokine release in response to bispecific T-cell-engaging antibody in humanized mice generated with different PBMC donors. The results show that PBMC engrafted NOD-scid Il2rgnull mice lacking expression of mouse MHC class I and II (NSG-MHC-DKO mice) and implanted with a tumor xenograft predict both efficacy for tumor control by CD19xCD3 BiTE and stimulated cytokine release. Moreover, our findings indicate that this PBMC-engrafted model captures variability among donors for tumor control and cytokine release following treatment. Tumor control and cytokine release were reproducible for the same PBMC donor in separate experiments. The PBMC humanized mouse model described here is a sensitive and reproducible platform that identifies specific patient/cancer/therapy combinations for treatment efficacy and development of complications.

Intrinsic host susceptibility among multiple species to intranasal SARS-CoV-2 identifies diverse virological, biodistribution and pathological outcomes.

SARS-CoV-2 exhibits a diverse host species range with variable outcomes, enabling differential host susceptibility studies to assess suitability for pre-clinical countermeasure and pathogenesis studies. Baseline virological, molecular and pathological outcomes were determined among multiple species-one Old World non-human primate (NHP) species (cynomolgus macaques), two New World NHP species (red-bellied tamarins; common marmosets) and Syrian hamsters-following single-dose, atraumatic intranasal administration of SARS-CoV-2/Victoria-01. After serial sacrifice 2, 10 and 28-days post-infection (dpi), hamsters and cynomolgus macaques displayed differential virus biodistribution across respiratory, gastrointestinal and cardiovascular systems. Uniquely, New World tamarins, unlike marmosets, exhibited high levels of acute upper airway infection, infectious virus recovery associated with mild lung pathology representing a host previously unrecognized as susceptible to SARS-CoV-2. Across all species, lung pathology was identified post-clearance of virus shedding (antigen/RNA), with an association of virus particles within replication organelles in lung sections analysed by electron microscopy. Disrupted cell ultrastructure and lung architecture, including abnormal morphology of mitochondria 10-28 dpi, represented on-going pathophysiological consequences of SARS-CoV-2 in predominantly asymptomatic hosts. Infection kinetics and host pathology comparators using standardized methodologies enables model selection to bridge differential outcomes within upper and lower respiratory tracts and elucidate longer-term consequences of asymptomatic SARS-CoV-2 infection.

An accurate and rapid single step protocol for enumeration of cytokine positive T lymphocytes.

Accurate determination of cellular subsets that secrete particular cytokine(s) is a significant parameter for functional characterization of an immunological response. The present study was conducted to develop a method for simultaneous measurement of intracellular cytokine positive CD4 and CD8 positive T lymphocytes in a single tube, with a no-wash protocol. We report here the development of a simplified, rapid procedure for precise enumeration of cytokine positive T lymphocytes using BD Trucount tubes. This single step protocol for accurate enumeration of cytokine positive T lymphocytes, will allow for better characterization of immune cell phenotype and function.

Plant virus particles carrying tumour antigen activate TLR7 and Induce high levels of protective antibody.

Induction of potent antibody is the goal of many vaccines targeted against infections or cancer. Modern vaccine designs that use virus-like particles (VLP) have shown efficacy for prophylactic vaccination against virus-associated cancer in the clinic. Here we used plant viral particles (PVP), which are structurally analogous to VLP, coupled to a weak idiotypic (Id) tumour antigen, as a conjugate vaccine to induce antibody against a murine B-cell malignancy. The Id-PVP vaccine incorporates a natural adjuvant, the viral ssRNA, which acts via TLR7. It induced potent protective anti-Id antibody responses in an in vivo mouse model, superior to the "gold standard" Id vaccine, with prevalence of the IgG2a isotype. Combination with alum further increased antibody levels and maintained the IgG2a bias. Engagement of TLR7 in vivo was followed by secretion of IFN-α by plasmacytoid dendritic cells and by activation of splenic CD11chi conventional dendritic cells. The latter was apparent from up-regulation of co-stimulatory molecules and from secretion of a wide range of inflammatory cytokines and chemokines including the Th1-governing cytokine IL-12, in keeping with the IgG2a antibody isotype distribution. PVP conjugates are a novel cancer vaccine design, offering an attractive molecular form, similar to VLP, and providing T-cell help. In contrast to VLP, they also incorporate a safe "in-built" ssRNA adjuvant.

Plasmacytoid dendritic cell-derived type I interferon is crucial for the adjuvant activity of Toll-like receptor 7 agonists.

There is a high demand for the development of adjuvants that induce cytotoxic T lymphocytes, which are crucial for the elimination of intracellular pathogens and tumor cells. Toll-like receptor (TLR) agonists are prime candidates to fulfill this role because they induce innate immune activation and promote adaptive immune responses. The successful application of the TLR7 agonist R837 for treatment of basal cell carcinoma shows the potential for exploiting this pathway in tumor immunotherapy. Imidazoquinolines like R837 and stimulatory ssRNA oligonucleotides both trigger TLR7-mediated immune activation, but little is known about their comparative ability to promote immunity induction. We investigated differences in innate immune activation and adjuvant activity between the imidazoquinoline R848 and the ssRNA TLR7 agonist polyUs21. In contrast to R848, polyUs21 induced detectable levels of intracellular interferon-alpha (IFN-alpha) in plasmacytoid dendritic cells (PDCs). In immunization studies, only polyUs21 led to robust priming of type 1 T helper cells and cytotoxic T lymphocytes, and it was more efficient in inducing antitumor immunity than R848. Notably, exogenous IFN-alpha augmented the adjuvant activity of R848, whereas depletion of PDC abrogated the adjuvanticity of polyUs21. This study, therefore, identifies sufficient IFN-alpha production by PDC as an important determinant of vaccine efficacy.

Immunoglobulin switch mu sequence causes RNA polymerase II accumulation and reduces dA hypermutation.

Repetitive DNA sequences in the immunoglobulin switch mu region form RNA-containing secondary structures and undergo hypermutation by activation-induced deaminase (AID). To examine how DNA structure affects transcription and hypermutation, we mapped the position of RNA polymerase II molecules and mutations across a 5-kb region spanning the intronic enhancer to the constant mu gene. For RNA polymerase II, the distribution was determined by nuclear run-on and chromatin immunoprecipitation assays in B cells from uracil-DNA glycosylase (UNG)-deficient mice stimulated ex vivo. RNA polymerases were found at a high density in DNA flanking both sides of a 1-kb repetitive sequence that forms the core of the switch region. The pileup of polymerases was similar in unstimulated and stimulated cells from Ung(-/-) and Aid(-/-)Ung(-/-) mice but was absent in cells from mice with a deletion of the switch region. For mutations, DNA was sequenced from Ung(-/-) B cells stimulated in vivo. Surprisingly, mutations of A nucleotides, which are incorporated by DNA polymerase eta, decreased 10-fold before the repetitive sequence, suggesting that the polymerase was less active in this region. We propose that altered DNA structure in the switch region pauses RNA polymerase II and limits access of DNA polymerase eta during hypermutation.

Pharmacology of a novel, orally active PDE4 inhibitor.

BACKGROUND: Intracellular cyclic adenosine monophosphate (cAMP) in inflammatory cells and airway smooth muscle is critical to the modulation of inflammatory response generation. Phosphodiesterase 4 (PDE4), an enzyme that catalyzes cAMP degradation, is therefore being actively explored as a molecular target for the treatment of airway inflammation, particularly asthma and chronic obstructive pulmonary disease. The field has undergone major advances in optimizing generation of compounds with a safe therapeutic margin; however, most PDE4 inhibitors tested so far have unacceptable side effects, particularly nausea and vomiting. METHODS: We evaluated NIS-62949 in a wide range of in vitro and ex vivo cell-based assays to ascertain its anti-inflammatory potential. The compound was evaluated in murine models of lipopolysaccharide-induced endotoxemia and pulmonary neutrophilia. Parameters of airway inflammation, airway hyperreactivity and bronchoconstriction were evaluated in a guinea pig model of antigen-induced allergy. In order to assess the emetic potential, the compound was evaluated biochemically for binding to high-affinity rolipram-binding site. Subsequently, the compound was tested in a surrogate model for emesis, and the results obtained were correlated directly to tests conducted in a Beagle dog model. RESULTS: NIS-62949 is a potent, highly selective PDE4 inhibitor. The compound demonstrated potent ability to inhibit tumor necrosis factor-alpha release from human peripheral blood mononuclear cells, lymphocyte proliferation and cytokine production. The in vitro profile of NIS-62949 prompted further evaluation of the compound in vivo and the compound was found to be comparable to roflumilast in several experimental models of pulmonary inflammation. Importantly, NIS-62949 displayed a safer profile compared to roflumilast. CONCLUSIONS: Our results report the development of a promising, novel PDE4 inhibitor, NIS-62949, with a wider therapeutic window as compared to second-generation PDE4 inhibitors such as roflumilast.

Hijacked DNA repair proteins and unchained DNA polymerases.

Somatic hypermutation of immunoglobulin (Ig) genes occurs at a frequency that is a million times greater than the mutation in other genes. Mutations occur in variable genes to increase antibody affinity, and in switch regions before constant genes to cause switching from IgM to IgG. Hypermutation is initiated in activated B cells when the activation-induced deaminase protein deaminates cytosine in DNA to uracil. Uracils can be processed by either a mutagenic pathway to produce mutations or a non-mutagenic pathway to remove mutations. In the mutagenic pathway, we first studied the role of mismatch repair proteins, MSH2, MSH3, MSH6, PMS2 and MLH1, since they would recognize mismatches. The MSH2-MSH6 heterodimer is involved in hypermutation by binding to U:G and other mismatches generated during repair synthesis, but the other proteins are not necessary. Second, we analysed the role of low-fidelity DNA polymerases eta, iota and theta in synthesizing mutations, and conclude that polymerase eta is the dominant participant by generating mutations at A:T base pairs. In the non-mutagenic pathway, we examined the role of the Cockayne syndrome B protein that interacts with other repair proteins. Mice deficient in this protein had normal hypermutation and class switch recombination, showing that it is not involved.

Therapeutic benefit of PDE4 inhibitors in inflammatory diseases.

Intracellular levels of cyclic nuclec tides are closely regulated by distinct families of PD Es, which are responsible for the breakdown and degradation of cyclic nucleotides within cells. Type 4 PDEs have the potency to modulate the release of inflammatory mediators through cAMP-dependent and -independent mechanisms. Selective targeting of PDE4 is currently being investigated as a novel therapeutic approach in the treatment of inflammation-associated respiratory diseases such as asthma and COPD. The development of several PDE4 inhibitors, including roflumilast and cilomilast, reflects the success of this approach. In principle, therapeutic intervention of an inflammatory response by PDE4 inhibitors may be extended to other chronic inflammatory disease states such as psoriasis, rheumatoid arthritis and inflammatory bowel diseases (e.g., Crohns disease and ulcerative colitis). This retiiew explores the feasibility of PDE4 inhibitors as a promising alternative for therapeutic intervention in systemic inflammation and inflammation-based disease.

A role for the Hsp90 molecular chaperone family in antigen presentation to T lymphocytes via major histocompatibility complex class II molecules.

The heat shock protein (HSP) Hsp90 is known to chaperone cytosolic peptides for MHC class I (MHCI)-restricted antigen presentation to T lymphocytes. We now demonstrate a role for Hsp90 activity in presentation of antigens on MHCII. Treatment of mouse antigen-presenting cells (APC) with the pharmacological Hsp90 inhibitor, geldanamycin, inhibited MHCII-mediated presentation of endocytosed and cytosolic proteins as well as synthetic peptides to specific T cells. Ectopic expression of human Hsp90 in APC enhanced MHCII-mediated antigen presentation. Further, pharmacological Hsp90 inhibition reduced, while retroviral Hsp90 overexpression enhanced, the levels of stable compact MHCII heterodimers correlating with the antigen presentation phenotype. Pharmacological inhibition of Hsp90 activity in IFN-gamma-treated APC resulted in severe abrogation of MHCII-restricted presentation of cytosolic antigen, but only partially inhibited exogenous antigen presentation. Our data suggest a major role for Hsp90 activity in MHCII-mediated antigen presentation pathways, and implicate IFN-gamma-inducible Hsp90-independent mechanisms.

A cytosolic pathway for MHC class II-restricted antigen processing that is proteasome and TAP dependent.

By convention, presentation of major histocompatibility complex (MHC) class I-restricted epitopes involves processing by cytosolic proteasomes, whereas MHC class II-restricted epitopes are generated by endosomal proteases. Here, we show that two MHC class II-restricted epitopes within influenza virus were generated by a proteasome- and TAP-dependent pathway that was accessed by exogenous virus in dendritic cells (DCs) but not cell types with less permeable endosomes. Both epitopes were presented by recycling MHC class II molecules. Challenging mice with influenza or vaccinia viruses demonstrated that a substantial portion of the MHC class II-restricted response was directed against proteasome-dependent epitopes. By complementing endosomal activities, this pathway broadens the array of MHC class II-restricted epitopes available for CD4(+) T cell activation.

Diversity & overlap in the mechanisms of processing protein antigens for presentation to T cells.

The immune system needs to recognise target protein antigens from pathogens residing in both extracellular and intracellular locations. Intricate proteolytic processing events that follow antigen/ pathogen encounter provide the immune system with a complex display of a heterogeneous peptide mix, instrumental in the initiation of T cell immune responses, and allow the separation of extracellular and intracellular pathogen identification. However, recent evidence shows that this conventional dimorphism in the proteolytic processing of endogenous versus internalised antigen is less restrictive than originally recognized. The events that constitute the conventional major histocompatibility complex (MHC)-restricted processing pathways are accompanied by interesting deviations that provide novel adjuncts for the processing machinery to gain access to antigen in varied intracellular locations. This review discusses these aspects of classical and non-classical processing pathways for MHC-restricted protein presentation, which play significant roles in both optimising and diversifying the peptide repertoire available for immune recognition.

The pathway for MHCII-mediated presentation of endogenous proteins involves peptide transport to the endo-lysosomal compartment.

Antigen-presenting cells (APCs) are expected to present peptides from endocytosed proteins via major histocompatibility complex (MHC) class II (MHCII) molecules to T cells. However, a large proportion of peptides purified from MHCII molecules are derived from cytosolic self-proteins making the pathway of cytosolic peptide loading onto MHCII of critical relevance in the regulation of immune self-tolerance. We show that peptides derived from cytoplasmic proteins either introduced or expressed in the cytoplasm are first detectable as MHCII-peptide complexes in LAMP-1(+) lysosomes, prior to their delivery to the cell surface. These peptide-MHC complexes are formed in a variety of APCs, including peritoneal macrophages, dendritic cells, and B cells, and are able to activate T cells. This process requires invariant chain (Ii)-dependent sorting of MHCII to the lysosome and the activity of the molecular chaperone H-2M. This pathway is independent of the ER resident peptide transporter complex TAP and does not take place by cross-presentation from neighbouring cells. In conjunction with our earlier results showing that these peptides are derived by cytosolic processing via the proteasome, these observations provide evidence for a ubiquitous route for peptide transport into the lysosome for the efficient presentation of endogenous and cytoplasmic proteins to CD4 T cells.

Mimicry of native peptide antigens by the corresponding retro-inverso analogs is dependent on their intrinsic structure and interaction propensities.

Retro-inverso (ri) analogs of model T cell and B cell epitopes were predictively designed as mimics and then assayed for activity to understand the basis of functional ri-antigenic peptide mimicry. ri versions of two MHC class I binding peptide epitopes, one from a vesicular stomatitis virus glycoprotein (VSV(p)) and another from OVA (OVAp), exhibit structural as well as functional mimicry of their native counterparts. The two ri peptides exhibit conformational plasticity and they bind to MHC class I (H-2K(b)) similar to their native counterparts both in silico and in vivo. In fact, ri-OVAp is also presented to an OVAp-specific T cell line in a mode similar to native OVAp. In contrast, the ri version of an immunodominant B cell peptide epitope from a hepatitis B virus protein, PS1, exhibits no structural or functional correlation with its native counterpart. PS1 and its ri analog do not exhibit similar conformational propensities. PS1 is less flexible relative to its ri version. These observed structure-function relationships of the ri-peptide epitopes are consistent with the differences in recognition properties between peptide-MHC vs peptide-Ab binding where, while the recognition of the epitope by MHC is pattern based, the exquisitely specific recognition of Ag by Ab arises from the high complementarity between the Ag and the binding site of the Ab. It is evident that the correlation of conformational and interaction propensities of native L-peptides and their ri counterparts depends both on their inherent structural properties and on their mode of recognition.

IFN-gamma bioassay: development of a sensitive method by measuring nitric oxide production by peritoneal exudate cells from C57BL/6 mice.

Interferon-gamma (IFN-gamma) is an important immunomodulatory and pleiotropic cytokine produced, primarily, by activated T lymphocytes and natural killer (NK) cells. We have devised a nitric oxide (NO)-based bioassay for mouse IFN-gamma using resident peritoneal exudate cells (PECs) from C57BL/6 mice. Comparison with three existing bioassays demonstrated that this assay was very sensitive and detected IFN-gamma in the linear range of approximately 0.03-0.25 U/ml. Other cytokines, e.g. interleukin (IL)-2, IL-4, IL-6, IFN-alpha/beta and tumor necrosis factor-alpha (TNF-alpha), either alone or in combination with IFN-gamma, did not greatly modulate NO levels produced by resident peritoneal exudate cells. The presence of exogenous NO(3)(-) and H(2)O(2) did not interfere with the IFN-gamma induced NO production and detection. We also showed that the effect of lipopolysaccharide (LPS), which may be present in samples, could be suppressed by the use of Polymyxin B in the bioassay. The high sensitivity of the bioassay permitted the detection of low amounts of IFN-gamma in 1% mouse serum. In addition, this assay reproducibly detected bioactive IFN-gamma amounts in supernatants of activated T cells. The increase in IFN-gamma production by activated T cells in response to CD28 costimulation was approximately 3-fold by this bioassay and approximately 5-fold by ELISA. In summary, we have devised a simple, sensitive, inexpensive and high throughput method for the reproducible detection of bioactive IFN-gamma.

Role of IL-12-independent and IL-12-dependent pathways in regulating generation of the IFN-gamma component of T cell responses to Salmonella typhimurium.

Clearance of facultative intracellular pathogens such as Salmonella requires IFN-gamma from CD4 T cells. Mechanisms linking intracellular pathogen recognition with induction of IFN-gamma-producing T cells are still poorly understood. We show in this study that IL-12 is not required for commitment to the IFN-gamma-producing T cell response in infection with Salmonella typhimurium, but is needed for its maintenance. The IL-12-independent signals required for commitment depend on events during the first hour of infection and are related to Ag presentation. Even transient attenuation of Ag presentation early during infection specifically abrogates the IFN-gamma component of the resulting CD4 T cell response. The IL-12 needed for maintenance is also better induced by live rather than dead bacteria in vivo, and this difference is due to specific suppression of IL-12 induction by dead bacteria. Presence of exogenous IL-4 down-modulates IL-12 production by macrophages activated in vitro. Furthermore, macrophages from IL-4-null mice secrete high levels of both IL-12 and IL-18 in response to stimulation in vivo even with dead bacteria, but this does not lead to induction of IFN-gamma-secreting T cells in response to immunization with dead S. typhimurium. Early IL-4 is contributed by triggering of CD4 NK T cells by dead, but not live, bacteria. Thus, Ag presentation-related IL-12-independent events and IL-4-sensitive IL-12-dependent events play crucial complementary roles in the generation of the IFN-gamma-committed CD4 T cell component of the immune response in Salmonella infection.