Human circulating PD-1+CXCR3-CXCR5+ memory Tfh cells are highly functional and correlate with broadly neutralizing HIV antibody responses.

The vast majority of currently licensed human vaccines work on the basis of long-term protective antibody responses. It is now conceivable that an antibody-dependent HIV vaccine might be possible, given the discovery of HIV broadly neutralizing antibodies (bnAbs) in some HIV-infected individuals. However, these antibodies are difficult to develop and have characteristics indicative of a high degree of affinity maturation in germinal centers (GCs). CD4⁺ T follicular helper (Tfh) cells are specialized for B cell help and necessary for GCs. Therefore, the development of HIV bnAbs might depend on Tfh cells. Here, we identified in normal individuals a subpopulation of circulating memory PD-1⁺CXCR5⁺CD4⁺ T cells that are resting memory cells most related to bona fide GC Tfh cells by gene expression profile, cytokine profile, and functional properties. Importantly, the frequency of these cells correlated with the development of bnAbs against HIV in a large cohort of HIV⁺ individuals.

Bcl6 and Maf cooperate to instruct human follicular helper CD4 T cell differentiation.

Follicular helper CD4 T (Tfh) cells provide B cells with signals that are important for the generation of high-affinity Abs and immunological memory and, therefore, are critical for the protective immunity elicited by most human vaccines. Transcriptional regulators of human Tfh cell differentiation are poorly understood. In this article, we demonstrate that Bcl6 controls specific gene modules for human Tfh cell differentiation. The introduction of Bcl6 expression in primary human CD4 T cells resulted in the regulation of a core set of migration genes that enable trafficking to germinal centers: CXCR4, CXCR5, CCR7, and EBI2. Bcl6 expression also induced a module of protein expression critical for T-B interactions, including SAP, CD40L, PD-1, ICOS, and CXCL13. This constitutes direct evidence for Bcl6 control of most of these functions and includes three genes known to be loci of severe human genetic immunodeficiencies (CD40L, SH2D1A, and ICOS). Introduction of Bcl6 did not alter the expression of IL-21 or IL-4, the primary cytokines of human Tfh cells. We show in this article that introduction of Maf (c-Maf) does induce the capacity to express IL-21. Surprisingly, Maf also induced CXCR5 expression. Coexpression of Bcl6 and Maf revealed that Bcl6 and Maf cooperate in the induction of CXCR4, PD-1, and ICOS. Altogether, these findings reveal that Bcl6 and Maf collaborate to orchestrate a suite of genes that define core characteristics of human Tfh cell biology.

Corrigendum: Translatability of findings from cynomolgus monkey to human suggests a mechanistic role for IL-21 in promoting immunogenicity to an anti-PD-1/IL-21 mutein fusion protein.

[This corrects the article DOI: 10.3389/fimmu.2024.1345473.].

Translatability of findings from cynomolgus monkey to human suggests a mechanistic role for IL-21 in promoting immunogenicity to an anti-PD-1/IL-21 mutein fusion protein.

AMG 256 is a bi-specific, heteroimmunoglobulin molecule with an anti-PD-1 antibody domain and a single IL-21 mutein domain on the C-terminus. Nonclinical studies in cynomolgus monkeys revealed that AMG 256 administration led to the development of immunogenicity-mediated responses and indicated that the IL-21 mutein domain of AMG 256 could enhance the anti-drug antibody response directed toward the monoclonal antibody domain. Anti-AMG 256 IgE were also observed in cynomolgus monkeys. A first-in-human (FIH) study in patients with advanced solid tumors was designed with these risks in mind. AMG 256 elicited ADA in 28 of 33 subjects (84.8%). However, ADA responses were only robust and exposure-impacting at the 2 lowest doses. At mid to high doses, ADA responses remained low magnitude and all subjects maintained exposure, despite most subjects developing ADA. Limited drug-specific IgE were also observed during the FIH study. ADA responses were not associated with any type of adverse event. The AMG 256 program represents a unique case where nonclinical studies informed on the risk of immunogenicity in humans, due to the IL-21-driven nature of the response.

Survey Outcome on Immunogenicity Risk Assessment Tools for Biotherapeutics: an Insight into Consensus on Methods, Application, and Utility in Drug Development.

A survey conducted by the Therapeutic Product Immunogenicity (TPI) community within the American Association of Pharmaceutical Scientists (AAPS) posed questions to the participants on their immunogenicity risk assessment strategies prior to clinical development. The survey was conducted in 2 phases spanning 5 years, and queried information about in silico algorithms and in vitro assay formats for immunogenicity risk assessments and how the data were used to inform early developability effort in discovery, chemistry, manufacturing and control (CMC), and non-clinical stages of development. The key findings representing the trends from a majority of the participants included the use of high throughput in silico algorithms, human immune cell-based assays, and proteomics based outputs, as well as specialized assays when therapeutic mechanism of action could impact risk assessment. Additional insights into the CMC-related risks could also be gathered with the same tools to inform future process development and de-risk critical quality attributes with uncertain and unknown risks. The use of the outputs beyond supporting early development activities was also noted with participants utilizing the risk assessments to drive their clinical strategy and streamline bioanalysis.

Immunogenicity assessment of bispecific antibody-based immunotherapy in oncology.

With increasing numbers of bispecific antibodies (BsAbs) and multispecific products entering the clinic, recent data highlight immunogenicity as an emerging challenge in the development of such novel biologics. This review focuses on the immunogenicity risk assessment (IgRA) of BsAb-based immunotherapies for cancer, highlighting several risk factors that need to be considered. These include the novel scaffolds consisting of bioengineered sequences, the potentially synergistic immunomodulating mechanisms of action (MOAs) from different domains of the BsAb, as well as several other product-related and patient-related factors. In addition, the clinical relevance of anti-drug antibodies (ADAs) against selected BsAbs developed as anticancer agents is reviewed and the advances in our knowledge of tools and strategies for immunogenicity prediction, monitoring, and mitigation are discussed. It is critical to implement a drug-specific IgRA during the early development stage to guide ADA monitoring and risk management strategies. This IgRA may include a combination of several assessment tools to identify drug-specific risks as well as a proactive risk mitigation approach for candidate or format selection during the preclinical stage. The IgRA is an on-going process throughout clinical development. IgRA during the clinical stage may bridge the gap between preclinical immunogenicity prediction and clinical immunogenicity, and retrospectively guide optimization efforts for next-generation BsAbs. This iterative process throughout development may improve the reliability of the IgRA and enable the implementation of effective risk mitigation strategies, laying the foundation for improved clinical success.

Assay format diversity in pre-clinical immunogenicity risk assessment: Toward a possible harmonization of antigenicity assays.

A major impediment to successful use of therapeutic protein drugs is their ability to induce anti-drug antibodies (ADA) that can alter treatment efficacy and safety in a significant number of patients. To this aim, in silico, in vitro, and in vivo tools have been developed to assess sequence and other liabilities contributing to ADA development at different stages of the immune response. However, variability exists between similar assays developed by different investigators due to the complexity of assays, a degree of uncertainty about the underlying science, and their intended use. The impact of protocol variations on the outcome of the assays, i.e., on the immunogenicity risk assigned to a given drug candidate, cannot always be precisely assessed. Here, the Non-Clinical Immunogenicity Risk Assessment working group of the European Immunogenicity Platform (EIP) reviews currently used assays and protocols and discusses feasibility and next steps toward harmonization and standardization.

EAE mediated by a non-IFN-γ/non-IL-17 pathway.

Previous studies have shown that EAE can be elicited by the adoptive transfer of either IFN-γ-producing (Th1) or IL-17-producing (Th17) myelin-specific CD4(+) T-cell lines. Paradoxically, mice deficient in either IFN-γ or IL-17 remain susceptible to EAE following immunization with myelin antigens in CFA. These observations raise questions about the redundancy of IFN-γ and IL-17 in autoimmune demyelinating disease mediated by a diverse, polyclonal population of autoreactive T cells. In this study, we show that an atypical form of EAE, induced in C57BL/6 mice by the adoptive transfer of IFN-γ-deficient effector T cells, required IL-17 signaling for the development of brainstem infiltrates. In contrast, classical EAE, characterized by predominant spinal cord inflammation, occurred in the combined absence of IFN-γ and IL-17 signaling, but was dependent on GM-CSF and CXCR2. Our findings contribute to a growing body of data, indicating that individual cytokines vary in their importance across different models of CNS autoimmunity.

IL-23 modulated myelin-specific T cells induce EAE via an IFNγ driven, IL-17 independent pathway.

Experimental autoimmune encephalomyelitis (EAE) is an inflammatory demyelinating disease of the central nervous system (CNS) mediated by myelin-reactive CD4(+) T cells. An unresolved issue that has important clinical implications concerns the cytokines produced by myelin-reactive T cells that determine their pathogenicity. Initially, IL-12 polarized, IFNγ producing Th1 cells were thought to be essential for the development of EAE. More recently, IL-23 polarized, IL-17 producing Th17 cells have been highlighted as critical encephalitogenic effectors. There is growing evidence that parallel autoimmune pathways can result in common clinical and histopathological endpoints. In the current study, we describe a form of EAE induced by the transfer of IL-23 modulated CD4(+) T cells into IL-17 receptor (IL-17R) deficient hosts. We found that IL-23 stimulates myelin-reactive T cells to produce both IFNγ and IL-17. Surprisingly, in this model the development of EAE is IFNγ dependent. Our findings illustrate a novel mechanism by which IL-23 promotes encephalitogenicity and they further expand the spectrum of autoreactive T cells capable of mediating inflammatory demyelinating disease of the CNS.

Immunogenicity Risk Assessment for Multi-specific Therapeutics.

The objective of this manuscript is to provide the reader with a hypothetical case study to present an immunogenicity risk assessment for a multi-specific therapeutic as part of Investigational New Drug (IND) application. In order to provide context for the bioanalytical strategies used to support the multi-specific therapeutic presented herein, the introduction focuses on known immunogenicity risk factors. The subsequent hypothetical case study applies these principles to a specific example HC-12, based loosely on anti-TNFα and anti-IL-17A bispecific molecules previously in development, structured as an example immunogenicity risk assessment for submission to health authorities. The risk of higher incidence and safety impact of anti-drug antibodies (ADA) due to large protein complexes is explored in the context of multi-specificity and multi-valency of the therapeutic in combination with the oligomeric forms of the targets.

Immune Complex Formation Is Associated With Loss of Tolerance and an Antibody Response to Both Drug and Target.

AMG 966 is a bi-specific, heteroimmunoglobulin molecule that binds both tumor necrosis factor alpha (TNFα) and TNF-like ligand 1A (TL1A). In a first-in-human clinical study in healthy volunteers, AMG 966 elicited anti-drug antibodies (ADA) in 53 of 54 subjects (98.1%), despite a paucity of T cell epitopes observed in T cell assays. ADA were neutralizing and bound to all domains of AMG 966. Development of ADA correlated with loss of exposure. In vitro studies demonstrated that at certain drug-to-target ratios, AMG 966 forms large immune complexes with TNFα and TL1A, partially restoring the ability of the aglycosylated Fc domain to bind FcγRIa and FcγRIIa, leading to the formation of ADA. In addition to ADA against AMG 966, antibodies to endogenous TNFα were also detected in the sera of subjects dosed with AMG 966. This suggests that the formation of immune complexes between a therapeutic and target can cause loss of tolerance and elicit an antibody response against the target.

Clinical immunogenicity of the d-amino acid peptide therapeutic etelcalcetide: Method development challenges and anti-drug antibody clinical impact assessments.

The immunogenicity risk assessment and bioanalytical strategy for novel therapeutics should account for both unique biophysical properties and potential consequences of immunogenicity. When assessing the immunogenicity risk of etelcalcetide, a peptide agonist of the calcium-sensing receptor, we considered the potential that the d-amino acid 'backbone' and biotransformation of etelcalcetide could allow the drug to act as a hapten. As a consequence, we validated and implemented a surface plasmon resonance immunoassay platform with both etelcalcetide and etelcalcetide-'carrier' surfaces to detect anti-drug antibodies (ADA). No evidence of in-vitro neutralizing activity with surrogate controls was detected despite multiple immunization approaches and a sensitive cell-based activity assay. Therefore, a neutralizing assay was not implemented for clinical support. We conducted an integrated analysis of immunogenicity data pooled from two pivotal placebo-controlled trials to define the clinical impact of anti-etelcalcetide antibodies. While both pre-existing and developing anti-etelcalcetide antibodies were detected, we show here that they have no consequences for clinical exposure, efficacy, or safety of etelcalcetide.

Assay signal as an alternative to titer for assessment of magnitude of an antidrug antibody response.

BACKGROUND: Titer methods are commonly used to characterize the magnitude of an antidrug antibody response. Assay S/N is an appealing alternative, but the circumstances under which use of signal-to-noise (S/N) is appropriate have not been well defined. RESULTS: We validated both titer and S/N-based methods for several therapeutics. S/N correlated strongly with titer both in aggregate and when examined on a per subject basis. Analysis of impact of antibody magnitude on pharmacokinetics yielded the same result using either method. Each assay demonstrated excellent precision, good linearity, and adequate drug tolerance. CONCLUSION: Under these circumstances, assay S/N is a valid alternative to titer for assessment of the magnitude of an antidrug antibody response.

BCL6 orchestrates Tfh cell differentiation via multiple distinct mechanisms.

Follicular helper T cells (Tfh cells) are required for T cell help to B cells, and BCL6 is the defining transcription factor of Tfh cells. However, the functions of BCL6 in Tfh cells have largely remained unclear. Here we defined the BCL6 cistrome in primary human germinal center Tfh cells to assess mechanisms of BCL6 regulation of CD4 T cells, comparing and contrasting BCL6 function in T and B cells. BCL6 primarily acts as a repressor in Tfh cells, and BCL6 binding was associated with control of Tfh cell migration and repression of alternative cell fates. Interestingly, although some BCL6-bound genes possessed BCL6 DNA-binding motifs, many BCL6-bound loci were instead characterized by the presence of DNA motifs for AP1 or STAT. AP1 complexes are key positive downstream mediators of TCR signaling and external stimuli. We show that BCL6 can directly bind AP1, and BCL6 depends on AP1 for recruitment to BCL6-binding sites with AP1 motifs, suggesting that BCL6 subverts AP1 activity. These findings reveal that BCL6 has broad and multifaceted effects on Tfh biology and provide insight into how this master regulator mediates distinct cell context-dependent phenotypes.

Development and optimization of neutralizing antibody assays to monitor clinical immunogenicity.

The development of an unwanted immune response to a protein therapeutic is a constant concern and necessitates careful monitoring of this class of drugs during clinical development. Neutralizing antibodies can have a significant impact on bioavailability, efficacy and safety of a protein therapeutic. Consequently, immunogenicity testing is required prior to obtaining regulatory approval and in some cases even after a product is marketed. Given the importance of this testing, it is critical that sensitive and robust assays are developed for detection of clinically relevant neutralizing antibodies. This review will describe considerations and current best practices for developing assays to detect neutralizing antibodies to protein therapeutics.

GM-CSF-dependent, CD103+ dermal dendritic cells play a critical role in Th effector cell differentiation after subcutaneous immunization.

Dendritic cells (DCs) play an important role in CD4(+) T helper (Th) cell differentiation and in the initiation of both protective and pathogenic immunity. Granulocyte/macrophage colony-stimulating factor (GM-CSF) is a DC growth factor critical for the induction of experimental autoimmune encephalomyelitis (EAE) and other autoimmune diseases, yet its mechanism of action in vivo is not fully defined. We show that GM-CSF is directly required for the accumulation of radiosensitive dermal-derived langerin(+)CD103(+) DCs in the skin and peripheral lymph nodes under steady-state and inflammatory conditions. Langerin(+)CD103(+) DCs stimulated naive myelin-reactive T cells to proliferate and produce IFN-gamma and IL-17. They were superior to other DC subsets in inducing expression of T-bet and promoting Th1 cell differentiation. Ablation of this subset in vivo conferred resistance to EAE. The current report reveals a previously unidentified role for GM-CSF in DC ontogeny and identifies langerin(+)CD103(+) DCs as an important subset in CD4(+) T cell-mediated autoimmune disease.

IL-12- and IL-23-modulated T cells induce distinct types of EAE based on histology, CNS chemokine profile, and response to cytokine inhibition.

The interleukin (IL)-12p40 family of cytokines plays a critical role in the development of experimental autoimmune encephalomyelitis (EAE). However, the relative contributions of IL-12 and IL-23 to the pathogenic process remain to be elucidated. Here, we show that activation of uncommitted myelin-reactive T cells in the presence of either IL-12p70 or IL-23 confers encephalogenicity. Adoptive transfer of either IL-12p70- or IL-23-polarized T cells into naive syngeneic hosts resulted in an ascending paralysis that was clinically indistinguishable between the two groups. However, histological and reverse transcription-polymerase chain reaction analysis of central nervous system (CNS) tissues revealed distinct histopathological features and immune profiles. IL-12p70-driven disease was characterized by macrophage-rich infiltrates and prominent NOS2 up-regulation, whereas neutrophils and granulocyte-colony-stimulating factor (CSF) were prominent in IL-23-driven lesions. The monocyte-attracting chemokines CXCL9, 10, and 11 were preferentially expressed in the CNS of mice injected with IL-12p70-modulated T cells, whereas the neutrophil-attracting chemokines CXCL1 and CXCL2 were up-regulated in the CNS of mice given IL-23-modulated T cells. Treatment with anti-IL-17 or anti-granulocyte/macrophage-CSF inhibited EAE induced by transfer of IL-23-polarized, but not IL-12p70-polarized, cells. These findings indicate that autoimmunity can be mediated by distinct effector populations that use disparate immunological pathways to achieve a similar clinical outcome.

Th17 and Th1 responses directed against the immunizing epitope, as opposed to secondary epitopes, dominate the autoimmune repertoire during relapses of experimental autoimmune encephalomyelitis.

Experimental autoimmune encephalomyelitis (EAE) is an inflammatory demyelinating disease with similarities to multiple sclerosis (MS). It has been suggested that relapses of EAE and MS may be associated with, and even driven by, T cells specific for novel epitopes that are primed during the course of tissue destruction in the target organ or in secondary lymphoid tissues. We show, however, that IFNgamma and IL-17 responses against the immunizing epitope remain dominant through out the course of multiphasic EAE. Furthermore, induction of tolerance against a putative secondary epitope did not prevent clinical relapses.