CD4+ T Cells Drive Lung Disease Enhancement Induced by Immunization with Suboptimal Doses of Respiratory Syncytial Virus Fusion Protein in the Mouse Model.

Respiratory syncytial virus (RSV) infection of seronegative children previously immunized with formalin-inactivated (FI) RSV has been associated with serious enhanced respiratory disease (ERD). The phenomenon was reproduced in the cotton rat and the mouse, and both preclinical models have been routinely used to evaluate the safety of new RSV vaccine candidates. More recently, we demonstrated that immunizations with suboptimal doses of the RSV fusion (F) antigen, in its post- or prefusion conformation, and in the presence of a Th1-biasing adjuvant, unexpectedly led to ERD in the cotton rat model. To assess if those observations are specific to the cotton rat and to elucidate the mechanism by which vaccination with low antigen doses can drive ERD post-RSV challenge, we evaluated RSV post-F antigen dose de-escalation in BALB/c mice in the presence of a Th1-biasing adjuvant. While decreasing antigen doses, we observed an increase in lung inflammation associated with an upregulation of proinflammatory cytokines. The amplitude of the lung histopathology was comparable to that of FI-RSV-induced ERD, confirming the observations made in the cotton rat. Importantly, depletion of CD4+ T cells prior to viral challenge completely abrogated ERD, preventing proinflammatory cytokine upregulation and the infiltration of T cells, neutrophils, eosinophils, and macrophages into the lung. Overall, low-antigen-dose-induced ERD resembles FI-RSV-induced ERD, except that the former appears in the absence of detectable levels of viral replication and in the context of a Th1-biased immune response. Taken together, our observations reinforce the recent concept that vaccines developed for RSV-naïve individuals should be systematically tested under suboptimal dosing conditions.IMPORTANCE RSV poses a significant health care burden and is the leading cause of serious lower-respiratory-tract infections in young children. A formalin-inactivated RSV vaccine developed in the 1960s not only showed a complete lack of efficacy against RSV infection but also induced severe lung disease enhancement in vaccinated children. Since then, establishing safety in preclinical models has been one of the major challenges to RSV vaccine development. We recently observed in the cotton rat model that suboptimal immunizations with RSV fusion protein could induce lung disease enhancement. In the present study, we extended suboptimal dosing evaluation to the mouse model. We confirmed the induction of lung disease enhancement by vaccinations with low antigen doses and dissected the associated immune mechanisms. Our results stress the need to evaluate suboptimal dosing for any new RSV vaccine candidate developed for seronegative infants.

Recombinant factor VIII Fc fusion protein drives regulatory macrophage polarization.

The main complication of replacement therapy with factor in hemophilia A (HemA) is the formation of inhibitors (neutralizing anti-factor VIII [FVIII] antibodies) in ∼30% of severe HemA patients. Because these inhibitors render replacement FVIII treatment essentially ineffective, preventing or eliminating them is of top priority in disease management. The extended half-life recombinant FVIII Fc fusion protein (rFVIIIFc) is an approved therapy for HemA patients. In addition, it has been reported that rFVIIIFc may induce tolerance to FVIII more readily than FVIII alone in HemA patients that have developed inhibitors. Given that the immunoglobulin G1 Fc region has the potential to interact with immune cells expressing Fc receptors (FcRs) and thereby affect the immune response to rFVIII, we investigated how human macrophages, expressing both FcRs and receptors reported to bind FVIII, respond to rFVIIIFc. We show herein that rFVIIIFc, but not rFVIII, uniquely skews macrophages toward an alternatively activated regulatory phenotype. rFVIIIFc initiates signaling events that result in morphological changes, as well as a specific gene expression and metabolic profile that is characteristic of the regulatory type Mox/M2-like macrophages. Further, these changes are dependent on rFVIIIFc-FcR interactions. Our findings elucidate mechanisms of potential immunomodulatory properties of rFVIIIFc.

Inferior immunogenicity and efficacy of respiratory syncytial virus fusion protein-based subunit vaccine candidates in aged versus young mice.

Respiratory syncytial virus (RSV) is recognized as an important cause of lower and upper respiratory tract infections in older adults, and a successful vaccine would substantially lower morbidity and mortality in this age group. Recently, two vaccine candidates based on soluble purified glycoprotein F (RSV F), either alone or adjuvanted with glucopyranosyl lipid A formulated in a stable emulsion (GLA-SE), failed to reach their primary endpoints in clinical efficacy studies, despite demonstrating the desired immunogenicity profile and efficacy in young rodent models. Here, one of the RSV F vaccine candidates (post-fusion conformation, RSV post-F), and a stabilized pre-fusion form of RSV F (RSV pre-F, DS-Cav1) were evaluated in aged BALB/c mice. Humoral and cellular immunogenicity elicited after immunization of naïve, aged mice was generally lower compared to young animals. In aged mice, RSV post-F vaccination without adjuvant poorly protected the respiratory tract from virus replication, and addition of GLA-SE only improved protection in the lungs, but not in nasal turbinates. RSV pre-F induced higher neutralizing antibody titers compared to RSV post-F (as previously reported) but interestingly, RSV F-specific CD8 T cell responses were lower compared to RSV post-F responses regardless of age. The vaccines were also tested in RSV seropositive aged mice, in which both antigen forms similarly boosted neutralizing antibody titers, although GLA-SE addition boosted neutralizing activity only in RSV pre-F immunized animals. Cell-mediated immune responses in the aged mice were only slightly boosted and well below levels induced in seronegative young mice. Taken together, the findings suggest that the vaccine candidates were not able to induce a strong anti-RSV immune response in recipient mice with an aged immune system, in agreement with recent human clinical trial results. Therefore, the aged mouse model could be a useful tool to evaluate improved vaccine candidates, targeted to prevent RSV disease in older adults.

PCPP-Adjuvanted Respiratory Syncytial Virus (RSV) sF Subunit Vaccine: Self-Assembled Supramolecular Complexes Enable Enhanced Immunogenicity and Protection.

PCPP, a well-defined polyphosphazene macromolecule, has been studied as an immunoadjuvant for a soluble form of the postfusion glycoprotein of respiratory syncytial virus (RSV sF), which is an attractive vaccine candidate for inducing RSV-specific immunity in mice and humans. We demonstrate that RSV sF-PCPP formulations induce high neutralization titers to RSV comparable to alum formulations even at a low PCPP dose and protect animals against viral challenge both in the lung and in the upper respiratory tract. PCPP formulations were also characterized by Th1-biased responses, compared to Th2-biased responses that are more typical for RSV sF alone or RSV sF-alum formulations, suggesting an inherent immunostimulating activity of the polyphosphazene adjuvant. We defined these immunologically active RSV sF-PCPP formulations as self-assembled water-soluble protein-polymer complexes with distinct physicochemical parameters. The secondary structure and antigenicity of the protein in the complex were fully preserved during the spontaneous aqueous self-assembly process. These findings further advance the concept of polyphosphazene immunoadjuvants as unique dual-functionality adjuvants integrating delivery and immunostimulating modalities in one water-soluble molecule.

Feasibility of Freeze-Drying Oil-in-Water Emulsion Adjuvants and Subunit Proteins to Enable Single-Vial Vaccine Drug Products.

To generate potent vaccine responses, subunit protein antigens typically require coformulation with an adjuvant. Oil-in-water emulsions are among the most widely investigated adjuvants, based on their demonstrated ability to elicit robust antibody and cellular immune responses in the clinic. However, most emulsions cannot be readily frozen or lyophilized, on account of the risk of phase separation, and may have a deleterious effect on protein antigen stability when stored long term as a liquid coformulation. To circumvent this, current emulsion-formulated vaccines generally require a complex multivial presentation with obvious drawbacks, making a single-vial presentation for such products highly desirable. We describe the development of a stable, lyophilized squalene emulsion adjuvant through innovative formulation and process development approaches. On reconstitution, freeze-dried emulsion preparations were found to have a minimal increase in particle size of ∼20 nm and conferred immunogenicity in BALB/c mice similar in potency to freshly prepared emulsion coformulations in liquid form.

Immunization with Low Doses of Recombinant Postfusion or Prefusion Respiratory Syncytial Virus F Primes for Vaccine-Enhanced Disease in the Cotton Rat Model Independently of the Presence of a Th1-Biasing (GLA-SE) or Th2-Biasing (Alum) Adjuvant.

Respiratory syncytial virus (RSV) infection of children previously immunized with a nonlive, formalin-inactivated (FI)-RSV vaccine has been associated with serious enhanced respiratory disease (ERD). Consequently, detailed studies of potential ERD are a critical step in the development of nonlive RSV vaccines targeting RSV-naive children and infants. The fusion glycoprotein (F) of RSV in either its postfusion (post-F) or prefusion (pre-F) conformation is a target for neutralizing antibodies and therefore an attractive antigen candidate for a pediatric RSV subunit vaccine. Here, we report the evaluation of RSV post-F and pre-F in combination with glucopyranosyl lipid A (GLA) integrated into stable emulsion (SE) (GLA-SE) and alum adjuvants in the cotton rat model. Immunization with optimal doses of RSV F antigens in the presence of GLA-SE induced high titers of virus-neutralizing antibodies and conferred complete lung protection from virus challenge, with no ERD signs in the form of alveolitis. To mimic a waning immune response, and to assess priming for ERD under suboptimal conditions, an antigen dose de-escalation study was performed in the presence of either GLA-SE or alum. At low RSV F doses, alveolitis-associated histopathology was unexpectedly observed with either adjuvant at levels comparable to FI-RSV-immunized controls. This occurred despite neutralizing-antibody titers above the minimum levels required for protection and with no/low virus replication in the lungs. These results emphasize the need to investigate a pediatric RSV vaccine candidate carefully for priming of ERD over a wide dose range, even in the presence of strong neutralizing activity, Th1 bias-inducing adjuvant, and protection from virus replication in the lower respiratory tract.IMPORTANCE RSV disease is of great importance worldwide, with the highest burden of serious disease occurring upon primary infection in infants and children. FI-RSV-induced enhanced disease, observed in the 1960s, presented a major and ongoing obstacle for the development of nonlive RSV vaccine candidates. The findings presented here underscore the need to evaluate a nonlive RSV vaccine candidate during preclinical development over a wide dose range in the cotton rat RSV enhanced-disease model, as suboptimal dosing of several RSV F subunit vaccine candidates led to the priming for ERD. These observations are relevant to the validity of the cotton rat model itself and to safe development of nonlive RSV vaccines for seronegative infants and children.

Impact of formulation and particle size on stability and immunogenicity of oil-in-water emulsion adjuvants.

Oil-in-water emulsions have gained consideration as vaccine adjuvants in recent years due to their ability to elicit a differentiated immunogenic response compared to traditional aluminum salt adjuvants. Squalene, a cholesterol precursor, is a natural product with immunostimulatory properties, making it an ideal candidate for such oil-in-water emulsions. Particle size is a key parameter of these emulsions and its relationship to stability and adjuvanticity has not been extensively studied. This study evaluates the effect of particle size on the stability and immunogenicity of squalene emulsions. We investigated the effect of formulation parameters such as surfactant concentration on particle size, resulting in particles with average diameter of 80 nm, 100 nm, 150 nm, 200 nm, or 250 nm. Emulsions were exposed to shear and temperature stresses, and stability parameters such as pH, osmolarity, size, and in-depth visual appearance were monitored over time. In addition, adjuvanticity of different particle size was assessed in a mouse model using Respiratory Syncytial Virus Fusion protein (RSV-F) as a model antigen. Temperature dependent phase separation appeared to be the most common route of degradation occurring in the higher particle sizes emulsions. The emulsions below 150 nm size maintained stability at either 5 °C or 25 °C, and the 80 nm diameter ones showed no measurable changes in size even after one month at 40 °C. In vivo studies using the emulsions as an adjuvant with RSV F antigen revealed that superior immunogenicity could be achieved with the 80 nm particle size emulsion.

Crosstalk between muscularis macrophages and enteric neurons regulates gastrointestinal motility.

Intestinal peristalsis is a dynamic physiologic process influenced by dietary and microbial changes. It is tightly regulated by complex cellular interactions; however, our understanding of these controls is incomplete. A distinct population of macrophages is distributed in the intestinal muscularis externa. We demonstrate that, in the steady state, muscularis macrophages regulate peristaltic activity of the colon. They change the pattern of smooth muscle contractions by secreting bone morphogenetic protein 2 (BMP2), which activates BMP receptor (BMPR) expressed by enteric neurons. Enteric neurons, in turn, secrete colony stimulatory factor 1 (CSF1), a growth factor required for macrophage development. Finally, stimuli from microbial commensals regulate BMP2 expression by macrophages and CSF1 expression by enteric neurons. Our findings identify a plastic, microbiota-driven crosstalk between muscularis macrophages and enteric neurons that controls gastrointestinal motility. PAPERFLICK: