Ability of vaccine strain induced antibodies to neutralize field isolates of caliciviruses from Swedish cats

Background: Feline calicivirus (FCV) is a common cause of upper respiratory tract disease in cats worldwide. Its characteristically high mutation rate leads to escape from the humoral immune response induced by natural infection and/or vaccination and consequently vaccines are not always effective against field isolates. Thus, there is a need to continuously investigate the ability of FCV vaccine strain-induced antibodies to neutralize field isolates. Methods: Seventy-eight field isolates of FCV isolated during the years 2008–2012 from Swedish cats displaying clinical signs of upper respiratory tract disease were examined in this study. The field isolates were tested for cross-neutralization using a panel of eight anti-sera raised in four pairs of cats following infection with four vaccine strains (F9, 255, G1 and 431). Results: The anti-sera raised against F9 and 255 neutralised 20.5 and 11.5 %, and 47.4 and 64.1 % of field isolates tested, respectively. The anti-sera against the more recently introduced vaccine strains G1 and 431 neutralized 33.3 and 70.5 % and 69.2 and 89.7 %, respectively. Dual vaccine strains displayed a higher cross-neutralization. Conclusions: This study confirms previous observations that more recently introduced vaccine strains induce antibodies with a higher neutralizing capacity compared to vaccine strains that have been used extensively over a long period of time. This study also suggests that dual FCV vaccine strains might neutralize more field isolates compared to single vaccine strains. Vaccine strains should ideally be selected based on updated knowledge on the antigenic properties of field isolates in the local setting, and there is thus a need for continuously studying the evolution of FCV together with the neutralizing capacity of vaccine strain induced antibodies against field isolates at a national and/or regional level

A single site for N-linked glycosylation in the envelope glycoprotein of feline immunodeficiency virus modulates the virus-receptor interaction

Feline immunodeficiency virus (FIV) targets helper T cells by attachment of the envelope glycoprotein (Env) to CD134, a subsequent interaction with CXCR4 then facilitating the process of viral entry. As the CXCR4 binding site is not exposed until CD134-binding has occurred then the virus is protected from neutralising antibodies targeting the CXCR4-binding site on Env. Prototypic FIV vaccines based on the FL4 strain of FIV contain a cell culture-adapted strain of FIV Petaluma, a CD134-independent strain of FIV that interacts directly with CXCR4. In addition to a characteristic increase in charge in the V3 loop homologue of FIV<sub>FL4</sub>, we identified two mutations in potential sites for N-linked glycosylation in the region of FIV Env analogous to the V1-V2 region of HIV and SIV Env, T271I and N342Y. When these mutations were introduced into the primary GL8 and CPG41 strains of FIV, the T271I mutation was found to alter the nature of the virus-CD134 interaction; primary viruses carrying the T271I mutation no longer required determinants in cysteine-rich domain (CRD) 2 of CD134 for viral entry. The T271I mutation did not confer CD134-independent infection upon GL8 or CPG41, nor did it increase the affinity of the CXCR4 interaction, suggesting that the principal effect was targeted at reducing the complexity of the Env-CD134 interaction

The role of virus neutralisation in immunity to feline immunodeficiency virus infection

Feline immunodeficiency virus (FIV) is an important veterinary pathogen with comparative significance because of its similarities to its human counterpart HIV. Since FIV is the only non-primate lentivirus which induces AIDS-like symptoms in its natural host, it serves as a valuable animal model for both prophylactic and therapeutic studies of HIV. It is accepted that the induction of neutralising antibodies (NAbs) is a key element in the control of lentiviral infection, since T-cell based vaccines alone failed to prevent infection in most experimental animal model systems. In this project a robust and reproducible in vitro neutralisation assay was developed and optimised, permitting the assessment of the NAb response in naturally infected cats and with the potential to evaluate candidate vaccines. It was demonstrated that, in general, primary FIV strains in the UK belong to subtype A, and therefore the development of a regional, subtype A-specific, FIV vaccine could be considered for use in the UK. The identification of a neutralisation resistant isolate of FIV led to the finding that a linear neutralisation determinant was located within the V5 region of Env and mutations in this region may lead to immune evasion in vivo. In addition, a second neutralisation determinant was identified in the C3/V4 region of Env. Finally, it was observed that a small proportion of naturally infected cats generated NAbs against FIV. Of these, only a very small proportion of the cats had antibodies with the potential to cross neutralise strains within the same subtype as the homologous isolate. Nonetheless, a plasma sample from a single cat was identified that neutralised all strains tested, including strains from different subtypes and geographical regions. It is likely that studies of the homologous isolate that induced the broad NAb response may be capable of inducing a similar broad response in vaccinated cats. Such a finding would have important implications for the design of potential novel lentiviral immunogens

Neutralization of feline immunodeficiency virus by antibodies targeting the V5 loop of Env

Neutralising antibodies (NAbs) play a vital role in vaccine-induced protection against infection with feline immunodeficiency virus (FIV). However, little is known about the appropriate presentation of neutralisation epitopes in order to induce NAbs effectively; the majority of the antibodies that are induced are directed against non-neutralising epitopes. Here, we demonstrate that a subtype B strain of FIV, designated NG4, escapes autologous NAbs but may be rendered neutralisation-sensitive following the insertion of two amino acids, Lysine and Threonine, at positions 556-557 in the fifth hypervariable (V5) loop of the envelope glycoprotein (Env). Consistent with the contribution of this motif to virus neutralisation, an additional three subtype B strains retaining both residues at the same position were also neutralised by the NG4 serum and serum from an unrelated cat (TOT1) targeted the same sequence in V5. Moreover, when the V5-loop of subtype B isolate KNG2, an isolate that was moderately resistant to neutralisation by NG4 serum, was mutated to incorporate the K-T motif, the virus was rendered sensitive to neutralisation. These data suggest that even in a polyclonal sera derived from FIV infected cats following natural infection, the primary determinant of virus neutralising activity may be represented by a single, dominant epitope in V5

Feline Immunodeficiency Virus (FIV) Neutralization: A Review

One of the major obstacles that must be overcome in the design of effective lentiviral vaccines is the ability of lentiviruses to evolve in order to escape from neutralizing antibodies. The primary target for neutralizing antibodies is the highly variable viral envelope glycoprotein (Env), a glycoprotein that is essential for viral entry and comprises both variable and conserved regions. As a result of the complex trimeric nature of Env, there is steric hindrance of conserved epitopes required for receptor binding so that these are not accessible to antibodies. Instead, the humoral response is targeted towards decoy immunodominant epitopes on variable domains such as the third hypervariable loop (V3) of Env. For feline immunodeficiency virus (FIV), as well as the related human immunodeficiency virus-1 (HIV-1), little is known about the factors that lead to the development of broadly neutralizing antibodies. In cats infected with FIV and patients infected with HIV-1, only rarely are plasma samples found that contain antibodies capable of neutralizing isolates from other clades. In this review we examine the neutralizing response to FIV, comparing and contrasting with the response to HIV. We ask whether broadly neutralizing antibodies are induced by FIV infection and discuss the comparative value of studies of neutralizing antibodies in FIV infection for the development of more effective vaccine strategies against lentiviral infections in general, including HIV-1

Modulation of the virus-receptor interaction by mutations in the V5 loop of feline immunodeficiency virus (FIV) following in vivo escape from neutralising antibody

<b>BACKGROUND:</b> In the acute phase of infection with feline immunodeficiency virus (FIV), the virus targets activated CD4+ T cells by utilising CD134 (OX40) as a primary attachment receptor and CXCR4 as a co-receptor. The nature of the virus-receptor interaction varies between isolates; strains such as GL8 and CPGammer recognise a "complex" determinant on CD134 formed by cysteine-rich domains (CRDs) 1 and 2 of the molecule while strains such as PPR and B2542 require a more "simple" determinant comprising CRD1 only for infection. These differences in receptor recognition manifest as variations in sensitivity to receptor antagonists. In this study, we ask whether the nature of the virus-receptor interaction evolves in vivo.<p></p> <b>RESULTS:</b> Following infection with a homogeneous viral population derived from a pathogenic molecular clone, a quasispecies emerged comprising variants with distinct sensitivities to neutralising antibody and displaying evidence of conversion from a "complex" to a "simple" interaction with CD134. Escape from neutralising antibody was mediated primarily by length and sequence polymorphisms in the V5 region of Env, and these alterations in V5 modulated the virus-receptor interaction as indicated by altered sensitivities to antagonism by both anti-CD134 antibody and soluble CD134.<p></p> <b>CONCLUSIONS:</b> The FIV-receptor interaction evolves under the selective pressure of the host humoral immune response, and the V5 loop contributes to the virus-receptor interaction. Our data are consistent with a model whereby viruses with distinct biological properties are present in early versus late infection and with a shift from a "complex" to a "simple" interaction with CD134 with time post-infection.<p></p&gt

Subsequent Event Risk in Individuals with Established Coronary Heart Disease:Design and Rationale of the GENIUS-CHD Consortium

BACKGROUND: The "GENetIcs of sUbSequent Coronary Heart Disease" (GENIUS-CHD) consortium was established to facilitate discovery and validation of genetic variants and biomarkers for risk of subsequent CHD events, in individuals with established CHD. METHODS: The consortium currently includes 57 studies from 18 countries, recruiting 185,614 participants with either acute coronary syndrome, stable CHD or a mixture of both at baseline. All studies collected biological samples and followed-up study participants prospectively for subsequent events. RESULTS: Enrollment into the individual studies took place between 1985 to present day with duration of follow up ranging from 9 months to 15 years. Within each study, participants with CHD are predominantly of self-reported European descent (38%-100%), mostly male (44%-91%) with mean ages at recruitment ranging from 40 to 75 years. Initial feasibility analyses, using a federated analysis approach, yielded expected associations between age (HR 1.15 95% CI 1.14-1.16) per 5-year increase, male sex (HR 1.17, 95% CI 1.13-1.21) and smoking (HR 1.43, 95% CI 1.35-1.51) with risk of subsequent CHD death or myocardial infarction, and differing associations with other individual and composite cardiovascular endpoints. CONCLUSIONS: GENIUS-CHD is a global collaboration seeking to elucidate genetic and non-genetic determinants of subsequent event risk in individuals with established CHD, in order to improve residual risk prediction and identify novel drug targets for secondary prevention. Initial analyses demonstrate the feasibility and reliability of a federated analysis approach. The consortium now plans to initiate and test novel hypotheses as well as supporting replication and validation analyses for other investigators