Decreased Infectivity of a Neutralization-Resistant Equine Infectious Anemia Virus Variant Can Be Overcome by Efficient Cell-to-Cell Spread

Abstract

Two variants of equine infectious anemia virus (EIAV) that differed in sensitivity to broadly neutralizing antibody were tested in direct competition assays. No differences were observed in the growth curves and relative fitness scores of EIAVs of principal neutralizing domain variants of groups 1 (EIAV PND-1 ) and 5 (EIAV PND-5 ), respectively; however, the neutralization-resistant EIAV PND-5 variant was less infectious in single-round replication assays. Infectious center assays indicated similar rates of cell-to-cell spread, which was approximately 1,000-fold more efficient than cell-free infectivity. These data indicate that efficient cell-tocell spread can overcome the decreased infectivity that may accompany immune escape and should be considered in studies assessing the relative levels of fitness among lentivirus variants, including HIV-1.Equine infectious anemia virus (EIAV) induces a persistent lifelong infection characterized by recurrent febrile episodes. Eventually, most horses exert immunological control over replicating virus and enter a prolonged period of clinical quiescence associated with the presence of cytotoxic T cells and broadly neutralizing antibody (bNAb). Over time, however, viral genotypes that resist bNAb evolve, resulting in recrudescence of clinical disease (6, 12). Elucidating mechanisms of viral escape from bNAb is important for the design of effective vaccines for EIAV and related lentiviruses, such as HIV-1.The V3 region of the EIAV surface envelope glycoprotein (SU) is structurally similar to HIV-1 V1/V2 (5), contains two epitopes recognized by neutralizing monoclonal antibodies (1), and is termed the principal neutralizing domain (PND). Genetic variation in the PND is considered to play an important role in immune escape and EIAV persistence. We previously undertook a longitudinal study of variation in the V2-V4 region of EIAV SU in a pony experimentally inoculated with the virulent Wyo2078 strain of EIAV (EIAV Wyo2078 ) (12). The predominant PND variants clustered into 5 groups, designated PND-1 to PND-5. Genotypes representative of each group were used to generate chimeric infectious molecular clones, designated EIAV PND-1 through EIAV , that differed only in the V2-V4 region of SU (12). As infection progressed, the chimeric PND virus variants showed increasing resistance to neutralization by autologous and heterologous sera, such that EIAV PND-1 was highly sensitive to neutralization by broadly neutralizing sera, whereas EIAV PND-5 was neutralization resistant (12, 14). Genetic differences in the PND region included amino acid substitutions, size variation, and changes in the numbers and locations of predicted N-linked glycosylation sites. Similar changes in HIV-1 env that mask immune epitopes have been associated with a loss of virus replicative fitness (8-11), suggesting that resistance to bNAb may incur a cost in virus fitness. In the present study, we used growth competition and infectivity assays to determine if EIAV PND variants that differ in sensitivity to neutrali...

Viral Quasispecies Evolution

“…A fitness increase of retroviral immune escape variants need not affect directly the genomic regions related to immune escape (B-cell or T-cell epitopes or their neighborhood in the relevant viral proteins). Rather, fitness may be compensated for by enhancement of other, unrelated traits such as cell-to-cell spread (878). Exploitation of different pathways for fitness recovery has been observed with other viral systems (254), it is expected from quasispecies dynamics and from the connectivity of sequence space (see "Exploration of Sequence Space and Virus Adaptability: Fidelity Mutants" above), and it is highly relevant to vaccine design and to the mechanisms underlying progression of HIV-1 infection toward AIDS.…”

Cell-Free Transmission of Human Adenovirus by Passive Mass Transfer in Cell Culture Simulated in a Computer Model

“…Neurotropic viruses, for example, can be transmitted between synaptic contacts of adjacent cells, and retroviruses establish new cell-cell contacts for transmission, so-called virological synapses (see references 23, 68, and 69). For retroviruses, such as human immunodeficiency virus (HIV) or equine infectious anemia virus, cell-to-cell transmission reduces the neutralization efficacy of antiviral antibodies and antiviral drugs (66,91,113). This illustrates that viral transmission modes modulate the efficacy of immune defense and affect antiviral strategies, such as vaccine design and the development of new antiviral compounds.…”

Identification and characterization of small molecule inhibitors of porcine reproductive and respiratory syndrome virus

“…Compounds were assayed for anti-PRRSV activity in MARC-145 cells using a focusreduction assay as previously described (Wu et al, 2011;Evans et al, 2017). For most assays, 10 g of each compound, or DMSO diluent control, were incubated with varying amounts of PRRSV NVSL97-7895 for 1 hr at 37°C and inoculated in duplicate onto MARC-145 cells seeded the previous day at 3x10 5 cells/well in a 12-well plate.…”