Eliciting and isolating neutralizing antibodies against Powassan virus

SUMMARY Powassan virus (POWV) is a tick-disseminated flavivirus that causes severe encephalitis, meningitis, and long-term neurological damage. Although POWV infections are relatively rare, the virus is widely distributed among common vectors such as Ixodes scapularis (the deer tick) and the number of reported cases in the US is rising each year. There are no approved vaccines or treatments for POWV infection. The goals of this R21 proposal are two-fold. In Aim 1, we will investigate the potential of protein nanoparticle immunogens bearing recombinantly-expressed POWV glycoprotein E domain III (EDIII) to induce neutralizing antibody response in mice. EDIII is an attractive target for flavivirus subunit vaccine design because it is relatively small (~80 residues) and contains epitopes of protective antibodies against multiple flaviviruses such as Dengue virus (DENV), Zika virus (ZIKV), West Nile virus (WNV), and Looping Ill virus (LIV). However, EDIII as a monomer is poorly immunogenic because it lacks the capacity to crosslink surface B-cell receptors (BCRs) to stimulate a robust antibody response. This limitation can be overcome by presenting EDIII in multivalent format as part of a protein nanoparticle. We have generated a prototypic POWV EDIII nanoparticle vaccine using Spycatcher/Spytag conjugation technology, and pilot studies have demonstrated this nanoparticle can elicit neutralizing antibodies in mice. We will further optimize this and related POWV nanoparticle vaccines. In Aim 2, we will isolate a large panel of human monoclonal antibodies (hu-mAbs) from a living survivor of POWV infection by single B cell sorting. Hu-mAbs have strong potential as immunotherapies because they are highly specific and their human scaffold minimizes the risk for anti-drug antibody responses. Furthermore, profiling hu-mAbs provides direct information about human immune response that can then be used to inform vaccine design. We will test the POWV hu-mAbs for their capacity to bind POWV E and neutralize POWV reporter virus particles (RVPs). This work will provide new insights and candidates for prevention and treatment of POWV infection.