Optimizing the Generation of Monoclonal Antibodies for Prevention and Treatment of HSV Disease

"There are no effective vaccines or monoclonal antibodies available for the prevention or treatment of
herpes simplex viral infections. This application addresses this global public health priority. We developed
a novel single-cycle vaccine strain deleted in glycoprotein D (gD), designated DgD-2. DgD-2 completely
protects mice from lethal challenges with clinical isolates of both HSV-1 and HSV-2. Protection is
mediated by IgG2 antibodies that have little neutralizing activity but activate Fc gamma receptors to
promote antibody-dependent cellular cytotoxicity (ADCC). The central role for ADCC in mediating
protection is supported by the observations that immune serum from DgD-2 vaccinated mice completely
protects naïve wild-type, but not Fcg receptor IV knockout (FcgRIV-/-) mice. FcgRIV is the primary receptor
responsible for mediating ADCC in mice. We isolated a highly protective monoclonal antibody (mAb),
BMPC-23, from DgD-2 vaccinated mice that exhibits potent FcgRIV activating activity and mapped its
epitope to domain IV of viral glycoprotein B. Notably, in contrast to the response to DgD-2, the humoral
response to acute HSV infection or to vaccination with gD subunit protein vaccines in both mice and
humans is neutralizing with little or no ADCC. These observations suggest that gD may interfere with the
elicitation of ADCC antibodies. We hypothesized that this novel immune evasion mechanism may be
mediated by interactions between gD and the co-signaling molecule switch molecule herpes virus entry
mediator (HVEM), which is expressed by most immune cells. When gD binds HVEM, the interactions
between HVEM and its natural ligands (LIGHT, lymphotoxin-a, CD160 and BTLA) may be inhibited.
Supporting our hypothesis, IgG2 ADCC responses were reduced and protection against HSV was lost
when Hvem−/− (knockout) mice were vaccinated with DgD-2. This need for HVEM to elicit IgG2 ADCC
responses may be generalizable since similar results were obtained with other vaccines. Based on these
data, we propose that the enhanced ADCC response to DgD-2 compared to natural HSV infection or to
gD protein vaccines reflects differences in viral targets recognized, IgG subclasses generated and ability
to overcome gD-HVEM mediated immune evasion. We will isolate and characterize mAbs generated in
response to DgD-2, primary and recurrent HSV infection in wild-type compared to Hvem−/− mice to
determine how HVEM signaling contributes to the antigenic repertoire, subclass and antibody function.
We will test the mAbs that are generated in response to DgD-2 vaccination or infection individually and
in combination (with BMPC-23 and other combinations) for their ability to protect and treat acute or
recurrent HSV-1 and HSV-2 disease following vaginal and skin (male and female) infection as well as in
models of neonatal disease. Together, these studies will yield important new fundamental and
translational knowledge applicable to the development of vaccines and mAbs that mediate ADCC."