Antibody Gene Therapy for Rabies

Abstract

Once signs of rabies emerge, the disease is almost 100% fatal. Tens of thousands of people die annually from this rapidly progressive encephalitis. Rabies vaccines and post-exposure prophylaxis prevent infection, but no therapy is available for patients in which infection has progressed to clinical disease. To develop a therapy for rabies encephalitis, we created an adeno-associated viral vector expressing a broadly neutralizing monoclonal antibody against the glycoprotein (G) of rabies virus (AAV-Rab). To evaluate this strategy, initial proof-of-concept study in Chapter 1 established that a single intravenous injection of AAV-Rab in mice generated neutralizing antibody titers in serum >3,000-fold above the minimum presumptive level of adequate induction. Intravenous administration of AAV-Rab 14 days prior to rabies inoculation prevented disease in 100% (16 of 16) mice while in the post-exposure study, 92% (11 of 12) of mice survived when intravenously treated with AAV-Rab 3 days after infection with a virulent field strain of African canine rabies virus. Translation of this strategy into a larger animal was achieved using feline model (Chapter 2). Healthy cats treated intravenously with AAV-Rab produced high titers of neutralizing antibody in serum for at least one year, and antibody was detected in cerebrospinal fluid for 6 months. Immunohistochemistry confirmed the vector-produced antibodies in multiple regions of the brain, spinal cord and dorsal root ganglia of the high-dose treated cats. Finally, a clinical case involving a human rabies patient who received the AAV-Rab therapy intravenously through an FDA-approved, emergency IND was analyzed using immunohistochemistry. Although the patient did not survive, post-mortem analysis confirmed vector-produced antibody in the brain, 20 days after AAV-Rab administration (Hospital Day 29). This observation motivated a subsequent study to assess the time kinetics of antibody production after AAV treatment. Serum neutralizing antibodies were detected as soon as 24 hours and 72 hours post intravenous administration of AAV-Rab in mice and cats, respectively. Hence, we believe that earlier treatment with a higher AAV-Rab dose has real potential to benefit symptomatic patients. Collectively, these findings demonstrate that a single intravenous dose of AAV-Rab expressed rabies virus neutralizing antibodies in the brains of both mice and cats, and hence, is a promising modality for preventing or treating rabies encephalitis.