Viral Vector Gene Delivery to Trigeminal Sensory Neurons

Objective: We hypothesized that HSV-1-based vectors for gene therapy after orofacial inoculation do not spread in the central nervous system and that replication conditional defective vectors are more efficient in seeding sensory neuronal sites than replication defective vectors.

Methods: In three separate experiments, masseter muscle (MM, n=4) or whisker pads (WP, n=13) of male Sprague-Dawley rats were injected with replication conditional (n=10, MM: 4, WP: 6) or replication defective (n=7) HSV-1-based vectors (5-10 X 10⁷ PFU/mL).  Tissues from ipsilateral and contralateral trigeminal ganglion (TG), cerebral cortex, midbrain, pons, and brainstem were harvested ≥ 4 weeks post-vector injection. RNA from these tissues was isolated, processed, and analyzed by real-time PCR in duplicate for latency-associated transcripts (LAT), which wild-type HSV-1 abundantly transcribes during latency.

Results: HSV-1 LAT was detected in ipsilateral TG or pons obtained from 16/17 animals.  LAT was not detected in any of the remaining tissues.  The replication conditional vector was more effectively delivered to the TG (7/10) and pons (9/10) than was the replication defective vector, TG (3/7) and pons (4/7).  Masseteric injections resulted in more efficient delivery of HSV-1 to the TG (4/4) than WP injections (6/13).  PCR product was not detected in negative control reactions lacking template DNA or in tissues of sham-infected control animals, and immunofluorescence imaging corroborated the above findings.

Conclusions: This is the first study demonstrating that both replication conditional and replication defective HSV-1-based vectors delivered intradermally and intramuscularly migrate to, but not beyond, the TG or pons.  Second order synaptic transmission does not appear to occur.  These preliminary findings suggest that therapeutic genes can be delivered using these viral vectors to nervous system tissues that innervate orofacial regions.  Further, the safe biodistribution profile exhibited by these viral vectors suggests that they can be used in efficacy studies of chronic orofacial pain.