Expression of Murine CD80 by Herpes Simplex Virus 1 in Place of Latency-Associated Transcript (LAT) Can Compensate for Latency Reactivation and Anti-apoptotic Functions of LAT.

High rates of wild-type (WT) herpes simplex virus 1 (HSV-1) latency reactivation depend on the anti-apoptotic activities of latency-associated transcript (LAT). Replacing LAT with the baculovirus inhibitor of apoptosis protein (cpIAP) or cellular FLIP (FLICE-like inhibitory protein) gene restored the WT latency reactivation phenotype to that of a LAT-minus [LAT(-)] virus, while similar recombinant viruses expressing interleukin-4 (IL-4) or interferon gamma (IFN-γ) did not. However, HSV-1 recombinant virus expressing cpIAP did not restore all LAT functions. Recently, we reported that a similar recombinant virus expressing CD80 in place of LAT had higher latency reactivation than a LAT-null virus. The present study was designed to determine if this CD80-expressing recombinant virus can restore all LAT functions as observed with WT virus. Our results suggest that overexpression of CD80 fully rescues LAT function in latency reactivation, apoptosis, and immune exhaustion, suggesting that LAT and CD80 have multiple overlapping functions.IMPORTANCE Recurring ocular infections caused by HSV-1 can cause corneal scarring and blindness. A major function of the HSV-1 latency-associated transcript (LAT) is to establish high levels of latency and reactivation, thus contributing to the development of eye disease. Here, we show that the host CD80 T cell costimulatory molecule functions similarly to LAT and can restore the ability of LAT to establish latency, reactivation, and immune exhaustion as well as induce the expression of caspase 3, caspase 8, caspase 9, and Bcl2. Our results suggest that, in contrast to several other previously tested genes, CD80-expressing virus can completely compensate for all known and tested LAT functions.