[1] This page describes (in the order of development) the most notable variants—those tested in clinical trials: G207, HSV1716, NV1020 and Talimogene laherparepvec (previously Oncovex-GMCSF).

[2][3] A vital part of the normal mechanism of HSV-1, the ICP34.5 protein has been proposed to condition post-mitotic cells for viral replication.

With no ICP34.5 gene, the HSV-1716 variant is unable to overcome normal defences of healthy differentiated cells (mediated by PKR) to replicate efficiently.

[13][14][15] The results of the first trial were published simultaneously with the first trial of HSV1716 in 2000, with commentators praising the demonstration of safety of these viruses when injected into brain tumours but also expressing disappointment that viral replication could not be demonstrated due to the difficulty of taking biopsies from brain tumours.

[1] A direct comparison of NV1020 and G207 in a mouse model of peritoneal cancer showed that NV1020 is more effective at lower doses.

[21] It is a second-generation herpes simplex virus based on the JS1 strain and expressing the immune stimulatory factor GM-CSF.