Jennerex Biotherapeutics, Inc. (now owned by SillaJen) was an American private biopharmaceutical company[1][3] that developed the oncolytic viruses JX-594[1][4] and JX-929[1] among others.

Jennerex received its name in honor of Edward Jenner,[5] the pioneer of the smallpox vaccine[6] and "the father of immunology".

European Medicines Agency (EMA) designated Pexa-Vec as an orphan drug for Live Cancer.

Pexa-Vec is an engineered oncolytic virus that selectively destroys cancer cells and induces tumor immune response.

Deletion of thymidine kinase (TK) from the JX-594 genome prevents virus replication in normal cells.

Because JX-594 is based on the Wyeth strain vaccinia virus that is commonly used for vaccination, it is well tolerated by rats, rabbits, and humans.

[17] Initially, it was demonstrated that patients with refractory melanomas who received intratumoral injection of JX-594 (104-2x107 PFU/lesion; 104-8x107 PFU/session for 6 weeks) had mixed (3/7), partial (1/7), or complete (1/7) responses.

[16][17] Despite the presence of anti-vaccinia antibodies, virally encoded GM-CSF mRNA was detected at injection sites up to 31 weeks following the intratumoral JX-594 inoculation and was not present in the serum.

[18] Jennerex has partnered with Transgene, Green Cross, Lee's Pharmaceuticals, Rex Medical, and SillaJen for JX-594 development and commercialization.