Agenus Inc., a developer of therapeutic vaccines for cancer and infectious diseases, has completed patient screening in its phase II randomized, double-blind, multi-centre study for HerpV, a recombinant “off-the-shelf” therapeutic vaccine candidate for the treatment of genital herpes in herpes simplex virus-2 (HSV-2) positive patients.

HerpV contains Agenus’ QS-21 Stimulon adjuvant (QS-21 Stimulon).

The phase II study (designated as protocol C-400-02) has screened over 100 HSV-2 positive subjects and enrollment has been closed. The study will test the biological efficacy of HerpV as measured by effect on genital viral shedding after three injections of the therapeutic vaccine. A booster injection of HerpV will be given at six months after treatment to evaluate the potential durability of treatment effect.

The HerpV phase II study has been supported by leading clinical experts in the field who have expressed that a reduction in viral shedding could translate into clinical benefit. A therapeutic vaccine to treat HSV-2 infected patients has the potential to provide a major paradigm shift in the treatment of this infection as well as provide significant quality of life benefits.

Agenus’ QS-21 Stimulon is a novel adjuvant that is incorporated into 17 vaccines currently in clinical development, including four GlaxoSmithKline (GSK) phase III programmes. Results from GSK’s Phase 3 trials using MAGE-A3 cancer immunotherapeutic vaccines in lung cancer and melanoma, which incorporate QS-21 Stimulon, are anticipated this year.

HerpV is a recombinant therapeutic vaccine for the treatment of genital herpes, which is caused by the herpes simplex virus-2 (HSV-2). The vaccine is based on Agenus' HSP platform technology, and contains Agenus’ proprietary QS-21 Stimulon. HerpV consists of recombinant human heat shock protein-70 complexed with 32 distinct 35-mer synthetic peptides from the HSV-2 proteome. This broad spectrum of herpes antigens is intended to allow for more accurate immune targeting and surveillance, reducing the likelihood of immune escape. Further, the diversity of antigens in HerpV increases the chance of providing efficacy for a wide segment of the patient population.

In a four-arm, phase I study, 35 HSV-2 seropositive patients received HerpV (designated in the study as AG-707 plus QS-21), AG-707, QS-21 alone, or placebo. Patients received three treatments at two-week intervals. The vaccine was generally well tolerated, with injection site pain as the most common reported adverse event.

In the phase I study, all patients who were evaluable for immune response and received HerpV showed a statistically significant CD4+ T cell response (100 per cent; 7/7) to HSV-2 antigens as detected by IFN? Elispot, and the majority of those patients demonstrated a CD8+ T cell response (75 per cent; 6/8). This study was published in the scientific journal Vaccine.

Agenus’ flagship adjuvant, QS-21 Stimulon, is a saponin extracted from the bark of the Quillaja saponaria tree, also known as the soap bark tree or Soapbark, an evergreen tree native to warm temperate central Chile.  Agenus’ QS-21 Stimulon has become a key component in the development of investigational preventive vaccine formulations across a wide variety of infectious diseases, and appears to be essential for several investigational therapeutic vaccines intended to treat cancer and degenerative disorders.

QS-21 Stimulon has been widely studied in clinical development and tens of thousands of patients have received vaccines containing the adjuvant.  QS-21 Stimulon is being studied in clinical trials for approximately 17 vaccine indications and include GSK’s phase III vaccine programmes for RTS,S for malaria, MAGE-A3 cancer immunotherapeutic for non-small cell lung cancer and melanoma and HZ/su for shingles. In addition, Janssen’s QS-21 Stimulon-containing vaccine candidate is in phase II trials for the treatment of Alzheimer’s disease.

Agenus Inc. is focused on immunotherapeutic products based on strong platform technologies with multiple product candidates advancing through the clinic, including several product candidates that have advanced into late-stage clinical trials through corporate partners.