This approach was used in the drug talimogene laherparepvec, a variant of herpes simplex virus engineered to selectively replicate in tumor tissue and to express the immune stimulatory protein GM-CSF.
This enhances the anti-tumor immune response to tumor antigens released following viral lysis, creating a patient-specific vaccine.
If T-cells recognize the epitope as foreign, the adaptive immune system is activated and target cells that express the antigens.
[11] Using a combination of established cancer cell lines that resemble the patient's tumor can overcome these barriers, but this approach has yet to be effective.
Canvaxin, which incorporates three melanoma cell lines, failed phase III clinical trials.
In this strategy, the antigen-presenting dendritic cells directly stimulate T-cells rather than relying on processing of the antigens by native APCs after the vaccine is delivered.
[9] Peptide-based vaccines usually consist of cancer specific-epitopes and often require an adjuvant (for example, GM-CSF) to stimulate the immune system and enhance antigenicity.
It is marketed by Antigenics Inc.[18] Sipuleucel-T, Provenge, was approved by the FDA in April 2010 for metastatic hormone-refractory prostate cancer.
[19] Similar to Oncophage, it is not yet approved for use in the United States, although it is already undergoing phase II trials to that end.
[20][21] Bacillus Calmette-Guérin (BCG) was approved by the FDA in 1990 as a vaccine for early-stage bladder cancer.
[citation needed] Cancer vaccines seek to target a tumor-specific antigen as distinct from self-proteins.
An effective vaccine should also stimulate long term immune memory to prevent tumor recurrence.
Some scientists claim both the innate and adaptive immune systems must be activated to achieve total tumor elimination.
[citation needed] However, most vaccine clinical trials have failed or had modest results according to the standard RECIST criteria.
[26] The precise reasons are unknown, but possible explanations include: In January 2009, a review article made recommendations for successful oncovaccine development as follows:[27]