Immunotherapy vaccine shows promise in prostate cancer patients

ImmunityBio Inc. has published the results of a Phase I study evaluating the safety and immunogenicity of its multi-targeted recombinant human adenovirus (hAd5) immunotherapy vaccine in patients with incurable metastatic castration-resistant prostate cancer (mCRPC) in The Journal of ImmunoTherapy of Cancer.

The company’s hAd5 is designed to deliver tumour-associated antigens (TAAs) and neoepitopes (expressed only by cancer cells) and induce T-cell and antibody responses that may result in T-cell memory.

The study (NCT03481816) enrolled 18 patients with mCRPC who had advanced, incurable disease. They were given concurrently three hAd5 vaccines targeting prostate-specific antigen (PSA), brachyury and MUC-1 at a dose of 5×1011 viral particles (VPs) each, subcutaneously every three weeks for a maximum of three doses (dose de-escalation cohort), followed by a booster vaccine every eight weeks for a year (dose-expansion cohort only).

According to investigators, one patient achieved a partial response and five had confirmed stable disease (SD) for over six months, with confirmed PSA decline. Additionally, the median progression-free survival was 22 weeks, median overall survival (OS) was not reached and the 12-month OS probability for all patients was 83.3 percent.

Furthermore, all 17 patients included in the analysis mounted T-cell responses to at least one tumour-associated antigen and 94 percent (16 of 17) developed T-cell responses to more than one antigen encoded by the vaccine.

“The finding of T-cell-mediated immunity induced in 100 percent of 17 prostate cancer patients whose white blood cells were evaluated in the study validates the ability of our hAd5 vaccine platform to generate a potent response to antigens delivered,” stated Dr Patrick Soon-Shiong, Founder and Executive Chairman of ImmunityBio. “Furthermore, the demonstration that the vaccine can be administered repeatedly, without adverse effects at the dose of 5x 1011 viral particles, supports the application of this hAd5 platform in both cancer and infectious diseases such as COVID-19. These early results, which include signals of clinical activity and durable stable disease, are encouraging for patients with highly resistant advanced metastatic prostate cancer and warrants further study.”

ImmunityBio has developed multiple product candidates that use this hAd5 viral vector to deliver tumour-associated antigens as potential vaccines for the treatment of solid tumours. This same hAd5 viral vector has been applied for the treatment of infectious diseases and is in clinical trials for SARS-CoV-2 using hAd5 Spike plus Nucleocapsid proteins as antigen constructs.