Imugene Ltd (ASX: IMU) shares are catching the eye on Thursday morning.

In early trade, the ASX 300 healthcare stock is up almost 5% to 11 cents.

Investors have been buying the clinical stage immune-oncology company's shares after responding positively to an announcement.

According to the release, the company has received a notice of grant from the Chinese Patent Office. This follows earlier grants in Japan and South Korea.

The granted claims protect the ASX 300 stock's oncolytic virotherapy, CF33, including VAXINIA (CF33-hNIS) and CHECKvacc (CF33-hNIS-antiPDL1).

This is a big boost for the company given that China is the largest pharmaceutical market in Asia.

CF33 is a chimeric vaccinia poxvirus from the lab of inventor Professor Yuman Fong, Chair of Sangiacomo Family Chair in Surgical Oncology at City of Hope, and a noted expert in the oncolytic virus field.

Oncolytic viruses are designed to both selectively kill tumour cells and activate the immune system against cancer cells. Imugene notes that they have the potential to improve clinical response and survival.

The release explains that the patent is titled "Chimeric poxvirus composition and uses thereof" and protects the method of composition and method of use of Imugene's licensed oncolytic virotherapy all the way out to 2037.

The ASX 300 stock's managing director and CEO, Leslie Chong, was pleased with the news. She said:

Imugene receiving these patent grants for the CF33 family of oncolytic viruses is a crucial step forward and with China, Japan, and South Korea being the largest healthcare markets in Asia, this is a particularly important patent milestone.

Imugene is a clinical stage immuno-oncology company with a focus on developing a range of new and novel immunotherapies that seek to activate the immune system of cancer patients to treat and eradicate tumours.

It claims to have unique platform technologies that seek to harness the body's immune system against tumours, potentially achieving a similar or greater effect than synthetically manufactured monoclonal antibody and other immunotherapies.

As well as CF33, the ASX 300 stock's pipeline includes an off-the-shelf (allogeneic) cell therapy CAR T drug azer-cel (azercabtagene zapreleucel) which targets CD19 to treat blood cancers.

Unfortunately, over the last 12 months, the company's shares have underperformed the market. For example, despite today's gain, the Imugene share price remains down 15% since this time last year.