* Focus on T-cell based approach

* Up to 400 patients expected for phase I/II trials

* Phase three trial expected from Sept 2021

* Company says able to produce millions of doses

PARIS, Oct 19 (Reuters) - France's Ose Immunotherapeutics will enrol up to 400 patients for the first two stages of clinical trials of an experimental coronavirus vaccine it hopes will provide an extra weapon in battle against the global pandemic.

Chief executive Alexis Peyroles told Reuters Ose hoped to roll out its vaccine in Europe and the United States in 2022, potentially at least a year after the most advanced projects.

However, he said the different modus operandi of Ose's candidate meant it could still play an important role.

More than 40 drugmakers and research groups are conducting human trials into vaccines against a virus that has led to more than 1 million deaths and roiled economies.

Most of these vaccines are primarily designed to generate so-called "neutralising antibodies" to thwart the virus. While this is seen as the most promising approach, some researchers question whether the effect will last as the virus mutates.

Ose, which focuses on oncology and autoimmune diseases, believes a subgroup of T-cells, also known as "killer cells", can be trained to attack cells infected by a virus and recognise up to 11 of the coronavirus proteins - whereas traditional vaccines typically go after one.

"T-cells are like the infantry in our bodies," Peyroles said, adding Ose's vaccine could be given alone or in combination with other shots for some immuno-suppressed subjects or those suffering co-morbidities such as diabetes or cancer.

"If you inject an antibodies vaccine several times to extend protection, you may end up seeing adverse reactions to the vaccine, that is where our product could also complement well."

OSE is listed as the only company pursuing a T-cell based approach in the World Health Organization's tally of vaccines. https://bit.ly/3dH39As

The potential vaccine is one of a handful being developed by French companies or researchers, including by Sanofi, Valneva and Osivax as well as researchers at Institut Pasteur.

If the first two phases of clinical trials due to start around the end of the year - and which will help assess safety and immune response - go according to plan, Ose will aim to team up with a partner from the industry to conduct final Phase III studies from September 2021 and possibly distribute the vaccine.

Peyroles did not say if his company had started talks with potential partners, but said companies such as Sanofi, Merck & Co and AstraZeneca could be interested after they get the readouts from their own late stage trials.

"We have ensured they are aware of our data," he said of the three companies when asked if discussions were already underway.

Peyroles said production of the vaccine could be scaled up easily given the availability of the ingredients and OSE's existing supply agreements.

"We are not in the biologics space with this vaccine. We have the partnerships and we can produce millions of doses."

(Reporting by Matthias Blamont in Paris; Additional reporting by Ludwig Burger in Frankfurt; Editing by Mark Potter)