The companies signed a collaboration and licensing agreement in June 2014 for about five programs, including the lead NY-ESO TCR program. GSK can license the program if it elects to.
Under the expanded deal, the firms will accelerate the development of NY-ESO therapy into pivotal synovial sarcoma studies and also explore development in myxoid round cell liposarcoma.
The companies may also start about eight proof-of-principle studies evaluating combinations with other therapies, including checkpoint inhibitors.
Adaptimmune will undertake the trials, while GSK will provide funding for the studies and share the costs of the combination studies through a success-based milestone structure.
The expanded agreement gives potential development milestones to Adaptimmune, solely related to the NY-ESO program, of around $500m, if GSK exercises its option and develops NY-ESO in more than one indication and more than single human leukocyte antigen type.
Adaptimmune Therapeutics CEO James Noble said: "We believe that our affinity enhanced T-cell programs have the potential to deliver important clinical benefit to cancer patients, and it is therefore essential that we accelerate our efforts to meet their needs.
"We are working closely with GSK to expedite development of our affinity enhanced T-cell therapy targeting NY-ESO, and if we succeed in generating pivotal data consistent with that of our ongoing studies, we believe it has the potential to be the first engineered T-cell therapy to reach the market."
Meanwhile, GSK has submitted a a supplemental biologics license application to the US Food and Drug Administration to expand the scope of its flu vaccine FluLaval Quadrivalent.
The vaccine is currently approved to prevent flu for active immunisation against influenza A subtype viruses and type B viruses, in persons three years of age and older.
The submission seeks to expand the indication to include children aged six months through 35 months of age.