(Reuters) -Drugmaker AstraZeneca has agreed to buy Belgium-based biotechnology firm EsoBiotec for up to $1 billion, it said on Monday, seeking to accelerate the development of its cell therapy capabilities, particularly for cancer. "We are in the early stages in terms of clinical development, so our immediate plans will be to scale up the discovery efforts," Susan Galbraith, AstraZeneca's executive vice president for oncology R&D, told reporters on a call.