Biogen Idec Inc. and Eisai Co. Ltd. are joining forces to tackle Alzheimer’s disease (AD), initially focusing on two candidates from the Japanese company with an option to jointly develop and commercialize two early stage Biogen assets. The deal marshals the talents of a pharma behind the blockbuster AD drug Aricept (donepezil) and a big biotech with a solid track record in neurodegenerative disease.