** Adaptive Biotechnologies' ADPT.O shares down 5.5% in extended trading to $16.50 as co looks to raise capital and split its businesses

** Seattle, Washington-based ADPT announces private offering of $250 mln convertible bonds due 2031

** Co intends to use some net offering proceeds to repay OrbiMed purchase agreement, for general purposes and opportunistic initiatives in the Minimal Residual Disease (MRD) business

** Alongside the offering, co unveils plan to separate its MRD and Immune Medicine businesses

** "We believe this separation is the best way to unlock the full potential of both businesses, increasing their impact on patients and creating long-term value for shareholders," CEO and co-founder Chad Robins said

** ADPT stock closed down 0.8% at $17.46 on Mon. Stock up 7.5% YTD and about 70% over the past 12 months

** Co has about $2.8 bln market cap

** Avg rating of 8 analysts covering the stock is "buy"; median PT $20.50, per LSEG