Leukopoor: filters out WBC. why? Because wBCs elaborate cytokines/pyrogens/interleukins that are responsible for reactions like fever, chilling. Also to decrease antigen exposure, and decrease sensitization. 

CMV negative: all neonates must be given. We prefer CMV neg patients to get ~ blood on BMT, however if they get CMV + blood (as in an emergency) there is a 3% chance of getting infected. 

Irradiated: destroys dividing/proliferating cells; actually prevents proliferation of lymphocytes, thus preventing GVHD. Give to immunocompromised pts, including  kids < 4 m/o. lymphocytes are functional, and can be sensitized to make ab, but not proliferate. Side note: irradiated leukocytes can be given to persistently bacteremic/fungemic pts not responding to abx.

At CHLA, only BMT and NICU patients absolutely need CMV negative blood. All others may get leukopoor blood, which theoretically should have WBCs (and therefore CMV) mostly removed.