Immune Response to Influenza Vaccine in Adults With B-cell Malignancies Treated With Idelalisib

Key Inclusion Criteria: * Currently enrolled in a Gilead-sponsored study, receiving or scheduled to initiate treatment with idelalisib for at least 7 consecutive days prior to receiving an influenza vaccine * Will be receiving an influenza vaccine per standard of care * Willing to comply with scheduled visits, laboratory tests, other study procedures, and study restrictions * Signed informed consent form, indicating that the subject has been informed of the procedures to be followed, potential risks and discomforts, and other pertinent aspects of study participation Key Exclusion Criteria: * Administration of systemic steroids for more than 2 consecutive weeks within the past 3 months (i.e., 12 weeks) prior to receiving an influenza vaccination. Up to 3 single doses of systemic corticosteroids (e.g., given as a premedication) are permitted within 30 days prior to receiving an influenza vaccine, however none of these doses may be administered within 7 days prior to influenza vaccination. Topical and inhaled steroids are permitted * Intravenous immunoglobulin (IVIG) therapy within the past 3 months (i.e., 12 weeks) prior to receiving an influenza vaccination, and/or planned administration during the study period * Cytotoxic chemotherapy and chronic administration (more than 14 days) of immunosuppressants within 30 days of vaccination * Vaccination against influenza within the last 24 weeks prior to vaccination in this study, and/or planned administration of a second dose of influenza vaccine during the study period. * Receipt of any vaccine in the 4 weeks preceding the trial vaccination or planned receipt of any vaccine in the 4 weeks following trial vaccination * History of severe allergic or hypersensitivity reaction that is likely to be exacerbated by any component of an influenza vaccine including egg and chicken protein, or history of hypersensitivity to a previous dose of an influenza vaccine * Acute disease and/or fever at the time of baseline blood draw (fever is defined as temperature ≥ 38°C in an oral setting) * Presence of any condition that could, in the opinion of the investigator, compromise the subject's ability to participate in the study, such as history of substance abuse or psychiatric condition * Females who are pregnant or lactating (refer to the Gilead-sponsored parent study's definition of 'child-bearing potential' to determine if pregnancy testing is required. If a pregnancy test has been performed in the Gilead-sponsored parent study ≤ 6 weeks prior to the baseline blood draw, it may be used for eligibility purposes. Note: Note: Other protocol defined Inclusion/Exclusion criteria may apply.