In some aspects, the invention relates to compositions comprising marrow infiltrating lymphocytes (“MILs”). The MILs may be activated MILs. In some aspects, the invention relates to methods for activating MILs, comprising incubating MILs in an environment comprising less than 21% oxygen. In some aspects, the invention relates to methods for treating cancer in a subject, comprising administering to the subject a composition comprising activated MILs.