KLRB1 binding agents (in particular anti-KLRB1-antibodies and antigen binding portion thereof) with increased humanness and compositions thereof, as well as therapeutic methods of using the agents, e.g., for depleting cells or inhibiting cells or activating cells, (in particular, Th17, Th17.1, ex-Th17, Tc17, MAIT, iNKT, peTh2, ILC2, ILC3, NK cells, and/or neoplastic T or NK cells in vivo), for the treatment of autoimmune disease, allergic diseases, transplant rejection, hematologic malignancies, and cancer.