The present invention provides an anti-FSTL1 antibody or a fragment or functional equivalent thereof, wherein the antibody recognizes an epitope in a region selected from the group consisting of amino acid positions 48 to 100, 148 to 162, 193 to 216, 205 to 228, and 272 to 289 of SEQ ID NO: 1 (amino acid sequence of human FSTL1). The present invention also provides a combination product of a FSTL1 suppressor and additional cancer treatment. It is understood that immune defect such as immunosuppression or immunodeficiency is effectively mitigated by the present invention.
