Multivalent anti-platelet glycoprotein l(b)alpha antibodies can cause severe side effects. The present disclosure provides humanized antibodies specifically recognizing glycoprotein l(b)alpha and lacking a Fc portion, therefore do not interact with Fc receptor. The humanized antibodies are capable of preventing platelet activation and aggregation, and reducing thrombus size / growth and prevent vessel occlusion. They can be also very useful to decrease platelet-tumor cell interaction and decrease tumor metastasis. At therapeutic doses, the humanized antibodies lack the ability to induce platelet activation, induce thrombocytopenia; and/or prolong bleeding time.
