A new member of the lysyl oxidase (LOX) family, lysyl oxidase-like 4 (LOXL4), is overexpressed in head and neck squamous cell carcinoma (HNSCC) compared to normal squamous epithelium. A monoclonal antibody (mAb) derived from fusion of Balb/c mouse splenocytes immunized with LOXL4 specific peptide was used to evaluate its therapeutic efficacy in 15 HNSCC cell lines associated with LOXL4 overexpression. For xenograft experiments 41 severe combined immunodeficient (SCID) mice were used to analyze LOXL4-mAb mediated tumor regression. Cell viability was analyzed using cytotoxicity-, and clonogenic-assays. Significant suppression of tumor cell growth was observed in 12 out of 15 (80%) tumor cell lines after 48 hr exposure to the mAb (LD50 of 15 µg/ml to 45 µg/ml). The effect induced by the antibody could be blocked by pre-incubation of the antibody with the peptide used for immunization of the mice and antibody generation, indicating that the effect of the antibody is specific. In mice inoculated with HNSCC cells, i.v. injections of the LOXL4-mAb resulted within 70 days in extensive tumor destruction in all treated animals whereas no tumor regression occurred in control animals. In mice pre-immunized i.v. with LOXL4-mAb and subsequently injected with HNSCC cells, tumor development was considerably delayed in contrast to non LOXL4-mAb pre-immunized animals. These results demonstrate that the LOXL4-mAb has potent antitumor activity and suggest its suitability as a therapeutic immune agent applicable to HNSCC exhibiting tumor specific upregulation of LOXL4.