A multiple-antibiotic-resistant isolate of Y. pestis has been isolated, and drug resistance was shown to be mediated by a self-transferable plasmid [6, 7] . A subunit vaccine, which consists of two virulent factors, the F1 protein and V-antigen, is currently in human clinical trials [8] [9] [10] . Studies involving the vaccine antigens in various formats have provided the proof-of-concept data that humoral response can be efficient in protection against Y. pestis [11, 12] . There are multiple reports that mouse anti-plague monoclonal antibodies (mAbs) against a Y. pestis challenge can passively protect a mouse against plague [13] [14] [15] . Therefore, mAb therapy may be an attractive alternative to the existing treatments for plague. Despite the promising possibilities, there remains a major hurdle in the treatment against plague and that is the possible immune response of humans to the mouse mAbs that are currently available. One possibility to ameliorate the immune response against the mouse mAb is to humanize the mAb for use in humans, or another alternative is to develop new and fully human anti-plague monoclonal antibodies for clinical usage [16] .