Acute myeloid leukemia (AML) stem cells (LSC) are capable of surviving current standard chemotherapy and are the likely source of deadly, relapsed disease. While stem cell transplant serves as proof-of-principle that AML LSCs can be eliminated by the immune system, the translation of existing immunotherapies to AML have been met with limited success. Consequently, understanding and exploiting the unique immune mechanisms of AML LSCs is critical. To identify novel immunotherapeutic targets, we sourced multiple large, publicly available datasets and identified CD200 as a potential stem-cell specific immune checkpoint in AML. We hypothesized that CD200 was a stem-cell specific mechanism of evading immune detection and destruction and that anti-CD200 antibody therapy could effectively eliminate AML LSCs by engaging the patient’s immune system. To study the functional role of CD200 in AML, we established and characterized two isogenic cell line models of CD200 expression. Utilizing these cells, we investigated the effects of CD200+ leukemia on the effector functions of isolated T cells, NK cells, and macrophages in vitro. To study CD200 in a physiological setting, we established a PBMC-humanized mouse model, in which we could characterize progression of CD200+ and CD200- AML in the presence of an activate human immune response. Further, we used this model to compare the effects of CD200+ AML on the transcriptional activity and functional capacity of the human T cells. To therapeutically target CD200+ leukemia, we developed a novel, humanized CD200-IgG1 antibody. We investigated the potential of this antibody to both inhibit the immunosuppressive signaling through the CD200 receptor and initiate an antibody-mediated response. By comparing the therapeutic efficacy in both immunocompromised and PBMC-humanized mice, we confirmed that CD200-IgG1 could effectively eliminate CD200+ AML only in the presence of T cell-mediated response. Taken together, we conclude that CD200 is a marker of functional AML stem cells that aids in the escape of immune detection and destruction. Furthermore, these studies lay the groundwork for CD200-targeted therapeutic strategies to specifically eliminate LSCs and prevent relapse of AML
