Introduction: Acute myeloid leukemias (AML), a heterogeneous and complex group of diseases, is a clonal malignant disorder derived from a small number of leukemic stem cells (LSCs), which are sustained by self-renewing and responsible for the propagation of leukemic blasts (LBs). Monoclonal antibodies have emerged as effective targeted therapies for the treatment of human malignancies and their mechanisms of action are able to deliver the therapeutic effects with minimal toxicity.

Aim: The challenge is the identification of cell surface antigens which could be preferentially expressed on AML LSC compared with normal hematopoietics stem cells and that could be helpful to target therapies.

Materials and methods: On 16 AML patients (pts) at diagnosis (peripheral blood of 12 pts and bone marrow of 4 pts) myeloblast leukemic cells were identified using a FACSCanto flow cytometer (Becton Dickinson), based on low expression of CD45 and low side scatter (SSC) properties (CD45 low/SSC low). On these subpopulation we used an antibody panel against cell surface antigens, for the detection of immature markers and potential leukemia-associated antigens: CD34, CD38, CD90, CLEC12A (C-type lectin domain family 12 member A), CD44, CD99, TIM-3 (T cell immunoglobulin mucin-3), CD32, CD133, CD74, CD47, CD58, CD25, CD22, CD96.

Results:. The proportion of LBs was positively correlated with CD45 low/SSC low (median 51,8 %). This gated population of LBs were positive for CD34 (median 44,65%), CD38 (median 18,75%), CD90 (median 0,90%), CLEC12A (median 93,7%), CD44 (median 99,9%), CD99 (median 96,6%), TIM-3 (median 84,4%), CD32 (median 14%), CD123 (29,15%), CD133 (median (8,95%), CD58 (median 97,5%), CD47 (median 99,9%), CD74 (median 3,2%), CD25 (median 0,6%), CD96 (median 87%), CD22 (median 0,55%).

Conclusion: The expression of CD34 and CD38 antigens is heterogeneous in LBs. In particular we found that the 50% of patients were CD34+ and 50% were CD38+. CLEC12A, CD44, CD99, TIM-3, CD58, CD47 and CD96 were highly expresses in LCSs. CD90, CD32, CD123, CD133,CD74, CD25 and CD22 were low. Interestingly we identified that the expression of CLEC12A distinguished two different populations: the CLEC12Ahigh cells correlated with the blast cells CD45low/SSClow; on the other hand, CLEC12Alow cells could be compared with CD45high/SSChigh population, representing normal hematopoietic cells. In conclusion, this marker is a good candidate to target therapies against leukemic stem cells. However further studies with an higher number of patients must be carried out to confirm that CLEC12A is an appropriate antigen for a new monoclonal antibody-based therapy.

Acknowledgements: European LeukemiaNet, AIL, AIRC, PRIN 2010-2011, FP7 NGS-PTL project.

Citation Format: Viviana Guadagnuolo, Enrica Imbrogno, Andrea Ghelli Luserna di Rorà, Antonella Padella, Giorgia Simonetti, Emanuela Ottaviani, Cristina Papayannidis, Ilaria Iacobucci, Anna Ferrari, Simona Soverini, Giovanni Martinelli. Clec12a: A new AML stem cell-associated antigen. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3886. doi:10.1158/1538-7445.AM2014-3886