Monitoring the Chimerism Status of Subpopulation in HLA Haplo-Identical Stem Cell Transplantation Using the Anti HLA Antibodies: Based on the Study of HLA Distribution in Korean Population

Determining the chimerism in stem cell transplantation (SCT) is important in the monitoring of engraftment. Conventional monitoring methods such as short tandem repeat (STR) PCR are labor intensive and difficult in showing the changes of cell subpopulations. Nowadays, HLA-haploidentical SCT is performed actively and flow cytometric analysis using anti HLA antibody targeted for the different HLA between donor and recipient in HLA-haploidentical SCT can be useful by observing changes of cell subpopulations and determining the chimerism.

Based on the study of HLA distribution in Korean population, we designed the panel of HLA monoclonal antibody that can detect and differentiate major HLA of Korean population. This panel was verified against 23 cases of HLA-haploidentical SCT. Flow cytometric analysis was performed using anti-HLA-antibodies on one pediatric patient with aplastic anemia who underwent HLA-haploidentical SCT. Tests were performed every day since SCT. The appearance or disappearance of donor and/or recipient HLA was observed using antibodies against mismatched HLA. Donor and/or recipient T cells, B cells, NK cells, and monocytes were observed using CD3, CD19, CD56, and CD13 respectively. The flow cytometric results were interpreted by observing the changes in subpopulations of detected cells and determining the engraftment status of patients.

A total of 11 anti-HLA-A-antibodies and anti-HLA-B-antibodies were selected. They cover 97.9% of HLA-A and 8.6% of HLA-B in Korean population. In the verification of our panel of HLA monoclonal antibody, we distinguished donor and recipient cells in 21 of 23 HLA-haploidentical SCT cases. In our case, the patient had HLA-A2/A24 while the donor had HLA-A2/A33. Recipient type of CD3(+) and HLA-A33(-) T cells appeared in first few days but donor type CD3(+) and HLA-A33(+) T cells appeared at day 20 and were increased. Donor type CD56(+) and HLA-A33(+) cells were seen at analysis done in day 8 and continued to appear. HLA-A33(+) cells were consistently observed and increased throughout the follow up period, showing the process of engraftment of donor stem cells.

We were able to apply our flow cytometric analysis design using HLA monoclonal antibody for the detection of chimerism in HLA-haploidentical SCT. This method was more simple and sensitive than conventional monitoring techniques. Moreover, this method allowed us to observe the dynamics of changes in cell subpopulations after HLA-haploidentical SCT. Flow cytometric analysis can be considered as a strong tool for observing the changes in cell subpopulations and the monitoring the engraftment of HLA-haploidentical SCT.

No relevant conflicts of interest to declare.