Monitoring of hematopoietic chimerism after transplantation for pediatric myelodysplastic syndrome: real-time or conventional short tandem repeat PCR in peripheral blood or bone marrow?

Quantitative real-time PCR (qPCR) has been proposed as a highly sensitive method for monitoring hematopoietic chimerism and may serve as a surrogate marker for the detection of minimal residual disease minimal residual disease in myelodysplastic syndrome (MDS), until specific methods of detection become available. Because a systematic comparison of the clinical utility of qPCR with the gold standard short tandem repeat (STR)-PCR has not been reported, we retrospectively measured chimerism by qPCR in 54 children transplanted for MDS in a previous study. Results obtained by STR-PCR in the initial study served as comparison. Because the detection limit of qPCR was sufficiently low to detect an autologous background, we defined the sample as mixed chimera if the proportion of recipient-derived cells exceeded .5%. The true positive rates were 100% versus 80% (qPCR versus STR-PCR, not significant), and mixed chimerism in most cases was detected earlier by qPCR than by STR-PCR (median, 31 days) when chimerism was quantified concurrently in peripheral blood and bone marrow. Both methods revealed a substantial rate of false positives (22.7% versus 13.6%, not significant), indicating the importance of serial testing of chimerism to monitor its progression. Finally, we propose criteria for monitoring chimerism in pediatric MDS with regard to the subtypes, specimens, PCR method, and timing of sampling.

Cytotoxic Capacity of IL-15-Stimulated Cytokine-Induced Killer Cells Against Human Acute Myeloid Leukemia and Rhabdomyosarcoma in Humanized Preclinical Mouse Models.

Allogeneic stem cell transplantation (allo-SCT) has become an important treatment modality for patients with high-risk acute myeloid leukemia (AML) and is also under investigation for soft tissue sarcomas. The therapeutic success is still limited by minimal residual disease (MRD) status ultimately leading to patients' relapse. Adoptive donor lymphocyte infusions based on MRD status using IL-15-expanded cytokine-induced killer (CIK) cells may prevent relapse without causing graft-versus-host-disease (GvHD). To generate preclinical data we developed mouse models to study anti-leukemic- and anti-tumor-potential of CIK cells in vivo. Immunodeficient mice (NOD/SCID/IL-2Rγc(-), NSG) were injected intravenously with human leukemic cell lines THP-1, SH-2 and with human rhabdomyosarcoma (RMS) cell lines RH41 and RH30 at minimal doses required for leukemia or tumor engraftment. Mice transplanted with THP-1 or RH41 cells were randomly assigned for analysis of CIK cell treatment. Organs of mice were analyzed by flow cytometry as well as quantitative polymerase chain reaction for engraftment of malignant cells and CIK cells. Potential of CIK cells to induce GvHD was determined by histological analysis. Tissues of the highest degree of THP-1 cell expansion included bone marrow followed by liver, lung, spleen, peripheral blood (PB), and brain. RH30 and RH41 engraftment mainly took place in liver and lung, but was also detectable in spleen and PB. In spite of delayed CIK cell expansion compared with malignant cells, CIK cells injected at equal amounts were sufficient for significant reduction of RH41 cells, whereas against fast-expanding THP-1 cells 250 times more CIK than THP-1 cells were needed to achieve comparable results. Our preclinical in vivo mouse models showed a reliable 100% engraftment of malignant cells which is essential for analysis of anti-cancer therapy. Furthermore our data demonstrated that IL-15-activated CIK cells have potent cytotoxic capacity against AML and RMS cells without causing GvHD.