Beneficial effects of fetal-maternal microchimerism on the activated haplo-identical peripheral blood stem cell treatment for cancer

Background Previous studies have shown that activated haplo-identical peripheral blood stem cell (haplo-PBSC) treatment exerts an anti-tumor effect on patients with metastatic solid tumors. The purpose of this study was to test the hypothesis that fetal-maternal microchimerism enhances the beneficial effect of the haplo-PBSC treatment for cancer. Methods Twenty-five patients with advanced-stage solid tumors refractory to standard chemotherapy were treated with haplo-PBSC donated by parents or children. Fetal-maternal microchimerism status was determined using nested polymerase chain reaction typing using sequence-specific primers (PCR-SSP). Clinical outcomes, including therapeutic response by measuring tumor size changes using CT scanning and survival times, were evaluated. The donor-recipient mixed lymphocyte response (MLR) was detected using an MTT proliferation assay. Cytokine production was determined using an ELISA method. Results Six patients receiving maternal-child transplants were fetal-maternal microchimerism positive (+). The mean survival time of patients with the microchimerism(+) haplo-PBSC treatment was 30.17 +/- 5.32 months (median 17 months), which was significantly longer than that of patients with negative (-) microchimerism (mean +/- 16.953.29 months, median 8 months; P=0.043). The therapeutic response rate was significantly higher in microchimerism+ patients (83.3%) than that in microchimerism(-) patients (36.8%) (P=0.047). Furthermore, suppression of donor-recipient MLR and increased production of a T-helper type 1 (Th1) type cytokine, interferon (IFN)-gamma, were found in microchimerism(+) patients after haplo-PBSC treatment. Discussion This small study suggests that fetal-maternal microchimerism is associated with a statistically significant improvement in anti-tumor effect of activated haplo-PBSC treatment. Further study is required to elucidate the mechanism for this observation.