Objective: The traditional immunotherapy for patients with refractory metastatic solid tumors is limited because tumors induce immunosuppression. New treatment is, therefore, needed. The aim of this study was to evaluate the clinical efficacy of infusion of high-dose interleukin (IL)-2-activated allogeneic haploidentical peripheral blood stem cells (haplo-PBSCTs) on patients with an advanced stage of refractory solid tumors. Methods: This study involved 11 patients with refractory metastatic tumors and haploidentical relatives as donors for haplo-PBSCs. The therapeutic outcome of the IL-2-activated haplo-PBSC infusion and patients' cytokine levels were evaluated. The cytotoxicity of IL-2-activated haplo-PBSCs for tumor cells was determined using in vitro cytotoxicity assays. Results: A range from 2.5 to 5.6 × 1010 of activated haplo-PBSCs were harvested after exposure to rhIL-2, along with a significant increase in the proportion of natural killer (NK) cells and activated lymphocytes (CD69 + and CD25 +), and enhanced cytotoxicity of haplo-PBSCs for several tumor cell lines. Following treatment, 1 (1/11) patient achieved a partial response (PR), 1 (1/11) achieved a mild response (MR), 6 (6/11) achieved stable disease (SD), and 3 (3/11) achieved progressive disease (PD). For all of the 11 patients, the median progression-free survival (PFS) was 5 months (3–14 months). We also observed the phenomenon of Th2 shifted to Th1, which played a crucial role in cancer immunotherapy. Conclusions: The adoptive transfusion of IL-2-activated haplo-PBSCs has potent antitumor effects both in vitro and in vivo. This finding suggests that IL-2-activated haplo-PBSCs may serve as an alternative therapy for advanced-stage solid tumors, especially for those patients who are refractory or ineligible for chemo- or radiotherapy.
