Interleukin-15 administration increases graft-versus-tumor activity in recipients of haploidentical hematopoietic SCT.

Utilizing a clinically relevant haploidentical (HI) murine transplant model, lethally irradiated B6D2F1 (H2K(b/d)) mice were transplanted with T cell-depleted (TCD) BM from B6CBAF1 (H2K(b/k)) mice. We found that administration of IL-15 significantly increases the numbers of CD8+ T and natural killer (NK) cells in spleen and BM after transplantion without GVHD. Graft-versus-tumor (GVT) potency of the graft was evaluated upon tumor challenge using P815 tumor cells (H2(d)). IL-15 administration without T-cell infusion did not result in any survival improvement. However, IL-15 in combination with very low-dose T-cell infusion (1 × 10(4)) significantly increased GVT activity and improved survival in recipients of HI hematopoietic SCT (HSCT). This effect was observed when IL-15 was given at a later time point, rather than immediately following transplantation. IL-15 administration also specifically increased slow-proliferative CD8+ T-cell proliferation and IFN-γ secretion in CD8+ T cells in recipients of CFSE (carboxyfluorescein succinimidyl ester)-labeled HI T-cell infusion, whereas there was no effect on CD4+ T-cell proliferation, suggesting the critical effect of IL-15 on CD8+ T-cell homeostasis in HI host. We conclude that IL-15 can be used for enhancing antileukemia effect of HI-HSCT, which requires presence of donor-derived T cells.

Haploidentical hematopoietic SCT increases graft-versus-tumor effect against renal cell carcinoma.

Allogeneic hematopoietic SCT (HSCT) has been shown to be an effective treatment option for advanced renal cell cancer (RCC). However, tumor resistance/relapse remains as the main post transplant issue. Therefore, enhancing graft-versus-tumor (GVT) activity without increasing GVHD is critical for improving the outcome of HSCT. We explored the GVT effect of haploidentical-SCT (haplo-SCT) against RCC in murine models. Lethally irradiated CB6F1 (H2K(b/d)) recipients were transplanted with T-cell-depleted BM cells from B6CBAF1 (H2K(b/k)) mice. Haplo-SCT combined with a low-dose haploidentical (HI) T-cell infusion (1 × 10(5)) successfully provided GVT activity without incurring GVHD. This effect elicited murine RCC growth control and consequently displayed a comparative survival advantage of haplo-SCT recipients when compared with MHC-matched (B6D2F1CB6F1) and parent-F1 (B6CB6F1) transplant recipients. Recipients of haplo-SCT had an increase in donor-derived splenic T-cell numbers, T-cell proliferation and IFN-γ-secreting donor-derived T-cells, a critical aspect for anti-tumor activity. The splenocytes from B6CBAF1 mice had a higher cytotoxicity against RENCA cells than the splenocytes from B6 and B6D2F1 donors after tumor challenge. These findings suggest that haplo-SCT might be an innovative immunotherapeutic platform for solid tumors, particularly for renal cell carcinoma.