Michelle Panis

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 (H2Kb/d) mice were transplanted with T cell-depleted (TCD) BM from B6CBAF1 (H2Kb/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 (H2d). 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 × 104) 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.

New interleukin-15 superagonist (IL-15SA) significantly enhances graft-versus-tumor activity

Interleukin-15 (IL-15) is a potent cytokine that increases CD8+ T and NK cell numbers and function in experimental models. However, obstacles remain in using IL-15 therapeutically, specifically its low potency and short in vivo half-life. To help overcome this, a new IL-15 superagonist complex comprised of an IL-15N72D mutation and IL-15RαSu/Fc fusion (IL-15SA, also known as ALT-803) was developed. IL-15SA exhibits a significantly longer serum half-life and increased in vivo activity against various tumors. Herein, we evaluated the effects of IL-15SA in recipients of allogeneic hematopoietic stem cell transplantation. Weekly administration of IL-15SA to transplant recipients significantly increased the number of CD8+ T cells (specifically CD44+ memory/activated phenotype) and NK cells. Intracellular IFN-γ and TNF-α secretion by CD8+ T cells increased in the IL-15SA-treated group. IL-15SA also upregulated NKG2D expression on CD8+ T cells. Moreover, IL-15SA enhanced proliferation and cytokine secretion of adoptively transferred CFSE-labeled T cells in syngeneic and allogeneic models by specifically stimulating the slowly proliferative and nonproliferative cells into actively proliferating cells. We then evaluated IL-15SAs effects on anti-tumor activity against murine mastocytoma (P815) and murine B cell lymphoma (A20). IL-15SA enhanced graft-versus-tumor (GVT) activity in these tumors following T cell infusion. Interestingly, IL-15 SA administration provided GVT activity against A20 lymphoma cells in the murine donor leukocyte infusion (DLI) model without increasing graft versus host disease. In conclusion, IL-15SA could be a highly potent T- cell lymphoid growth factor and novel immunotherapeutic agent to complement stem cell transplantation and adoptive immunotherapy.

Double Haploidentical Hematopoietic Stem Cell Transplantation Results in Successful Engraftment of Bone Marrow from Both Donors without Graft-versus-Host or Graft-versus-Graft Effects

We established double-haploidentical (DH) hematopoietic stem cell transplantation (HSCT) murine models to explore competitive engraftment, graft-versus-graft effect and graft-versus-host disease (GVHD). T cell-depleted (TCD) bone marrow (BM) cells from B6SJF1 (donor 1 [D1]) and B6D2F1 (donor 2 [D2]) mice achieved >90% donor engraftment when transplanted into B6CBAF1 mice. B6CBAF1 recipients survived without evidence of GVHD when undergoing HSCT with TCD-BM from 2 haploidentical donors, D1 and D2. DH-HSCT recipients had significantly higher leukocyte and neutrophil counts than single-haploidentical HSCT recipients from either D1 or D2. DH recipients consistently showed successful mixed chimerism in both BM and spleen. Two other DH-HSCT models, B6D2F1 + C3D2F1→B6C3F1 and B6CBAF1 + B6SJLF1→B6D2F1, showed similar engraftment patterns. Low-dose T cell infusion from both D1 and D2 increased the degree of early engraftment of the respective donors in BM and spleen; however, this early engraftment pattern did not determine long-term engraftment dominance. In the long term, minimally engrafted D1 BM recovered and comprised >50% of all donor- derived B, T, and natural killer cells. We conclude that early BM engraftment is determined by donor T cell immunodominance, but long-term engraftment is related to the engraftment potential of stem cells after DH-HSCT.

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 (H2Kb/d) recipients were transplanted with T-cell-depleted BM cells from B6CBAF1 (H2Kb/k) mice. Haplo-SCT combined with a low-dose haploidentical (HI) T-cell infusion (1 × 105) 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.