Immune Mobilization with IL-2 and Growth Factors: Differential in Vivo Effects of the NKG2D Receptor on CD8+ and CD56+ Effector Cells

Background: NKG2D, one of four NK cell activating receptors characteristically found on NK cells, has been identified on some CD8+T cells that mediate TCR-independent and non-MHC restricted tumor cell killing. These cytotoxic NKG2D+CD8+ effector cells aggressively kill myeloma cells. Since the NKG2D receptor recognizes ligands expressed on myeloma cells, NKG2D+ CD8+ effector cells provide a unique immunotherapy opportunity.

Methods: We designed an immune mobilization trial to mobilize autologous cytotoxic effector cells, with peripheral CD34+ hematopoietic progenitor cells. IL-2 (dose escalation) began on day 0 of mobilization and continued as a daily SQ injection for 11 days. On day 7 of mobilization, GM-CSF (7.5 mcg/kg/d) and G-CSF (5 mcg/kg/d) were initiated for 5 days (days 7–11). Leukapheresis was performed on Day 11.

Results: Eleven of 12 patients completed therapy (myeloma, n=11; NHL, n=1). One patient (NHL) progressed during treatment. The MTD of IL-2 was 6×10⁵ IU/m²/d. All patients successfully mobilized and received an autologous transplant with normal engraftment (ANC recovery: day 13 median; range 10–14 days; platelet recovery: day 12 median; range of 0–13 days). When compared to baseline, the immune-mobilized cells demonstrate an increase in CD3+CD8+ T cells (p = 0.01), CD3+CD8+CD56+ T cells (p = 0.01) and CD56+ NK cells (p = 0.002). Cytotoxicity directed against a human myeloma cells increased from 9% (baseline) to 43% (p=0.02). Importantly, immune mobilization resulted in an IL-2 dose-dependent expression of NKG2D on CD8+T cells or CD56+ NK cells. Low dose IL-2 (6 × 10⁵ IU/m²/d) moderately increased NKG2D expression on CD8+ T cells when compared to baseline (p = 0.02). High dose IL-2 (1.5 × 10⁶ IU/m²/d) strongly enhanced NKG2D expression on CD 8+ T cells (p = 0.004). Low dose IL-2 (6 × 10⁵ IU/m²/d) and high dose IL-2 (1.5 × 10⁶ IU/m²/d) increased NKG2D expression on CD3-CD 56+ NK cells, with p values of 0.03 and 0.002, respectively. Preliminary data indicate these effects are sustained in vivo post-transplant.

Conclusions: Immune mobilization resulted in an IL-2 dose-dependent expression of NKG2D on CD8+T cells and CD56+ NK cells, thereby altering the cellular components of the mobilized cells. Since the NKG2D receptor recognizes ligands expressed on myeloma cells, NKG2D+ CD8+ effector cells provide a unique immunotherapy opportunity for the treatment of myeloma.