166 : IL-7tv, a modified interleukin-7 protein, is a potent agent for immune reconstitution

The success of stem cell transplantation depends on the reconstitution of the recipient’s immune system. The lymphocyte growth factor, Interleukin-7 (IL-7), has the potential to improve immune reconstitution; however, at the supraphysiologic doses being tested in clinical trials, consequences such as down-regulation of the IL-7 receptor (IL-7R), altered CD4:CD8 ratios or a change in the homing of T-cells could affect the quality of the immune reconstitution. Our research objective was to design a new form of IL-7 that retained its capacity for supporting lymphocyte expansion without the need for a high dosing regimen. To this end, we developed IL-7tv , an IL-7R ligand with a mutation adjacent to the receptor binding domain. Using surface plasmon resonance, (SPR), we showed that, compared to IL-7, binding of IL-7tv to IL-7Ra was slightly reduced, while the total binding constant (K D ) remained the same. This could be due to the mutation decreasing accessibility of IL-7tv to the IL-7Ra. To test whether IL-7tv would deliver a sustained growth signal through the IL-7R, we used an IL-7-dependent murine T-cell, line, D1, human T-cells, and hematopoietic stem cells (HSCs). Using D1 cells, we found that IL-7tv supported survival through phosph-STAT5 activation, at doses 10-fold lower than the optimal concentration of native IL-7, and did not down-regulate the IL-7R. Applied to human T-cells in culture, IL-7tv promoted the growth of both CD4 and CD8 subsets at a dose 40-fold less than IL-7, without causing expression of the activation receptor, CD69. Importantly, IL-7tv , at lower doses, drove the ex vivo expansion of CD34 + HSCs more effectively than IL-7. These results support the use of IL-7tv as a novel agent for immune reconstitution and indicate that modulation of ligand binding to the IL-7R is a powerful means by which to harness the growth potential of the cytokine.