Effect of in vivo administration of IL-3 and IL-6, alone and in combination with G-CSF, GM-CSF or IL-1, on haematopoiesis, graft-versus-host disease and survival after murine haematopoietic stem cell transplantation.

We have explored the effect of IL-3 and IL-6, each alone and in combination with G-CSF, GM-CSF or IL-1, on neutrophil and platelet recovery in BALB/c mice (H-2d) given 10 Gy total body irradiation followed by 10(7) bone marrow cells and 10(6) spleen cells from C57BL6 donors (H-2b), as well as the effect of IL-3 alone and IL-6 alone on graft-versus-host disease (GVHD) and survival. Neither IL-3 alone nor IL-6 alone significantly increased the circulating absolute neutrophil count (ANC) at day 6 post transplant when compared with mice given saline injections (ANC 0.31 x 10(9)/l). G-CSF and IL-1, each alone, significantly raised the day-6 ANC (0.58 x 10(9)/l, p = 0.02; 0.67 x 10(9)/l, p = 0.007 respectively). However, IL-3, 200 ng twice daily, significantly increased the day-6 ANC when used in combination with GM-CSF (0.49 x 10(9)/l, p = 0.003) or with IL-6 (0.66 x 10(9)/l, p = 0.004), as well as with G-CSF (0.62 x 10(9)/l, p = 0.007) or with IL-1 (0.49 x 10(9)/l, p = 0.003). Apart from the combination with IL-3, IL-6 significantly raised the day-6 ANC only in combination with G-CSF (0.79 x 10(9)/l, p = 0.007). When used alone, both IL-6 and G-CSF raised the day-6 platelet count (312 x 10(9)/l, p = 0.02 and 309 x 10(9)/l, p = 0.01 respectively) compared with control mice (216 x 19(9)/l). IL-3 alone resulted in a platelet count of 303 x 10(9)/l (p = 0.06). In combination, only IL-3 with G-CSF significantly increased the value over that of saline control mice (328 x 10(9)/l, p = 0.02). IL-3 200 ng alone twice daily and IL-6 200 ng alone twice daily for 14 days post transplant resulted in survival not different from that of mice given saline injections. However, IL-3 500 ng twice daily for 14 days resulted in impaired survival and accelerated weight loss. In summary, while neither IL-3 nor IL-6 (nor GM-CSF) used alone accelerated neutrophil recovery post transplant, the combinations of IL-3 plus IL-6 and IL-3 plus GM-CSF did so. IL-6 (and G-CSF) accelerated platelet recovery post transplant, but combining IL-3 or IL-6 with the other cytokines was generally unsuccessful in this regard. Higher-dosage IL-3 appeared to accelerate graft-versus-host disease and impair survival, thus providing indirect evidence of the involvement of this cytokine in the mediation of GVHD.