Complex Alterations in Serum Cytokines and Increased Il-4 Levels Characterize Patients Developing Chronic Thrombocytopenia after Allogeneic Hematopoietic Cell Transplantation.

Isolated chronic thrombocytopenia (CT) following allogeneic HCT is associated with an increased risk of transplant-related mortality and a reduction in long-term survival. Although the pathogenesis of CT is not entirely clear, it has been speculated that immune activation and cytokine dysregulation characteristic of chronic GVHD (CGVHD) play a similar role in the pathogenesis of this disorder. To better understand the impact of endogenous cytokine expression on platelets, we analyzed pro and anti-inflammatory cytokines in the serum of patients with CT following allogeneic HCT, comparing levels to healthy donors and to patients with normal platelet counts after allo-transplantation. Serum was obtained from 3 patient groups; Group 1- healthy donor controls (n=12): Group 2- post-transplant from allogeneic HCT patients with normal platelet counts (n=31): Group 3- post transplant from patients with CT (n=11). Using micro sphere-based Luminex flow cytometry, serum was analyzed for levels of the pro-inflammatory cytokines IL-6, IL-8, and TNF-α as well as Th(1) cytokines IL1-b, IL-2, IL-12, IFN-g and Th(2) cytokines IL-4, IL-5, and IL-10.

Results: Both post transplant cohorts (Group 2 and 3) had higher mean levels of GM-CSF (110 and 120 pg/ml), IFN-g (17 and 16 pg/ml), and IL-12 (318 and 202 pg/ml) compared to their respective non-transplant (Group-1) controls (GM-CSF 23 pg/ml: p<.001; IFN-g 4 pg/ml: p<0.01; IL-12 60 pg/ml: p<0.05). Compared to group 2 patients, Group 3 patients with CT had significantly lower mean levels of TNF-α (46 vs 26pg/ml: p<0.03), IL-12 (318 vs 202 pg/ml: P<0.05) and IL-8 (83 vs 59: p<0.05). In contrast mean serum levels of IL-4 (43 vs 26 pg/ml: p<0.001) and IL-5 (51 vs 9 pg/ml: p<0.05) were significantly higher in group 3 CT patients compared to Group 2 patients without thrombocytopenia. When subdivided into groups based on the presence or absence of chronic GVHD, mean IL-4 levels were significantly higher in CT patients with or without CGVHD (33 and 44 pg/ml respectively) compared to post transplant patients without CGVHD with normal platelet counts (18pg/ml: p<0.05). In contrast, patients with CT with or without CGVHD had significantly lower mean levels of IL-8 (89 and 49 pg/ml respectively) compared to patients with or without CGVHD (200 and 126 pg/ml respectively: p<0.05) who did not have thrombocytopenia. We conclude that complex alterations in both pro and anti-inflammatory cytokines are involved in the pathophysiology of CT following allogeneic HCT; based on these data, studies investigating the therapeutic potential of IL-4 inhibition in patients developing CT might be considered.