Recovery of innate lymphoid cells after allogeneic stem cell transplant: A single institution pilot study

The response of Innate Lymphoid Cells (ILCs) to conditioning regimens and subsequent recovery in the setting of allogeneic hematopoietic stem cell transplant (aHSCT) in pediatric patients is not known. The impact of this recovery pattern on graft versus host disease (GVHD) has not been prospectively studied. We aim to study the recovery of ILCs after aHSCT in children and discover its role in GVHD. Pediatric patients undergoing aHSCT were enrolled in a prospective translational study since May 2019. Patients blood were analysed by flow cytometry at following time points: prior to the conditioning regimen, weekly starting on day 0 until +30 (+/− 3 days), then +60, +90 and +180 days. Ten patients have been enrolled to date - demographics: median age 9.5 years; 4 malignant, 6 non-malignant; haploidentical donor (n=1), matched sibling (n=3), unrelated (n= 6). Graft source was bone marrow for all patients. Most common conditioning regimen was fludarabine, busulfan and rabbit antithymocyte globulin (40%). GVHD prophylaxis for most patients was tacrolimus with mini-methotrexate (90%). We saw substantial drop in number of ILCs in response to conditioning regimen in all patients, with nadir on +14 that plateaued through +30, followed by a spike on +60 and return to normal levels by +90. Similar trend was seen in type 1 ILCs (Lin− CD127+ CRTH2− CD117−) but showed a slower drop, reaching nadir on +21 with slow recovery by +60. Type 2 ILCs (Lin− CD127+ CRTH2+) and Type 3 ILCs (Lin− CD127+ CRTH2-ve CD117+) however showed a small increase on +7 compared to day 0 with both cell types recovering by +60. We showed that it is feasible to prospectively study the recovery of ILCs after aHSCT. Continued enrollment will allow us to evaluate the correlation between ILCs and GVHD.