Rituximab Responsive Cytopenia Following Allogeneic Stem Cell Transplantation

Background: In a subset of post-transplant patients, cytopenia persists without clear explanations, even after ruling out common causes like infections, sepsis, Graft-versus-Host Disease (GVHD), nutritional deficiencies, myelotoxic drugs, and relapsed malignancy. This retrospective analysis seeks to assess the effectiveness of Rituximab in treating cytopenia post-allograft with an immune or uncertain origin.Methods: This single-centre retrospective analysis of post-transplant cytopenia was conducted with data collected from electronic records, case notes, and the haematology database. The data spanned the period from January 2012 to August 2023.Results: 169 patients(M/F:123/46, median age: 56 yr.) underwent Rituximab treatment after allograft (n=104) or autograft (n=63) for haematological malignancy or bone marrow failure syndrome. Among these, thirty patients received Rituximab for cytopenia, with 29 cases post-allograft and 1 post-autograft (M/F: 23/7; median age: 56 yr). Diagnosis was Ac. Leukaemia (n=10), Lymphoma (n=10), or other (n=10). In post-allograft patients, cytopenia presented as trilineage in 7 cases, bi-lineage in 13, and single lineage in 9 cases. The median haematological parameters were as follows: Haemoglobin (Hb) 84g/L (68-152), White Blood Cell (WBC) count 2.5x10^9/L (0-12), and Platelets 45x10^9/L (4-638). DCT was positive in 8/19 cases with available results. Of the 29 cases undergoing bone marrow evaluation, nineteen showed hypocellular marrow with no signs of malignancy. Cytopenia showed no correlation with infection, viruses, Vitamin B12, or folate deficiency.

The response to rituximab was defined as follows: CR: normal counts, transfusion independence, and no need for steroids or G-CSF; Stable or Partial Response (PR): platelets >50, Hb >100, and ANC >1.0 without additional support; or NR. Rituximab was administered weekly at a dose of 375mg/m2 for 4 weeks.

Fifteen patients attained a CR (50%), four achieved stabilization (13%), and eleven showed no response (37%), with an overall response rate of 63%. There was no statistical difference in the response rate between those with a positive DCT at 62% (5/8) and those with a negative DCT at 64% (7/11) (P=0.96). The response rates were 78% in single lineage cytopenia (7/9), 62% in bi-lineage cytopenia (8/13), and 57% in trilineage cytopenia (4/7) [p=0.64]. Three patients underwent a second course of Rituximab due to a recurrence of cytopenia, and all achieved a second complete response. Notably, all three cases were associated with autoimmune haemolysis.

The small sample size prevents the identification of predictors, but was a trend towards improved outcomes in patients with Hodgkin's disease (100% CR). There was no impact of gender, diagnosis, age, or the intensity of conditioning. The primary limitation to the analysis was the significant amount of missing data, including DCT results (11/30) and reticulocyte counts (18/30), hampering further identification of predictors or trends.Conclusions: Rituximab is a possible option for managing post-allograft cytopenia with presumed immune aetiology or no identified cause. The substantial response rate and sustained benefits observed support its consideration in such cases. Larger cohorts are needed to identify predictors and trends and to address the current limitations of missing data. However, even within the constraints of this single-centre study, the results are highly promising.

Castleton:Pfizer: Speakers Bureau; Amgen: Honoraria, Speakers Bureau; AstraZeneca: Honoraria, Speakers Bureau; Kite/Gilead: Honoraria, Speakers Bureau.