Influence of Ptcy on Lymphopenia Following Allogeneic Hematopoietic Stem Cell Transplantation

Document Type

Conference Proceeding

Publication Date

2-1-2026

Publication Title

Transplant Cell Ther

Keywords

abatacept, biological marker, calcineurin inhibitor, methotrexate, mycophenolate mofetil, adult, allogeneic hematopoietic stem cell transplantation, Caucasian, child, conference abstract, controlled study, drug therapy, female, graft rejection, graft versus host reaction, hematopoietic stem cell, Hispanic, human, immune reconstitution, immune response, lymphocytopenia, major clinical study, male, pre B lymphocyte, retrospective study

Abstract

Age-related loss of lymphoid-biased Hematopoietic Stem Cells (HSCs) and the accumulation of myeloid-biased HSCs lead to reduced T- and B-cell precursors, a state that can be marked by low blood lymphocyte levels and impaired immune responses. Since accelerating senescence can happen post chemotherapy especially high dose of chemotherapy used in stem cell transplant which may also include the increased use of post-transplant (PTCy), a chemotherapy that is given after giving stem cells. In addition, the recovery of the peripheral blood Absolute Lymphocyte Count (ALC) in the early post-transplant period (Days 30 and 100) is a crucial biomarker for immune reconstitution. This retrospective analysis compared the kinetics of ALC recovery among three distinct graft-versus-host disease (GVHD) prophylaxis regimens. Methods: Peripheral blood ALC (k/μL) was analyzed at Day 30 (D30) and Day 100 (D100) for three groups: 1) Calcineurin Inhibitor (CNI)-based, with methotrexate or mycophenolate mofetil with or without ATG, 2) Abatacept-based (ABA) and 3) PTCy-based. Median and average ALC values were calculated for each time point Results: A total of 154 patients who had SCT between 2019 -2025 were identified, with 57% males and 43% females. Median age at SCT was 62 (range 29-75). 76% White, 16% Black, 3% Hispanic, and 5% others. 70% received RIC, 29% MAC, 1% NMA. Donors were 61% MUD, 20% MRD, 9% MMUD, 10 % Haplo. For GVHD prophylaxis 18% received PTCy based, 10% received ABA based, 72% received CNI based. The median ALC at D30 was 0.2 k/uL for PTCy group, 0.6 k/uL for ABA group and 0.51 k/uL for CNI based group. The median ALC at D100 was 0.49 k/uL for PTCy group, 0.6 k/uL for ABA group and 0.7 k/uL for CNI based with or without ATG group. PTCy group was significantly more likely to have an ALC<0.5 K/Ul at D30 compared to those receiving ABA (p= 0.0339) and CNI based with or without ATG (p= 0.0001). In addition at D100, PTCy group was also more likely to have an ALC<0.5 compared to those receiving CNI based (p= 0.0027), and more likely to have an ALC<0.5 at D100 compared to those receiving ABA but not statistically significant (p= 0.077). Conclusions: In this small single center retrospective analysis, the choice of GVHD prophylaxis regimen significantly dictated the kinetics of early lymphocyte reconstitution post-SCT. PTCy induced severe early lymphopenia at D30 and although it went up by D100, PTCY group was till the lowest ALC. These results confirm that while PTCy is an effective prophylaxis strategy, it induces a more sustained delay in achieving critical thresholds of immune reconstitution and need for optimizing dose and combination in the future.

Volume

32

Issue

2

First Page

S471

Last Page

S472

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