Early Immune Reconstitution Post Allogeneic Transplant and Its Impact on Outcomes According to Type of Transplant
Authors: Saha Saswata , Jain Disha , Tembhare Prashant , Jindal Nishant , Bhuibhar Puja Ramchandra , Mathew Libin Jacob , Mirgh Sumeet , Chichra Akanksha , Nayak Lingaraj , Gokarn Anant , Punatar Sachin , Bagal Bhausaheb , Rajpal Sweta , Chatterjee Gaurav , Patkar Nikhil , Subramanian Papagudi Ganesan , Menon Hari , Khattry Navin 
Published: December 2024

Introduction
Immune reconstitution (IR) following hematopoietic stem cell transplant (HSCT) is an important determinant of outcomes. Recent studies have demonstrated an association between delayed IR of major immune-cell subsets and transplant-related outcomes. However, the clinical relevance of in-depth IR studies focusing on comprehensive immune-cell profiles in allo-HSCT still needs to be determined. We studied in-depth IR patterns of early IR at day-30 and day-90 and their correlation with transplant outcomes.
Methods
This is a single center retrospective study of patients who underwent HSCT from November 2018 to April 2024 and had IR done at day 30 and/or at day 90. One hundred fourteen patients were included (ALL [n=48], AML [n=30], MPAL [n=7], CML [n=15], HL [n=6], MDS [n=4], NHL [n=2] PMF [1] and CLL [n=1]). Eighty-two patients (71.9%) underwent matched related donor (MRD), 24 (21.1%) haploidentical transplant (HIT) and 8 (7.1%) matched unrelated donor (MUD) transplant. Peripheral blood graft was used in all patients. Standard GVHD prophylaxis included calcineurin inhibitors (CNI) and MTX/MMF for MRD and MUD transplants, and PTCY-CNI-MMF for HIT. Rabbit ATG was used in all MUD and single allele mismatch MRD transplants. IR was done at day 30, 90, 180 and at 1-year post-transplant. IR profile included evaluation of 98 immune-cell subset levels (absolute counts) using a two-tube 16-color antibody panel that included antibodies for CD3/CD4/CD8/CD11c/CD14/CD15/CD16/CD19/CD20/CD27/CD31/CD38/CD45/CD45RA/CD56/CD123/CD127/CXCR3/CCR4/CCR6/CCR7/CCR10/TCRγδ and HLA-DR. Immune cells analyzed included T-cells, B-cells, NK cells, monocytes, dendritic cells, and their subsets. IR at day-30 and day-90 were compared between donor types. Day-30 immune cell subsets were correlated with incidence of acute GVHD (aGVHD), CMV and non-relapse mortality (NRM) and day 90 immune subsets were correlated with chronic GVHD (cGVHD). Immune-cell subset cut-off levels were determined using receiver operator characteristic (ROC) curve analysis, and the association of immune-cell subset levels with outcomes was evaluated using the odds ratio (OR).
Results
Median age was 24.5 years (range 2 - 53 years) of the whole cohort. Median CD34 dose was 4.785 million/Kg and median CD3 dose was 158.95 million/Kg. The incidence of grade II-IV aGVHD was 42.1% and that of cGVHD was 22.8%. The median follow-up of the entire cohort was 10 months. The incidence of NRM was 24.6% and the risk of relapse was 19.3%.
At day 30, the median T cell and B cell counts were significantly lower in HIT and MUD compared to MRD (median T cell 82.2/mcL in vs. 110.88/mcL vs. 350.96/mcL, p &lt; 0.001; median B cell 0.16/mcL vs. 1.31/mcL vs. 1.97/mcL, p &lt; 0.001). A similar pattern was seen in all major T-cell subsets, including CD4, CD8, γδ-T cells, Treg, and CD31+T cells. Median NK cell level was also lower in HIT as compared to MUD and MRD (median NK-cells 74.33/mcL vs. 370.22/mcL vs. 213.58/mcl, p = 0.005). At day 90, a similar pattern emerged with lower T and B cell counts in HIT and MUD. NK cell reconstitution was however similar in HIT and MUD as compared to MRD (median NK cell 157.67/mcL vs. 203.28/mcL vs. 97.29/mcL respectively, p = 0.096).
In MRD cohort at day 30, lower CD8+naïve T cells (&lt;27.2/mcL) and intermediate monocytes (&lt;65.508/mcL) predicted a higher risk of CMV reactivation (OR 0.93, CI 0.88-0.99, p=0.03 for naïve CD8 cells; OR 0.97, CI 0.95-0.99, p=0.02 for intermediate monocytes). A lower plasmacytic dendritic cell count (&lt;1.474/mcL) predicted a higher risk of grade II-IV aGVHD (OR 0.87, CI 0.79-0.97, p=0.01). A lower absolute basophil count (&lt;15.4/mcL) predicted a higher risk of TRM (OR 0.95, CI 0.91-0.99, p=0.01). At day 90, higher monocytic myeloid-derived suppressor cells (&gt;19.4/mcL) predicted an increased risk of extensive cGVHD (OR 1.04, CI 0.99-0.1.09, p=0.01).
There was no statistically significant effect of any cell subset on the various outcomes in HIT and MUD transplant.
Conclusion
Immune reconstitution was impaired among HIT and MUD transplants with lower T, B and NK cell counts at day 30. However, NK cell subset improved significantly in alternate donor transplants and was comparable to MRD by day 90. In MRD transplant, levels of CD8+naïve T cells, intermediate monocytes, plasmacytic dendritic cells, absolute basophil count and monocytic myeloid-derived suppressor cells have effect on transplant outcomes.