An Assessment of Marrow-Infiltrating T Cells in Early Relapsed Hematologic Cancer Patients Post Allogeneic Hematopoietic Stem Cell Transplantation

Background: Relapse is the major treatment failure of allogeneic hematopoietic stem cell transplantation (HSCT) in patients with hematologic malignancies. Especially, early relapse had seriously bad prognosis. And tumor-infiltrating T cells play an important role in disease progression and recurrence. However, there is lack of data about the marrow-infiltrating T cell of early relapsed patients compared to those with complete remission (CR) at an early timepoint after HSCT. Therefore, we analyzed the differentiation stage and expression of inhibitory receptors of the marrow-infiltrating T cell in the early stages of allogeneic HSCT.

Method: A total of 40 samples from patients treated at Chungnam National University Hospital were collected between April 2021 and October 2022. We used flow cytometry to classify T cells into five subtypes using CD45RA, CD95, and CCR7: naïve, stem cell memory (SCM), central memory (CM), effector memory (EM) and effector memory with positive CD45RA (EMRA). Otherwise, we analyzed regulatory T cell (Treg) by defining as CD25 ^highCD127 ^low and divided them into three categories using CD25 and CD45RA: naïve, active and non-suppressive Treg. We defined early relapse (ER) as relapse within 6 months of allogeneic HSCT. High-throughput single-cell RNAseq assays from BM lymphocytes isolated by density gradients were performed to determine the expression and cell composition of previously irradiated markers.

Results: With this approach, marrow-infiltrating T cells were analyzed in 40 patients (10 patients with early relapse) with a median age of 57 years (ranged from 30 to 71). AML is the most common disease at 60%, followed by MDS (20%), ALL (15%) and PMF (2.5%). Stem cell sources were 32.5% from matched sibling donor, 37.5% from haplo-identical donor and 27.5% from matched unrelated donor. All patients received mobilized peripheral blood stem cell transplantation. Marrow-infiltrating CD3+T cell counts were lower in patients with allogeneic HSCT compared to normal subjects (CD3+T cells: 13.89% in HSCT patient and 9.116% in ER patients vs. 34.19% in normal subjects, p< 0.0001). In addition, CD3+CD8+T cells were higher in CR than ER patients (CD3+CD8+T cells: 50.39% in CR vs. 30.41% in ER patients, p< 0.0033). In HSCT patients, naïve was higher, and EM and EMRA were lower than those in normal subjects among CD4+T cells (naïve; 8.629% in ER patients and 5.119% in CR patient's vs 45.76% in normal subjects, p< 0.0001/EM; 54.04% in ER patients and 55.93% in CR patients vs 18.61 in normal subject, p= 0.0003 and p< 0.0001 respectively). Of CD3+T cells, the proportion and expression level of TIM-3 was higher ER patients than in CR patients (56.33% in ER patients vs 39.20% in CR patients, p= 0.0185/MFI; 1873 in ER patients vs. 826.7 in CR patients, p= 0.0331). Of CD4+T cells, the percentage of TIM-3 was lower in normal subjects than in allogeneic HSCT patients (7.794% in normal vs 30.11% in CR patients and 26.04% in ER patients, p= 0.0002 and p= 0.0102 respectively). In patients with ER, naïve and EM was higher than those in CR patients among CD8+T cells (naïve; 8.680% in ER patients vs 4.066% in CR patients, p= 0.4001 /EM; 54.44% in ER patients vs 44.33% in CR patients, p= 0.3039). Of CD8+ EMRA T cell, the expression of TIM-3 was higher in ER patients than in CR patients (MFI; 1441 in HSCT patients vs 421.7 in normal, p=0.1038). Otherwise, of CD3+CD4-CD8-, The percentage of TIM3 was higher in ER patients than CR patients (80.33 % in ER patients vs 62.49% in CR patients, p= 0.0333). Treg levels were no significant difference between CR and ER. We have obtained single-cell sequencing data from two CR (complete response) patients and two ER (early relapse) patients, representing each group. Since the classified groups exhibited ambiguous phenotypes, they were reclassified based on specific markers of cell groups. The reclassified groups showed a higher proportion of HCS (Hematopoietic Stem Cell)-like cells in relapsed patients (+10.14%, P=0.368) and a lower proportion of CD8+ T cells (-13.40%, p=0.068). The HSC-like cells in relapsed patients exhibited higher expression of TIM3 ligand than in CR patients

Conclusion: Among the IRs, TIM3 had the highest expression of all cell groups (CD4 T cells, CD8 T cells and Treg) compared with other IRs at the early stage of allogeneic HSCT. So, TIM3 might be a potential target for preventing relapse in hematologic cancer patients after allogeneic HSCT in the future.