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4937 Lymphocyte Reconstitution after Naïve T Cell-Depleted Hematopoietic Cell Transplantation

Program: Oral and Poster Abstracts
Session: 722. Allogeneic Transplantation: Acute and Chronic GVHD, Immune Reconstitution: Poster III
Hematology Disease Topics & Pathways:
Research, Translational Research, immunology, Biological Processes
Monday, December 11, 2023, 6:00 PM-8:00 PM

Melinda Ann Biernacki, MD1, Kyle B Woodward, PhD1*, Hugh R. MacMillan1*, Madhavi Lakkaraja, MD, MPH2,3, Diego Archila-Diaz, PhD1*, Reema Jain, PhD1*, Heather Persinger1*, Barbara Hilzinger, RN1*, Jacqueline Diaz1*, Warren Shlomchik, MD4*, Evan W. Newell, PhD1* and Marie Bleakley, PhD, MBBS, MMSc5,6

1Fred Hutchinson Cancer Center, Seattle, WA
2Department of Pediatrics, Division of Hematology/Oncology, University of Washington School of Medicine, Seattle, WA
3Clinical Research Division, Fred Hutchinson Cancer Center, Seattle, WA
4Startzl Transplant Institute, Pittsburgh, PA
5Translational Science and Therapeutics, Fred Hutchinson Cancer Center, Seattle, WA
6Division of Pediatric Hematology, Oncology, Bone Marrow Transplant & Cellular Therapy, Seattle Children's Hospital and University of Washington, Seattle, WA

Background: Allogeneic hematopoietic cell transplantation (HCT) is curative for many high-risk hematological malignancies. However, graft-versus-host disease (GVHD) causes morbidity, mortality, and reduced quality of life after HCT. Removal of all T cells from hematopoietic cell grafts (pan-T cell depletion; pan-TCD) significantly reduces GVHD but is associated with impaired immune reconstitution and increased non-relapse mortality due partly to opportunistic infections. We developed a novel strategy to remove CD45RA+ naïve T cells (TN) from peripheral blood stem cell grafts (PBSC) that is associated with a low incidence of serious acute GVHD (aGVHD) and an exceptionally low incidence of chronic GVHD (cGVHD) (Bleakley, JCO 2022). Although CD45RA-depletion removes TN and other CD45RA-expressing effector T cell populations from PBSC along with most NK and B cells, TN-depletion (TND) does not appear to increase infections or have a major negative impact on immune reconstitution. Understanding subtle differences in lymphocyte population dynamics after TND compared to T cell-replete (TR) HCT will enable further graft engineering advances and may provide broader insights into human HCT immunobiology.

Objective: To evaluate lymphocyte reconstitution after TND HCT.

Methods and Results: We compared blood lymphocyte populations in TND HCT recipients (n=47) to those in TR HCT controls (n=19) at days 28, 56, 90, 180, and 360 post-HCT using multiparametric flow cytometry. To complement standard Boolean analysis, we employed a metaclustering approach to simultaneously evaluate ~20 cell surface markers for each class of lymphocytes (CD8+ and CD4+ T cells, NK cells, and B cells) over scores of batches of recipient and control samples. Absolute numbers of total CD8+ T cells were similar in TND compared to TR at all timepoints, whereas total CD4+ T cell numbers were consistently lower in TND until 1 year post-HCT. Using conventional gating and high-dimensional clustering analyses, we identified several key differences in T cells after TND. CD45RA-expressing populations (TN and effector memory re-expressing CD45RA [TEMRA]) in CD8+ and CD4+ T cells were rare in CD45RA-depleted PBSC and remained decreased in TND HCT recipients until around 1 year (CD8+, Fig. 1). Activated CD8+ and CD4+ central and effector memory (TCM, TEM) T cells were increased proportionally and in absolute numbers in TND early post-HCT (CD8+, Fig. 1). Absolute numbers of regulatory T cells (Treg) were decreased in TND; consequently, ratios of activated CD8+ and CD4+ to Treg were both markedly increased early post-HCT, despite a similar incidence of aGVHD in TND and TR recipients. Although most NK cell populations were removed from CD45RA-depleted PBSC, absolute numbers of NK cells in all compartments, including both activated and inhibited, were increased in TND recipients early post-HCT compared to TR. Like NK cells, most B cells except for plasmablasts and plasma cells were removed by CD45RA-depletion of PBSC. Immature, naïve, and memory B cells were reduced very early post-TND HCT, but substantial B cell recovery occurred within the first 2-3 months.

Conclusions: We present the first detailed description of lymphocyte reconstitution after TND HCT. Despite the major effect CD45RA-depletion has on graft composition—removing all TN and TEMRA from the T cell compartment and most NK and B cells—NK and B cell recovery occurred early, and by 1 year post-HCT there was little difference in lymphocyte populations between TND and TR. This is consistent with hematopoietic progenitors, not mature lymphocytes, as the source of B and NK cell reconstitution. Among T cells, the most striking findings were an increase in activated TCM and TEM CD4+ and CD8+ T cells early after TND HCT, and increased ratios of activated T cells to Treg. Although elevated blood T effector/Treg ratios have been associated with cGVHD, cGVHD was uncommon and steroid-responsive after TND HCT. Whether increased activated T cells reflect a reduction in Treg-mediated suppression after HCT, bystander T cell activation, activation by antigen (e.g., alloantigen, latent herpes viruses, microbiota), or multiple factors are questions we are now investigating. We are also exploring associations between lymphocyte populations early post-TND HCT and clinical outcomes; these could serve as biomarkers to facilitate early intervention to prevent or treat GVHD, relapse, or infection.

Disclosures: Shlomchik: BlueSphere Bio: Current Employment, Current holder of stock options in a privately-held company, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Orca Bio: Consultancy, Current holder of stock options in a privately-held company. Newell: Immunoscape: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Neogene Therapuetics: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Nanostring Technologies: Membership on an entity's Board of Directors or advisory committees. Bleakley: Miltenyi Biotec: Other: scientific advisory board meeting, Research Funding; Orca Bio: Consultancy; High Pass Bio/ Elevate Bio: Consultancy, Current equity holder in private company, Patents & Royalties, Research Funding; Promicell Therapeutics Inc: Patents & Royalties, Research Funding.

*signifies non-member of ASH