Alloreactivity forms the basis of allogeneic hematopoietic cell transplantation (HCT), with donor-derived T cell response to recipient antigens mediating clinical responses either in part or entirely. These encompass the different manifestations of graft-versus-host disease (GVHD), infection risk, and disease response. While the latter is contingent on disease biology and thus may be less predictable, the former 2 manifestations are more likely to be directly proportional to the magnitude of donor-derived T cell recovery. Herein we explore the quantitative aspects of immune cell recovery following allogeneic HCT and clinical outcomes in 2 cohorts of HLA-matched allograft recipients who received rabbit antithymocyte globulin (ATG) on different schedules (days -9 to -7 versus days -3 to -1). Monocyte as well as donor-derived T cell (ddCD3) recovery was superior in those given ATG early in the course of disease (days -9/-7). This difference was related to a more rapid rate of ddCD3 recovery, driven largely by CD3+/CD8+ cells in the first month post-transplantation. Early monocyte recovery was associated with later T cell recovery and improved survival. In contrast, rapid and early ddCD3 expansion out of proportion to monocyte recovery was associated with a high likelihood of acute GVHD and poor survival. This analytic methodology demonstrates that modeling "early-term immune reconstitution" following HCT yields insights that may be useful in the management of post-transplantation immunosuppression and adaptive cellular therapy to optimize clinical outcomes. © 2021 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc.
Keywords: Allogeneic stem cell transplantation; Antithymocyte globulin; Dynamical system; Graft-versus-host disease; Immune reconstitution; T cells.
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