  Systems that evolve over time and follow mathematical laws as they do so, are
called dynamical systems. Lymphocyte recovery and clinical outcomes in 41
allograft recipients conditioned using anti-thymocyte globulin (ATG) and 4.5
Gray total-body-irradiation were studied to determine if immune reconstitution
could be described as a dynamical system. Survival, relapse, and graft vs. host
disease (GVHD) were not significantly different in two cohorts of patients
receiving different doses of ATG. However, donor-derived CD3+ (ddCD3) cell
reconstitution was superior in the lower ATG dose cohort, and there were fewer
instances of donor lymphocyte infusion (DLI). Lymphoid recovery was plotted in
each individual over time and demonstrated one of three sigmoid growth
patterns; Pattern A (n=15), had rapid growth with high lymphocyte counts,
pattern B (n=14), slower growth with intermediate recovery and pattern C, poor
lymphocyte reconstitution (n=10). There was a significant association between
lymphocyte recovery patterns and both the rate of change of ddCD3 at day 30
post-SCT and the clinical outcomes. GVHD was observed more frequently with
pattern A; relapse and DLI more so with pattern C, with a consequent survival
advantage in patients with patterns A and B. We conclude that evaluating immune
reconstitution following SCT as a dynamical system may differentiate patients
at risk of adverse outcomes and allow early intervention to modulate that risk.
