Long-term effects of alemtuzumab on regulatory and memory T-cell subsets in kidney transplantation

BACKGROUND. Induction with lymphocyte-depleting antibodies is routinely used to prevent rejection but often skews T cells toward memory. It is not fully understood which memory and regulatory T-cell subsets are most affected and how they relate to clinical outcomes. METHODS. We analyzed T cells from 57 living-donor renal transplant recipients (12 reactive and 45 quiescent) 2.8±1.4 years after alemtuzumab induction. Thirty-four healthy subjects and nine patients with acute cellular rejection (ACR) were also studied. RESULTS. We found that alemtuzumab caused protracted CD4 more than CD8 T-lymphocyte deficiency, increased proportion of CD4 memory T cells, and decreased proportion of CD4 regulatory T cells. Reactive patients exhibited higher proportions of CD4 effector memory T cells (TEM) and CD8 terminally differentiated TEM (TEMRA), with greater CD4 TEM and CD8 TEMRA to regulatory T cell ratios, than quiescent patients or healthy controls. Patients with ongoing ACR had profound reduction in circulating CD8 TEMRA. Mixed lymphocyte assays showed significantly lower T-cell proliferation to donor than third-party antigens in the quiescent group, while reactive and ACR patients exhibited increased effector molecules in CD8 T cells. CONCLUSIONS. Our findings provide evidence that T-cell skewing toward TEM may be associated with antigraft reactivity long after lymphodepletion. Further testing of TEM and TEMRA subsets as rejection predictors is warranted.