Naive CD4⁺ T Cells Exert Superior Alloreactive Capacity Than Central Memory CD4⁺ T Cells in Fully HLA-Matched Setting

Allogeneic stem cell transplantation provides donor-derived mature T cells which are involved in post-transplant immune reactions including engraftment, graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) activity, and thus play a major role in determining clinical outcome. In a prior clinical study, we showed that receiving a high percentage of CD4⁺CCR7+ T cells that includes naive and central memory (CM) subsets, was correlated with increased incidence and severity of acute GVHD. In a recent update of our results on 126 patients, we confirmed our previous results with a particular impact of CD4+ naive subset on acute GVHD development. The aim of the present study was to investigate in vitro the alloreactive response of CD4⁺CCR7⁺CD45RA⁺ naïve T cells and CD4⁺CCR7⁺CD45RA^neg central memory T cells in HLA-A, -B, -C, -DRB1 and -DQB1 allele matched setting (so called 10/10 match)

The alloreactivity was investigated by mixed lymphocyte dendritic cell reaction using five HLA-identical healthy male and female sibling pairs to include at least a H-Y mismatch. Stimulators were mature dendritic cells (derived from monocytes of the male sibling) co-cultured with each one of the three highly purified CD4+ T cell subsets (naive, central memory and effector memory) from the female sibling. Alloreactive response was assessed by 3H thymidine incorporation at day 5, and functionally at day 4, 6 and 10 by IFN-gamma ELISpot and measurement of Th1/Th2/Th17 cytokines in co-culture supernatants.

Four out of five sibling pairs developed an alloreactive response to mHAs. Maximal proliferation was supported by the CCR7⁺CD45RA⁺ naive CD4⁺ T cells with proliferation indices from 1.75 to 3.85. This proliferation was accompanied by a functional differentiation: only naive CD4⁺ T cells were able to produce significant amounts of IL-6, TNF-alpha and IFN-gamma at day 6 and day 10 (120 to 174 IFN-gamma spots at day 10).

This study demonstrates the superior capacity of naive CD4⁺ T cells to mount a primary alloreactive response as compared to central memory T cells. Their proliferative response associated with a pro-inflammatory differentiation makes naive CD4⁺ T cells potential acute GVHD inducers. These in vitro results confirm what we have observed in clinical studies and may also lend support to approaches of selective T cell depletion for GVHD prevention.

No relevant conflicts of interest to declare.