Increased Functional T Cell Defects in Patients with low CD4 Counts after Allogeneic Hematopoietic Stem Cell Transplantation

The recovery of the host immune system after allogeneic hematopoietic stem cell transplantation is pivotal to prevent infections, relapse and secondary malignancies. In particular, numerical CD4 T-cell reconstitution is delayed and CD4-helper cell function considered impaired as consequence of the transplant procedure and concommitant immunosuppressive medication. From HIV/AIDS patients it is known that numerical and functional CD4 defects increase the risk of opportunistic infections. Therefore, even in the absence of immunosuppressants and graft-vs-host disease, anti-infective prophylaxis is usually given for at least six months. We hypothesized that the numerical CD4 defect in patients may be reflected by immunosuppressive RNA fingerprints previously established for certain immuno-inhibitory molecules and tested whether the functional CD4 capacity was different according to the CD4 cell number.

RNA was separated from CD4 T-cells of 10 patients with CD4 counts >500/µl, 10 patients with CD4 counts <200/µl and four healthy controls. All patients had to be off immunosuppression and without any clinical signs of graft-vs-host disease. Transcriptional activity was assessed with regard to previously defined fingerprints motives for CTLA-4, IL-10, PD-1, TGF-β and PGE-2. CD4 T-cells from all groups were further tested for their proliferative capacity and cytokine production.

Hierarchical clustering segregated the three groups. Applying the immunosuppressive fingerprints, patients with CD4 T-cells >500/µl were demonstrated to be under the influence of PGE2, whereas patients with CD4 T-cells <200/µl were demonstrated to be under the influence of PGE2 and CTLA-4. In normal controls, no association was found. The proliferative capacity of patient CD4 T-cells upon CD3-CD28-bead stimulation was not significantly different from healthy controls. The production of IL-2 by stimulated CD4 T-cells was significantly downregulated in patients with CD4 T-cells <200/µl, while there was no difference in IFN-ƴ and TNF-α secretion.

The severity of the CD4 numerical defect reflects the state of immunosuppression as demonstrated by RNA immuno-inhibitory fingerprint motives. This partially translates into functional differences as measured by decreased IL-2 secretion. In addition to time after transplant, CD4 T-cell numbers should be considered for the decision to stop or maintain anti-microbial prophylaxis in patients after allogeneic stem cell transplantation.

(UH, LPF and CW, JMC contributed equally to this work.)

No relevant conflicts of interest to declare.