Persistence of Recipient-Derived Antiviral T cells Severely Influence Donor Chimerism Post Allogeneic HSCT,

Abstract 3240

Analysis of donor chimerism is a well established technique to monitor engraftment and detect pending relapse in patients after allogeneic hematopoietic stem cell transplantation (HSCT). Over the last decade, use of unrelated and/or mismatched donors as well as alternative grafts like cord blood (CB) has increased, and, in addition reduced intensity conditioning regimens are widely applied. Thus, recipients are increasingly being exposed to both persistent mixed chimerism and infectious complications because of delayed immune reconstitution.

Donor chimerism is analyzed routinely from peripheral blood cells in all recipients. In addition, in a prospective study to evaluate usefulness of subset chimerism, T cell chimerism is analyzed in selected patients since 2007. Reconstitution of CMV-specific CD8 T cells (CMV-CTL) is monitored by multimers (multimeric dye-labeled recombinant-MHC-I-peptide-complexes) since 2006 to evaluate CMV-specific immune reconstitution post HSCT. Using this method, HLA-restriction of the multimers enables detection of residual recipient CMV-CTLs in mismatched transplantations.

Interestingly, we found that CMV reactivation is accompanied by a decline in donor chimerism in some patients and that recipient CMV-CTLs persisting post HSCT expand upon CMV reactivation. Table 1 summarizes first data of this analysis in patients transplanted between 2007 and 2011 in our centre.

Patient 7 received a double mismatched cord-blood graft. As expected the recipient-CMV-CTLs declined after HSCT and by day +50 post-HSCT no CMV-CTLs (A*0201-NLVP multimer) could be detected anymore. The patient had a CMV reactivation on day +85 as shown by pp65 antigenemia assay. On day +90, 72 CMV-CTLs/μl were detected, further increasing to over 200/μl by day +152. To further analyze the origin and functionality, CMV-CTLs detected on day +90 were enriched by MACS to a purity of 97% in the CD3+CD8+ T cells. Donor chimerism was only 4%. After reconstitution of autologous CMV-CTLs, the patient experienced an additional subclinical CMV reactivation on day +113, not requiring any treatment at this time.

In patient 8 a subclinical CMV reactivation on day +33 led to proliferation of CMV-CTLs and HLA-A*24 restricted and -B*35 restricted CMV-CTLs rose from 0 cells/μl (A*24 0.05%, B*35 0.04% of CD3CD8 T-cells) to 1 cell/μl and 21 cells/μl (A*24 0.28%, B*35 4.05% of CD3CD8 T-cells), respectively. Donor chimerism decreased from 51% on day +33 to 0% by day +62. Chimerism analysis of T-cell subsets on day +62 and of CMV-CTLs on day +69 revealed a 0% donor chimerism in these subsets. We speculate that in this patient CMV reactivation led to an inflammatory environment, which might have promoted loss of the graft.

Our data indicate that T cell-subset chimerism analyses may contribute to a better understanding of chimerism kinetics. Furthermore, recipient-derived CMV-CTLs may be able to control CMV reactivation, especially after reduced intensity conditioning but also after standard conditioning regimens (i.e. in patient 5), but can severely influence donor chimerism and thus might have negative effects as well. We are currently investigating donor chimerism in T cell subsets and CMV-CTL reconstitution to gain insight into the complex immune responses and reconstitution processes occurring after allogeneic HSCT or CB-SCT.