Early Mixed T-Cell Chimerism After Allogeneic Hematopoietic Stem Cells Transplantation Is Highly Predictive For Progression Free Survival
Authors: Cornillon Jérôme , Absi Lena , Bourmaud Aurélie , Srour Micha , Tinquaut Fabien , Tavernier Emmanuelle , Guyotat Denis 
Published: October 2019

Abstract

Introduction
Chimerism analysis after allogeneic hematopoietic stem cells transplantation (HSCT) allows documentation and understanding of important clinical events such as engraftment, graft failure, and/or relapse. Few data are available on whether T-cell chimerism might be more informative than global chimerism. In this study, we focused on selective CD3+ T-cell chimerism and its interest to predict events after allogeneic HSCT.

Methods
This is a single center retrospective study. Only patients with a survival more than 3 months were included. Information concerning donors, recipients, conditioning regimen, graft harvesting and follow-up were collected in our center using prospective forms from Promise database. Evaluation of T-cell chimerism was performed on CD3+ blood cells after immunomagnetic sorting, by PCR-STR (short-tandem repeats) multiplex technique using 15 different markers. Analysis of the tandem repeat polymorphism was performed by sequencer and Genscan software (Applied Biosystem Inc.). Chimerism was evaluated in 2 ways: positive or negative, and % of recipient. An analysis with repeated measures was also performed to determine the utility of a positive measure of chimerism, independently of the date of sample after allograft, to predict a relapse.

Results
Between January 2006 and December 2011, 148 patients (pts) were admitted in our unit for allogeneic HSCT (32% with myeloablative conditioning and 68% with reduced conditioning). Median age was 54.3 years, 59 male, 89 female. Diagnosis included AML/MDS (n=77), ALL (n=23), Aplastic anemia (n=4), lymphoma and CLL (n=23), myeloma (n= 8) and myeloproliferative disorders (n=13). The donor was matched sibling (n=51), matched unrelated (10/10) (n=74) or mismatched unrelated (9/10)(n=23). Graft source was PBSC (n=97), BM (n=33) or CB (n=18). At transplant, 108 pts (73%) were in complete remission, 19 (13%) presented partial response and 21 (14%) have progressive disease. At time of analysis, median follow-up was 1.75 years. Median overall Survival (OS) was estimated at 2 years. Forty-seven pts (32%) presented relapse. Seventy pts (47%) are still alive. Main causes of death were HSCT related (n=38), relapse or progression (n=33) and other (n=7). Acute GVHD grade II-IV incidence was 32% (13.5% grade III-IV) and 58% for chronic GVHD. At day +30, 56% of pts presented a mixed T-cell chimerism with 36 (24.3%) pts with a chimerism higher than 25% recipient. At day +90, 41% have remained positive. For NRM, aGVHD and age were the only prognostic parameters statistically identified. For PFS, only T-cell chimerism with a positive 25% cut-off at D+30 was identified as a prognostic factor (p=.0017, HR(IC 95%) 2.52(1.39; 4.58). PFS was not reached if T-cell chimerism was inferior to 25% at D+30 versus 1.35 years (figure 1). The results were concordant in a subgroup analysis performed according to the myeloid or lymphoid neoplasia status. Otherwise, cGVHD incidence was higher if T-cell chimerism was less than 25% at D+30 (70% vs. 18%). Finally, the analysis with repeated measures confirmed that positive T-cell chimerism is strongly correlated with relapse (p=.001; HR (CI95%) 90.18(30.11; 270.13)).

Conclusion
After allogeneic HSCT, mixed T-cell chimerism higher than 25% at day +30 is strongly correlated with poor PFS, independently of source of cells, donors, intensity of conditioning, diagnosis or disease status at transplant. Considering this high-risk population, early intervention should probably be considered.

Disclosures:
No relevant conflicts of interest to declare.