Early Reconstitution of T-Cell Immunity to CMV After HLA-Haploidentical Hematopoietic Stem Cell Transplantation Is a Strong Surrogate Biomarker for Lower Non-Relapse Mortality Rates
Authors: Noviello Maddalena , Forcina Alessandra , Stanghellini Maria Teresa Lupo , Carrabba Matteo , Assanelli Andrea , Carbone Maria Rosaria , Magnani Zulma , Corti Consuelo , Bernardi Massimo , Peccatori Jacopo , Ciceri Fabio , Bonini Chiara , Bondanza Attilio 
Published: October 2019

Abstract
Abstract 4191

Introduction:
HLA-haploidentical hematopoietic stem cell transplantation (haplo-HSCT) is a readily available therapeutic option for patients suffering from high-risk hematological malignancies who lack an HLA-compatible donor or for whom there is no time to find one. To avoid GVHD, haplo-HSCT has been classically performed under conditions of strict T-cell depletion, in the form of CD34-selected (“naked”) grafts. Unfortunately, naked haplo-HSCT is followed by a profound state of immune incompetence, which associates with high non-relapse mortality (NRM) rates, mainly due to opportunistic infections. Over the last decade, different strategies have been developed in order to speed-up immune reconstitution after haplo-HSCT, including the delayed infusion of donor T cells (DLI), the selective depletion of T-cell subsets from the graft or the use of an unmanipulated graft followed by novel strategies of immune suppression.

Aim:
To analyze in depth the early phenomena of immune reconstitution following haplo-HSCT in order to find early surrogate biomarkers of NRM.

Results:
From 2004 to 2010, we prospectively studied multiple parameters of T-cell immune reconstitution in 89 pts treated at our Center with haplo-HSCT. Time-points of analysis were pre-transplant, at day 30, day 90 and day 180 post-transplant. Underlying diseases included: high-risk AML 53 pts (60%), ALL 11 pts (12%), CLL 2 pts (2%), tyrosine kinase inhibitors-resistant CML 4 pts (5%), Hodgkin lymphoma 6 pts (7%), NHL 2 pts (2%), MDS with high International Prognostic Scoring System 7 pts (7%), other 4 pts (4%). Eighteen patients (20%) were given prophylactic suicide gene-modified DLI starting at day 30 post-transplant, while 64 patients (80%) received an unmanipulated graft followed by rapamycin until day 100. Overall, the incidence of grade III-IV acute GvHD was as low as 12%. Chronic extensive GvHD developed in 28% of pts. Compared with historical naked haplo-HSCT, the recovery of T-cell counts was accelerated: at day 90, median CD3+ cells were 378 per μL (0–2817), CD4+ 127 (0–804), CD8+ 173 (0–1922). Higher T-cell counts, however, did not clearly associate with lower NRM rates. After the initial expansion of effector memory cells (CD45RA−/CD62L−) in patients given DLI (P<0.01) and of central memory cells (CD45RA−/CD62+) in patients receiving rapamycin (P<0.05), there was a progressive normalization of the memory differentiation phenotype with late appearance of naïve cells (CD45RA+/CD62L+), which displayed a TCR spectratyping complexity score similar to pre-transplant values. Nevertheless, none of these biomarkers performed enough to be considered for surrogating lower NRM rates. In this series at high risk for CMV reactivation (CMV serostatus: H+/D+ 68%, H+/D- 27%) the event was observed in 46 pts (52%) and CMV disease in 8 pts (9%), all treated according to guidelines. By using Receiver Operating Characteristics (ROC) curve analysis of CMV-specific IFN-γ ELISPOT results at day 30–90, we found that cut-off values of 1000 spots/mL allowed to discriminate with high specificity (>95%) pts that did not reactivate the virus at later time points. Strikingly, while in pts with <1000 spots/mL, the 2-yrs NRM rate was 32%, in those with >1000 spots/mL, this was 0% (P<0.05). Interestingly, when comparing NRM rates in pts that achieved or not a CD4+cell value of 200 per μL, the result was not significant (21% vs 30%, P=0.8).

Conclusions:
These results clearly indicate that the early reconstitution of T-cell immunity to CMV after haplo-HSCT does not only protect from subsequent viral reactivation, but also surrogates for lower NRM rates. Moreover, they warrant the investigation of a CMV-specific IFN-γ ELISPOT cut-off value of 1000 spots/mL as a predictive biomarker in larger, multicenter series.

Disclosures:
No relevant conflicts of interest to declare.