Early Expansion of CD56dim NKG2Alow with Late Surge and Persistence of CD56dimNKG2AnegNKG2Cbright NK Cells Attenuate Cytomegalovirus (CMV) Replication and Recurrence As Well As Leukemia Relapse Following Haploidentical HSCT with T Cell Co-Stimulation Blockade and Ptcy

Abstract

CMV related morbidity and mortality remains a major limiting factor in Haploidentical HSCT. We have developed a novel approach to Haploidentical PBSCT combining T cell Costimulation Blockade (T-COSB) with PTCy and Cyclosporine or Sirolimus (BBMT 2018). We studied the pattern of CMV reactivation (CMV-R) and its progression in 60 patients undergoing Haploidentical HSCT in this protocol in relation to the kinetics of Immune Reconstitution (IR) and pattern of leukemia relapse. PCR based CMV monitoring was carried out until 180 days with preemptive anti-CMV therapy. All patients and donors were CMV seropositive. CMV-R was 54.2% with median onset at 32 days (14-75) in the study group [compared to 52.5% in 42 who had received PTCy alone (p=0.8)]. The median peak viral load was 5.7 × 103/ml (1.8-25.8). The median duration of anti-CMV therapy was 16 days (7-60 days). There was no recurrence noted before100 days and only 2/32 (6.2%) beyond 100 days with no CMV disease. CMV-R was higher in those transplanted for malignant diseases compared to non-malignant diseases (62.5% vs 8.2%, p=0.01). Analysis of IR in relation to CMV-R showed no difference in CD3 or CD4+T cell reconstitution. However, CD56dimCD16+ NK cells at D+60 were significantly higher in patients without CMV-R (median 95 vs 45 cells/µl, p=0.02) and the same population of cells were associated with lower peak of viral load (p=0.04). In those with a lower viral peak and lower duration of viral replication, CD56dimCD16+ NK cells had a higher KIR repertoire with lower NKG2A expression. In those with CMV-R, a subsequent surge in absolute NK cells was observed (median 188 vs 112 cells/µl, p=0.01). This was primarily contributed by massive expansion of CD56dimNKG2AnegNKG2Cbright NK cells (median 7.8% [5-14.6%] at day +30 to 35% [28-65%] at day +90, p=0.01, Fig 1). This phenomenon was not witnessed in patients treated with PTCy alone. Peak viral load inversely correlated with NKG2C+ NK cells and CD45RO+CD8+ T cells at day +90 (p=0.03). The incidence of aGVHD (10.2%), cGVHD (18%), NRM (9.5%), and overall survival (75.8%) were not influenced by CMV-R. Incidence of relapse was 23.5 % at 28-144 days (median 85 days). However, none of the patients who relapsed before 100 days had proliferation of NKG2C+ NK cells and only 1/38 patients with proliferation and persistence of this subpopulation beyond 100 days experienced leukemia relapse at a median follow-up of 18 months (p=0.01). The kinetics of NK cell reconstitution in relation to the pattern of viral replication suggests that an early surge of CD56dimNKG2Alow NK cells with cytotoxic potential is responsible for the initial containment of viral replication followed by late surge and persistence of memory type NKG2C+NK cells preventing late recurrence as well as leukemia relapse. This unique synaptic response was possibly responsible for improved outcome with this novel approach of T-COSB based haploidentical HSCT.