Coco de Koning

Viral reactivations and associated outcomes in the context of immune reconstitution after pediatric hematopoietic cell transplantation

Background: Viral reactivations (VRs) after hematopoietic cell transplantation (HCT) contribute to significant morbidity and mortality. Timely immune reconstitution (IR) is suggested to prevent VR. Objectives: We studied the relation between IR (as a continuous predictor over time) and VR (as a time‐varying predictor) and the relation between VR and other clinical outcomes. Methods: In this retrospective analysis all patients receiving a first HCT between January 2004 and September 2014 were included. IR (CD3/CD4/CD8 T, natural killer, and B cells) was measured biweekly until 12 weeks and monthly thereafter. Main outcomes of interest were VR of adenovirus, EBV, human herpesvirus 6 (HHV6), cytomegalovirus (CMV), and BK virus screened weekly. Clinical outcomes included overall survival (OS), event‐free‐survival, nonrelapse mortality (NRM), and graft‐versus‐host disease. Cox proportional hazard and Fine and Gray competing risk models were used. Results: Two hundred seventy‐three patients (age, 0.1–22.7 years; median follow‐up, 58 months) were included. Delayed CD4 reconstitution predicted reactivation of adenovirus (hazard ratio [HR], 0.995; P = .022), EBV (HR, 0.994; P = .029), and HHV6 (HR, 0.991; P = .012) but not CMV (P = .31) and BK virus (P = .27). Duration of adenovirus reactivation was shorter with timely CD4 reconstitution, which was defined as 50 × 106 cells/L or greater within 100 days. Adenovirus reactivation predicted lower OS (HR, 2.17; P = .0039) and higher NRM (HR, 2.96; P = .0008). Concomitant CD4 reconstitution abolished this negative effect of adenovirus reactivation (OS, P = .67; NRM, P = .64). EBV and HHV6 reactivations were predictors for the occurrence of graft‐versus‐host disease, whereas CMV and BK virus reactivation did not predict clinical outcomes. Conclusion: These results stress the importance of timely CD4 reconstitution. Strategies to improve CD4 reconstitution can improve HCT outcomes, including survival, and reduce the need for toxic antiviral therapies.

Human herpesvirus 6 viremia affects T-cell reconstitution after allogeneic hematopoietic stem cell transplantation

Human herpesvirus 6 (HHV6) viremia is a common cause of morbidity following allogeneic hematopoietic cell transplantation (HCT). We previously associated T-cell reconstitution with HHV6 viremia. Here, we investigated whether HHV6 viremia affects T-cell reconstitution after HCT in a time-dependent retrospective analysis. We included 273 pediatric patients (0.1-22.7 years; median follow-up, 58 months) receiving a first HCT between 2004 and 2014. HHV6 was screened weekly in plasma via polymerase chain reaction and occurred in 79 patients (29%) at a median time of 19 days after transplant. Main outcome of interest was immune reconstitution (IR) (CD3/CD4/CD8 T cells), measured biweekly until 12 weeks and monthly thereafter. Cox proportional-hazard models were used with IR and HHV6 as time-dependent variables in multivariate analysis with serotherapy in conditioning, graft source, graft-versus-host disease, age, and other viruses (Epstein-Barr virus, cytomegalovirus, and adenovirus) as covariates. Only patients with very high HHV6 viremia (>105 copies/mL) showed hampered CD4+ (hazard ratio [HR], 0.913; 95% confidence interval [CI], 0.892-0.934; P < .001) and CD8+ (HR, 0.912; 95% CI, 0.891-0.933; P < .001) reconstitution in comparison with patients without HHV6, from ∼6 months after HCT. Especially naïve CD4+ IR was affected (P = .028) but not effector memory CD4+ IR (P = .33). Interestingly, T-cell reconstitution was improved in patients treated with antivirals (HR, 1.572; 95% CI, 1.463-1.690; P < .001). These findings suggest that HHV6 viremia affects late but not early T-cell reconstitution.

Filgrastim enhances T-cell clearance by antithymocyte globulin exposure after unrelated cord blood transplantation

Residual antithymocyte globulin (ATG; Thymoglobulin) exposure after allogeneic hematopoietic (stem) cell transplantation (HCT) delays CD4+ T-cell immune reconstitution (CD4+ IR), subsequently increasing morbidity and mortality. This effect seems particularly present after cord blood transplantation (CBT) compared to bone marrow transplantation (BMT). The reason for this is currently unknown. We investigated the effect of active-ATG exposure on CD4+ IR after BMT and CBT in 275 patients (CBT n = 155, BMT n = 120; median age, 7.8 years; range, 0.16-19.2 years) receiving their first allogeneic HCT between January 2008 and September 2016. Multivariate log-rank tests (with correction for covariates) revealed that CD4+ IR was faster after CBT than after BMT with <10 active-ATG × day/mL (P = .018) residual exposure. In contrast, >10 active-ATG × day/mL exposure severely impaired CD4+ IR after CBT (P < .001), but not after BMT (P = .74). To decipher these differences, we performed ATG-binding and ATG-cytotoxicity experiments using cord blood- and bone marrow graft-derived T-cell subsets, B cells, natural killer cells, and monocytes. No differences were observed. Nevertheless, a major covariate in our cohort was Filgrastim treatment (only given after CBT). We found that Filgrastim (granulocyte colony-stimulating factor [G-CSF]) exposure highly increased neutrophil-mediated ATG cytotoxicity (by 40-fold [0.5 vs 20%; P = .002]), which explained the enhanced T-cell clearance after CBT. These findings imply revision of the use (and/or timing) of G-CSF in patients with residual ATG exposure.

How to define and measure thymopoiesis after transplantation

With great interest we read the recently published paper by Duinhouwer et al. [1], evaluating signal joint T-cell receptor excision circles (sjTREC) levels as measure for thymopoiesis after double umbilical cord blood transplantation (dUCBT). They report sjTRECs as soon as 3 months after dUCBT in their cohort of 55 adult patients, which they ascribe to fastened thymopoiesis because of the reduced intensity conditioning (RIC) without anti-thymocyte globulin in the conditioning regimen of their cohort. In addition, they evaluated the predictive value of sjTREC levels for outcome measures, and conclude that lower sjTREC levels at 3 months predict severe infections (grade 3–4 according to according to the NCI common toxicity criteria [CTC]). Although the report of Duinhouwer et al. includes important topics in the field of hematopoietic transplantation, we have some concerns regarding their findings. First, we find the conclusion that sjTREC levels at 3 months after dUCBT predicts grade 3–4 CTC preliminary. In fact, most grade 3–4 CTC events in their cohort occur within the first 3 months (cumulative incidence is 80% at 3 months and 87% at 12 months), and the highest frequency of grade 3–4 CTC events occurs even within the first 30 days after transplantation. The relation might thus even be inverse, since others have shown that sjTREC levels can decrease upon T-cell expansion [2–5], such as during infections or graft-versus-host disease (GvHD). Therefore, a time-toevent model is pivotal to correctly evaluate the predictive value of sjTREC levels at 3 months for severe infections (grade 3–4 CTC) that mostly occur within this time frame. The other question is whether the sjTREC levels, which are very low (below lower limit of normal), in the study from Duinhouwer et al. correctly reflect thymopoiesis. While it was historically believed that thymopoiesis was absent in adults, we now know that especially in case of lymphopenia the adult thymus is able to regenerate and increase thymic output [6, 7]. It is thus not unthinkable that there indeed is thymic output after hematopoietic transplantation in adult patients. This might especially be the case with RIC, without anti-thymocyte globulin (ATG), as these drugs are known to affect thymus cells [7–9]. It is, however, unlikely that sjTREC levels as soon as 3 months after hematopoietic (stem) cell transplantation reflect actual thymopoiesis, especially as levels at 12 months (more likely reflecting thymopoiesis) are several logs higher, as also shown by others [10]. Measurable sjTREC levels early after dUCBT might be caused by infusion of the very naive Tcells that are present within cord blood grafts, which contain high sjTREC levels [10]. The observed increase in sjTREC levels from 3 to 12 months, by Duinhouwer et al., might imply thymic output. However, it is unclear whether the increase in sjTREC levels observed at 12 months is indeed due to increased thymopoiesis, or an artefact from patients lost to follow up at this time point because of death. An important observation supporting active thymopoiesis in the cohort of Duinhouwer et al. is the inverse relation between sjTREC level and age [1]. But in their analysis, the authors did not correct for covariates that might affect this relation, such as GvHD or infections. Also here, expanding T-cell effector populations in GvHD or during infections might decrease sjTREC levels in older patients [2–5]. A multivariate analysis, taking into account competing risks, is needed to correct for covariates influencing sjTREC levels after hematopoietic transplantation. To conclude, we agree that investigating the influence of thymopoiesis in the context of T-cell reconstitution on clinical outcome after allogeneic stem cell transplantation is * Jaap Jan Boelens j.j.boelens@umcutrecht.nl

Innate immune recovery predicts CD4+ T-cell reconstitution after Hematopoietic Cell Transplantation

Innate immune cells are the first to recover after allogeneic hematopoietic cell transplantation (HCT). Nevertheless, reports of innate immune cell recovery and their relation to adaptive recovery after HCT are largely lacking. Especially predicting CD4+ T cell reconstitution is of clinical interest, because this parameter directly associates with survival chances after HCT. We evaluated whether innate recovery relates to CD4+ T cell reconstitution probability and investigated differences between innate recovery after cord blood transplantation (CBT) and bone marrow transplantation (BMT). We developed a multivariate, combined nonlinear mixed-effects model for monocytes, neutrophils, and natural killer (NK) cell recovery after transplantation. A total of 205 patients undergoing a first HCT (76 BMT, 129 CBT) between 2007 and 2016 were included. The median age was 7.3years (range, .16 to 23). Innate recovery was highly associated with CD4+ T cell reconstitution probability (P < .001) in multivariate analysis correcting for covariates. Monocyte (P < .001), neutrophil (P < .001), and NK cell (P < .001) recovery reached higher levels during the first 200days after CBT compared with BMT. The higher innate recovery after CBT may be explained by increased proliferation capacity (measured by Ki-67 expression) of innate cells in CB grafts compared with BM grafts (P = .041) and of innate cells in vivo after CBT compared with BMT (P = .048). At an individual level, patients with increased innate recovery after either CBT or BMT had received grafts with higher proliferating innate cells (CB; P = .004, BM; P = .01, respectively). Our findings implicate the use of early innate immune monitoring to predict the chance of CD4+ T cell reconstitution after HCT, with respect to higher innate recovery after CBT compared with BMT.