M.R.M. van den Brink

Septic shock and multiple organ failure after hematopoietic stem cell transplantation: treatment with recombinant human activated protein C.

Severe sepsis with multiple organ failure after hematopoietic stem cell transplantation (HSCT) results in extremely high morbidity and mortality. Recent studies have highlighted the importance of sepsis-induced activation of the coagulation system in the pathophysiology of severe sepsis. Activated protein C is an important modulator of coagulation and inflammatory derangements during severe sepsis. Low levels of protein C occur in severe sepsis and are predictive of poor outcome. Recombinant human activated protein C (drotrecogin alfa (activated)) was recently approved by the Food and Drug Administration (FDA) for severe sepsis. The phase III trial that resulted in the approval of this agent, however, enrolled a general sepsis population and excluded patients undergoing HSCT. We report a case of fulminant septic shock and multiple organ failure after HSCT that was treated with drotrecogin alfa (activated) in addition to standard therapy, and recovered. The high mortality rates of patients who develop severe sepsis after HSCT demand that new avenues of treatment be considered for this very high-risk patient population. This case illustrates the potential application of a novel therapeutic approach. Clinical trials are warranted to further investigate the safety and efficacy of drotrecogin alfa (activated) in patients with severe sepsis after HSCT.

Clonal B cells in Waldenström's macroglobulinemia exhibit functional features of chronic active B-cell receptor signaling

Waldenström’s macroglobulinemia (WM) is a B-cell non-Hodgkin’s lymphoma (B-NHL) characterized by immunoglobulin M (IgM) monoclonal gammopathy and the medullary expansion of clonal lymphoplasmacytic cells. Neoplastic transformation has been partially attributed to hyperactive MYD88 signaling, secondary to the MYD88 L265P mutation, occurring in the majority of WM patients. Nevertheless, the presence of chronic active B-cell receptor (BCR) signaling, a feature of multiple IgM+ B-NHL, remains a subject of speculation in WM. Here, we interrogated the BCR signaling capacity of primary WM cells by utilizing multiparametric phosphoflow cytometry and found heightened basal phosphorylation of BCR-related signaling proteins, and augmented phosphoresponses on surface IgM (sIgM) crosslinking, compared with normal B cells. In support of those findings we observed high sIgM expression and loss of phosphatase activity in WM cells, which could both lead to signaling potentiation in clonal cells. Finally, led by the high-signaling heterogeneity among WM samples, we generated patient-specific phosphosignatures, which subclassified patients into a ‘high’ and a ‘healthy-like’ signaling group, with the second corresponding to patients with a more indolent clinical phenotype. These findings support the presence of chronic active BCR signaling in WM while providing a link between differential BCR signaling utilization and distinct clinical WM subgroups.

Sex steroid ablation: an immunoregenerative strategy for immunocompromised patients

Age-related decline in thymic function is a well-described process that results in reduced T-cell development and thymic output of new naïve T cells. Thymic involution leads to reduced response to vaccines and new pathogens in otherwise healthy individuals; however, reduced thymic function is particularly detrimental in clinical scenarios where the immune system is profoundly depleted such as after chemotherapy, radiotherapy, infection and shock. Poor thymic function and restoration of immune competence has been correlated with an increased risk of opportunistic infections, tumor relapse and autoimmunity. Apart from their primary role in sex dimorphism, sex steroid levels profoundly affect the immune system in general and, in fact, age-related thymic involution has been at least partially attributed to the increase in sex steroids at puberty. Subsequently it has been demonstrated that the removal of sex steroids, or sex steroid ablation (SSA), triggers physiologic changes that ultimately lead to thymic re-growth and improved T-cell reconstitution in settings of hematopoietic stem cell transplant (HSCT). Although the cellular and molecular process underlying these regenerative effects are still poorly understood, SSA clearly represents an attractive therapeutic approach to enhance thymic function and restore immune competence in immunodeficient individuals.

Inducible T-cell receptor expression in precursor T cells for leukemia control

Co-transplantation of hematopoietic stem cells with those engineered to express leukemia-reactive T-cell receptors (TCRs) and differentiated ex vivo into precursor T cells (preTs) may reduce the risk of leukemia relapse. As expression of potentially self-(leukemia-) reactive TCRs will lead to negative selection or provoke autoimmunity upon thymic maturation, we investigated a novel concept whereby TCR expression set under the control of an inducible promoter would allow timely controlled TCR expression. After in vivo maturation and gene induction, preTs developed potent anti-leukemia effects. Engineered preTs provided protection even after repeated leukemia challenges by giving rise to effector and central memory cells. Importantly, adoptive transfer of TCR-transduced allogeneic preTs mediated anti-leukemia effect without evoking graft-versus-host disease (GVHD). Earlier transgene induction forced CD8+ T-cell development was required to obtain a mature T-cell subset of targeted specificity, allowed engineered T cells to efficiently pass positive selection and abrogated the endogenous T-cell repertoire. Later induction favored CD4 differentiation and failed to produce a leukemia-reactive population emphasizing the dominant role of positive selection. Taken together, we provide new functional insights for the employment of TCR-engineered precursor cells as a controllable immunotherapeutic modality with significant anti-leukemia activity.

Adoptive precursor cell therapy to enhance immune reconstitution after hematopoietic stem cell transplantation

Strategies to enhance post-transplant immune reconstitution without aggravating graft-vs-host disease (GVHD) can improve the outcome of allogeneic hematopoietic stem cell transplantation. Recent preclinical studies demonstrated that the use of T cell depleted allografts supplemented with committed progenitor cells (vs stem cells only) allows enhanced immune reconstitution of specific hematopoietic lineages including myeloid, B, T, and natural killer lineages in the absence of GVHD. This novel adoptive therapy resulted in significantly improved resistance to microbial pathogens and could, in some cases, even mediate tumor immunity. Clinical protocols using adoptive transfer of committed hematopoietic progenitor cells are currently being evaluated.

Long-term prognosis for 1-year relapse-free survivors of CD34+ cell-selected allogeneic hematopoietic stem cell transplantation: a landmark analysis

CD34+ cell selection significantly improves GvHD-free survival in allogeneic hematopoietic stem cell transplantation (allo-HSCT). However, specific information regarding long-term prognosis and risk factors for late mortality after CD34+ cell-selected allo-HSCT is lacking. We conducted a single-center landmark analysis in 276 patients alive without relapse 1 year after CD34+ cell-selected allo-HSCT for AML (n=164), ALL (n=33) or myelodysplastic syndrome (n=79). At 5 years’ follow-up after the 1-year landmark (range 0.03–13 years), estimated relapse-free survival (RFS) was 73% and overall survival (OS) 76%. The 5-year cumulative incidence of relapse and non-relapse mortality (NRM) were 11% and 16%, respectively. In multivariate analysis, Hematopoietic Cell Transplantation Comorbidity Index score⩾3 correlated with marginally worse RFS (hazard ratio (HR) 1.78, 95% confidence interval (CI) 0.97–3.28, P=0.06) and significantly worse OS (HR 2.53, 95% CI 1.26–5.08, P=0.004). Despite only 24% of patients with acute GvHD within 1 year, this also significantly correlated with worse RFS and OS, with increasing grades of acute GvHD associating with increasingly poorer survival on multivariate analysis (P<0.0001). Of 63 deaths after the landmark, GvHD accounted for 27% of deaths and was the most common cause of late mortality, followed by relapse and infection. Although prognosis is excellent for patients alive without relapse 1 year after CD34+ cell-selected allo-HSCT, risks of late relapse and NRM persist, particularly due to GvHD.

Antibiotic prophylaxis in allogeneic stem cell transplantation—what is the correct choice?

In this month’s issue, Weber et al. reported the results of a single-center retrospective study of two cohorts of patients receiving allogeneic stem cell transplantation (allo-SCT) treated with different prophylactic antibiotic regimens. The potential of antibiotics to modulate outcomes after allo-SCT was first observed in mouse models followed by clinical studies. In both types of studies, intestinal bacteria were found to contribute to acute GvHD, and total decontamination led to a benefit. Subsequent clinical studies, however, did not consistently demonstrate a reduction in GvHD from antibiotics, possibly due to unreliable total decontamination. Total gut decontamination is now routinely attempted at only a small minority of transplant centers and has been largely supplanted by fluoroquinolonebased prophylaxis. Ciprofloxacin and levofloxacin are both commonly used based on many studies of neutropenic patients with cancer, where fluoroquinolone use prevented febrile events and bloodstream infections, and a meta-analysis was associated with a reduction in all-cause mortality. An alternative to fluoroquinolone-based prophylaxis practiced at some transplant centers involves the addition of metronidazole, which in a single-center prospective randomized study, was found to reduce the development of acute GvHD. The use of prophylactic metronidazole, however, has recently come under scrutiny due to several recent findings: use of metronidazole was associated with loss of intestinal microbiota diversity and an expansion of Enterococcus during allo-SCT, and loss of intestinal microbiota diversity is associated with poor outcomes after alloSCT; this loss of diversity can manifest as expansion of intestinal Enterococcus, which was associated with active or subsequent gastrointestinal GvHD, or alternatively as loss of a common obligately anaerobic commensal from the genus Blautia, which often preceded subsequent GvHD-related mortality. In response to these findings, the transplant center in Regensburg, Germany, chose to switch their institutional practice from prophylaxis with ciprofloxacin and metronidazole to rifaximin, in 2012. A poorly absorbed member of the rifamycin family, rifaximin has activity against staphylococcal, streptococcal and enterococcal species but has lesser activity against species of Enterobacteriaceae. It has been widely utilized to treat a variety of gastrointestinal conditions, including irritable bowel syndrome and inflammatory bowel disease. In patients with hepatic encephalopathy, rifaximin was found to modulate metabolite production by the intestinal microbiota with only modest changes in overall bacterial composition. In the current study, Weber et al. found that, compared with historical controls from the same center treated with ciprofloxacin and metronidazole, patients treated with rifaximin showed significantly improved overall survival, reduced treatment-related mortality and reduced intestinal GvHD. While this was not a prospectively controlled clinical trial, the differences seen are remarkable. Importantly, use of rifaximin was not associated with increased rates of developing fevers or documented infections. Finally, stool samples were prospectively collected and analyzed for measures of microbiota preservation, including urinary 3indoxyl sulfate and fecal enterococcal PCRs; these showed reduced perturbation of the microbiota in patients who received prophylaxis with rifaximin. In summary, use of prophylactic rifaximin may be superior to ciprofloxacin and metronidazole in patients undergoing allo-SCT, and additional studies regarding ideal choice of antibiotic prophylaxis in this patient population are warranted.