Neutrophil defense in patients undergoing bone marrow transplantation: bactericidal/permeability-increasing protein (BPI) and defensins in graft-derived neutrophils

Neutrophil function in children following allogeneic hematopoietic stem cell transplant

HSCT is a lifesaving procedure for children with malignant and non-malignant conditions. The conditioning regimen renders the patient severely immunocompromised and recovery starts with neutrophil (PMN) engraftment. We hypothesize that children demonstrate minimal PMN dysfunction at engraftment and beyond, which is influenced by the stem cell source and the conditioning regimen. Peripheral blood was serially collected from children at 1 to 12 months following allogeneic HSCT. PMN superoxide (O2-) production, degranulation (elastase), CD11b surface expression, and phagocytosis were assessed. Twenty-five patients, mean age of 10.5 yr with 65% males, comprised the study and transplant types included: 14 unrelated cord blood stem cells (cords), seven matched related bone marrow donors, three matched unrelated bone marrow donors, and one peripheral blood progenitor cells. Engraftment occurred at 24 days. There were no significant differences between controls and patients in PMN O2- production, phagocytosis, CD11b surface expression, and total PMN elastase. Elastase release was significantly decreased <6 months vs. controls (p < 0.05) and showed normalization by six months for cords only. The conditioning regimen did not affect PMN function. PMN function returns with engraftment, save elastase release, which occurs later related to the graft source utilized, and its clinical significance is unknown.

Identification of single nucleotide polymorphisms in hematopoietic cell transplant patients affecting early recognition of, and response to, endotoxin

Hematopoietic cell transplant (HCT) is a life-saving therapy for many malignant and non-malignant bone marrow diseases. Associated morbidities are often due to transplant-related toxicities and infections, exacerbated by regimen-induced immune suppression and systemic incursion of bacterial products. Patients undergoing myeloablative conditioning for HCT become endotoxemic and display blood/plasma changes consistent with lipopolysaccharide (LPS)-induced systemic innate immune activation. Herein, we addressed whether patients scheduled for HCT display differences in recognition/response to LPS ex vivo traceable to specific single nucleotide polymorphisms (SNPs). Two SNPs of LPS binding protein (LBP) were associated with changes in plasma LBP levels, with one LBP SNP also associating with differences in efficiency of extraction and transfer of endotoxin to myeloid differentiation factor-2 (MD-2), a step needed for activation of TLR4. None of the examined SNPs of CD14, bactericidal/permeability-increasing protein (BPI), TLR4 or MD-2 were associated with corresponding protein plasma levels or endotoxin delivery to MD-2, but CD14 and BPI SNPs significantly associated with differences in LPS-induced TNF-α release ex vivo and infection frequency, respectively. These findings suggest that specific LBP, CD14 and BPI SNPs might be contributory assessments in studies where clinical outcome may be affected by host response to endotoxin and bacterial infection.

Plasma level of lipopolysaccharide-binding protein is indicative of acute graft-versus-host disease following allogeneic hematopoietic stem cell transplantation

Acute graft-versus-host disease (aGVHD) is the major cause of non-relapse mortality following allogeneic hematopoietic stem cell transplantation. To date, there are no consensus specific plasma biomarkers for aGVHD. We recently identified several candidates differentially expressed in aGVHD patients. Here, we have validated one such candidate: lipopolysaccharide-binding protein (LBP). We detected plasma LBP level by ELISA in 73 patients and performed correlation analysis with the progression and severity of aGVHD. We found that plasma LBP level increased during the period of aGVHD and decreased markedly as aGVHD was resolved. LBP level in patients with moderate aGVHD (25-50 % skin rash area of grade 1 and grade 2) was higher than in patients with no, little (skin rash area <25 % of grade 1), or severe aGVHD (grade 3-4). Higher LBP level indicated higher probability of aGVHD. Multivariate analysis showed that LBP level above 15000 ng/ml was significantly associated with an increased risk of aGVHD (HR 2.43; 95 % CI 1.29-4.58; P = 0.006). If LBP level exceeded 15000 ng/ml at d7 and d14 after HSCT, the subsequent probability of aGVHD increased markedly, especially at the time point of d14. There was no correlation between LBP level and the site of aGVHD. In conclusion, our study demonstrated that an elevated LBP level of >15000 ng/ml may serve as a biomarker for the prediction and monitoring of aGVHD.

Deficient expression of bactericidal/permeability-increasing protein in immunocompromised hosts: translational potential of replacement therapy

BPI (bactericidal/permeability-increasing protein) is a 55 kDa anti-infective molecule expressed in neutrophil and eosinophil granules and on some epithelial cells. BPI's high affinity for the lipid A region of endotoxin targets its opsonizing, microbicidal and endotoxin-neutralizing activities towards Gram-negative bacteria. Several immunocompromised patient populations demonstrate BPI deficiency, including newborns, those with anti-neutrophil cytoplasmic antibodies (as in cystic fibrosis and HIV infection) and those exposed to radiochemotherapy. BPI may be replenished by administering agents that induce its expression or by administration of recombinant BPI congeners, potentially shielding BPI-deficient individuals against Gram-negative bacterial infection, endotoxemia and its toxic sequelae.

Bactericidal/permeability-increasing protein (BPI) and BPI homologs at mucosal sites

At mucosal surfaces, we must co-exist with a high density of diverse microorganisms; therefore, protection against these occurs on multiple levels. Leukocyte- and epithelial derived-antimicrobial peptides and proteins (AMPs) comprise an essential component of immune defense. These molecules possess antibacterial, antifungal and signalling properties and probably contribute to defence and maintenance of homeostasis between the host and commensal microorganisms. Among these AMPs is bactericidal/permeability-increasing protein (BPI), an antimicrobial protein with potent endotoxin-neutralising activity, and several homologs. This review explores the roles of BPI and and its homologs at the mucosal interface. Congeners of BPI are under biopharmaceutical development as novel anti-infective agents, highlighting the potential therapeutic relevance of this protein family.

Endotoxemia and elevation of lipopolysaccharide-binding protein after hematopoietic stem cell transplantation

BACKGROUND

Hematopoietic stem cell transplantation (SCT) carries a significant risk of severe therapy-associated complications chief among which is acute graft vs.host disease (aGVHD). Animal models indicate that myeloablative chemotherapy compromises the mucosal barrier, thereby allowing translocation of intestinal flora-derived lipopolysaccharides (or endotoxin) that subsequently trigger aGVHD, but there are no comparable data in humans. Our aim was to gain insight into the potential role of endotoxin and endotoxin-induced acute phase proteins in children undergoing SCT.

METHODS

Plasma concentrations of C-reactive protein (CRP) and lipopolysaccharide-binding protein (LBP) were measured in 57 pediatric patients undergoing SCT. In addition plasma endotoxin levels were measured in 25 patients.

RESULTS

The previously described rise in CRP was confirmed, and a marked elevation of LBP was observed that peaked at Day 7 (median value, 6.6 microg/ml; P < 0.03 for all pairwise comparisons). CRP and LBP values were significantly correlated (r = 0.77, P < 0.001). A significant but complex relationship was noted between LBP concentrations at Day 0 and severity of subsequent aGVHD (P = 0.02). Of the 25 patients assayed, 11 (44%) had detectable endotoxemia, including 4 who were endotoxin-positive at Day 0.

CONCLUSIONS

The detection of endotoxemia coupled with marked elevations in LBP at Day 7 raises the possibility that inflammatory responses early after SCT may be driven in part by the entry of lipopolysaccharide into the bloodstream.