Double umbilical cord blood (DUCB) transplantation is an accepted transplantation strategy for patients without suitable human leukocyte antigen (HLA)-matched donors. However, DUCB transplantation is associated with increased morbidity and mortality due to slow recovery of immunity and a high risk of infection. To define the differences in immune reconstitution between DUCB transplantation and HLA-matched unrelated donor (MUD) transplantation, we performed a detailed, prospective analysis of immune reconstitution in 42 DUCB recipients and 102 filgrastim-mobilized unrelated peripheral blood stem cell recipients. Reconstitution of CD3 T cells was significantly delayed in the DUCB cohort compared with the MUD cohort for 1–6 months post-transplantation (p<0.001), including naive (CD45RO−) and memory (CD45RO+) CD4 T cells, regulatory (CD4CD25) T cells, and CD8 T cells. In contrast, CD19 B cells recovered more rapidly in the DUCB cohort and numbers remained significantly greater from 3–24 months after transplantation (p=0.001). CD56CD16 natural killer (NK) cells also recovered more rapidly in DUCB recipients and remained significantly greater from 1–24 months after transplantation. B cell activating factor (BAFF) levels were higher in the DUCB cohort at 1 month (p<0.001), were similar in both cohorts at 3 and 6 months, and were lower in the DUCB cohort at 12 months (p=0.002). BAFF/CD19 B cell ratios were lower in the DUCB cohort at 3 (p=0.045), 6 (p=0.02), and 12 months (p=0.002) after transplantation. DUCB recipients had more infections within the first 100 days after transplantation (p<0.001), and there was less chronic graft-versus-host disease (cGVHD) (p<0.001), but there were no differences in cumulative incidence of relapse, non-relapse death, progression-free survival or overall survival between the two groups. These results suggest that increased risk of infections is specifically associated with delayed reconstitution of all major T cell subsets, but the increased risk is limited to the first 3 months after DUCB transplantation. There is no increased risk of relapse suggesting that graft-versus-leukemia (GVL) activity is maintained. Early reconstitution of B cells and NK cells may, in part, account for these findings.

In hematopoietic cell transplantation (HCT), permissive HLA-DPB1 mismatches between patients and their unrelated donors (UD) are associated with improved outcomes compared to non-permissive mismatches, but the underlying mechanism is incompletely understood. Here we used mass spectrometry, T-cell receptor-beta (TCRb) deep sequencing, and cellular in vitro models of alloreactivity to interrogate the HLA-DP immunopeptidome and its role in alloreactive T cell responses. We find that permissive HLA-DPB1 mismatches display significantly higher peptide repertoire overlaps compared to their non-permissive counterparts, resulting in lower frequency and diversity of alloreactive TCRb clonotypes in healthy individuals and transplanted patients. Permissiveness can be reversed by the absence of the peptide editor HLA-DM, or the presence of its antagonist HLA-DO, through significant broadening of the peptide repertoire. Our data establish the degree of immunopeptidome divergence between donor and recipient as the mechanistic basis for the clinically relevant permissive HLA-DPB1 mismatches in HCT, and show that permissiveness is dependent on HLA-DM-mediated peptide editing. Its key role for harnessing T-cell alloreactivity to HLA-DP highlights HLA-DM as a potential novel target for cellular and immunotherapy of leukemia.

Even in the era of PCR‐based monitoring, prophylaxis, and preemptive therapy, Cytomegalovirus (CMV) viremia remains a relevant cause of non‐relapse mortality (NRM) after allogeneic hematopoietic cell transplantation (HCT). However, studies using binary analysis (presence/absence of CMV) reported contradicting data for NRM, overall survival and leukemia relapse. Here, we analyzed CMV replication kinetics in 11 508 whole blood PCR samples of 705 patients with HCT between 2012 and 2017. Using two independent models based on CMV peak titers and on the time point of first CMV reactivation, we stratified patients into risk cohorts. Each cohort had distinct cellular immune reconstitution profiles and differentiated for relevant clinical outcomes. Patients with high CMV peak titers had significantly reduced overall survival (HR 2.13, 95% CI 1.53–2.96; p < .0001), due to high NRM. Early impaired T cell reconstitution was a risk factor for high CMV peak titers, however relevant CMV viremia also related to boosted T cell reconstitution. Importantly, intermediate CMV peak titers associated with a significantly reduced relapse probability (HR 0.53, 95% CI 0.31–0.91; p = .022). In short, CMV kinetics models distinguished relevant clinical outcome cohorts beyond the R+ serostatus with distinct immune reconstitution patterns and resolve in part contradicting results of previous studies exclusively focused on the presence or absence of CMV.

Allogeneic hematopoietic stem cell transplantation (HSCT) recipients frequently develop acute respiratory failure (ARF) with pulmonary infiltrates. Molecular- and biomarker-based assays enhance pathogen detection, but data on their yield in this population are scarce. This was a retrospective single-center study of 156 consecutive HSCT recipients admitted to the intensive care unit (ICU) between May 2013 and July 2017. Findings from a microbiologic diagnostic workup using currently available methods on bronchoalveolar lavage (BAL) and blood samples from 66 patients (age, 58 years [range, 45 to 64]; HSCT to ICU, 176 days [range, 85 to 407]) with ARF and pulmonary infiltrates were analyzed. In 47 patients (71%) a causative pathogen was identified (fungal, n = 28; viral, n = 26; bacterial, n = 18). Polymicrobial findings involving several pathogen groups occurred in 20 patients (30%). Culture (12/16, 75%), galactomannan (13/15, 87%), and Aspergillus-PCR (8/9, 89%) from BAL but not serum galactomannan (6/14, 43%) helped to diagnose invasive aspergillosis (n = 16, 24%). Aspergillus-PCR detected azole resistance in 2 cases. Mucorales was found in 7 patients (11%; BAL culture, n = 6; Mucorales-PCR, n = 1). Patients with identified pathogens had higher Simplified Acute Physiology Score II scores (P = .049) and inferior ICU survival (6% versus 37%, P < .01), which largely related to the presence of an invasive fungal infection. Eight patients (12%) had 1 or more viruses with uncertain lung pathogenicity as the sole microbiologic finding. A diagnostic microbiologic workup incorporating molecular- and biomarker-based assays identified pathogens in most HSCT recipients with ARF and pulmonary infiltrates admitted to the ICU. Implications of polymicrobial infection and pathogen patterns in these patients warrant further investigation.