Low incidence of de novo HLA antibodies after COVID-19 vaccination: A cohort study of patients awaiting kidney transplantation.

BACKGROUND: Antibodies against human leukocyte antigen (anti-HLA Abs) are associated with an increased risk of allograft loss. Herein, we report the prospective follow-up for anti-HLA Abs formation in 103 patients with end-stage kidney disease on the waiting list for transplantation who underwent COVID-19 vaccination. PATIENTS AND METHODS: Sera were tested before and after vaccination using Luminex technology. The cohort comprised of 62 males and 41 females with a mean age of 56 ± 14 years. The patients received BNT162b2 (80.4%), mRNA-1273 (18.5%), AZD1222 (0.40%), or ChAdOx1-S (0.80%) vaccine. Patients were tested before and within 119 ± 50, 95 ± 46 and 25 ± 26 days after the first, second, and third dose of the vaccine, respectively. RESULTS: No significant change in calculated panel reactive antibody (cPRA) after vaccination was seen. Although 98.1% of patients had no change in anti-HLA Abs profile or cPRA after vaccination, two patients (1.9%) developed de novo anti-HLA Abs against class I or II HLA antigens. In those two patients, the cPRA changed from 0% and 63% at baseline to 9% and 90% after vaccination, respectively. Both patients received the BNT162b2 mRNA-based vaccine. The earliest detected anti-HLA Abs was 18 days after the first dose. CONCLUSION: In rare cases, new anti-HLA antibodies were observed after COVID-19 vaccination, with potential implications for transplantation. The low incidence of this phenomenon is outweighed by the clinical benefits of vaccination.

Next-generation sequencing identifies two novel HLA class II alleles, HLA-DRB1*01:115 and HLA-DRB1*14:224.

We identified two novel HLA class II alleles by NGS, HLA-DRB1*01:115 and HLA-DRB1*14:224.

The novel HLA class II allele, DPB1*1284:01, identified using next-generation sequencing.

Our laboratory has identified DPB1*1284:01 as a novel HLA Class II allele by NGS.

SARS Cov-2 vaccination induces de novo donor-specific HLA antibodies in a renal transplant patient on waiting list: A case report.

The ability of COVID-19 vaccination to induce anti-HLA antibodies (Abs) formation in renal transplant candidates is not well studied. A 42-year-old man on a renal transplant waitlist, with no sensitization history, was tested for DSA before and after COVID-19 vaccination. Patient has consistently tested negative for COVID-19 virus. Eighteen days after receiving first dose of mRNA-based vaccine, flow cytometry crossmatch (FCXM) was strongly positive with de novo donor-specific Ab (dnDSA) against B57 and de novo non-DSA against B58. Before vaccination, preliminary FCXM was negative with no anti-HLA Abs. This event prompted the transplant team to cancel the surgery. COVID-19 vaccination could be associated with anti-HLA Abs formation in renal patients on waitlists that could affect future transplantability.

Four novel HLA class II alleles identified using next-generation sequencing.

We describe here four novel HLA class II alleles, DPA1*01:33, DPB1*1082:01, DPB1*1144:01, and DQA1*01:45, identified in our laboratory following the implementation of next generation sequencing (NGS) for routine high resolution HLA typing of donors and recipients for solid organ transplant and hematopoetic stem cell transplant. The NGS technology has improved our ability to match at all clinically HLA loci and to facilitate the interpretation of allele specific antibody and eplet matching.

Paracrine Factors Released by Osteoblasts Provide Strong Platelet Engraftment Properties.

Ex vivo expansion of hematopoietic stem cell (HSCs) and progenitors may one day overcome the slow platelet engraftment kinetics associated with umbilical cord blood transplantation. Serum-free medium conditioned with osteoblasts (i.e., osteoblast-conditioned medium [OCM]) derived from mesenchymal stromal cells (MSC) was previously shown to increase cell growth and raise the levels of human platelets in mice transplanted with OCM-expanded progenitors. Herein, we characterized the cellular and molecular mechanisms responsible for these osteoblast-derived properties. Limiting dilution transplantation assays revealed that osteoblasts secrete soluble factors that synergize with exogenously added cytokines to promote the production of progenitors with short-term platelet engraftment activities, and to a lesser extent with long-term platelet engraftment activities. OCM also modulated the expression repertoire of cell-surface receptors implicated in the trafficking of HSC and progenitors to the bone marrow. Furthermore, OCM contains growth factors with prosurvival and proliferation activities that synergized with stem cell factor. Insulin-like growth factor (IGF)-2 was found to be present at higher levels in OCM than in control medium conditioned with MSC. Inhibition of the IGF-1 receptor, which conveys IGF-2' intracellular signaling, largely abolished the growth-promoting activity of OCM on immature CD34+ subsets and progenitors in OCM cultures. Finally, IGF-1R effects appear to be mediated in part by the coactivator ß-catenin. In summary, these results provide new insights into the paracrine regulatory activities of osteoblasts on HSC, and how these can be used to modulate the engraftment properties of human HSC and progenitors expanded in culture. Stem Cells 2019;37:345-356.

Human Bone Marrow Mesenchymal Stromal Cell-Derived Osteoblasts Promote the Expansion of Hematopoietic Progenitors Through Beta-Catenin and Notch Signaling Pathways.

Coculture of hematopoietic stem cells (HSC) with primary stromal cells from HSC niches supports the maintenance and expansion of HSC and progenitors ex vivo. However, a major drawback is the availability of primary human samples for research and clinical applications. We investigated the use of in vitro derived osteoblasts as a new source of feeder cells and characterized the molecular pathways that mediate their growth-promoting activities. First, we compared the growth and differentiation modulating activities of mesenchymal stromal cells (MSC)-derived osteoblasts (M-OST) with those of their undifferentiated precursor on umbilical cord blood (UCB) progenitors. Feeder-free cultures were also included as baseline control. Cell growth and expansion of hematopoietic progenitors were significantly enhanced by both feeder cell types. However, progenitor cell growth was considerably greater with M-OST. Coculture also promoted the maintenance of immature CD34+ progenitor subsets and modulated in a positive fashion the expression of several homing-related cell surface receptors, in a feeder-specific fashion. Serial transplantation experiments revealed that M-OST coculture supported the maintenance of long-term lympho-myeloid reconstituting HSC that provided engraftment levels that were generally superior to those from MSC cocultures. Mechanistically, we found that coculture with M-OST was associated with enhanced beta-catenin (ß-Cat) activity in UCB cells and that abrogation of ß-Cat/T-cell factor activity blunted the growth-promoting activity of the M-OST coculture. Conversely, Notch inhibition reduced UCB cell expansion, but to a much lesser extent. In conclusion, this study demonstrates that M-OST are excellent feeder cells for HSC and progenitors, and it identifies key molecular pathways that are responsible for the growth-enhancing activities of osteoblasts on UCB progenitors.

Impact of osteoblast maturation on their paracrine growth enhancing activity on cord blood progenitors.

BACKGROUND: Osteoblasts possess strong growth modulatory activity on haematopoietic stem cells and progenitors. We sought to characterise the growth and differentiation modulatory activities of human osteoblasts at distinct stages of maturation on cord blood (CB) progenitors in the context of osteoblast conditioned medium (OCM). METHODS: OCM was produced from MSC-derived osteoblasts (M-OST) at distinct stages of maturation. The growth modulatory activities of the OCM were tested on CB CD34+ cells using different functional assays. RESULTS: OCMs raised the growth of CB cells and expansion of CD34+ cells independently of the maturation status of M-OST. However, productions of immature CB cells including committed and multipotent progenitors were superior with OCM produced with immature osteoblasts. Osteogenic differentiation was accompanied by the upregulation of IGFBP-2, by several members of the Angpt-L family of growth factor, and by the Notch ligands Dll-1 and Dll-4. However, the growth activity of OCM and the in vivo engraftment properties of OCM-expanded CB cells were retained after IGFBP-2 neutralisation. Similarly, OCM-mediated expansion of CB myeloid progenitors was largely independent of Notch signalling. CONCLUSIONS: These results demonstrate that immature osteoblasts possess greater regulatory activity over haematopoietic progenitors, and that this activity is not entirely dependent on Notch signalling.

Characterization of the growth modulatory activities of osteoblast conditioned media on cord blood progenitor cells.

Engraftment outcomes are strongly correlated with the numbers of hematopoietic stem and progenitor cells (HSPC) infused. Expansion of umbilical cord blood (CB) HSPC has gained much interest lately since infusion of expanded HSPC can accelerate engraftment and improve clinical outcomes. Many novel protocols based on different expansion strategies of HSPC and their downstream derivatives are under development. Herein, we describe the production and properties of serum-free medium (SFM) conditioned with mesenchymal stromal cells derived-osteoblasts (OCM) for the expansion of umbilical CB cells and progenitors. After optimization of the conditioning length, we show that OCM increased the production of human CB total nucleated cells and CD34+ cells by 1.8-fold and 1.5-fold over standard SFM, respectively. Production of immature CD34+ subpopulations enriched in hematopoietic stem cells was also improved with a shorter conditioning period. Moreover, we show that the growth modulatory activities of OCM on progenitor expansion are regulated by both soluble factors and non-soluble cellular elements. Finally, the growth and differentiation modulatory activities of OCM were fully retained after high dose-ionizing irradiation and highly stable when OCM is stored frozen. In summary, our results suggest that OCM efficiently mimics some of the natural regulatory activities of osteoblasts on HSPC and highlight the marked expansion potentials of SFM conditioned with osteoblasts.

Advances in umbilical cord blood stem cell expansion and clinical translation.

Umbilical cord blood (CB) is a rich source of hematopoietic stem cells (HSCs) with important applications in allogeneic stem cell transplantation. However, the low numbers of hematopoietic stem and progenitor cells (HSPCs) in banked units remain a major limitation. Protocols developed for HSPC expansion ex vivo or to improve HSPC homing to the marrow represent solutions to overcome this shortcoming. In recent decades, wide arrays of functionally divergent approaches were developed for the amplification of HSPCs. These include optimization of cytokine cocktails, coculture systems, small molecules, and delivery systems for HSPC-expansion genes. Herein, we review past and current strategies, focusing on studies that characterize the contribution of expanded CB HSPC to short- and long-term engraftment in transplantation models or in clinical trials. Also discussed are homing effectors used to promote engraftment. In summary, these studies underscore that early-acting cytokines alone can expand HSPC with short-term engraftment activity, but that robust expansion of HSPCs with long-term engraftment necessitates the synergistic action of multiple HSC-expansion agonists. In support of this, early clinical trials based on cytokine-driven HSPC-expansion protocols delivered disappointing results, whereas recent trials based on the synergistic action of cytokines and HSPC-expansion agonists reported significant improvements in engraftment and therapeutic outcomes. Conversely, molecules that enhance homing of HSPC may represent a complementary approach to improve and perhaps accelerate engraftment. Optimization of the next generation of HSPC-expansion and priming strategies should support a paradigm shift in CB transplantation in which smaller, better matched units may preferentially be used.

Rapid monitoring of immune reconstitution after allogeneic stem cell transplantation--a comparison of different assays for the detection of cytomegalovirus-specific T cells.

OBJECTIVES: Cytotoxic T cells (CTLs) play an important role in controlling cytomegalovirus (CMV) infection after allogeneic hematopoietic stem cell transplantation (HSCT). The purpose of this study was to compare four different assays to detect CMV antigen-specific T cells for the monitoring of CMV-specific immune reconstitution after HSCT. METHODS: Comparative monitoring of CMV-specific T cells was performed using HLA tetramer, interferon-gamma enzyme-linked immunospot (ELISPOT), intracellular IFN-γ (IC-FACS), and real-time polymerase chain reaction (RT-PCR) assays with immunodominant CMV pp65-HLA-A2-restricted peptide and recombinant pp65-protein in 18 patients after allogeneic HSCT. RESULTS: Using pp65-peptide to stimulate T cells in HLA-A2-positive patients, antigen-specific T cells have been detected in 43% (10 of 23) by IC-FACS, 62% (13 of 21) by tetramer, 68% (15 of 22) by RT-PCR, and 53% (10 of 19) by ELISPOT. No T-cell responses were detected in HLA-A2-negative patients by all assays. Stimulating with combination of both pp65-peptide and pp65-protein detected 72% (18/25) by IC-FACS, 88% (22/25) by RT-PCR, and 59% (12/22) by ELISPOT. Comparing the different methods of T-cell detection we found a significant positive correlation between RT-PCR and tetramer analysis, IC flow cytometry and ELISPOT assay. Using pp65-protein for T-cell activation overcomes the HLA restriction of the HLA-A2-restricted pp65-peptide stimulation, thus increasing the detection limit of antigen-specific T cells. CONCLUSION: CMV-specific T cells have been most frequently detected using RT-PCR suggesting a higher sensitivity compared with IC-FACS, tetramer, and ELISPOT assays. This technique allows rapid and sensitive monitoring of CMV-specific immune reconstitution after HSCT, which could guide prophylactic and therapeutic strategies to avoid active CMV disease.

Methylenetetrahydrofolate reductase genotype association with the risk of follicular lymphoma.

The metabolism of folate is essential in DNA synthesis, and polymorphisms of genes involved in such metabolism have been implicated in many types of cancer. Among these, the methylene tetrahydrofolate reductase gene (MTHFR) encodes an enzyme that converts folate to a methyl donor used for DNA methylation. We studied the association between the different genotypes of the two most common MTHFR polymorphisms, C677T and A1298C, and the risk of follicular lymphoma (FL). For this purpose, 55 previously diagnosed FL patients and 170 normal control subjects were examined using polymerase chain reaction followed by restriction fragment length polymorphism. The frequency of the A1298C CC homozygous mutant genotype was significantly higher in patients with FL than in control subjects (OR = 3.51, 95% CI = 1.39-8.86, P = 0.008). No such association was found for the heterozygous A1298C AC genotype (OR = 1.08, 95% CI = 0.55-2.12, P = 0.83). On the other hand, no significant association was found for either the C677T CT heterozygous genotype (OR = 0.79, 95% CI = 0.42-1.51, P = 0.49) or the C677T TT homozygous mutant genotype (OR = 0.55, 95% CI = 0.12-2.65, P = 0.46). The present findings add to the very few reports suggesting a link between the A1298C CC homozygous MTHFR genotype and a higher risk of developing FL, and the first such in a Jordanian population.

Comparison of platelet aggregation using light transmission and multiple electrode aggregometry in Glanzmann thrombasthenia.

We examined platelet aggregation in platelet-rich plasma (PRP) and in whole blood in nine patients with Thrombasthenia Glanzmann (TG). In PRP, aggregation was measured by monitoring the changes in light absorbance that occurred in response to adenosine 5-diphosphate (ADP), collagen and ristocetin. To measure platelet aggregation in whole blood, we used multiple electrode Impedance aggregometry using the same aggregating agents. In PRP, the patient's platelets showed defective aggregation in response to ADP, collagen, epinephrine and partially to ristocetin in all patients. In whole blood, platelet aggregation in response to the same aggregating agents showed similar response and appeared to be very similar to that which occurred in PRP. Whole blood impedance aggregometry seems to give similar results to PRP light transmission aggregometry in patients with TG. Multiple electrode aggregometry (MEA) is faster and more convenient to use in these patients.

Expression of the lysophospholipid receptor family and investigation of lysophospholipid-mediated responses in human macrophages.

Some of the biological effects of lipoproteins have been attributed to their association with lysophosphatidic acid (LPA), lysophosphatidylcholine (LPC), sphingosine-1-phosphate (S1P) and sphingosylphosphorylcholine (SPC). These lysophospholipids mediate multiple biological responses via several G protein-coupled receptors (GPR). The expression of these receptors, however, has not been systematically investigated in primary human monocytes and macrophages as major cells involved in atherosclerosis. The mRNAs for all 15 receptors described so far were detected in monocytes, macrophages, foam cells and high density lipoprotein (HDL(3))-treated cells using real time RT-PCR. Immunoblots revealed that S1P(1), S1P(2), S1P(4), LPA(1), LPA(2) and GPR65 are expressed in monocytes and macrophages, while S1P(5) and LPA(3) have not been detected. S1P(3) was induced during differentiation but down-regulated by lipid-loading and HDL(3), whereas LPA(1) was down-regulated in differentiated macrophages. The influence of S1P on macrophages was investigated and the induction of CD32 indicates an enhanced phagocytic activity. Altogether, these data give insights into the expression and regulation of lysophospholipid receptors in primary human monocytes, macrophages and foam cells.