The ICCS-recommended high-sensitivity flow cytometry protocol was effective for detecting major and minor PNH clones in Russian PNH patients, and showed high reproducibility between laboratories.

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We have previously demonstrated that the detergent Tyloxapol is effective in preventing reactions to endotoxin. We studied the effects of Tyloxapol on the morbidity and mortality from endotoxemia in rabbits and on the mortality in rats with sepsis. The effects of Tyloxapol on endotoxin binding and macrophage activation were studied in the macrophage cell line RAW264.7 and CHO cells expressing CD14. Isolated human leukocytes were used to study the effects of Tyloxapol on immune reactions, leukocyte motility, and phagocytosis. Intravenous Tyloxapol (200 mg/kg), given prior to or at the time of endotoxin infusion protected rabbits from developing shock. In rats with peritoneal sepsis, a lipid-rich diet and Tyloxapol given at the time of induction of peritonitis protected them from septic death. In vitro, Tyloxapol blocked the binding of endotoxin to murine macrophages and CHO cells expressing CD14, activation of macrophages, and also some antigen-antibody immune reactions (mediated by CD2, CD4, CD22, HLA-DR). Tyloxapol may prevent the reaction to endotoxin by desensitizing endotoxin-recognizing receptors.

Introduction: Pathogenetic relationship of aplastic anemia (AA) and paroxysmal nocturnal hemoglobinuria (PNH) was registered a long time ago. Approximately in 50-60% of patients with AA is detected PNH-clone, and during long-term observation the transformation of AA into classic PNH is likely. At the time of diagnosis PNH-clone sizes range from small proportion of PNH-cells, requiring only monitoring, up to combination of clinically manifested AA and PNH requring combined therapy. Nevertheless, the peculiar characteristics of the disease in cases of different AA-PNH-combinations still remain unclear. Aim: to evaluate the relationship between size and dynamics of PNH-clone with clinical features of AA/PNH. Materials and methods: We have evaluated blood samples of 81 patients with AA (whole group) for the presence of PNH-clone using flow cytometry according to ICCS standards. 23 patients aged 23 to 54 years (median 46 years) were under constant observation for 3 years or more, control examination was performed once every 6 months (dynamic observation group). Of them 17 had severe AA (SAA) and 6 - nonsevere AA (NAA). Twelve patients received standard immunosupressive therapy (IST) for the treatment of AA, other patients were in remission and did not require IST. Results: In the whole group of patients (n=81) 47 patients (58%) were AA/PNH-positive (PNHpos) with clone size ranging from 0.01% to 97.9%. PNH-clone less than 1% was identified in 10% of subjects; PNH-clone more than 10% was observed in 50% of subjects. In dynamic observation group 18 patients were AA/PNHpos with initial clone size from 0.1% to 95.9%, and 5 patients - AA/PNH negative (AA/PNHneg). In AA/PNHneg patients pathological clone still has not been detected in repeated studies for the observed period. Among patients with AA/PNHpos stable clone was observed in 11 subjects (61%), it increased to 10% and more in 5 subjects (28%) and decreased in 2 patients (11%) with small PNH-clone. Clinical and laboratory signs of chronic intravascular hemolysis were usually observed in patients with pathological clone over 25%. PNH-clone less than 10% was not accompanied by significant deviations in clinico-laboratory indices. Most of patients in whom PNH-clone size increased, had remission of AA. Four patients had clonal evolution to manifest classical PNH, of them in 2 patients with SAA аplasia of hematopoiesis persisted. In one patient, with complete remission of SAA lasting more than 3 years and minor PNH-clone, was observed transformation into myeloid leukemia leading to death. Ekulizumab was prescribed to 4 patients: 2 with clinically manifest hemolysis and clone size > 90% (1 - in conjunction with IST for AA), and 2 with clone size 24% and 70% and LDH > 1.5 ULN due to unplanned pregnancies (both on Cyclosporin therapy). All of them achieved the target level of LDH <1.5 ULN in the first 2 weeks of therapy. Of 2 transfusion-dependent patients, one still does not require transfusion support after the Ekulizumab initiation, and in other patient transfusion dependency decreased, despite refractory TAA. In one patient with PNH-clone 70% Ekulizumab therapy was initiated in III trimester of pregnancy, delivery was without complications, full-term baby, 8-9 points Apgar. In the 2nd pregnant patient with PNH-clone 24% Ekulizumab was prescribed because of pre-eclampsia and LDH>4 ULN at 21-22 weeks with antenatal fetal death, and it allowed for accelerating cure of pathological symptoms. Conclusion: PNH-clone was detected in 58% of patients with AA. Our data confirm the need for monitoring of PNH clone in patients with AA and for timely adequate therapy, including inhibitors of intravascular hemolysis, according to specific indications in each case. Disclosures Fominykh: Novartis Pharma: Honoraria; BMS: Honoraria.

The main histocompatibility complex — HLA system (Human Leukocyte Antigens) is among the most important genetic factors determining response of humans to infectious agents. The key role that HLA molecules play in immune response is to present the pathogen-derived peptides. Enormous molecular variability of HLA alleles in human populations have attracted close attention and became the basis for numerous studies aimed at evaluating the role of HLA genotypes for individual features of immune response to COVID-19, the new infection caused by SARS-CoV-2 β-coronavirus. Many studies have focused on search of specific alleles associated with both susceptibility and resistance to this disease. Separate HLA patterns were reported already. These patterns may be either universal to several populations, or rather peculiar, since distribution of HLA genes is different for various populations, depending on the living conditions, including specific protection from environmental pathogens. Therefore, it is evident that individual effects of HLA genotype upon occurrence and course of SARS-CoV-2 infection should be performed in comparison with the HLA distribution among the residents of appropriate region. The objective of this study was to compare the distribution of HLA-A*, B*, DRB1* allele groups, and to analyze the frequencies of HLA-AB-DRB1 haplotypes in subjects with COVID-19 (n = 138), compared with the control group presented by residents of the North-Western Russia (n = 1456). The most significant differences between COVID-19 patients compared with a group from control population were revealed for the groups of HLA-A* alleles: the frequencies of HLA-A*02 and HLA-A*26 were significantly reduced (39.86% versus 51.72%, χ2 = 7,58, and 4.35% versus 9.07%, χ2 = 4.17, respectively). At the same time, the frequency of HLA-A*29 was increased more than 2-fold (5.80% versus 2.47%, χ2 = 4.03). This finding suggests that the allele groups A*02 and A*26 are associated with reduced likelihood of the disease, while A*29, is an apparent factor predisposing for susceptibility to the disease. It was found that occurrence of definite HLA haplotypes, including the A*02 allele group, is less common in persons who have undergone COVID-19, and are ranged at the 4th, 7th and 10th positions in frequency, while in the population control group such HLA haplotypes took the 3rd, 4th, 7th and 8th places. Further evaluation of the HLA gene polymorphism will allow to understand the predetermined immunogenetic basis for susceptibility, as well as clinical severity of COVID-19.