The Fc-effector function of COVID-19 convalescent plasma contributes to SARS-CoV-2 treatment efficacy in mice

COVID-19 convalescent plasmas (CCPs) are chosen for plasma therapy based on neutralizing titers and anti-Spike immunoglobulin levels. However, CCP characteristics that promote SARS-CoV-2 control are complex and incompletely defined. Using an in vivo imaging approach, we demonstrate that CCPs with low neutralizing (ID50 ≤ 1:250), but moderate to high Fc-effector activity, in contrast to those with poor Fc function, delay mortality and/or improve survival of SARS-CoV-2-challenged K18-hACE2 mice. The impact of innate immune cells on CCP efficacy depended on their residual neutralizing activity. Fractionation of a selected CCP revealed that IgG and Ig(M + A) were required during therapy, but the IgG fraction alone sufficed during prophylaxis. Finally, despite reduced neutralization, ancestral SARS-CoV-2-elicited CCPs significantly delayed Delta and Beta-induced mortality suggesting that Fc-effector functions contribute to immunity against VOCs. Thus, Fc activity of CCPs provide a second line of defense when neutralization is compromised and can serve as an important criterion for CCP selection.

Rhesus D Antigenic Determinants on Residual Red Blood Cells in Apheresis and Buffy Coat Platelet Concentrates

Background

The level of residual red blood cells (RBCs) in platelet concentrates (PCs) is of interest because of clinical concerns related to alloimmunization to RBC antigens in transfused patients. This work aims at characterizing and quantifying the levels of intact and fragmented RBCs in apheresis (AP-PCs) and buffy coat PCs (BC-PCs) to assess their potential risk for RhD antigen alloimmunization.

Methods

After staining with anti-CD41 (platelets) and anti-CD235a (RBCs) antibodies, the size and density of RhD antigen on intact and fragmented RBCs were analyzed by flow cytometry.

Results

Residual RBC counts were 29 ± 22 × 10⁶/unit in AP-PCs and 121 ± 54 × 10⁶/unit in BC-PCs, which correspond to about 3 and 11 µL of RBCs by product, respectively. RhD expression was about 4 times higher on RBC particles in AP-PCs, and these particles contribute to 66 and 75% of the total antigenic load in BC-PCs and AP-PCs, respectively.

Conclusions

Processing methods influence the quantity and nature of contaminating residual RBCs and RBC-derived particles in PCs. The estimation of residual RBCs in these blood products is generally based on measurements of intact RBCs, which might underestimate the risk for alloim-munization in transfused patients. The question of whether these RBC-derived particles can produce an immune response and, thus, should then be taken into consideration for Rh immune prophylactic treatments, remains to be clarified.

Quality and safety of red blood cells stored in two additive solutions subjected to multiple room temperature exposures

BACKGROUND AND OBJECTIVES

Many international standards state that red blood cell (RBC) products should be discarded if left out of controlled temperature storage for longer than 30 min to reduce the risk of bacterial growth and RBC loss of viability. This study aimed to verify whether repeated short-time exposures to room temperature (RT) influence RBCs quality and bacterial proliferation.

MATERIALS AND METHODS

Saline-adenine-glucose-mannitol (SAGM) and AS-3 RBC units were split and exposed to RT for 30 or 60 min on day 2, 7, 14, 21, and 42 of storage while reference units remained stored at 1-6°C. Red blood cell in vitro quality parameters were evaluated after each exposure. In a second experiment, SAGM and AS-3 RBC units were split and inoculated with Staphylococcus epidermidis (5 CFU/ml), Serratia marcescens (1 CFU/ml), and Serratia liquefaciens (1 CFU/ml). Reference units remained in storage while test units were exposed as described previously. Bacterial concentrations were investigated after each exposure.

RESULTS

No differences were noticed between reference and test units in any of the in vitro parameters investigated. S. epidermidis did not grow in either reference or exposed RBCs. While S. marcescens did not grow in AS-3, bacterial growth was observed in RT-exposed SAGM RBCs on day 42. Similar growth was obtained for S. liquefaciens in the two additive solutions for both reference and test units.

CONCLUSION

Short-time exposures to RT do not affect RBC quality and do not significantly influence bacterial growth. An expansion of the '30-minute' rule to 60 min should be considered by regulatory agencies.

Estimation of the number of CD154 molecules in membrane extracts used as a source of CD40 stimulation of human B lymphocytes

The CD40-CD154 interaction is better exemplified by a rheostat than by an on-off switch, and variations in its intensity can play a role in the regulation of B lymphocyte activation following primary and/or secondary humoral immune response. The CD40-CD154 interaction is often studied in co-culture models using CD154+ adherent cells, which can be problematic when performing protein or gene analyses. The use of membrane extracts prepared from CD154+-transfected cells can eliminate possible interferences caused by the presence of contaminating feeder cells. Given the dose-response effect of CD154 on target B cells, it is important to measure the amount of CD154 when using soluble membranes. We hereby report a simple method, based on cytometry analysis, to estimate the relative number of CD154 molecules in membrane extracts, allowing reproducibility in human B-cell activation level.

Immunomodulation of human B cells following treatment with intravenous immunoglobulins involves increased phosphorylation of extracellular signal-regulated kinases 1 and 2

In the treatment of autoimmune diseases, intravenous Igs (IVIg) are assumed to modulate immune cells through the binding of surface receptors. IVIg act upon definite human B cell populations to modulate Ig repertoire, and such modulation might proceed through intracellular signaling. However, the heterogeneity of human B cell populations complicates investigations of the intracellular pathways involved in IVIg-induced B cell modulation. The aim of this study was to establish a model allowing the screening of IVIg signal transduction in human B cell lines and to attempt transposing observations made in cell lines to normal human B lymphocytes. Nine human B cell lines were treated with IVIg with the goal of selecting the most suitable model for human B lymphocytes. The IgG(+) DB cell line, whose response was similar to that of human B lymphocytes, showed reduced IVIg modulation following addition of PD98059, an inhibitor of extracellular signal-regulated protein kinase 1/2 (ERK1/2). The IVIg-induced ERK1/2 phosphorylation was indeed proportional to the dosage of monomeric IVIg used when tested on DB cells as well as Pfeiffer cells, another IgG(+) cell line. In addition, two other intermediates, Grb2-associated binder 1 (Gab1) and Akt, showed increased phosphorylation in IVIg-treated DB cells. IVIg induction of ERK1/2 phosphorylation was finally observed in peripheral human B lymphocytes, specifically within the IgG(+) B cell population. In conclusion, IVIg immunomodulation of human B cells can thus be linked to intracellular transduction pathways involving the phosphorylation of ERK1/2, which in combination with Gab1 and Akt, may be related to B cell antigen receptor signaling.

Characterization of mononuclear cells remaining in the leukoreduction system chambers of apheresis instruments after routine platelet collection: a new source of viable human blood cells

BACKGROUND

The yield of white blood cells (WBCs) extracted from whole-blood leukoreduction filters can be affected by the storage conditions and delay before filtration. Platelets (PLTs) collected with apheresis instruments (Trima Accel, Gambro BCT) are leukoreduced during the procedure on a fluidized particle bed in a leukoreduction chamber (LRS chamber). In this report, the residual cell content of these LRS chambers was characterized to determine whether it would be a valuable source of viable human blood cells.

STUDY DESIGN AND METHODS

The content of LRS chambers was eluted by gravity, and peripheral blood mononuclear cells (PBMNCs) were purified on a Ficoll-Paque gradient. Analyses were performed before and after freezing. Proportions of CD3+, CD14+, CD16+, CD19+, CD34+, and CD45+ cells were determined by flow cytometry. The frequency of T cells expressing CD4, CD8, and CD27 and of B cells expressing immunoglobulin G (IgG), IgM, and CD27 was also determined.

RESULTS

LRS chambers held approximately 10(9) CD45+ cells representing the normal proportions of CD3+, CD14+, CD16+, and CD19+ cell populations of PBMNCs. A small fraction of these CD45+ cells were CD34+CD38+ cells (0.3 +/- 0.2%). The viability of these cells, measured before and after freezing, was more than 95 percent.

CONCLUSION

The residual cell content of Trima Accel LRS chambers recovered after PLT collection is a good source of viable monocytes and lymphocytes. These PBMNCs, containing CD3+, CD14+, CD16+, CD19+, and CD34+ cells can be frozen to prepare cell banks, which opens new avenues for utilization in several physiologic studies or even in cellular therapy applications.