Isolation of maternal mononuclear cells from placentas for use in in vitro functional assays

A Possible Sterilizing Cure of HIV-1 Infection Without Stem Cell Transplantation

BACKGROUND

A sterilizing cure of HIV-1 infection has been reported in 2 persons living with HIV-1 who underwent allogeneic hematopoietic stem cell transplantations from donors who were homozygous for the CCR5Δ32 gene polymorphism. However, this has been considered elusive during natural infection.

OBJECTIVE

To evaluate persistent HIV-1 reservoir cells in an elite controller with undetectable HIV-1 viremia for more than 8 years in the absence of antiretroviral therapy.

DESIGN

Detailed investigation of virologic and immunologic characteristics.

SETTING

Tertiary care centers in Buenos Aires, Argentina, and Boston, Massachusetts.

PATIENT

A patient with HIV-1 infection and durable drug-free suppression of HIV-1 replication.

MEASUREMENTS

Analysis of genome-intact and replication-competent HIV-1 using near-full-length individual proviral sequencing and viral outgrowth assays, respectively; analysis of HIV-1 plasma RNA by ultrasensitive HIV-1 viral load testing.

RESULTS

No genome-intact HIV-1 proviruses were detected in analysis of a total of 1.188 billion peripheral blood mononuclear cells and 503 million mononuclear cells from placental tissues. Seven defective proviruses, some of them derived from clonally expanded cells, were detected. A viral outgrowth assay failed to retrieve replication-competent HIV-1 from 150 million resting CD4+ T cells. No HIV-1 RNA was detected in 4.5 mL of plasma.

LIMITATIONS

Absence of evidence for intact HIV-1 proviruses in large numbers of cells is not evidence of absence of intact HIV-1 proviruses. A sterilizing cure of HIV-1 can never be empirically proved.

CONCLUSION

Genome-intact and replication-competent HIV-1 were not detected in an elite controller despite analysis of massive numbers of cells from blood and tissues, suggesting that this patient may have naturally achieved a sterilizing cure of HIV-1 infection. These observations raise the possibility that a sterilizing cure may be an extremely rare but possible outcome of HIV-1 infection.

PRIMARY FUNDING SOURCE

National Institutes of Health and Bill & Melinda Gates Foundation.

Evaluation of various methods of maternal placental blood collection for immunology studies

The collection of maternal placental intervillous blood (IVB), without contamination of fetal blood and with an accurate mononuclear cell profile, is essential for immunological studies of placental malaria and other infectious diseases of the placenta. We have compared five documented methods of IVB collection: perfusion, incision, biopsy, tissue grinding, and puncture (prick) for fetal blood contamination and mononuclear cell profiles using flow cytometry. Twenty-five placentas were obtained from Plasmodium falciparum and human immunodeficiency virus-negative primigravid and secundigravid women delivering at Nyanza Provincial Hospital in Kisumu, western Kenya. Each of the five methods was performed on the same placenta. Fetal red blood cell contamination was significantly lower for the prick and perfusion methods (4.1% and 8.3%, respectively) than for incision (59.5%), biopsy (42.6%), and tissue grinding (19.9%). Significant variation was noted among the five methods in the percentages of monocytes, total T cells, CD4+ and CD8+ T cells, B cells, and NK cells. Further, a pairwise comparison of prick and perfusion, the two methods with low fetal blood contamination, showed that they were not different for fetal red blood cell contamination levels; however, prick yielded significantly higher percentages of CD4 T cells and CD4 memory T cells than perfusion. Collection by prick was determined to be the best method of intervillous blood collection for immunology studies, and perfusion represented the next best method of choice due to high sample volume yield. Overall, in considering the advantages/disadvantages of the two methods with low fetal cell contamination, we conclude that a combination of prick and perfusion is most suitable for immunology studies.

The immunology and pathogenesis of malaria during pregnancy

Women in endemic areas become highly susceptible to malaria during first and second pregnancies, despite immunity acquired after years of exposure. Recent insights have advanced our understanding of pregnancy malaria caused by Plasmodium falciparum, which is responsible for the bulk of severe disease and death. Accumulation of parasitized erythrocytes in the blood spaces of the placenta is a key feature of maternal infection with P. falciparum. Placental parasites express surface ligands and antigens that differ from those of other P. falciparum variants, facilitating evasion of existing immunity, and mediate adhesion to specific molecules, such as chondroitin sulfate A, in the placenta. The polymorphic and clonally variant P. falciparum erythrocyte membrane protein 1, encoded by var genes, binds to placental receptors in vitro and may be the target of protective antibodies. An intense infiltration of immune cells, including macrophages, into the placental intervillous spaces, and the production of pro-inflammatory cytokines often occur in response to infection, and are associated with low birth weight and maternal anemia. Expression of alpha and beta chemokines may initiate or facilitate this cellular infiltration during placental malaria. Specific immunity against placental-binding parasites may prevent infection or facilitate clearance of parasites prior to the influx of inflammatory cells, thereby avoiding a cascade of events leading to disease and death. Much less is known about pathogenic processes in P. vivax infections, and corresponding immune responses. Emerging knowledge of the pathogenesis and immunology of malaria in pregnancy will increasingly lead to new opportunities for the development of therapeutic and preventive interventions and new tools for diagnosis and monitoring.

Malaria in the pregnant woman

Women become more susceptible to Plasmodium falciparum malaria during pregnancy, and the risk of disease and death is high for both the mother and her fetus. In low transmission areas, women of all parities are at risk for severe syndromes like cerebral malaria, and maternal and fetal mortality are high. In high transmission areas, where women are most susceptible during their first pregnancies, severe syndromes like cerebral malaria are uncommon, but severe maternal anemia and low birth weight are frequent sequelae and account for an enormous loss of life. P. falciparum-infected red cells sequester in the intervillous space of the placenta, where they adhere to chondroitin sulfate A but not to receptors like CD36 that commonly support adhesion of parasites infecting nonpregnant hosts. Poor pregnancy outcomes due to malaria are related to the macrophage-rich infiltrates and pro-inflammatory cytokines such as tumor necrosis factor-alpha that accumulate in the intervillous space. Women who acquire antibodies against chrondroitin sulfate A (CSA)-binding parasites are less likely to have placental malaria, and are more likely to deliver healthy babies. In areas of stable transmission, women acquire antibodies against CSA-binding parasites over successive pregnancies, explaining the high susceptibility to malaria during first pregnancy, and suggesting that a vaccine to prevent pregnancy malaria should target placental parasites. Prevention and treatment of malaria are essential components of antenatal care in endemic areas, but require special considerations during pregnancy. Recrudescence after drug treatment is more common during pregnancy, and the spread of drug-resistant parasites has eroded the usefulness of the few drugs known to be safe for the woman and her fetus. Determining the safety and effectiveness of newer antimalarials in pregnant women is an urgent priority. A vaccine that prevents pregnancy malaria due to P. falciparum could be delivered before first pregnancy, and would have an enormous impact on mother-child health in tropical areas.

Less HLA-G expression in Plasmodium falciparum-infected third trimester placentas is associated with more natural killer cells

During pregnancy, maternal immune tolerance of the fetal semi-allogeneic graft is partly the consequence of extravillous trophoblast HLA-G expression and its interaction with natural killer (NK) cells. Plasmodium falciparum malaria is frequently associated with maternal and fetal complications. Local HLA-G expression and the number of NK cells were evaluated immunohistochemically in P. falciparum-infected and uninfected placentas (15 each) collected in a seasonal malaria-hypoendemic area. In control placentas, HLA-G was almost always expressed in extravillous trophoblast whereas, in infected placentas, it was significantly more weakly expressed in extravillous trophoblast but was also detected in intervillous space macrophages. NK cells were evaluated in intervillous and intravillous spaces and in basal plate. NK cells were always more abundant in basal plate than in intervillous and intravillous spaces in infected or control placentas. For each area, more NK cells were seen in infected than control placentas. These data suggest that HLA-G down-regulation and more NK cells in placentas may be among the mechanisms involved in poor birth outcome associated with P. falciparum infection.

Comparative flow cytometric analysis of term placental intervillous and peripheral blood from immediate postpartum women in Western kenya

Understanding maternal immune responses in the placenta is critical for management of pregnancy failures and haematogenous infections during pregnancy. However, it is unknown whether maternal placental intervillous blood (IVB) mononuclear cell populations are distinct from those found in maternal peripheral blood (PB). In this study, cell populations in the IVB and PB from immediate postpartum women were compared by flow cytometry. While levels of B and CD4+ and CD8+ T lymphocytes were similar, IVB contained significantly higher levels of monocytes (10.9+/-5.9 versus 5.5+/-2.5 per cent, respectively) and natural killer cells (14.3+/-9.6 versus 5.9+/-3.2 per cent, respectively) than the PB. Expression of the early activation marker CD69 was increased on T cells in the IVB, whereas levels of HLA-DR, a late activation marker, were similar between IVB and PB. These results suggest that maternal cells that circulate through the intervillous compartment may be subject to local influences that affect their distribution, phenotype and function. Further comparative study of these blood compartments will be necessary to elucidate the mechanisms by which the local placental milieu influences the IVB.

An optimized technique for separation of human decidual leukocytes for cellular and molecular analyses

PROBLEM

Human decidua contains a significant number of leukocytes, phenotypically and functionally different from peripheral blood. In vitro studies of decidual leukocytes require constant improvement of cell isolation technique in order to obtain highly purified viable and functionally active cells.

METHOD OF STUDY

Optimized isolation procedure of decidual leukocytes, based on non-enzymatic cell dispersion, Percoll gradient centrifugation and purification step involving immunomagnetic beads is compared with a similar procedure with Lymphoprep gradient.

RESULTS

The method based on Percoll gradient gave a viable leukocyte fraction with higher amount of alphabetaT- and gammadeltaT cells compared with Lymphoprep gradient. The leukocytes exhibited a well-preserved ultrastructure and surface marker expression and were suitable for molecular analysis. The magnitude and the kinetics of their proliferative response were comparable with peripheral blood lymphocytes.

CONCLUSIONS

The results provide an optimized method for isolation and enrichment of decidual leukocytes, suitable for phenotypic, ultrastructural, molecular and functional analyses.

A simple perfusion technique for isolation of maternal intervillous blood mononuclear cells from human placentae

A noninvasive perfusion method for the recovery of maternal placental (intervillous) blood for use in immunologic assays is described. 60% of the perfused blood samples tested for fetal red blood cell (RBC) contamination were found to be pure maternal blood; in the remainder, fetal RBC contamination, with a single exception, was less than 6%. The intervillous mononuclear cells (IVBMC) isolated from this blood were of predominantly maternal origin as demonstrated by a polymerase chain reaction-based DNA typing technique. The number of IVBMC obtained was within the range of 9 to 55 X 10(6) cells. Phenotypic analysis of IVBMC surface antigens revealed that 61% of the cells were CD3 + T-cells and 18% were CD19 + B-cells. The CD4 + and CD8 + T-lymphocyte subsets accounted for 28 and 26% of the IVBMC, respectively. The IVBMC were functionally competent as evidenced by in vitro lymphoproliferation and cytokine production in response to mitogen and PPD stimulation. This technique allows for rapid and safe isolation of large numbers of IVBMC which are functionally active up to 12 h post-delivery, thus representing a significant improvement over previously described methods. It should facilitate more vigorous research in the study of uteroplacental immunity and infectious disease research, particularly in field settings where sample collection and laboratory facilities are distant.

Characterization of macrophages isolated from the maternal surface of human term placenta by a new method of urokinase treatment

OBJECTIVES

This study was performed to establish a new method for isolating macrophages from the maternal surface of human term placenta by urokinase treatment and to characterize their immunological functions.

METHODS

Macrophages were recovered from the maternal surface of 6 human term placentas by urokinase treatment, adherence to plastic, and density gradient centrifugation using Percoll. The cells retrieved were tested for their surface markers by immunofluorescent staining. Their antigen-presenting capacity was examined by use of a mixed lymphocytes culture (MLC) test. In 2 cases, human leucocyte antigen (HLA) typing was performed.

RESULTS

An average of 4 x 10(6) macrophage-like cells were obtained per whole placenta. More than 90% of them were positive for CD14, HLA-DR, and DQ surface antigens. An MLC test revealed that they had antigen-presenting capacity. Of the 6 cases, 2 showed positive MLC test results with maternal peripheral-blood mononuclear cells. In 1 of the 2 cases, macrophages with paternal HLA phenotypes were identified.

CONCLUSION

The urokinase treatment is a new useful method for isolating macrophages from the maternal surface of human term placenta. Using this method, we obtained macrophages of paternal HLA phenotypes (fetal origin) that might have migrated to the maternal surface of human term placenta.

Relationships between maternal malaria and malarial immune responses in mothers and neonates

Immune responses of 97 Gambian women and their neonates were studied. New methods distinguished between active and previous placental malaria, were used to examine relationships between maternal malaria and neonatal immune responses. Many placentas (61%) had active or previous malarial infection. Maternal and cord malarial IgG levels correlated (P < 0.001). Malarial IgG was raised in cord blood in active placental malaria; IgM was not detected. Mean lymphoproliferation and the proportion of responders to soluble P. falciparum antigens (F32) and conserved regions of p190 expressed on trophozoites and schizonts (190L and 190N) were higher in neonates than mothers. There was no clear relationship between maternal malaria and neonatal mean lymphoproliferation to malarial antigens, although fewer neonates responded when mothers were actively infected. Matched maternal and neonatal lymphoproliferation responses did not correlate. However, first born neonatal lymphoproliferation to PPD and malarial antigens appeared lower than other neonates, in agreement with lower lymphoproliferation in primigravidae compared with multigravidae. Also in common with mothers, autologous plasma suppressed neonatal lymphoproliferation to PPD and malarial antigens, suggesting common immunoregulation. Higher cortisol or other circulating factors in first pregnancies may be implicated. The relevance of cell-mediated malarial immune responses detected at birth remains to be established.

Placental malaria. I. Pathological classification

Pregnant women are more likely to contract malaria than their non-pregnant counterparts. The aim of this study was to develop a simple classification system for the histopathological diagnosis of placental malaria infection applicable to placentas collected in field conditions. The placentas were classified into four groups depending on the presence and distribution of parasites and malaria pigment: active infection, active-chronic infection, past-chronic infection, not infected. The frequency of parasitized placentas (26.4%) was in keeping with the prevalence of placental parasitaemia documented in epidemiological studies. An additional 29.8% placentas showed pigment in fibrin only, indicating past-chronic infection. Chronic placental malaria infection was most common in primigravidae, possibly reflecting ineffective clearance of parasites from the placenta. Seasonal fluctuations between infection categories support progression of placental infection with delayed clearance of pigment from fibrin. The proposed classification system has allowed diagnosis of different categories of placental malaria infection by two independent observers. A standardized method of diagnosis may enhance understanding of placental pathology and reduced birth weight in malaria infection during pregnancy.