A Self-Assembling Pfs230D1-Ferritin Nanoparticle Vaccine Has Potent and Durable Malaria Transmission-Reducing Activity

Malaria is caused by eukaryotic protozoan parasites of the genus Plasmodium. There are 249 million new cases and 608,000 deaths annually, and new interventions are desperately needed. Malaria vaccines can be divided into three categories: liver stage, blood stage, or transmission-blocking vaccines. Transmission-blocking vaccines prevent the transmission of disease by the mosquito vector from one human to another. Pfs230 is one of the leading transmission-blocking vaccine antigens for malaria. Here, we describe the development of a 24-copy self-assembling nanoparticle vaccine comprising domain 1 of Pfs230 genetically fused to H. pylori ferritin. The single-component Pfs230D1-ferritin construct forms a stable and homogenous 24-copy nanoparticle with good production yields. The nanoparticle is highly immunogenic, as two low-dose vaccinations of New Zealand White rabbits elicited a potent and durable antibody response with high transmission-reducing activity when formulated in two distinct adjuvants suitable for translation to human use. This single-component 24-copy Pfs230D1-ferritin nanoparticle vaccine has the potential to improve production pipelines and the cost of manufacturing a potent and durable transmission-blocking vaccine for malaria control.

Structure-guided design of VAR2CSA-based immunogens and a cocktail strategy for a placental malaria vaccine

Placental accumulation of Plasmodium falciparum infected erythrocytes results in maternal anemia, low birth weight, and pregnancy loss. The parasite protein VAR2CSA facilitates the accumulation of infected erythrocytes in the placenta through interaction with the host receptor chondroitin sulfate A (CSA). Antibodies that prevent the VAR2CSA-CSA interaction correlate with protection from placental malaria, and VAR2CSA is a high-priority placental malaria vaccine antigen. Here, structure-guided design leveraging the full-length structures of VAR2CSA produced a stable immunogen that retains the critical conserved functional elements of VAR2CSA. The design expressed with a six-fold greater yield than the full-length protein and elicited antibodies that prevent adhesion of infected erythrocytes to CSA. The reduced size and adaptability of the designed immunogen enable efficient production of multiple variants of VAR2CSA for use in a cocktail vaccination strategy to increase the breadth of protection. These designs form strong foundations for the development of potent broadly protective placental malaria vaccines.

mRNA vaccines expressing malaria transmission-blocking antigens Pfs25 and Pfs230D1 induce a functional immune response

Malaria transmission-blocking vaccines (TBV) are designed to inhibit the sexual stage development of the parasite in the mosquito host and can play a significant role in achieving the goal of malaria elimination. Preclinical and clinical studies using protein-protein conjugates of leading TBV antigens Pfs25 and Pfs230 domain 1 (Pfs230D1) have demonstrated the feasibility of TBV. Nevertheless, other promising vaccine platforms for TBV remain underexplored. The recent success of mRNA vaccines revealed the potential of this technology for infectious diseases. We explored the mRNA platform for TBV development. mRNA constructs of Pfs25 and Pfs230D1 variously incorporating signal peptides (SP), GPI anchor, and Trans Membrane (TM) domain were assessed in vitro for antigen expression, and selected constructs were evaluated in mice. Only mRNA constructs with GPI anchor or TM domain that resulted in high cell surface expression of the antigens yielded strong immune responses in mice. These mRNA constructs generated higher transmission-reducing functional activity versus the corresponding alum-adjuvanted protein-protein conjugates used as comparators. Pfs25 mRNA with GPI anchor or TM maintained >99% transmission reducing activity through 126 days, the duration of the study, demonstrating the potential of mRNA platform for TBV.

Aotus nancymaae model predicts human immune response to the placental malaria vaccine candidate VAR2CSA

Placental malaria vaccines (PMVs) are being developed to prevent severe sequelae of placental malaria (PM) in pregnant women and their offspring. The leading candidate vaccine antigen VAR2CSA mediates parasite binding to placental receptor chondroitin sulfate A (CSA). Despite promising results in small animal studies, recent human trials of the first two PMV candidates (PAMVAC and PRIMVAC) generated limited cross-reactivity and cross-inhibitory activity to heterologous parasites. Here we immunized Aotus nancymaae monkeys with three PMV candidates (PAMVAC, PRIMVAC and ID1-ID2a_M1010) adjuvanted with Alhydrogel, and exploited the model to investigate boosting of functional vaccine responses during PM episodes as well as with nanoparticle antigens. PMV candidates induced high levels of antigen-specific IgG with significant cross-reactivity across PMV antigens by enzyme-linked immunosorbent assay. Conversely, PMV antibodies recognized native VAR2CSA and blocked CSA adhesion of only homologous parasites and not of heterologous parasites. PM episodes did not significantly boost VAR2CSA antibody levels or serum functional activity; nanoparticle and monomer antigens alike boosted serum reactivity but not functional activities. Overall, PMV candidates induced functional antibodies with limited heterologous activity in Aotus monkeys, similar to responses reported in humans. The Aotus model appears suitable for preclinical downselection of PMV candidates and assessment of antibody boosting by PM episodes.

Structure-based design of a strain transcending AMA1-RON2L malaria vaccine

Apical membrane antigen 1 (AMA1) is a key malaria vaccine candidate and target of neutralizing antibodies. AMA1 binds to a loop in rhoptry neck protein 2 (RON2L) to form the moving junction during parasite invasion of host cells, and this complex is conserved among apicomplexan parasites. AMA1-RON2L complex immunization achieves higher growth inhibitory activity than AMA1 alone and protects mice against Plasmodium yoelii challenge. Here, three single-component AMA1-RON2L immunogens were designed that retain the structure of the two-component AMA1-RON2L complex: one structure-based design (SBD1) and two insertion fusions. All immunogens elicited high antibody titers with potent growth inhibitory activity, yet these antibodies did not block RON2L binding to AMA1. The SBD1 immunogen induced significantly more potent strain-transcending neutralizing antibody responses against diverse strains of Plasmodium falciparum than AMA1 or AMA1-RON2L complex vaccination. This indicates that SBD1 directs neutralizing antibody responses to strain-transcending epitopes in AMA1 that are independent of RON2L binding. This work underscores the importance of neutralization mechanisms that are distinct from RON2 blockade. The stable single-component SBD1 immunogen elicits potent strain-transcending protection that may drive the development of next-generation vaccines for improved malaria and apicomplexan parasite control.

A potent and durable malaria transmission-blocking vaccine designed from a single-component 60-copy Pfs230D1 nanoparticle

Malaria transmission-blocking vaccines (TBVs) reduce disease transmission by breaking the continuous cycle of infection between the human host and the mosquito vector. Domain 1 (D1) of Pfs230 is a leading TBV candidate and comprises the majority of transmission-reducing activity (TRA) elicited by Pfs230. Here we show that the fusion of Pfs230D1 to a 60-copy multimer of the catalytic domain of dihydrolipoyl acetyltransferase protein (E2p) results in a single-component nanoparticle composed of 60 copies of the fusion protein with high stability, homogeneity, and production yields. The nanoparticle presents a potent human transmission-blocking epitope within Pfs230D1, indicating the antigen is correctly oriented on the surface of the nanoparticle. Two vaccinations of New Zealand White rabbits with the Pfs230D1 nanoparticle elicited a potent and durable antibody response with high TRA when formulated in two distinct adjuvants suitable for translation to human use. This single-component nanoparticle vaccine may play a key role in malaria control and has the potential to improve production pipelines and the cost of manufacturing of a potent and durable TBV.

Preclinical evaluations of Pfs25-EPA and Pfs230D1-EPA in AS01 for a vaccine to reduce malaria transmission

Malaria transmission-blocking vaccine candidates Pfs25-EPA and Pfs230D1-EPA target sexual stage development of Plasmodium falciparum parasites in the mosquito host, thereby reducing mosquito infectivity. When formulated on Alhydrogel, Pfs25-EPA has demonstrated safety and immunogenicity in a phase 1 field trial, while Pfs230D1-EPA has shown superior activity to Pfs25-EPA in a phase 1 US trial and has entered phase 2 field trials. Development continues to enhance immunogenicity of these candidates toward producing a vaccine to reduce malaria transmission (VRMT) with both pre-erythrocytic (i.e., anti-infection) and transmission-blocking components. GSK Adjuvant Systems have demonstrated successful potency in pre-erythrocytic vaccine trials and might offer a common platform for VRMT development. Here, we describe preclinical evaluations of Pfs25-EPA and Pfs230D1-EPA nanoparticles with GSK platforms. Formulations were stable after a series of assessments and induced superior antibody titers and functional activity in CD-1 mice, compared to Alhydrogel formulations of the same antigens.

Structural and immunological differences in Plasmodium falciparum sexual stage transmission-blocking vaccines comprised of Pfs25-EPA nanoparticles

Development of a malaria vaccine that blocks transmission of different parasite stages to humans and mosquitoes is considered critical for elimination efforts. A vaccine using Pfs25, a protein on the surface of zygotes and ookinetes, is under investigation as a transmission-blocking vaccine (TBV) that would interrupt parasite passage from mosquitoes to humans. The most extensively studied Pfs25 TBVs use Pichia pastoris-produced recombinant forms of Pfs25, chemically conjugated to a recombinant carrier protein, ExoProtein A (EPA). The recombinant form of Pfs25 first used in humans was identified as Pfs25H, which contained a total of 14 heterologous amino acid residues located at the amino- and carboxyl-termini including a His6 affinity tag. A second recombinant Pfs25, identified as Pfs25M, was produced to remove the heterologous amino acid residues and conjugated to EPA (Pfs25M-EPA). Here, monomeric Pfs25M was characterized biochemically and biophysically for identity, purity, and integrity including protein structure to assess its comparability with Pfs25H. Although the biological activities of Pfs25H and Pfs25M, whether generated by monomeric forms or conjugated nanoparticles, appeared similar, fine-mapping studies with two transmission-blocking monoclonal antibodies detected structural and immunological differences. In addition, evaluation of antisera generated against conjugated Pfs25H or Pfs25M nanoparticles in nonhuman primates identified polyclonal IgG that recognized these structural differences.

Design of a stabilized RBD enables potently neutralizing SARS-CoV-2 single-component nanoparticle vaccines

Waning immunity and emerging variants necessitate continued vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Improvements in vaccine safety, tolerability, and ease of manufacturing would benefit these efforts. Here, we develop a potent and easily manufactured nanoparticle vaccine displaying the spike receptor-binding domain (RBD). Computational design to stabilize the RBD, eliminate glycosylation, and focus the immune response to neutralizing epitopes results in an RBD immunogen that resolves issues hindering the efficient nanoparticle display of the native RBD. This non-glycosylated RBD can be genetically fused to diverse single-component nanoparticle platforms, maximizing manufacturing ease and flexibility. All engineered RBD nanoparticles elicit potently neutralizing antibodies in mice that far exceed monomeric RBDs. A 60-copy particle (noNAG-RBD-E2p) also elicits potently neutralizing antibodies in non-human primates. The neutralizing antibody titers elicited by noNAG-RBD-E2p are comparable to a benchmark stabilized spike antigen and reach levels against Omicron BA.5 that suggest that it would provide protection against emerging variants.

Design of a stabilized non-glycosylated Pfs48/45 antigen enables a potent malaria transmission-blocking nanoparticle vaccine

A malaria vaccine that blocks parasite transmission from human to mosquito would be a powerful method of disrupting the parasite lifecycle and reducing the incidence of disease in humans. Pfs48/45 is a promising antigen in development as a transmission blocking vaccine (TBV) against the deadliest malaria parasite Plasmodium falciparum. The third domain of Pfs48/45 (D3) is an established TBV candidate, but production challenges have hampered development. For example, to date, a non-native N-glycan is required to stabilize the domain when produced in eukaryotic systems. Here, we implement a SPEEDesign computational design and in vitro screening pipeline that retains the potent transmission blocking epitope in Pfs48/45 while creating a stabilized non-glycosylated Pfs48/45 D3 antigen with improved characteristics for vaccine manufacture. This antigen can be genetically fused to a self-assembling single-component nanoparticle, resulting in a vaccine that elicits potent transmission-reducing activity in rodents at low doses. The enhanced Pfs48/45 antigen enables many new and powerful approaches to TBV development, and this antigen design method can be broadly applied towards the design of other vaccine antigens and therapeutics without interfering glycans.

Design of the SARS-CoV-2 RBD vaccine antigen improves neutralizing antibody response

The receptor binding domain (RBD) of the SARS-CoV-2 spike protein is the primary target of neutralizing antibodies and is a component of almost all current vaccines. Here, RBD immunogens were created with stabilizing amino acid changes that improve the neutralizing antibody response, as well as characteristics for production, storage, and distribution. A computational design and in vitro screening platform identified three improved immunogens, each with approximately nine amino acid changes relative to the native RBD sequence, and four key changes conserved between immunogens. The changes are adaptable to all vaccine platforms and compatible with mutations in emerging variants of concern. The immunogens elicit higher levels of neutralizing antibodies than native RBD, focus the immune response to structured neutralizing epitopes, and have increased production yields and thermostability. Incorporating these variant-independent amino acid changes in next-generation COVID vaccines may enhance the neutralizing antibody response and lead to longer duration and broader protection.

Efficient infection of non-human primates with purified, cryopreserved Plasmodium knowlesi sporozoites

Background

Plasmodium falciparum (Pf) sporozoite (SPZ) vaccines are the only candidate malaria vaccines that induce > 90% vaccine efficacy (VE) against controlled human malaria infection and the only malaria vaccines to have achieved reproducible VE against malaria in adults in Africa. The goal is to increase the impact and reduce the cost of PfSPZ vaccines by optimizing vaccine potency and manufacturing, which will benefit from identification of immunological responses contributing to protection in humans. Currently, there is no authentic animal challenge model for assessing P. falciparum malaria VE. Alternatively, Plasmodium knowlesi (Pk), which infects humans and non-human primates (NHPs) in nature, can be used to experimentally infect rhesus macaques (Macaca mulatta) to assess VE.

Methods

Sanaria has, therefore, produced purified, vialed, cryopreserved PkSPZ and conducted challenge studies in several naïve NHP cohorts. In the first cohort, groups of three rhesus macaques each received doses of 5 × 10², 2.5 × 10³, 1.25 × 10⁴ and 2.5 × 10⁴ PkSPZ administered by direct venous inoculation. The infectivity of 1.5 × 10³ PkSPZ cryopreserved with an altered method and of 1.5 × 10³ PkSPZ cryopreserved for four years was tested in a second and third cohort of rhesus NHPs. The lastly, three pig-tailed macaques (Macaca nemestrina), a natural P. knowlesi host, were challenged with 2.5 × 10³ PkSPZ cryopreserved six years earlier.

Results

In the first cohort, all 12 animals developed P. knowlesi parasitaemia by thick blood smear, and the time to positivity (prepatent period) followed a non-linear 4-parameter logistic sigmoidal model with a median of 11, 10, 8, and 7 days, respectively (r² = 1). PkSPZ cryopreserved using a modified rapid-scalable method infected rhesus with a pre-patent period of 10 days, as did PkSPZ cryopreserved four years prior to infection, similar to the control group. Cryopreserved PkSPZ infected pig-tailed macaques with median time to positivity by thin smear, of 11 days.

Conclusion

This study establishes the capacity to consistently infect NHPs with purified, vialed, cryopreserved PkSPZ, providing a foundation for future studies to probe protective immunological mechanisms elicited by PfSPZ vaccines that cannot be established in humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-022-04261-z.

Plasmodium falciparum in Aotus nancymaae: A New Model for Placental Malaria

Plasmodium falciparum-infected erythrocytes that display the variant surface antigen VAR2CSA bind chondroitin sulfate A (CSA) to sequester in placental intervillous spaces, causing severe sequelae for mother and offspring. Here, we establish a placental malaria (PM) monkey model. Pregnant Aotus infected with CSA-binding P. falciparum CS2 parasites during the third trimester developed pronounced sequestration of late-stage parasites in placental intervillous spaces that express VAR2CSA and bind specifically to CSA. Similar to immune multigravid women, a monkey infected with P. falciparum CS2 parasites over successive pregnancies acquired antibodies against VAR2CSA, with potent functional activity that was boosted upon subsequent pregnancy infections. Aotus also developed functional antibodies after multiple acute PM episodes and subsequent VAR2CSA immunization. In summary, P. falciparum infections in pregnant Aotus monkeys recapitulate all the prominent features of human PM infection and immunity, and this model can be useful for basic mechanistic studies and preclinical studies to qualify candidate PM vaccines. Clinical Trials Registration: NCT02471378.

Protein-protein conjugation enhances the immunogenicity of SARS-CoV-2 receptor-binding domain (RBD) vaccines

Several effective SARS-CoV-2 vaccines have been developed using different technologies. Although these vaccines target the isolates collected early in the pandemic, many have protected against serious illness from newer variants. Nevertheless, efficacy has diminished against successive variants and the need for effective and affordable vaccines persists especially in the developing world. Here, we adapted our protein-protein conjugate vaccine technology to generate a vaccine based on receptor-binding domain (RBD) antigen. RBD was conjugated to a carrier protein, EcoCRM®, to generate two types of conjugates: crosslinked and radial conjugates. In the crosslinked conjugate, antigen and carrier are chemically crosslinked; in the radial conjugate, the antigen is conjugated to the carrier by site-specific conjugation. With AS01 adjuvant, both conjugates showed enhanced immunogenicity in mice compared to RBD, with a Th1 bias. In hACE2 binding inhibition and pseudovirus neutralization assays, sera from mice vaccinated with the radial conjugate demonstrated strong functional activity.

Detection of early myocardial cell death in owl monkeys (Aotus nancymai) using complement component C9 immunohistochemistry in formalin-fixed paraffin-embedded heart tissues: A retrospective study

BACKGROUND

Owl monkeys are commonly used in biomedical research which is affected by the high incidence of cardiomyopathy in this species. Occasionally, owl monkeys with no clinical signs of heart disease are found dead and at necropsy show no, or very mild, cardiomyopathy. A possible explanation for sudden death is acute myocardial infarction; however, early myocardial changes may be difficult to assess by conventional stains and light microscopy.

METHODS

Complement component C9 immunohistochemistry was performed in paraffin-embedded heart tissue samples from owl monkeys who died suddenly, or were euthanized due to sickness, to determine whether these animals suffered from acute myocardial infarcts.

RESULTS AND CONCLUSION

C9 deposits were found in the myocardium of 19 out of 20 (95%) animals. The findings in this study suggest owl monkeys suffer from acute myocardial infarcts, and complement component C9 immunohistochemistry may be a useful diagnostic tool.

Design of the SARS-CoV-2 RBD vaccine antigen improves neutralizing antibody response

The receptor binding domain (RBD) of the SARS-CoV-2 spike protein is the primary target of neutralizing antibodies and is a component of almost all vaccine candidates. Here, RBD immunogens were created with stabilizing amino acid changes that improve the neutralizing antibody response, as well as characteristics for production, storage, and distribution. A computational design and in vitro screening platform identified three improved immunogens, each with approximately nine amino acid changes relative to the native RBD sequence and four key changes conserved between immunogens. The changes are adaptable to all vaccine platforms, are compatible with established changes in SARS-CoV-2 vaccines, and are compatible with mutations in emerging variants of concern. The immunogens elicit higher levels of neutralizing antibodies than native RBD, focus the immune response to structured neutralizing epitopes, and have increased production yields and thermostability. Incorporating these variant-independent amino acid changes in next-generation vaccines may enhance the neutralizing antibody response and lead to pan-SARS-CoV-2 protection.

Pfs230 yields higher malaria transmission-blocking vaccine activity than Pfs25 in humans but not mice

BACKGROUNDVaccines that block human-to-mosquito Plasmodium transmission are needed for malaria eradication, and clinical trials have targeted zygote antigen Pfs25 for decades. We reported that a Pfs25 protein-protein conjugate vaccine formulated in alum adjuvant induced serum functional activity in both US and Malian adults. However, antibody levels declined rapidly, and transmission-reducing activity required 4 vaccine doses. Functional immunogenicity and durability must be improved before advancing transmission-blocking vaccines further in clinical development. We hypothesized that the prefertilization protein Pfs230 alone or in combination with Pfs25 would improve functional activity.METHODSTransmission-blocking vaccine candidates based on gamete antigen Pfs230 or Pfs25 were conjugated with Exoprotein A, formulated in Alhydrogel, and administered to mice, rhesus macaques, and humans. Antibody levels were measured by ELISA and transmission-reducing activity was assessed by the standard membrane feeding assay.RESULTSPfs25-EPA/Alhydrogel and Pfs230D1-EPA/Alhydrogel induced similar serum functional activity in mice, but Pfs230D1-EPA induced significantly greater activity in rhesus monkeys that was enhanced by complement. In US adults, 2 vaccine doses induced complement-dependent activity in 4 of 5 Pfs230D1-EPA/Alhydrogel recipients but no significant activity in 5 Pfs25-EPA recipients, and combination with Pfs25-EPA did not increase activity over Pfs230D1-EPA alone.CONCLUSIONThe complement-dependent functional immunogenicity of Pfs230D1-EPA represents a significant improvement over Pfs25-EPA in this comparative study. The rhesus model is more predictive of the functional human immune response to Pfs230D1 than is the mouse model.TRIAL REGISTRATIONClinicalTrials.gov NCT02334462.FUNDINGIntramural Research Program of the National Institute of Allergy and Infectious Diseases, National Institutes of Health.

Comparison of carrier proteins to conjugate malaria transmission blocking vaccine antigens, Pfs25 and Pfs230

Malaria transmission blocking vaccines (TBV) target the sexual stage of the parasite and have been pursued as a stand-alone vaccine or for combination with pre-erythrocytic or blood stage vaccines. Our efforts to develop TBV focus primarily on two antigens, Pfs25 and Pfs230. Chemical conjugation of these poorly immunogenic antigens to carrier proteins enhances their immunogenicity, and conjugates of these antigens to Exoprotein A (EPA) are currently under evaluation in clinical trials. Nonetheless, more potent carriers may augment the immunogenicity of these antigens for a more efficacious vaccine; here, we evaluate a series of proteins to identify such a carrier. Pfs25 and Pfs230 were chemically conjugated to 4 different carriers [tetanus toxoid (TT), a recombinant fragment of tetanus toxin heavy chain (rTThc), recombinant CRM197 produced in Pseudomonas fluorescens (CRM197) or in E. coli (EcoCRM®)] and compared to EPA conjugates in mouse immunogenicity studies. Conjugates of each antigen formulated in Alhydrogel® elicited similar antibody titers but showed differences in functional activity. At a 0.5 µg dose, Pfs230 conjugated to TT, CRM197 and EcoCRM® showed significantly higher functional activity compared to EPA. When formulated with the more potent adjuvant GLA-LSQ, all 4 alternate conjugates induced higher antibody titers as well as increased functional activity compared to the EPA conjugate. IgG subclass analysis of Pfs230 conjugates showed no carrier-dependent differences in the IgG profile. While Alhydrogel® formulations induced a Th2 dominant immune response, GLA-LSQ formulations induced a mixed Th1/Th2 response.

A primate model of severe malarial anaemia: a comparative pathogenesis study

Severe malarial anaemia (SMA) is the most common life-threatening complication of Plasmodium falciparum infection in African children. SMA is characterised by haemolysis and inadequate erythropoiesis, and is associated with dysregulated inflammatory responses and reduced complement regulatory protein levels (including CD35). However, a deeper mechanistic understanding of the pathogenesis requires improved animal models. In this comparative study of two closely related macaque species, we interrogated potential causal factors for their differential and temporal relationships to onset of SMA. We found that rhesus macaques inoculated with blood-stage Plasmodium coatneyi developed SMA within 2 weeks, with no other severe outcomes, whereas infected cynomolgus macaques experienced only mild/ moderate anaemia. The abrupt drop in haematocrit in rhesus was accompanied by consumption of haptoglobin (haemolysis) and poor reticulocyte production. Rhesus developed a greater inflammatory response than cynomolgus macaques, and had lower baseline levels of CD35 on red blood cells (RBCs) leading to a significant reduction in the proportion of CD35⁺ RBCs during infection. Overall, severe anaemia in rhesus macaques infected with P. coatneyi has similar features to SMA in children. Our comparisons are consistent with an association of low baseline CD35 levels on RBCs and of early inflammatory responses with the pathogenesis of SMA.

Plasmodium vivax chloroquine resistance links to pvcrt transcription in a genetic cross

Mainstay treatment for Plasmodium vivax malaria has long relied on chloroquine (CQ) against blood-stage parasites plus primaquine against dormant liver-stage forms (hypnozoites), however drug resistance confronts this regimen and threatens malaria control programs. Understanding the basis of P. vivax chloroquine resistance (CQR) will inform drug discovery and malaria control. Here we investigate the genetics of P. vivax CQR by a cross of parasites differing in drug response. Gametocytogenesis, mosquito infection, and progeny production are performed with mixed parasite populations in nonhuman primates, as methods for P. vivax cloning and in vitro cultivation remain unavailable. Linkage mapping of progeny surviving >15 mg/kg CQ identifies a 76 kb region in chromosome 1 including pvcrt, an ortholog of the Plasmodium falciparum CQR transporter gene. Transcriptional analysis supports upregulated pvcrt expression as a mechanism of CQR.

Genetic diversity of Klebsiella pneumoniae isolates during an outbreak in a non-human primate research colony

BACKGROUND

Klebsiella pneumoniae can be a serious pathogen in non-human primates, particularly Neotropical monkeys.

METHODS

During a K. pneumoniae outbreak in an owl monkey research colony, 13 K. pneumoniae isolates were DNA fingerprinted by automated repetitive extragenic palindromic-polymerase chain reaction and the profiles compared to isolates obtained from other non-human primate species during the same time period and isolates from previous outbreaks.

RESULTS

Eleven different types of K. pneumoniae were circulating in the owl monkey colony at the time of the outbreak. When comparing owl monkey isolates relatedness to previous colony outbreak isolates and squirrel monkey and capuchin monkey isolates, all were different.

CONCLUSIONS

These results agree with recent reports where K. pneumoniae nosocomial isolates in hospital settings can have high genetic diversity, and multiple strains can be circulating simultaneously. This potential genetic diversity should be considered when designing strategies for controlling K. pneumoniae outbreaks in captive non-human primate colonies.

A PfRH5-based vaccine is efficacious against heterologous strain blood-stage Plasmodium falciparum infection in aotus monkeys

Antigenic diversity has posed a critical barrier to vaccine development against the pathogenic blood-stage infection of the human malaria parasite Plasmodium falciparum. To date, only strain-specific protection has been reported by trials of such vaccines in nonhuman primates. We recently showed that P. falciparum reticulocyte binding protein homolog 5 (PfRH5), a merozoite adhesin required for erythrocyte invasion, is highly susceptible to vaccine-inducible strain-transcending parasite-neutralizing antibody. In vivo efficacy of PfRH5-based vaccines has not previously been evaluated. Here, we demonstrate that PfRH5-based vaccines can protect Aotus monkeys against a virulent vaccine-heterologous P. falciparum challenge and show that such protection can be achieved by a human-compatible vaccine formulation. Protection was associated with anti-PfRH5 antibody concentration and in vitro parasite-neutralizing activity, supporting the use of this in vitro assay to predict the in vivo efficacy of future vaccine candidates. These data suggest that PfRH5-based vaccines have potential to achieve strain-transcending efficacy in humans.

•

Vaccines based on the P. falciparum merozoite antigen PfRH5 were tested in Aotus monkeys

•

PfRH5-based vaccines afforded protection against heterologous strains of P. falciparum

•

Protection correlated with anti-PfRH5 IgG concentration and in vivo neutralization

Pancreatic endocrine tumour with disseminated pulmonary thromboembolism in an owl monkey (Aotus nancymae)

Pulmonary thromboembolism associated with pancreatic endocrine neoplasia is extremely uncommon in man and animals. Post-mortem examination of an adult owl monkey (Aotus nancymae) revealed extensive pulmonary arterial thromboembolism and a well-demarcated mass attached to the pancreas. Microscopically, the mass consisted of areas of interstitial fibrosis with loss of acini and islets and replacement by nests and sheets of polygonal cells with amphophilic cytoplasm, an eccentric round nucleus with stippled chromatin and, in some cells, with a single prominent eccentric nucleolus. Clusters of these cells were noted within vessels and adjacent lymph nodes. The cells did not express S100 or insulin, but were labelled strongly with SP-1/chromogranin. Rare individual cells expressed glucagon and somatostatin. A few cells in pulmonary thrombi/emboli and the adjacent lymph node also expressed SP-1/chromogranin. Based on cell morphology, location and immunohistochemistry the tumour was classified as pancreatic endocrine (islet cell) carcinoma with metastasis to regional lymph nodes and lung.

Ureteral fibroepithelial polyp in an owl monkey (Aotus nancymae)

Ureteral fibroepithelial polyps are benign mesodermal tumors in humans that occur predominantly in the proximal ureter. During a routine necropsy of a wild-caught, research naïve, adult, male, Aotus nancymae, the left ureter just distal to the renal pelvis contained a pedunculated, lobulated neoplasm with a narrow stalk at the base projecting into the lumen. The left renal pelvis was found to be mildly dilated. The histologic characteristics of the ureteral mass were consistent with a fibroepithelial polyp. To our knowledge, this is the first report describing a ureteral fibroepithelial polyp in a nonhuman primate.

Characterization of the antigen-presenting cell and T cell requirements for induction of pulmonary eosinophilia in a murine model of asthma

A model of allergic pulmonary inflammation is described in which the intraperitoneal injection of antigen (Ag)-pulsed cells resulted in T cell priming. Mice received two injections of 10(6) elicited peritoneal macrophages, which had been incubated with Ag for 48 hr, on Days 0 and 6, followed by an aerosol Ag challenge on Day 19. Bronchoalveolar lavage fluid harvested on Day 21 contained increased eosinophil numbers and resembled the cell influx observed following immunization with Ag in alum. Incubation of Ag-presenting cells with interferon-gamma resulted in increased expression of the costimulator molecule B7-2 and of MHC Ags, but did not enhance priming capacity. Using this system, antibodies to CD4 and CD8 were tested for their ability to block sensitization by Ag-pulsed cells. Both anti-CD4 and anti-CD8 antibodies completely blocked the airway eosinophil response following aerosol Ag challenge. This model will be very useful for characterization of the interactions between Ag-presenting cells and T cells which ultimately result in the induction of pulmonary eosinophilia.

Polymorphism in the beta chain of IAq versus IAp influences presentation of protein but not peptide antigens

T cells play a critical role in the development of collagen-induced arthritis (CIA). Immunization with heterologous (chick) type II collagen (cII) results in chronic inflammation with progressive damage to the joints. The expression of specific MHC Class II alpha beta dimers, including IAq, is critical to induction of disease. The alpha chains of IAq and IAp are identical in sequence. The IAq and IAp beta chains differ by only four amino acid residues: 85, 86, 88, and 89. However, mice of the H-2p haplotype are not susceptible to CIA. To examine the impact of these structural differences in IA molecules on T cell Ag recognition, we studied presentation of cII peptides and denatured cII by APCs obtained from H-2q and H-2p mice. We also assessed presentation of ovalbumin, myelin basic protein (MBP), and MBP peptides by these APC populations. H-2q APCs presented both peptides and proteins to our T cell hybrids. In contrast, APCs obtained from H-2p mice presented peptides, but were defective in the processing and/or presentation of protein Ags. We then altered pairs of the residues in IAq to those found in IAp using site-directed mutagenesis and transfected these constructs into M 12.C3 B cells. All transfectants were able to present peptides, but those expressing IAp were unable to present protein Ags. The use of transfectants expressing hybrid molecules (residues 85 and 86 from IAp, 88 and 89 from IAq, or vice versa) allowed us to localize the region responsible for this defect to residues 85 and 86 of the beta chain. The presence of IAp residues (glu and thr versus gly and val in IAq) at these sites severely compromised the capacity for protein presentation. Resistance to CIA in H-2p haplotype mice may be a reflection of the limited repertoire of epitopes to which these mice can respond relative to susceptible H-2q mice.

The importance of DR4Dw4 beta chain residues 70, 71, and 86 in peptide binding and T cell recognition

The expression of specific alleles of the human HLA-DR locus is associated with increased risk for the development of rheumatoid arthritis. Examination of the amino acid sequence of the DR beta chain has revealed that risk for RA correlates with a cluster of polymorphic residues located between positions 67 and 86, and in particular with the identity of residues 70, 71, and 86. To examine the contributions of these HLA-DR polymorphic residues to antigen-specific T cell responses, the DRB1*0401 gene was subjected to site-directed mutagenesis and forms possessing alanine in place of the naturally occurring amino acid at positions 70, 71, 86, and 70/71 were generated. The mutated genes were coexpressed with the DRA gene in Chinese hamster ovary cells and the transfectants were tested as stimulator cells for a panel of three human influenza virus hemagglutinin-specific T cell clones. Additionally, soluble forms of the mutant DR molecules were examined for their ability to bind peptide. All of the mutants had a modest loss of affinity for the peptide relative to the wild type, but there were no significant differences in peptide binding ability among the substituted molecules. In contrast to the relatively uniform influence on peptide binding, the impact of these mutations on T cell stimulation was heterogeneous. Specifically, these studies indicate that residue 71 plays a critical role in T cell stimulation either through direct contact with the T cell receptor or by changing the orientation or conformation of the peptide-MHC complex. Replacement of residue 71 with alanine abrogated stimulation of all of the T cell clones. Two of three clones were affected by changes at residue 70 while none lost recognition when amino acid 86 was converted from Val to Ala. These data emphasize that subtle alterations in structure can have a profound impact on T cell recognition.

Effects of an S-adenosyl-L-homocysteine hydrolase inhibitor on murine macrophage activation and function

The S-adenosyl-L-homocysteine (AdoHcy) hydrolase inhibitor MDL 28,842 has been demonstrated to be a potent inhibitor of T-cell activation, both in vitro and in vivo. Although the inhibition of T cells in vitro was independent of macrophages, the direct effect of MDL 28,842 on macrophages is unknown. In this report the effects of MDL 28,842 on macrophage cytokine production, cell-surface antigen expression, and antigen processing and presentation were examined. Lipopolysaccharide (LPS) stimulation of IL-1 synthesis by peritoneal macrophages was not effected by MDL 28,842 using cells obtained from B10.A and B10.B mice and weakly inhibited using cells from BALB/C mice (IC50 > 10 microM). In contrast, TNF-alpha synthesis by BALB/C macrophages was inhibited by MDL 28,842 with an IC50 < 0.1 microM. B10.A and B10.B macrophages did not produce detectable TNF-alpha in response to LPS in this system. Treatment with 1-10 microM MDL 28,842 resulted in a modest decrease in major histocompatibility complex class II (MHC-II) determinant expression by Interferon-gamma-activated macrophages. The expression of other cell-surface markers was not altered in the presence of MDL 28,842. The processing of antigen and its presentation by MHC class-II-positive macrophages to a T-cell hybridoma was also not affected by incubation with MDL 28,842.)

Structural requirements for recognition of a type II collagen peptide by murine T cell hybridomas

T lymphocytes play a critical role in the development of murine collagen-induced arthritis (CIA), a syndrome which shares many features with rheumatoid arthritis. In susceptible mouse strains, immunization with type II collagen (cII) results in chronic inflammation with progressive joint destruction. To examine T cell recognition of cII we have isolated T cell hybridomas specific for a cII peptide fragment, cII260-270 (IAGFKGEQGPK). We assessed the importance of particular amino acid residues to formation of the MHC Class II-peptide complex and interaction of this complex with TCRs. Our results indicate that critical residues are concentrated in the N-terminal half of the peptide, with Lys264 and Glu266 having the greatest influence. Replacement of these residues with alanine resulted in loss of detectable activity. Three other residues, Ile260, Gly262, and Phe263, are also important to T cell stimulation because alanine substitution substantially decreased peptide activity. Truncation analyses supported the conclusion drawn from Ala substitutions that C-terminal residues were dispensable. Other alterations in peptide structure resulted in dramatic increases in stimulatory capacity. For example, replacement of either Gly265 or Gly268 with alanine resulted in a 10-fold increase in potency. The addition of 2-5 residues to the N-terminus of the peptide decreased the dose required for maximal T cell stimulation by > 100-fold. The T cell hybridomas exhibited remarkable similarity in their peptide recognition profiles although they express different TCR V beta elements.

A protective role for nitric oxide in the oxidative modification of low density lipoproteins by mouse macrophages

Low density lipoproteins (LDL) oxidatively modified by macrophages have been shown to be atherogenic in ex vivo studies. We studied the potential role of nitric oxide (NO), a free radical produced by macrophages, in LDL modification. Human LDL (1 mg/ml) were incubated with mouse peritoneal macrophages in Ham's F-10 medium. The cells were then stimulated by interferon-gamma and tumor necrosis factor-alpha to increase their production of NO from 1.3 to 12.2 microM in 24 h, as measured by nitrite. Lipid peroxidation of LDL, as measured by thiobarbituric acid-reactive materials (TBARS), was reduced in stimulated cells in a time-dependent manner. At 24 h, the decrease was about 27%. In the presence of an NO synthase inhibitor (NG-aminophomoarginine), the generation of NO was diminished and the protection against LDL lipid peroxidation was reversed. The extent of LDL protein modification was also assessed by examining its electrophoretic mobility. It was found that macrophage NO reduced the change in LDL electromobility. These data indicate that the production of NO may inhibit the oxidative modification of LDL with cytokine-stimulated macrophages. We suggest that NO plays a protective role in limiting macrophage-induced LDL modification.

Characterization of cell selectivity of two novel inhibitors of nitric oxide synthesis

We have assessed the capacity of two novel inhibitors to block cytokine-induced nitric oxide (NO) synthesis by macrophages and vascular smooth muscle cells, as well as NO production by the constitutive enzyme in central nervous system tissue. NG-Cyclopropyl-L-arginine selectively inhibited Ca2+/calmodulin-dependent NO synthesis, with an IC50 of 0.55 microM in brain versus 184 and 258 microM in macrophages and vascular smooth muscle cells, respectively. In contrast, NG-amino-L-homoarginine blocked NO production by all of the cell types examined, with IC50 values ranging from 6.6 to 26 microM. Both inhibitors were active in an in vivo model of endotoxic shock.

Nitric oxide synthase inhibitors inhibit interleukin-1 beta-induced depression of vascular smooth muscle

Interleukin-1 beta (IL-1) reduces vascular smooth muscle contractility. The purpose of the present study was to investigate the role of nitric oxide synthesis in mediating this effect of IL-1. We studied the influence of inhibitors of nitric oxide synthesis on the depression of norepinephrine-induced contractions of rat aortic rings by IL-1. Also, we examined the ability of IL-1 to increase the production of nitric oxide by rat aortic smooth muscle cells in culture as determined indirectly by measuring nitrite concentrations. NG-amino-L-arginine blocked the effect of IL-1 on norepinephrine-induced contractions of rat aortic rings whereas NG-monomethyl-L-arginine and NG-nitro-L-arginine were considerably less effective. In addition, this effect of IL-1 was prevented by coincubation of the rings with cycloheximide. IL-1 greatly elevated nitrite production by rat aortic smooth muscle cells, and this effect could also be blocked completely by the arginine analogs. NG-amino-L-arginine was the most potent inhibitor of nitrite synthesis (IC50 = 1.7 microM) whereas NG-monomethyl-L-arginine and NG-nitro-L-arginine were about 10-fold less potent (IC50 = 16 and 22 microM, respectively). These results suggest that IL-1-induced depression of norepinephrine-induced vascular contraction is mediated by the increased synthesis of nitric oxide synthase by vascular smooth muscle cells. The relative potency of the arginine analogs for the inhibition of nitrite synthesis suggests that the synthase in vascular smooth muscle is similar to the synthase in macrophages.

Nitric oxide synthesis in the CNS endothelium and macrophages differs in its sensitivity to inhibition by arginine analogues

Inhibition of nitric oxide production by arginine analogues was examined in three cell systems; macrophages, CNS tissue and endothelial cells. Nitric oxide production was assessed indirectly using in vitro assays measuring nitrite production (macrophages), cGMP elevation (CNS) and acetylcholine-induced relaxation of aortic ring segments (endothelium). NG-monomethyl-L-arginine and NG-amino-L-arginine possessed similar inhibitory activity in all three assays, while NG-nitro-L-arginine displayed a striking selectivity for inhibition of brain and endothelial cell nitric oxide synthesis, with IC50 values of 0.05 microM in the CNS versus 200 microM in macrophages. These results suggest that distinct enzymes are responsible for nitric oxide synthesis in different cell types, and indicate that it may be possible to selectively modulate nitric oxide production in vivo.

Identification and characterization of monoclonal antibodies specific for macrophages at intermediate stages in the tumoricidal activation pathway

Macrophage activation for tumor cell killing is a multistep pathway in which responsive macrophages interact sequentially with priming and triggering stimuli in the acquisition of full tumoricidal activity. A number of mediators have been identified which have activating capability, including in particular IFN-gamma and bacterial LPS. Although the synergistic functional response of normal macrophages to sequential incubation with these activation signals has been well-established, characterization of the intermediate stages in the activation pathway has been difficult. We have developed a model system for examination of various aspects of macrophage activation, through the use of the murine macrophage tumor cell line, RAW 264.7. These cells, like normal macrophages, exhibit a strict requirement for interaction with both IFN-gamma and LPS in the development of tumor cytolytic activity. In addition, these cells can be stably primed by the administration of gamma-radiation. In the studies reported here, we have used RAW 264.7 cells treated with IFN-gamma alone or with IFN-gamma plus LPS to stimulate the production of rat mAb probes recognizing cell surface changes occurring during the activation process. In this way we have identified three Ag associated with intermediate stages of the activation process. One Ag, TM-1, is expressed on RAW 264.7 cells primed by IFN-gamma or gamma-radiation. This surface Ag thus identifies cells at the primed cell intermediate stage of the tumoricidal activation pathway regardless of the mechanism of activation. A second Ag, TM-2, is expressed on IFN-treated RAW 264.7 cells but not on RAW 264.7 cells primed with gamma-radiation alone. Expression of this Ag can be induced by treatment of irradiated cells with IFN-gamma, but is not induced by IFN-gamma treatment of a noncytolytic cell line, WEHI-3. This Ag thus appears to be an IFN-inducible cell surface protein associated specifically with macrophage activation for tumoricidal activity. Finally, Ag TM-3 is detectable on RAW 264.7 cells primed by either IFN-gamma or gamma-radiation, after subsequent triggering of the primed cells with LPS. The addition of the mAb recognizing this antigen to the function assay of tumor cell killing can inhibit they lytic activity of both triggered cells. Thus, this Ag may play a role in the antitumor effector functions of activated macrophages. Overall, the results suggest that these mAb can serve as useful tools for identification of molecules associated with the process of macrophage activation for tumor cell killing.

Identification and characterization of monoclonal antibodies specific for macrophages at intermediate stages in the tumoricidal activation pathway

Macrophage activation for tumor cell killing is a multistep pathway in which responsive macrophages interact sequentially with priming and triggering stimuli in the acquisition of full tumoricidal activity. A number of mediators have been identified which have activating capability, including in particular IFN-gamma and bacterial LPS. Although the synergistic functional response of normal macrophages to sequential incubation with these activation signals has been well-established, characterization of the intermediate stages in the activation pathway has been difficult. We have developed a model system for examination of various aspects of macrophage activation, through the use of the murine macrophage tumor cell line, RAW 264.7. These cells, like normal macrophages, exhibit a strict requirement for interaction with both IFN-gamma and LPS in the development of tumor cytolytic activity. In addition, these cells can be stably primed by the administration of gamma-radiation. In the studies reported here, we have used RAW 264.7 cells treated with IFN-gamma alone or with IFN-gamma plus LPS to stimulate the production of rat mAb probes recognizing cell surface changes occurring during the activation process. In this way we have identified three Ag associated with intermediate stages of the activation process. One Ag, TM-1, is expressed on RAW 264.7 cells primed by IFN-gamma or gamma-radiation. This surface Ag thus identifies cells at the primed cell intermediate stage of the tumoricidal activation pathway regardless of the mechanism of activation. A second Ag, TM-2, is expressed on IFN-treated RAW 264.7 cells but not on RAW 264.7 cells primed with gamma-radiation alone. Expression of this Ag can be induced by treatment of irradiated cells with IFN-gamma, but is not induced by IFN-gamma treatment of a noncytolytic cell line, WEHI-3. This Ag thus appears to be an IFN-inducible cell surface protein associated specifically with macrophage activation for tumoricidal activity. Finally, Ag TM-3 is detectable on RAW 264.7 cells primed by either IFN-gamma or gamma-radiation, after subsequent triggering of the primed cells with LPS. The addition of the mAb recognizing this antigen to the function assay of tumor cell killing can inhibit they lytic activity of both triggered cells. Thus, this Ag may play a role in the antitumor effector functions of activated macrophages. Overall, the results suggest that these mAb can serve as useful tools for identification of molecules associated with the process of macrophage activation for tumor cell killing.

Analysis of the interaction of peptide hen egg white lysozyme (34-45) with the I-Ak molecule

We examined the structural characteristics of a peptide Ag that determine its ability to interact with class II-MHC molecules and TCR. The studies reported here focused on recognition of the hen egg white lysozyme (HEL) tryptic fragment HEL(34-45) by two I-Ak-restricted T cell hybridomas. HEL(34-45) bound to I-Ak created more than one antigenic specificity. Experiments with truncated peptides and alanine-substituted peptides indicated that two T cell hybrids either recognized distinct regions of the HEL(34-45) peptide, or different determinants generated by interaction of the peptide with I-Ak. Although we identified residues of HEL(34-45) that were critical to T cell recognition, no positions in the peptide were identified as I-Ak contact sites using single alanine substitutions. This suggests that more than one site or region of the peptide contributes to the binding to I-Ak. Finally, the murine lysozyme equivalent of 34-45 did not bind to I-Ak. Substitution of the corresponding murine lysozyme (self) residue at position 41 of HEL(34-45) abrogated I-Ak binding of the peptide.

Analysis of the interaction of peptide hen egg white lysozyme (34-45) with the I-Ak molecule

We examined the structural characteristics of a peptide Ag that determine its ability to interact with class II-MHC molecules and TCR. The studies reported here focused on recognition of the hen egg white lysozyme (HEL) tryptic fragment HEL(34-45) by two I-Ak-restricted T cell hybridomas. HEL(34-45) bound to I-Ak created more than one antigenic specificity. Experiments with truncated peptides and alanine-substituted peptides indicated that two T cell hybrids either recognized distinct regions of the HEL(34-45) peptide, or different determinants generated by interaction of the peptide with I-Ak. Although we identified residues of HEL(34-45) that were critical to T cell recognition, no positions in the peptide were identified as I-Ak contact sites using single alanine substitutions. This suggests that more than one site or region of the peptide contributes to the binding to I-Ak. Finally, the murine lysozyme equivalent of 34-45 did not bind to I-Ak. Substitution of the corresponding murine lysozyme (self) residue at position 41 of HEL(34-45) abrogated I-Ak binding of the peptide.

Differential induction of activation markers in macrophage cell lines by interferon-gamma

Macrophage cell lines were used in these studies as a model system to dissect the biochemical and functional mosaic of the macrophage activation process. In particular, the requirements for the induction of tumoricidal and bactericidal activity in the RAW 264.7 and WEHI-3 cell lines by interferon-gamma (IFN-gamma) and bacterial lipopolysaccharide (LPS) were determined. Changes in expression of a series of macrophage markers traditionally associated with macrophage activation were monitored during stimulation of the cells in order to determine whether a detectable pattern of activation-associated changes is associated with the development of a particular functional activity. These markers included changes in the cell surface expression of major histocompatibility complex-encoded Class I and Class II antigens and antigens in the Mac-1/LFA-1 family, alterations in the levels of membrane enzymes (5' nucleotidase and alkaline phosphodiesterase), and production of secretory products including hydrogen peroxide and the monokines interleukin-1, interferons-alpha/beta, and tumor necrosis factor-alpha. Our results demonstrate that a given homogeneous macrophage population expresses a distinct subset of functional activities in response to single, defined activating signals such as IFN-gamma and LPS. The display of a variety of macrophage surface antigens, enzymes, and secreted products is activated simultaneously by such treatment; however, the particular pattern of such activation-associated markers cannot reproducibly be used to predict the ability of an activated cell to perform a particular function. The results also suggest that macrophage cell lines expressing differential response patterns following IFN-gamma stimulation provide a valuable system for dissection of the molecular and cell biology of macrophage activation.

Modulation of macrophage function by gamma-irradiation. Acquisition of the primed cell intermediate stage of the macrophage tumoricidal activation pathway

Macrophage activation for tumor cell killing is a multistep pathway in which responsive macrophages interact sequentially with priming and triggering stimuli in the acquisition of full tumoricidal activity. Although this synergistic response of normal macrophages to sequential incubation with activation signals has been well established, characterization of the intermediate stages in this pathway has been difficult, due in large measure to the instability of the intermediate cell phenotypes. We have developed a model system for examination of macrophage-mediated tumor cell lysis, with the use of the murine macrophage tumor cell line RAW 264.7. These cells, like normal macrophages, exhibit a strict requirement for interaction with both interferon-gamma (IFN-gamma, the priming signal) and bacterial lipopolysaccharide (LPS, the triggering signal) in the development of tumor cytolytic activity. In this system, the priming effects of IFN-gamma decay rapidly after withdrawal of this mediator and the cells become unresponsive to LPS triggering. We have recently observed that gamma-irradiation of the RAW 264.7 cells also results in development of a primed activation state for tumor cell killing. The effects of gamma-radiation on the RAW 264.7 cell line are strikingly similar to those resulting from incubation with IFN-gamma, with the exception that the irradiation-induced primed cell intermediate is stable and responsive to LPS triggering for at least 24 hr. Treatment with gamma-radiation also results in increased cell surface expression of major histocompatibility complex-encoded class I antigens; however, class II antigen expression is not induced. Irradiation-induced development of the primed phenotype is not solely the result of cytostatic effects as treatment of the cells with a radiomimetic drug, mitomycin C, results in decreases in [3H]thymidine incorporation that are similar to those observed after irradiation, without concomitant development of cytolytic potential. In addition, priming by gamma-radiation does not appear to be mediated by the release of soluble autoregulatory factors. This alternate pathway for induction of the primed macrophage activation state should serve as a useful tool for identification of molecules important to the functional potential of primed cells, and for elucidation of the biochemical mechanisms of the priming event in tumoricidal activation.

Modulation of macrophage function by gamma-irradiation. Acquisition of the primed cell intermediate stage of the macrophage tumoricidal activation pathway

Macrophage activation for tumor cell killing is a multistep pathway in which responsive macrophages interact sequentially with priming and triggering stimuli in the acquisition of full tumoricidal activity. Although this synergistic response of normal macrophages to sequential incubation with activation signals has been well established, characterization of the intermediate stages in this pathway has been difficult, due in large measure to the instability of the intermediate cell phenotypes. We have developed a model system for examination of macrophage-mediated tumor cell lysis, with the use of the murine macrophage tumor cell line RAW 264.7. These cells, like normal macrophages, exhibit a strict requirement for interaction with both interferon-gamma (IFN-gamma, the priming signal) and bacterial lipopolysaccharide (LPS, the triggering signal) in the development of tumor cytolytic activity. In this system, the priming effects of IFN-gamma decay rapidly after withdrawal of this mediator and the cells become unresponsive to LPS triggering. We have recently observed that gamma-irradiation of the RAW 264.7 cells also results in development of a primed activation state for tumor cell killing. The effects of gamma-radiation on the RAW 264.7 cell line are strikingly similar to those resulting from incubation with IFN-gamma, with the exception that the irradiation-induced primed cell intermediate is stable and responsive to LPS triggering for at least 24 hr. Treatment with gamma-radiation also results in increased cell surface expression of major histocompatibility complex-encoded class I antigens; however, class II antigen expression is not induced. Irradiation-induced development of the primed phenotype is not solely the result of cytostatic effects as treatment of the cells with a radiomimetic drug, mitomycin C, results in decreases in [3H]thymidine incorporation that are similar to those observed after irradiation, without concomitant development of cytolytic potential. In addition, priming by gamma-radiation does not appear to be mediated by the release of soluble autoregulatory factors. This alternate pathway for induction of the primed macrophage activation state should serve as a useful tool for identification of molecules important to the functional potential of primed cells, and for elucidation of the biochemical mechanisms of the priming event in tumoricidal activation.

Changes in coronary bypass surgery leading to improved survival

Coronary bypass surgery was performed on 439 patients between the years 1969 and 1973 (group A) and on 1,760 patients between the years 1974 and 1979 (group B). The operative mortality for group A was 3.9%; for group B, 1.3%; four-year survival for group A patients was 88.9% +/- 1.5% (mean +/- SE); for group B patients, 92.5% +/- 0.9%. The difference between the relative four-year survival rates (based on age- and sex-matched Oregon population) between group B and A was 6.2%; the lower operative mortality would account for only 2.6%. We conclude that the results of coronary bypass surgery have improved because of (1) a lower operative mortality, and (2) other factors that cannot be precisely defined at the present time but probably are the long-term result of better and more complete operative and perioperative techniques.

The ultimate prognosis after valve replacement: an assessment at twenty years

Our experience over a 20-year period consists of 2,135 patients with initial caged-ball valve replacement: 52% aortic, 34% mitral, 12% double, and 2% triple-valve replacements, with 59.2, 39.8, 10.3, and 2.7 patient-centuries of follow-up, respectively. Fifteen-year actuarial survival (+/- standard error) was 43 +/- 2% for aortic and 44 +/- 3% for mitral valve replacement, and 27 +/- 5% for double-valve and 23 +/- 7% for triple-valve replacement. Restricting attention to patients operated on since 1973 divides the series almost in half and does not dramatically improve the 5-year actuarial survival (from 66 +/- 2% to 71 +/- 3% and from 70 +/- 2% to 78 +/- 3% for aortic valve replacement and mitral valve replacement, respectively). There was some alteration in the causes of late death: the largest percentage of deaths in both the earlier and current groups, 52%, was cardiac related whereas only 24% and 13%, respectively, were valve related. Over the past two decades operative mortality has declined and, to a lesser extent, late survival after mitral valve replacement has improved. The incidence of embolism has decreased significantly, most notably with the Silastic ball valves. Dramatic improvements in late results will occur primarily by modifying the cardiac-related death rate through earlier operation and improvements in the medical management of postoperative arrhythmias and congestive heart failure.

Year of operation as a risk factor in the late results of valve replacement

The actuarial thromboembolic rates of aortic and mitral silicone ball valves used during the second decade of cardiac valve replacement are significantly lower than the rates for the same prostheses implanted during the first decade, as shown in the following table: (Formula: see text). The embolus-free rates are significantly different (p < 0.01) in both the mitral and aortic series. Five-year embolus-free rates for the composite-strut caged-ball, Björk-Shiley tilting disc, and porcine xenograft valves all fall in the range of from 81% to 92% for the mitral position and from 91% to 97% for the aortic. Thus the standard silicone ball-valve prosthesis, used during the current era, has a thromboembolic risk as low as that reported with other concurrently utilized valve substitutes. This striking reduction in thrombogenicity demonstrates that the time frame of implantation must be considered when evaluating the results of cardiac valve replacement.

The use of time-interrelated covariates to predict survival following aortic valve replacement

One hundred four patients survived isolated aortic valve replacement with the model 1200 prosthesis between 1965 and 1968, with a 12-year survival of 64%. Multiple regression survival analysis was employed in an attempt to determine which of 26 preoperative variables affected late survival and to devise a formula to predict survival for a given individual. The most important variables in the regression equation were right atrial mean pressure, etiology, and sex. The effect of the last two were found to vary with time over the 12-year post-operative period. An extension of the standard regression analysis technique was developed to incorporate time-related cofactors into the model. Based on the multiple regression model, 12-year survival was estimated to range from 92% to 14% for the best and worst combinations, respectively, of the three significant variables. The advantages of the regression method are outlined and the findings of other studies with regard to factors affecting survival after aortic valve replacement are summarized and discussed.

Non--cloth-covered caged-ball prostheses. The second decade

The Starr-Edwards Models 6120 mitral and 1200/60 aortic valves are caged-ball prostheses with cloth-covered sewing rings and bare-metal struts. Introduced in 1965, they have been in continuous clinical use longer than any other currently available heart valve prostheses. Late results with this valve are analyzed and compared with recent series employing other current valve prostheses. One hundred thirty-four mitral 6120 prostheses were inserted at the University of Oregon Health Sciences Center from 1965 through 1977, with 118 operative survivors followed for a mean of 5.4 years. Twelve-year survival rate (+/- standard error) was 50 (+/-8) percent. Twelve percent of late deaths were valve related. Eighty-eight (+/-5) percent of valves were still in place at 12 years. The embolic rate was 5.8 (+/-1.0) percent per patient-year for all emboli and 2.2(+/-0.6) percent per patient-year for serious emboli. Two hundred forty-nine operative survivors among 282 patients undergoing aortic valve replacement during the same period of time were followed for a mean of 4.3 years. Twelve-year survival was 61 (+/-6) percent and the removal-free rate was 92(+/-5) percent. Six percent of late deaths were valve related. Embolic rates were 5.0 (+/-.7) percent and 1.8 (+/-.4) percent per patient-year for all emboli and serius emboli, respectively. Structural failure, specifically ball variance, was not encountered with this prosthesis. Ninety percent of 10 year survivors are in N.Y.H.A. Functional Class I or II. There was one anticoagulant-related death in 1,698 patient-years of follow-up. The current non--cloth-covered caged-ball valves provide unquestionable durability and well-documented results into their second decade of use. They provide a base line for comparison with newer prostheses and offer a valid, current choice for both aortic and mitral valve replacement.

Correction of aortic coarctation in neonates: mortality and late results

To determine those factors that affect mortality and to analyze long-term results, the records of 44 infants who underwent repair of aortic coarctation at less than 90 days of age were examined. There were 14 operative and 8 late deathes (mean, 4.3 months postoperatively). Subsequent operation, generally to repair or palliate associated anomalies, was required 22 times in 20 patients and was a source of considerable mortality. There is evidence that earlier total repair of associated anomalies might improve survival. Sufficient data were available on 17 of the 22 survivors to assess long-term results. The outcome was considered excellent in 8 patients, fair in 4, and poor in 5. Revision of the coarctation repair due to growth failure of the anastomosis was required in 1 patient. Aggressive surgical management is recommended in these infants because, despite a high early mortality, a considerable proportion of excellent results can be anticipated in what is otherwise a hopeless situation.

The Starr-Edwards model 6000 valve. A fifteen-year follow-up of the first successful mitral prosthesis

The Starr-Edwards model 6000 mitral valve was the first successful mitral prosthesis. A fifteen year follow-up of 110 patients undergoing isolated mitral valve replacement with this prosthesis from 1960 to 1966 is presented. There were 22 (20%) operative and 37 (42%) late deaths at a mean of 8.6 years postoperatively. Preoperative variables leading to late death and thromboembolism are analyzed. Seventeen of 25 operative survivors had improvement in their NYHA Functional Class status and eight other remained unchanged an average of 13.1 years after surgery. There are 5000 patients world-wide currently relying on this prosthesis. Despite a high rate of thromboembolism in the past, elective replacement is not recommended except in selected patients.

Aortic valve replacement: a ten-year follow-up of non-cloth-covered vs cloth-covered caged-ball prostheses

From 1965 to 1976, 721 isolated aortic valve replacements were performed at the University of Oregon hospitals, utilizing Starr-Edwards caged-ball prostheses. Three models of aortic prostheses were introduced during this period: a non-cloth-covered model has been in continuous use since 1965; a cloth-covered model was begun in 1968 and has been supplanted by the modified composite-strut or "track" model since 1972. The 5-year actuarial survival rate for operative survivors is about 80% for both non-cloth-covered and cloth-covered valves, while the 10-year survival is 61%, based on the older model only. The actuarially-determined percentages of patients experiencing significant thromboembolic episodes (i.e., all except transient ischemic episodes) at 5 years are 7% for the cloth-covered and 9% for the non-cloth-covered model. If transient ischemic attacks are included, the cloth-covered model has only an 8% incidence at 5 years compared to a 22% incidence for the older model. However, the cloth-covered valves are subject to a higher risk of reoperation because of the possibility of cloth injury. The "track" valve, therefore, was designed with exposed metal on the inner surface of each strut to prevent ball-cloth contact. In 107 patients (mean follow-up period 1 year) receiving anticoagulation, this prosthesis has maintained the same low incidence of thromboembolism as the previous cloth-covered model, with no reoperations for valve failure.

An improved statistical method for assessing the results of operation

The advantages of the acturarial method of analyzing postoperative survival are now widely accepted. In evaluating the late results of heart valve replacement operations, however, certain nonfatal complications must also be considered. The use of individual event-free rates does not portray individual risk, since some valves have multiple complications. By using cummulative complication-free rates, however, it is possible to estimate the percentage of valves active and free from certain major complications for each postoperative interval. A series of actuarial curves is used, each of which represents a different major complication. These curves are subtracted progressively from the total of valves at risk, and an acturial representation of complication-free survival results.