Imperfect vaccines may increase transmission of highly virulent pathogens

Vaccines that let the host live but do not prevent transmission of the pathogen are called leaky or imperfect vaccines. In the early 2000s, it was proposed that such vaccines could lead to the emergence of highly virulent pathogens by creating ecological conditions that would allow the emergence of hotter and deadlier strains. 

A recent article published in July issue of PLos Biology, investigated this theory. In this study, the authors used Marek’s disease (MD) virus to show experimentally that immunization of chickens with a vaccine against MD virus can create conditions that promote transmission of lethal strains of the virus.  MD virus is a highly contagious oncogenic virus of poultry. At present, all MD virus vaccines are live viruses. The vaccinated birds can become infected and shed wild type viruses.

The authors performed a series of experiments to show that vaccination with MD vaccine increases the infectious period of the most virulent strain of MD virus by preventing the death of the host. As virulent strains have a deadly effect on the host, they are eliminated before infecting other hosts. The prolonged infectious period causes more shedding of the virus in the environment. They also showed that all the unvaccinated birds co-housed with vaccinated infected birds became infected and died.  Thus, vaccination allowed onward transmission of most virulent strains and could be risky for unvaccinated birds. 

The authors note that their data doesn’t show that vaccination caused the evolution of more virulent strains of MD virus. They further emphasize that despite the evolution of deadly strains, vaccination has greatly reduced the mortality due to MD viruses. Previous studies have observed that more virulent pathogens are overcoming more effective vaccines. A vaccine that not only protects host but also prevents onward transmission of the virus could be an answer to this problem.

A new biomarker for assessing resistance to therapy in rheumatoid arthritis

According to a recently published study, low expression of CD39 on regulatory T cells (Tregs) could be used as a biomarker for resistance to methotrexate (MTX) therapy in rheumatoid arthritis (RA). MTX, an antimetabolic drug, is the first line of therapy for RA patients. However, up to 40% of patients are unresponsive to MTX (or UR-MTX resistant). There is a need to early diagnose MTX resistance as the resistance generally appears after 3 months of therapy and that means worsening of RA symptoms during that time. The study published in January issue of PNAS shows that low expression of CD39 on circulating Tregs is a rapid, reliable and convenient biomarker for MTX resistance.

RA is an inflammatory autoimmune disease associated with joint destruction and severe morbidity. MTX has been generally used as drug to treat RA. MTX has two known functions: inhibitor of dihydrofolate reductase/folic acid metabolism and reducing inflammation by elevation of extracellular adenosine (ADO). Tregs are regulatory T cells responsible for keeping the immune system in check by suppressive activation and proliferation of wide variety of cell types. One of the mechanisms through which Treg suppress other cells is through production of extracellular ADO by CD39/CD73, expressed on the surface of Tregs.

Given that the MTX also exerts its effect through generation of ADO by CD39/CD73 and that CD39/CD73 are also important in Tregs activity, the authors investigated possible link between MTX unresponsiveness and expression of CD39 on Tregs in RA patients. The authors first observed that parameters related to disease severity were significantly higher in UR-MTX patients than in R-MTX (responsive) patients. Furthermore, the number of circulating Tregs was lower in UR-MTX than in R-MTX. Encouraged by these findings, the researchers compared expression of CD39 and CD73 on Tregs from R-MTX and UR-MTX RA patients. The expression of CD39 on Trges from UR-MTX RA patients was significantly lower than that in R-MTX patients. To find out if the increase in number of CD39+Tregs in R-MTX was a result of MTX treatment, the authors followed some patients and studied CD39+ expression on T regs before and after treatment. Although there was no difference in percentage of CD39+ tregs in R and UR-MTX before treatment, their numbers increased much more in R-MTX patients than in UR-MTX patients following treatment. They further observed that the density of expression of CD39 was low in UR-MTX patients before and after treatment in comparison to R-MTX patients.

Various attempts have been made in the past to identify a biomarker for MTX unresponsiveness. This study provides a unique non-invasive approach of using CD39 expression on Tregs as biomarker for unresponsiveness.

How do vaccines interact with human cells?

In a recently published study, scientists have identified various transcriptional programs induced in human antigen presenting cells (APCs) by various vaccines. The article published in October issue of Nature Communications sheds new light on the mechanisms of vaccine interaction with human dendritic cells (DCs), a primary APC involved in vaccination response.

Previous studies have shown that vaccination mostly depend on dendritic cells. DCs are highly efficient in presentation of antigen. In response to a pathogen, DCs transcribe various set of genes that then interact with each other. Although, many sub-populations of DCs have been identified in human blood, skin and other tissues, the role of these populations in eliciting specific immune response to different vaccines is not entirely known. Furthermore, it is not much known about the various transcriptional programs initiated in response to different vaccines.

Romain Banchereau and colleagues from Baylor Institute for Immunology Research, Dallas and Jackson Laboratory for Genomic Medicine, Farmington used a unique multi-step approach to understand how human DCs respond to vaccine challenge in vitro. They studied transcriptional changes in DCs that were first generated by culturing monocytes (a precursor to DC) with different cytokines and then exposing them to a number of pathogens. The researchers observed a broad spectrum of unique and common transcriptional responses to pathogens over time. To further understand the biological significance of these transcriptional responses, the scientists generated a framework that groups transcripts into modules based on their co-expression across pathogens, time points, and DCs. They found that modules represented alteration of many biological pathways including interferon response, inflammation, antigen processing and presentation, DC maturation and T cell activation.

The investigators then applied the same approach to study transcriptional responses of various APCs to 13 commercially available vaccines in vitro and observed that response to different vaccine was mediated through unique APC subsets. In a further effort to understand the differences in immune pathways required for vaccination to those that are responsible for pathogenesis of a particular disease, the scientists applied the same framework to analyze transcriptional profile of individuals vaccinated with influenza vaccine and individuals with asymptomatic and symptomatic influenza infections. They found that vaccinated individuals showed similar transcriptional profiles to asymptomatic individuals and both showed a mild signature. In contrast, symptomatic individuals showed strong response. The researchers acknowledge that this approach can help in identifying which pathways are require for vaccination and which for establishing infection and this distinction between two pathways can help in development of safer and more effective vaccines in future.

Overall, this study provides a good understanding of transcriptional response of DCs to current vaccines and will certainly add in development of next generation vaccines, in which specific sub-populations of APCs can be targeted for a more effective response to a particular pathogen.

LL37 identified as an auto antigen in Psoriasis

According a new study published in nature communications, anti-microbial peptide (AMP) LL37 acts as an auto antigen in psoriasis. The study shows that LL37 was recognized as an antigen by circulating T cells in 46% of psoriatic patients. This recognition was shown by proliferation of T cells and production of interferon gamma in response to LL37. None of the controls showed such response.

Roberto Lande and colleagues from Italy and Switzerland published their findings in December issue of Nature communications. They performed their research using blood from psoriasis patients.

Psoriasis is a common condition of skin characterized by development of red scaly plaques on skin. Although it is sometimes considered an autoimmune disease, the nature of the auto antigen that leads to development of auto reactive T cells is not known. LL37 is an AMP that has been shown to be overexpressed in psoriatic skin and play important roles in pathogenesis of psoriasis. It forms complexes with extracellular self-nucleic acid. These complexes then activate plasmatoid and myeloid DCs which in turn leads to activation of T helper cells. This process then starts an inflammatory cascade. However, it was not known if LL37 can directly serve as an auto-antigen and stimulate T cells.

In this study, the authors established that psoriatic T cells were specifically responding to LL37 by showing that T cells respond only to LL37 when stimulated with a variety of other AMPs. The authors also looked at correlation of response to LL37 and disease status and found that up to 75% of psoriatic patients with moderate to severe plaque psoriasis and with a Psoriasis Activity Severity Index (PASI) score of more than 10 responded to LL37. The LL37 specific T cells in psoriasis patients showed production of pathogenic cytokines including IL17 as well as showed direct chemo tactic activity for inflammatory cells and cytotoxic ability. The study also showed that these T cells possess the ability to migrate into psoriatic skin lesions. This was further validated by finding of LL37 specific cell from skin biopsy of a psoriatic patient who earlier showed positive response of blood T cells to LL37.

In conclusion, this study shows that LL37 is an auto antigen in psoriasis and could be an appealing target to treat psoriasis.

Link between placental microbiome and pre-term birth

According to a recently published study in Science translation medicine, the placental microbiome might be associated with pre-term birth less than 37 weeks, and a remote history of antenatal infection in the first trimester. In this study, which was based on placental collection from 320 subjects, the investigators analyzed the human placental microbiome and provided details on microorganisms present, their probable functions and overall structure of placental microbial community.

Due to recent advances in sequencing technologies, a large number of studies have looked at the structure, function and diversity of human microbiome across multiple body sites in both healthy and disease states. Studies conducted on newborn babies have shown that the gut microbiome of neonates show complex microbial communities in the first few weeks of life. However, the source of these microbes and the time at which the infants acquire those is not yet known. It has also been shown that gut microbiome of full-term infants is different from that of low birth weight infants during the first few weeks of life, indicating that the infants might acquire these microbes in utero through a common source and that the composition of the microbiome might change with length of gestation. The authors of this study hypothesized that the human placenta could be that source.

The investigators of this study used whole-genome shotgun (WGS), a technique involving sequencing long strands of DNA, to determine the taxonomic classification of placental microbiome. They noted that several species of oral microbiome were detected in the placenta. These included Prevotella tannerae and non-pathogenic Neisseria species. They also found high abundance of E. coli in most individuals. The authors further compared the microbial community observed in placenta with those reported from other body sites (oral, stool, skin, nasal and vaginal) from non-pregnant healthy subjects using publicly available HMP (Human Microbiome Project) data. They observed that placental microbiota showed similarity to oral phyla only. Furthermore, the relative abundance of metabolic pathways was different in placenta when compared to other body sites. For example, the metabolism of co-factors and vitamins showed a greater relative abundance in placental functional gene profile.

The authors found a statistically significantly association between placental microbiome and pre-term birth less than 37 weeks. The researchers also identified various placental taxa whose abundance was enriched or diminished among women who experienced pre-term births. They also observed a statistically significant association between placental microbial community and a remote history of antepartum infection. Streptococcus and Acinetobacter were found to be enriched in women with a remote history of antepartum infection.

In conclusion, Aagaard and colleagues show that in contrast to the widespread believe that intra-uterine environment is sterile, human placenta harbors a variety of non-pathogenic commensal species, and the overall microbiome profile of placenta is most similar to that of non-pregnant human oral cavity. They also observed correlation between placental microbiome and pre-term birth and a history of antenatal infection.

The authors also noted several limitations of the study. The authors compared the placental microbiome with microbiome of other body sites from non-pregnant subjects. Moreover, the authors were not able to characterize the placental microbiome in early preterm gestation in women who had a full term delivery. Still, the study presents some interesting findings and indicates towards an essential role of placental microbiota in human pregnancy.

An interesting paper on HERVs

Expression of Human Endogenous Retrovirus Type K Envelope Protein is a Novel Candidate Prognostic Marker for Human Breast Cancer

I recently happened to read an interesting short report published in August 2011 issue of Genes and Cancer. In this study, the authors evaluated the use of expression of envelope (env) protein of human endogenous retroviruses-K (HERV-K) as a prognostic marker of breast cancer. HERVs constitute about 8% of human genome. There are many distinct families of HERVs present in human genome. Most of these families are defective and could not encode complete viruses. However, HERV-K family shows a conservation of seemingly intact retroviral genes as it is one of the most recently integrated viruses.   In a previously conducted study, the authors observed the expression of HERV-K env mRNA and protein in breast cancer tissues obtained from US women. To further study the role of HERV-K env mRNA as a prognostic marker for breast cancer, the authors looked at expression of HERV-K env mRNA and protein in breast cancer tissues obtained from both Chinese and US women. The authors also analyzed the relationship between HERV-K env expression and disease severity in these women.

Methodology and Results:

One hundred and twenty tissues from Chinese women including 40 breast cancer tissues, 40 matched adjacent uninvolved breast tissues and 40 breast tissues from benign breast diseases but not cancer were used in this study. HERV-K env mRNA was detected in 70% of breast cancer samples and 20% of surrounding uninvolved tissues from breast cancer patients. No HERV-K env mRNA was detected in breast tissues from control patients. Similar to mRNA results, HERV-K env protein expression was also higher in cancer tissues in comparison to controls. The authors also found medium to strong expression of env protein in cancerous tissues and weak to no expression in adjacent non-cancerous tissues.

The authors then looked at relationship between expression level of HERV-K protein and clinical features of the patients. 82% of the patients with high expression of HERV-K in their tumor had a tumor size greater than 3 cm. HERV-K env expression also correlated with other clinical and pathological characteristics in these patients. Furthermore, the scientists conducted a Kaplan-Meier survival analysis and found that the patients with high expression of HERV-K env protein had a significantly shorter overall survival in comparison with patients with moderate to low HERV-K env protein expression.

Taken together, all these results indicate that HERV-K env protein expression is highly upregulated in human breast cancer tissues and not in adjacent non-cancerous tissues or normal breast tissues.

In all the paper is nicely written and all the experiments seems to be nicely conducted. However, this paper exclusively talks about env but what about pol and gag? Expression of pol is particularly important as pol encodes for reverse transcriptase, which is required for production of new virus progenies.

The study did not observe any association between HERV-K env expression and ER/PR status. These results were surprising as earlier studies have observed that expression of HERV-K mRNA and protein was higher in breast cancer cell lines treated with estradiol and progesterone than in cells without treatment

Preterm infants' T cell responses to inactivated Poliovirus vaccine

I am writing a new blog after a long long time. Well, what a better way to start than this article published in 2009 issue of JID. http://jid.oxfordjournals.org/content/201/2/214.long

Background: Preterm infants are more susceptible to infection as their immune system is immature. earlier studies have examined humoral immune responses to many viral and bacterial vaccines in preterm infants. These studies have found disparity in antibody production between preterm and term infants. However, not much is known about T cell response to these vaccines in preterm infants. Since, adequate antibody production depends upon T cell help to B cells, the disparities in antibody production may reflect disparity in T cell responses in these two groups.
In the present study, the authors recruited 33 preterm and 50 term infants and studies their T cell response to vaccines.

Results: Of the 33 preterm infants, final results were available for 27 infants and of the 50 term infants, final results were available for 35 infants. First, the authors looked at the frequency of circulating CD4+ T cells in these two groups at 2 months and 7 months of age. There was no change in the frequency at these two time periods. Next, the authors looked at memory Cd4+ cells (Cd4+CD45RO+) in these infants. They observed that 7 month old preterm infants had fewer memory cells than seven month old term infants.
Furthermore, the authors stimulated CD4+ cells from both set of infants with Staphylococcus entertoxin B, Sabin Oral polio vaccine, serotype 3 strain and uninfected vero cell lysate by culturing whole blood with these in the presence of costimulatory monoclonal antibodies to CD28 and CD49d. Then they looked for percentage of CD4+ cells positive for CD69 and IFN-g. In response to stimulation with SEB, preterm infants had lower frequency of CD4+CD69+IFN-g+ cells than did term infants at 2 and seven months of age. The authors then compared the frequency of CD69+ and IFN-g+ cells among CD4 and CD45RO cells in both group of infants before and after vaccination with OPV serotype 3. Both the groups of infants developed a significant increase in poliovirus specific Cd69+IFg+ cells relative to prevaccination responses.
When the authors compared the CD69+ IFN-g+ responses between preterm and term infants after vaccination, they observed that frequency of CD4+CD69+, CD4+CD69+IFN-g+, CD4+CD45RO+CD69+ and CD4+CD45RO+CD69+IFN-g+ cells was comparable in two groups. To evaluate cell mediated immunity, PBMCs were isolated from both groups of infants (pre and post vaccination) and stimulated with OPV serotype 3. A positive proliferative response was defined as stimulation index of 3. It was observed that mean poliovirus-type 3 specific proliferation after vaccination was significantly lower in preterm infants than in term infants.
The authors next looked at neutralizing antibody response to all three subtypes of poliovirus in the sera of these infants after vaccination. All the infants showed neutralizing anitbodies post vaccination. There was no significant difference in geometric mean titer (GMT) to serotype 2 and 3 in the two groups of infants. However, GMT to serotype 1 was significantly low in preterm infants. To compare the safety of this vaccine in preterm and term infants, the authors looked for medically attended events (MAE) in both groups for 30 days. There were no significant events.

Discussion: The present study establishes that preterm infants, similar to term infants, generate a poliovirus type 3–specific T cell response and that the frequency of circulating poliovirus-specific responder T cells is comparable between preterm and term infants.
The study however, detected differences in circulating T cell populations between term and preterm infants.