Sterling has a Spectacular Summer!

PMI Ph.D. candidate Cade Sterling has closed out a productive summer with a slew of accolades. After a first author publication in the Journal of Virology in June, Cade received his Notice of Award for his submitted F31 award from the NIH! He will be wrapping up the loose ends of his superb work with the Hartman lab over the next year as he nears completion of his Ph.D. program as an F31 Fellow!

This past week, Cade was also honored by the Biomedical Graduate Student Association here at Pitt’s School of Medicine. Cade was named First Runner-Up for the Stephen L. Phillips “Best Peer-Reviewed Publication” Award!

Cade’s magnificent new plaque presented to him by the Biomedical Graduate Student Association.

Amazing work as always, Cade!

A new Rush LRP1 paper in JGV!

Extra! Extra! Hear all about it! Our premier post-doc Dr. Rachael Rush has a new publication in the Journal of General Virology! Entitled, “Rift Valley fever virus infects trophoblast cell lines in an LRP1-dependent manner,” the paper suggests LRP1 to be a determinant of RVFV infection at the maternal-fetal interface as evidenced by RVFV’s ability to replicate within human trophoblast cell lines efficiently. This publication ALSO happened to be one of the most read papers in the Journal of General Virology in the past month!

Immortalized human trophoblast cell lines can provide insight into the mechanisms of cellular infection at the maternal-fetal interface. JEG-3 and JAR cells provide a model cell morphologically similar to cytotrophoblasts while the HTR-8/SVneo (HTR-8) cell line exhibits extravillous morphology which provides a useful analog for syncytiotrophoblast cells along the uterine wall. We have previously demonstrated evidence of the ability of RVFV to infect and replicate within both cytotrophoblasts and syncytiotrophoblasts of primary human placenta explants. The work of this paper uses the aforementioned cell lines to elucidate how RVFV infection is mediated within these cells and provide perspective on the mechanisms of RVFV vertical transmission and infection of the placenta.

In vitro infections of JEG-3, JAR, and HTR-8 cells at MOIs of 0.01, 0.1, and 1.0 all showed evidence of RVFV infection and the expression of LRP1. HTR-8 appeared to be less permissive of RVFV infection when examining vRNA as a demonstration of infectious virus within the system. This was supported by immunofluorescent staining that showed less RVFV antigen staining in HTR-8 cells than the JEG-3 and JAR counterparts at 24 hours post infection (Figure 1C). This coincides with the expression of LRP1 within these cell lines, in which HTR-8 cells are shown to exhibit comparatively less LRP1 through immunofluorescent staining as well as western blot.

In order to further understand the dependency of LRP1 in RVFV of these trophoblast cell lines, we used receptor-associated protein (RAP) as a competing ligand to bind to LRP1, blocking the interaction of RVFV with LRP1 on the surface of these cells. Treatment of cells with RAP reduced RVFV viral titres in both JEG-3 and JAR cells, with the vRNA levels of HTR-8 cells already being so close to the limit of detection that significant difference could not be discerned. This was not true of cells treated with RAP before infection with Zika virus (ZIKV), a flavivirus not previously known to interact with LRP1 or similar LDLRs. Immunofluorescent staining also demonstrates this relationship between RAP treatment and decreased presence of RVFV within the cells (Figure 2C). This suggests that the results showing the reduction in vRNA and antigen staining is specific to the function of RAP treatment as a competitive inhibitor of LRP1.

The specific RAP used for these treatments is Murine RAP domain 3 (mRAP D3) which binds to all LDLRs, not solely LRP1. In order to examine the role of LRP1 inhibition more exclusively, we utilized recombinant LRP1 decoy proteins for the extracellular domain clusters II and IV (CLII and CLIV) fused to a human Fc. When pre-treating RVFV inoculum with these CLII and CLIV decoy proteins it resulted in a significant reduction of vRNA and relative infectivity in all cell lines when compared to control-treated cells. This relationship was not seen when ZIKV inoculum was treated the same way. These results support the notion that RVFV requires binding to CLII and CLIV, and the blocking of that interaction reducing infectivity indicates that LRP1 is used by RVFV to enter and infect these trophoblast cell lines.

Outstanding work by Rachael and all who contributed! LRP1 and RVFV infection become better understood every day because of hard work like this!

Journal of Virology - OROV Acute Hepatitis Mouse Model

It’s been a busy summer here at the Hartman lab. Among the many projects going on currently, we have a new Sterling et al. publication in the Journal of Virology to show for all of this hard work!

Published earlier this summer, “Oropouche virus causes acute hepatitis in mice controlled by type I interferons,” presents two models of Oropouche virus hepatic disease in mice. Fatal cases of OROV in humans have been attributed to severe coagulopathy within the liver, as well as mild liver injury for those with mild cases of Oropouche fever. However, the role of the liver in the pathogenesis of OROV is still rather unexplored.

Cade has developed a lethal model of OROV infection that causes severe liver necrosis similar to what is seen in fatal cases of OROV infections in human, as well as a non-lethal model of self-resolving acute hepatitis that serves as an analog for a milder disease case. Both models cause focal hepatic cell death in mice which can progress to more severe liver necrosis and death when Type I interferon receptors are blocked. These models can serve as valuable tools for the preclinical evaluation of OROV vaccine platforms and therapeutics as well as a means of understanding how OROV causes liver damage.

In Cade’s non-lethal model, immunocompetent C57BL/6 mice were infected with the prototypical OROV strain BeAn19991 via the footpad. These mice were euthanized at 1, 3, and 5 days post-infection for their tissues to be harvested for quantification of viral load and histology (Figure 1A). There was no infectious virus found in the spleen, kidney, lung, or brain at any of the euthanasia time points. Meanwhile, the livers of infected mice had detectable levels of OROV as early as 1 day post-infection (dpi), with the viral titers peaking at 3dpi (Figure 1D).

The presence of virus in the liver along with elevated liver enzymes at 3dpi (Figure 1B) suggested there was damage in the liver, so histopathology was performed. The beautiful images shown below were obtained through hematoxylin and eosin (H&E) and TUNEL staining, and they reveal OROV-induced necrotic and inflammatory areas across the livers of infected mice.

Cade’s exceptional liver-imaging capabilities help paint the picture of how OROV infection progresses through the liver over time. Histopathological damage induced by the infection increases from 1dpi to 3dpi, before showing signs of recovery and repair by 5dpi through the visible lack of focal damage or accumulation of immune cells.

Cade’s lethal model of OROV infection utilizes a MAR1-5A3 clone monoclonal antibody to bind the Type I IFN receptor complexes and immunocompromise the mice by preventing recognition of Type I interferons. Treating mice with MAR1 prior to OROV infection resulted in near-uniform lethality at the highest dose by 5dpi. Severe disease and liver damage were seen in these mice which prompted a timed euthanasia study to assess viral titers, blood chemistry, and histopathology. This timepoint study revealed the rapid onset of hepatic damage. Necroinflammatory foci, necrosis, and hemorrhage are severe by 3dpi (Figure 6D). The deficient immune response caused by the presence of MAR1 prior to OROV infection shows a course of disease in which OROV can overwhelm the tissues of these mice and cause severe hepatic disease, necrosis, and death. In both the sublethal and lethal model the elevated liver enzymes and similar histopathology by 2dpi suggest a similar disease progression. However, the ability of the murine immune system to mount a sufficient response seems to determine whether the infection resolves and the liver repairs, or the more severe outcomes prevail.

A more contemporary OROV outbreak isolate (CDC240024) was also used with the MAR1 lethal model, causing markedly less lethality than the historical prototype strain (BeAn19992). Histopathological outcomes were similar, although the clinical window was compressed and the time to death was delayed by approximately one day. This may suggest current human isolates may be less adapted to infecting laboratory mice as opposed to a strain with a rich passage history such as BeAn19991. Together, these lethal and sublethal models of OROV infection paint the picture of how OROV hepatic disease progresses within immunocompetent and immunocompromised mice. This work prompts further investigation into the mechanisms which determine whether or not OROV will be controlled by the immune response within the liver or progress into severe hepatic necrosis. Stellar work, Cade!

ASV 2026

This July some of our lab members had the pleasure of attending and presenting their work at the American Society for Virology 2026! The annual meeting was hosted by the University of Minnesota in Minneapolis this year. We’ve been all over the country and world so far in 2026!

Our IDM PhD candidate Elon Holmes presented a poster on some of her work on RVFV infection during pregnancy using human trophoblast stem cells as an in vitro model for vertical transmission.

Our newly graduated Dr. Austin Hertel also presented his work on maternal vaccination as a protective measure against in utero transmission of RVFV in rats! He gave a talk comprising of lots of work from his recent publication in mBio. We are incredibly proud of our strong Hartman lab representation at ASV this year! Great work Elon and Austin! I wonder where our brilliant young scientists will be presenting next…

Hartman Lab Outing 2026: Kennywood!

Every year the Hartman lab ventures out from the walls of the Center for Vaccine Research for some extracurricular fun. This year’s adventures took us to Kennywood to ride some rollercoasters and enjoy a beautiful summer day!

Joining us for this year’s festivities were some of our CVR technician friends who constantly help us on our many projects, Alex, Brooke, and Katelyn!

After a long day of high-speed thrills some of us decided to slow things down with a visit to Page’s Dairy Mart. An iconic Pittsburgh summer day for the Hartman lab!

Congratulations, Dr. Austin Hertel, Ph.D.!

On July 22nd our very own Austin Hertel masterfully delivered his Ph.D. defense to a jam-packed conference room here at the CVR! After years of dedication to learning and honing his skills, Austin successfully defended his work, “Defending the vulnerable: Maternal vaccination with live-attenuated Rift Valley fever virus prevents maternal disease, in utero transmission and neonatal mortality in rats.” Austin earned his doctorate as a candidate in Pitt’s Program in Microbiology and Immunology while advised by Dr. Amy Hartman to a committee consisting of chair Dr. Anita McElroy, MD, PhD, Dr. Kevin McCarthy, PhD, Christina Megli, MD, PhD, and Kerry Empey, PharmD, PhD.

Afterwards, the lab joined Austin, his family, and friends to celebrate this momentous occasion. Congratulations, Dr. Hertel!

Bunyavirus 2026

On July 8th through July 10th members of our lab traveled to Bilbao, Spain for Bunyavirus 2026. Dr. Hartman was featured as the keynote speaker for the conference and delivered a presentation on the viral tropism and protecting against vertical transmission of Rift Valley fever virus!

Our fearless leader about to begin her talk!

As part of Bunya 2026, our Postdoctoral Associate Dr. Rachael Rush and PhD candidate Cade Sterling presented posters on their recent work within the Hartman lab. Rachael even won a prize for her poster presentation! Fantastic work representing the lab Cade and Rachael!

While in Bilbao the Hartman group also had an opportunity to catch up with fellow collaborators and engage with others in the field of bunyavirus research. What a successful trip to Spain! I wonder where our collaboration will take the lab next…

Congratulations, Elon!

On July 9th our very own Elon Holmes passed her PhD Comprehensive Examination! This was the culmination of so much hard work, dedication, and studying from Elon. We are incredibly proud of her and can’t wait to see what she does as she continues her journey as a PhD candidate. Here are some photos of Elon and the lab celebrating post-comps!

A New Hertel et al. Publication in mBio!

Our very own Austin Hertel’s 2nd publication as first author was just made available in the American Society for Microbiology’s mBio! “Maternal vaccination protects dams and prevents in utero transmission of Rift Valley fever virus in rats,” focuses on vertical transmission of Rift Valley fever virus (RVFV) between mother and fetus in rats, specifically evaluating the safety and protective ability of a live-attenuated RVFV vaccination in dams.

RVFV causes spontaneous fetal loss among domesticated livestock populations, and has also been shown to cause fetal loss and hepatic disease in human infants born to pregnant individuals infected with RVFV. The disease poses a serious threat to vulnerable pregnant populations, especially without licensed vaccines currently available for human use. Previously developed live-attenuated vaccines retained partial virulence causing fetal death and congenital defects and thus are not suitable for human use. The vaccine used in this study is a live-attenuated version of the ZH501 strain of RVFV which has been generated by reverse genetics to lack the virulence genes encoding the non-structural proteins NSs and NSm. Vaccination with RVFV-delNSs/Nsm protects mother and fetus from wild-type viral challenge while also being avirulent.

Immune response titers demonstrated pregnant and non-pregnant rats responded similarly to vaccination with RVFV-delNSs/NSm. Titers of RVFV-specific IgG1 and IgG2a in pregnants rats vaccinated with the live-attenuated RVFV strain indicated the Th2- and Th1-mediated responses of rats are similar regardless of pregnancy status. There were some slight differences in IgG response, although neutralization capacity between pregnant and non-pregnant rats were comparable.

Immunofluorescent images of Vero E6 cells inoculated with placental homogenate.

The live-attenuated RVFV vaccine also spreads minimally throughout the pregnant dam when vaccinated during early gestation at a high dose (1 x 10^5 PFU of RVFV-delNSs/Nsm). Live virus could not be isolated from placental homogenates of two pregnant dams sacrificed prior to giving birth. Two other pregnant dams vaccinated during early gestation delivered normal litter sizes with no apparent congenital abnormalities. These results indicate that there is limited clinical impact on the health of offspring when pregnant individuals receive the live-attenuated vaccine during gestation even at high doses.

We also demonstrated vaccinated pregnant animals survive challenge from RVFV after vaccination with the live-attenuated RVFV-delNSs/NSm and sufficiently protect fetuses from in utero transmission of RVFV. Surviving animals had very low levels of vRNA detected in maternal and placental samples, with vRNA found in the fetal viscera. Infectious virus was also not found in maternal, placental, or fetal samples from these vaccinated animals indicating vaccination reduced viral burden and in utero transmission, protecting both dam and pup from RVFV clinical disease.

Mock-vaccinated dams delivered pups with visually apparent visceral hemorrhage and lower birth weights in comparison to vaccinated dams after surviving viral challenge. 3 of the 8 delivered pups from the lone surviving mock-vaccinated dam had this congenital abnormality while vaccinated dams that survived viral challenge delivered largely healthy litters with only 4 pups out of 70 being found dead at delivery. Viral RNA in the fetal viscera of vaccinated dams was also minimal especially in comparison to the high levels of vRNA in the fetal viscera of the mock-vaccinated dams.

Vaccination prior to pregnancy was also shown to protect dams and fetuses from RVF during future pregnancy, with female rats paired with males 10 days post vaccination that became pregnant surviving viral challenge with wild-type RVFV while all mock-vaccinated dams succumbed to lethal infection.

All in all, these findings display robust evidence for the safety and efficacy of the RVFV-delNSs/NSm in pregnant animals. This work provides a useful platform and building block for the use of the live-attenuated RVFV strain as a safe and viable vaccine platform for pregnant individuals. Incredible work, Austin!

CVR Trainee Day 2026

On Friday, June 5th the CVR held its fourth annual Trainee Day! The festivities of this year’s presentations were managed in-part by our very own Cade Sterling and Elon Holmes (grad students)!

Our superstar post doc Dr. Rachael Rush opened the slate of talks for the day with a bang, presenting her work “Translational approaches to combating peribunyaviruses: the Revampp strategy.”

Rachael, pictured above casually hitting an astonishing pose while presenting to a room full of distinguished peers.

In between running around the 6th floor keeping things in line, our PhD candidate Cade also had time to deliver a fantastic presentation of his work, entitled “Oropouche virus causes acute hepatitis in mice controlled by Type I interferons.”

A dapper Mr. Sterling gesturing to his slides (not shown).

Former master’s student, current Master of Science and lab tech Andrew Wheeler also presented at Trainee Day! He shared his project, “Comparing virulence of historical and contemporary Oropouche strains in the context of pregnancy.”

Master Wheeler, being introduced by Cade!

A pensive, distinguished Andrew fielding a question from the audience.

Rachael, Cade, and Andrew did a tremendous job representing the Hartman Lab and contributed to another wonderfully successful Trainee Day!

An updated lab family photo for the record books!