The Impaired Neurodevelopment of Human Neural Rosettes in HSV-1-Infected Early Brain Organoids

Intrauterine infections during pregnancy by herpes simplex virus (HSV) can cause significant neurodevelopmental deficits in the unborn/newborn, but clinical studies of pathogenesis are challenging, and while animal models can model some aspects of disease, in vitro studies of human neural cells provide a critical platform for more mechanistic studies. We utilized a reductionist approach to model neurodevelopmental outcomes of HSV-1 infection of neural rosettes, which represent the in vitro equivalent of differentiating neural tubes. Specifically, we employed early-stage brain organoids (ES-organoids) composed of human induced pluripotent stem cells (hiPSCs)-derived neural rosettes to investigate aspects of the potential neuropathological effects induced by the HSV-1 infections on neurodevelopment. To allow for the long-term differentiation of ES-organoids, viral infections were performed in the presence of the antiviral drug acyclovir (ACV). Despite the antiviral treatment, HSV-1 infection caused organizational changes in neural rosettes, loss of structural integrity of infected ES-organoids, and neuronal alterations. The inability of ACV to prevent neurodegeneration was associated with the generation of ACV-resistant mutants during the interaction of HSV-1 with differentiating neural precursor cells (NPCs). This study models the effects of HSV-1 infection on the neuronal differentiation of NPCs and suggests that this environment may allow for accelerated development of ACV-resistance.

Virulence of herpes simplex virus 1 harbouring a UAG stop codon between the first and second initiation codon in the thymidine kinase gene

Herpes simplex virus 1 (HSV-1)-TK(8UAG) expresses a truncated thymidine kinase (TK) translated from the second initiation codon due to a stop UAG codon at the 8th position (counted from the first initiation codon). Here, we showed that the sensitivity of HSV-1-TK(8UAG) to acyclovir (ACV) is similar to that of control HSV-1 wild-type (WT), which expresses an intact TK protein. However, HSV-1-TK(44UAG), which expresses a truncated TK due to a UAG codon at position 44, showed lower sensitivity to ACV. A mouse infection model was used to compare the virulence of HSV-1-TK(8UAG) and HSV-1-TK(44UAG) with that of HSV-1 wild-type (WT). The 50% lethal dose (LD₅₀) value of HSV-1-TK(44UAG) was 7.8-fold higher than that of HSV-1-TK(8UAG), whereas the LD₅₀ value of HSV-1-TK(8UAG) was the same as that of the parental HSV-1 WT. There were no statistically significant differences between HSV-1-TK(44UAG), HSV-1-TK(8UAG), and HSV-1 WT with respect to replication capacity and viral TK mRNA expression in mouse brain. Thus, the virulence of HSV-1 expressing a truncated viral TK translated from the second initiation codon might depend on the position of the UAG stop codon.

Herpes Simplex Virus Type 1 Clinical Isolates Respond to UL29-Targeted siRNA Swarm Treatment Independent of Their Acyclovir Sensitivity

Acyclovir is the drug of choice for the treatment of herpes simplex virus (HSV) infections. Acyclovir-resistant HSV strains may emerge, especially during long-term drug use, and subsequently cause difficult-to-treat exacerbations. Previously, we set up a novel treatment approach, based on enzymatically synthesized pools of siRNAs, or siRNA swarms. These swarms can cover kilobases-long target sequences, reducing the likelihood of resistance to treatment. Swarms targeting the UL29 essential gene of HSV-1 have demonstrated high efficacy against HSV-1 in vitro and in vivo. Here, we assessed the antiviral potential of a UL29 siRNA swarm against circulating strains of HSV-1, in comparison with acyclovir. All circulating strains were sensitive to both antivirals, with the half-maximal inhibitory concentrations (IC₅₀) in the range of 350–1911 nM for acyclovir and 0.5–3 nM for the UL29 siRNA swarm. Additionally, we showed that an acyclovir-resistant HSV-1, devoid of thymidine kinase, is highly sensitive to UL29 siRNA treatment (IC₅₀ 1.0 nM; I_max 97%). Moreover, the detected minor variations in the RNAi target of the HSV strains had no effect on the potency or efficacy of UL29 siRNA swarm treatment. Our findings support the development of siRNA swarms for the treatment of HSV-1 infections, in order to circumvent any potential acyclovir resistance.

Delay of alternative antiviral therapy and poor outcomes of acyclovir-resistant herpes simplex virus infections in recipients of allogeneic stem cell transplant - a retrospective study

Acyclovir is commonly used to prevent and treat herpes simplex virus (HSV) reactivation after hematopoietic cell transplant (HCT), and only few reports have been published on acyclovir-resistant HSV in HCT recipients. We reviewed the medical records of patients with a microbiologic diagnosis of acyclovir-resistant HSV by plaque reduction test who received an HCT from 2002 through 2014. A total of 4 028 HCTs were performed during the study period, and 18 of the recipients met the diagnostic criteria for acyclovir-resistant HSV. All cases had undergone allogeneic HCTs. Most patients were in the pre-engraftment period or on systemic corticosteroid therapy for graft-versus-host disease (GVHD). The median time between diagnosis and susceptibility testing was 15 days, and antiviral therapy was changed at a median of 27 days. Patients required prolonged therapy (~80 days), and many had serious complications including renal failure and hospitalization. In conclusion, acyclovir-resistant HSV infection is more likely during the period of profound deficit in T-cell-mediated immunity and is associated with significant morbidities. Higher doses of acyclovir prophylaxis might be needed for patients with history of HSV during pre-engraftment or GVHD treatment. In patients who do not respond or progress after 1 week of acyclovir therapy, testing for drug-resistant HSV, and early switch to an alternative antiviral should be considered.

Antiviral Drug-Resistance Typing Reveals Compartmentalization and Dynamics of Acyclovir-Resistant Herpes Simplex Virus Type-2 (HSV-2) in a Case of Neonatal Herpes

A neonate suffering from herpes simplex virus type 2 disease with central nervous system involvement developed an early recurrence under acyclovir therapy. Isolates from the cerebrospinal fluid and skin lesions were acyclovir resistant, while viruses from blood and trachea were not. Acyclovir combined with foscavir followed by long-term suppressive acyclovir therapy supported normal neurological development.

Fatal varicella due to the vaccine-strain varicella-zoster virus

We describe a death in a 15-mo-old girl who developed a varicella-like rash 20 d after varicella vaccination that lasted for 2 mo despite acyclovir treatment. The rash was confirmed to be due to vaccine-strain varicella-zoster virus (VZV). This is the first case of fatal varicella due to vaccine-strain VZV reported from the United States. The patient developed severe respiratory complications that worsened with each new crop of varicella lesions; vaccine-strain VZV was detected in the bronchial lavage specimen. Sepsis and multi-organ failure led to death. The patient did not have a previously diagnosed primary immune deficiency, but her failure to thrive and repeated hospitalizations early in life (starting at 5 mo) for presumed infections and respiratory compromise treated with corticosteroids were suggestive of a primary or acquired immune deficiency. Providers should monitor for adverse reactions after varicella vaccination. If severe adverse events develop, acyclovir should be administered as soon as possible. The possibility of acyclovir resistance and use of foscarnet should be considered if lesions do not improve after 10 d of treatment (or if they become atypical [e.g., verrucous]). Experience with use of varicella vaccine indicates that the vaccine has an excellent safety profile and that serious adverse events are very rare and mostly described in immunocompromised patients. The benefit of vaccination in preventing severe disease and mortality outweigh the low risk of severe events occurring after vaccination.

Acyclovir prophylaxis predisposes to antiviral-resistant recurrent herpetic keratitis

PURPOSE

Long-term acyclovir (ACV) prophylaxis, recommended to prevent recurrent herpes simplex virus type 1 (HSV-1) ocular disorders, may pose a risk for ACV-refractory disease due to ACV resistance. We determined the effect of ACV prophylaxis on the prevalence of corneal ACV-resistant (ACV(R)) HSV-1 and clinical consequences thereof in patients with recurrent HSV-1 keratitis (rHK).

METHODS

Frequencies of ACV(R) viruses were determined in 169 corneal HSV-1 isolates from 78 rHK patients with a history of stromal disease. The isolates' ACV susceptibility profiles were correlated with clinical parameters to identify risk factors predisposing to ACV(R) rHK.

RESULTS

Corneal HSV-1 isolates with >28% ACV(R) viruses were defined as ACV(R) isolates. Forty-four isolates (26%) were ACV-resistant. Multivariate analyses identified long-term ACV prophylaxis (≥12 months) (odds ratio [OR] 3.42; 95% confidence interval [CI], 1.32-8.87) and recurrence duration of ≥45 days (OR 2.23; 95% CI, 1.02-4.87), indicative of ACV-refractory disease, as independent risk factors for ACV(R) isolates. Moreover, a corneal ACV(R) isolate was a risk factor for ACV-refractory disease (OR 2.28; 95% CI, 1.06-4.89).

CONCLUSIONS

The data suggest that long-term ACV prophylaxis predisposes to ACV-refractory disease due to the emergence of corneal ACV(R) HSV-1. ACV-susceptibility testing is warranted during follow-up of rHK patients.

Acyclovir-resistant herpetic keratitis in a solid-organ transplant recipient on systemic immunosuppression

Purpose

To report a case of acyclovir-resistant herpetic keratitis in a solid-organ lung transplant recipient that was effectively treated with topical trifluridine.

Methods

A case of a 35-year-old female with herpetic epithelial keratitis resistant to acyclovir is described. The patient presented following treatment for 4 weeks with topical acyclovir ointment five times per day and oral valacyclovir 1 g three times per day for herpetic keratitis with no resolution of the epithelial defect or symptoms. Corneal scrapes and swabs were taken for confirmation of the diagnosis and resistance testing. The results were positive for herpes simplex virus 1 and showed acyclovir resistance (inhibitor concentration 90 = 200 μg/mL) and foscarnet sensitivity (inhibitor concentration 90 = 200 μg/mL). The patient was treated with topical trifluridine 2-hourly for 3 weeks and weaned off the drops over the following week.

Results

The patient showed resolution of the epithelial defect, but did have significant corneal toxicity associated with the use of the trifluridine. At 8 weeks, the patient had some stromal shadowing associated with the recent active infection, but symptoms had settled.

Conclusion

This case documents the effective use of topical trifluridine in proven acyclovir-resistant herpetic keratitis. It highlights three things: (1) the importance of considering topical trifluridine as an alternative to topical acyclovir in unresponsive disease; (2) the need to consider solid-organ transplant recipients in the immunocompromised population with resistant herpetic disease, and (3) the need to look for alternatives to treatment of resistant herpetic disease.