Transcriptional signature of durable effector T cells elicited by a replication defective HCMV vaccine

The guinea pig as a relevant preclinical model in the rat race for a vaccine against congenital cytomegalovirus infection

Cytomegalovirus (CMV) is a leading cause of congenital disease in newborns causing cognitive impairment and hearing loss as a result of placental and fetal infection. Primary infection establishes a life-time persistent viral state with potential for severe disease in immune suppressed individuals. Natural convalescent immunity does not prevent re-infection or congenital CMV (cCMV) by a new viral strain. Despite decades of research, an effective vaccine against cCMV remains an elusive goal. The guinea pig is an important model for various human diseases and the only small-animal model for cCMV. Human CMV (HCMV) is highly species-specific, and animal studies require species-specific CMV. Guinea pig cytomegalovirus (GPCMV) exhibits similarities to HCMV for tissue tropism, cell entry pathways, receptors and functional homolog proteins as pathogenicity factors or vaccine target antigens. Consequently, studies in this model potentially enable a better understanding of CMV disease and preclinical development of therapeutic and intervention strategies against cCMV and cross strain protection. This review provides a summary of CMV research carried out in this model and advancements made towards the development of an effective cCMV vaccine.

Developing a Vaccine Against Human Cytomegalovirus: Identifying and Targeting HCMV's Immunological Achilles' Heel

Human cytomegalovirus (HCMV) is a critical pathogen in immunocompromised populations, such as organ transplant recipients as well as congenitally infected neonates with immature immune systems. Despite decades of research and the growing financial burden associated with the management of HCMV, there is no licensed vaccine to date. In this review, we aim to outline the complexity of HCMV and the antigens it presents and the journey and challenges of developing an effective HCMV vaccine, as well as further highlight the recent analyses of the most successful vaccine candidate so far-gB/MF59.

Glycoprotein L-deleted single-cycle rhesus cytomegalovirus vectors elicit MHC-E-restricted CD8+ T cells that protect against SIV

Strain 68-1 rhesus CMV (RhCMV) vectors induce immune responses that mediate early, complete replication arrest of SIV infection in ∼60% of vaccinated rhesus macaques (RMs). This unique efficacy depends on the ability of these vectors to elicit effector memory (EM)-biased CD8+ T cells recognizing SIV peptides presented by MHC-E, rather than MHC-Ia. These efficacious responses still occurred when spread of the 68-1 vector was impaired by deletion of the viral anti-host intrinsic immunity factor phosphoprotein 71 (pp71), but efficacy was lost with a more stringent attenuation strategy based on destabilization of Rh108, the ortholog of the essential human CMV (HCMV) transcription factor UL79 that is required for late viral gene expression. Although unable to produce infectious progeny (ie single-cycle infection), Rh108-deficient vectors elicited durable, high frequency, EM-biased, SIV-specific CD8+ T-cell responses in RMs, but these responses were MHC-Ia-restricted and therefore non-efficacious. Here, we tested a different single-cycle attenuation strategy based on deletion (Δ) of the glycoprotein L (gL) that is essential for viral entry but allows for late gene expression and viral assembly. ΔgL 68-1 RhCMV/SIV vectors, grown on gL-complementing fibroblasts, were robustly immunogenic at doses above 105 PFU, generating high frequency, EM-biased, SIV-specific CD8+ T-cell responses that were also unconventionally restricted, including the MHC-E restriction associated with efficacy. Indeed, these single-cycle vectors manifested replication arrest efficacy in 70% of vaccinated RMs, further linking MHC-E restriction with efficacy, and demonstrating that 68-1 RhCMV/SIV efficacy does not require vector dissemination within the host.

A vaccine against cytomegalovirus: how close are we?

The pursuit of a vaccine against the human cytomegalovirus (HCMV) has been ongoing for more than 50 years. HCMV is the leading infectious cause of birth defects, including damage to the brain, and is a common cause of complications in organ transplantation. The complex biology of HCMV has made vaccine development difficult, but a recent meeting sponsored by the National Institute of Allergy and Infectious Diseases in September of 2023 brought together experts from academia, industry, and federal agencies to discuss progress in the field. The meeting reviewed the status of candidate HCMV vaccines under study and the challenges in clinical trial design in demonstrating efficacy against congenital CMV infection or the reduction of HCMV disease following solid organ transplantation or hematopoietic stem cell transplantation. Discussion in the meeting revealed that, with the numerous candidate vaccines that are under study, it is clear that a safe and effective HCMV vaccine is within reach. Meeting attendees achieved a consensus opinion that even a partially effective vaccine would have a major effect on the global health consequences of HCMV infection.