High‐frequency interferon‐γ‐secreting splenocytes specific for murine cytomegalovirus immediate‐early‐1 (IE‐1) peptide ¹⁶⁸YPHFMPTNL¹⁷⁶ are insufficient to provide complete protection from viral challenge

Abstract

Infection of Balb/c mice with murine cytomegalovirus (MCMV) has been used extensively as a model system with which to study host mechanisms of immunity to cytomegaloviruses. In this model, the cytotoxic T-lymphocyte (CTL) response crucial for clearing infected cells is dominated by CTLs specific for the MCMV nonapeptide 168YPHFMPTNL176 encoded by the immediate-early 1 (IE-1) gene. The intradermal injection of plasmid pcDNA89 encoding IE-1 has been shown to offer some protection from viral challenge. In the present studies, the protective efficacy of immunisation with pcDNA89 given by intradermal injection was compared with particle-mediated DNA delivery (PMDD) and contrasted with that induced by injection with the K181 MCMV strain and with temperature-sensitive mutants (tsm) derived from the K181 strain. Modest protection was afforded by pcDNA89 immunisation given by PMDD, but none was observed after intradermal injection. PMDD immunisation induced a frequency of 168YPHFMPTNL176-specific interferon-gamma (IFN-gamma)-secreting splenocytes, which was equivalent to that after K181 infection and significantly higher than tsm immunisation. Whereas tsm-immunised mice were completely protected from MCMV challenge, PMDD-immunised mice were only weakly protected. Tsm immunisation protected mice completely against challenge with natural isolates having sequence variation in the IE-1 nonapeptide, while PMDD-immunised mice were weakly protected from isolates encoding 168YPHFMPTNL176 and were not protected against isolates encoding 168YPHFMPPSL176 or 168YLDFMPPNL176. Thus, while IE-1-specific IFN-gamma-secreting splenocytes do contribute to immunity from MCMV challenge, their presence in isolation is insufficient to provide complete protection and they may not be involved in the protection observed against MCMV isolates having IE-1 sequence variation.

Mixed infection with multiple strains of murine cytomegalovirus occurs following simultaneous or sequential infection of immunocompetent mice

“…As also demonstrated by Wheat et al (2003), real-time qPCR is more sensitive than plaque assay and ELISA for detecting MCMV infection. Following the immunization of BALB/c mice with a TCV stock of G4, Morley et al (2003) could not detect viral titres in mice challenged 90 days later with a salivary gland-derived stock of K181. The technique used in our experiments, real-time qPCR, was a more sensitive method of detection, with mixed infections identified at early times post-infection.…”

Targeted Deletion of Regions Rich in Immune-Evasive Genes from the Cytomegalovirus Genome as a Novel Vaccine Strategy

“…Therefore, our data suggested that WT-MCMV may affect the functionality of the cellular immune response, while CTL clones induced by ⌬m01-17ϩm144-158-MCMV perform better in terms of cytokine induction. CTL clones directed against the IE-1-derived epitope YPHFMPTNL (16) have been shown to mediate a strong but not sterilizing immunity (31,54). Similarly, CTL specific for the HCMV IE-1 protein define immune protection against HCMV in patients who have undergone transplantation (10).…”

Role of mutations identified in ORFs M27, M36, m139, m141, and m143 in the temperature‐sensitive phenotype of murine cytomegalovirus mutant tsm5

“…tsm 5 induced high antibody titers and a significant CD8 + CTL response to the BALB/c immunodominant IE‐1 nonapeptide (YPHFMPTNL) as determined by an interferon (IFN)‐γ ELISPOT assay although this response was lower than that induced by K181 infection [Morley et al, 2003]. Tsm 5 immunization protected mice completely against challenge with natural isolates having sequence variation in the IE‐1 nonapeptide [Morley et al, 2003]. Additionally, CTLs specific for m04 (YGPSLYRRF) and M84 (AYAGLFTPL) peptides could be detected at low frequency after K181 and tsm 5 immunization [Morley et al, 2003].…”

“…Tsm 5 immunization protected mice completely against challenge with natural isolates having sequence variation in the IE‐1 nonapeptide [Morley et al, 2003]. Additionally, CTLs specific for m04 (YGPSLYRRF) and M84 (AYAGLFTPL) peptides could be detected at low frequency after K181 and tsm 5 immunization [Morley et al, 2003]. Thus, we have a virus which may prove very useful to the design of HCMV vaccines if the mutations contributing to the phenotype could be identified.…”